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Will a plane takeoff if it's put on a large treadmill?
- Thread starter samoth
- Start date
Depends.
PICK3
New member
Strongbow
New member
LOL, you mean the high weight capacity one?
redsamurai
Banned
I have a feeling this is some sort of trick question cause the obvious answer is no. If the plane stays stationary because of the ginormous treadmill, it would seem that the airflow required to create lift wouldn't be there......unless the treadmill moving at that high rate of speed would cause enough friction with the air to throw it "downhill" at the plane thus generating the necessary flow. That one's beyond me.
mrplunkey
New member
Sure it will.
Get a very long treadmill and place the plane on the very end with the plane's brakes locked to prevent it from rolling. Then while the plane is stationary on the treadmill relative to the belt, it's still experiencing airflow as it moves toward the front of the treadmill. Assuming it can generate enough lift as it's being accelerated, it will take off.
Problem solved.
Get a very long treadmill and place the plane on the very end with the plane's brakes locked to prevent it from rolling. Then while the plane is stationary on the treadmill relative to the belt, it's still experiencing airflow as it moves toward the front of the treadmill. Assuming it can generate enough lift as it's being accelerated, it will take off.
Problem solved.
Sorry, I thought the hypo was universally known.
To the best of my understanding: Assume a quasi-idealized plane with frictionless (non-zero mass) wheels placed on a treadmill such that regardless of the velocity achieved by the treadmill, the plane is kept stationary in space. Does the plane achieve takeoff? Qualify argument.
nimbus
New member
airplanes don't use friction between the wheels and the ground to achieve take-off speed, they use thrust from the engine while the wheels spin freely. A conveyor belt isnt going to do anything to a plane with its engines on, except make the wheels spin faster and provide a TINY amount of backwards force due to friction. A conveyor belt powerful enough to make that frictional force substantial could probably never exist though.
nimbus
New member
it's not sitting on the belt becaaaaause the plane's engines are blasting air out the back to push the plane forwaaaard
How does horizontal engine thrust affect lift when horizontal motion is zero as compensated for by the treadmill?
How does horizontal engine thrust affect lift when horizontal motion is zero as compensated for by the treadmill?
yeah!
nimbus
New member
How does horizontal engine thrust affect lift when horizontal motion is zero as compensated for by the treadmill?
compensating for the horizontal motion of a jet engine using friction from a treadmill is all but impossible.
but if it were possible. IF IT WERE: the plane wouldn't take off because lift requires air to be passing over the wings fast enough to create a pressure difference between the air above and below the wing that is great enough to overcome the weight of teh plane
I think this is the hypo. I'm not exactly sure, though. Apparently Mythbusters did this and got a lot of criticism for doing it wrong, but I've neither seen the show nor know precisely what the original hypo is.
PICK3
New member
How does horizontal engine thrust affect lift when horizontal motion is zero as compensated for by the treadmill?
see post #4
http://www.elitefitness.com/forum/c...s-put-large-treadmill-662322.html#post8955244
mrplunkey
New member
Sorry, I thought the hypo was universally known.
To the best of my understanding: Assume a quasi-idealized plane with frictionless (non-zero mass) wheels placed on a treadmill such that regardless of the velocity achieved by the treadmill, the plane is kept stationary in space. Does the plane achieve takeoff? Qualify argument.
In the absence of airflow generated by the belt moving, the plane isn't going anywhere.
Now let's assume the belt can produce enough laminar or turbulent airflow so that there's a differential between the upper and lower side of the wing. That would still be a problem here, because the air below the wing should be moving faster than the air above the wing so the Bernoulli effect would be working to push the plane down -- not up.
Wings work by forcing air to take a longer path on the upper portion of the wing than the lower portion. Unless you could get a really strange airflow coming off the belt, it shouldn't work.
redsamurai
Banned
but there's still friction between the planes wheel and the treadmill regardless. And given the obviously hypothetical nature of this discussion, we have to assume that any forward force created by the wheels is counteracted by the reverse motion of the treadmill......end result is the plane has no forward momentum and therefore isn't going to be generating lift with it's wings.
How does horizontal engine thrust affect lift when horizontal motion is zero as compensated for by the treadmill?
good question!
Last edited:
nimbus
New member
lol people get confused
PICK3
New member
redsamurai
Banned
here's the pertinent excerpt.....
