[Guest]

This is a very highly debated topic, even though scaled tests have been conducted. The popular Mythbusters show on discovery did it full scale, but some still dispute the way they did it. You can probably find thousands of forums that host this same question, and I wouldn't be suprised if it has even been posted here before. So here goes!

A large passenger jet sits on a tredmill the size of a normal runway that they would normally take off on. When the jet starts up, it climbs in speed slowly. The tredmill matches the jet's speed EXACTLY. For every mile an hour the jet climbs, the tredmill goes in REVERSE that exact amount as-well.

The grand question: Will the plane take-off?

Assume that:

The wind is at 0 MPH

The Jet is powered by turbines

Edited September 6, 2008 by RedRum

[Guest]

This is a very highly debated topic, even though scaled tests have been conducted. The popular Mythbusters show on discovery did it full scale, but some still dispute the way they did it. You can probably find thousands of forums that host this same question, and I wouldn't be suprised if it has even been posted here before. So here goes!

A large passenger jet sits on a tredmill the size of a normal runway that they would normally take off on. When the jet starts up, it climbs in speed slowly. The tredmill matches the jet's speed EXACTLY. For every mile an hour the jet climbs, the tredmill goes in REVERSE that exact amount as-well.

The grand question: Will the plane take-off?

Assume that:

The wind is at 0 MPH

The Jet is powered by turbines

The aircraft will take off.

The reason people suspect this is because doing the same to a car will cause it to stay stationary. How ever this is not how a car works.

If you have ever seen aircraft wheels but they are free spinning. Therefore by having an aircraft on a treadmill ( if you could make one big enough) the wheels will just spin. Aircraft apply their force through the air and by doing this the force will still be applyed even though the wheels are spinning.

If you put the plane in a big wind tunnel it will be a different story. The aircraft wont be able to move as the forces (thrust from engine) and wind ( in wind tunnel) are equal. However the same force which would stop the aircraft from moving forward (gound speed) it what an aircraft uses to fly. Therefor the aircraft will take off without moving..

[Guest]

The aircraft will take off.

The reason people suspect this is because doing the same to a car will cause it to stay stationary. How ever this is not how a car works.

If you have ever seen aircraft wheels but they are free spinning. Therefore by having an aircraft on a treadmill ( if you could make one big enough) the wheels will just spin. Aircraft apply their force through the air and by doing this the force will still be applyed even though the wheels are spinning.

If you put the plane in a big wind tunnel it will be a different story. The aircraft wont be able to move as the forces (thrust from engine) and wind ( in wind tunnel) are equal. However the same force which would stop the aircraft from moving forward (gound speed) it what an aircraft uses to fly. Therefor the aircraft will take off without moving..

Very well explained!

[Guest]

Very well explained!

Thanks, I would hope I can explain it since I am a pilot (almost)!

[Guest]

I think it has been done by the great BN

There is something missing to the explanation - when will it take off?

[Guest]

Thanks, I would hope I can explain it since I am a pilot (almost)!

I'm not sure if you are familiar with mythbusters, but when they did their experiment, they took a small plane, placed it on a canvas-like material, and had a pickup truck pull it from under them. The pilot (who did take off) predicted he would stay in the same place. I'm glad you're more educated than him!

A point that I made in another thread, is that if the tredmill rolled backwards, then the wheels of the plane would actually roll forward instead of backward.

[Guest]

I think it has been done by the great BN

There is something missing to the explanation - when will it take off?

The same time a plane on a regular runway would?

[Guest]

I think it has been done by the great BN

There is something missing to the explanation - when will it take off?

It will take off then the pilot pulls back on the flight stick ( or yoke), or if on Auto Pilot will happen automatically. This happens at a speed call Vr ( Rotate Velocity). Vr is a set number based on weight/balance etc. and is measured against the IAS ( Indicated Air Speed) or the speed the Aircraft is traveling through the Air.

What is my point by all this?

All calcluations/proformace figures are taken in reference to the Air. And because of this, the moving of the ground ( tredmill) does not effect the charactericistics ( spelt wrong ) of the aircraft in any way. Therefor just a norma takeoff..

Hopefully this explains it better

[Guest]

I'm not sure if you are familiar with mythbusters, but when they did their experiment, they took a small plane, placed it on a canvas-like material, and had a pickup truck pull it from under them. The pilot (who did take off) predicted he would stay in the same place. I'm glad you're more educated than him!

A point that I made in another thread, is that if the tredmill rolled backwards, then the wheels of the plane would actually roll forward instead of backward.

He was a microlight pilot, [depending on the countries] in which you dont have to do any exams or any theory, and can get a license with very little flying experiance. Some countries/planes you dont even need a licence at all.

