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If A Plane Took Off A Conveyor Belt...  
User currently offlineSovietjet From Bulgaria, joined Mar 2003, 2599 posts, RR: 17
Posted (8 years 8 months 4 weeks 1 day 5 hours ago) and read 32767 times:
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hey guys there is a huge debate over at another forum concerning this question...

Imagine a plane is sat on the beginning of a massive conveyor belt/travelator type arrangement, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.
There is no wind.
Can the plane take off?

Just wanted to know what you guys thought about it. I say it's not taking off.

951 replies: All unread, showing first 25:
 
User currently offlineBA From United States of America, joined May 2000, 11153 posts, RR: 59
Reply 1, posted (8 years 8 months 4 weeks 1 day 5 hours ago) and read 32767 times:

As long as the aircraft is moving at lift speed regardless of how it is moving at that speed, it can take-off.

If the wings are generating enough lift, the plane will lift into the air.



"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran
User currently offlineJoness0154 From United States of America, joined Nov 2005, 667 posts, RR: 0
Reply 2, posted (8 years 8 months 4 weeks 1 day 5 hours ago) and read 32767 times:

No, the plane will not takeoff.

The reason? Relative wind.

Planes make lift by air moving over the wings. Whether the wind is blowing, or the engines pushing the plane forward, air is moving over the wings to provide lift.

If you are stationary on a conveyor belt, there is absolutely no wind moving over the wings, and hence no lift.



I don't have an attitude problem. You have a perception problem
User currently offlineBA From United States of America, joined May 2000, 11153 posts, RR: 59
Reply 3, posted (8 years 8 months 4 weeks 1 day 5 hours ago) and read 32767 times:

Oops, I think I misunderstood your question Sovietjet...

I thought you were stating if the conveyor built is run at a high enough speed to propel the aircraft up to lift speed, but I just noticed you meant running the conveyor belt in the opposite direction, while the aircraft moves forward at that same exact speed. Thus it stays stationary.

So what you're saying is if the plane is running on a treadmill.  

Then yes, it will not fly as it is not physically moving forward. It's position is remaining fixed the entire time.

[Edited 2005-11-29 07:51:02]


"Generosity is giving more than you can, and pride is taking less than you need." - Khalil Gibran
User currently offlineDiamond From United States of America, joined Apr 2004, 3279 posts, RR: 63
Reply 4, posted (8 years 8 months 4 weeks 1 day 4 hours ago) and read 32767 times:

It's not about how fast you can make the wheels spin. It's about how fast the air moves over the wings.

So the plane will roll along but never lift off.



Blank.
User currently offlineNighthawk From UK - Scotland, joined Sep 2001, 5134 posts, RR: 33
Reply 5, posted (8 years 8 months 4 weeks 1 day 4 hours ago) and read 32767 times:

yes the aircraft would take off, the conveyor belt will cause the wheels to spin in the opposite direction of movement, but eventually the thrust from the engines will counter the push of the conveyor belt. The wheels will spin at an infinite speed, but this will not push the aircraft back, the force of the engines will move the aircraft forward and it will eventually take off normally. The aircraft will continue to move forward at takeoff speed, but the wheels may well be spinning at 1000+ mph.

Just because the wheels are turning doesnt mean the aircraft is moving with them!



That'll teach you
User currently offlineJoness0154 From United States of America, joined Nov 2005, 667 posts, RR: 0
Reply 6, posted (8 years 8 months 4 weeks 1 day 3 hours ago) and read 32767 times:

Hmmm interesting. The more that I think about it, the more I think it could happen. I don't really know how to put it into words though.

I guess you can say the thrust of the A/C is pushing against the air, and would therefore propel it forward, regardless if the conveyor belt was matching the speed of the wheels or not.

So, the speed of the wheels could be equivalent to, say, 100mph, but the airplane could actually be going 300mph, or have a 200mph relative wind.

So yes, I change my mind. It would be possible, but it would take a longer distance than a regular runway due to lack of friction. (ie a car on ice accelerating vs a car on pavement)



I don't have an attitude problem. You have a perception problem
User currently offlineAirplanepics From United Kingdom, joined Jun 2003, 2732 posts, RR: 41
Reply 7, posted (8 years 8 months 4 weeks 1 day 3 hours ago) and read 32767 times:

I think we have another "How many pigeons would it take to lift a 747" thread! Big grin


Simon - London-Aviation.com
User currently offlineJoness0154 From United States of America, joined Nov 2005, 667 posts, RR: 0
Reply 8, posted (8 years 8 months 4 weeks 1 day 3 hours ago) and read 32767 times:

Think about a plane taking off on ice, with all the wheels locked

The plane would still accelerate, even though the wheels are not moving.

Its a similar situation if you can visualize it.



I don't have an attitude problem. You have a perception problem
User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 9, posted (8 years 8 months 4 weeks 1 day 3 hours ago) and read 32767 times:

Quoting Nighthawk (Reply 5):
The wheels will spin at an infinite speed, but this will not push the aircraft back

The conveyor belt in the question is not designed to push the aircraft back, just match the rotation speed of the wheels.

The wheels on an aircraft are just freewheeling at takeoff, with forward thrust provided by the engines but the traction and forward motion is still a component of the wheel/ground interaction. An aircraft at takeoff is never going faster than the rotation speed of the wheels.

If the conveyor belt exactly cancelled out the motion of the wheels, then as others on this thread have said, there would be no air movement over the wings and thus no lift produced. The engines could be generating 100% thrust but if theres no forward motion because its cancelled out by the moving ground then the aircraft will never get into the air.

Quoting Joness0154 (Reply 6):
I guess you can say the thrust of the A/C is pushing against the air, and would therefore propel it forward, regardless if the conveyor belt was matching the speed of the wheels or not.

However the thrust is provided, the actual motion is set against whatever the aircraft is sitting on at the time. If that 'ground' acts negatively on the forward motion in any way then you reduce the effect of the thrust.

Thust doesnt produce some magical component that makes aircraft fly, it needs to produce forward motion. If that motion is retarded by the ground moving backward at the same speed as the forward motion, then you are never going to get air movement over the wing.

Think of how a tail wind affects an aircraft on takeoff - it reduces the lift produced by the wing and can prove to be costly as now you need to either go faster to lift off, or climb slower. Just think of this that you have a tail wind that ALWAYS matches the speed of the aircraft.


User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 10, posted (8 years 8 months 4 weeks 1 day 3 hours ago) and read 32767 times:

If you can generate that speed on the Belt & have the Engines at T/O thrust at the same time  Smile
regds
MEL



Think of the brighter side!
User currently offlineJoness0154 From United States of America, joined Nov 2005, 667 posts, RR: 0
Reply 11, posted (8 years 8 months 4 weeks 1 day 3 hours ago) and read 32767 times:

Quoting RichardPrice (Reply 10):
However the thrust is provided, the actual motion is set against whatever the aircraft is sitting on at the time. If that 'ground' acts negatively on the forward motion in any way then you reduce the effect of the thrust.

Then, by your account, an aircraft would never fly. Thrust acts in relation to the air, not anything on the ground.

Quoting RichardPrice (Reply 10):
An aircraft at takeoff is never going faster than the rotation speed of the wheels.

Again, I would have to disagree. If you held the brakes on ice, and firewalled the throttle, you would still move forward, even though your wheels are not. There are a few situations in which the wheels could be moving slower than the aircraft.

The airplane would move forward in relation to the solid ground even though it is on the conveyor belt. Anyone have a model airplane and a treadmill?



I don't have an attitude problem. You have a perception problem
User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 12, posted (8 years 8 months 4 weeks 1 day 3 hours ago) and read 32767 times:

Quoting Joness0154 (Reply 9):
Think about a plane taking off on ice, with all the wheels locked

The plane would still accelerate, even though the wheels are not moving.

Its a similar situation if you can visualize it.

Wouldnt work.

ALl of you claiming it will work are overlooking one fairly major point:

The thread starter said that the conveyor belt moved backwards to match the forward speed of the wheels at all times.

This will cancel out all forward motion, totally and utterly. You could stick a million jet engines behind the aircraft, but it must be moving forward to generate lift and if the conveyor belt cancels out that forward motion then the aircraft isnt going anywhere. Until take off, the forward motion is a component of the wheel/ground interaction and since you are removing this component then the aircraft cannot go forward.

Aircraft are just big road vehicles until they move quick enough to generate lift. An aircraft doesnt just leap into the air and its off.


User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 13, posted (8 years 8 months 4 weeks 1 day 3 hours ago) and read 32767 times:

Quoting Joness0154 (Reply 12):
Then, by your account, an aircraft would never fly. Thrust acts in relation to the air, not anything on the ground.

Thrust acts accordingly to Newtons Third Law of Motion - every action has an equal and opposite reaction. In the case of an aircraft, the reaction of the engines is that of forward motion, against whatever medium it is stationary. But the ground the aircraft is sitting on in this case is NOT stationary, its providing an exactly CANCELLING force pushing the aircraft back.

Quoting Joness0154 (Reply 12):

Again, I would have to disagree. If you held the brakes on ice, and firewalled the throttle, you would still move forward, even though your wheels are not. There are a few situations in which the wheels could be moving slower than the aircraft.

Yes, because ice is not frictionless. What we are talking about here is a PERFECTLY NEGATIVE FRICTIONAL surface, a surface that provides exactly the opposite friction to the wheels and thus an opposite force to the forward thrust of the engines.

To the laws of physics gentlemen, the aircraft will be moving forward at take off speed, but since an opposite force is being exerted on the aircraft, it isnt actually going anywhere.


User currently offlineNighthawk From UK - Scotland, joined Sep 2001, 5134 posts, RR: 33
Reply 14, posted (8 years 8 months 4 weeks 1 day 3 hours ago) and read 32767 times:

Quoting RichardPrice (Reply 14):
Thrust acts accordingly to Newtons Third Law of Motion - every action has an equal and opposite reaction. In the case of an aircraft, the reaction of the engines is that of forward motion, against whatever medium it is stationary. But the ground the aircraft is sitting on in this case is NOT stationary, its providing an exactly CANCELLING force pushing the aircraft back.

But the engines are acting on the air, which is stationary, so the engines by newtons theory will still produce forward thrust, moving the aircraft forward relative to the air.

The conveyor belt speed is set to cancel the speed of the wheels turning, not the forward movement of the aircraft. The thrust of the engines will push the aircraft forward, and the conveyor belt will rotate the wheels in the opposite direction. The turning of the wheels will not excert any force on the aircraft, so it will continue to move forward.



That'll teach you
User currently offlineJoness0154 From United States of America, joined Nov 2005, 667 posts, RR: 0
Reply 15, posted (8 years 8 months 4 weeks 1 day 2 hours ago) and read 32767 times:

Quoting RichardPrice (Reply 14):
To the laws of physics gentlemen, the aircraft will be moving forward at take off speed, but since an opposite force is being exerted on the aircraft, it isnt actually going anywhere.

Ahh, yes. Physics. I was actually a physics major for 3 years. There is no opposite force being exerted on the aircraft.

There is no force counteracting the thrust of the aircraft, therefore, the thrust would propel the aircraft forward.

At first I thought of it your way Richard, but after thinking about it for a while and the physics side of things it will be possible for the aircraft to build speed.



I don't have an attitude problem. You have a perception problem
User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 16, posted (8 years 8 months 4 weeks 1 day 2 hours ago) and read 32767 times:

Wheres the lift coming from in order for the aircraft to take off?

Thats all you need to work out.

If the force exterted backward on the aircraft is the same as the force exterted forward by the engines, then theres going to be no lift. Simple as that.

In this case, theres no air movement because the air is technically acting as a tail wind in exactly the same proportion as the forward motion of the aircraft. Thus no lift.


User currently offlineJoness0154 From United States of America, joined Nov 2005, 667 posts, RR: 0
Reply 17, posted (8 years 8 months 4 weeks 1 day 2 hours ago) and read 32767 times:

I don't think you're seeing the full picture. You have to look at the overall scheme of things.

There is no force being exerted backwards on the plane. None at all. The wheels are not physically connected to the engine, so the speed they move at is irrelevent to the speed of the actual aircraft itself.

Because the wind is calm, we are assuming, the thrust from the engines will work against it, therefore propelling the plane forward in relation to the air. The wheel speed and conveyor speed can totally be neglected. As long as that air is calm, the thrust will propel the plane forward, which will produce airflow over the wings.



I don't have an attitude problem. You have a perception problem
User currently offlineRichardPrice From , joined Dec 1969, posts, RR:
Reply 18, posted (8 years 8 months 4 weeks 1 day 2 hours ago) and read 32767 times:

Ok, after all my arguing AGAINST the aircraft taking off, Im going to swallow my pride and change my stance  Smile

The aircraft will take off.

Why?

Start the conveyor moving without the engines on. In a perfect world (since we dont know anything other than the question, we have to assume perfection), the plane will sit still because the wheels will freewheel backward.

The engines add an additional thrust component to the equation, which is not affected by the conveyor. Thus forward motion can be generated and thus also lift.

Apologies  Smile


User currently offlineJoness0154 From United States of America, joined Nov 2005, 667 posts, RR: 0
Reply 19, posted (8 years 8 months 4 weeks 1 day 2 hours ago) and read 32767 times:

 Smile

I originally saw it like you did, but I changed my mind also.

Its a very confusing problem to envision, but I had to change sides too  Smile

Welcome to the darkside...



I don't have an attitude problem. You have a perception problem
User currently offlineNighthawk From UK - Scotland, joined Sep 2001, 5134 posts, RR: 33
Reply 20, posted (8 years 8 months 4 weeks 1 day 2 hours ago) and read 32767 times:

Quoting RichardPrice (Reply 17):
If the force exterted backward on the aircraft is the same as the force exterted forward by the engines, then theres going to be no lift. Simple as that.

In this case, theres no air movement because the air is technically acting as a tail wind in exactly the same proportion as the forward motion of the aircraft. Thus no lift.

How is the air acting as a tailwind? The convayor belt isnt moving the air! Its not even moving the aircraft, its simply spinning the wheels.

It doesnt matter how fast the wheels spin, the aircraft will still move forward as the engines push against the air and generate thrust.



That'll teach you
User currently offlineHT From Germany, joined May 2005, 6525 posts, RR: 23
Reply 21, posted (8 years 8 months 4 weeks 1 day 2 hours ago) and read 32767 times:

Quoting Sovietjet (Thread starter):
The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

With this description, the a/c will not move relative to the surrounding. So there will not be any air flowing over the wing thus no lift is produced.

See it the other way ´round:
Your build a really BIG ventilator and place it in front of the a/c.
You apply the brakes of the a/c and then turn on your very big ventilator producing a stable wind at 200 knots. As this head wind is greater than the rotating speed of the aircraft, the wings will produce enough lift to let the a/c take off from the ground - but only as long as it is within the produced currents and the relative airspeed is maintained: This will require the a/c to be kept on a leash, making this a 100 ton-kite ... Big grin
(I hope you got the point ?!).
-HT



Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !
User currently offlineQFA380 From Australia, joined Jul 2005, 2061 posts, RR: 1
Reply 22, posted (8 years 8 months 4 weeks 1 day 2 hours ago) and read 32767 times:

Quoting RichardPrice (Reply 13):
Aircraft are just big road vehicles until they move quick enough to generate lift. An aircraft doesnt just leap into the air and its off.

