Mythbusters, Plane on a treadmill..

[Herman Bloom]

I guess that would be me then. The demonstration portrayed on the show did not meet the elements of the test in a very necessary way. Namely, the conveyor belt (tarp) was not moving as fast as the plane's wheels were moving. As evidence, you can see the traffic cones marking the takeoff distance. If the tarp was being pulled the same speed as the wheels, the plane would not have passed a single cone. Instead, it passed the last one at lift off.

The error in the test design was moving the tarp at takeoff speed and not the plane's wheel speed which was faster.

I have not yet realized an error in my original thinking and do, in fact, insist that a plane tested under the right conditions will not take off.

Is this a joke?
Just focus on keeping the blue side up, Andy. God help us.

 

[siucavflight]

people are dumb

 

[Trogdor]

If anything, they should've dragged the "conveyor belt" faster since the nay sayers actually believe the speed of the belt matters.

My thought exactly. I was saying that while I was watching the show. I wish Jamie would have driven at 75 mph just to prove that the reverse motion of the treadmill has absolutely no bearing on the acceleration of the aircraft.

 

[dash8driver]

the only difference between flying 1' above a moving treadmill and taking off on a moving treadmill is the wheels spinning.

so tell me, just how fast do you have to spin the wheels to get the plane to stop in mid air?

 

[CFI2766]

It doesn't have to be "very scientific". It's basic physics, Newton's 3rd law. The RC plane on the treadmill was more conclusive than the full-scale test.

If anything, they should've dragged the "conveyor belt" faster since the nay sayers actually believe the speed of the belt matters. They just gave them more ammo.

-Brett

What was the tire limitation speed on that "airplane"? (once again, note very generous use of term airplane...)

Again, it's ALL in the wording of the orginal theorem: There are two major possible interpretations. First, can the airplane fly if it's relative motion is zero? This is usually what is strongly implied, though not stated, as the criteria for this debate. That is, if the airplane isn't moving forward through the realtive wind, would there be any of the conditions necessary for flight? (Even NASA concludes that flight is a combination of Bernoulli and Newton.) Clearly, no.

The second option, the one actually tested, refers to what would happen if the friction of the wheels and bearings of the "airplane's" landing gear were negligible. Negligible, as in the thrust or power of the airplane was able to overcome that friction and move the airplane forward through the relative wind. For all practical purposes, the Mythbusters guys -two very obvious 40+ year old virgins- did exactly that. The tires of the airplane, which reduced the friction of the object relative to the ground, allowed the power of mighty Rotax engine to propel the "airplane" forward through the relative wind, therefore producing lift around the various airfoils of the "airplane". (Also, I tend to think that the volume of air being moved aft of the "airplane" over the airfoils of the airplane by the propeller also contributed to the flight. [NOTE: Real airplanes have propellers.])

For a counterpoint to the opinion that the landing gear is irrelevant, remove the landing gear from the airplane and firmly attach it to a trailer/sled/moving object that happened to be moving in the opposite direction of the powerplants of the airplane. (You know, similar to the scene where Maverick is riding the motorcycle shaking his fist at the F-14, yet immediatetly before he slams into the approach lights for the opposite runway...) Spin the Rotax, or CF-34x or PW-127, for that matter, and see what happens. I think what would happen would be loud, colorful, and very expensive, but I doubt you would be able to call it flight.

This entire subject boils down to how the question is worded.

 

[CFI2766]

[

so tell me, just how fast do you have to spin the wheels to get the plane to stop in mid air?[/quote]


Missin' the point: Spin the tires at a velocity of zero. With no tires, the airplane is firmly attached to the conveyor belt, it does not get to move forward through the air, it is earthbound.

Now, once the "airplane" is in flight, the tires are nearly as useless as the stewardesses.

 

[ackattacker]

the Mythbusters guys -two very obvious 40+ year old virgins-

I don't think they're virgins. I doubt they've ever been with a woman, though. The show is set in San Francisco.

 

[Andy Neill]

What was the tire limitation speed on that "airplane"? (once again, note very generous use of term airplane...)

Again, it's ALL in the wording of the orginal theorem: There are two major possible interpretations. First, can the airplane fly if it's relative motion is zero? This is usually what is strongly implied, though not stated, as the criteria for this debate. That is, if the airplane isn't moving forward through the realtive wind, would there be any of the conditions necessary for flight? (Even NASA concludes that flight is a combination of Bernoulli and Newton.) Clearly, no.

