Plane on a conveyor belt

[JacksonDean]

... etc... Both answers #1 and #2 are correct I would say.

Spoken like a politician!

In the same vein, to reduce a planes speed on the runway, or increase it, you throttle back on the prop/engine. The engine doesn't turn the wheels, like in a car, the thrust turns the wheels but only as a by product of the thrust from the prop...

Do planes have brakes on the tires like a car? I'm sure they do. But I would guess that it's the loss of inerta (sp) from the throttled down engines that stop the plane. The brakes just bring it to a complete stop...

Call me John Kerry cuz I'm a flip floppin'...

Yes, aircraft have brakes like a car does (in fact, I believe anti-lock brakes on vehicles is modeled after aircraft brakes). There are several different ways to slow/stop an aircraft, depending on its make. Commercial airliners have brakes, spoilers, reverse thrust, and to a lesser (and generally airborne) aspect Flaps.

We're dealing with a relatively simple plane like a Cessna. Contrary to believe, in proper attitude flying, pitch controls airspeed and thrust controls altitude. When you're making an approach to the runway, you've reduced the throttle and adjusted the pitch to form your approach profile. To settle the mains onto the runway, you gently pull back on the yoke to give the aircraft a nose up attitude. As the nose gear settles to the ground, you throttle back power and use brakes to slow to a taxi speed (max taxi speed is 25 KIAS).

While no drive shaft is connected to the wheels from the engine, they are not really 'free spinning' like a Hot Wheels car. The mass of the aircraft will have to be overcome before the plane will roll. The same friction will keep the aircraft still while the wheels spin underneath it as the tarp/conveyor moves away from the aircraft until the aircraft's inertia is overcome. The aircraft will then move with the conveyor if unpowered.

Powered, the aircraft's engine can counteract the force of the conveyor. Given the same force in opposite directions, the aircraft will be still. With the engine producing enough thrust to counteract the force against the aircraft, free spinning wheels will eventually negate any forces on them. As inertia's equalized, the aircraft will be essentially stationary and the wings will not generate lift.

The outcome on the show will actually depend on how the experiment's set up. The deciding factor will be the forces involved. I'm arguing from an empirical/engineering standpoint that the aircraft will not fly. As to what will happen on the show, someone will have to tell me because I don't have cable and will be unable to watch it. I'm highly interested in the outcome, whatever it is.

You were posting this as I was writing that novel:

You fail to see that the conveyor backwards speed only very minimally affects the forward aircraft speed.

Possibly, but more likely it's just poorly stated. This was a bad example, actually since speed and force are two different things.

[audiophile]

In the same vein, to reduce a planes speed on the runway, or increase it, you throttle back on the prop/engine. The engine doesn't turn the wheels, like in a car, the thrust turns the wheels but only as a by product of the thrust from the prop...

Do planes have brakes on the tires like a car? I'm sure they do. But I would guess that it's the loss of inerta (sp) from the throttled down engines that stop the plane. The brakes just bring it to a complete stop...

Call me John Kerry cuz I'm a flip floppin'...

Planes do have heavy duty braking, else you couldn't throttle up 100% and stay still. Don't recall the part of the wing used to slow, but thats only good for higher speeds and initial landing, brakes and weight do the rest.

http://youtube.com/watch?v=cJ5ZGV3Vxo8

[JacksonDean]

Planes do have heavy duty braking, else you couldn't throttle up 100% and stay still. Don't recall the part of the wing used to slow, but thats only good for higher speeds and initial landing, brakes and weight do the rest.

http://youtube.com/watch?v=cJ5ZGV3Vxo8

You could be referring to either flaps or speed brakes/spoilers.

Speed brakes and spoilers are the same equipment, and are referred to in their usage. They're flat panels along the surface of the wing which, when activated, interrupt the airflow across the wing.

They're speed brakes when used in the air; they're spoilers when they're on the ground. Typically, as an aside, the spoilers are deployed automatically when the wheels start turning on landing. Also, on aircraft so equipped, the brakes are also automatically activated when the wheels start turning.

The other thing you may be referring to is the flap(s). Flaps deploy along the trailing edge of the wing and effectively change the shape of the airfoil (wing). On equipped aircraft, there are slats along the leading edge of the wing which assists this.

Flaps/slats are normally used at low speeds because the changed shape of the wing allow the aircraft to generate more lift at these lower speeds. Without them, aircraft would need longer runways to accommodate the higher speeds necessary for take offs and landings.

[zeegler]

I would like to make this into a bet, for real money. I will bet all of you guys that say the plane won't fly, that as long as the plane isn't tethered, and that it is powered as usual by either jets or props, that it will indeed take off, and fly as usual.

$10 each. Put your money where your mouth is chumps.

[Axewielder]

Spoken like a politician!