Some can, like helicopters and Harriers.

Just one question, how is a plane supposed to land, if the runway is just one big conveyor belt? Big grin

QFA380


User currently offlineSudden From Sweden, joined Jul 2001, 4130 posts, RR: 6
Reply 23, posted (8 years 8 months 4 weeks 1 day 1 hour ago) and read 32767 times:

Quoting Sovietjet (Thread starter):
as long as a runway

That would not be enough to get up to rotation speed. It would require a rwy that is veeeeery long.  Wink

Aim for the sky!
Sudden



When in doubt, flat out!
User currently offlineNighthawk From UK - Scotland, joined Sep 2001, 5134 posts, RR: 33
Reply 24, posted (8 years 8 months 4 weeks 1 day 1 hour ago) and read 32767 times:

Quoting Sudden (Reply 24):
That would not be enough to get up to rotation speed. It would require a rwy that is veeeeery long. Wink

Aim for the sky!
Sudden

He didnt specify which runway... If its LCY, good luck, but edwards air force base might just be long enough... Silly



That'll teach you
25 PMN : Surely the conveyor belt wouldn't really make a difference. The aircraft is moved forward by the engines, not the wheels as in the case of a car. Ther
26 Saintsman : Rubbish. The wheels will stay still and the whole aircraft will move with the conveyor belt. This is no different to running on a treadmill. In order
27 Joness0154 : You didn't read the original post. Anyways, in a perfect world physically, when the conveyor belt moved, the wheels would turn (freewheel) and the pl
28 Sudden : A valid point, and also rather logical. If no thrust is applied to compensate for the movement of the belt, the A/C would naturally move with the bel
29 Post contains images Alessandro : Nicked from AD.com...
30 Nighthawk : I agree entirely, the spinning of the wheels is irrelevent, it does not excert any physical force on the aircraft, they mearly spin. The thrust of th
31 Nighthawk : I think the logic here is flawed? If the aircraft moves forward down the runway, the wheels rotate clockwise, ie backwards. If the belt moves in the
32 Kay : Folks, If it was a free rotating conveyor belt, then yes, we could argue that eventhough it would make it difficult for the plane to move forward, and
33 A346Dude : The answer to the question is, of course, absolutely not. If the speed of the conveyor belt is exactly equal and opposite to the speed of the wheels,
34 PMN : The most patronising perhaps... Paul
35 A346Dude : After considering the problem further, I am going to have to amend my answer. The plane will take off, however the landing roll will be slightly longe
36 Post contains images Joness0154 : See, everyone changes their mind People, whether the wheels spin or not, the plane will still move forward, because nothing is hindering it. There is
37 Nighthawk : actually, I am going to alter my oppinion slightly: ive posted this to another forum (http://www.gamedev.net/community/forums/topic.asp?topic_id=36097
38 Post contains images Flyingbabydoc : The plane is a BAE Harrier. It just shifts the vents of the Pegasus engine and it flies away safely...regardless of conveyor belt. cheers Alex
39 Joness0154 : I don't know how to explain this any better than I have. The wheels are not connected to the motor as in a car. If you put a car on a treadmill, and s
40 CHRISBA777ER : LOL You lot crease me up.
41 Post contains images Kay : Hmm, I will throw in the following: since the belt is rotating at the same speed as the wheels, then, sorry, but yes, there is a force stopping the ai
42 Nighthawk : In order to move forward the tires would need to skid forward along the conveyor belt, losing friction. You would need a rocket powerful enough to br
43 Post contains images PMN : Ah yes, sorry Kay, I missed the all important smile! Paul
44 Post contains images Joness0154 : I think my brain is about to explode from this topic. I'm done here, its too confusing, and too many variables
45 Saintsman : Something for you to ponder upon. If you are doing engine runs on an aircraft, with the brakes on you can go to full power. So, just because the engin
46 CHRISBA777ER : ...yes but the brakes will be off otherwise its going backwards!
47 SlamClick : The plane would not take off but for a reason I've not seen mentioned. Airplane tires have a speed limit. 225 MPH is a very common speed limit for air
48 A346Dude : Whoops, I meant to say take-off roll, not landing roll. Anyways, this problem is obviously pretty difficult to visualize. I still hold, however, that
49 Ariis : This is the key to the answer. Since conveyor belt is somehow designed this way (assumption), the wheels will never move an inch. And the airplane wi
50 SlamClick : Ridiculous. You still think the wheels are pushing the airplane. I've moved airplanes with the wheels not turning at all - on ice. The wheel rotation
51 Nighthawk : the key here being that it was on ice..the wheels were sliding over the surface. In order to take off friction between the tire and belt must be brok
52 SlamClick : Nonsense. The friction between the wheels and conveyor belt is not even an issue since the tires are free to rotate. If I clamp a toy car in a vise w
53 Post contains images A346Dude : Whoa - now THAT would be something to see!
54 Ariis : Why do you think that I think so? Am I talking about a car or something? Your comment proves my fault: I have not expressed myself clearly enough. I
55 SlamClick : Because the only way the moving surface could affect the speed of the mass of the airplane is if the wheels were driving the plane. They are not. The
56 Kay : The way i see it is that the concept of having a conveyor belt designed to spin exactly the same speed as the wheels, is like having a hand come out o
57 Amy : Even if the aircraft was moving forwards at rotation speed, if the conveyor belt was moving backwards I think the gear asssembly would reach maximum r
58 Post contains images JBirdAV8r : The sheer fact that this thread has gone on as long as it has is, quite frankly, pretty disturbing. I'd hate to see the high school physics scores of
59 Post contains images A346Dude : No, it isn't! You have made the leap from the conveyor belt moving at a speed that is exactly equal and opposite to the speed of the wheels, to the a
60 Navymidn : The plane will not take off. Assuming we are on Earth, and friction is a factor, the wheels will never make forward movement. This is because the conv
61 Joness0154 : Yes, the boat would move. Boat sails work on the principle of lift. Anyways, I see you're at Purdue....as am I.
62 Kay : Not this engineer. A346Dude, you have a huge mistake in your analysis: the belt spins at a speed equal to the *wheels* not equal to the aircraft as y
63 SlamClick : Hello! Running is an activity where the wheels (your feet) propel the vehicle. Strap a rocket to your back and get on a treadmill and tell me what ha
64 Post contains images A346Dude : Kay, I think you've run into a circular argument here. What you are arguing is that the plane could be sitting perfectly stationary, with the conveyor
65 Jean Leloup : This is definitely the new pigeon thread. As for my 'vote' (not that it's really up to popular decision, of course), the plane will definitely take of
66 SlamClick : It is absolutely staggering! Educated people who persist in believing that the wheels are somehow driving the airplane. Don't think of the contact pa
67 Post contains images MiCorazonAzul : My physics calculations show that it does take off.........
68 Post contains images SlamClick : "Show your work." - three generations of physics teachers
69 A346Dude : That doesn't make sense. Why would the wheels be rotating at 300 knots (/mph - whatever)? The airplane is travelling at 150 knots, so the wheels shou
70 CPH757 : First I didn't think the plane would take off. Then I understood the point of the free spinning wheels, making it able to take off. However, one forge
71 Post contains images Kay : The reason is, guys, that a conveyor like this is something that doesn't exist, and cannot be pictured in our heads, really! I think there is a differ
72 SlamClick : Okay, related question: A train is going fifty miles per hour. That means the center of each axle is going 50 MPH. However, the bottom surface of each
73 Kay : No man. You said: 1- plane goes at 150, 2- replace floor with belt moving at 150 backwards, then wheels will run at 300 and plane will take off at 15
74 Post contains links MD-90 : Everyone needs to listen to SlamClick, because he's got it right. What propels an aircraft is AIR, either compressed and heated by a turbine or simply
75 Post contains images A346Dude : Why must you torment us SlamClick?? We already made it to 70 posts arguing the first question!
76 A346Dude : No, no, no! It has been designed to rotate backwards at exactly the speed of the wheel! So if you place a wheel spinning at 150 knots on it, it will
77 Fokker Lover : I'm amazed that a website for aviation enthusiasts has so many people that don't understand how an airplane works, yet they will argue to their last b
78 SlamClick : The tires are not trying to turn. IT IS NOT A CAR. The tires will only turn as a byproduct of the motion of the plane above the surface on which it r
79 Post contains images Kay : I don't know why but I had to laugh when I read your reaction The wheel is trying to turn because that is the only way it knows for moving forward. T
80 A346Dude : Hehe, I suppose this discussion has become a little heated. Agree to disagree?
81 Fokker Lover : But we ARE talking about free turning wheels, and that is why your argument is totally and completely wrong. The wheels don't start to turn until the
82 Post contains images Kay : Yes I agree to disagree on this, after all, very minor thing. Hoping that everyone is cool too... Kay
83 Petertenthije : The plane will take of. The reason for that is that the forward motion is not supplied by the wheels (like a car/train), but by the jet engines. They
84 Fokker Lover : Here's a simple experiment that everyone can do. Put a Tonka truck on a treadmill and turn it on. See what happens? The truck moves with the belt and
85 Post contains links and images Nighthawk : Heres a thread about this on a physics forum: http://forum.physorg.com/index.php?showtopic=2417&st=0 16 pages worth, and im guessing an answer was nev
86 Post contains images Joness0154 : Mythbusters anyone? This topic is hilarious now
87 RichardPrice : While I am decidedly with the 'it will take off' group, you are making one fatal mistake with this analogy. The treadmill in the question is 'designe
88 Post contains images Falcon84 : Has Anet sunk to THIS?
89 Joness0154 : The thing is, if the conveyor EXACTLY matched the speed of the wheels, the wheels would not turn, period. If the conveyor were just a fraction of a se
90 Post contains links Kay : I browsed their whole website, couldn't figure out how to just submit an idea, their forum isn't a formal channel, and there's only an application to
91 SlamClick : If the wheels are inducing the motion. They aren't! All the treadmill can do is increase or decrease the RPM of the wheels. It cannot change the acce
92 Fokker Lover : Ok, the conveyor will match the speed of the wheels. Lock the brakes. The wheels won't turn, the conveyor won't turn. The thrust of the engine will s
93 Post contains links Joness0154 : THE VIDEO THAT SOLVES IT ALL!!! http://videos.streetfire.net/player....E964D9-38DB-4EFD-BE8D-D6BA1A43A06B
94 Post contains links Joness0154 : and an avweb article http://www.avweb.com/news/columns/191034-1.html
95 Post contains links Petertenthije : already on their site http://community.discovery.com/group...ms/a/tpc/f/9701967776/m/7451937218 maybe someone can send them the "flying birds in 747"
96 Post contains images JBirdAV8r : Upon closer examination, doing a little calculus, and actually playing with a treadmill, you're right. I didn't think it all the way through before p
97 Post contains images MD-90 : There is a fundamental difference between airspeed and groundspeed... I think there is an easy way to visualize this. Imagine a gargantuan convey belt
98 Post contains images Mir : Would you like A vs. B? We can do A vs. B. ------- After reading the replies in this thread, I would think that in an ideal case (zero friction), the
99 Post contains images A346Dude : Couldn't you at least entertain the possibility that we do?
100 Post contains links Fokker Lover : Well, if that's how you see it, I guess it's settled then. But then again, maybe you should pay attention to what the professionals have to say, or a
101 Ralgha : I'm not reading this whole thread, but everyone who thinks the airplane will not take off has the same basic misunderstanding of airplanes that plague
102 SlamClick : Sorry but this is not Slam's day to cut any slack. "ideal?" "zero friction?" Even my puny little A-320 has fifty-four thousand pounds of thrust. Just
103 SlamClick : Well said.
104 Matt72033 : ok....ive joined this late, but i thought i'd throw my analogy in for the hell of it! lol ok.....flat conveyor belt in aircraft terminal.....we've all
105 Post contains images Matt72033 : i think someone should start the "do engines push or pull the aircraft" thread now!!
106 CosmicCruiser : I couldn't bring myself to read all these posts so forgive me if I'm repeating something already said. Let's make this real simple...If you're a runne
107 Matt72033 : i suggest you read the posts!
108 SlamClick : Perhaps you should have read some of them. Your feet propel you when you run. On a treadmill the place where your foot lands on the belt is constantl
109 Ariis : No, they will not spin at higher RPM, read the assumption. The conveyor is never slower! Having read all the good points by all participants (includi
110 Jean Leloup : Unfortunately, airplanes are not runners.
111 A346Dude : And furthermore, it has no practical applications since even in the best case scenario it lengthens the take-off roll by a little bit. I guess it's j
112 SlamClick : Ah, but it it does work then we could just reverse the direction of the treadmill and all the airliners would get a free takeoff to start them on the
113 Post contains images Mir : If you mean that the treadmill would be running in the same direction as the airplane, then the airplane would take off after the 6000' of travel wit
114 A346Dude : True enough, but the wheels would of course have to be locked!
115 Ariis : I absolutely agree, just in case I sound otherwise. This is a great thread; reminds me of that one about airplane filled with pigeons, the one someon
116 Post contains images Ariis : That is known as 'catapult', by the way. You know, Tomcats, Hornets, etc . FAO
117 Navymidn : Okay, now that I am back from class, I will be able to say more on this subject. Unless the wheels slide down the belt, the aircraft will never take o
118 SlamClick : Well there is another argument. Surely a nuclear aircraft carrier has the power to install a treadmill that accelerates from zero to whatever in the
119 Ralgha : No, they don't. You are not grasping the fact that airplanes do not depend at all on the ground for propulsion or flight. So have the rope run throug
120 Post contains images David L : I've joined this too late, too. Having rushed through the posts, I was so looking forward to having a go at the conveyor-belt-gripping-the-axles idea,
121 Fokker Lover : Listen, Slamclick and I are both telling you the same thing. The wheels and landing gear have one purpose, and one purpose only. That is to keep the
122 Ariis : It is sliding against the belt (although hovering). This is exactly, what, I believe, Navymidn is trying to tell you. If the airplane takes off (as y
123 Post contains images David L : Apparently not... NO! Wheels (dragged by the aircraft) move at 150 kts in one direction, the belt moves at 150 kts in the opposite direction - ground
124 Post contains images A346Dude : You just had to get that out, didn't you.
125 Post contains images David L : Sure did! I have to confess it did take a while for my brain to get into gear on this one. Now all I need is for someone to come out with old "everyt
126 Post contains images David L : Misunderstanding of basic shopping trolley physics. The wheels would wobble all over the place. The trolley would do a triple sulko, shoot off to the
127 Ralgha : You're both trying to explain something that won't happen. The belt can try all it wants to stop the wheels from making forward progress, but it can'
128 SlamClick : Let's put to rest a side issue that is not part of the question. That is the "exactly match the speed of the wheels at any given time, moving in the o
129 SlamClick : That would only be true if the plane was driven through the wheels like a car. How many times does that have to be said?
130 Airfoilsguy : In order for the plane to reach takeoff speed it needs to over come the friction of the air and the tires and inertia. The friction that the tires cau
131 Post contains images David L : Strictly speaking, it's the friction of the wheel bearings - tyres are designed to provide as much friction as possible. But your point is valid.  
132 SlamClick : Well bring them on! Until everyone grasps the simple truth that the airplane will take off unless something stops the motion of the CENTER OF THE AXL
133 David L : Well, assuming you could find one that behaves, I think the shopping trolley analogy is a good one. The argument that an external force pulling the t
134 Ariis : This is all probably because of incostintency in how one understands the initial post, in terms of the 'design' of the conveyor. As I understand it,
135 SlamClick : I think I don't understand which side of this you are arguing. Let me ask you for a one-word answer. Would the plane take off? Yes. No.[Edited 2005-1
