if the wheels can't move froward I can't see any reason for air to move over the wings

11/19/2007 9:55:55 PM

The wheels CAN move forward.

11/19/2007 9:57:14 PM

Again, if you could make a "treadmill" with the air - ie. a very strong wind - THEN the plane would not move, because the motive force has nothing to do with the ground - only the air.

[Edited on November 19, 2007 at 9:58 PM. Reason : ]

11/19/2007 9:58:01 PM

but the treadmill is moving them backwards at the same speed as the plane is moving fowrad

11/19/2007 9:58:24 PM

AAAhahahaaha. Trolled again. Twice in one day. I commend you, hdrive.

11/19/2007 9:58:57 PM

thanks

11/19/2007 10:00:59 PM

11/19/2007 10:55:00 PM

Quote :

"and a plane with an extremely short take off distance."

that part is easy. there are STOL airplanes that can take off in 50-100' or maybe less.

Quote :

"he plane will not move unless the wheels can create net horiz. distance. "

haha.

I give up. This is becoming one of those "If you have to ask..." scenarios.

Quote :

"If we are to assume that the treadmill doesn't actually matter and the plane will move forward as planned, then the entire premise of this myth is null because it can never happen. It WILL NOT take off because this is an invalid scenario. So, for those of you saying it will take off, you are still wrong."

[NO]

The treadmill doesn't matter (well, it does to a very small extent, but it's basically inconsequential with all but the most severely underpowered airplanes, and even they might be ok). There is no "assuming"--it's a pretty clear-cut thing.

Quote :

"Of course MythBusters will probably screw this up as usual by not putting their model on a variable speed treadmill. I remember once they were baffled because a steel cable rated at 5,000 pounds kept snapping when tied to a car traveling double digit mph. "But the car only weighs 3,000 pounds, so we don't know why the cable is snapping." I hate that show."

Yeah, I really want to bet some money against any of the people who don't realize they're wrong, but I'm not sure I trust Mythbusters to be the deciding factor.

and yeah, a 3000lb car towed at a constant speed applies only the rolling frictional force and aerodynamic drag to the cable...but when you are accelerating that car--and especially if you shock-load the cable to any appreciable degree--it's a different ballgame (although a 5000 lb rated cable would be sufficient to accelerate a 3000 lb car if you exercised some caution and restraint).

Quote :

"It would be funny to reverse the treadmill right as the plane is trying to take off and watch it sling it off the runway"

it wouldn't do much of anything.

and i hope that was sly sarcasm against the people who think it won't take off.

Quote :

"For those still thinking it wouldn't: if you had a constant wind blowing against the plane at a speed equal that which would be produced by the engines, it would still take off, but to a ground observer it would appear to have no horizontal motion...and that would be a freakin' sight..."

Yep, I've hovered a radio-controlled airplane in this scenario. in fact, I've flown one backwards.

For that matter, I've come pretty close to hovering (like this) in some full-size airplanes. You could actually hover a jet on a strong day in the jet stream...I've always wanted to do that, but always had other stuff to do with my limited supply of jet fuel.

Quote :

"ok - the plane would not take off, if the treadmill was canceling out the plane's forward movement. the plane would* take off if the treadmill was assisting the plane in moving forward, however that is a big god damn treadmill. bottom line here is aerodynamics. if the plane is stationary, it isn't going anywhere. /thread"

the airplane will take off regardless of what the treadmill does. it can do whatever speed it wants in either direction, and even change back and forth in the middle of takeoff, and the airplane will barely know the difference.

Quote :

"Lift is generated by the movement of air over the airfoils...if there is no forward movement of the plane then the air is not being moved over the airfoil and lift cannot be generated. End of Story"

You are absolutely right! But the airplane will take off.

___________________________________________________________


Here's the deal: I have radio controlled and full-scale airplanes at my disposal (Cessnas, not just military jets). If any of you can beg, steal, borrow, or build a suitable conveyor belt, I'll take off and land either or both from it.

and if putting my own pink body on the line isn't enough, I'm just itching to bet any amount of money that I foresee anyone in this thread putting down on this argument. We just need to find a good way of settling it and a trustworthy middleman to hold our money until I take it all.

