The runway sized treadmill is going backwards and increases speed as throttle is applied.

Would it be able to take off?

There was a huge debate about this one on another forum.
I'm just wondering what You Guy's think. :D

No, no air speed.

I Don't think so,as i understand it planes take off by using forward momentum to force air under the wings generating lift, so if the plane wasn't "really" moving it couldn't be making the lift necessary to get off the ground. i could be wrong but i think thats the deal.

No. No airflow over the wing equals no lift.

Agreed. No lift equals...well...no lift :D

Planes fly from the forward momentum which pushes air under and over the wings, with their unique shape, the air pushes up against the wing (or down against the wing depending on the direction of the flaps (I know that's the wrong word)).

ditto.. no fly

Think of it this way....even if you are standing still you are moving as fast as the world is turning......so if you go as fast as the world is turning in the opposite direction are you standing still ??????

I am going to put my head phones on now and listen to some pink floyd!!!!!!!!

The plane would take off and fly just fine. The only thing that holds the plane back is the small friction of the wheels and the conveyor belt would have to attain some tremendous speeds to generate enough friction in the wheels to overcome the thrust of the engines.

The treadmill wouldn't have any effect on the airplane. Airplanes move by their engines forcing air backwards, not anything to do with the ground underneath them like a car. The airplane would move itself off of the treadmill and continue down the runway normally. The only way to do it would be to blow air past the airplane, possbly allowing it to achieve sufficient lift to take off, possibly even hovering in place - kind of like a wind tunnel, However, as soon as the plane left the airstream it would immediately crash, as it wouldn't have any true airspeed to hold it aloft.

ditto.. no fly
:clonk: Darn, I fell hard for that one, didn't I...rather obvious I suppose that the plane (whose engines push against air, not runway....) would simply drive right off the treadmill into the wild blue yonder! :clonk:

i agree with onova that it would fly fine. the thrust from the jets is used to push the plane forward. the wheels just keep friction at its minimum. the wheels will just spin at a faster rate on the threadmill.

if it were a car, the car would stand still as it uses its wheels for power. now, if you used a giant fan from the rear of the plane pushing air forward, the plane would just roll around.

my question would be, ...i will continue this on another thread since i dont want to distract from this one.

angel

But if you got a big enough FAN, then you could get lift and fly the plane when it was standing still.

I think there might be some confusion over whether it is a powered treadmill, or the kind that just move when you walk on it and move the tread with your feet.

Hmm I didn't really read the question the first time... I don't think there would be much effect.

I believe it would be tough for the plane to initially get going, as there would definitely be some opposing friction between the tires and the treadmill surface.

Assuming the engines possess enough thrust, it would take longer for the thrust of the engines to overcome the (backwards) friction and push the aircraft forward fast enough to move off the end of the belt. The "treadmill runway" wouldn't be long enough though. It would have to be longer than a typical concrete runway.
The ground isn't moving when a plane takes off at your local airport, but the belt would be, acting against the aircraft. Eventually, the plane would gain lift and fly off the belt though, if the engines didn't spit parts out first.

I believe that a plane needs to have the resistance of air pushing underneath the wings to give an upward lift (via the ailerons (sp?) ) The wheels would just spin the treadmill and as the jets "wound up", the wheels would go faster...If the belt could keep up with the planes wheels, it would just spin and the engines would scream. You NEED air forcing the wings upward to get lift. It also depends on what type of plane we're talking about ;) A harrier jet can lift off almost vertically! I suppose that there's a reason they don't use gigantic treadmills for take offs and landings :D

Dano :beers:

Its all about lift across the wing. Sitting still or on a treadmill produces zero windspeed. It's the engine propelling the plane forward and producing air force under the WING that creates lift. The propulsion forward forces the wing to engage the air and the design of the foil (wing) produces continued lift across that foil. Reduce or eliminate the speed and it will glide to the ground or fall like a rock.

Here is a great illustration. Drive your car at any MPH above 25 miles per hour. Stick you hand outside the window and tilt it up or down. The leading edge will determine the direction your hand will go. THEN, put your car on jackstands or on a dyno, run the speedo up to or equal to the MPH you were going in experiment #1. Notice that nothing happens. You just look goofy.

The engines thrust isn't pushing against the ground. The thrust is pushing against the air. The wheels/tires have nothing to do with forward motion, other than to create a bit of friction which the aircraft has to overcome.
The plane would slowly move forward, just like on a static runway.