136 David L : Why should the belt accelerate any faster than the aircraft (or its wheels)? If the belt were spinning infinitely fast, it wouldn't match the speed o
137 David L : Yes, definitely. I agree with you so I've goofed somewhere. Let me take another look at what I said.
138 SlamClick : I took this as meaning that your opion was NO it would not take off and you were lining up quotes in support of that. My dumb.
139 Ariis : I said 'the belt and the wheels'. The wheels are spinning infinitely fast too. The belt is only trying to catch up to the speed of the wheels (which
140 Post contains images David L : I was saying that this, which shows how it would take off, is a good analogy: Then I was attempting to show how this, which attempts to show that it
141 Post contains images David L : I'm sorry, I just don't see where infinite speed comes into it . If the aircraft starts to move at 5 kts, the belt will start to move at 5 kts in the
142 David L : Ah, I think I know what the problem was. People tend to fall asleep about halfway through my first sentence! (What you'll actually see is "People ten
143 Mir : I think this is one of the reasons why people are having trouble visualizing this (the other being the difference between the wheels moving the plane
144 Fokker Lover : Stick with computers. In the real world of aviation the axles are pulled forward by the rest of the plane. The wheels are just along for the ride. Th
145 Chksix : Strange thread..... I can't see any correlation between the speed of the wheels and getting airborne.... If the conveyor is set to prevent the wheels
146 Ralgha : I'm quite aware of that. In my first post I said "equivilant" since the actual RPM will depend on the diameter of the wheel. I assumed people would u
147 David L : No, Slamclick, it was my dumb! I assumed it was my prior post that had clouded the issue. Having read what you actually said, it's clear that my initi
148 SlamClick : The wheels don't drive the airplane. The wheels don't drive the airplane. The wheels don't drive the airplane. The wheels don't drive the airplane. T
149 Post contains images Ralgha : [Edited 2005-11-30 02:33:17]
150 Post contains images David L : Yes (I did allude to this interpretation earlier). Very true but I don't think either interpretation would stop the aircraft taking off. Either the w
151 SlamClick : Exactly! I think a person's take on this issue might tell us something about them: If you get it right the first time you might be a sailor. If you g
152 Ralgha : If you factor in bearing friction, you could eventually get to a speed that would prevent the airplane from moving forward since the rotational frict
153 Ralgha : I must disagree, I've tried to explain it to many "normal" people who were never convinced. Additionally, I am an engineer by education, and I do get
154 PPVRA : The wheels would freewheel backwards - cancelling the conveyor belt - even with the engines powered off. Once you turn them on, they will exert forwar
155 Post contains images A346Dude : Hey, take that back! If you look back in the posts, you will find I understood the question a lot sooner than you did, mister.
156 Post contains images SlamClick : Well, that is why I said "might be." There are three engineers in the world who have common sense. I wonder who the other two are.
157 Post contains images Keta : LOL at first when I saw the question I thought "what a silly question, how can there be 100+ posts?" But then I realized that it's not that easy. This
158 Ralgha : Which is why SlamClick and I have both stated the correct phrasing of the question.
159 A346Dude : Keta, A really good summary of the fundamental problem that I think is responsible for the size of this thread.
160 Bond007 : That's it right there. The fact that wheels aren't being turned by the engine is irrelevant. The wheels DO need to turn in order to takeoff - and bef
161 Ralgha : True, however there is nothing preventing the wheels from making forward movement, which is the flaw in your understanding. Speed does not equal forc
162 Post contains images Ralgha : Right, I overlooked the "might be" part...
163 Bond007 : Yes, the conveyor moving in the opposite direction at the same speed is doing that - that's the whole purpose of this conveyor! Jimbo
164 Post contains images Ralgha : No, it's not! The wheels are free spinning, that's the whole idea of a wheel, it allows the object to which the wheels are attached (which includes t
165 PPVRA : Wait a second - The wheels will be spinning fast, really fast. That means there will be less friction that the engines have to overcome, no? Kinda lik
166 Ralgha : No, there are two types of friction, static and dynamic. Each is a constant, which the dynamic being less (much less often) than static. The friction
167 Bond007 : Hmmmm....so I'm watching from the control tower and for every one foot my airplane moves forward, the runway magically moves backward one foot ....wh
168 Jean Leloup : And this has no effect on the motion of the plane; it simply means that the wheels will be spinning twice as fast. JL
169 Ralgha : No, from your vantage point in the tower, the takeoff would look completely normal. The airplane is moving forward just as normal, only the wheels are
170 Turnit56N : While I don't want to wade knee-deep into the debate, I'm reminded of the old saying "You know you've landed gear-up when it takes full power to taxi
171 MD-90 : Holy cow. Action = opposite equal reaction Airspeed does not necessarily = groundspeed
172 No1racer : Hey all, Something that I feel hasn't been brought up is this: We are all here talking about the wheels being free-standing. However, how do planes st
173 Ralgha : True, and also not influenced at all by the belt. Airplanes do not move fast enough when on the ground for this effect to occur (if indeed we are thi
174 PPVRA : Ok, air friction - right? Thanks for clearing that up. Cheers
175 SlamClick : Okay if finally occurs to me that there is a language trap in the way the problem is being posed. Let me give you an example: Three guys check into a
176 Ralgha : No, this is discounting air friction. This is just friction between the block and the surface.
177 Post contains images Bond007 : I guess the clear explanation that I haven't seen (or probably missed), is that a jet engine, or a piston prop even, acts on the air around it, which
178 PPVRA : Hmmm... been a while since my last physics class. So you're saying that after a certain speed the friction with the surface will increase? I remember
179 SlamClick : Okay, before I get accused of hijacking the thread let me answer: The way I phrase that question only makes it more difficult to answer. The trick is
180 Ralgha : SlamClick and I have said that many times.
181 Ralgha : The friction is constant, the force imparted by that friction is dependent on the speed of the object.
182 Zarniwoop : Initially I was convinced that it wouldn't take off but Slamclick changed my mind (check rply 56, cable & winch analogy) & I agree with Bond007, the k
183 Post contains images Bond007 : Like I said, it wasn't obvious to me anyway. It was said many, many times that the wheels were not 'driving' the aircraft, but not too clear why it w
184 Navymidn : A historic moment: I swallow my pride and admit that the aircraft will take off. After many tests, I have determined that either way the belt is turni
185 Post contains images NAV20 : When you get to my age the oddest things stir memories of long ago. This time it's a long-lost uncle of mine who was an 'erk' (aircraftsman) during th
186 Jean Leloup : NAV20; You seem not to have read the thread, as the examples you bring up (biking and treadmill) have been brought up and dismissed. I think just abou
187 Sovietjet : How can the wheels spin faster than the belt though....if they are both equal the plane will never move no matter how much thrust(assuming no slippage
188 Sovietjet : I think the original question was poorly worded IMHO...the problem doesn't specify whether the belt matches the wheel's speed in RPM, tangential speed
189 NAV20 : I have read the thread, Jean Leloup. I 'lost it' at the point where people said that 'relative wind' would be generated. An aeroplane (as opposed to
190 BuckFifty : The belt matching the speed of the wheels...hmmm. Okay. Let's think about it this way. Thrust is added. Aircraft has forward momentum. If the aircraft
191 Jean Leloup : Nav20, the conveyor is not neutralising engine thrust. It is not able to do so. The plane will generate lift the old fashioned way, as the engines pul
192 Post contains images Matt72033 : lol you are quite correct, but, my logic was, we're talking about a 10,000 foot or whatever conveyor belt here, if we've got one of those, im sure we
193 LeanOfPeak : Uhhh, folks... Assuming the tires are not slipping, the have two problems here. The relative motion problem says that wheels turning at x mph on a tre
194 Post contains images Keta : Uh you still arguing... That's the problem. The answer to the question is not "yes" neither "no". The way the question is proposed makes it an impossi
195 Kay : Traditional answers from the "it will move" group: 1- a plane is not a car. 2- the wheels can rotate freely. True, the plane is not a car. It doesn't
196 Post contains images Saintsman : As others have mentioned, it is an impossible situation. People have been giving examples to prove their points but none of the examples are comparabl
197 Post contains links VirginFlyer : Before starting, I think it is very important to describe the frame of reference here, and the words I am going to use, to avoid any confusion: A) Whe
198 Post contains images Ariis : Unless airplane slides, the wheels MUST turn. Do not confuse the cause and the result. The spinning wheels are not the cause, they are the result of
199 Post contains images David L : Yes, as Slamclick pointed out, but the aircraft would still accelerate in the desired direction, which is really the point. If you mean the wheels as
200 Sudden : Am really surprised that this thread is still alive and kicking! Just as the fact that some folks think the A/C will take off!? It would rotate, but a
201 NAV20 : Meeting myself coming back here! I first of all thought that the aeroplane would stand still. Then I imagined it 'gaining' on the conveyor, and theref
202 Sudden : Am not totally with you on that one. The belt would not work as a break as it's just a substitue for the rwy. All it would cause, in my narrow mind,
203 Post contains images NAV20 : Not by any means sure myself, Sudden. But I'm going on the 'terms of reference' as stated in the thread-starter:- So more thrust equals more 'speed' -
204 A346Dude : It seems like just as everyone has agreed that the aircraft will take off, someone new enters and says it won't. The point is, even though the conveyo
205 Post contains images Sudden : This theory works totally the other way around for me. The A/C will not move an inch, and also not rotate as there is no airflow over the wings. I am
206 Post contains images Keta : That's where you fail to understand. It's impossible for the belt to negate the movement; when the belt accelerates to catch the wheels' speed, the w
207 Pihero : My two cents : 1/ aircraft/wheels/belt do not form a closed system as in the theory, the only force considered comes from the engine thrust, and we mi
208 CosmicCruiser : First let me say I should have stayed out of this. I immediately thought of a runner on a treadmill which lead to my post and later realised the true
209 Darrenthe747 : so far i think slamclick has hit the nail on the head. when i first read the original post i was convinced it would not move. my opinion has changed..
210 NAV20 : Look at it another way, guys. The aeroplane is travelling at 90 knots. The wheels are therefore turning at the appropriate revolutions for that speed.
211 Sovietjet : the skateboard analogy doesn't work....if you pull on the rope to make it go faster the conveyor will go faster in the opposite direction. Then the sk
212 Post contains images Chksix : It stands still relative to you if you are also standing on the conveyor. You, the plane and the belt will be accelerating at the aircraft T/O power a
213 Post contains images Bond007 : That is what I was originally thinking....BUT a jet engine, or propellor, produces forward movement relative to the air around it, NOT relative to th
214 SlamClick : I have to take my dog to the vet or I would address some of the last twenty or so posts. (My dog understands, by the way, that the plane would take of
215 Post contains images David L : Agreed! NO! Look at the skateboard on the moving walkway in Reply 210. Stand just beyond one end of the walkway with a rope attached to the skateboar
216 Post contains images David L : I didn't notice that it was you who asked the original question! So, in other words, if you're sticking to your guns about the conditions, the situat
217 NAV20 : I agree, Bond007, that in real life the engines would move the aeroplane, the conveyor wouldn't be able to cope, and the wheels would skid until the
218 NAV20 : Very little to do with the subject, SlamClick, but I also recall him telling us about his squadron being sent to Malta in 1941. They were flown off f
219 Bond007 : The only thing in this scenario that would stop the jet engine from moving the plane forward would be friction between the wheels and the conveyor. S
220 LeanOfPeak : And there would be no debate about that question. Absolutely the aircraft would take off as normally. However, given the question asked, until tracti
221 Post contains images Chksix : So if the tarmac refuses to budge, the aircraft can never start to taxi.... Or a sailboat can't sail if the water don't push it? Just pulling your le
222 Sudden : I give it a rest here. Anyone else who got an email from a none A.net member by name Tom LaPrise? He stated that Pihero had the correct answer. Aim fo
223 Bond007 : So do those who say, yes it will takeoff, agree that the wheels MUST be going faster than the conveyor in order to get forward motion, and therefore
224 A346Dude : Absolutely not. As SlamClick has already indicated (I'm sure many more times than he would have liked to!), wheel rotation is not required to get for
225 LeanOfPeak : However, getting forward motion without wheel rotation requires that the traction of the tires be broken (NOW we're getting somewhere).
226 Joness0154 : Here's another thing. Its all in what the conveyor belt is moving in relation to, and whether you measure the conveyor belt speed at the point of the
227 David L : Assuming we're going with the "silly" version, I see the point about the wheels needing to rotate at half the speed I was thinking of (i.e. slipping)
228 Post contains images Kay : They will not spin as fast as you are saying, but only as a result of the wheel struts wanting to move forward, they will want to spin, but the turni
229 David L : The wheel strut is not in contact with the conveyor belt. Imagine your foot was a wheel strut. Now put on a pair of roller skates and put your foot o
230 LeanOfPeak : OK, let's go with the roller-skates analogy. If you are on a treadmill on roller skates, your roller-skate wheels have a speed with respect to the tre
231 David L : I "get your drift" but I'm still not convinced that this is the same as having the brakes locked. I'm running out of ways to picture this - as you sa
232 BuckFifty : I think people still don't get it, haha. This question, again, is quite farcical. It's akin to the problem of "if a tree falls in the forest, and no o
233 LeanOfPeak : DavidL, you are exactly correct. It is not necessary (Or desirable) to lock the wheels. Doing so would flat-spot the tires before blowing them out and
234 Post contains images David L : Yeah. The bottom line is that the question as stated isn't nearly as interesting to discuss as a lot of us thought it was.
235 MD-90 : Obviously, this is a calculus problem, and there is a limit. I think that this paradox was thought up by someone who accidentally misunderstood the pr
236 Post contains images David L : ... or was thinking about a conveyor belt which moves at an equal and opposite speed to that of the aircraft, like all the same discussions elsewhere
237 Post contains images David L : Little did I realise at the time how much the question resembles that routine.
238 Post contains images FLY2HMO : I would happily volunteer to fly my remote controlled airplane off a conveyor if somebody is willing to build a conveyor for it.
239 LeanOfPeak : Also an easy question. The statement is a lie. The correct half of the reasoning that leads to the impression that this is an unresolvable vicious ci
240 Post contains images David L : You've ruined Star Trek.
241 Post contains images VSIVARIES : This problem has always had a certain condition: To consider that condition you have to make a certain number of assumptions mainly dealing with speed
242 Darrenthe747 : ok guys, i have been thinking about this ALL DAY!!!!! AAARRGGHHH!!! but here's what I concluded... there is a KEY point to this theoretical problem: Q
243 Post contains images LeanOfPeak : The only context in which I've heard that problem posed with Star Trek is that there are two tribes on a planet, one 100% truthful and one 100% decei
244 Post contains images David L : We're way past that. Those of us unfortunate enough to have our minds set in the "real world" were clinging to the hope that the question had been in
245 VSIVARIES : It was a theoretical problem that had some theoretical conditions. It also has a theoretical answer. I can't prove the answer either. Good fun to watc
246 SlamClick : Obviously you are overthinking it. It is no such thing unless you want to apply real numbers to it and that is not necessary to find the answer. It i
