If A Plane Took Off A Conveyor Belt...

MQTmxguy · Thu Jan 31, 2008 5:50 am

Quoting Sovietjet (Reply 898):
Yes but Mythbusters did the "classic" scenario where the belt matches the aircraft ground speed. There is no way to test the original problem of the belt matching the wheel speed instantaneously. I didn't get to see the episode but AFAIK they were matching the plane speed. I'll watch it soon to make sure.

(I know it has been beat to death over and over and over but...) the test was fine because it doesn't matter how instantaneously the belt matches the tire speed, there is still no significant force to counteract the aircraft's thrust from moving the aircraft forward. The wheels are simply spinning twice your forward velocity. Imagine skiing down a snowy conveyer belt that was moving up hill. Doesn't matter how quickly that belt matches your speed, gravity will keep accelerating you forward, same thing with the thrust of an aircraft.

I think they did the best practical test of your OP that could be done in the real world.

Awseome! I got the 900th post!

[Edited 2008-01-30 21:51:54]

HAWK21M · Thu Jan 31, 2008 10:55 am

Quoting GrandTheftAero (Reply 897):
They did it on Mythbusters Jan 30. Conveyor Belt + Plane = Plane took off

Any link to the clip?
regds
MEL.

sjc4me · Thu Jan 31, 2008 1:07 pm

Quoting GrandTheftAero (Reply 897):
Much better topics have been closed long before the 894th reply. Shame on the moderators for letting this go on for so long.

Get a grip. If you dont like it, dont read it.

Also, I posted this in another thread but thought it might be useful here if anyone wants to debate it.

Quoting SJC4Me (Reply 24):
I think another thing to consider is that its physically impossible for a conveyor to match the speed of the wheels. Because If the conveyor is going 150mph backwards, and the plane moves 150mph forwards, the wheels are cruisin along at 300mph. If the conveyor speeds up to 300mph to match, the wheels would then be going 450mph. So, if the myth were to be executed based on that wording, it would be impossible to replicate. But were it to match the speed of the plane, such as what the mythbusters did, then obviously the plane will have no problems taking off, save for the uncertainty of the tires/bearings holding up to double the speed of Vr.

David L · Thu Jan 31, 2008 1:59 pm

Quoting SJC4Me (Reply 902):
Also, I posted this in another thread but thought it might be useful here if anyone wants to debate it.

Isn't that the basis for Option 3, the one that requires magic forces... and stuff? Smile

gregarious119 · Thu Jan 31, 2008 3:10 pm

I gotta admit, I was pretty impressed with the conditions they made for the test - doesn't get much more straight forward then that. Jamie even said he floored it, which means it's possible he was going faster backward with the belt than the pilot was.

OK, admission number 2, I'm a convert. It's really hard to get it through your head that it can take off until you see it. But really, the conveyor belt can go as fast as it wants and it won't stop the dumb thing from moving forward.

OMG Neil Boortz is talking about this right now on his talk radio show as I'm writing this....What the heck? He had it right.

flexo · Thu Jan 31, 2008 3:31 pm

Quoting MQTmxguy (Reply 900):
I think they did the best practical test of your OP that could be done in the real world.

That is very true and I believe also the reason why this thread got so many posts as people mix up theory and real world.

What the OP is suggesting can not be built in the real world and therefore can not be proven. A belt that matches every tire speed instantaneously would require ludicrous investment.

But the real and actually quite simple answer for the real world is: If a belt would be built that can go faster than the aircraft's tires can the plane won't take off, otherwise it will. Period.

Jetlagged · Thu Jan 31, 2008 4:28 pm

Quoting Flexo (Reply 905):
But the real and actually quite simple answer for the real world is: If a belt would be built that can go faster than the aircraft's tires can the plane won't take off, otherwise it will. Period.

The belt can go faster than the tyres and the aircraft will still take off (subject to the usual caveats about tyres overheating, etc). Belt speed is completely irrelevant.

