Sovietjet From Bulgaria, joined Mar 2003, 1781 posts, RR: 14 Posted (3 years 7 months 1 week 9 hours ago) and read 32767 times:
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.
Joness0154 From United States, joined Nov 2005, 667 posts, RR: 0 Reply 2, posted (3 years 7 months 1 week 8 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
BA From United States, joined May 2000, 10427 posts, RR: 72 Reply 3, posted (3 years 7 months 1 week 8 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
Nighthawk From United Kingdom (Scotland), joined Sep 2001, 4066 posts, RR: 43 Reply 5, posted (3 years 7 months 1 week 7 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!
"Thats why you need people like me in the secret service" Random Drunk. Manchester. 01/08
Joness0154 From United States, joined Nov 2005, 667 posts, RR: 0 Reply 6, posted (3 years 7 months 1 week 7 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
Airplanepics From United Kingdom (England), joined Jun 2003, 2700 posts, RR: 54 Reply 7, posted (3 years 7 months 1 week 7 hours ago) and read 32767 times:
I think we have another "How many pigeons would it take to lift a 747" thread!
RichardPrice From , joined Dec 1969, posts, RR: Reply 9, posted (3 years 7 months 1 week 6 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.
Joness0154 From United States, joined Nov 2005, 667 posts, RR: 0 Reply 11, posted (3 years 7 months 1 week 6 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
RichardPrice From , joined Dec 1969, posts, RR: Reply 12, posted (3 years 7 months 1 week 6 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.
RichardPrice From , joined Dec 1969, posts, RR: Reply 13, posted (3 years 7 months 1 week 6 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.
Nighthawk From United Kingdom (Scotland), joined Sep 2001, 4066 posts, RR: 43 Reply 14, posted (3 years 7 months 1 week 6 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.
"Thats why you need people like me in the secret service" Random Drunk. Manchester. 01/08
Joness0154 From United States, joined Nov 2005, 667 posts, RR: 0 Reply 15, posted (3 years 7 months 1 week 6 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
RichardPrice From , joined Dec 1969, posts, RR: Reply 16, posted (3 years 7 months 1 week 6 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.
Joness0154 From United States, joined Nov 2005, 667 posts, RR: 0 Reply 17, posted (3 years 7 months 1 week 5 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
RichardPrice From , joined Dec 1969, posts, RR: Reply 18, posted (3 years 7 months 1 week 5 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
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.
Nighthawk From United Kingdom (Scotland), joined Sep 2001, 4066 posts, RR: 43 Reply 20, posted (3 years 7 months 1 week 5 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.
"Thats why you need people like me in the secret service" Random Drunk. Manchester. 01/08
HT From Germany, joined May 2005, 4886 posts, RR: 29 Reply 21, posted (3 years 7 months 1 week 5 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 ...
(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 !
QFA380 From Australia, joined Jul 2005, 1779 posts, RR: 3 Reply 22, posted (3 years 7 months 1 week 5 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?
PMN From United Kingdom, joined Mar 2005, 535 posts, RR: 1 Reply 25, posted (3 years 7 months 1 week 3 hours ago) and read 32767 times:
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. Therefore, as the wheels are free spinning, the thrust of the engines should still move the aircraft forwards, even though the wheels themselves may be spinning at twice the speed the aircraft is physically moving.
Just the way I see it, but I'm more than happy to be proved wrong!
Paul
EDIT: I thought I'd just come up with something almost intelligent to say, but I've forgotten what it was.
[Edited 2005-11-29 12:59:26]
Edith in his bed, a plane in the rain is humming, the wires in the walls are humming some song - some mysterious song
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
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,
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 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 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
41 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 PMN: Ah yes, sorry Kay, I missed the all important smile! Paul
44 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 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 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 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 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 MiCorazonAzul: My physics calculations show that it does take off.........
68 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 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 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 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 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 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 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 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
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 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 Joness0154: THE VIDEO THAT SOLVES IT ALL!!! http://videos.streetfire.net/player....E964D9-38DB-4EFD-BE8D-D6BA1A43A06B
94 Joness0154: and an avweb article http://www.avweb.com/news/columns/191034-1.html
95 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 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 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 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 A346Dude: Couldn't you at least entertain the possibility that we do?
100 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
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 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
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 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 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 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 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 A346Dude: You just had to get that out, didn't you.
125 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 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 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 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 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
150 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 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 David L: Little did I realise at the time how much the question resembles that routine.
238 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
241 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 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 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 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 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 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 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 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 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 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 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 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
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 Chksix: OE-LDA, there's no way to make the "no fly zone" guys to understand LOL
277 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 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 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 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 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 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 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 NAV20: David L, please forget the wheels. The engine thrust generates forward movement. The conveyor negates it.
291 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 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
303 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 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 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 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 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 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 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 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 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 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 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 ZSOFN: Is anyone going to read my posts? They seem to be ignored yet I feel they answer these latest questions.
325 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,
331 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 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 XORDLLAA: ...and yet, I don't know how to count I'm sorry, small correction - "over 300 posts"
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 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 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 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 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 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 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 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 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 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 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
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 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 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 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 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 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
399 David L: No. You haven't read the posts either, have you? How many times is that now? Not even slightly.
400 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 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 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 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
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 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 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 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 Starlionblue: When I saw this thread again I wanted to go out back and shoot the computer.
421 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
423 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 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 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 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 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 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 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
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