247 SlamClick : Okay, I've been rereading some of the arguments regarding the specific language of the thread-starter question. When I first read that post I assumed
248 Post contains images SlamClick : Besides, I'm not going to waste my five thousandth post on this thread. I feel like I've done that many here alone.
249 Post contains images VSIVARIES : Slam you are normally right on most things esp. to do with being a pilot. You are not dealing with a real world situation here. Some of the condition
250 VSIVARIES : Just read post 248. Understood. B/R
251 Post contains images Ralgha : Sorry Slam, I've been sleeping and working so I wasn't here to back you up. To all the people who argue that the question as worded at the beginning o
252 Post contains links David L : No, I know the one you mean but this was a different one. I couldn't remember the details but apparently it's from Episode 41, "I, Mudd": "The landin
253 Post contains images Keta : Yes that's what we have been saying since long ago.
254 VSIVARIES : Into your own argument. Infinity means infinity. Sorry my friend given the condition of the original question (which is actually a puzzle), "The conv
255 DarkBlue : Here's my two cents... Can the aircraft move down the runway? No. Can it take off? Yes. Now before you all gasp at this absurd combination of statemen
256 Ralgha : You do not understand infinity. It is not a quantity, it can not be compared as a quantity. Infinity > Infinity Infinity < Infinity Infinity != Infin
257 Post contains images FlyMKG : PEOPLE! The question is all relative to the way you read it. You can either picture it as: (a) the conveyor moves 150 kts, the plane stays put, the c
258 Ralgha : Conveyor speed CAN NOT equal wheel speed. The reason for this is that there is nothing holding the airplane back. Nothing counters the engine force.
259 Ralgha : Unless you put an anchor on the airplane, this situation will not happen. Speed is not linear. A wheel's speed is typically measured in RPMs. I made
260 A346Dude : Ralgha is correct, his statement is true and that is why the airplane will take off. The conveyor belt is not holding the airplane back, even though
261 Post contains images Darkblue : New approach.... change your frame of reference from the ground to the conveyor. If you imagine the conveyor as fixed, and instead of the conveyor mov
262 Flyf15 : *sigh* I don't have time to read the entire arguements in this thread but it is pretty friggen sad to see that this discussion could go on so long. Of
263 Fokker Lover : Let's ask ourselves, Why is the belt turning? Because the wheels are turning. Why are the wheels turning? Because the plane is moving forward. If the
264 LeanOfPeak : If we have a magic conveyor that, as the question was put, always matches exactly the speed of the wheels, the only way to have groundspeed or airspee
265 Flyf15 : If you were to push forward on the model on a treadmill, say, make it go 10mph forward. Well, the treadmill then assumes that speed in reverse... Now
266 LeanOfPeak : ...And you've just broken the cardinal rule of the question at hand. You said it yourself. The treadmill is going 10 mph. The wheels are turning 20.
267 LeanOfPeak : Nope. The corollary to the question at hand would make the speed through the water the speed with respect to the treadmill and the speed with respect
268 Post contains images Flyf15 : Wait wait wait, so the treadmill and wheels have to be moving at the same speed? I guess I must've read this wrong. Then this problem can't exist. The
269 Navymidn : Through the fact that I can't seem to get this problem out of my head, I will try to explain why the aircraft will take off. If the conveyor belt spin
270 Post contains images LeanOfPeak : Yes, this is exactly what the original post says, and I did say that there is no way for the engines to generate this motion, but granted that, if mo
271 Navymidn : Okay, I am rethinking what I said about the rear moving belt.
272 Flyf15 : Reading through the thread, I see that ralgha has already come to the conclusion I mentioned, with the difference of stating that things still go on a
273 Post contains images ScarletHarlot : My brain hurts.
274 SlamClick : You ain't the lone ranger there lady. After spending two hours reviewing the posts on here I'd have to say that I haven't felt this foolish since the
275 OE-LDA : This is the greatest thread I can remember since I am a member here. It is interesting, how complicated one can think about such a simple setup. The p
276 Post contains images Chksix : OE-LDA, there's no way to make the "no fly zone" guys to understand LOL
277 Post contains images Kay : I'm ready to stand there!!! and take beautiful photos Really, I think we can remove the plane and simplify the example. If I put a wheel on a treadmi
278 Post contains images David L : The wheels would have to skid - the question didn't say they couldn't. But where does this magic force come from, the one that causes the wheels to s
279 Flyf15 : Uhh, why? It seems like it'd be totally and completely obvious that you wouldn't have any trouble moving the wheel in this situation.
280 Post contains images Mighluss : I'm sorry, I'm to lazy to read the hole threat, but after reading a few takes, and thinking about it, I say... If the belt can really match the speed
281 Keta : You still don't understand... you will never get a treadmill that will match the wheels' speed. No matter the belt, you will move.
282 ZSOFN : Guys, this is how it works. OK, some overlooked points. --------------------------- Firstly the the beginning of the experiment... So the plane is sit
283 Post contains images Vikkyvik : I guess I kind of agree with both sides (are there still just two? ) Both of the above statements are accurate in the real world. However, the problem
284 OE-LDA : Incredible, isn't it? Why and how on earth should the plane accelerate the belt? It is the other way round, the belt will accelerate or decelerate th
285 Post contains images Kay : Welcome to the irreversible zone of the "It will fly" group.   My views exactly. The treadmill will match the wheels' speed exactly because that's a
286 Vzlet : Another way to look at it. (Please consider these questions as rhetorical!) A plane intending to do a touch-and-go lands on the conveyor, touching dow
287 Post contains images NAV20 : One last try to convert the 'must-flys'. You step on a moving walkway and then realise that you're going the wrong way and start walking back. But wal
288 Post contains images David L : NO! You're still thinking about a force being applied by the person/aircraft to the belt. The force of the aircraft's engines is not transmitted to t
289 David L : For those who think the force of the belt travelling at the same speed in the opposite direction cancels the aircraft's speed, what do you think will
290 Post contains images NAV20 : David L, please forget the wheels. The engine thrust generates forward movement. The conveyor negates it.
291 Post contains images Kay : I was going to answer you to tell you "you will now be attacked by the 'it will fly' group saying that the wheels of the plane have no role" The "It
292 Keta : No, the force is not made by the wheels. Your legs yes they do a force. It's different. Once again... [Edited 2005-12-01 15:24:40]
293 ZSOFN : NAV20, you seem to still be thinking in quite simplistic terms. See my post further above about this. Think about it this way: The analogy of walking
294 David L : You cannot forget the wheels - they are crucial! Stand on a plank of wood while you're wearing rubber-soled shoes. Get someone to lift one end of the
295 Fokker Lover : This is where you are making your mistake. You are using the walkway to propel yourself. The airplane is not. I like to take things apart to see how
296 David L : They have a role - to isolate the aircraft from the horizontal force from the conveyor belt (excluding wheel bearing friction, which can't be that mu
297 ZSOFN : Further to what I said, I am with the people who say it can fly in general, however something that is yet to be argued over: Once the plane gets to r
298 Post contains images Kay : ZSOFN: The wheels don't drive the plane. Planes can take off with wheels turning at zero speed. But this plane here won't take off because the wheel
299 ZSOFN : Eh? Read what I said again! And the struts will move forward as I thought we were assuming the wheels to be able to turn without resistance.[Edited 2
300 Kay : Finally you are looking at it from the right angle: the conveyor is infinite resistance. Kay
301 ZSOFN : HAHA! I've figured it out... The aircraft applies thrust The aircraft initially remains almost stationary and the wheels spin up rapidly The ground ef
302 ZSOFN : ?
303 Post contains images David L : Go back to the example given earlier. You lift up a bicycle, in the upright position, and carry it along forwards. Now get someone to take a plank of
304 Fokker Lover : Tell me exactly how you are keeping the struts from moving forward. Don't say by spinning the wheels backwards, because you would be wrong. The only
305 Post contains images ZSOFN : The only way in which the belt can transfer energy is: a) into the wheels, and if we're modelling them as frictionless, this energy cannot be transmit
306 NAV20 : Guys, about speed. Take an aeroplane on the runway (an ORDINARY one!). You can express its speed any number of ways - in knots, in mph, in kph, or as
307 Mighluss : The plane is not accelerating the belt, the belt is accomoding to the speed of the wheels. anyway, after seeing that graphic of the man pushing, I st
308 Post contains images David L : Why not? The wheels isolate the movement of the conveyor belt from the aircraft. You're still thinking of a car. Look again at the bicycle example wh
309 ZSOFN : Guys, NAV20 does have a point. If the plane was to move forward, it would have to mean that the wheels were spinning faster than the conveyor belt was
310 Saintsman : I can believe that this is still going. Its an impossible situation, therefore all your comparisons and assumptions are invalid. Because its an imposs
311 Fokker Lover : Yes, it will move!!!!! The conveyor has no way of transferring its energy past the wheels. We have 2 opposing forces here. One is trying to drag the
312 ZSOFN : Fokker Lover, Yes, physics would normally dictate that the aircraft would move forward. BUT as one can assimilate from the question, this belt in its
313 Post contains images Bond007 : This is a perfect example, but you have it completely wrong! Of course it will move! It's quite the opposite of what you said. It's already been said
314 Kay : Yes, except by skidding the wheels! If the person with the ply of wood works like this belt, he will counter exactly any movement from the wheels. An
315 Post contains images David L : I think that's been well established now but there is still an element of the debate about a conveyor belt moving at the same speed as the aircraft b
316 Post contains images Kay : If the belt is moving opposite the aircraft's speed, it will fly. The wheels will just turn double. Alllllll this argument is about the belt turning
317 Post contains images Bond007 : Ignore my previous post I completely understand the theories from the "It will fly" crowd, but there is one thing wrong with the whole theory. You rea
318 Fokker Lover : Stop it how? A free wheeling wheel can do only one thing. That is rotate on its axis. It cannot stop a plane from moving. It can only spin. That's wh
319 Fokker Lover : I should have been in bed 3 hours ago. If you guys figure out how to make an airplane stop moving by spinning its wheels backwards wake me up. I plan
320 Post contains images Bond007 : I'm with you Kay A silly situation, but it cannot happen unless the belt and wheels are going at different speeds. Example: Imagine a wheel fixed at
321 Post contains images Mighluss : Now I caught the idea, if you don't push the brakes, the plane will not skid, but is an impossible anyway, as plane start moving forward, the wheels
322 Post contains images Kay : Bingo Jimbo! Fokker_Lover, I totally agree with you. Totally. But, how can a wheel (regardless of anything else, no plane, nothing) move forward on a
323 Post contains images Keta : I thought so too... It's the opposite way. The rules of the game are wrong, the first question is based on a false statement. It's impossible that yo
324 Post contains images ZSOFN : Is anyone going to read my posts? They seem to be ignored yet I feel they answer these latest questions.
325 Post contains images Bond007 : I read it You are correct. The plane will take off, but only by the wheels going faster than the conveyor. The question says this cannot happen...so
326 ZSOFN : Well this is my point of contention that no-one's addressing. With a conveyor belt moving SO fast, the airflow above it that it creates, whilst turbu
327 Kay : ZSOFN, you still have to establish that the conveyor will turn so fast. There's no telling if it will turn at all. We have a weird deadlock situation
328 ZSOFN : Well the assumptions that lead to the conveyor belt turning so fast: When the whole system is at rest it is in unstable equilibrium, that is, all it t
329 Kay : hmm. Which means the belt will run at infinite speed. If this inifinite energy indeed creates an airflow, it could just snap the wings of the plane,
330 Post contains images ZSOFN : I agree 100%!
331 Post contains images David L : No but, as I stated several times, I've lost interest in the question as stated - it's just too ridiculous to contemplate. However, there is still an
332 XORDLLAA : I cannot believe this thread has almost 900 posts..... It seems like some of the people don't know what makes an airplane fly, why there are engines a
333 Post contains images David L : This is a situation which can't happen so whether the plane would take off is irrelevant, undefined.
334 Bond007 : So are you saying it'll fly? Or are you agreeing it's a scenario that could never happen? I'm sure that most of the people that say it won't fly, and
335 Post contains images XORDLLAA : ...and yet, I don't know how to count I'm sorry, small correction - "over 300 posts"
336 Sovietjet : What have I created.....
337 XORDLLAA : Under the circumstances given in thread starter it will NOT fly. It is impossible. It is like arguing: how far can you jump, while running on gym's e
338 VuelingAirbus : can someone here please make a list of people who think it can fly opposed to one with people who say it can't? I will put all people who say it can't
339 Ralgha : That's not what ground effect is. Invalid comparison. When you jump, you are propelling yourself via the ground. Airplanes do not do this. Everyone w
340 Ralgha : It's not at all like this. If you attach the magnet to the car, it is a rigid attachment. Free spinning wheels DO NOT ATTACH ANYTHING TO ANYTHING ELS
341 A346Dude : 340 posts and counting and yet the "no" crowd still doesn't get it. The fact that the belt is moving backwards at the same speed that the wheels are m
342 Wingscrubber : Sod the airplane, but a helicopter on the conveyer belt, that'd bloody well take off. This thread is pointless.
343 Mdaigle : If this is taken at face value, this just means the belt will stop the wheel from turning and the "ground" will move in the same direction as the air
344 Keta : I'm not going to try to explain again why the airplane would move. Read again SlamClick, David L and many other's posts, they're very clear. In the s
345 Wingscrubber : Put a helicopter on the conveyer belt, that'll bloody well take off! This thread is so pointless...!
346 OE-LDA : If someone can proof to me that the plane does not take off, then I will voluntarily return my pilots license. Regards, OE-LDA
347 VuelingAirbus : Lets make it easier for everyone. Lets take a cart on ice skates with a big engine on top and if you apply thrust it would move (even if you move the
348 DarkBlue : Or maybe the "yes" crowd needs to step back and think about what you are saying. All here seem to agree that the question is flawed and is an impossi
349 ZSOFN : Ok, but is my point not valid? Would a fast-moving large conveyor belt not create airflow?
350 A346Dude : Sorry, but you just proved that the aircraft will take off. Your ice skate analogy is an accurate representation of the problem we are discussing, sin
351 VuelingAirbus : To clarify my previous point. The plane does accelarate - and thats out of discusion. So if the plane sits on ice skates it will accelarate depending
352 Keta : Well I can't agree with you. The belt and wheels work the same way the ice does i.e. there is no friction thus no force acting against the airplane.
353 ZSOFN : Whilst I want this thing to fly and generally agree with the theories of those who think it will, these supporters seem to overlook the initial rule a
354 NAV20 : Because the wheels are causing so many misunderstandings, I thought I might update my walkway analogy to include wheels - by introducing a baggage car
355 Post contains images David L : I don't think that's generally true. Pretty much every "yes" merchant has stated, quite some time ago, that the belt is an impossibility. I, for one,
356 NAV20 : Oddly enough, I don't think it would be mechanically impossible to set this up (though entirely pointless). If it was a light aeroplane its maximum sp
357 VuelingAirbus : Give me your licence number and I will gladly arrange it for you. Another thought just crossed my mind. Assume the airplane does not lift off. I acce
358 Post contains images A346Dude : Your baggage cart analogy is not a fair one, since feet are not wheels. Essentially, your analogy represents the problem posed initially, except that
359 Zarniwoop : Here goes..... Taking the "ideal world" case, as some other people have already said, this situation is impossible. Let me explain. There are 2 comple
