Poll: Mythbusters - Will the plane take off?

MidlifeFlyer said:
I was disappointed. I always thought the myth involced the treadmill's and the airplane's wheelspeed being identical.
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It is...or at least should be.

When you run on a treadmill, you stay in the same place. Your legs and the treadmill go the same speed (roughly...it isn't exact obviously). You certainly don't go running into the bar or the control panel.

I didn't see it but it sounds like they let the airplane have forward motion relative to fixed objects on the ground. Obviously the airplane will takeoff if it's capable of moving forward relative to the fixed objects on the ground. I don't see how this is disputable. :confused:

-mini
 
minitour said:
I didn't see it but it sounds like they let the airplane have forward motion relative to fixed objects on the ground.
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Because they had no choice. Thats what the myth (and physics) show! There is nothing the mythbusters could have done (short of welding the airplane to the pavement) that would have prevented it from moving forward relative to fixed objects on the ground.
 
Clocks said:
The point continues to be that the treadmill's impact on the airplane is almost zero. The speed (slightly below takeoff speed, exactly at wheel speed, or 50 times greater than wheel speed) is irrelevant. Friction is a function of weight (normal force * a coefficient). Velocity is tellingly missing from the equation.
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You may very well be right, and an understanding of the physics (both motion and aerodynamic) involved makes it clear why. But that's not what the experiment yesterday evening tested for. If, as you suggest in response to mini's post, they had no choice, that itself suggests the test was irrelevant.
 
PCL_128 said:
Someone please close this thread before I pop a blood vessel! I can't believe this didn't settle this crap once and for all!!!
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Hey, I've never even read more than 2-3 posts in any other thread on the subject - just enough to know that the silly controversy existed. Even now, I'm more interested in what I see as a failure of the experiment to test what I though it was going to test than in the controversy.

So please excuse me for bothering someone who could, um, let's see ... ignore the thread :rolleyes:
 
MidlifeFlyer said:
Even now, I'm more interested in what I see as a failure of the experiment to test what I though it was going to test than in the controversy.
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What part of the experiment failed?

Is the only point you're stuck on that the treadmill was not moving at exactly the speed of the airplane? Would the friction or drag equations have approached infinity if the two numbers had matched perfectly?
 
I told my mom about the scenario this morning. I asked her if an airplane with it's engine running would take off from a moving treadmill.

She said yes, and she's not even a pilot! I haven't asked my dad (an A&P IA and a CMEL pilot) or my brother (a software engineer) yet what they think.

As for locking this, I don't want to have to. Unless it gets nasty, I'll leave it.
 
MidlifeFlyer said:
You may very well be right, and an understanding of the physics (both motion and aerodynamic) involved makes it clear why. But that's not what the experiment yesterday evening tested for. If, as you suggest in response to mini's post, they had no choice, that itself suggests the test was irrelevant.
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:yeahthat::yeahthat::yeahthat:.

The experiment was poorly executed. It may have gotten the same result as it would have were it executed properly, but it was not done exactly as phrased by the question
 
Clocks said:
Because they had no choice. Thats what the myth (and physics) show! There is nothing the mythbusters could have done (short of welding the airplane to the pavement) that would have prevented it from moving forward relative to fixed objects on the ground.
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That's the point of the myth...the treadmill moves backwards letting the wheels spin up (who cares what the wheels do) while the airplane doesn't move forward (relative to fixed objects on the ground).

Unless I misunderstood the myth.

-mini
 
Clocks said:
What part of the experiment failed?

Is the only point you're stuck on that the treadmill was not moving at exactly the speed of the airplane? Would the friction or drag equations have approached infinity if the two numbers had matched perfectly?
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That's what I mean about the controversy being over the question. I thought a given of the experiment would be that the speed of tire rotation was the same as the speed of the treadmill for all of the time that the aircraft would be in full contact with it.

As far as I could tell with my untrained eye, (1) tire rotation speed was not measured in any way and (2) tire rotation speed was greater than treadmill speed from the moment power was applied (before I would expect any lift would be generated).

"Friction and drag equiations" are niceand probably answers the question, but what reference do they have to the validity of supposedly empirical test that doesn't measure or validate its underlying conditions?
 
minitour said:
Unless I misunderstood the myth.

-mini
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I think you did misunderstand. Why do you assume the airplane won't move forward? That's not one of the conditions of the test; the myth doesn't say anything about the aircraft remaining stationary.
 