Look at it this way, when a normal jet aircraft is already at altittude and the pilot increases the thrust from the engines, what happens?
The aircraft increases air speed. The thrust is pushing against the atmosphere, not a solid object.

The plane will move at it's own speed until it gains enough lift for the wings to lift it off the ground. The moving "ground" under it will just make it a little harder for the plane to initially get going.

This is one for The Myth Busters!!

Wow didn't expect this one!

In reponse to Bill's original question, No the aircraft can not fly unless it has lift. Sitting statically on a treadmill, regardless of the speed of the treadmill, the aircraft has no airflow over the wings. Until the air is accelerated over the wing enough to produce the lower air pressure above the wing in comparison to the air pressure below the wing nothing will happen. The reason for the flaps and leading edge slats being extended for take-offs and landings is to increase the effects of lift on the wing, accelerates the airflow over the wing even more resulting in further decrease in pressure over the wing which equals more lift even if airspeed remains constant.

For fun I thought about how Bill's teadmill would effect other systems on board. No airspeed seen by the air data computers due to no forward movement of air into the pitot probes, the engine P2T2 inlet probes will also see no increase in air pressure or decrease in atmosperic pressure into them so the engine will continue to operate without the effects of the ram air causing the rollback in thrust if at take-off power settings, the BASC computers would see the speeds generated from the landing gear wheel tach generators and arm the anti-skid braking systems. But since the accelerometers will sense no forward motion by the aircraft the logic circuitry programmed into the BASC may fail the anti-skid systems since decelleration cannot provide a feedback input to compare to the wheel reference speeds. The IRU or AHRS will not sense any change in location and send that information out onto the digital data buses to any other equipment requiring that data. So what you'll end up doing at least on a modern day high perf jet aircraft is cause havoc with it, but no it won't fly.

Can a jet aircraft fly sitting statically, no, but you can make it think it is. I had to do this last week. Crew reported wing anti-ice system failed at climb and higher power settings. Since it's forbidden to turn on the wing anti-ice at these high power settings on the ground (no airflow over the wings to cool them) we make the aircraft think it's flying. Put all 6 ground flight sensors into the flight mode, using a pitot static bench pump up the airspeed and altitude on both air data computers, as far as the aircraft is concerned it thinks it's flying, and if you left your transponders on so does the air traffic control!

Bill you question reminded me of one the other day that someone walked over and asked me while at the hangar. This poor guy asked my how an aircraft stops because his buddies told him they don't have brakes because they'd be ineffective. They actually do have very large multi-disc brakes and thrust reversers. Before I could explain to him how the reversers work a co-worker who wasn't as kind answered his question. To quote him he asked me "what stops the airplane when it hits the ground?" My co-worker told him usually the dirt and rocks!

I'll side with the people who say it will fly. What does the treadmill (powered or not) have to do with air speed or air pressure? If the flying device (plane) is propelled forward above its stall speed, whether by the treadmill or the jets, it creates high pressure under the airfoil (wing) and low pressure over the airfoil (wing). What about coming in for a landing with the same circumstances?

OK, I'm going to have a beer now, but isn't it a given that, "anything will fly if you get it going fast enough". Increases speed as throttle increases (if equivalent) is the part I missed. My mistake.

If a plane is on a treadmill, the wheels are going to spin the belt. The wheels will be moving the belt. The faster the engines go, the faster the wheels will spin the belt. The airflow over the wings will be non-existent because the plane will not be moving down the runway...it will be spinning the treadmill belt. The flaps on the back of the wings guide the air and give the airplane lift. If the Captain moves the flaps on the wings or the tail section when the plane is at a stop, nothing happens. You need to have momentum, speed/velocity to have the flaps make an effect on the planes direction. I can't wait to hear the explanation/answer to this question... :D

Dano :beers:

How are the wheels supposed to move the belt?? The wheels aren't driven.
The engines thrust provides the forward momentum. The wheels are just along for the ride.
I say it'll fly..... given enough length.

Well, I through an answer in, but it didn't show up, and at this hour, I don't feel like typing it again.

the original question asked about a treadmill going BACKWARDS.. would that mean that if you were to stand on it, you would go forward, like those "moving sidewalk" things at the airport?
if so, then the wings would indeed generate lift if it was going fast enough, and it would fly. provided, of course, that the brakes were applied on the landing gear to keep them from rolling at all and thus allowing the plane to just sit there while the treadmill runway moves underneath it...
but if the engines weren't started up at some point, it would quickly crash- right into a treadmill that's moving along at a couple of hundred mph or so. that would be mildly scary when you got to the end of the treadmill inside a plane that just crashlanded on the moving runway..

