747 on a treadmill conundrum..

[Anomalocaris]

Ah, but what happens if this is a special conveyor that drags the air over the conveyor belt with it as it moves?

That would solve the no wind over wings problem, would' title?



Talking about wind over wing problem, there is a extraordinary Russian utility biplane designed to be able to take off or land at air speed of less than 30 miles an hour. Russian pilots in their off time apparently like to play stunts with this plane by finding an air strip where the wind is blowing at more than 30 miles an hour, and then stun the onlookers by taking off and landing while apparently going backwards relative to the ground.

[FreeTony]

A slight caveat. Depending on the exact treadmill programming, it could potentially create enough drag to stop it taking off by creating a feedback loop ( though it would burst the tyres first). In fact it could try and spin the wheels infinitely fast, if the plane didn't get off the ground.

[lifesagift]

Ah, but what happens if this is a special conveyor that drags the air over the conveyor belt with it as it moves?

That would solve the no wind over wings problem, would' title?



Talking about wind over wing problem, there is a extraordinary Russian utility biplane designed to be able to take off or land at air speed of less than 30 miles an hour. Russian pilots in their off time apparently like to play stunts with this plane by finding an air strip where the wind is blowing at more than 30 miles an hour, and then stun the onlookers by taking off and landing while apparently going backwards relative to the ground.

Well you sidestepped the problem, but very interesting nonetheless.. any links available?

[BrianSoddingBoru4]

If I'm on a plane and the plane is on a conveyor belt matching the speed of the plane's wheels, the beverage cart service better be fucking awesome.

Boru

[Anomalocaris]

Ah, but what happens if this is a special conveyor that drags the air over the conveyor belt with it as it moves?

That would solve the no wind over wings problem, would' title?



Talking about wind over wing problem, there is a extraordinary Russian utility biplane designed to be able to take off or land at air speed of less than 30 miles an hour. Russian pilots in their off time apparently like to play stunts with this plane by finding an air strip where the wind is blowing at more than 30 miles an hour, and then stun the onlookers by taking off and landing while apparently going backwards relative to the ground.

Well you sidestepped the problem, but very interesting nonetheless.. any links available?

Antonov An-2 Cub

[jesus_wept]

The problem is that in the real world, no such treadmill would be able to be made.

Could it not be done easier on a smaller scale? Say indoors with a remote control plane on rollers. I presume the physics involved would be the same.

I think this is an interesting question btw. I'm going to ask my dad, who designs jet engines for rolls royce, what he thinks about it tomorrow.

[Anomalocaris]

Surely you guys have seen this before?

"Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"

This is a forum norm, and I'm still not convinced either way !

Depends on whether the plane turns on its engines. If it does, then yes, it can. If it does not, the no, it can't. The engines of an airplane is a reaction engine. It doesn't work by pushing against the ground, or even the air. It works by shoving large mass of air backwards. If you throttle up 747's engines up to full power, the thrust of the engine will power the plane forward no matter what the wheels and the treadmill is doing. The wheel can spin twice as fast than it normally would to accommodate the treadmill, or not. If not, it will drag the wheels across the treadmill. The friction of the tires will not hold the 747 against the full thrust of its engines.

[Jenny A]

Consider three rewordings of the question:

1) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I begin to attempt to take flight in the plane, and you attempt to match my speed to try to keep me stationary. Will the plane take off?

2) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I throttle up the airplane and you turn on the treadmill, and we conspire by our joint effort to try to keep the plane stationary relative to the ground. Will the plane take off?

3) An airplane is sitting at rest on a very powerful treadmill. You are at the controls of the treadmill, while I am at the controls of the airplane. On some signal, I attempt to take flight in the plane, but you match my speed with the treadmill and keep me stationary relative to the ground. Will the plane take off?


Here are the absolute, 100%, bet-your-life-on-it answers to these rewordings:


Yes.
No.
Whoever asked this question is an idiot.

Airplane on a Treadmill January 21, 2008

It comes down to this. Planes take off and remain airborne because of the lift created by airflow over the wings. No airflow, no lift. As long as the plane is stationary relative the air over the wings it won't fly. What's happening to it's wheels is irrelevant.

The best way to think about lift is also the most obvious, at least to a physicist: according to Isaac Newton's third law of motion, if air gives an upward force to a plane, the plane must give an (equal and opposite) downward force to the air. So a plane really generates lift by using its wings to push air downward behind it. That happens because the wings aren't completely flat, as you might suppose, but tilted back very slightly so they hit the air at an angle of attack: As a result, the wings direct the airflow downward, which pushes them upward and produces the lift. To produce extra lift at takeoff and landing (when the plane is moving slower), the planes have flaps on their wings they can extend to push more air down.

How Stuff Works: Airplanes by Chris Woodford. Last updated: May 17, 2014.

So if the plane doesn't move relative to the air, it don't take off. Now say you added a fan in front of the plane in scenario 2. Then we'd get lift-off.

[naimless]

If the plane's engines can generate enough air resistance without needing to move forward on the ground then surely it could just lift off like a helicopter and then fly off like a rocket as soon as the wheels weren't touching the treadmill...

I don't know enough about 747 engines to know if it is specifically possible in this case but I'd imagine it is possible in theory.

In reality I don't think it would ever be possible to exactly match the wheels of the plane with the speed of the treadmill as you'd need a large treadmill with a feedback loop that goes up to some insane speeds.

And even then the plane's wheel has to move before the treadmill can adjust its speed.

[Exian]

Why not just take the wheels off and stand the plane up on its "landing pegs". Isn't that the same thing? Could a plane take off just sitting on pegs?

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Wait... Nevermind. The engines would keep increasing thrust and it'd tip over.