The thing which makes belt speed appear important is the OP's constraint about matching tyre speed which can never be the done once the aircraft starts to gain groundspeed. This allegedly means flight is impossible so the constraint can be met (aka Option 3). A very strange form of inverted logic to an engineer like me, but probably normal sounding to a quantum physicist. Wink

HAWK21M · Thu Jan 31, 2008 4:36 pm

Quoting GrandTheftAero (Reply 897):
Much better topics have been closed long before the 894th reply. Shame on the moderators for letting this go on for so long.

This is Tech ops forum.Threads are rarely locked up as new discussions can go on being added.
regds
MEL

A346Dude · Thu Jan 31, 2008 5:02 pm

Quoting Flexo (Reply 905):
But the real and actually quite simple answer for the real world is: If a belt would be built that can go faster than the aircraft's tires can the plane won't take off, otherwise it will. Period.

The real answer is the plane will take off regardless of belt speed. Period.

sovietjet · Thu Jan 31, 2008 7:27 pm

I too am a convert, I originally thought it won't take off and then I realized it will(this was before Mythbusters) but with the tires spinning at infinity and sliding(aka translating) along the belt. Of course this can't be tested but essentially that is the most logical answer to the original question I posted. That way the constraint that the belt matches wheel speed is met, AND the logical physical outcome that thrust pushes the airplane forward is also in effect. The wheels would be like a bowling ball, both spinning and sliding along the belt.

Now mythbusters pretty much did it except for the crazy infinity speeds that would results from the original problem.

KELPkid · Thu Jan 31, 2008 7:40 pm

Quoting Sovietjet (Reply 909):

Congratulations on your 10 minutes of fame on TV (even if they didn't mention you at all-were it not for you, none of this ever would have happened) Big grin

Heck, they didn't even give airliners.net a mention Angry

, they just nebulously cited "the internet."

sjc4me · Thu Jan 31, 2008 11:33 pm

Quoting KELPkid (Reply 910):
Heck, they didn't even give airliners.net a mention Angry , they just nebulously cited "the internet."

Have you googled this topic? This can be found on tons of forums across the internet, most of them not even aviation related. Whether or not it 'originated' on a.net might be impossible to know, I can assure you that this is not the only place it was discussed. They did themselves a favor by calling it "the internet".

Starlionblue · Fri Feb 01, 2008 12:28 am

Quoting Gregarious119 (Reply 904):
OK, admission number 2, I'm a convert. It's really hard to get it through your head that it can take off until you see it. But really, the conveyor belt can go as fast as it wants and it won't stop the dumb thing from moving forward.

Quoting Sovietjet (Reply 909):
I too am a convert, I originally thought it won't take off and then I realized it will(this was before Mythbusters) but with the tires spinning at infinity and sliding(aka translating) along the belt.

Respect to both of you! It takes guts to admit you were wrong.

Quoting Flexo (Reply 905):

But the real and actually quite simple answer for the real world is: If a belt would be built that can go faster than the aircraft's tires can the plane won't take off, otherwise it will. Period.

Nope. You're wrong. The wheels would simply spin faster and the plane would still take off.

sovietjet · Fri Feb 01, 2008 4:27 am

Yes I've seen this topic on many places online.

Now here's the next question....

A helicopter on a giant turntable...does it take off? stirthepot

MQTmxguy · Fri Feb 01, 2008 6:49 am

Quoting Sovietjet (Reply 913):
Now here's the next question....

A helicopter on a giant turntable...does it take off?

Of course, the helicopter will still be ugly, thus the Earth will still repel it. Smile

But if your loking for a real answer, it's still yes.

If turing in the direction of main rotor rotation the aircraft will lift off sooner than normal.

If turning the opposite direction of main rotor rotation, once the rotors get up to speed the anti-torque rotor will compensate for the rotation, arrest the spinning motion, and the aircraft will lift off normally

Starlionblue · Fri Feb 01, 2008 9:03 am

It all depends on the speed of the turntable.

Quoting MQTmxguy (Reply 914):

If turing in the direction of main rotor rotation the aircraft will lift off sooner than normal.