The second option, the one actually tested, refers to what would happen if the friction of the wheels and bearings of the "airplane's" landing gear were negligible. Negligible, as in the thrust or power of the airplane was able to overcome that friction and move the airplane forward through the relative wind. For all practical purposes, the Mythbusters guys -two very obvious 40+ year old virgins- did exactly that. The tires of the airplane, which reduced the friction of the object relative to the ground, allowed the power of mighty Rotax engine to propel the "airplane" forward through the relative wind, therefore producing lift around the various airfoils of the "airplane". (Also, I tend to think that the volume of air being moved aft of the "airplane" over the airfoils of the airplane by the propeller also contributed to the flight. [NOTE: Real airplanes have propellers.])

For a counterpoint to the opinion that the landing gear is irrelevant, remove the landing gear from the airplane and firmly attach it to a trailer/sled/moving object that happened to be moving in the opposite direction of the powerplants of the airplane. (You know, similar to the scene where Maverick is riding the motorcycle shaking his fist at the F-14, yet immediatetly before he slams into the approach lights for the opposite runway...) Spin the Rotax, or CF-34x or PW-127, for that matter, and see what happens. I think what would happen would be loud, colorful, and very expensive, but I doubt you would be able to call it flight.

This entire subject boils down to how the question is worded.

I agree entirely. Can a plane take off from a convetor belt that is moving faster than the airspeed of the plane. Absolutely.

Can a plane takeoff from a conveyor belt that is moving the same speed as the tires (which will only happen when it is going so fast that tire rotation speed and/or the limits of rolling friction and bearing friction is reached). No because it will cease to make sufficient progress along the belt to achieve the necessary relative wind over the wings. I thought this was the way the original question was posted.

What I saw was that the takeoff distance was relatively unaffected relative to the runway under the belt. It was much greater (doubled?) relative to the belt.

 

[JimNtexas]

Of course the plane takes off:

F = MA

 

[Max Q]

What was the tire limitation speed on that "airplane"? (once again, note very generous use of term airplane...)

Again, it's ALL in the wording of the orginal theorem: There are two major possible interpretations. First, can the airplane fly if it's relative motion is zero? This is usually what is strongly implied, though not stated, as the criteria for this debate. That is, if the airplane isn't moving forward through the realtive wind, would there be any of the conditions necessary for flight? (Even NASA concludes that flight is a combination of Bernoulli and Newton.) Clearly, no.

Yes, I agree that a major source of controversy has been a product of misinterpretation of the original question. However, I'd like to think this question was thought up by Hummer-driving soccer moms at a scrap booking meet who never thought to add things like "frictionless bearings" and "tire limitation speed" into the equation. It was a question for the laymen. One day when you and I are sitting down having a beer, you'll have to explain to me how "tire limitation speed" is of any relevance to the spirit of the question.

With that said, I disagree that the plane having zero relative motion was implied by the original question as there were no elements in the original question that would inhibit forward motion. That is a false assumption by the reader and the whole point of the question to begin with. Think about it, how many no-takeoff people have you spoke with that their first analogy was "imagine a car on a dyno..."?

Of course the plane wouldn't takeoff with zero relative motion! That is so painfully obvious, not even my grandmother would assume that a plane with zero forward motion (relative wind) could take off.

The second option, the one actually tested, refers to what would happen if the friction of the wheels and bearings of the "airplane's" landing gear were negligible. Negligible, as in the thrust or power of the airplane was able to overcome that friction and move the airplane forward through the relative wind. For all practical purposes, the Mythbusters guys -two very obvious 40+ year old virgins- did exactly that. The tires of the airplane, which reduced the friction of the object relative to the ground, allowed the power of mighty Rotax engine to propel the "airplane" forward through the relative wind, therefore producing lift around the various airfoils of the "airplane". (Also, I tend to think that the volume of air being moved aft of the "airplane" over the airfoils of the airplane by the propeller also contributed to the flight. [NOTE: Real airplanes have propellers.])

The friction in the bearings are negligible. Yes, if the conveyor belt was spinning backwards at 2000 mph, the bearings would blast out in all directions, killing the pilot and copilot, and there would be no takeoff. If the treadmill accelerated backwards to Vr (or heck even Vr x 2) as the airplane added power, there is not a chance on Earth that the friction from the bearings alone would inhibit forward motion.

Also, you're saying that the airflow from the prop alone on a single-engine fixed high-wing contributes to (even a remote amount of) lift?

This entire subject boils down to how the question is worded.

Word!

-Brett

 

[dash8driver]

so tell me, just how fast do you have to spin the wheels to get the plane to stop in mid air?

Missin' the point: Spin the tires at a velocity of zero. With no tires, the airplane is firmly attached to the conveyor belt, it does not get to move forward through the air, it is earthbound.

