Plane on conveyor... Will it ever take off? - Page 6

Avatard · 07-20-2009, 03:06 PM

Quote:

Originally Posted by Adeptus_Minor

Read back a bit.
The movement of the plane has nothing to do with anything touching the conveyor. The thrust from the jet engines will push it forward while the wheels spin free.
We're sort of pre-wired to think only in terms of movement based on pushing against the ground... that's not how planes operate.

There's one other factor [er, two].

Because the plane (due to its being essentially temporarily "immobilized" on a treadmill) is not really moving against the ambient air (well, no more air than the thrusters will provide in airflow); the plane is essentially taking off with a matching tailwind, as the ambient air is not aided in differential movement across the plane by any takeoff-speed-provided airflow.

I agree that beyond this factor (and the minor issue of increased wheel speed, and a corresponding increase in bearing losses) the wheels play essentially no part in this.

The plane will still fly, because its true interaction (primary exchange of thrust) is via the air, not the ground via the tires, as they free-spin (as you pointed out).

fasternyou929 · 07-20-2009, 03:14 PM

Quote:

Originally Posted by Avatard

There's one other factor [er, two].

Because the plane (due to its being essentially temporarily "immobilized" on a treadmill) is not really moving against the ambient air (well, no more air than the thrusters will provide in airflow); the plane is essentially taking off with a matching tailwind, as the ambient air is not aided in differential movement across the plane by any takeoff-speed-provided airflow.

I thought that was the point of the riddle, that the conveyor cannot immobilize the plane since the plane propels itself using air, not the wheels. So if the thrusters are set for 240mph and the treadmill is set for 240mph in the other direction, the plane still moves at 240mph but the wheels spin freely against the conveyor at 480mph. Or no?

Rider · 07-20-2009, 03:20 PM

Quote:

Originally Posted by fasternyou929

I thought that was the point of the riddle, that the conveyor cannot immobilize the plane since the plane propels itself using air, not the wheels. So if the thrusters are set for 240mph and the treadmill is set for 240mph in the other direction, the plane still moves at 240mph but the wheels spin freely against the conveyor at 480mph. Or no?

Yes

anthonyk · 07-20-2009, 03:21 PM

The problem with this whole thing is that it's impossible for the magical treadmill to match the wheel speed of the plane. Unless some laws of physics are seriously tweaked, the plane will always move forward, and that means the wheels will always spin faster than the belt on the treadmill. If you made something in the real world that tried to constantly match the speed of the belt to the wheels, the belt would quickly keep going faster until something blew up (a la AMJ). The plane would continue on, blissfully unawares.

LOL, damn those smilies...

Flexin · 07-20-2009, 03:34 PM

Quote:

Originally Posted by anthonyk

The problem with this whole thing is that it's impossible for the magical treadmill to match the wheel speed of the plane. Unless some laws of physics are seriously tweaked, the plane will always move forward, and that means the wheels will always spin faster than the belt on the treadmill. If you made something in the real world that tried to constantly match the speed of the belt to the wheels, the belt would quickly keep going faster until something blew up (a la AMJ). The plane would continue on, blissfully unawares.

LOL, damn those smilies...

That wouldn't be impossible. If someone had pockets deep enough that could be built. But they done this on tread mills with remote control planes so its not to hard to believe.

And a float plane can take off on water. I think the floats would cause more drag then the wheels/wheel bearings being over worked and it has no problem taking off.

If you stand on a tread mill with roller skates on you are like a plane before the engines are turned off. Don't try to skate, just stand there because the plane doesn't get forward movement from its wheels. They are just like casters on your office chair. The wheels allow the object they are attached to to move freely across the ground when they pushed.

You push your office chair with your feet to move it. The plane uses and engine that will pull/push it self through the air, Once it is moving fast enough through the are for the wings to work it takes off. The speed of the ground under the wheels has no affect.

The ground is a moving platform on a aircraft carrier.

James

Lucky3623 · 07-20-2009, 03:38 PM

I asked this to a buddy whom is a retired AF Maj. Here is his answer:

Despite what Mythbusters says, this is not possible. If the treadmill is traveling at the same speed as the plane, there is no airflow over the wings. Without airflow, there is no lift.