Yes

Quoting MQTmxguy (Reply 914):
If turning the opposite direction of main rotor rotation, once the rotors get up to speed the anti-torque rotor will compensate for the rotation, arrest the spinning motion, and the aircraft will lift off normally

That won't work. If the helicopter is sitting on the turntable the anti-torque rotor can't scrape the skids/gear against the surface.

MQTmxguy · Fri Feb 01, 2008 11:48 am

Quoting Starlionblue (Reply 915):
That won't work. If the helicopter is sitting on the turntable the anti-torque rotor can't scrape the skids/gear against the surface.

phffft, I'm using a UH-60, duh Wink

David L · Fri Feb 01, 2008 11:58 am

Quoting SJC4Me (Reply 911):
I can assure you that this is not the only place it was discussed.

And most of those concern the classic problem involving a conveyor belt that tries to oppose the aircraft's speed.

Quoting Starlionblue (Reply 915):
That won't work. If the helicopter is sitting on the turntable the anti-torque rotor can't scrape the skids/gear against the surface.

Agreed. Even if it did, there'd be an almighty yaw in the opposite direction once the skids left the surface.!

This is a different ball game where the turntable would directly affect the rotor blades' airspeed. The engine turns the rotor against the helicopter.

The rotor would be rotating in the air at a rate equal to rotor RPM (relative to the helicopter) plus turntable RPM.

If the turntable rotates in the opposite direction from the the rotor, the turntable speed is negative so the rotor speed will be rotor RPM (relative to the helicopter) minus turntable RPM.

If the turntable rotates faster in the opposite direction than the maximum engine speed, the rotor will be rotating "backwards" through the air.

Starlionblue · Fri Feb 01, 2008 12:09 pm

Quoting David L (Reply 917):
This is a different ball game where the turntable would directly affect the rotor blades' airspeed. The engine turns the rotor against the helicopter.

And that should be the end of the discussion. But somehow I doubt that it will be. Wink

Starlionblue · Fri Feb 01, 2008 1:06 pm

I found this analogy floating around. It explains the physics perfectly:
A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.

The rope is equivalent to the aircraft's engines. Any forces on the rope are independent of the treadmill.

And while we're at it, here's a little item those of you who understand physics might want to acquire:

http://www.cafepress.com/planetakesoff

[Edited 2008-02-01 05:10:15]

Jetlagged · Fri Feb 01, 2008 1:42 pm

Quoting Flexo (Reply 905):
But the real and actually quite simple answer for the real world is: If a belt would be built that can go faster than the aircraft's tires can the plane won't take off, otherwise it will. Period.

With due respect to Flexo, three of us criticised his statement, but all missed one significant word which makes it true. "Can". What he says is if the belt goes faster than the tyres can then the plane won't take off because of the tyre's physical limitations.

David L · Fri Feb 01, 2008 1:57 pm

Quoting Starlionblue (Reply 918):
And that should be the end of the discussion. But somehow I doubt that it will be.

Yes, we need an Option 3 for the helicopter on a turntable. duck

Quoting Jetlagged (Reply 920):
With due respect to Flexo, three of us criticised his statement, but all missed one significant word which makes it true. "Can". What he says is if the belt goes faster than the tyres can then the plane won't take off because of the tyre's physical limitations

Well, OK, but... the aircraft would have considerable momentum by the time the wheels reached their "maximum" speed so I suspect they would begin to drag along the surface, even if the tyres have shredded and/or burst into flames - no-one said the aircraft had to reach its destination in one piece Smile

. It would reduce the aircraft's acceleration but not necessarily cancel it altogether. I suppose it would depend on whether or not the belt could withstand the damaged gear without it digging in.

Starlionblue · Fri Feb 01, 2008 3:34 pm

So I watched the Mythbusters episode:
- The result was no surprise.
- The tests, animations and "science content" were very good. Adam's demonstration with the car on the treadmill was excellent.
- The pilot was totally clueless. I can't believe someone who doesn't understand the very basic physics of how his aircraft works can hold a pilot's license. I'm not asking pilots to solve aerodynamics problems in their heads, but come on!

