Plane on a Treadmill: debate/poll

[m0fats]

You may have heard this classic quandary, but the online debate has really intensified so much so that mythbusters have tested it and will be airing the show on Jan 30th. So after much debate with my friends/colleagues I thought I would post the question for the wildcat nation to decide:

If a treadmill was constructed of infinite length, designed to match the speed of an airplanes wheels perfectly in the opposite direction, will the treadmill be capable of preventing the plane from liftoff?


I thought about posting the top rationales for each side, but I hope you will chip in your reasonings along with the poll. I'm very interested in the way my friends have approached this problem.

my answer: the plane will fly. I'll discuss later.

[Coldstream]

The wheels have no role in the liftoff of the plane, it is the engines that handle the "lift". The wheels only support it until it lifts off so that's what fools people here in this scenario. Once the engines "pull" the air at a high enough velocity for the wings to gain lift, the plane will fly like a bird.

My father-in-law (wife's stepdad actually) is a retired Avionics Engineer. I am going to ask him in an email if I am right. ;-)

[Brandon]

Heh, this has been debated quite a bit on another site I frequent. Some people were quite upset because apparently they were supposed to air the episode tonight, but it got pushed back for some reason.

Anyway, the plane clearly will take off. As Coldstream mentioned, it is the engines that cause the plane to move forward, and thus it will fly despite the treadmill.

[Chaz]

Heh, this has been debated quite a bit on another site I frequent. Some people were quite upset because apparently they were supposed to air the episode tonight, but it got pushed back for some reason.

Anyway, the plane clearly will take off. As Coldstream mentioned, it is the engines that cause the plane to move forward, and thus it will fly despite the treadmill.
If the treadmill and the thrust of the planes engines are sync'd to the point that the plane maintains a static position, the plane will not fly! The only reason the plane can fly is the flow of air over the wings which provide the lift. The questions is, does the engines drawing air through them, also create a draft (air movement) moving air across the wings at the same time, thus creating the lift? The thrust of the engines will not by itself cause the plane to fly. It takes flowing air across the WINGS to provide lift.

[Littlemeyer]

If the treadmill and the thrust of the planes engines are sync'd to the point that the plane maintains a static position, the plane will not fly! The only reason the plane can fly is the flow of air over the wings which provide the lift. The questions is, does the engines drawing air through them, also create a draft (air movement) moving air across the wings at the same time, thus creating the lift? The thrust of the engines will not by itself cause the plane to fly. It takes flowing air across the WINGS to provide lift.

This sounds good. What you have to have in order to take off is a pressure difference above and below the wings. Once the pressure above the wings is lower than the pressure below the wings, lift will be attained. The velocity of the air and the shape of the wings help to create the pressure difference. (If I remember correctly...from some physics classes years ago...)

The question, then, becomes: Can the jet engine alone create this pressure difference? Or does it also need the velocity of the plane?

My gut tells me that velocity is needed.

Unfortunately, my gut is batting about .333 for the season.

[m0fats]

remember: treadmill is synched with the forward movement of the wheels, not necessarily the speed of the jet propulsion.

[Littlemeyer]

remember: treadmill is synched with the forward movement of the wheels, not necessarily the speed of the jet propulsion.

:thumbup::big_grin: Gotcha now.

Plane will fly.

[UK78ALUM]

What you have to have in order to take off is a pressure difference above and below the wings.

Well, not exactly. That is indeed the principle of sustaining flight, especially unpowered flight like a glider. However, that is not necessarily what is needed to invoke flight. That can be done with pure thrust alone - for example, the vertical take off capability of the Harrier. (I suppose a rocket is a more pure example, but I wanted to focus on planes)

In the meantime, I'm going to vote. When all is said and done, I personally think this is completely analogous to walking the wrong way on one of those moving sidewalks at the airport. When you time your steps perfectly, your net true speed is zero, nor do you feel any wind, nor do you go either direction. That being he case, neither should the plane.

I look forward to the definitive answer!

[Chaz]

What you have to have in order to take off is a pressure difference above and below the wings.

Well, not exactly. That is indeed the principle of sustaining flight, especially unpowered flight like a glider. However, that is not necessarily what is needed to invoke flight. That can be done with pure thrust alone - for example, the vertical take off capability of the Harrier. (I suppose a rocket is a more pure example, but I wanted to focus on planes)

In the meantime, I'm going to vote. When all is said and done, I personally think this is completely analogous to walking the wrong way on one of those moving sidewalks at the airport. When you time your steps perfectly, your net true speed is zero, nor do you feel any wind, nor do you go either direction. That being he case, neither should the plane.

I look forward to the definitive answer!
Having thought more about the above, the treadmill will have no bearing on the plane. The treadmill only affects those machines (or humans) whose movement is directly contacted with solid a plane (ie ground etc.) A plane is pulled or pushed by props or turbines not wheels, legs, or tracks etc., therefore the treadmill will have no effect.

[JawadtheChinchilla]

Having thought more about the above, the treadmill will have no bearing on the plane. The treadmill only affects those machines (or humans) whose movement is directly contacted with solid a plane (ie ground etc.) A plane is pulled or pushed by props or turbines not wheels, legs, or tracks etc., therefore the treadmill will have no effect.