Wont fly. I believe the original question stated that the speed of the treadmill is directly linked to the engine speed. The talk about friction and tires is a non starter, thats not the issue. A planes engine (prop) doesnt create 'wind' that goes over the wings, the forward motion, thru space, creates lift over the wing. If the plane was throttled up to max speed, and the treadmill matched the same speed, the plane would be motionless, as far as forward/rearward movement, therefore no lift over the wings. A plane has to have physical movement in space, forward movement, in order to take off. To think of it the other way, take a swamp boat and put it on a treadmill (although friction would be an issue in that case, lol, cause there arent any tires, but it takes the mystery out of it a bit), if the treadmill matched the speed of the swamp boats engine, it wouldnt move forward, in reality, the engines speed would keep it from being flung off the treadmill. Same thing with the plane, if the engine stopped but the treadmill didn't, the plane would be shot off the end of the treadmill, the two forces equal each other out, but still, no forward movement = no lift.

the original question asked about a treadmill going BACKWARDS.. would that mean that if you were to stand on it, you would go forward, like those "moving sidewalk" things at the airport?
if so, then the wings would indeed generate lift if it was going fast enough, and it would fly.

I thought about that too..... what is 'backwards'? Backwards as in the belt is moving under the plane from front to back, or backwards as in moving against normal operation?

what is 'backwards'?

I took it to mean from front to back as viewed by someone on the treadmill, like how the road looks while driving (a Camaro perhaps lol) as opposed to the treadmill moving forwards as if driving backwards. If you painted a white dot on the treadmill and turned it on so it went 'backwards', the dot would appear far in front of you and come towards you, if you flipped a switch and made it go 'forwards' the dot would appear closer to you and move away from you.

Wow, we've got some serious deep thinkers on here ;)

Wont fly. I believe the original question stated that the speed of the treadmill is directly linked to the engine speed. The talk about friction and tires is a non starter, thats not the issue. A planes engine (prop) doesnt create 'wind' that goes over the wings, the forward motion, thru space, creates lift over the wing. If the plane was throttled up to max speed, and the treadmill matched the same speed, the plane would be motionless, as far as forward/rearward movement, therefore no lift over the wings. A plane has to have physical movement in space, forward movement, in order to take off. To think of it the other way, take a swamp boat and put it on a treadmill (although friction would be an issue in that case, lol, cause there arent any tires, but it takes the mystery out of it a bit), if the treadmill matched the speed of the swamp boats engine, it wouldnt move forward, in reality, the engines speed would keep it from being flung off the treadmill. Same thing with the plane, if the engine stopped but the treadmill didn't, the plane would be shot off the end of the treadmill, the two forces equal each other out, but still, no forward movement = no lift.


The friction is the entire issure. If the plane's wheels had no friction, the treadmill would not have any effect at all. Since the force of the plane's engine(s) - jet, prop, etc - is orders of magnitude larger than the force of the friction, the speed of the belt would have to be enormous to create enough friction force to counteract the force of the engines. At some point, the treadmill would create its own wind due to the friction of the air against the belt.

The propeller on an airplane doesn't push air under the wings so it can fly, it pushes against the air to create motion of the plane. The motion of the plane through the air is what makes it fly.

This thread makes for entertaining reading. Lesson #1. Lift is created when air passes over an airfoil NOT under it. That's why Formula 1 cars and AA fuellers have inverted airfoil(s) installed thus producing "negative" lift which assists in holding the vehicles on the track at speed. The spoilers on Formula 1 cars are so effective that in theory when the down force created by the airfoils exceeds the weight of the vehicle, it could be driven inverted. Example: during the Monaco Gran Prix a Formula 1 car could be driven through the tunnel up side down, pinned to the ceiling and in total control. Bottom line is air has got to be in motion over an airfoil to create lift.

The friction is the entire issure. If the plane's wheels had no friction, the treadmill would not have any effect at all. Since the force of the plane's engine(s) - jet, prop, etc - is orders of magnitude larger than the force of the friction, the speed of the belt would have to be enormous to create enough friction force to counteract the force of the engines. At some point, the treadmill would create its own wind due to the friction of the air against the belt.