David L · Fri Feb 01, 2008 3:52 pm

Quoting Starlionblue (Reply 922):
- The pilot was totally clueless. I can't believe someone who doesn't understand the very basic physics of how his aircraft works can hold a pilot's license. I'm not asking pilots to solve aerodynamics problems in their heads, but come on!

I haven't seen it yet but perhaps it's just something he's never thought about before and he had to rush to a conclusion?

Starlionblue · Fri Feb 01, 2008 4:24 pm

Quoting David L (Reply 923):
I haven't seen it yet but perhaps it's just something he's never thought about before and he had to rush to a conclusion?

You are so kind. Wink

But yes that may be so.
.

HAWK21M · Fri Feb 01, 2008 4:24 pm

Quoting Starlionblue (Reply 922):
So I watched the Mythbusters episode

Any link?

regds
MEL

DaBuzzard · Fri Feb 01, 2008 5:27 pm

Quoting Jetlagged (Reply 920):
if the belt goes faster than the tyres can then the plane won't take off because of the tyre's physical limitations

Just because the sidewall says 160 mph max speed does not mean it won't spin any faster, it's not like there are brakes inside the tire that apply when the max speed is reached.

Tires overspeed, they will likely come apart....but there is no reason the plane will not take off with blown tires.....

David L · Fri Feb 01, 2008 5:27 pm

Quoting Starlionblue (Reply 924):
You are so kind. But yes that may be so.

Well, I'm reminded of the mess I made in an earlier thread about birds flying inside an aircraft - not the one from a couple of years ago but one shortly after I joined. It took a few posts before I started thinking about it clearly.

Quoting HAWK21M (Reply 925):
Quoting Starlionblue (Reply 922):
So I watched the Mythbusters episode

Any link?

Video clip of the actual test in the now locked (phew!) duplicate thread here:

Plane On A Conveyor Belt - Will It Work? (by KaiGywer Jan 30 2008 in Civil Aviation)

[Edited 2008-02-01 09:32:48]

tdscanuck · Fri Feb 01, 2008 7:08 pm

Quoting MQTmxguy (Reply 914):
Of course, the helicopter will still be ugly, thus the Earth will still repel it.

No no no...this principal of flight only applies to military helicopters.

Normal helicopters don't fly either...they just beat the air into submission.

Tom.

MQTmxguy · Fri Feb 01, 2008 11:22 pm

Quoting Tdscanuck (Reply 928):
No no no...this principal of flight only applies to military helicopters.

Normal helicopters don't fly either...they just beat the air into submission.

Of course, they taught us that way back in AMT101, how amature of me (stupid!stupid!stupid!)

(I still say a tailwheel helo would lift off as long as the mains were equidistant from the center of rotation.)

[Edited 2008-02-01 15:24:13]

Jetlagged · Fri Feb 01, 2008 11:39 pm

Quoting DaBuzzard (Reply 926):
Just because the sidewall says 160 mph max speed does not mean it won't spin any faster, it's not like there are brakes inside the tire that apply when the max speed is reached.

Tires overspeed, they will likely come apart....but there is no reason the plane will not take off with blown tires.....

Obviously real tyres will operate some way above their rated speed, and most of the arguments on this thread assumed no friction so no tyre burst or bearing overheat. However if all the tyres came apart it would add a lot of drag. Bear in mind that at 160 mph (airspeed) the tyres will be doing 320 mph because of the conveyor belt....

Quoting Starlionblue (Reply 922):
I can't believe someone who doesn't understand the very basic physics of how his aircraft works can hold a pilot's license. I'm not asking pilots to solve aerodynamics problems in their heads, but come on!

I can. I've met one or two who, although perfectly safe when flying, don't think before they speak on the ground. Wink

Starlionblue · Sat Feb 02, 2008 12:42 am

Quoting HAWK21M (Reply 925):
Quoting Starlionblue (Reply 922):
So I watched the Mythbusters episode

Any link?

I watched a recording like. But if you're willing to go shady the entire episode is most likely available on torrent sites.

HAWK21M · Sat Feb 02, 2008 9:40 am

Quoting Starlionblue (Reply 931):
I watched a recording like. But if you're willing to go shady the entire episode is most likely available on torrent sites.