Now, once the "airplane" is in flight, the tires are nearly as useless as the stewardesses.

no, i think you missed the point. the question wasnt "would a plane take off if it was bolted to a trailer/conveyor belt". sounds like we're re-writing the question to match our answers now.

i agree that the majority of the controversy is from thinking the plane will not have relative motion.. thats an assumption the reader is making.

now i dont know how it was where everyone else went to school, but where i went to school if you got a question wrong because you didnt understand the question or made an incorrect assumption in the process of solving the problem, you're still wrong.

 

[CFI2766]

Max,

Want to play some softball this year? It's almost that time...

Let's get together for that beer (x5) sometime.

-G

 

[Max Q]

Max,

Want to play some softball this year? It's almost that time...

Let's get together for that beer (x5) sometime.

-G

I'm down. Left-field, catcher, 3rd or even 4th string waterboy, I'm your guy.

You know me, man. Just tell me when and where. Tues-Thurs are my days off. They've got me on the back end of the power curve this month.

-Brett

 

[COOPERVANE]

Told





YA





SO!


"sounds like we're re-writing the question to match our answers now"

Dash, thats the finest explanation for this phenomenon.

People read the original question and make an assumption based in their own mind. When they realize they are wrong and feel DUMB they have to claim semantics so they can still be right.

 

[Captzaahlie]

I guess that would be me then. The demonstration portrayed on the show did not meet the elements of the test in a very necessary way. Namely, the conveyor belt (tarp) was not moving as fast as the plane's wheels were moving. As evidence, you can see the traffic cones marking the takeoff distance. If the tarp was being pulled the same speed as the wheels, the plane would not have passed a single cone. Instead, it passed the last one at lift off.

The error in the test design was moving the tarp at takeoff speed and not the plane's wheel speed which was faster.

I have not yet realized an error in my original thinking and do, in fact, insist that a plane tested under the right conditions will not take off.

MAYBE YOU CAN GET THE PILOT TO HOLD THE BRAKES (THE WAY I'M HOLDING THE CAP LOCKS KEY) TO HELP PROVE YOUR POINT!

If you really mean what you posted I feel sorry for the entire world of aviation, because you just might be related to flying in "hopefully" some small fashion................

uke:


You really are kidding right?

 

[JimNtexas]

Consider:

F = MA

with respect to the horizontal axis of the plane (looked at from the side). The plane has some mass, M. There is a force from the engines directed along the horizontal axis. This is the force that causes the airplane to accelerate down the runway on a 'normal' runway.

Now consider a runway moving in the opposite direction of takeoff. The force from the engines is still the same. The mass is still the same. Therefore the acceleration down the runway will be the same regardless of the movement of the runway!

 

[Captzaahlie]

Consider:

F = MA

with respect to the horizontal axis of the plane (looked at from the side). The plane has some mass, M. There is a force from the engines directed along the horizontal axis. This is the force that causes the airplane to accelerate down the runway on a 'normal' runway.

Now consider a runway moving in the opposite direction of takeoff. The force from the engines is still the same. The mass is still the same. Therefore the acceleration down the runway will be the same regardless of the movement of the runway!

Another excellent explanation for a concept that really is not that overwhelmingly difficult to grasp.
We are talking really basic physics here. Nicely put Jim.
:beer:

 

[Say Again Over]

Consider:

F = MA

with respect to the horizontal axis of the plane (looked at from the side). The plane has some mass, M. There is a force from the engines directed along the horizontal axis. This is the force that causes the airplane to accelerate down the runway on a 'normal' runway.

Now consider a runway moving in the opposite direction of takeoff. The force from the engines is still the same. The mass is still the same. Therefore the acceleration down the runway will be the same regardless of the movement of the runway!

__________________

Yes I agree, great post, although sad to say, I was in the no fly camp several months ago, this formula straightens things out.

 

[ImbracableCrunk]

Told





YA





SO!


"sounds like we're re-writing the question to match our answers now"

Dash, thats the finest explanation for this phenomenon.

People read the original question and make an assumption based in their own mind. When they realize they are wrong and feel DUMB they have to claim semantics so they can still be right.

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.

Again, the original question is right there.

When I read your question, the answer seems to me, No the airplane won't fly. No relative motion = no fly.

Now, if you want to change your question, to what they did on MythBusters, then the plane will fly.

Oh, and I had Kari Byron (MythBuster CHick) on my flight from ANC the other day. Niiiice.

 

[wrxpilot]

I'm also surprised there is still any doubt about the outcome - particularly after the Mythbusters show. Anyway, another way to think about it is this:

Let's say an airplane is on a perfectly smooth, frozen lake. The friction coefficient is essentially zero, and the parking brake is on. When takeoff power is set, will the airplane takeoff? If you agree that it does, then why would a treadmill have any effect on the takeoff? Using the lake example, it is clear that the airplane does not care what is happening at the wheels.