The propeller on an airplane doesn't push air under the wings so it can fly, it pushes against the air to create motion of the plane. The motion of the plane through the air is what makes it fly.

EXACTLY!
:thumbsup:

I still say this is one for The Myth Busters. If anyone can recreate this wacky scenerio, THEY can!

If it's a matter of how much thrust it'll take from a jet engine to overcome the initial force of the belt working against the tires, then stick an F-15 on the treadmill. I'll bet anything that it would roll right along the belt FORWARDS and take off, no matter how much the belt worked against the aircraft.
It's the forward motion created by the engines thrust that moves an aircraft..... not anything to do with the wheels. The treadmill can go 2 times as fast as the aircraft is trying to move forward, and sooner or later the thrust is going to propell the aircraft forward, gaining flight. But as I said earlier.... the "treadmill runway" would have to be a few times longer than a typical concrete runway a jet aircraft would use.

The wheel speed would have nothing to do with the air speed. An aircraft needs air speed not ground speed to fly. Sure it would fly, although the wheels on a treadmill would be spinning a lot faster than normal. Kevin

Wait wait wait lol. I understand clearly that the wheels have nothing to do with flight, but the wheels (or ski's or pontoons, whatever) and the rest of the plane have to make forward movement, do they not? In order to create lift, the planes wings (and therefore the rest of the plane) must physically move forward in space, or am I nuts on this? lol. The only way to create lift is air passing over the wing, the only way to make the air pass over the wing is to propel the plane forward. Isn't it the same as if you put your car on the treadmill? I understand the lift issue, maybe Im retarded, but it requires forward movement to fly a plane, so based on that premis (of forward movement) wouldn't yall agree that if I put my car on a powered treadmill, and the car goes 60 and the treadmill goes 60, my car aint movin forward an inch.... correct? (or am I now going 120, lol. Or maybe it has to be a nonpowered treadmill for that to work, since in the case of the car, the tires, in contact with the treadmill are actually the force behind movement) In my mind (scary), the plane would act like its being anchored to the ground, not allowed to move forward (in space, due to the treadmills equal speed), but the more I think about it, my head hurts and I wonder if thats even right.
I understand that in real life the prop or jet could overpower the treadmill, but this is a hypothetical question, the treadmill goes the exact speed as the throttle on the plane. Someone email Mythbusters, lol, this is a good one, and Im feeling pretty dumb at this point.

If you put a gas powered model airplane on a treadmill and it can keep up with the treadmill I bet it doesnt liftoff. Need airflow under the wings for a plane to fly. Just like a bird needs air under its wings to fly. If he doesnt flap them he will fall.
I found this same question asked for mythbusters here:
http://community.discovery.com/groupee/forums/a/tpc/f/9701967776/m/6501920808/p/1

The Feller that started this thread needs to define "backwards". On a normal treadmill
the belt goes from in front of you to behind you. So "backwards" to me meant the belt going from behind me to in front of me. If thats the case then the treadmill would help move the plane forward. Physics is physics and trick questions are trick questions. :D

Back to the 120mph question...lol. Thats a good one. If a treadmill is going 60 mph and you drive your car on it to keep up I think you will be going 0 mph but your speedo will say 60.

hey i got it! put a giant fan in front of it! will it fly then?

Wait wait wait lol. I understand clearly that the wheels have nothing to do with flight, but the wheels (or ski's or pontoons, whatever) and the rest of the plane have to make forward movement, do they not? In order to create lift, the planes wings (and therefore the rest of the plane) must physically move forward in space, or am I nuts on this? lol. The only way to create lift is air passing over the wing, the only way to make the air pass over the wing is to propel the plane forward. Isn't it the same as if you put your car on the treadmill? I understand the lift issue, maybe Im retarded, but it requires forward movement to fly a plane, so based on that premis (of forward movement) wouldn't yall agree that if I put my car on a powered treadmill, and the car goes 60 and the treadmill goes 60, my car aint movin forward an inch.... correct? (or am I now going 120, lol. Or maybe it has to be a nonpowered treadmill for that to work, since in the case of the car, the tires, in contact with the treadmill are actually the force behind movement) In my mind (scary), the plane would act like its being anchored to the ground, not allowed to move forward (in space, due to the treadmills equal speed), but the more I think about it, my head hurts and I wonder if thats even right.
I understand that in real life the prop or jet could overpower the treadmill, but this is a hypothetical question, the treadmill goes the exact speed as the throttle on the plane. Someone email Mythbusters, lol, this is a good one, and Im feeling pretty dumb at this point.