I'll try searching for it.
Thanks.
regds
MEL

David L · Sat Feb 02, 2008 10:37 am

Quoting Tdscanuck (Reply 928):
Quoting MQTmxguy (Reply 914):
Of course, the helicopter will still be ugly, thus the Earth will still repel it.

No no no...this principal of flight only applies to military helicopters.

Normal helicopters don't fly either...they just beat the air into submission.

And helicopter pilots will tell you the rotor remains stationary and the world revolves around it. duck

Quoting MQTmxguy (Reply 929):
(I still say a tailwheel helo would lift off as long as the mains were equidistant from the center of rotation.)

It seems to me that it's assumed that the helicopter has to revolve with the turntable... otherwise, what's the point of it being there?

sjc4me · Sat Feb 02, 2008 1:42 pm

I say we all gang up on Sovietjet and beat the crap out of him for bringing this up. box

flexo · Sun Feb 03, 2008 10:06 am

Quoting Starlionblue (Reply 912):
Nope. You're wrong. The wheels would simply spin faster and the plane would still take off.

Spin faster than what? Wheels have a limited speed range and after exceeding it they will explode eventually. If you build a belt that goes faster than that speed, it is at least very unlikely to still be able to gain ground speed with bare steel grinding along a rapidly backwards speeding belt.
Maybe some vastly overpowered military jet might still do it, but an airliner? Nope.

flexo · Sun Feb 03, 2008 10:18 am

Quoting David L (Reply 921):
Well, OK, but... the aircraft would have considerable momentum by the time the wheels reached their "maximum" speed so I suspect they would begin to drag along the surface, even if the tyres have shredded and/or burst into flames

Not sure if it is smart to enter this discussion at the 935th post, but here I go:
I don't think the plane would have any momentum remotely considerable if you keep the OPs original constraint in mind: Match speed instantaneously.
Meaning that by the time the airplane starts gaining significant ground speed the conveyor belt will have already reached its maximum speed and the tires will already have exploded.

David L · Sun Feb 03, 2008 11:18 am

Quoting Flexo (Reply 936):
I don't think the plane would have any momentum remotely considerable if you keep the OPs original constraint in mind: Match speed instantaneously.

That would be Option 3, the "magic" one, which I dissociated myself from. Jetlagged and I have been following the path of Option 1 so comments from both of us relate to that.

Quoting Flexo (Reply 935):
Wheels have a limited speed range and after exceeding it they will explode eventually.

Again, in Option 1, the "classic" version as demonstrated in Mythbusters,, the aircraft takes of at the usual airspeed with the wheels rotating twice as fast as usual. We agreed that the gear might not stand up to it but the point is that the belt does not prevent the aircraft from accelerating at almost the usual rate, contrary to what the doubters of the classic version believe.

Quoting Flexo (Reply 936):
Not sure if it is smart to enter this discussion at the 935th post, but here I go:

Hmm... tricky. There's an awful lot covered already. Smile

Starlionblue · Sun Feb 03, 2008 1:12 pm

Quoting Flexo (Reply 935):
Quoting Starlionblue (Reply 912):
Nope. You're wrong. The wheels would simply spin faster and the plane would still take off.

Spin faster than what? Wheels have a limited speed range and after exceeding it they will explode eventually. If you build a belt that goes faster than that speed, it is at least very unlikely to still be able to gain ground speed with bare steel grinding along a rapidly backwards speeding belt.
Maybe some vastly overpowered military jet might still do it, but an airliner? Nope.

David L already handled your objections. I will say that the post of yours I replied to didn't talk about wheel constraints the way your later defense of it does.

iwok · Fri Feb 08, 2008 11:03 am

Quoting Sovietjet (Reply 898):
Yes but Mythbusters did the "classic" scenario where the belt matches the aircraft ground speed. There is no way to test the original problem of the belt matching the wheel speed instantaneously. I didn't get to see the episode but AFAIK they were matching the plane speed. I'll watch it soon to make sure.

I do agree with you for sure. Its just not possible.

So is this law 1a????