OK, so I'm officially on the "plane will fly" side of the debate.

[Sunbane]

A plane pulls/pushes itself through the air with a propeller, just like how you'd swim through water.

Ah yes, of course!
The aircraft will pull itself forward regardless of if there is a still runway, or a moving conveyor belt under it. I see it now.

[SeventhSon]

You could be referring to either flaps or speed brakes/spoilers.

Speed brakes and spoilers are the same equipment, and are referred to in their usage. They're flat panels along the surface of the wing which, when activated, interrupt the airflow across the wing.

They're speed brakes when used in the air; they're spoilers when they're on the ground. Typically, as an aside, the spoilers are deployed automatically when the wheels start turning on landing. Also, on aircraft so equipped, the brakes are also automatically activated when the wheels start turning.

The other thing you may be referring to is the flap(s). Flaps deploy along the trailing edge of the wing and effectively change the shape of the airfoil (wing). On equipped aircraft, there are slats along the leading edge of the wing which assists this.

Flaps/slats are normally used at low speeds because the changed shape of the wing allow the aircraft to generate more lift at these lower speeds. Without them, aircraft would need longer runways to accommodate the higher speeds necessary for take offs and landings.

so do you think the plane will fly?

[guitarsjb]

What happens if it lands in water; will it float? :ROTF:

Of course it will goofy, the forward thrust from the engines, along with the upward push of the air in the wheels (unless they are still spinning backwards from the conveyor) will push it up AND propel it forward, which eventually will even lead to dry land :ROTF:. The downside of course is if the dippy pilot reversed thrusters and lowered tire air pressure to compensate for the conveyors actions..in which case it will sink like a rock.

so, I've had a beer or twelve...

[z1n]

SO what happens if you hooked a chain to the back of a plane and kept it from going foward? Would it lift?

[dg]

Definitely not. It has to move forward through the air for there to be any lift.

-edit- or air has to be blown over the wings, like in a wind tunnel.

[mm2002]

If the plane is sitting still, as on the treadmill, how is it building air speed for the wings to create lift? A plane taking off has nothing to do with the wheels turning, they simply reduce friction allowing the plane to move forward and build enough air speed so the wings provide lift. For that to happen, the plane has to be moving into the relative wind, not sitting still. So I guess my vote is, it ain't gonna fly. Not unless they have it in a wind tunnel.

[mm2002]

SO what happens if you hooked a chain to the back of a plane and kept it from going foward? Would it lift?

No, a prop cannot provide enough relative wind over the surface of the wings to provide lift. It's only for forward propulsion.

[JacksonDean]

so do you think the plane will fly?

I do not think the plane will fly.

There are a couple of reasons:
1) I think, given the proper set up, the forces on the plane will counteract each other giving the aircraft a forward force of zero. Which we are debating

2) I think the speed necessary for the aircraft to lift off, should the forces not counter act each other, will not be sufficient to generate enough lift to allow the plane to become airborne.

OK, so I'm officially on the "plane will fly" side of the debate.

Well, I wasn't saying pick a side; I was just amused. And I think you've got some valid points because the outcome can be skewed by the setup.

I have a friend who is an astronautical engineer, and I plan to pose this question to her when I can. I'd be grateful if someone had the ability to post the episode (or relevant parts) some where because I'd love to see this.

[mm2002]

I would like to make this into a bet, for real money. I will bet all of you guys that say the plane won't fly, that as long as the plane isn't tethered, and that it is powered as usual by either jets or props, that it will indeed take off, and fly as usual.

$10 each. Put your money where your mouth is chumps.

OK Zeegs, If the plane isn't tethered, how are they going to keep it on the treadmill???
OK, here's my 10 bucks. Matter of fact, make that 20.

[dg]

If the plane is sitting still, as on the treadmill, how is it building air speed for the wings to create lift? A plane taking off has nothing to do with the wheels turning, they simply reduce friction allowing the plane to move forward and build enough air speed so the wings provide lift. For that to happen, the plane has to be moving into the relative wind, not sitting still. So I guess my vote is, it ain't gonna fly. Not unless they have it in a wind tunnel.

I'm 100% with you, if they can build a conveyor that can make the plane stay in place. That's the crux of the problem. Since the wheels are free-spinning and the propulsion comes from the prop (or jet engines), wheel bearing friction and a small amount of angular momentum are the only forces that the conveyor can exert to keep the plane from going forward, so it will require a conveyor belt that can accelerate almost indefinitely.

I think the guys on Mythbusters will fail to build a conveyor belt that can do this (if it can even be done at all, ever, by anyone, with an unlimited budget), and therefore their plane will move forward on the conveyor and take off. Like I said before, I think the whole problem either relies on a failed premise (that you can build a conveyor belt that makes it stay in place), or was a trick question.