Berkut said:
the myth doesn't say anything about the aircraft remaining stationary.
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The difference between what is being said and the information being received.

It's in your FOI. Apparently I had a picture in my head of the airplane not moving. Otherwise, why use a treadmill? :confused: The plane is going to take off if it has enough relative wind to produce the lift sufficient to move the mass off of the ground.

I guess the picture was supposed to be that the treadmill just happened to be moving in the opposite direction with no apparent bearing on the aircraft's movement over the ground.

I also would have to say, that's the dumbest "myth" I've ever heard of. Private pilots...hell, darn near all student pilots that are soloing should know that if the airplane has enough relative wind to (help) produce the correct amount of lift, the airplane will takeoff. I thought that was self explanatory.

So what exactly are we "testing"?:confused: Bernoulli?

-mini
 
Can a treadmill prevent an aircraft from taking off?

If I have an aircraft that takes off at 25 KIAS, and has an engine only capable of propelling it to 50 KIAS, would it be able to take off on a treadmill with the surface moving at a steady 200 knots opposite the takeoff direction?
 
minitour said:
It is...or at least should be.

When you run on a treadmill, you stay in the same place. Your legs and the treadmill go the same speed (roughly...it isn't exact obviously). You certainly don't go running into the bar or the control panel.

I didn't see it but it sounds like they let the airplane have forward motion relative to fixed objects on the ground. Obviously the airplane will takeoff if it's capable of moving forward relative to the fixed objects on the ground. I don't see how this is disputable. :confused:

-mini
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The reason your legs move the same speed as the treadmill is that your legs are your source of propulsion. It's not so in an airplane. An airplane is moved forward by it's propeller. They had no choice but to allow the airplane to move forward. Otherwise, they would have just sat the airplane on the end of the treadmill in the "off" position and watched the treadmill slide out from under it. Sort of like a tablecloth under all the dishes.

The point of the experiment wasn't to show a stationary airplane in a no wind environment achieve lift off. Most people imagine a stationary aircraft because they first imagine a stationary car and then can't let go of the concept. This is not meant to be any more than a trick question...two different ideas. Car on conveyor belt vs. Plane on Conveyor belt. The point of the experiment was to show that whether or not the airplane was sitting on a backward moving conveyor belt is irrelevant.

Here is the original myth:
"A plane is standing on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?"

It says nothing about the conveyor belt and wheels matching speed. It says conveyor and PLANE. Obviously if the wheels and belt match, the plane will remain stationary and under no-wind circumstances the plane will not take off. However, the conveyor belt matching the PLANE'S speed is irrelevant. The conveyor belt can go 100x the plane's speed and the plane will still achieve forward motion and take off.
 
Berkut said:
Can a treadmill prevent an aircraft from taking off?

If I have an aircraft that takes off at 25 KIAS, and has an engine only capable of propelling it to 50 KIAS, would it be able to take off on a treadmill with the surface moving at a steady 200 knots opposite the takeoff direction?
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It will take off.
 
Berkut said:
Can a treadmill prevent an aircraft from taking off?

If I have an aircraft that takes off at 25 KIAS, and has an engine only capable of propelling it to 50 KIAS, would it be able to take off on a treadmill with the surface moving at a steady 200 knots opposite the takeoff direction?
Click to expand...

Here's a better one:

I have an airplane that is propelled by the wheels up to the moment of take-off where it is seamlessly and instantaneously transferred over to the propeller. If I put it on a tread mill moving the opposite direction and at the same speed, will it be able to achieve lift off under no wind circumstances. FINALLY, the answer is NO!!!



P.S. The mythbusters board has over 50 pages in at least 3 different threads now.
 
MidlifeFlyer said:
but what reference do they have to the validity of supposedly empirical test that doesn't measure or validate its underlying conditions?
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Because the underlying conditions are irrelevant, is only included to produce an image in your mind of a car on a treadmill, and is what makes the riddle a "riddle"?

minitour said:
Apparently I had a picture in my head of the airplane not moving.
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That's the point! The airplane will ALWAYS move in EVERY possible "imagining" of every possible interpretation of this riddle. The picture in your head was wrong, will always be wrong, is not supported by any physics, and can never be right under any circumstances (short of chaining the airplane to the concrete).

That incorrect "picture" what makes it a riddle, and the fact that you were wrong is what makes it stupid in your head :)

Dictionary.com
Riddle
a question or statement so framed as to exercise one's ingenuity in answering it or discovering its meaning; conundrum.
 
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