You still have to have airflow over the wings, and the jet engines alone do not create enough flow to give the wings lift. In order to have airflow, you have to have velocity. By having a treadmill underneath the wheels, it causes the plane to have zero actual velocity. Therefore, it will NOT take off.

Edit: If they could take off this way, why would they need 8,000 foot runways at airports or steam catapults on aircraft carriers?

[Littlemeyer]

You still have to have airflow over the wings, and the jet engines alone do not create enough flow to give the wings lift. In order to have airflow, you have to have velocity. By having a treadmill underneath the wheels, it causes the plane to have zero actual velocity. Therefore, it will NOT take off.

Edit: If they could take off this way, why would they need 8,000 foot runways at airports or steam catapults on aircraft carriers?

This is what I was thinking at first.

But, I then realized that the treadmill will only have the affect of turning the plane wheels extra fast. The plane will still move forward, relative to space, due to the movement of air through the jet engines. The wheels just go along for the ride.

[Chaz]

This is what I was thinking at first.

But, I then realized that the treadmill will only have the affect of turning the plane wheels extra fast. The plane will still move forward, relative to space, due to the movement of air through the jet engines. The wheels just go along for the ride.
Exactly. The thrust from the engines will move the plane forward regardless of what the treadmill does.

[gerntz]

You may have heard this classic quandary, but the online debate has really intensified so much so that mythbusters have tested it and will be airing the show on Jan 30th. So after much debate with my friends/colleagues I thought I would post the question for the wildcat nation to decide:

If a treadmill was constructed of infinite length, designed to match the speed of an airplanes wheels perfectly in the opposite direction, will the treadmill be capable of preventing the plane from liftoff?


I thought about posting the top rationales for each side, but I hope you will chip in your reasonings along with the poll. I'm very interested in the way my friends have approached this problem.

my answer: the plane will fly. I'll discuss later.

If the plane's not moving, why does the treadmill need to be any longer than the diameter of the tire? Ergo, the plane must move.

Also, you could take the wheels off & sit the plane body on the ground & it would take off if the engines generate enough thrust to overcome the higher static friction (Which is what doomed even commercial seaplanes -that higher friction.).

[m0fats]

This question is less about physics than reading comprehension. It was never stated that the plane is not moving, only that the treadmill is matching the speed of the wheels.

[gerntz]

This question is less about physics than reading comprehension. It was never stated that the plane is not moving, only that the treadmill is matching the speed of the wheels.

Who did say it wasn't? Someone posed it as an "if". Talk about comprehension issues.

[m0fats]

If the plane's not moving

um.

[BrassowFan]

I'm assuming that the treadmills speed will keep up with the engines, therefore the wheels will spin but the plane will not move forward. Basically, the same premise of a person running on one of these devices.

With that in mind, since the mass of the plane isn't moving forward, there shouldn't be any lift on the wings, therefore I think it will remain on the ground.

[Coldstream]

Check out this Bush plane in an Alaska competition... barely uses any runway which, IMO, shows that a plane can take off without needing to actually move on the runway itself (you just need to get the flow of air to move across the wings, not whether or not the wheels actually move or not).

7ZW85T_1LTA (http://www.spikedhumor.com/articles/134466/Alaska_Bush_Pilots.html)

[misterbluecat]

That aircraft is designed with STOL capability. It is not your run of the mill plane and being a competition, was probably near dry weight. They were also probably facing into a stiff wind too, it is Alaska after all. As you said, as long as you have airflow over the wings that is sufficient enough to create the pressure differential needed to generate lift, you don't need a runway. I've seen Pilatus PC6s take-off from a dead stop into a 40mph wind.

[Coldstream]

That aircraft is designed with STOL capability. It is not your run of the mill plane and being a competition, was probably near dry weight. They were also probably facing into a stiff wind too, it is Alaska after all.

Doesn't really matter here. Let's say it was a commercial airliner, as long as the turbines can generate wind power to cause enough air flow to move over the wings, it is going to lift. The treadmill would end up working in overdrive just to keep the plane stationary to the ground but once the wind speeds are sufficient (remember, it will be moving because of the turbines pulling air from forward to backwards) it will get off the ground.

(the question posed above does NOT take in any mechanical limitations, it is a question of physics here)

[misterbluecat]

Doesn't really matter here. Let's say it was a commercial airliner, as long as the turbines can generate wind power to cause enough air flow to move over the wings, it is going to lift. The treadmill would end up working in overdrive just to keep the plane stationary to the ground but once the wind speeds are sufficient (remember, it will be moving because of the turbines pulling air from forward to backwards) it will get off the ground.

I am not talking about the question at hand nor was I making any attempt to answer the question being posed. Infact I would like to hear more rationales from people before I make any attempt at throwing mine into the ring. I was merely pointing out a fact about the video. That being the aircraft in the video has special characteristics which allow it to do what it did. Also, it was facing directly into a headwind which assisted in it's short take off.