360 Bri2k1 : Bloody Bollocks! If the wheel rotates about its axis, does it move or not? Answer that question first. If the wheel rotates about its axis, can its ce
361 NAV20 : But what if the belt's max. speed is equal to or greater than that of the aeroplane, Zarniwoop - which we must assume from the original question? I t
362 Keta : Please read SlamClick's posts. Don't they make any sense to you? Wrong!! First you accelerate the airplane to 340 knots relative to the air or ground
363 ZSOFN : Can we assume any airflow to be created by the moving belt? By the way conveyor belts are often used in wind tunnels as they can affect airflow quite
364 Post contains images David L : Sorry, NAV20 but... NO!   That represents a car towing a trailer. The motive power is still provided by transmitting force from your feet to the bel
365 Keta : You're right, but I think that's too complicated. I mean, the question and assumptions are very basic, there is no need to consider everything. Are y
366 Post contains images ZSOFN : OK, fair enough. If we forget about airflow generated, then I got to say that the aircraft's going nowhere. David L, remember the initial conditions
367 Post contains images Kay : Keta, there are two groups, and I think you are describing the scneario where the belt will match the speed of the plane. In that case yes it will fl
368 Post contains images David L : And let me say, yet again, that the question as stated is of no interest to me anymore (it just can't happen) but I'm perfectly happy to continue dis
369 Killjoy : Good luck finding a job and congratulations for not being able to spell your own profession. I'm not going to take part in the debate as the initial
370 Post contains images Keta : I fully agree. I know that most of us agree that the initial question is impossible, but there is still people like NAV20 and VuelingAirbus who say t
371 David L : I wonder if there's another anomaly in the opening thread. Can we have links to the same discussion elsewhere? I can only find discussions about the
372 DarkBlue : I've mentioned this previously. This is a form of Couette flow. Nope, not too complicated, it's a very real phenomenon and is fundamental topic in an
373 VuelingAirbus : Well - what can I say except that it was a typo and I am not an English native speaker. I didn't know I have to pass a grammar exam to be able to pos
374 VuelingAirbus : No - at the technical university in Munich Lets brin in another example. I put a plane on the belt with parking brake on. I let the belt run (lets sa
375 Post contains images David L : Oh yes they can (well, it is panto season)!   I assume you're adressing the "conveyor belt matches aircraft speed" situation. How does the belt tran
376 David L : OK, I misunderstood - so you're starting with an airspeed of -150 kts? That's not supposed to happen - the belt is supposed to match and oppose the s
377 Killjoy : I'm sure you're right, but clearly the problem didn't have this in mind. Perhaps it would be better to ignore the wings and just ask whether the plan
378 Lehpron : No, the wind speed the wings see would be zero, hence no lift. So what if the engines are on full countering the rolling drag of a conveyer belt, doe
379 VuelingAirbus : Maybe I am missing something. In normal conditions I am taking off with a certain acceleration rate it takes me about 30 seconds and i cover 2000 mete
380 Post contains images David L : Oh dear! Be honest - you haven't read the posts in between, have you?
381 David L : Ha! If the plane is on skates it would also accelerate. So, it's summer and you want to "ice-skate" on concrete. What do you do? You take off your ic
382 Post contains links VuelingAirbus : You would be right if the belt would match the speed of the aircraft. If the aircraft moves 150 kts in one direction but the belt with 150 kts in the
383 Post contains images David L : OK, we can stop right there because:
384 VuelingAirbus : No matter what source of power I have or whether the wheels are free spining or not. The plane taxies with 20 kts and the belt underneath moves with 2
385 David L : You're preaching to the converted. We all know what the question is. We all know it's not a real world situation. Most of us have been saying so for
386 Fokker Lover : You do realise that for any wheel to turn, the contact surface MUST move in the opposite direction. For every action there is an equal and opposite r
387 Post contains images Aloges : Has anyone yet mentioned the bleedin' conveyor belt can't even move as fast as the wheels spin? If the belt tries to make the wheels spin slower, it w
388 727EMflyer : Many sorrys, I couldn't possibly read the whole thread, but I see there are still some Yes'er's out there. The definitive answer is no, the plane can
389 Post contains images David L : Yes, just about everybody. An aircraft at rest has inertia. You're saying the engines can't overcome that? How do planes move? The point is that the
390 Post contains images David L : My apologies - another read tells me you're not saying that but I still don't see how the belt can "drag" the aircraft backwards unless it's allowed
391 727EMflyer : DavidL, Yes the engines overcome the inertia, like I said, and the airplane moves. However in our scenario with the conveyor belt, the conveyor belt p
392 Post contains images David L : Ah, OK. I'll but out of that one. As I said, I just don't care about the "magic" conveyor belt anymore. I just feel a need to continue the discussion
393 Killjoy : Note to everyone: He's actually quoting VuelingAirbus. The engines must generate enough thrust to overcome drag and the wings enough lift to overcome
394 VuelingAirbus : Why? Because 727EMflyer made a valid point? Its totally out of the question that the airplane would pick up speed and take off normally with just dou
395 Jamesbuk : ill try and simplify this for everyone ok on the ground the aircraft acts like a car as it isnt in the air as such so that would mean the aircraft wou
396 727EMflyer : Killjoy, 1. If an aircraft starts it's take-off run, it is not yet flying, therefore drag has not yet become a major player. I think in this scenario
397 Post contains images David L : Again... oh dear! This was introduced 347 posts ago! We agreed to forget that for the sake of discussion because there were people claiming that the
398 Post contains images David L : Aren't you?
399 Post contains images David L : No. You haven't read the posts either, have you? How many times is that now? Not even slightly.
400 Post contains images David L : Indeed - no problem! But the problem is that a lot of things which have already been covered are being brought up again and again and some of those r
401 Jamesbuk : yeh your right i didnt read all the post as it wouldve taken me hours lol so i only said what i thought was correct and so i guess there was a misund
402 Post contains images David L : No problem but you have to understand that after 4 days of explaining why an aircraft on a conveyor belt is different from a car on a conveyor belt,
403 CCA : I've tried to read most of the post and got through almost all. If you want to be true to the question you have to pick whether you want the "speed" t
404 Pihero : Ok, I'll try one last time . Just imagine a 4x4 on the ice of a frozen lake. Its wheels are spinning and its make no headway whatsoever as the surface
405 ATCme : So are most of us in agreement, "The plane could take off."? I for one say, YES.
406 Sovietjet : I still say no. Although I see the other side of the story the way I understood the question I say no. I see why some people say yes though and it rea
407 Post contains images HAWK21M : I'd say yes too.Now why dont we start a Part II of this thread.People are getting old waiting for the Thread to appear. regds MEL
408 Abbs380 : I have read most of this, I think. And I believe the a/c could take off. But the other night my brain was so frazzeled thinking about it that I had to
409 Post contains images Chksix : Joe wouldn't have to add power to stay besides Sue since he had to be at zero speed. The only thing to compensate for would be the slight rolling resi
410 Bri2k1 : I'm glad we've reached the conclusion the plane would fly. It appears to be sound. The only other comment I must make is to those who wish to say that
411 GRZ-AIR : YES, it can TAKE OFF!
412 Jetmatt777 : I'm sending this to the Mythbusters. Really, I am. -Matt
413 ThirtyEcho : This has to be the STUPIDEST thread ever on A.net. This doesn't belong in Tech/Ops: it belongs in a shredder or a looney bin. Suggesting deletion.
414 Post contains images SilverComet : Thought this thread had been locked a long time ago. If it isn't, then it should be. Not suggesting deletion though, as it is interesting to see how s
415 BoeingOnFinal : The ground has nothing to do with the thrust being created to create lift. All it does, is increase or decrease friction which will have an certain am
416 Flexo : What all of you who vote for a possible take off are forgetting is that the fictional conveyor belt will match ANY speed the tires will accelerate to.
417 Post contains images Keta : Who brought this up again?? I can't believe it's been more than a year since we almost went mad, and it's still kicking! Anyway, I suggest blocking th
418 Sovietjet : Wow I can't believe my thread is still going lol. Either way, I talked to both my dynamics teacher and my aerodynamics teacher about this some time ag
419 Post contains images SilverComet : You didn't understand the question properly. Had it been stated differenty i.e. the conveyor belt is designed to match any forward speed of the aircr
420 Post contains images Starlionblue : When I saw this thread again I wanted to go out back and shoot the computer.
421 Post contains images Chksix : LOL This is fun! I've posted before in this thread but.... If the belt is designed to match the rotation of the wheels it means that the belt will sta
422 Post contains links and images Jutes85 :
423 Post contains images Starlionblue : That's hilarious Jutes85. Especially the owls!
424 SilverComet : LOL nice one. But still wrong, assuming the conditions laid down in the original post.
425 Post contains images SilverComet : AAARGH!! I hate this thread. Changed my mind again. The conveyor will NEVER be able to match the speed of the wheels, even in theory. Friction between
426 CptSpeaking : In this situation, because there is no wind, the airspeed and the groundspeed are ALWAYS going to be equal. No matter how much thrust you have, you ha
427 BoeingOnFinal : Ok, I mistook the explanation on how the conveyor belt is working. So it actually cancels the speed of the wheels? So, unless you have an enormous amo
428 Post contains images Mir : I was going to write a big detailed post about why the plane will take off, but then I decided that it would be less painful to beat myself over the h
429 Sovietjet : Jutes85 - Lol so I see you're also on NASIOC....
430 MD-90 : lol, Jutes should make a graphic that shows the wheels exploding (which, according to the paradox that is this question, is what I believe would happe
431 Jetlagged : Both your dynamics teacher and aerodynamics teacher should go back to school. They appear to be confusing static friction with rolling friction. Ther
432 Post contains images CptSpeaking : Reminds me of something else...can this guy generate any forward airspeed and if he had wings, take off? Your CptSpeaking
433 BoeingOnFinal : No, because he gains speed by moving on the ground. And if an aircraft gained speed to take off by turning the wheel like a car, it wouldn't take off
434 Post contains images David L : No! That's the fundamental mistake made so many times in this thread. The animal propels the the wheel by applying a rearward force to the bottom of
435 Moriarty : If you start running on a treadmill, will the wind blow in your hair just because you're running? My answer would be: no, it won't (unless you put a f
436 David L : "Running on a treadmill" is not the same thing! The wheels do not propel the aircraft!
437 MidEx216 : I was gonna say no at first, but Nighthawk is right. Though the conveyor belt is moving in the opposite direction, that's not going to slow the plane
438 Post contains images CptSpeaking : I understand the difference in propulsion...my point in that is, if your speed over the ground (not the belt or in my example, wheel) remains at ZERO
439 Jetlagged : Another false assumption: that the aircraft will not move forward relative to the ground because the belt is running backwards. In fact the conveyor
440 Mir : If one were to disregard friction between the wheels and the axles, the airplane wouldn't move at all - the wheels would just spin. Since there is fr
441 Post contains images Jetlagged : True, but you are only allowing the pilot to add just enough thrust to counter the increased rolling friction. If the pilot sets takeoff thrust, roll
442 CptSpeaking : No Wind: TAS=GS. If you generate TAS, regardless of the type of propulsion...it doesn't matter, then you have generated GS. If you've generated GS, t
443 Bond007 : Simple question .... and no it's not completely obvious in the original question. what does this mean?? That the aircraft does not move in relation to
444 DarkBlue : Uggh, not this again. Please reread the question. The question is over-constrained. Everytime you state that the wheels are irrelevant you are choosin
445 Zeke : This is a very simple problem in physics .... The problem is F=ma, where F is the thrust - (rolling resistance + aerodynamic drag) m is the mass of th
446 CptSpeaking : LOL thank you ...finally somebody who thinks the same...
447 Jetlagged : 1. Yes 2. Yes 3. NO. Belt speed is not ground speed, nor does it cancel out ground speed. Whatever the conveyor belt does the aircraft accelerates. I
448 Post contains images Vzlet : Let's make the conveyor belt a tabletop model. Then take an American Junior Classics Hornet balsa plane and place it on the belt, keeping your hand o
449 MD-90 : There is a paradox, mainly because I think whoever worded the initial question was thinking in terms of the wheels propelling the aircraft like a car
450 CptSpeaking : This would be correct if you were talking relative lateral velocities. The wheels and the belt underneath would be moving laterally at the same veloc
451 Post contains images Keta : Well said, I agree. There's simply no way that the belt will stop the aircraft. No matter how fast it moves, it exerts no force (or a very little one
452 Starlionblue : Second that. How about in the ass? Centerline thrust is better. That's a bit like what aircraft carriers do. You gain a good 20-30 knots depending on
453 Chksix : Cancelling wheel speed means to me that the belt moves forward when the wheel tries to roll when thrust is applied. That means wheel rpm will be zero,
454 Bond007 : Well, I think it worded that way exactly to get the hundreds of anwers that this thread has got. Yes, that it the answer. Not sure ... see above ...
455 Post contains images Starlionblue : Can we enter a feature request for a little whiteboard in the posting window?
456 Sovietjet : Exactly. There's two interpretations and therefore two answers. They aren't wrong, as I said they came up with two answers based on two interpretatio
457 Bond007 : Not sure that affects the outcome though .. since regardless of what the belt does (or can do), all rules of physics say that the aircraft WILL move
458 Post contains images Mir : -Mir
459 Post contains images Starlionblue : I thought you gave up on this one. How is the truncheoning going?
460 Flexo : Even the tiniest amount of friction on the wheels, insignificant it may seem, becomes a great force once it is multiplied by infinity. As the hypothet
461 Post contains images Starlionblue : It will in fact be infinite if multiplied by infinity. For any of this stuff to work, we have to assume zero friction. Then again, since we are deali
462 DarkBlue : Ah, see that's where the confusion is. We in the "no fly" group understand (at least most of us do) that there is no physical or mechanical constrain
463 Post contains links and images Keta : I'd just like to note that I didn't say that The friction between the conveyor and the wheels is independent on the velocity, it just depends on the
464 Jetlagged : Explain please, because the wording seems very clear to me. I see no artificial contraint, just a theoretical belt working in a specified way. Any pa
465 Post contains images Moriarty : This thread is hilarious! A model is the way to go! Ok, I will move back from assumptions to speculations then! Seriously, it makes sense when I think
466 MD-90 : Ain't no tires ever built that have an infinite speed rating. Well, maybe on one or two ricers that drive pimped Civics, but they don't count.
467 Starlionblue : The song "Hot Shot City" was especially good.
468 DarkBlue : The theoretical constraint I see is the part of the question that says: As I've said many times before, I understand that wheels are not a physical c
469 Post contains images Jutes85 : haha, OT ftw. which reminds me:
470 Zeke : Any traction powered machine is an example, be it a tank, snow mobile, escevator, the wheels on the tank move at the same speed at the track (the con
471 Post contains images Mir : I guess I discovered my masochistic side. The truncheoning is going bludgeoningly. -Mir
472 Post contains images SilverComet : I used to be in the 'no fly zone'. Then I saw the light. The truth of the matter is all the occupants of said aircraft get off the plane and everyone
473 Post contains images Iwok : There are two solutions to this problem. Since we are assuming that the conveyor belt would have the same speed as the wheels (but in opposite direct
