A jet plane on a large treadmill

[GeezerSteve]

Explain to me how the plane takes of or the drag chute inflates if the treadmill is moving backwards at the same speed you are moving forwards.

Explanation:

1. wheels spin

2. airplanes are propelled by jets or propellers, not by wheels, i.e., an airplane is not a car

[f2f]

Does it just fucking levitate?

yes. that is the correct term. a vertical takeoff plane levitates. as does a helicopter.

goddamn this thread makes me so mad. off to drink beer.

[OverTurn]

if i hear one more of this sort of argument I swear i'm going to start slapping people over standard TCP/IP.

some jets can do vertical takeoff. your argument is invalid.

sweet jesus tapdancing on a cracker!

yes. that is the correct term. a vertical takeoff plane levitates. as does a helicopter.

goddamn this thread makes me so mad. off to drink beer.

The Harrier Jet (and I assume you mean a harrier because an osprey/helicopter uses rotating blades that are their own airfoils and do have air rushing over them to generate lift) generates lift by vectoring the thrust produced by it's engines downwards. When this thrust opposes the downward weight force of the aircraft, the aircraft will lift of. This is entirely different than a jet accelerating down a runway and generating lift from the air rushing over it's wings. A 747 is not a vertical lift aircraft with vectored thrust engines.

Read this.

http://www.aerospaceweb.org/question...s/q0102a.shtml

[ncskier]

Fucking airplanes how do they work. A mystery like magnets

[GeezerSteve]

A 747 is not a vertical lift aircraft with vectored thrust engines.

Yes, of course, but a 747 has wheels that spin freely and is powered by jet thrust. The conveyor belt makes the wheels spin faster but does not inhibit the 747 from moving forward. An airplane on a conveyor belt is not like a car on a conveyor belt.

[f2f]

The Harrier Jet (and I assume you mean a harrier because an osprey/helicopter uses rotating blades that are their own airfoils and do have air rushing over them to generate lift) generates lift by vectoring the thrust produced by it's engines downwards. When this thrust opposes the downward weight force of the aircraft, the aircraft will lift of. This is entirely different than a jet accelerating down a runway and generating lift from the air rushing over it's wings. A 747 is not a vertical lift aircraft with vectored thrust engines.

i guess you didn't see the QSRA video posted by me couple of pages ago. but hey, it's all about the 747. in fact a specific 747 on a conveyor belt, right? do not attempt to generalize the problem

[doughboyshredder]

If the treadmill matches the speed of the plane, the plane takes off. If the treadmill matches the speed of the wheels, the wheel bearings seize before the plane takes off.

It's really a matter of interpretation of the question. The plane has to move forward to generate lift. If the treadmill matches the wheel speed then no lift is generated. If (as in the mythbusters scenario), the treadmill matches the speed of the plane then the plane still moves forward and lift is generated.

Everyone is right, and everyone is wrong.

[OverTurn]

I'm not debating the 747 on a conveyor belt thing here, but merely your comparison of vertical takeoff aircraft to this question. Not the same thing. Two entirely different mechanisms.

[f2f]

I'm not debating the 747 on a conveyor belt thing here, but merely your comparison of vertical takeoff aircraft to this question. Not the same thing. Two entirely different mechanisms.

you can generate enough "lift from the air rushing over [an aircraft's] wings" even when you have a stationary aircraft. it's 50s technology, nothing "special".

[OverTurn]

True, but that has nothing to do with helicopters or vtol aircraft.

[f2f]

oh, fuck off.

[OverTurn]

Ok, I'm done. But just so long as nobody continues to use helicopters and vtols to explain why can take off with no air moving over the wings.

[stuckathuntermtn]

I guess I just assume in this ridiculous hypothetical situation that no matter how fast the wheels spin, the conveyor belt goes exactly in reverse. This would create a situation in which the plane does not move through the air.

[Chainsaw_Willie]

Oh. My. God.

I cannot believe there are people who still don't get this.

Forget the fucking wheels. They are meaningless. They're just along for the ride on an airplane, they are the lowest friction option so that an airplane can move across a solid surface until it gets enough speed to take off. They have nothing to do with moving the plane.

If you think an airplane can't take off because of a conveyer belt, you must really be confused by airplanes that don't even have wheels. How the fuck does a float plane take off? Or an airplane with skids that can land on ice? How the hell does that work?

But what about this?