However regarding your statement, to generate sufficient dynamic pressure over the wings to sustain/obtain flight in conventional aircraft, you must have forward velocity. In aviation we call our aircrafts operating speeds V Speeds for a reason. You can read about V Speeds here. http://en.wikipedia.org/wiki/V_Speeds . However, you may also substitute wind into the equation to lower the amount of forward velocity required to sustain/obtain flight. That is why aircraft take off and land in the general direction of the wind. Aircraft also have flaps which increase the camber of the wing, generating more lift at low speed. Also on conventional aircraft, engines generate thrust. They do not generate lift directly, but instead indirectly as a result of the forward velocity they provide. Hence we have arrived full circle. I have included some other links you may find interesting regarding aerodynamics.

http://en.wikipedia.org/wiki/Aerodynamics

http://www.grc.nasa.gov/WWW/K-12/airplane/short.html

EDIT: When exactly is this particular episode going to air again?? Mythbusters has had some of the better aircraft 'myths' on their show. Yunno, along with blowing sh*t up, which is cool too.

[m0fats]

Jan. 30th is the air date.

I think taking this debate into the thrust/velocity issue is going too far. Just because the treadmill matches the forward speed of the wheel does not mean that the plane could not be propelled forward.

Imagine placing a model card on a treadmill, no matter how fast you crank up the speed of the treadmill (thus increases the speed of the car wheels) the slightest push forward from your had will send the car forward while the speed of the wheels/treadmill stays the same. All the wheels have done is reduce friction, and the force of your hand is moving the car forward without making the wheels spin faster.

I say the plane will take flight using the normal velocity/thrust/lift as it is propelled forward despite the the wheel speed being negated by a treadmill.

[surveyor]

This question is less about physics than reading comprehension. It was never stated that the plane is not moving, only that the treadmill is matching the speed of the wheels.

Well, taking comprehension into account, IF the treadmill is indeed matching the speed of the wheels, how fast is the plane moving forward? Or is it even moving forward at all?

If a runner is running on a treadmill and the treadmill is matching the runner's speed, is the runner going to run forward off of the treadmill?

If so, why? If not, why?

The answer should be obvious.

The engines generate thrust. That thrust propels the plane FORWARD at a speed sufficient to create pressure difference above the wing, due to the wing's shape.
The treadmill would prevent the forward motion of the plane, would it not? The plane would be stationary if the treadmill is matching the speed of the wheels.

[surveyor]

I think taking this debate into the thrust/velocity issue is going too far. Just because the treadmill matches the forward speed of the wheel does not mean that the plane could not be propelled forward.

If the speed is matched why would there be forward motion? If there is forward motion, the speed is not matched. If the plane goes backward, the speed is not matched.


Imagine placing a model card on a treadmill, no matter how fast you crank up the speed of the treadmill (thus increases the speed of the car wheels) the slightest push forward from your had will send the car forward while the speed of the wheels/treadmill stays the same.

The slightest push means the speed of the treadmill is not matched. That would void the posited scenario - changing the rules of the experiment, if you will.


I say the plane will take flight using the normal velocity/thrust/lift as it is propelled forward despite the the wheel speed being negated by a treadmill.

Consider this.

If a plane (commercial jetliner) requires 150 mph to reach take-off, what speed must be reached in order to achieve take-off with a 30 mph tail wind? A 30 mph headwind?
In both scenarios, the required take-off speed is different.

Why?

[surveyor]

That aircraft is designed with STOL capability. It is not your run of the mill plane and being a competition, was probably near dry weight. They were also probably facing into a stiff wind too, it is Alaska after all. As you said, as long as you have airflow over the wings that is sufficient enough to create the pressure differential needed to generate lift, you don't need a runway. I've seen Pilatus PC6s take-off from a dead stop into a 40mph wind.

Certainly.

Light aircraft require as little as 70 mph to achieve take-off. The stronger the headwind, the less forward airspeed required. in a 30 mph headwind, 40 mph would be required to achieve take-off.

[surveyor]

remember: treadmill is synched with the forward movement of the wheels, not necessarily the speed of the jet propulsion.

:thumbup::big_grin: Gotcha now.

Plane will fly.

The forward movement of the wheels is driven by the thrust. If the treadmill matches that, how is lift achieved?

[surveyor]

When all is said and done, I personally think this is completely analogous to walking the wrong way on one of those moving sidewalks at the airport. When you time your steps perfectly, your net true speed is zero, nor do you feel any wind, nor do you go either direction. That being he case, neither should the plane.

I look forward to the definitive answer!

Exactly.

I look forward to it as well.

[Littlemeyer]

What you have to have in order to take off is a pressure difference above and below the wings.

Well, not exactly. That is indeed the principle of sustaining flight, especially unpowered flight like a glider. However, that is not necessarily what is needed to invoke flight. That can be done with pure thrust alone - for example, the vertical take off capability of the Harrier. (I suppose a rocket is a more pure example, but I wanted to focus on planes)

In the meantime, I'm going to vote. When all is said and done, I personally think this is completely analogous to walking the wrong way on one of those moving sidewalks at the airport. When you time your steps perfectly, your net true speed is zero, nor do you feel any wind, nor do you go either direction. That being he case, neither should the plane.

I look forward to the definitive answer!

Exactly.

I look forward to it as well.

I'm looking forward to it too. Pretty interesting question.