474 FutureUALpilot : It will takeoff. Ignoring the wheel bearing limits, etc, the thrust comes from the engines. If the aircraft had powered wheels, it would not move. How
475 Post contains images CptSpeaking : That was my point to begin with...as long as that belt is moving at the same speed as the wheels, you're not getting any groundspeed and therefore no
476 Yellowstone : If a plane is taking off a normal runway, it is traveling at a finite forward velocity, and its wheels (with radius r) have a finite rotational veloc
477 Post contains images Keta : I think you're still confused... there is no way that the belt will move at the same speed as the wheels, the plane will always run faster than the b
478 Bond007 : It really needs no interpretation of the question, since you are immediately breaking a basic rule of physics if you say the aircraft never moves for
479 SilverComet : That's another fine way of putting it in simple terms. Newton's 3rd law says if you push back on the air, the air pushes you forward relative to it,
480 BoeingOnFinal : I have to agree with others here, this is not correct. It would only apply if the belt moved the mass of air above it along at the same speed as the
481 DarkBlue : The point that CptSpeaking and I are trying to make is not if in a realistic scenario would the aircraft move -- we understand that wheels are irrele
482 Post contains images Bond007 : Congratulations.. you've also answered a different question The question was "can the plane take off?" . You say "No", but also "yes the aircraft wil
483 DarkBlue : Ha, yeah okay, fine. How's this: No, the scenario of an aircraft that takes off and has wheels matched to the conveyor cannot occur. The only reason
484 Post contains images David L : I agree wholeheartedly with that...
485 Bhill : Sounds like a dynomometer to me...the wheels spin and the car does not move forward...
486 Post contains images David L : Aaargh! Aircraft wheels do not drive the aircraft! Even in this magical scenario, the belt is not being driven by the aircraft wheels (unlike a dynam
487 CptSpeaking : Good grief...it is a hypothetical question. The question is impossible in the real world, but given the variables we were given, NOT ADDING ANYTHING,
488 Post contains images Iwok : Right, BUT we are assuming that the plane is starting from a zero thrust situation at the end of the conveyor belt. Correct the two answers are: Zero
489 CptSpeaking : Yes, BUT the question doesn't say otherwise, and this is what a normal takeoff consists of. Any other situation (i.e. rolling start, touch and go, et
490 StealthZ : Groundspeed has NOTHING to do with airspeed!!!
491 DarkBlue : Please read the original question.
492 Bond007 : To what question again ??? "can the plane take off??" The answer isn't 'zero and infinity' ! Jimbo
493 Post contains images Keta : OK, now I see what you mean. You're right, but that's like answering "if something stands still, it stands still" I don't like quoting myself, but an
494 SilverComet : And to think that all this has been unleashed becasue the OP didn't choose the right words...
495 Post contains images CptSpeaking : I guess that one is too hard for some here then also, eh? Agreed... Your CptSpeaking
496 Jetlagged : I see a pattern here. People dive into the thread and initially say the aircraft cannot move because the ground under it is moving backwards at exactl
497 Post contains images DarkBlue : Yes, I am obviously confused.    I interpreted the question as: Can an aircraft take off and have wheels matched to a conveyor? I still say, no, th
498 StealthZ : You are right there in the no fly group aren't you. I read the question and the activity of the wheels, rotating forward or backward or locked has no
499 Post contains images Starlionblue : Because it's still entertaining. I would think they're placing bets by now.
500 SlamClick : To whom will go the dubious honor of the 500th post?
501 Post contains images Starlionblue : Well well well... Look what the treadmill dragged in...
502 Post contains images Iwok : This is a really cool thread so please dont delete is mods Well, if the headwind=0, then groundspeed is equal to airspeed, which is what was stated in
503 Post contains images Chksix : There are longer ones Why are the "No Fly Zone" so hung up on the wheels? I'll reiterate my point: The belt is computer controlled to make sure it wil
504 Post contains images SilverComet : LOL trust SlamClick to chime in at the right time.. glad to know he's still watching over us helpless Tech/Oppers. What's so hard to understand is ho
505 XT6Wagon : Uhm, Its very simple. The conveyor belt/treadmill has NO effect on the airplane other than a highly likely overspeeding of the tires and hub bearings.
506 ThirtyEcho : This thread is for all of you folks who think that the airplane is steered on the ground with the yoke and that the floor pedals are gas and brake. If
507 Post contains images David L : But the best the belt can do is to go so fast in the opposite direction that friction in the wheel bearings and between the tyres and the belt become
508 StealthZ : I think others above have answered this but it's speed relative to a fixed point is NOT zero, it's speed relative to a point on the conveyor belt may
509 DarkBlue : Perfect? Ehhhh really? Now it seems to me it's the fly group that is confused. You now have the conveyor running in the opposite direction! With the
510 Post contains images SilverComet : Exactly! However, the answer to the 'classic' situation is quite straightforward and the thead would have died pretty quickly. Tech/Ops, true to its
511 BoeingOnFinal : I might get in on that as well. I say that the aircraft will take off if such a scenario is created, because there is no way that a conveyor belt can
512 Post contains images CptSpeaking : But if it does move forward, then as I've stated dozens of times before, the question has been ignored. Work with what you've got! Don't get us going
513 StealthZ : This has nothing to do with a car on a dyno. The car on a dyno, the wheels drive the dyno, this does not happen with an aircraft with reactive propul
514 Post contains images DarkBlue : Ah, but see that's exactly the point. Realistically, yes this has nothing to do with a car on a dyno, yeah yeah, wheels are irrelevant i think someon
515 SilverComet : I say about 40-50 days.
516 Post contains images David L : I didn't say that. I said the situation couldn't happen. I don't agree at all. I only said, explicitly, that the aircraft would fly in the classic sc
517 Post contains images DarkBlue : Now we're getting somewhere. I'll agree with you that for the "classic" question the aircraft will fly, however the question stated was not the "clas
518 Chksix : By "matching the wheel speed" is see a solution where the belt is trying to keep the wheel rpm at zero. To read the function the opposite way it shoul
519 Post contains images David L : Once the reality of the thread dawned, I and several others explicitly said we were happy to continue the "classic" debate but that the question as s
520 Post contains images Chksix : No matter how many times I read the question I understand it as the wheels will be stopped from rolling by the belt. My jet is taking off from left to
521 Post contains images David L : That was another option entertained by those of us who wanted to deal with real physics, i.e. something that could actually happen. Alas, we were eff
522 Post contains images Keta : Pretty much what I think I understand it the other way, that the belt tries to stop the wheels relative to the surrounding, not just stop rotating.
523 Post contains images David L : I know, I think I borrowed this... from something you said earlier... like, about a year ago. I think there are 4 possibilities: 1. Belt opposes airc
524 Starlionblue : Correct. The belt cannot prevent the plane from moving forward since it has no effect on the engines.
525 Post contains images David L : Unless you believe the conditions determine that "it just does - we don't know how or why or what other aspects of the universe need to be changed to
526 Jetlagged : I studied logic at school too. Two statements which can never be true at the same time will always produce a false result when ANDed, but that is not
527 Mrocktor : The belt can prevent the plane from moving forward if it generates enough friction on the wheels to balance out the thrust. Yes, the treadmill would
528 Post contains links and images Keta : I've seen many times this statement, and I'm going to discuss only this . Rolling friction is not dependent on the speed, it only depends on the norm
529 Post contains images David L : Ah, yes, you're right. I got carried away pointing out that only "ridiculous" forces could allow the belt to prevent a jet aircraft from moving forwa
530 Starlionblue : Well, ok. But I doubt the original poster intended to include friction. I seriously doubt that "it just does" holds up to some solid scientific exper
531 Post contains images Iwok : Impossible scenario with this miraculous treadmill. As I said, I belive the question is an impossibility. Reviewing the original OP again, it does no
532 StealthZ : why is it not possible? Some people seem to forget that the only purpose of the undercarraige on an aeroplane is to hold it off the ground, they only
533 XT6Wagon : The speed of the treadmill is near on meaningless. The direction of the treadmills movement is of some importance since if it operates at a direction
534 Post contains images David L : You know that and I know that but that's what some people are saying. Are you saying that the aircraft can't accelerate to gain airspeed because the
535 Iwok : What I am saying that that, irregardless of the initial wheel/conveyor belt speed: it is impossible for the plane to achieve an air speed greater tha
536 Mir : Groundspeed STILL has nothing to do with airspeed in this case, because the ground (treadmill) is moving. You could spin the treadmill at 200kts, whi
537 Post contains images David L : Ah, OK. If you're in the group that interprets the problem as meaning "whatever happens and however illogical and unrealistic it may be, the aircraft
538 MidEx216 : Not quite, because even though the belt is matching the wheel speed, that doesn't mean it undoes the affect of the engines any. Once it starts gettin
539 Post contains images CptSpeaking : Groundspeed has everything to do with it because in a no wind situation, as the OP specifies, Groundspeed will always equal true airspeed. Holy Smoke
540 Post contains images David L : No, I don't "finally understand". I've been differentiating between the "classic" version, other feasible interpretations and the version "as stated"
541 Post contains images Jetlagged : Actually it's static friction that is related to normal reaction. Rolling friction is partially speed dependent. However, rolling friction is a relat
542 Post contains images David L : I agree but, according to some, the conditions in the thread starter dictate that the belt "somehow" prevents the aircraft from gaining airspeed... t
543 Mir : In relation to what? If you're talking about the belt, then it doesn't matter, for reasons that I've described. If you're talking about the ground, t
544 Post contains images David L : Except that CptSpeaking is arguing option 3, the impossible, illogical, non-aviation one so he doesn't need to "explain" why the aircraft can't gain
545 StealthZ : Can you not see that it does not matter what the wheels rotation is relative to, the only important thing is the airspeed and I see nothing in this q
546 Post contains images Keta : I'm interested in seeing that. All sources I have seen say that rolling friction is just a kind of static friction, related to the deformation of the
547 Post contains images David L : I'm not quite sure what's happening there but let's just make sure we agree there's a ground speed, an air speed and a belt speed (aircraft speed rel
548 Post contains images CptSpeaking : Good grief...I suppose as long as you know what I'm talking about, then I'm done with it. I'll be happy to agree with you with your "option" 1 and 2
549 Jetlagged : Clearly the faster the tyre rolls the more power is consumed deforming the tyres. The coefficient of rolling friction may be speed independent but th
550 Iwok : Well, its is indeed a word: disputed, but a bonafide word listed in dictionaries. Dictionary.com Unabridged (v 1.1) - Cite This Source ir·re·gard·
551 NWADC9 : This is a really old thread... Besides, like what the others said, a plane can't take off a conveyer belt matching the plane's speed (or attempt of)
552 BoeingOnFinal : Ohh, so that is what all the delays are about? Lack of wind? Some say that because the belt is designed to cancel any forward thrust by increasing ba
553 Keta : Please read reply 528 and tell me what's wrong there. The force is always the same, it's just the rolling friction coefficient times the normal force
554 Post contains images Mir : I do see that, and I agree! The reasons you mention are the very ones that explain why the plane CAN take off. -Mir
555 Starglider : The plane will fly, regardless of rotating wheels and contra-rotating conveyor belt. Jet engines produce thrust against the surrounding air, they are
556 Post contains images David L : Aircraft take off in still air all the time. I assume you're talking about option 1, belt opposing aircraft's ground speed. In option 1, you just end
557 Post contains images DarkBlue : I apologize, I missed this part of the conversation. Agreed, of the "fly group" David L has done the best job of showing that he understands both sid
558 Post contains images David L : It was bound to happen from time to time - it's like three independent football matches taking place on the same field, using the same lines and goal
559 Mrocktor : Thats right. Too long since high school, too long thinking about aerodynamics. Mea culpa. Thats for sure, one way or the other.
560 Post contains links Aviateur : I wrote and published an entire article on this topic, if you'd like to read it. The piece ran some months ago on Salon.com. It was inspired by David
561 Post contains images David L : " target=_blank>http://www.salon.com/tech/col/smith/...t215/ "For good measure, the treadmill itself, as described, could never be built. It can't "ex
562 ANITIX87 : I cannot believe we're this far into the thread and it's still going. The plane would not fly. If you put it down on a conveyor belt, with ALL its wei
563 ANITIX87 : Oops. I just spoke with a colleague of mine. I was half-wrong. If the belt moves without any thrust to the aircraft, then the plane will remain statio
564 David L : Is this Option 1, Option 2 or the magical Option 3 you're talking about?
565 Bond007 : No, quite the opposite. In a 'realistic' setting ... i.e. real physics and no 'magic' ... the plan WILL fly, and it WILL gain airspeed. In a 'non-rea
566 David L : Assuming Option 1 or Option 2, this part bothers me: The speed of rotation of the wheels does not depend solely on the speed of the aircraft, it depe
567 ANITIX87 : After more discussion with my colleagues, many of which disagree with one opinion or the other, I'm starting to see why my opinion is wrong, and why
568 Starlionblue : Well, they already did the "pigeons flying in a truck" myth.
569 Post contains images David L : As long as you only suggest Option 1 and/or Option 2.
570 DarkBlue : Actually it might be quite humurous to see them try to build the imaginary Option 3 machine. I'm sure there's someplace on ebay where you purchase so
571 ANITIX87 : I just basically wrote what the opening poster wrote, I'll leave the theories up to them, so as not to bias their opinionis. TIS
572 Post contains images David L : Well... yeah, I suppose... kind of... A former work colleague of mine managed to burn his back quite badly in an alcohol-related T-shirt incident. Wh
573 Starlionblue : They try that kind of stuff on a regular basis. My favorites are the personal flying machine (plans on eBay) and all the 100mpg devices. BTW the Myth
574 Sovietjet : I can't believe this is still going, and that Mythbusters havent tried this yet. Although it would be kind of hard to realistically pull off a conveyo
575 Bond007 : There is a simple way, and it's called basic physics ... which says the plane will move. Anything else means breaking these fundamental rules. Jimbo
576 DL787932ER : Okay, I've read the entire thread (there are some hours of my life I'll never get back) and after much thought, I can picture each of the two question
577 Post contains images David L : Correct - that would be Option 3. Yes, excellent summary... except we've been discussing 3 scenarios (Option 4 doesn't really warrant discussion). Ex
578 Access-Air : I cant believe that ANCFlyer has not locked this thread. I think its abssurd that I am even responding to this but its like saying If a rocket was lau
579 Post contains images Starlionblue : He can't lock it now. You just added new data! AAAAAAAAAAAAH!
580 Post contains images Iwok : MODS!!! Do not delete this thread. The same mystical force that propells the treadmill is propelling this thread on to infinity... This is a great th
581 Jetlagged : Don't delete it, just lock it now the no fly arguments are becoming even more circular than the conveyor belt. Then A.netters in years to come can see
582 Superstring : Well this topic is one of the longest I have ever seen, however I think to discuss also very "strange" questions is never wrong: It is illuminating be
583 Post contains images David L : I think the number of responses indicates the level of interest. Somebody might want clarification of a point they don't quite get. Do we really want