Any REAL pilot would refuse to mess around with a Aircraft like they did, there is 1000 things that could of gone wrong, cloth in the propeller, or tangeled in the wheels ( nearly happened). Which could have seriously damaged the expensive aircraft or killed the pilot. I lost respect ( if I ever had any) after watching him on that show.

[Guest]

The same time a plane on a regular runway would?

Depends on when the treadmill starts, if the treadmill is moving before the aircraft it will apply a small reverse thrust on the aircraft, which reduces the initial thrust. This is increase the time to take off ( and distance ) by fractions of a second..

If the tradmill starts at the same time as the Aircraft, the aircraft would just fly right off the end, and same as normal.

You have to remember that the wheels are free spinning, reminds me of a can of baked beans on a checkout ( on its side) at a supermarket. The can will roll and stay in the same place. This is what happens in the aircraft, the only conenction between the Treadmill and the Aircraft is friction produced in the wheels as it spins. Which is negliable.

[Guest]

I think what makes this scenario difficult for most people to wrap their brains around is that when they think of a treadmill they base it on their own experience with treadmills in which they exert effort but do not move forward. But since the forward movement of a plane is not generated by its wheels but instead by the thrust of its engines all the treadmill would do is make the tires spin twice as fast.

[Prof. Templeton]

The same time a plane on a regular runway would?

Edit. Nevermind. After reading jelling's post.

Edited September 6, 2008 by Prof. Templeton

[dms172]

just wondering, if the treadmill keeps plane in place while the plane gets up to speed, then wouldn't it be kind of like a semi starting to high of a gear? cuz the there wouldn't be any wind going by the plane.

[Guest]

just wondering, if the treadmill keeps plane in place while the plane gets up to speed, then wouldn't it be kind of like a semi starting to high of a gear? cuz the there wouldn't be any wind going by the plane.

I agree, but the treadmill diesn't keep the plane in the same place.. It just makes the wheels turn faster!

[unreality]

it's like the plane still goes forward, with the treadmill sort of sliding underneath to double the wheels' speed to go normal speed, right?

[Guest]

it's like the plane still goes forward, with the treadmill sort of sliding underneath to double the wheels' speed to go normal speed, right?

Yeah, that is exactly what I ment..

[Guest]

I started a thread on this subject over a year ago.

http://brainden.com/forum/index.php?showtopic=457

Since mine got only one response, Brainden has done some growing, I'm going to lock it and leave this one open.

[Guest]

Isn't a plane's ability to fly a result of lift created by air moving over the wing? If so, with the plane standing still, no air is moving over the wing - therefore no lift is being created... On myth busters, the propeller was pushing air over the wings. in a jet - that is not the case.. I am no expert in flight physics, but this seems like a no brainer - the answer is NO - it will not take off...

[Guest]

Isn't a plane's ability to fly a result of lift created by air moving over the wing? If so, with the plane standing still, no air is moving over the wing - therefore no lift is being created... On myth busters, the propeller was pushing air over the wings. in a jet - that is not the case.. I am no expert in flight physics, but this seems like a no brainer - the answer is NO - it will not take off...

Why is the plane standing still?

[Guest]

Why is the plane standing still?

In space it is standing still - it is on a tread mill that is matching its speed in the opposite direction - the only thing moving on the plane is its wheels...

[Guest]

imagine being on a skateboard on a treadmill - is the wind blowing through your hair?

[Guest]

In space it is standing still - it is on a tread mill that is matching its speed in the opposite direction - the only thing moving on the plane is its wheels...

This is where you mis understand. The wheels on an aircraft are free spinning, and therefore no force can be transfured through them. The treadmill will therefore have no effect on the aircraft because there is no way to get the force of the treadmill into the aircraft.

[Guest]

This is where you mis understand. The wheels on an aircraft are free spinning, and therefore no force can be transfured through them. The treadmill will therefore have no effect on the aircraft because there is no way to get the force of the treadmill into the aircraft.

What??

[Guest]

This is where you mis understand. The wheels on an aircraft are free spinning, and therefore no force can be transfured through them. The treadmill will therefore have no effect on the aircraft because there is no way to get the force of the treadmill into the aircraft.

If your contention were correct then the jets would not be needed at all to stand still. When the proposed scenario begins, leave the jets off- would the airplane not move backwards?

[Prof. Templeton]

This is where you mis understand. The wheels on an aircraft are free spinning, and therefore no force can be transfured through them. The treadmill will therefore have no effect on the aircraft because there is no way to get the force of the treadmill into the aircraft.

What about friction?

[Guest]

Very well explained!

Very well explained, but completely inaccurate - in the wind tunnel - assuming it is large enough the plane WOULD take off - it takes wind (moving air) over the wings to create lift - groundspeed is irrelevant.

Theoretically - in a steady 300 MPH headwind - I could hover in a jet with a 0 MPH groundspeed...