As for the "moving sidewalk" comparison. I think this is a completely different scenario. The forward motion that humans/animals attain is accomplished by pushing off of the ground. The forward motion that a jet attains is accomplished by pushing off of the air. The wheels are simply there to 1) keep the body of the plane off of the ground, and 2) along the same lines, limit the effects of friction.

I'm reminded of statics/dynamics courses from years ago. If a force is applied from "outside" of the system, there will be a resultant reaction. In this case, the wheels and the ground/treadmill would (I think) only result in internal forces, whereas the jet engine/propulsion would be an external force.

In other words, the forces of the wheels and the treadmill (if moving at the same speed) should offset each other. The jet propulsion would result in displacement.

(I just thought of something else. The "moving sidewalk" example actually can support this side of the debate. As UK78ALUM says, equilibrium can be reached by moving your legs/feet at a certain "speed", which will match the speed of the conveyor belt. Now, imagine that you sustain this "speed" of your feet/legs, and a force NOT attached to the conveyor (for example, a person with really big arms standing just to the side of it) pushes you in the back. You WILL have a net forward displacement, even though neither the conveyor speed or your leg speed changes.)

[surveyor]

I'm looking forward to it too. Pretty interesting question.

As for the "moving sidewalk" comparison. I think this is a completely different scenario. The forward motion that humans/animals attain is accomplished by pushing off of the ground. The forward motion that a jet attains is accomplished by pushing off of the air. The wheels are simply there to 1) keep the body of the plane off of the ground, and 2) along the same lines, limit the effects of friction.

Actually, thrust is due to creating differences in air pressure in. If the plane is on a treadmill, how is air moved across the wings? The treadmill allows the plane to remain stationary in relationship to the air and ground. The wheels allow the plane to travel at sufficient speed through the air in order to attain lift. The treadmill would prevent that from happening.


I'm reminded of statics/dynamics courses from years ago. If a force is applied from "outside" of the system, there will be a resultant reaction. In this case, the wheels and the ground/treadmill would (I think) only result in internal forces, whereas the jet engine/propulsion would be an external force.

In other words, the forces of the wheels and the treadmill (if moving at the same speed) should offset each other. The jet propulsion would result in displacement.


The propeller / jet engine is merely a means of power / propulsion. A formula one car can achieve enough lift given the proper structure due to the speed at which it travels.
The engine of a plane allows for continuous forward motion. The treadmill creates a stationary condition in relation to the ground and air. The plane must travel through the air in order to achieve lift.
The only other way that lift can occur is sufficient headwind to create that lift on a stationary plane.

[surveyor]

Then here's Cecil's take. There's also a link to an earlier article within this one:

http://www.straightdope.com/columns/060303.html

Curioser and curioser..............

[Littlemeyer]

Actually, thrust is due to creating differences in air pressure in. If the plane is on a treadmill, how is air moved across the wings? The treadmill allows the plane to remain stationary in relationship to the air and ground. The wheels allow the plane to travel at sufficient speed through the air in order to attain lift. The treadmill would prevent that from happening.

That (the bolded part), really, is the crux of the whole debate. I don't think anybody doubts air needs to move across the wings in order for this plane to take-off. The question, worded a bit differently, is "will the plane move despite the treadmill?".

My guess is "yes", because of the reasons described in the earlier post.

A treadmill moving the same speed, opposite direction, as the wheels, does NOT necessarily mean "plane doesn't move".

The Formula One example still describes a system in which the forces that cause movement are between machine and ground. The jet engine does not need the ground to achieve motion. It uses the surrounding air.

Let's imagine a car on ice. (Theoretical ice, much like the treadmill. :icon_biggrin:) Imagine that no matter what we do with the mechanisms provided by the car, all we are able to accomplish is spinning the tires out and not moving. But if we apply an external force, a force independent of the car/tires/ice system (say, a chain attached between the car and a helicopter; or, even better, a jet engine attached to the top of the car), the car will move.

[Littlemeyer]

Then here's Cecil's take. There's also a link to an earlier article within this one:

http://www.straightdope.com/columns/060303.html

Curioser and curioser..............

:icon_mrgreen: Ugh. All of that "acceleration" talk takes the fun out of it.

[misterbluecat]

Been doing alot of posting huh surveyor? :icon_mrgreen:

[surveyor]

That (the bolded part), really, is the crux of the whole debate. I don't think anybody doubts air needs to move across the wings in order for this plane to take-off. The question, worded a bit differently, is "will the plane move despite the treadmill?".

My guess is "yes", because of the reasons described in the earlier post.

A treadmill moving the same speed, opposite direction, as the wheels, does NOT necessarily mean "plane doesn't move".

The Formula One example still describes a system in which the forces that cause movement are between machine and ground.

Sure, but the car could achieve lift with sufficient speed.

Let's imagine a car on ice. (Theoretical ice, much like the treadmill. :icon_biggrin:) Imagine that no matter what we do with the mechanisms provided by the car, all we are able to accomplish is spinning the tires out and not moving. But if we apply an external force, a force independent of the car/tires/ice system (say, a chain attached between the car and a helicopter; or, even better, a jet engine attached to the top of the car), the car will move.

