[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]

I hope this provides some clarity. (I'm also an aspiring pilot and I've been interested in aeronautics for many many years. Being an engineer helps a bit.)

Good Luck on you PPL

[Guest]

That being said, I will concede that the exact way the original question was worded, the plane would take off (because it talks about MPH). My only problems are 1) a car would move under the same rules, and 2) that's not the way I have heard the question posed before, and not the way I think it should be posed (since that is frankly a simplistic and boring answer).

How have you heard the question posed? Of the hundreds of arguments this problem has caused on message boards, it's always about a treadmill keeping up with the plane's speed, and many thinking the plane can't take off. There's at least five in this thread that think the plane can't take off with these very circumstances. It's this division that makes for a non-boring riddle, just as in the Monty Hall problem.

[Guest]

I agree. Regardless of what the wheels or treadmill are doing, the plane needs LIFT to takeoff.

Wow. Have you guys even read any of the previous posts? I actually took the time to read all 18 pages, and frankly, this argument is starting to sound like a broken record. Sorry if I'm too blunt. You should read the entire thread.

[bonanova]

... what does the aircraft push against if not the ground?

We know from Newton that every action has an equal and opposite reaction.

It has to push against the air.

One way to prove that the props (or jets) push against the air is to ...

Facts (prop or jet):

1. Aircraft wheels do not power (move) an aircraft
   
2. Air specifically moved by the powerplant of the aircraft over lifting surfaces provides negligable lift (prop wash or jet wash)
   
3. Powerplants push against the air
   
4. Air must be moving over the lifting surfaces to make the aircraft climb
   

I'm ... an aspiring pilot and I've been interested in aeronautics for many many years.

Being an engineer helps a bit.

Interesting. But let me guess: your engineering major is not rocket science.

[1] I think we all agree the wheels are a red herring, and so is the treadmill. Skis on snow, or pontoons on water, wouldn't change things.

[4] And lift is provided by airflow over [and under] the wings, courtesy of Bernoulli's principle. [Wings don't provide lift in space, e.g.] So it is all about air speed.

[3] If props "push against air" to provide thrust, they wouldn't work in space. OK. They don't.

We agree on everything, so far. [see my answer to Martini's original statement of this puzzle.]

But ...

[3] But if jets "push against the air" they wouldn't work in space, either. Ooops.

[Guest]

Interesting. But let me guess: your engineering major is not rocket science.

[1] I think we all agree the wheels are a red herring, and so is the treadmill. Skis on snow, or pontoons on water, wouldn't change things.

[4] And lift is provided by airflow over [and under] the wings, courtesy of Bernoulli's principle. [Wings don't provide lift in space, e.g.] So it is all about air speed.

[3] If props "push against air" to provide thrust, they wouldn't work in space. OK. They don't.

We agree on everything, so far. [see my answer to Martini's original statement of this puzzle.]

But ...

[3] But if jets "push against the air" they wouldn't work in space, either. Ooops.

Was there something in the original question that mentioned space, as in a vaccuum, that I missed? It did mention zero wind speed, but that's not saying there is no air. I'm puzzled.

[bonanova]

Was there something in the original question that mentioned space, as in a vaccuum, that I missed? It did mention zero wind speed, but that's not saying there is no air. I'm puzzled.

Would a propeller and a jet perform the same in space?

If not, does that change any of your statements?

[Guest]

Would a propeller and a jet perform the same in space?

If not, does that change any of your statements?

It depends on what you mean by "jet." Most people use the term "jet engine" to refer to a turbojet or turbofan engine, which requires a flow of air to be compressed for combustion, and would thus not work in space. Some people, though, include rockets under the term "jet," which do not require and external source of oxygen and do work in space.

[soop]

I still don't get it. How can it take off with no airflow to create lift?

A simpler experiment would be to obtain a model (jet) plane and fix it to an adjustable clamp. Power it on, warm up the jets, then adjust the arialons. Now assuming the clamp can rotate on the X axis, if the nose of the airplane is raised, the plane can take off.

However, from my point of view, the lack of airflow means the arialons will not function.

[Guest]

I still don't get it. How can it take off with no airflow to create lift?

A simpler experiment would be to obtain a model (jet) plane and fix it to an adjustable clamp. Power it on, warm up the jets, then adjust the arialons. Now assuming the clamp can rotate on the X axis, if the nose of the airplane is raised, the plane can take off.

However, from my point of view, the lack of airflow means the arialons will not function.

If we propose your experiment, (elevators control pitch around the pitch axis) then the nose will not raise, but if you had strain gauges on your clamp we would see an increase in tension building on the clamp setup -- indicating the aircraft is indeed trying to move forward.

I think we need to make an animation to demonstrate the force relationships. I particularly liked the "truck pulling the plane" example. Stay tuned, I may attempt hand drawings.

[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

Here is the original post. It clearly backs up Scraffs assertion that the plane will take off. I must say after reading this entire thread, that he was very rude to some members and blinkered to their arguments. Not understanding or forgiving of their misreading of the above.

I prefer the premise that the conveyor matches the wheels instantaneously. It makes for a better thought experiment. And in that case the plane does not take off. Yes the engineering to produce it is fantastic but it is a thought experiment after all.

And no matter how hard you push me on my skate board, if the conveyor keeps spinning up we will reach a standstill.

But according to the boring original post... Fasten your seat belts. We are sky bound.

[Guest]

Here is the original post. It clearly backs up Scraffs assertion that the plane will take off. I must say after reading this entire thread, that he was very rude to some members and blinkered to their arguments.

I disagree that I was rude to anyone, but if you think i was, no need to call me out- report me.

What is "blinkering to arguments" and where did I do that?

I prefer the premise that the conveyor matches the wheels instantaneously. It makes for a better thought experiment. And in that case the plane does not take off.

In what way does the treadmill stop the plane from taking off? Can it even go 1 MPH? If not- why?

[soop]

If we propose your experiment, (elevators control pitch around the pitch axis) then the nose will not raise, but if you had strain gauges on your clamp we would see an increase in tension building on the clamp setup -- indicating the aircraft is indeed trying to move forward.

I think we need to make an animation to demonstrate the force relationships. I particularly liked the "truck pulling the plane" example. Stay tuned, I may attempt hand drawings.

Indeed - the clamp is analogous to the conveyor belt in this respect. If you could do a drawing, it would be appreciated. And, yes, you've grasped my argument perfectly; thrust is not what makes the aircraft take off; it's lift.

[soop]

I disagree that I was rude to anyone, but if you think i was, no need to call me out- report me.

What is "blinkering to arguments" and where did I do that?

In what way does the treadmill stop the plane from taking off? Can it even go 1 MPH? If not- why?

Blinkering refers to "blinkers" on horses. They're devices that restrict vision to a narrow straight-aheead field of view. That's the anology.

[soop]

OHHH!!! I get it now. I read this:

http://www.straightdope.com/columns/read/2...-plane-take-off

And it explains it; the plane doesn't stay in the same place. It goes forwards. That clears it up.

[Guest]

OHHH!!! I get it now. I read this:

http://www.straightdope.com/columns/read/2...-plane-take-off

And it explains it; the plane doesn't stay in the same place. It goes forwards. That clears it up.

so now you can envisage a car chasing a plane on a tread mill...... and the winner is?

[soop]

I like the "rollerblading on a treadmill whilst hauling on a rope" anology

[Guest]

so now you can envisage a car chasing a plane on a tread mill...... and the winner is?

Welcome back LIS1