There's no myth to bust here, it's simple physics. In order for the treadmill to keep the plane standing still, it will have to create a force on the wheels equal to the force of the engines pushing against the air. The friction of the tires against the belt and the friction of the wheel bearings is basically all you've got to work with. The surface speed of the treadmill would have to be many thousands of miles per hour.

Hey Guy's, I didn't mean to post and run. I just didn't want to sway any answers.
The question was posted exactly as it was on the other forum that I got this from.
The thread went 400 replies in 3 hours and hit autolock over there, and after some of the other members started searching for answers it seems that this question has already been on a few other forums.
Here is how I answered early in the thread...(although none of the smilies copy and pasted)
Yeah it would lift off the ground...
































if there were runway sized fans blowing air across the wings,
And then replied with this...
Why did I click on this thread...

No thrust, the plane would be carried backwards by the treadmill.
My initial thought was the engines should be able to be able to hold the plane in at least a fixed position.
Just didn't think ahead at what would happen if even more thrust were applied

At that point, I cracked open a beer and watched the other's "interpret" this question :D

The runway sized treadmill is going backwards and increases speed as throttle is applied.

Would it be able to take off?

No, the treadmill would not be able to take off regardless of the plane. :p

HA!
There ya go! The answer!!
:beers:

Orville, Wilbur, and Daniel (Webster) are all rolling over in their graves...

It has to fly... for the same reason that a Rocket can take off from earth.

Think about it this way. If you're jogging on a treadmill, going as fast as you can, but just stationary there... then I come along and give you a good boot in the a**, you're going to go forward.

Your legs are the wheels and my leg is the jet engine. :D

JD

The runway sized treadmill is going backwards and increases speed as throttle is applied.

Would it be able to take off?

There was a huge debate about this one on another forum.
I'm just wondering what You Guy's think. :D


Okay lets break down what is actually being asked here. First off all he states is a "runway sized treadmill", so based on where I work that's 8,000 feet long and 200 feet wide. He says it's moving "backwards", while that can be taken to say it is moving in either direction you have to assume he means backwards in relation to the direction the aircraft wants to move. He says the treadmill "increases speed as throttle is applied". Again way too vague but again you're left to assume the thrust is increased extremely slowly and linearly so as to allow the treadmill to accellerate to the same speed as the opposing force being applied by the thrust of the engine, rendering the airplane stationary.

If this is what he is asking then NO the aircraft will NOT takeoff. The aircraft is stationary. Like I said previously the only system on the airplane reporting any change in any condition is the wheel tach generators reporting to the BASC the wheel reference speeds. There is no lift because there is no airflow over the wings to generate lift. It's impossible, case closed.

Now if you apply real world logic and don't look at it from a theory only point of view again what will happen is the inertia of the drive drums of the giant treadmil would not be able to accelerate quick enough to compensate for the rapid increase in thurst as experienced in most take off power lever movements and the airplane will roll forward. Depending on what he means by a runway sized treadmill it may gain enough forward movement to reach V1 speed and take off.

Bottom line is the question is way, way too vague and you'll need a lot more details to answer what the aircraft will do. But if the first case stated here is what he is asking NO way the aircraft does anything but sit there. It's nothing more than a Functional Check of the wheel tach generators. I drive all the wheel generators at a common forward speed to test the anti-skid systems on our aircraft regularly, they don't take off, they sit there....in one spot. The same way it would on a treadmil if you can match inversely the forces of overcoming the inertia to accelerate the treadmill at the same rate the engine thrust is increasing to keep it stationary.

Don't bother calling Discovery Channel this one is BUSTED.

Would it be able to take off?

NO the aircraft will NOT takeoff.....Depending on what he means by a runway sized treadmill it may gain enough forward movement to reach V1 speed and take off.


Would that be a maybe?

How much power does it take to do the wheel-tach testing? How much force is required to hold your wheels stationary during testing? If your test belt was tilted at a 45° angle, what surface speed would be sufficient to keep the wheels from rolling down the slope?

What would the surface speed of the runway-sized belt be in order to keep an F-15 stationary with the engine producing full thrust? Do you think that a surface as big as a runway traveling at this elevated speed would create some wind of its own?