For that to be similar, the ice has to move in the opposite direction.

The sticking point for me is if the plane is stationary to the air (due to the treadmill) how is air moved across the wings?

A plane in a wind tunnel will float if air is moved across the wings at sufficient velocity. Of course, it has to be tethered in some fashion. However, a plane tethered to the ground, with, say 1,000 feet of rope, will not remain aloft because air ceases to pass the wings.

[surveyor]

Been doing alot of posting huh surveyor? :icon_mrgreen:

Nah. This is the first I've seen of this question. :)

[BrassowFan]

If the treadmill can keep up with the acceleration, there might be a possibility that the jet engines create the air movement that would result in some lift but if so, I think that it would possibly raise the plane, but not enough for flight.

[surveyor]

The more I think on it, the more I believe the plane would be able to take off, though I'm no longer 100% sure either way, lol. It might still be able to accelerate through the air at sufficient air speed to attain lift. The treadmill going 100 mph in the opposite direction would mean the wheels would be spinning 200 mph (if 100 mph air speed was necessary for lift).

The treadmill is more or less a detractor from the actual mechanics of the problem - and I initially focused erroneously on the treadmill.

[gerntz]

Check out this Bush plane in an Alaska competition... barely uses any runway which, IMO, shows that a plane can take off without needing to actually move on the runway itself (you just need to get the flow of air to move across the wings, not whether or not the wheels actually move or not).

7ZW85T_1LTA (http://www.spikedhumor.com/articles/134466/Alaska_Bush_Pilots.html)

Took a river cruise in Fairbanks a couple years back. Bush plane demonstration took off & landed in about 200 feet on river bank.

[Coldstream]

My father-in-law who is a retired engineer who worked for Boeing and later UPS (for their airlines) wrote the email below in response to the question posed in this thread (He sent me the video I posted earlier but I misinterpreted what he was saying as I thought he was saying "Yes" to the original question):

The answer must be prefaced with the statement, "That depends." Confusion can occur when terms are not defined.
The situation was described as, "A plane is standing on a runway that can move." What is a plane? The Free Dictionary by Farlex defines plane as an airplane or
hydroplane. What is an airplane? The same dictionary defines an airplane as, "Any of various winged vehicles capable of flight, generally heavier than air and driven by jet engines
or propellers."

My e-mail considered the airplane to be a conventional commercial air transport. A conventional commercial air transport, either prop or jet powered, would not be able to take off from the conveyor belt because its air speed would be zero. The video I sent you showed light-weight short take off and landing (STOL) aircraft. Under special conditions STOL aircraft can operate as VSTOL (Vertical or Short Take Off and Landing) aircraft.
If the STOL airplane is:
(1) carrying a minimum load and
(2) is flying into a significant headwind and
(3) is operating at or close to sea level and
(4) the outside air temperature is below 60 degrees F.
a vertical takeoff may be accomplished. A vertical takeoff is defined as no forward movement of the airplane before the landing gear lifts off the runway.
If the STOL airplane is propeller powered, light weight and the propeller(s) provide sufficient flow of air over the wing(s), a headwind may not be necessary provided conditions
(1), (3), and (4) are met. The plane could be VSTOL capable such as the AV-8A Harrier or the Bell V-22 Osprey.

In this case movement of the conveyor belt runway is superfluous.

[BrassowFan]

A conventional commercial air transport, either prop or jet powered, would not be able to take off from the conveyor belt because its air speed would be zero.

That has been the crux of my belief in this debate.

[Littlemeyer]

That has been the crux of my belief in this debate.

As can be seen by my posts in this thread, I've gone back and forth on this. I'm currently of the belief that plane speed is different than wheel speed, so the plane will take-off. But...like Surveyor, I'm not 100% committed to that. :icon_smile:

Here's a rather crude experiment that, in a way, shows what I believe to be the case. (They also, ironically, touch on what I mentioned earlier; that it would be different for a car, or any other vehicle that attains forward motion due to forces between the vehicle and the ground; jet engines don't rely on that connection.)

http://www.youtube.com/watch?v=-EopVDgSPAk

[m0fats]

great find little meyer. This is exactly the demonstration I was looking for. Nice to see father/son working on fun problems like this.

part II:
http://www.youtube.com/watch?v=4owlyCOzDiE

[BrassowFan]

Nice video Littlemeyer... I have to say, it makes me wonder if the wheels remain in constant contact with the ground.

[Mr. Peanut]

Haven't read all the posts here, so I'm probably just repeating ppl based on the first few posted...

But, the treadmill wouldn't make any difference whatsoever. Plane would take off just as it would otherwise, just with the wheels spinning at twice the normal rate.

Unless I am missing something, I don't see why there would really be much "debate". Seems pretty straightforward to me.

[surveyor]

Haven't read all the posts here, so I'm probably just repeating ppl based on the first few posted...

But, the treadmill wouldn't make any difference whatsoever. Plane would take off just as it would otherwise, just with the wheels spinning at twice the normal rate.

Unless I am missing something, I don't see why there would really be much "debate". Seems pretty straightforward to me.