[OverTurn]

I guess I just assume in this ridiculous hypothetical situation that no matter how fast the wheels spin, the conveyor belt goes exactly in reverse. This would create a situation in which the plane does not move through the air.

It depends on how you determine the speed that the treadmill is matching.

Read this, it'll make things clearer: http://blog.xkcd.com/2008/09/09/the-...amn-treadmill/

[JimmyCarter]

But what about this?

No, it's a toy helicopter.

[DJSapp]

NOW WE'RE TALKIN! Except the answer is obvious. It will fly, turntables turn clockwise, heli-rotors turn counter.

What if we put a osprey on it?

[stuckathuntermtn]

um.....................................
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I still can't picture how the plane moves forward relative to the air if the wheels and the treadmill negate each other.
Yeah, I know it's being powered by the jets. So what?
If it were on floats and pointed up river and the river speed matched the speed the floatplane would be going at full power, it wouldn't move relative to the river bank (or the air).

[GeezerSteve]

Picture this: the conveyor belt causes the wheels to spin really fucking fast but the 747's jets continue to move the plane forward. That is, the wheels and conveyor do not "negate each other." You're stuck on the driven wheel vehicle thing.

Read this, it'll make things clearer: http://blog.xkcd.com/2008/09/09/the-...amn-treadmill/

Sound analysis, but the hypothetical posed in that discussion (treadmill matches wheels' speed) is different than OP's. In OP's hypothetical, a given is that the conveyor belt matches the airplane's speed. The only reasonable definition of "plane" as used in OP's hypothetical is the entire body of the plane, not the outer diameter of the wheel.

[stuckathuntermtn]

I still don't get it. It's wheels are the only part touching the ground. You're basically saying, yet it would take off because it would overpower the treadmill.
I thought we were saying the treadmill matches the wheels speed and negates it. I don't see why it matters where the thrust comes from, as long as it's forward(backward?) and not up(down?).

[GeezerSteve]

I thought we were saying the treadmill matches the wheels speed and negates it.

No, OP's hypothetical assumes the conveyor matches the airplane's speed, not the wheels' speed. The conveyor does not negate anything -- they are not driven wheels -- but it does make the wheels spin faster while the jet moves forward

[Chainsaw_Willie]

Oh good lord.

Go get a toy car and a treadmill. Turn the treadmill on and set the toy car on it and hold the car in place by hand.

Now, push the car forward against the motion of the treadmill. You are providing thrust to the car the same way the plane's engines provide thrust to it. Can you do it? Do you think it will matter how fast the treadmill is going?

This is not a question of whether the wheels will be destroyed or if the bearings can handle the added speed or about friction in the wheelbearings or whatever - that's a separate question. The original question simply deals with the effect of the surface the plane is sitting on having the ability to move in the opposite direction of the plane. Assume zero friction wheelbearings and indestructable wheels. If we keep it that simple then the example above makes it perfectly clear that the plane will move forward and take off.

Now, if the premise of your argument demands the inclusion of the physical reality of spinning wheels and bearing friction and whatnot, then you could make a case that the plane won't achieve sufficient airspeed before the wheels seize or fly apart and I'd go along with that depending on what kinds of speeds we're talking about.

[DJSapp]

um.....................................
um.....................................
I still can't picture how the plane moves forward relative to the air if the wheels and the treadmill negate each other.
Yeah, I know it's being powered by the jets. So what?
If it were on floats and pointed up river and the river speed matched the speed the floatplane would be going at full power, it wouldn't move relative to the river bank (or the air).

When you ski slowly, do your feet feel like they're dragging behind you? What about when you ski fast? Is there an appreciable difference on the drag force on your feet between going slow and fast?

No. There isn't. The skis are a low friction platform that don't really give two fucks about how fast or slow they're going across snow. These are the airplane wheels, a low friction platform. The jets act on the airplane, and the treadmill acts on the low friction platform. Guess what, the low friction platform can't transfer the force needed to stop the jets.

Your example of a float plane is a good troll, but also wrong. If the plane wasn't moving relative to the river bank or air, the water wouldn't be moving either. Float planes just have a larger amount of resistance to overcome, but would still take off. You keep trying to re-word the concept in your head to: if the plane cannot ever move, will the wheels under it spin? The wheels and treadmill do not negate each other.

[GeezerSteve]

But what about this?

Stop with the mindfuck shit, Will

[Chainsaw_Willie]

why do you want to ruin my fun, Steve?