Mythbusters, Plane on a treadmill..

[Say Again Over]

Thedude, you are quite correct, unfortunately you will not stop airflow with a treadmill, jeez!

 

[SplitBar]

Think of a seaplane taking off into a strong current moving in the opposite direction. It will still lift off.

Not necessarily. Assume the water current was flowing at 100MPH. If the sea plane was taking off against the current it would have to attain a "waterspeed" of 101 mph just in order to get air flowing over the wings. The drag from the floats and the lack of power from the engine would never get the sea plane moving that fast thru the water. Add full power to the sea plane into a 100mph water current and the sea plane is going to do nothing but move backwards and never achieve any headwind airflow over the wings.

 

[COOPERVANE]

Not necessarily. Assume the water current was flowing at 100MPH. If the sea plane was taking off against the current it would have to attain a "waterspeed" of 101 mph just in order to get air flowing over the wings. The drag from the floats and the lack of power from the engine would never get the sea plane moving that fast thru the water. Add full power to the sea plane into a 100mph water current and the sea plane is going to do nothing but move backwards and never achieve any headwind airflow over the wings.

That is VERY accurate, the drag on a seaplane would never let it make any headway against a 100kt current, but the drag generated by the tiny tires of a conventional airplane would be 1,000 times less.

Try the roller skate on a treadmill analogy again.

 

[COOPERVANE]

Jeez....no airflow = no fly

I agree, but there WILL be airflow. Don't be so quick to judge without thinking it through. It is a little bit of a trick question. The question states that the treadmill will compensate for any forward speed of the aircraft. The trick is that it CANNOT do it.


The airplane WILL accelerate on the tradmill, thats the point. The tradmill CANT HOLD IT STATIONARY!!! It will try but it CANNOT DO IT

A little later when the light bulb illuminates, there will be some people who will then blame the wording of the original question for their lack of understanding.

 

[ackattacker]

I guess a lot of pilots failed high-school physics.

Reminds me of the time I was flying with another pilot (ATP even, multiple type ratings) and I suggested we alter course to avoid the thunderstorm at our 12 O'Clock and 30 miles. He said no need... the wind was blowing from our right and the storm would be blown away by the time we got there. I tried to explain about heading vs. course and same air mass and all that and ended up just giving up. Not worth arguing I guess.

 

[BGSkyGuy]

when does it air. I want to put some money on this sh!t

 

[ImbracableCrunk]

People are bickering over two different questions. <Sigh>.

If you think the question is "Could a plane on a treadmill accelerate?" then you might get a different answer than "If a treadmill held a plane stationary, would if fly?"

Remember this is a physics question, so theoretical frictionless bearings, etc. would usually apply in a PHY100 class. And therefore, you could create a treadmill that could hold a plane stationary.

Figure out what the givens are and try to answer the same question!

 

[blzr]

I would like to see a segment on wheel rotation prior to touchdown. How much rubber would it actually save????

 

[Rekks Inbound]

People are bickering over two different questions. <Sigh>.

If you think the question is "Could a plane on a treadmill accelerate?" then you might get a different answer than "If a treadmill held a plane stationary, would if fly?"

Remember this is a physics question, so theoretical frictionless bearings, etc. would usually apply in a PHY100 class. And therefore, you could create a treadmill that could hold a plane stationary.

Figure out what the givens are and try to answer the same question!

If the bearings were frictionless, then it would not matter how fast you ran the treadmill. The aircraft would remain stationary. But as soon as you applied a thrust vector to the aircraft it would move of it's own accord regardless of treadmill speed.

Peace.

Rekks

 

[ImbracableCrunk]

If the bearings were frictionless, then it would not matter how fast you ran the treadmill. The aircraft would remain stationary. But as soon as you applied a thrust vector to the aircraft it would move of it's own accord regardless of treadmill speed.

Peace.

Rekks

Okay, so you're choosing the "plane can accelerate ?" version, not the plane stays in one place version of the question.