584 Airfoilsguy : I dub this the new SUPER THREAD!!!!
585 Post contains images Vikkyvik : I think that needs to be nominated for the Tech/Ops "Quote of the Week"? Well, I'm glad there was at least ONE decent reason for me to re-open this t
586 Post contains images Starlionblue : What, not Peter Max?
587 Post contains images Iwok : AMBIT: noun; "the scope, extents or bounds of something" It seems $5 words are required in this thread. So; what is consensus here? It appears to me
588 StealthZ : No we DO NOT... no one has put forward a half plausible argument why the plane will not move forward relative to a point on the ground or in the stil
589 HAWK21M : Thats true. Increasing the Relative Airflow past the Aircrat would. regds MEL
590 Post contains images David L : Given that Option 3 is not a real world scenario, I think it's fair to say the aircraft cannot move simply because of the wording of the problem. The
591 Bond007 : Whatever your options are ... if you believe in physics ... the aircraft will move. It's simple. Jimbo
592 Jetlagged : Apologies for my sense of humour, Iwok. For anyone who doesn't know what the phrase "begging the question" really means, this is a classic example. N
593 Post contains images David L : Neither do I, it's not my option! I was simply clarifying that some people were pursuing that option and it was getting interwoven and confused with
594 Post contains images Jetlagged : More than that, it is not even necessary to fully comply with the conditions of the OP. It is a fantasy for those who want to be able to find a way t
595 DarkBlue : Uhhh, why not? That's the fundamental idea behind calculating the speed of a person walking on a train. A train is traveling at 100 km/hr in one dire
596 Post contains images David L : Well, I suppose I did name it. I think that's true in some cases but I also think there are others who do interpret the wording of the problem as dic
597 DarkBlue : Your comments go both ways.... people who instinctively jumped into the "fly group" at some point realize that the there is a problem with the wordin
598 Post contains images DarkBlue :    Yes, unfortunately that makes a debate much more difficult when people throw in incorrect assumptions and inappropriate analogies. I still smile
599 Post contains images David L : I have nightmares about that football match! I wish I hadn't thought of it.
600 Jetlagged : 600 up, doesn't time fly![Edited 2007-06-05 19:19:32]
601 Iwok : Well its tricky and tied to the magical treadmill which is designed to rotate in the same rate but NEGATIVE to the wheels. Hence the plane cannot mov
602 Jetlagged : Because if you want to match the speeds they must have the same frame of reference, otherwise the whole thing is meaningless. Hang on a minute, the w
603 DarkBlue : No they don't. If I'm on a train that's crawling along at 5km/hr (relative to the ground) and I walk backwards at 5 km/hr (relative to the train), I
604 Post contains images Starlionblue : 602 posts later...
605 Jetlagged : Right, but you also said the belt would move (backwards) at the same speed as the relative speed between it and the wheels. So the magnitude of belt
606 Post contains images DarkBlue :    Yep, agreed. Although I consider this more of the result of the relationship of speeds and not the definition. I define the belt speed relative
607 Post contains images David L : Another example of where confusion can arise. Just for the record, I was considering the various speeds thus: Ground speed = aircraft speed relative
608 Post contains images DarkBlue : Must... not... let... thread... die... It's been more than 2 days since the last post, soooooo, let's change the question.... How about the aircraft i
609 Post contains images Starlionblue : You answered your own question.
610 Post contains images Mir : I was going to respond to that, but I think it might be more productive to post this: Breakfast time.... -Mir
611 Post contains images David L : Hmm... well, in this case, due to the curvature of the hamster wheel, the aircraft will transfer a slightly larger (but still quite small) tangential
612 Post contains images Vatveng : Wow... how have I missed this thread all this time??? I think some poster about 200+ posts back started on the right track to an explanation... Here's
613 Post contains images David L : On reflection, it's quite likely that there would come a time when the aircraft would find itself going past the vertical with insufficient energy to
614 Mir : Not if it were going fast enough. -Mir
615 David L : I think I covered that in my first attempt. However, that ignored the fact that early on it would quite possibly find itself having gone 1/3 of the w
616 DarkBlue : Yeah, I suppose any aircraft with a thrust-to-weight ratio greater than 1.0 would be able to accomplish the full circle. When it comes to high thrust
617 HAWK21M : You are forgetting about relative Airflow over the Control surfaces. regds MEL
618 Vatveng : Did you stop reading at this line? There's going to be plenty of airflow over the control surfaces once the plane starts skidding on the bloody stump
619 Post contains images David L : But a thrust to weight ratio of "just over"1 would only allow it to crawl up to the vertical. Once it got past the vertical, the thrust would no long
620 Post contains images Keta : Doing some calculations, I ended up wit the different situations the aircraft would face, quite interesting ones. I assumed that the airplane starts
621 HAWK21M : And the pitch down moment,since the wheels are not present. regds MEL
622 Post contains images David L : Excellent. I certainly wasn't about to do any calculations!   On further reflection, as I was trying to get to sleep, I hadn't taken into account th
623 XT6Wagon : Ok, seriously you have to assume that the wheelbearings are frictionless, have an infinite speed capacity, or simply admit that the plane taking off o
624 Chksix : In your scenario, it will drive off the belt runway in a relative position 45 degrees from it's starting point and then keep on accelerating on the gr
625 Post contains images David L : Yes, that was assumed for Option 1, where the wheels turn at twice the normal speed. It doesn't apply to Option 2, as the wheels don't turn at all in
626 XT6Wagon : Momentum would keep the plane heading at the 45 degrees to the direction its facing for a while. And yes, you are correct that Its a question of can
627 Post contains images David L : While I didn't say so explicitly, I believe that's what I implied... Note "transition", not "suddenly change".
628 XT6Wagon : Hmm... Thinking on it more, you COULD take off with the "magic force" treadmill that keeps the groundspeed of the aircraft at 0. First you build two l
629 NZ107 : This is amazing that you can keep going on about this! I'm sure it won't have a difference. Theroretically, there is still a forward motion (from the
630 Post contains images David L : Then it wouldn't make a difference only theorectically. In reality, however...
631 Post contains images Keta : While there's a forward motion, the side speed also plays a role in the flow. The airflow going through the wings won't be straight, it will come at
632 Post contains images David L : Exactly. That's where the crosswind limit comes in. Real crosswind limits are much lower than that 150 kts I took "theoretically" to mean "you can ig
633 Oly720man : Not true since the action of the belt would only be on the tyres, there'd be no wind loading on the fuselage. It would be like running across a runni
634 David L : If the runway heading is north, the aircraft will be thrusting itself northwards and the belt will be moving, let's say, eastwards. The aircraft woul
635 Post contains images David L : Forgot this one... Yes, but I have to assume we're talking about the same aircraft as we were in Options 1, 2 and 3 (assuming it actually had wheels)
636 Oly720man : Misinterpretation from me then. I didn't think the plane would be carried sideways by the belt, in which case, there would be a crosswind.
637 Post contains images David L : Phew! The last thing I need is a wind tunnel manager telling me I'm talking rubbish about... wind. There'd be no way out of that hole for me.
638 NZ107 : Haha maybe one day they will invent a rotating airport where 2 or more runways turn on a turntable to face the wind.. Then that problem will be solve
639 Post contains images Starlionblue : They already did that.
640 NZ107 : Hmm.. The picture doesn't want to display. Damn. I don't have any other ideas! Nevermind.. I guess they could just close the airport.
641 Post contains images David L : Yes, that's one solution. Another would be to avoid having conveyor belt runways that move sideways at the same rate as the aircraft's moving forward
642 Starlionblue : For those who can't see the picture, it's an aircraft carrier.
643 NZ107 : Boy would I love to see an A380 being catapulted off it! (crunch, can't support the force from the catapult) Imagine a 3km long aircraft carrier made
644 Post contains images Iwok : this scenario is one of the more realistic options (aside from the aircraft carrier ). In this case the plane would take off. Right: but the 0 ground
645 Post contains images David L : But they wouldn't be dragging in the fore and aft direction, i.e. in the direction the aircraft's trying to go so the thrust wouldn't be competing wi
646 XT6Wagon : even a car would not really notice, the acceleration the tires see would be at a 45 to the direction the car is facing. The only traction issues woul
647 Post contains images David L : But notice I said "if a car's wheels skidded sideways" - I didn't say they would skid sideways. My point was that a car's wheels losing grip would af
648 Post contains images Iwok : not to nit pick, but the loss of grip could affect the aircraft's ability to show a negative acceleration i.e. braking, which is exactly what would b
649 Post contains images SilverComet : w00t w00t the beast has been revived? Run for your sanity ppl!! (the plane will take off)
650 Post contains images David L : Aaargh... "I am just going outside and may be some time..." Um, what "infinite thrust"? My comments were relevant to the cross-runway conveyor belt (P
651 Superstring : Yes, Yes, Yes... I am No. 651. And still counting...
652 Ralgha : Good Lord are you people seriously still arguing about this? Every possible argument for why the airplane will not take off has been shredded by eithe
653 Superstring : Well we could construct a situation where the aircraft wont fly. Simply use some tons of glue and put the aircraft into the glue on the conveyor belt,
654 David L : For one option of one of the three different scenarios, yes, but what about the later ones? Incidentally, while SlamClick's contributions were immens
655 Zak : hilarious thread, shows the amount of hot air between the ears present, sadly. of course it will fly, slamclick > tecops
656 David L : In which scenario? One of the two original scenarios, the "hampster wheel" scenario or the cross-runway conveyor belt scenario?
657 Deltaamtrak058 : Lift is generated by the wings, the engine just pulls it forward. Thus I agree in that the engines will generate thrust, however if the wheels are "fi
658 XT6Wagon : If you secure the airplane to the ground such that the ground speed can't exceed 0mph, you can still take off. This is why I suggested the windtunel
659 Vikkyvik : Disclaimer: I haven't read all the replies since probably reply 150 or so.... How do you figure? Even with the most powerful jet engines out there rig
660 Zak : come on, you cant be serious.
661 SlamClick : Okay it is time for me to settle this. The plane would take off but you would not be able to guess where it was going to end up. Proof: They put your
662 David L : I think you're on to something there. If you tag the luggage to go to the airport it's already at and put it into the hold, the aircraft would have t
663 MidEx216 : To address the subject of the belt moving at the exact same speed as the wheels, this is much like the idea of an un-movable object meeting and unstop
664 XT6Wagon : Very serious. A jet engine moves alot of air. Given a long tunnel of minimum area the jet engines are plenty capible of generating a hell of a huge m
665 David L : That would Option 3 above. I think we've all agreed that just can't happen.
666 Jetlagged : Dangerous ground. The one thing that we're all agreed on is that we aren't all agreed on anything. I think this thread is like Halley's Comet, it re-
667 FredT : A tunnel will not do the trick. There's a reason that most wind tunnels are closed loops. Think about it. And the take off speed will still be quite
668 Post contains images David L : I didn't really want to go there but, since you mention it... It seems to me that, although you could obviously get the engines to generate an airflo
669 Post contains images Jetlagged : I'm not disagreeing, I just thought it was tempting fate to say so though.
670 Aauzou : The plane will indeed lift into the air, that is if the indicated air speed is equal to that which it would usually have at Vr, however the engines mu
671 Post contains images SilverComet : Umm I **think** you misunderstood the question. The conveyor belt runs the opposite way to that which you are probably assuming. Read the 650 or so p
672 Post contains images BAe146QT : Why don't you just tell him to take some Ketamine and curl up in the corner? Yeesh.
673 SilverComet : Heh my personal record on this thread is like 250 posts or so in a day. Yes, there was a time when I was interested to know if the plane would finall
674 Newagebird : longest thread ever! it wont take off, aircraft produces thrust but isnt going anywhere, it has to be in motion to develop lift. This is assuming the
675 SlamClick : Remarkable. People still jump on here believing that they could possibly offer an opinion or "facts" that have not already been considered, disputed,
676 Post contains images Jetlagged : Oh, well, that settles it then..... I suppose 673 replies are hard to wade through, but I'm amazed there are still posts like this. Even the no-fly g
677 Post contains images David L : It sure is. Which option are you addressing? If it's the one I think you're addressing, I think you have 600+ posts to review - hint: the wheels don'
678 SlamClick : Exactly. I see this thread as rather like the "Police Squad" or "Airplane!" movies, or even like demolition derby. Totally stupid and you are free to
679 Post contains images AirframeAS : It wont fly. I'm surprised that this thread is still going after all this time! Wow! Impressed!
680 Post contains images David L : Which one?
681 Newagebird : Remarkable the same blokes arguing about this for months, clearly im not in the loop. Well enjoy yourselves gday all newagebird
682 Post contains images FLY2HMO : So this beast of a thread is dangerously close to braking 700 replies, yet the correct answer was given in reply 2. Only in tech-ops
683 Post contains images Zak : its not about facts and figures, its about that fetish this thread here kind of proves the proliferation of the "magic fantasy wonderland" plane feti
684 StealthZ : Gonna bust thru 700 and then some if you consider reply 2 as the correct answer. Cheers
685 Post contains images David L : And still some haven't noticed there were at least 6 different scenarios discussed, only one of which involved "magic". Now that's remarkable.
686 Post contains images AirframeAS : See reply #2.
687 SlamClick : Without explaining what force is holding the plane back.
688 SlamClick : Actually every solution permitted infinity to be used, as if it was a real option. Magic enough for you?
689 AirframeAS : Maybe the conveyor belt is off. Maybe its on. But still....the relative wind over the wing is still needed to provide lift. If the belt was on, and t
690 StealthZ : You have not explained why the plane is not moving, have you forgotten the only role the wheels play on an aircraft is to stop the gear struts scrapi
691 Post contains images David L : That deals with one interpretation of one of the options. For other interpretations and scenarios, see replies 3 to 600+ I was referring to these opt
692 SlamClick : We agree on this. It is this: Explain this. It doesn't matter a damn if there is an airplane or a skateboard attached to those wheels. The belt could
693 SlamClick : Disagree with you on this one point: I was thinking along this line too then I realized something. Without getting into equations that never "prove" a
694 Post contains images David L : Before someone else chips in without reading the rest of the thread, it's probably worth a reminder that we agreed that failure of the bearings and/o
695 Bond007 : Correct. The airplane WILL move forward. It really is that simple. You can all discuss whether the belt can match the speed of the wheels, etc. etc.
696 NEMA : Just done a quick calculation. With the amount of rubber needed to construct a conveyor belt as wide and as long as the average runway you would need
697 Tdscanuck : The problem is all in the way the original question was formulated (yes, I have read all of the posts down to here...I'm bored at work). From the OP:
698 SlamClick : In other words - MAGIC. Simplify the question: "If a plane can be kept from moving will it take off? It is just silly. Move ONE STEP toward the real
699 Post contains images David L : OK, I'm going to have to think about that. Thanks ever so much. In the meantime... Option 1 was supposed to be the classic scenario, where the belt s
700 SlamClick : This is the 700th post. And it contributes as much as any other post to our understanding of this issue.
701 WPIAeroGuy : Before I throw this out there i just want to say that I agree with everything that SlamClick has been saying about infinite speeds, and if I had an ac