[Edited on November 20, 2007 at 2:00 AM. Reason : How's that for a guarantee that I'm right?]

11/20/2007 1:59:25 AM

also, achilles can never catch the turtle.

11/20/2007 2:16:51 AM

IT'S A TRICK, BECAUSE PLANES CAN'T FLY!


oh wait that doesn't work here

11/20/2007 2:25:01 AM

theDuke866 I'd be willing to bet money that any non-carrier rated plane (such as the F-16) could not do it

11/20/2007 2:32:44 AM

i'd bet my life because shit is never going on mythbusters

[Edited on November 20, 2007 at 2:33 AM. Reason : i cannot spell in the presence of Baonest]

11/20/2007 2:33:14 AM

the only way that plane will take off is through some commie magic...

heathens.

11/20/2007 2:34:41 AM

Quote :

"Why do they even test myths like this? Simple common sense could prove it wrong. "

The way the scenario is worded kind of sets your brain up to think it won't take off. It seems like common sense once you get it, but for most people, it takes a bit of thought to realize what's going on. It's like the 3 guys in the hotel riddle, the scenario is set up to trick you.

Quote :

"but the treadmill is moving them backwards at the same speed as the plane is moving fowrad "

Just in case you aren't trolling...

What made me get it the first time this thread came around was someone using the Tonka truck on a treadmill example. I can hold the Tonka truck still regardless of how the treadmill is moving. I can push it forward very easily, without having to worry about how fast the treadmill is going. The engines on the airplane are like your hand, able to easily move the plane, and the wheels are just like the Tonka truck's, they spin freely.

[Edited on November 20, 2007 at 2:40 AM. Reason : ]

11/20/2007 2:37:46 AM

i wish i was a pilot

and im with duke on this one

11/20/2007 2:38:14 AM

eh...most planes won't be able to take of in this situation. The wheels will be spinning twice as fast as the plane is moving, your either going to blow out the tires or fuck the wheel bearings up pretty badly. I would bet most carrier launched planes would be able to do it though, they make those landing gear tough. Either that or a plane with a very low take off speed





[Edited on November 20, 2007 at 3:35 AM. Reason : a]

11/20/2007 3:29:33 AM

^^^^^^ I will personally do it with a CESSNA (152 or 172) if you somehow find a suitable conveyor belt.

I'll do it with a radio controlled airplane when I'm in NC in a few weeks, too, if you can somehow find a conveyor big enough for that (could prob make do with 30' or so, although it would need to be at least 5-6' wide)


and if you just want to bet the money, I'll do that too provided we meet the aforementioned conditions. Maybe a poll of 5-10 mechanical/aerospace engineering professors?



^ V1 is decision speed, and I don't see how that really is very applicable here. I mean, that is also a function of other stuff completely external to the airplane (runway length, for example).

Maybe you mean Vr (which still isn't that big of a deal for our purposes, but it's arguably more applicable for what you're trying to say).


at least you seem to recognize that the airplane moves forward normally (for all practical purposes). You're just concerned about the structural integrity of various landing gear components.

While aircraft don't always have as high of factors of safety designed in as some other things (due to weight considerations), I guarantee you that a single takeoff run at double the wheel speed isn't gonna do anything.

[Edited on November 20, 2007 at 3:43 AM. Reason : asdf]

11/20/2007 3:34:14 AM

Radio Controlled air planes = very low take off speed.

On paper the plane will take off, in reality on most planes you're going to blow the bearings or the wheels

^I was thinking Vlof...but its 3 am and my brain is fried

[Edited on November 20, 2007 at 3:45 AM. Reason : tired]

11/20/2007 3:36:56 AM

No way in hell.