Okay lets break down what is actually being asked here. First off all he states is a "runway sized treadmill", so based on where I work that's 8,000 feet long and 200 feet wide. He says it's moving "backwards", while that can be taken to say it is moving in either direction you have to assume he means backwards in relation to the direction the aircraft wants to move. He says the treadmill "increases speed as throttle is applied". Again way too vague but again you're left to assume the thrust is increased extremely slowly and linearly so as to allow the treadmill to accellerate to the same speed as the opposing force being applied by the thrust of the engine, rendering the airplane stationary.

If this is what he is asking then NO the aircraft will NOT takeoff. The aircraft is stationary. Like I said previously the only system on the airplane reporting any change in any condition is the wheel tach generators reporting to the BASC the wheel reference speeds. There is no lift because there is no airflow over the wings to generate lift. It's impossible, case closed.

Don't bother calling Discovery Channel this one is BUSTED.

Sorry, but I respectfully disagree... Try this real world experiment.

Tape a bottle rocket to a Hot Wheels car and put it on a moving treadmill, then light it. Then do the same with the treadmill off. The car will move forward at the same speed both times. The only difference is that the wheels would be turning faster when the tread mill is on.

If you'd rather not blow up your Hot Wheels car (they can be valuable), just hold the car in your hand and move your arm up the treadmill. It won't take any more effort to move it while the treadmill is moving than when it's stationary. It's the same difference. The only way this wouldn't work was if the WHEELS were driving the airplane.


JD

See, SY1 is thinking the same way I did, except he sounds a lot more official when he wrote his answer. There's no forward movement of the plane, no forward movement, no lift. The example of getting kicked is nice, but you forgot that the speed of the treadmill matches the thrust of the plane, so if you "kick me in the butt" the treadmill's speed would match that extra thrust applied by your foot and it still would equal out - no movement.

The thrust of the engines will be pushing against the air, not the ground. You can increase the tread mill all you want the airplane will over come the ground speed because the plane will always move in the opposite direction as the engine thrust.
The wheels will be spinning at twice the speed as normal for take off, but unless you strap the plane down it will move forward as soon as you apply thrust and release the brakes.

It cant be possible because if it were, all airfields and carriers would be saving valuable real estate, doing away with steam catapults etc. etc., I don't think the size of the treadmill would matter either, just that it be able to match the thrust(speed) produced by the engine.the only way to take off would be to overpower the treadmill. which you couldn't do because the original question says your forward momentum is being cancelled out by the matching backwards motion of the mill. with that in mind,the only way your gettin off the ground is as Mr Doyle put it "a boot in the arse" to hurl you off the mill. The "boot" would have to rely soley on thrust to get you airborne not lift(air over the wings),therefore your butt being the plane, J.D.'s leg would then have to be a rocket.:thumbsup:
ok,my eye is starting to twitch so i'm gonna have to go have a beer and sort my wrenches or something!:clonk:

This is certainly interesting. and how the solution is communicated is obviously a difficult task. I am not the best at explaining but....

The treadmill will simply spin the tires around the axle.
as the treadmill speeds up so do the tires. But the treadmill does not directly apply a restraining force on the plane. it applies a torque to the wheel. (the force is just the friction in the wheel bearing.)
The force from the thrust results in forward motion of the plane, relative to the ground.

Since the thrust force is larger than the restraining friction (assumed to be zero) The plane will take off.

TTFN
Mat

http://www.roymech.co.uk/images11/friction.gif

Factors affecting the friction between surfaces

Dry surfaces
1. For low surface pressures the friction is directly proportional to the pressure between the surfaces. As the pressure rises the friction factor rises slightly. At very high pressure the friction factor then quickly increases to seizing
2. For low surface pressures the coefficient of friction is independent of surface area.
3. At low velocities the friction is independent of the relative surface velocity. At higher velocities the coefficent of friction decreases.

Well lubricated surfaces
1. The friction resistance is almost independent of the specific pressure between the surfaces.
2. At low pressures the friction varies directly as the relative surface speed
3. At high pressures the friction is high at low velocities falling as the velocity increases to a minimum at about 0,6m/s. The friction then rises in proportion the velocity squared.
4. The friction is not so dependent of the surface materials
5. The friction is related to the temperature which affects the viscosity of the lubricant

http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm

Note that once you overcome the coefficient of friction, it takes no more force to keep it going. Any additional force results in continued acceleration of the airplane.