Remember, some people word the question as, "So you build a treadmill that keeps a plane in one place. . . "

Pax.

 

[Rekks Inbound]

And thereby lies the problem; it is not possible to build said treadmill, because the movement of the aircraft is not predicated upon friction with the ground, but rather a force against the air through which it moves.


Think of it this way: assume Vr is 100kts, so for good measure, we will run theadmill at 200kts. Now, if we reach out and grab the prop (with the engine not running, of course), could we then pull the aircraft forward? The answer is yes, because we are pulling the aircraft independent of the treadmill. Crank it up to 300kts, it doesn't matter, for the above reason.

Peace.

Rekks

 

[Papps]

I'm still willing to bet anything that the plane hits 85 and travels back to 1955.

 

[ImbracableCrunk]

And thereby lies the problem; it is not possible to build said treadmill, because the movement of the aircraft is not predicated upon friction with the ground, but rather a force against the air through which it moves.

Let's say you had a giant treadmill with an airplane on it.

As you add power and begin to move for the takoff roll, the treadmill speeds up and keeps the plane in the same relative position. As the plane goes faster, the treadmill speeds up, always maintaining the aircraft's relative position.

That's why I'm pointing out the givens.

"Always maintaining the aircraft's relative position" is a given in this question.

Then, if you say treadmill like this can't be built, then you're saying the question is bunk.

About half the people say the plane will accelerate, about half go with the no relative motion, and a few just like to stir up trouble.

I'm on reserve, so I gots nuthin' better to do.

 

[Seadogrun]

I guess a lot of pilots failed high-school physics.

Reminds me of the time I was flying with another pilot (ATP even, multiple type ratings) and I suggested we alter course to avoid the thunderstorm at our 12 O'Clock and 30 miles. He said no need... the wind was blowing from our right and the storm would be blown away by the time we got there. I tried to explain about heading vs. course and same air mass and all that and ended up just giving up. Not worth arguing I guess.

But if you have a crosswind the storm that is at your 1200 it isn't on your course because you are crabbing.

It's not the reason your friend gave, but depending on conditions he might be right.

 

[ImbracableCrunk]

But if you have a crosswind the storm that is at your 1200 it isn't on your course because you are crabbing.

It's not the reason your friend gave, but depending on conditions he might be right.

Uh oh.

 

[COOPERVANE]

That's why I'm pointing out the givens.

"Always maintaining the aircraft's relative position" is a given in this question.

Then, if you say treadmill like this can't be built, then you're saying the question is bunk.

About half the people say the plane will accelerate, about half go with the no relative motion, and a few just like to stir up trouble.

I'm on reserve, so I gots nuthin' better to do.

I completely agree with you. When I worded that question that way, it was the way I heard it and I thought it would not fly. I thought it was so obvious, any idiot could see it.

Insert "the treadmill is designed to keep the aircraft in it's relative position" and suddenly it will fly. It would not be able to keep the relative position.

 

[ackattacker]

But if you have a crosswind the storm that is at your 1200 it isn't on your course because you are crabbing.

It's not the reason your friend gave, but depending on conditions he might be right.

Well, I said it wasn't worth arguing so I'm not going to argue it... but I think you've just proved my point about high school physics and pilots. Course over the ground is irrelevant to the problem... much like wheel speed.

 

[Alltheway]

Ok now I get it, wheel speed does not matter because the plane has ole timey flapping wings

 

[Captzaahlie]

That's why I'm pointing out the givens.

"Always maintaining the aircraft's relative position" is a given in this question.

Then, if you say treadmill like this can't be built, then you're saying the question is bunk.

About half the people say the plane will accelerate, about half go with the no relative motion, and a few just like to stir up trouble.

I'm on reserve, so I gots nuthin' better to do.

http://dd01.frontierairlines.com/penguin_game/index.html

now you have something better to do!

 

[Amish RakeFight]

http://dd01.frontierairlines.com/penguin_game/index.html

now you have something better to do!

Gosh...that's a little addicting isn't it?