Now, with that said, here is how they get around the issue. By using a propeller to generate the thrust needed to “move” the airplane at the same speed as the treadmill, the propeller is pushing air over the wings, causing some lift. In very light aircraft, you might even create enough lift to get the aircraft airborne, but you have changed the original equation. If you use a jet engine which bypasses the wings, the answer is a little clearer. Better yet, use a glider that matches the speed of the treadmill by having a support that keeps the glider from moving backwards. Unless you can get the treadmill going fast enough to generate airflow over the wings, it’s not gonna happen!

If you stick to the physics involved in the original setup, it is not possible. Mythbusters “disproved” the myth, but in both cases (model and full size) the aircraft was moving forward when it got airborne.

Tmall · 07-20-2009, 03:48 PM

No. Just because he is in the air force does not mean he controls the laws of physics.

The plane will absolutely positively move forward and take off. The only purpose the wheels serve us to keep the belly of the plane from rubbing on the ground.

The turbine or prop will produce forward motion through the air. The wheels will just spin uselessly as wheels do not move a plane.

Once enough forward momentum is reached by this plane moving forward (not stationary) then lift will be created and the plane will take off.

In fact, if the plane originally could take off on 100 feet of runway, it would only need 100 feet of conveyor.

Tmall · 07-20-2009, 03:51 PM

Sorry lucky.

There is your disconnect.

The question isn't whether it could take off from a standstill on a conveyor, its whether or not the thrust of the prop or turbine would move it forward enough on the conveyor to reach take off speed.

HurricaneHeather · 07-20-2009, 03:52 PM

Quote:

Originally Posted by Tmall

No. Just because he is in the air force does not mean he controls the laws of physics.

Well there goes my whole belief system.

askmrjesus · 07-20-2009, 03:55 PM

Quote:

Originally Posted by HurricaneHeather

Well there goes my whole belief system.

Yeah, if the Air Force doesn't control the laws of physics, who does?

JC

07-20-2009, 03:21 PM	#54
anthonyk WERA White Plate Join Date: Nov 2008 Location: Austin, TX Moto: '01 Aprilia Falco Posts: 1,041	The problem with this whole thing is that it's impossible for the magical treadmill to match the wheel speed of the plane. Unless some laws of physics are seriously tweaked, the plane will always move forward, and that means the wheels will always spin faster than the belt on the treadmill. If you made something in the real world that tried to constantly match the speed of the belt to the wheels, the belt would quickly keep going faster until something blew up (a la AMJ). The plane would continue on, blissfully unawares. LOL, damn those smilies...

07-20-2009, 03:38 PM	#56
Lucky3623 Official Thread Killer Join Date: Nov 2008 Posts: 554	I asked this to a buddy whom is a retired AF Maj. Here is his answer: Despite what Mythbusters says, this is not possible. If the treadmill is traveling at the same speed as the plane, there is no airflow over the wings. Without airflow, there is no lift. Now, with that said, here is how they get around the issue. By using a propeller to generate the thrust needed to “move” the airplane at the same speed as the treadmill, the propeller is pushing air over the wings, causing some lift. In very light aircraft, you might even create enough lift to get the aircraft airborne, but you have changed the original equation. If you use a jet engine which bypasses the wings, the answer is a little clearer. Better yet, use a glider that matches the speed of the treadmill by having a support that keeps the glider from moving backwards. Unless you can get the treadmill going fast enough to generate airflow over the wings, it’s not gonna happen! If you stick to the physics involved in the original setup, it is not possible. Mythbusters “disproved” the myth, but in both cases (model and full size) the aircraft was moving forward when it got airborne.

07-20-2009, 03:48 PM	#57
Tmall Aspiring Rapper Join Date: Nov 2008 Location: Halifax, NS Moto: '12 CB1000R Posts: 3,569	No. Just because he is in the air force does not mean he controls the laws of physics. The plane will absolutely positively move forward and take off. The only purpose the wheels serve us to keep the belly of the plane from rubbing on the ground. The turbine or prop will produce forward motion through the air. The wheels will just spin uselessly as wheels do not move a plane. Once enough forward momentum is reached by this plane moving forward (not stationary) then lift will be created and the plane will take off. In fact, if the plane originally could take off on 100 feet of runway, it would only need 100 feet of conveyor.

07-20-2009, 03:51 PM	#58
Tmall Aspiring Rapper Join Date: Nov 2008 Location: Halifax, NS Moto: '12 CB1000R Posts: 3,569	Sorry lucky. There is your disconnect. The question isn't whether it could take off from a standstill on a conveyor, its whether or not the thrust of the prop or turbine would move it forward enough on the conveyor to reach take off speed.