Essentially, that's my thought as I've pondered more on it and revisited my physics. I initially was certain the plane wouldn't be able to attain airspeed sufficient to generate lift due to the treadmill, but the treadmill is the decoy in the problem - derails the thought process and causes the reader to think more into it than what it really is.

As Cecil Adams points out in the link I posted earlier, the wheel bearings will be taking a beating, but the plane will take off.

The analogy posted earlier about pulling one's self with a rope while wearing skates on a treadmill helps to frame it. The propeller is pulling through the air as one would be pulling on a rope - the wheels merely spin faster.

[BrassowFan]

The more I think about it, I think you guys are right, the wheels and the treadmill are red herrings, the plane will still move forward and take off.

[oruacat2]

If the plane's not moving, why does the treadmill need to be any longer than the diameter of the tire? Ergo, the plane must move.

Also, you could take the wheels off & sit the plane body on the ground & it would take off if the engines generate enough thrust to overcome the higher static friction (Which is what doomed even commercial seaplanes -that higher friction.).

Yeah, and why would we even need runways if the engines "pull" the required amount of air over the plane's own wings?

Wouldn't every plane with sufficient engine power have vertical-take-off capability were this true?

Ever see those devices that turn an ordinary bicycle into a stationary-bike? Could we utilize similar technology in lieu of runways at all our airports?

KD

[surveyor]

Ever see those devices that turn an ordinary bicycle into a stationary-bike? Could we utilize similar technology in lieu of runways at all our airports?

KD

No.

The plane would still be travelling forward for the prescribed distance necessary to achieve lift (depending on wind conditions - tail or head wind).

The engines don't "pull" air across the wings. They pull the plane through the air, enabling air to pass over and under the wings - creating lift.

[Chaz]

Yeah, and why would we even need runways if the engines "pull" the required amount of air over the plane's own wings?

Wouldn't every plane with sufficient engine power have vertical-take-off capability were this true?

Ever see those devices that turn an ordinary bicycle into a stationary-bike? Could we utilize similar technology in lieu of runways at all our airports?

KD
You are forgetting that the bicycle is powered forward by mechanical means through the wheels. The plane gets its power from the engine pulling or pushing the plane with props or jets. No mechanical power is transmitted to the wheels.

[matt57]

i'd just take a helicopter....:icon_mrgreen:

[BrassowFan]

Yeah, and why would we even need runways if the engines "pull" the required amount of air over the plane's own wings?

Wouldn't every plane with sufficient engine power have vertical-take-off capability were this true?

Ever see those devices that turn an ordinary bicycle into a stationary-bike? Could we utilize similar technology in lieu of runways at all our airports?

KD

I can think of at least 4 reasons why we would prefer runways...

4) They're more practical than building giant treadmills.
3) The maintenance on the treadmills would be cost prohibitive.
2) The liability of such a contraption would be tremendous. The thought of a mishap during takeoff could propel a plane forward towards a runway that wouldn't exist. It could be catastrophic.

and the number one reason.... the plane would still have to land somewhere!

[UedK]

Take the wheels away and put the plane on it's belly.

Forgetting if it could overcome the friction to keep up with the treadmill, if it slid along at the same rate of speed as the treadmill it would never take off unless there was a heck of a headwind.

Wheels, Belly, Whatever, it will never take off.

[Mr. Peanut]

Take the wheels away and put the plane on it's belly.

Forgetting if it could overcome the friction to keep up with the treadmill, if it slid along at the same rate of speed as the treadmill it would never take off unless there was a heck of a headwind.

Wheels, Belly, Whatever, it will never take off.

Are you saying you don't think it would take off? Are you thinking the treadmill would cause the plane to stand still?

The purpose of the wheels is to reduce the friction between the plane and the earth to a negligible amount. So, for your analogy to work, you'd have to figure out a way for the plane's belly to be frictionless vs the treadmill... then, since there is no friction - it wouldn't matter what speed (or even what direction) the treadmill was running. Plane moves based strictly on the thrust from the engines, regardless of what is going on beneath it (so long as the wheels or belly serve to remove significant friction).

The treadmill just spins the plane's wheels faster - it does not affect the speed of the plane relative to the ground. The plane still moves forward at exactly the same rate as if there was no treadmill... and therefore, the plane takes off.

[surveyor]

Imagine this (with three people):

One person wearing roller skates standing on an airport "people conveyor"/motorized walkway.
One person on either side of him holding on to his arms.
Set the treadmill at whatever speed you wish going in the opposite direction.
Imagine now that the two people on either side holding his arms start pulling him the opposite direction of the walkway/conveyor.
All three will get to the other end of the conveyor/walkway no problem.

Same with the plane taking off.

The propeller pulls the plane through the air. A jet will push it.

If the treadmill is set to go 100 mph in the opposite direction and the plane needs 100 mph to attain lift, that only means the planes wheels are spinning comparitively 200 mph - but the plane is STILL moving forward.

[BrassowFan]

We were talking about this today at work, the best analogy that I could come up with my theory is snow skiing. Gravity is an independent force pulling you down the hill, the ski is just there to reduce contact with the ground. If you are on a steep hill, you're going to go down, regardless of whether the ground is pushing backwards or not.