702 Post contains images David L : Given the history of this thread, there will now follow a further 50-odd posts disputing that.
703 SlamClick : Truth is, I was thinking about what Steven Hawking said in the acknowledgements of "A Brief History Of Time" that someone told him that each equation
704 SlamClick : Ah yes! Like that other piece of logic, The Six Million Dollar Man keeping a helicopter from taking off by hanging onto the skid - while standing fla
705 Post contains images WPIAeroGuy : The weakest point would be the contact between him and the ground. If, by whatever magic laws we're assuming his feet are not permitted to leave the
706 David L : Sounds like a "magic" version of Option 2 with extra conditions: However, I should repeat that Options 1 and 2 weren't meant to have any magic coupli
707 SlamClick : Only by increasing the diameter of the axle to equal that of the wheel. (in other words by retarding and stopping rotation) Which, unless he has gum
708 AirframeAS : Right. That means the plane on the belt cannot move, except for the wheels. The plane is stand still, again, except for the wheels. Hence, no airflow
709 SlamClick : What force is retarding the forward motion?
710 Post contains images FLY2HMO : Alright, I've been lurking the thread for too long without adding to it. I guess its about time, don't think this situation has been mentioned yet, if
711 Post contains images David L : Ah, I see what you mean. That's a new "What's the point of that?" scenario. However, if the belt isn't allowed to move, how can we say it's trying to
712 Post contains images David L : Um, actually it has been discussed and it was decided to ignore it because the central issue was to explain that an aircraft on a conveyor belt behav
713 Post contains images WPIAeroGuy : Well it's allowed to move, just in infinitesimal amounts. I say your tires would burst first, followed by the destruction/melting of the hub/axle, an
714 Post contains images David L : The available options need to be updated: "Real" Options: A1. Belt opposes aircraft's ground-speed, not its "belt-speed" ("classic" scenario) A2. Belt
715 WPIAeroGuy : Its philospophical only if you assume that its a magic belt keeping the wheels stationary. You can acheive the same result by anchoring the wheels dow
716 AirframeAS : Easy...if its off. Its a no-brainer. You need forward movement (which the belt does not really provide.) and relative wind over the wing. Its hard to
717 Post contains links and images SlamClick : You don't get it! YOU are the one arguing that there is some motion the conveyor belt would have that could affect the movement of the airplane. We a
718 Post contains images Vikkyvik : Eh, instead of typing a new post, I'll just quote myself (David, you can feel free to figure out which option I am replying to, since I don't know no
719 Vzlet : I'd explain that, but then I'd have to kill you. Signed, Steve Austin (Astronaut, AMBA)
720 Post contains images David L : I feel your pain. I'm having great difficulty reconciling this... (in other words, there's nothing stopping the aircraft from gaining airspeed) with
721 StealthZ : If rotation of the wheels in the direction of travel is a requirement for take off? Does that mean the floatplanes that take our Northern friends fish
722 Post contains images David L : Hang on a minute. Are you only applying thrust if the belt doesn't move and not applying thrust if it does move? I think you covered most of them. I
723 HAWK21M : Where is the relative wind generated from in this case. regds MEL
724 StealthZ : By the airframe propelled by it's engines, moving forward in the still air. Cheers
725 David L : I'm becoming deeply suspicious that some people are picturing an un-powered aircraft remaining stationary on a running conveyor belt, hence the notion
726 Post contains images HAWK21M : I'm referring to Relative wind over the Wings to generate Lift regds MEL
727 David L : I've been thinking again about the grouping of the different scenarios. Perhaps we should split the "real" scenarios from the "magic" scenarios thus:
728 WPIAeroGuy : In that case every real scenario should have the plane taking off. And by aircrafts speed do you mean wheel speed? Even if the conveyor was coupled in
729 HAWK21M : The conveyor belt moving will turn the wheels not generate the relative Airflow to the extend to serve Bernoulli's principle. regds MEL
730 SlamClick : Please, please read a few of the other posts. No one said the engines aren't running. No one said the thing is tied down. Did you read this? From tha
731 David L : No, the aircraft's speed. We assumed still air so airspeed would equal the aircraft's speed relative to the ground (not the conveyor belt). Of course
732 WPIAeroGuy : DavidL, I think we're saying the same things just putting different names on them. In the OP's question though he said implying that its the wheel spe
733 Post contains images David L : Yes, hence the reason Option 1 came about for those who wanted to talk about the "classic" scenario in terms of physics, rather than having a philoso
734 Post contains images SlamClick : There are a couple of mental challenges associated with that question alone. Picture an airplane at 100 MPH on the takeoff roll. The axle of the whee
735 WPIAeroGuy : SlamClick, you're incorporating velocity vectors and using the ground/runway as your frame of reference. I was just assuming the very edge of the tire
736 AirframeAS : I feel the same way, too. Its really hard to explain it.
737 Post contains images David L : That's why most of the 700+ posts exist. "Everything" discussed in this thread doesn't all relate to one big scenario. There are several different sc
738 SlamClick : There is another possible "real" scenario that might shed some light on the rest. It was not asked, but I'll volunteer it. If you wanted to prove that
739 Post contains images WPIAeroGuy : What if the plane was full of a load of pigeons and they all took off, then would it be possile?
740 Post contains images David L : That would do it. It's the new, improved Option 1 Mark II. And you could do the same with the belt but in the opposite direction for the new, improve
741 Post contains images Keta : Can't believe it, we're gonna make it over 1000! Yes that's more or less what it seems. It's hard for somebody who just arrived to read 600+ posts, so
742 Post contains images Ralgha : Wait...isn't it a given that we can?
743 SlamClick : I've come to believe that one reason we've come this far with people still disputing the obviously correct answer is a little matter than man has str
744 Post contains images HAWK21M : True its debatable & would need an entirely different thread regds MEL
745 WPIAeroGuy : Who still doesn't agree it won't take off? I'm pretty sure everyone agrees it will. @SlamClick and Everyone else, I'm not sure if you're referring to
746 Ralgha : There are a few...otherwise this wouldn't be post 745.
747 FredT : The only thing the conveyor belt can do is to impart a force on the tyre contact patch, in this context in the negative x direction (rearwards). The
748 Ralgha : Yep, I said basically the same thing about 600 posts ago, but that's ok it bears repeating again!
749 Post contains images Iwok : I still think the only plausible reasons the plane would take off are: 1) The wind tunnel 2) The very slick treadmill which could allow a certain amo
750 Post contains images David L : Yes, that's what was agreed. However, we separated the conveyor belt into two types: one that "magically" matches the aircraft's speed instantaneousl
751 Iwok : No no no no... I was only using SC's analogy to disprove the theory of the "driven conveyor"; in other words if the ground the CAT is on is muddy, th
752 Ralgha : The OP's intent is impossible, and the question was restated as it was intended a few posts in (somewhere less than 100). The OP's intent is impossib
753 Jetlagged : Iwok uses the word "treadmill" rather than "conveyor belt" which betrays his mindset about the effect it has on the aircraft. For completeness, there
754 Post contains images David L : Ah... oops. Sorry about that.
755 Post contains images Iwok : Exactly. The other solution is zero of course. Unfortunately, without the slick conveyor belt or the wind tunnel, the plane will NOT take off. The or
756 Post contains images Mandala499 : Let's continue on the crazy subject... Try and ski down a slope in a vacuum... Will you reach terminal velocity? No air resistance, you'd probably bur
757 Post contains images Iwok : The problem with the hovercraft analogy is that it violates the teachings of Sovietjet who specified that the treadmill must go backwards at a speed
758 Post contains images Airfoilsguy : Isn't there someone with access to a sim that could put this thread to rest?
759 Post contains images Mandala499 : Iwok, The relevance of the treadmill and the hovercraft is ONLY on the "resistance" offered by the wheel and the river in the case of the hovercraft.
760 Jetlagged : No more unlikely than the magic conveyor, surely? Exactly how are you defining wheel speed, because as has been pointed out the speed of the wheel re
761 Mandala499 : Jetlagged, Well in that case, do you take into account wheel axle resistance? Mandala499
762 Jetlagged : Doesn't matter, in the scheme of things rolling friction is a low force compared to thrust and drag.
763 Mandala499 : In that case the aircraft will move forward and reach the required airspeed and take off (just don't forget to apply the brakes before retracting the
764 Iwok : But, it would if the belt were slick. I think its a clear and reasonable solution to this problem. Highly unlikely, but I think the Soviets tried it
765 RussianJet : It's like being on a runnning machine - you're running but not going anywhere, which is also why you don't feel the wind in your face. No airflow over
766 StealthZ : No, No, No!!!! Nothing at all like being on a running machine!
767 Post contains images David L : Sorry, RussianJet, but there are a few hundred posts above explaining why that is not the case with an airliner. All together now... "Aircraft do not
768 RussianJet : I know that, but the aircraft is still dependent on the air flow to get lift, doesn't matter what causes the wheels to move or how fast they're going
769 RussianJet : It's a forward motion, regardless of whether it's caused by engine thrust or wheel drive (which in aircraft, believe it or not, I understand it is no
770 WPIAeroGuy : Right. And the conveyor is a backward motion, however, it ONLY makes the wheels spin. It does not affect the motion of the fuselage and wings at all.
771 RussianJet : Yes, when you exert a force greater than the opposite motion, of course it will move forward. What you're basically saying is that you would in fact
772 Post contains links BoeingOnFinal : Quoting RussianJet (Reply 771): Yes, when you exert a force greater than the opposite motion, of course it will move forward. And you don't think the
773 RussianJet : Right, which would never happen sufficiently in this case, because as the OP states, the conveyer would move at the same speed as the wheels. The fra
774 David L : The method of propulsion makes a huge difference. An aircraft moves by applying a force, from its engines, on the surrounding air (accelerates it rea
775 BoeingOnFinal : Q&A&W (Question & Answer & Why) Imagine a coin (or a wheel if you please), and place it on a conveyor belt. Now, the conveyor belt is totally still. Q
776 Post contains images Keta : That video is pretty amazing! Finally we have a visual proof Don't quite understand what that scary* face is, though *replace with a more suitable ad
777 RussianJet : Yes, but (originating post) - So how does that work? (I'll admit, I'm no physics expert, so it's a genuine question). Surely that coin can only repre
778 BoeingOnFinal : That is true, and I'll try to explain: This problem is not valid in many ways, and that is probably why it has been so many speculations. But consider
779 RussianJet : That does not necessarily imply any element of 'catching up' with the wheels - it says match. No problem - this is a hypothetical scenario. Thanks fo
780 HangarRat : I can't believe I'm posting in this thread, but here goes... The wheels are are a dependent factor in the problem. To say the conveyor belt matches th
781 Iwok : Unless the treadmill is somewhat slick of course. In that case, the front wheels would have a higher rotational speed than the rear wheels. The reaso
782 Post contains images David L : It's a decent summary. That would be nice, except that producing... ... which meets the OP's requirements in matching instantaneously, not even allow
783 Ralgha : Iwok, you do not understand why the OPs premise is impossible. If it were true, then both the wheels and conveyer speeds would approach infinity, howe
784 Chksix : Here I go again:: No-one has stepped up and responded to why everyone reads the original Question as a conveyor that will accelerate to infinity inste
785 Post contains images Iwok : It is most definitately possible, and there are several scenarios which are possible and which meet the principles of the original post. Since we all
786 Dmmoore : The original problem stated: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite directi
787 Post contains images David L : That would be Option 2.   That would be Option 3. [Edited 2007-09-17 13:33:10]
788 Post contains images Kay : Why is this topic still on? I think anyone with the slightest interest in aviation should come to terms with the reality that if a converyor belt that
789 StealthZ : No one else has, and you have not, explained how or why the conveyor cancels the aircrafts movement!
790 Kay : Dmmoore, I think this "complex, super intelligent, magic" conveyor belt is not what is commonly refered to in the conveyor belt problem that we are t
791 HangarRat : Fine, its a giant supermarket checkout belt, but how do you make it *exactly* match the wheels' speed? I don't contend that the belt will prevent the
792 WPIAeroGuy : The same way every physics problem never takes friction into account and occurs in a perfect vacuum, and how every shape you will ever use is a spher
793 Post contains images David L : Correct.
794 Post contains images Kay : I think the problem posted by the OP does not present alot of relevance physically. because it is so close to a very common and intuitive problem (pu
795 Post contains images David L : Speaking as a proponent of the "classic" belt scenario, I agree but... the thread starter and fans of the "magic" belt might argue that discussion of
796 Airfoilsguy : Ok, after 795 posts I will let you in on a secret. I know what the answer is. The plane will not take off nor will the plane not take off. After rotat
797 Post contains images Kay : you have a point. But maybe the OP has now had the chance to see the difference and has converted to "classic"? But are you pro-classic or pro-magic?
798 Post contains images David L : We gave him plenty of opportunities but he wouldn't change his mind. Yeah, classic black hole or magic black hole? I still like SlamClick's idea of i
799 Post contains images Iwok : Not so sure yet. Could it the black hole be countered by the black hole from the conveyor belt running in the opposite direction and hence opposite e
800 Post contains images FLY2HMO : 800 posts... 800!!!! Simply amazing. Heck this thread is even slowing down my computer, and my computer ain't no slouch either
801 KPWMSpotter : hehe...not that I'm trying to re-open debate, but apparently the Mythbusters will attempt to settle this once and for all in a little more than a week
802 Starlionblue : I'm sorry. What did you say? Kari was talking and I was distracted. It's slow loading for me, but no performance issues. Are you using IE? I have fou
803 Post contains images Jetlagged : Well of course not! Whichever way the experiment goes, the losing side will be arguing even more over the experimental technique, most obviously that
804 Sovietjet : Exactly, remember...the belt has to instantaneously match the speed of the wheels....not the airspeed of the plane. That's the tricky part, and there'
805 Iwok : Unless its slick of course and the wheels never actually turn.... I think I am going to have to send an e-mail to Myth Busters and tell them to read
806 Post contains images Res : Won't take off - no question about it. Why has this gone on for over 800 posts?? Some people watch too many cartoons
807 HAWK21M : Im surprised that this ebate is carrying on Still.Probably the longest thread on Tech/ops till date. And yet no decision reached. I still believe.It w
808 StealthZ : Of course it will!! Damn, don't believe I got dragged into this again
809 Post contains images Mir : Yes, but returning us to the original problem.....in a parallel universe. -Mir
810 Post contains images David L : I guess you didn't read many of them . Which of the many scenarios discussed are you referring to - one of the "magical" ones or one of the realistic
811 Post contains images FLY2HMO : I have firefox but some of my school's websites don't really like it so I'm stuck with IE
812 Sovietjet : Well, I actually agree that it will take off...and that it won't. I understand both sides of the story. The question is tricky, so people interpret it
813 Post contains images Sovietjet : Damn and you guys missed the 2 year anniversary of this thread
814 Evan767 : I wonder how the hell mythbusters is going to have a conveyer belt big enough for this.
815 Post contains images HAWK21M : Just Three types of opinions Yes,No & confused regds MEL
816 IFEMaster : There is an incredibly easy way to test this. I think I posted it somewhere above, but it got largely ignored. Essentially, the plane could take off