Well, ok...you MIGHT could find an airplane with landing gear not up to the task or so underpowered that it would be unable to overcome the little bit of extra friction in the wheel bearings, but I think it would be a difficult search, if not a completely futile effort.

but in general, the airplane would have no trouble at all.



and most R/C airplanes don't even have wheel bearings--that's a huge DISADVANTAGE for them in this scenario (not that it would matter).

11/20/2007 3:46:53 AM

go ask the next Crew Chief (or whatever Marine equivalent) you see , if he thinks the bearings and tire could hold up to twice take off speed and I'll ask one of my crew chief friends. We'll compare notes later.

[Edited on November 20, 2007 at 3:52 AM. Reason : a]

11/20/2007 3:52:10 AM

When i think of the treadmill, i'm not thinking of the 10MPH max speed variety. I"m thinking of a treadmill that will automatically match the speed of the airplanes wheels as it accellerates. Does that change anything?

p.s. my limited experiences with emergency landings tell me that the tires on the airplane will explode if you land at too high of a speed. I think the tires will give before the bearings.

[Edited on November 20, 2007 at 7:06 AM. Reason : ]

11/20/2007 7:04:08 AM

Quote :

"it wouldn't do much of anything. and i hope that was sly sarcasm against the people who think it won't take off."

lol, yeah. I was just messing with you. I can't believe this thread.

11/20/2007 8:38:39 AM

Quote :

"Does that change anything?"

No.

11/20/2007 8:43:56 AM

if there is no wind (0mph) and the plane is stationary, it will not take off, no matter how much thrust is exerted.

air over/under the wings at a certain speed is what is necessary to experience lift.

11/20/2007 8:52:49 AM

Quote :

"p.s. my limited experiences with emergency landings tell me that the tires on the airplane will explode if you land at too high of a speed. I think the tires will give before the bearings."

the difference in a landing is that the wheels are instantaneously accelerated to that speed and there is considerable frictional force. In this case the acceleration of the wheels is more gradual so all that matters is the maximum speed capability of the bearings and the tires.

[Edited on November 20, 2007 at 9:24 AM. Reason : ]

11/20/2007 9:19:47 AM

^^you can stop trolling now, its old and not funny.

[Edited on November 20, 2007 at 9:24 AM. Reason : ^]

11/20/2007 9:23:53 AM

oh stfu

11/20/2007 9:25:46 AM

Regardless of whether or not the landing gear can take it, that isn't the question. The theory behind the flight still holds true. If it were an ideal situation with ideal, infinitely strong landing gears/bearings, it would take off without any problem.

btw, all you people who think it won't take off, stop ending all your posts with "/thread" or "End of story" or whatever.

[Edited on November 20, 2007 at 9:51 AM. Reason : ]

11/20/2007 9:41:38 AM

alright, i've changed my opinion, come to the light, woke up...whatever you want to call it. i'm going to go with the airplane will take off. the example that i could not get past is the guy with rollerblades on the treadmill pulling himself with a rope. sorry guys for bringing this back up, but i don't want to look back and see a wrong answer after Dec. 12.

11/20/2007 10:24:54 AM

Even if the Mythbusters are unable to prove that it can take off, it will be due to outside variables. It won't be because the plane is unable to move forward.

11/20/2007 10:38:46 AM

yeah, having the plane move forward regardless of conveyor speed is pretty much going to put an end to this

11/20/2007 10:40:39 AM

Attention: the problem from the very beginning is ill-stated because it leaves to the reader to make two key assumptions. The correct answer depends on what you assume. First, let's make the simplifying assumption (not as key) that there is no headwind.

Quote :

"If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?"

Assumptions to make:

(1) plane is traveling at takeoff speed (relative to what, air/land or conveyor belt?)

(2) belt is matching that speed in the opposite direction (relative to what, air/land or plane?)

I. Start by choosing (1) to be relative to the conveyor belt. This seems logical because the questions says "on a conveyor belt". In this case then the belt is by default moving the same speed relative to the plane in the opposite direction. We can then decide that (2) is a redundant statement and the belt acts no different than a normal runway, so of course the plane will be flying.