[surveyor]

We were talking about this today at work, the best analogy that I could come up with my theory is snow skiing. Gravity is an independent force pulling you down the hill, the ski is just there to reduce contact with the ground. If you are on a steep hill, you're going to go down, regardless of whether the ground is pushing backwards or not.

That's a very good visual aid as well. :thumbup::beer:

[Kentucker]

remember: treadmill is synched with the forward movement of the wheels, not necessarily the speed of the jet propulsion.

The treadmill would have to be synchronized with the speed of rotation of the wheels. No forward movement is possible under this scenario. Ergo, the plane won't lift off.

[surveyor]

The treadmill would have to be synchronized with the speed of rotation of the wheels. No forward movement is possible under this scenario. Ergo, the plane won't lift off.

How would that be measured?

Would the plane be able to move forward in relation to the air and the fixed ground?

Where does the energy go that's generated by the thrust of the propeller / jet engine?

[UedK]

How would that be measured?

Would the plane be able to move forward in relation to the air and the fixed ground?

Where does the energy go that's generated by the thrust of the propeller / jet engine?

Ground Speed adjusted for any headwind. That's the only way I have ever heard an airplanes take off speed described.

If the ground were the treadmill and it equalled the speed of the plane the plane is standing still and will not leave the ground. The plane does not have air speed until it leaves the ground.

[surveyor]

But where does the energy developed by the thrust of the engine, be it jet or prop, go?

With a vehicle, the energy is transfered through the wheels to the ground.

With a plane it's not.

The propeller would "pull" the plane through the air around it, regardless of what was beneath it.

I'm still not 100% certain the plane would fly, but I'm at about 70-80 percent, lol.

[UedK]

But where does the energy developed by the thrust of the engine, be it jet or prop, go?

With a vehicle, the energy is transfered through the wheels to the ground.

With a plane it's not.

The propeller would "pull" the plane through the air around it, regardless of what was beneath it.

I'm still not 100% certain the plane would fly, but I'm at about 70-80 percent, lol.

The energy is transfered to the wheels against the ground until the plane lifts off.

The wings create lift via the Bernoulli Principle (negative pressure on underside of wing creates lift). Upon lift off the same thrust that pushed the plane along the ground now pushes the plane through the air.

Until it's off the ground the engine thrust is pushing the plane along the ground.

I really have no real idea, I am just going by gut reaction. I emailed this question to a pilot buddy and will see if he comes back with anything.

[UedK]

Well I said I really have no idea.

I copied this from another board. Now I am on the "It will take off bandwagon."


"If there was no forward movement then you would certainly be correct, however there will be forward movement and so the plane can fly.

Again, you must keep in mind that because the rotation of the wheels is NOT what moves the plane around, the wheels can spin at any speed, totally independent of how fast the plane is moving with respect to the fixed earth.

The jet engine produces a certain amount of force which pushes the plane forward, and this force is completely unrelated to how fast the treadmill is spinning. That's why I used the analogy of a cable pulling the plane forward rather than the exhaust "shoving" it forward, it's a little easier to visualize.

Here's a more familiar example to show why the wheels can spin at any speed you want, so long as they are not providing the force that moves the vehicle.

Get your roller blades (Perfect Physics rollerblades...no friction in the wheel bearings) and go over to the gym. Put on the skates and hop on a level treadmill. Turn on the treadmill.

No matter how fast the treadmill is spinning, you won't go anywhere - the wheels spin at the same speed as the treadmill surface and you stay at 0mph with respect to the fixed floor.

In other words, it's EXACTLY like you were standing on a smooth, frictionless surface. Play with the treadmill speed all that you want, it makes no difference, you don't move. There is NO FORCE causing you to move backward. Set the treadmill to 1mph or 100mph, you don't go anywhere, even though the skate wheels will be spinning like mad.

Now let's apply some forward thrust. Your buddy comes up behind you, standing on the floor, and starts to shove you forward. You begin to move up the treadmill at exactly the speed he is pushing. If he pushes you at 1mph, you move at 1mph, even though you've got the treadmill moving at 100mph.

And that's exactly what happens with the airplane on the conveyor belt - it's just a plane on a frictionless runway. The jet engine provides thrust which causes forward motion regardless of how slippery the runway is. The wheels can revolve at 1mph, 100mph or 1000mph, it makes no difference at all."

[Dr. H Lecter]

I think it depends if it is a commercial grade treadmill or a residential grade. A residential grade treadmill's warranty does not cover this type of experiment so therefore the plane will not fly.

The experiment basically proves that the plane would fly. In fact if the treadmill could switch instantly from 10mph forward to 10mph backward, the wheels would simply spin backward as the plane moves forward through space because of the thrust from the engine.

The wheels are there only to confuse.

[BrassowFan]

I think it depends if it is a commercial grade treadmill or a residential grade. A residential grade treadmill's warranty does not cover this type of experiment so therefore the plane will not fly.


The other issue is whether they are union pilots, I seriously doubt that union safety guidelines would allow their members to attempt to take off from a treadmill, it would require less runway space, therefore less construction, reducing the demand for contract labor in the market... in which case, the planes would never leave the ground :icon_lol:

[Mr. T]

Plane takes off.... and here is why...