Quoting Sovietjet (Reply 909):
I too am a convert, I originally thought it won't take off and then I realized it will(this was before Mythbusters) but with the tires spinning at infinity and sliding(aka translating) along the belt. Of course this can't be tested but essentially that is the most logical answer to the original question I posted.

Which is what I'v been saying all along! banghead

Quoting Sovietjet (Reply 913):
A helicopter on a giant turntable...does it take off?

If the tail rotor is working, then it will definitely take off.

Glad to see this thread is still alive and well. I of course missed the damn show, and so I'll have to wait for the re-run.

iwok

Starlionblue · Fri Feb 08, 2008 11:49 am

Quoting Iwok (Reply 939):

Glad to see this thread is still alive and well. I of course missed the damn show, and so I'll have to wait for the re-run.

I have "heard" of this thing called bittorrent. Wink

SP90 · Sat Feb 09, 2008 3:26 am

I think the Mythbuster episode proves that a plane can indeed take off on a conveyor belt. Recall Jamie saying how if the wheels on that model car were left to spin freely it took almost no effort to keep it stationary on a moving treadmill. This is how the wheels on planes work, they spin freely. So regardless if the conveyor belt was moving or not the plane's engine will move the plane right along for takeoff.

Starlionblue · Sat Feb 09, 2008 6:28 am

Quoting SP90 (Reply 941):
I think the Mythbuster episode proves that a plane can indeed take off on a conveyor belt. Recall Jamie saying how if the wheels on that model car were left to spin freely it took almost no effort to keep it stationary on a moving treadmill. This is how the wheels on planes work, they spin freely. So regardless if the conveyor belt was moving or not the plane's engine will move the plane right along for takeoff.

That was quite a good demo. Showing how you can drive along the conveyor with power to the wheels, or push with your hand (aircraft engine) with free spinning wheels.

BTW it was quite clear what Jamie and Adam thought. Despite their efforts not to sound biased.

sovietjet · Sat Feb 09, 2008 7:10 am

The episode is on youtube...search for mythbusters conveyor or something like that. I watched it yesterday...the pilot of that plane shouldn't be a pilot based on what he said Smile

jetblueguy22 · Wed Feb 27, 2008 12:38 am

Wow. This is a huge thread! Anyone think of doing a part 2, 3, or 4? Just wanted to be post 945 Big grin

Blue

Viscount724 · Wed Feb 27, 2008 6:44 am

Quoting Jetblueguy22 (Reply 945):
Wow. This is a huge thread! Anyone think of doing a part 2, 3, or 4?

I had the same thought. In other forums when postings get to the 200 or so mark it goes to Part 2 etc. Why is this one different?

Considering the many A.net technical problems over the past few months, I'm concerned that when this thread reaches 1000 posts it may cause the entire A.net system to shut down as there appears to be no room for a 4-digit number of posts on the forum index pages.

Starlionblue · Wed Feb 27, 2008 2:00 pm

Quoting Viscount724 (Reply 946):
Considering the many A.net technical problems over the past few months, I'm concerned that when this thread reaches 1000 posts it may cause the entire A.net system to shut down as there appears to be no room for a 4-digit number of posts on the forum index pages.

Combine that with Rule 3 and it might just collapse the Universe.

tdscanuck · Wed Feb 27, 2008 5:50 pm

Quoting Viscount724 (Reply 946):
In other forums when postings get to the 200 or so mark it goes to Part 2 etc. Why is this one different?

It's the forum equivalent of a car crash...you want to see just how bad it can actually get. Besides, no other thread deserves to be tainted with the level of lunacy present in this one. Let's keep the damage contained.

Tom.

Starlionblue · Fri May 16, 2008 1:13 am

Ok. So what if you filled the tires with water and then tried to take off from a conveyor belt?

vikkyvik · Fri May 16, 2008 4:20 am

Quoting Starlionblue (Reply 949):
Ok. So what if you filled the tires with water and then tried to take off from a conveyor belt?

You bastard. You and 2H4. The both of you. devil

Are we talking theoretical - the tires are completely filled with water, balanced, and won't burst?

Better yet, what if the conveyor belt was in a water tunnel???

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