II. Assume again that (1) is relative to the conveyor belt. Again, by default the belt will be moving the same speed but opposite relative to the plane. But if we choose that (2) is not meant to be a redundant statement then we could assume the belt is matching the plane's takeoff speed, but relative to the ground. NOW, this assumption constrains the problem by statement - not by propulsion physics - that the plane has a zero velocity relative to the air/ground, and so will not have lift and will not fly.

III. & IV. Assume that (1) is relative to the air/ground. The plane flies regardless of what the belt does.

Most of the debate has been due to unclarified disagreement in these assumptions. If the real interest is what would a plane do if it tried to take off on a treadmill, or say even a long stretch of ice, just do a free body diagram. The wheel/rolling friction is no match for the thrust of a jet or prop engine, so the plane would accelerate and then go on to generate lift. I think that part was pretty well covered.

11/20/2007 11:00:40 AM

^ That's all well and good, but ask yourself this: does it really make physical sense that the airplane, under power of its own engines, could be traveling at takeoff speed relative to the conveyor belt and NOT have any forward movement? The problem says nothing about headwind, I see no reason to introduce variables it doesn't call into question. I believe it's pretty sensible to use Occam's Razor and default the headwind to zero.

11/20/2007 5:50:58 PM

Ok, so asked my friend who is a KC-10 crew chief...he believes the landing gear would definitely fail before take off.. The tires are rotating twice as fast and accelerating (in terms of rotational speed) twice as quickly. No one way in hell would landing gear be able to take that kind of punishment. Smaller planes should be able to do it, but you're still going to stress the hell outta the gear



[Edited on November 20, 2007 at 6:08 PM. Reason : a]

11/20/2007 5:56:39 PM

that's so not part of what's worth debating..and I highly doubt they're right

11/20/2007 7:02:07 PM

Please tell me how you are more qualified than a guy who has been repairing aircraft for 10 years.

And the whole flight thing isn't worth debating, because its simple, the plane will lift off if the gear will support the craft.

[Edited on November 20, 2007 at 7:14 PM. Reason : a]

11/20/2007 7:13:53 PM

it's probably already in this thread, but I don't feel like looking through it.

Of course it's far from a perfect setup. Can't wait to see what mythbusters comes up with


http://www.youtube.com/watch?v=-EopVDgSPAk




[Edited on November 20, 2007 at 8:49 PM. Reason : d]

11/20/2007 8:35:21 PM

what the hell does landing gear have to do with the theoretical question at hand?

11/20/2007 9:32:24 PM

^not much of anything - it doesn't power, or retard the plane's movement.

11/20/2007 9:39:20 PM

The landing gear would fail before the plane could take off. Either the bearings would be destroyed or the tires would blow out.

11/20/2007 10:04:53 PM

so the plane can't take off

11/20/2007 10:11:34 PM

theoretical question

11/20/2007 10:14:11 PM

real answer

11/20/2007 10:14:55 PM

Provided the plane's landing gear could survive the high speed of take-off, the plane will easily take off.

/thread

11/20/2007 10:23:32 PM

ok lets say they are super dynamite krypton wheel bearings.

11/20/2007 10:24:02 PM

^ you're an idiot, only super dynamite adamantium bearings would work.

11/20/2007 10:27:26 PM

well i cant afford adamantium

11/20/2007 10:29:01 PM

baonest

my nig

i would REALLY appreciate it if you sent me the correct answer to this thread

this is like the 3rd time i've seen this thread on tww

and i still dont know the answer


dont post the answer in this thread obviously


pm me what the real answer is...personally...i dont think it would take off

11/20/2007 10:37:14 PM

lol, every 2 years i ask this Q.

my other thread was seriously like 20 pages. and it was the first time anyone has heard that riddle/Q so twas good.

why dont you think it will take off?




my nig

11/20/2007 10:41:08 PM

because its connected to some rope thats connected to a pulley and not actually on a runway...plus its not moving...its on a treadmil that moving that fast, its not actually moving that fast, its on a treadmill

11/20/2007 10:42:11 PM