The treadmill then speeds up to match the speed of the wheels but in doing so the relative speed of the wheels increases causing another increase in the speed of the treadmill much in the fashion of Zeno's Paradox. What we have here is an infinite acceleration loop in the presence of friction and unless the airplane has titanium-reinforced, Teflon-coated, out of this world space wheels, the tires and eventually the axles as well will melt into a pool of molten lava. Since the airplane has no wheels now, the treadmill's speed drops to zero and the airplane takes off amidst a cloud of smoke with Samuel L. Jackson onboard
so is he saying that the airplane will actually move down the runway? Which is what "HAS" to happen in order for sufficient airflow to lift the plane. It sounds like he's saying that the plane will eventually melt it's tires off because of this "infinite acceleration loop" and as soon as everything drops off it fly's away? Is he saying that because the plane is pushed by jet engines instead of the force of friction between the wheels and the ground that the wheels will always be "slightly" ahead of the treadmill in terms of speed? If this is true, it would take one seriously long fucking runway/treadmill for the plane to eventually generate enough speed to satisfy lift requirements......unless we're talking about an ultralight or something.
cryptosporidium
New member
wheres the lift coming from?
redsamurai
Banned
I think he's saying that "eventually", the plane will get up to lift speed. OF course this requires one heck of fucking long runway....even for a small plane. The acceleration curve will practically look like a flat line.
cryptosporidium
New member
all depends on how fast the treadmill goes, the friction and acceleration of the plane... but yeah whoever thought up this question needs some better drugs.
redsamurai
Banned
I actually think the question is flawed. If we're talking about a theoretical physics problem than wouldn't you have to "assume" that the treadmill is frictionless and therefore cancels out all forward momentum? Otherwise the answer is simple......you need one long ass runway. I think we all originally made that assumption as to there being a zero sum force between the wheels and treadmill which of course is impossible in "real life" because of "some" internal friction in the belt.....but then so is tyring to launch a plane off a treadmill.
cryptosporidium
New member
lol
U
UA_Iron
Guest
Miplank, FTW.
In an idealized case the friction of the wheels and treadmill surface play no part in the engines pushing against air.
In an idealized case the friction of the wheels and treadmill surface play no part in the engines pushing against air.
mrplunkey
New member
Yup. The wheels and the belt are irrelevant for this problem.
You can model then entire plane as a wing. If air is flowing over the wing faster than the underside, the plane would lift off.
Case I: Wing doesn't move with respect to the treadmill. There will be no airflow hence zero lift
Case II: Wing moves forward with respect to treadmill. If enough airflow is generated, wing will get lift. But Samoth already said the plane was stationary relative to the treadmill, hence this isn't happening.
You could dream-up a scenario where the belt generates airflow which would pass over the underside of the wing, but Bernoulli effect would be acting backward -- so you'd still get no lift.
U
UA_Iron
Guest
Dream up the scenario then dream up a heated treadmill with temperature gradients and we'll start running into a bitch of a problem.
redsamurai
Banned
That got me thinking about an interesting question. If a plane were flying down a runway and just as it was about to take off it encountered a pocket of seriously superheated air. Since such air is expanding and therefore rising, one would think it would help in the lift. But couldn't it also adversely fuck with the bernouli effect?
U
UA_Iron
Guest
It has more of an effect on landings I believe. Here in AZ the ground is so damn hot that when air planes land its always kind of bumpy.
Depends on the magnitude of the air pocket I believe.
mrplunkey
New member
Consider the gap between the belt of the treadmill and the bottom of the wing. At low speeds, the airflow would be laminar but would be pushing the wing down. As you speed-up the treadmill, you could induce a turbulent, plug-style flow but I still think it would continue to push the wing down.
I think Bernoulli is gonna win this one regardless.
redsamurai
Banned
My initial instinct was that heated air should provide more lift because it's rising, but it's also less dense. I can see how it would make things bumpy cause the airflow becomes less uniform.
redsamurai
Banned
also, don't you then have the phenomenon where the cooler air above drops down to take the place of the rising air only to be heated than rise itself?
No it wont
walliwalibus
New member
Nah, it isn't going to lift at all. But, I wanna see a treadmill/conveyor belt large enough to try it. That in itself would be just plain huge. Imagine how many people could fit on that. If they bought a year membership to get on that thing they could buy a plane that flies.
PICK3
New member
I want to see a treadmill with a belt = 26 miles and 385 yards
1 revolution = 1 marathon
nimbus
New member
it is gonna make it harder for the plane to take off because the air is less dense
jnevin
New member
Oh dude.
redsamurai
Banned
but it is rising. Ever notice when one of those dumbass stuntment fly some old piece of crap off a ramp and over, say, a line of choppers with the rotors spooled up.....ever notice the firebomb the light off at regular intervals during the jump? I always thought those were just stupid effects for ADD hillbilly's who aren't stimulated enough by the prospect of a man dying infront of them. No, turns out they do it to provide extra lift to the car inflight. The explosions aren't big enough to cause lift themselves, so it has to be the hot air that get's shot upward as the result of being superheated. Unless someone else has another explanation...??
nimbus
New member
maybe the explosions are causing shockwaves? Doubt heat lift is going to make a difference to a heavy ass plane, at least nothing that can counteract the reduced air density