If the plane's engine(s) are at full thrust, how fast does the belt have to travel to counteract this force? Can it travel at this speed? At what point does the boundary layer of air accompanying the belt either cause the tires of the plane to lose contact with the surface or create enough wind speed for the plane to lift off?

can't we all just get along?

ScottB - "The thrust of the engines will be pushing against the air, not the ground. You can increase the tread mill all you want the airplane will over come the ground speed because the plane will always move in the opposite direction as the engine thrust" BUT (lol), the question stated that the mill will equal the thrust of the engine - add all the thrust you want, if the mill equals it in speed of rotation (maybe not possible, but thats not the point, the questions is hypothetical anyway), you gain nothing. You could strap 20 JATO's to the wings, but if the treadmill's speed counteracts the thrust, its pointless.
OK, who has a treadmill and a radio controlled plane?

Here's a video of a wind-powered skateboard on a moveable runway:

http://videos.streetfire.net/player.aspx?fileid=35E964D9-38DB-4EFD-BE8D-D6BA1A43A06B

Ignoring all the techie stuff about wheel-speed generators, ABS systems, etc., the plane will take off and fly just fine if the treadmill is long enough for a takeoff run sufficient to attain takeoff airspeed. The airplane could care less about the treadmill or which way the wheels are turning - all that matters is airflow over the wings, which is a function of relative airspeed, which is produced by engine thrust (unless the airplane is bolted to the ground and can't move). Thrust is pulling power when the engines are tied to the airframe - they're not "pushing against the air" - they don't "push" against anything.

(40-year pilot here, 7700 hours, jet-rated) :)

This has been discussed to death all over the web even on Physic related forums with the same results.

http://forum.physorg.com/index.php?showtopic=2417&st=0

http://community.discovery.com/groupee/forums/a/tpc/f/9701967776/m/7451937218/p/2

http://www.physicsforums.com/showthread.php?threadid=101259

http://forums.diabloii.net/showthread.php?t=402395&page=1&pp=10

Here is your answer, its pretty long but a simple read.

http://www.avweb.com/news/columns/191034-1.html

Yea, see, just like I said, IT WILL FLY lol. OK, I'll take that link as truth, clearly he has more air time than me ;) Guess it makes sense, and yes, all those who have been saying the same thing, yes, you were right, I was wrong. Now, what if it was a sea plane? lol j/k

O.K So the same plane is coming in for a landing on the same treadmill only the speed of the treadmill decreases with decreased engine thrust. How long does the treadmill have to be and how far will the plane travel before it stops?? :D :D

Yes and No. Could I be anymore ambivalent?

I think what we have here is a question written so vague that there is no correct answer because there is so much left up to interpretation. It all depends on how you read into what is being asked (not enough detail to know what the intentions of the test are). So we are all left to assume what is being asked.

I assumed he meant the aircraft power is advanced so slowly to allow the treadmill to counteract any forward ground movement, while probably impossible considering the forces in play here it is possible in theory. If that is the intention then the airplane won't fly anymore than my drag chute won't open if I spin a treadmil under it because there is no flow of air over the wings. If he's saying the thurst is completely counteracted to result in no forward ground speed then it's the same as my spinning up all the wheel tach generators in the hangar, the aircraft sees forward movement to it's BASC computers, but it is not moving and does not take off and fly inside the hangar. If I take my drag chute and hold it over top of a spinning treadmill it doesn't open because regardless of how fast the treadmil spins there is no airspeed, no air flow to open the chute.

Now in real life the aircraft will overcome the treadmill because it is capable of rapid power changes and the treadmill would not possibly be able to keep up and yes the aircraft would take off because it will be moving forward along the 8000 foot long treadmill. A much higher ground speed will be required to take off, but you'll still need the same TAS (true air speed) for rotation and this will be much less than the ground speed due to the treadmill acting against the forward movement.

I don't want to get into the convergent, divergent exhaust nozzle theory to understand thrust developement in this post.

This is an interesting post and it's good to see all the thought put into everyones ideas. We kicked it around last night at the hangar, every pilot and mechanic on duty last night that commented all agreed in theory stationary aircraft No can't fly, in real world it will overcome the treadmill and if enough movement can develope to reach rotational speed it will fly. There is no right answer because the question is incomplete in it's description. Until we know what is being asked we can't really answer this.

FAA Airframe and Powerplant Technician, FAA Inspection Authorization, Falcon Crew Chief 26 years experience.

Dave