At center of the issue is that a perfect treadmill is assumed (in other words capable of reaching any speed with instantaneous acceleration). Well, if we assume that then we must assume perfect wheel bearings meaning they have a 0 coefficient of friction. Given those assumptions no matter the speed of the treadmill, no rearward force will be applied to the plane (since the bearings offer no resistance).

By changing your assumptions you can change the outcome. If you do NOT assume perfect wheel bearings but DO assume a perfect treadmill then the treadmill will always be able to reach a speed high enough to cause substantial rearward force on the plane enough to keep it from taking off.

[Kentucker]

The debate centers on, and is apparently all about, assumptions. It could go on forever. Dumb. :icon_rolleyes:

[Dr. H Lecter]

You know....we could save a lot of money on building runway by just installing much smaller treadmills instead.

Think of all the land we'd save and could turn into greenspace.

The next question would need to be addressed. Could you land on a treadmill?

[surveyor]

That's erroneously assuming the engines pull / push against the ground and not the air..............

[dougwhit]

If I cant drive i wont go

[Dr. H Lecter]

That's erroneously assuming the engines pull / push against the ground and not the air..............

That depends upon if it is a controlled landing or not.

[UKSam]

Ok...............I am now hooked. If someone finds out when this Mythbuster episode will air please post.

Thanks

[surveyor]

That depends upon if it is a controlled landing or not.

Well, if it's uncontrolled (see crash) it's likely moot..................:icon_lol:

[UedK]

Ok...............I am now hooked. If someone finds out when this Mythbuster episode will air please post.

Thanks

I hear it's January 30.

[Dr. H Lecter]

...which leads to another question.

If you place one treadmill upside down on top of another treadmill and turn them both on......are any calories burned?

[surveyor]

Depends on if it's powered by solar energy or coal......................

[BrassowFan]

This will be on Mythbusters tonight at 9:00.

[surveyor]

WooHOOOO!

[Chaz]

WooHOOOO!
I'm tuned in and ready for this one. :icon_smile: :thumbup:

[Littlemeyer]

:thumbup::icon_lol: Been a long time a comin'.

[Chaz]

Short treadmill---plane moves forward

[Chaz]

And it flies!!!

[surveyor]

WoooHOOOOOOOOOOOOO!

Plane takes off.
Model scale and full scale - plane takes off.

Funny seeing the pilot's reaction when he landed. He was positive (as I originally was) that it wouldn't take off.

Myth busted. :thumbup:

[Chaz]

WoooHOOOOOOOOOOOOO!

Plane takes off.
Model scale and full scale - plane takes off.

Funny seeing the pilot's reaction when he landed. He was positive (as I originally was) that it wouldn't take off.

Myth busted. :thumbup:
My initial thought was that it would not fly. After thinking about it for a day or so, I then changed my mind and felt that it would fly because of the propulsion of the plane being different from a car or person, i.e. ground driven.

[VirginiaBlue]

I guess I'm confused, or not thinking about this scientifically, but I saw the thing and I'm not convinced one way or another.

I thought the whole idea was that the plane's wheels would be turning at exactly the same speed as the conveyor belt. They weren't! They had to be turning faster, because the plane was moving forward - you could tell by the stuff in the background. The plane must have traveled 30 or 40 feet from the spot where it first sat, which for an ultralight would be about what it would need to get the lift to fly, treadmill or no treadmill.

I wanted to see the plane sitting in one spot, rolling in place while the treadmill turned beneath it, then see if at a high enough engine speed it would have enough lift to fly.

Somebody please splain to me how they proved anything...

[Coldstream]

I originally thought it would fly but my father-in-law who is a retired aerospace engineer was wrong! :icon_mrgreen::eek:

[surveyor]

I thought the whole idea was that the plane's wheels would be turning at exactly the same speed as the conveyor belt. They weren't! They had to be turning faster, because the plane was moving forward - you could tell by the stuff in the background. The plane must have traveled 30 or 40 feet from the spot where it first sat, which for an ultralight would be about what it would need to get the lift to fly, treadmill or no treadmill.

The wheels will always turn faster due to the forward motion created by the propeller. The treadmill / wheels issue is a distraction from what actually drives the plane - thrust created by the propeller. The wheels merely allow the plane to "roll" in the direction being pulled by the propeller.


I wanted to see the plane sitting in one spot, rolling in place while the treadmill turned beneath it, then see if at a high enough engine speed it would have enough lift to fly.

The plane will NEVER sit in one spot, regardless of how fast the "conveyor" pulled by the truck in the opposite direction.
A plane doesn't move forward by transferring motion through the wheels, it moves forward via "pulling" through the air with the propeller.

The plane needed 25 mph air speed in order to achieve lift. Therefore, the truck speed pulling the "conveyor" the opposite direction was 25 mph. Balancing that speed per the "myth", should have resulted in it sitting stationary, but it didn't, and it won't due to the laws of physics with relation to air.
The affect to the wheels of the plane is irrelevant. What's relevant is the plane STILL "pulls" through the air with the necessary airspeed to achieve lift.
The wheels spinning in the opposite direction doesn't affect that dynamic.

[BrassowFan]

http://www.plowsunlimited.com/images/mythbusters/bustedplacard.jpg