Physics Question

[Mellow]

Imagine a plane is sat on the beginning of a massive conveyor belt type
arrangement, as wide and as long as a runway, and intends to take off.

The conveyer belt is designed to exactly match the speed of the wheels
at any given time, moving in the opposite direction of rotation.

There is no wind.

Can the plane take off?

[Computer Nerd]

No. :)

[Mark]

No lift... no go unless it is a VTOL... :D

[Imrubicon]

only if the thrust provides enough lift over the wings ?

[Computer Nerd]

Aircraft do not direct thrust over the wings.

This question is similar to ones that ask "If you fired a rifle off the back of a train that is traveling at the speed of the exiting bullet, what would the bullet do?"

The answer is, nothing. Foreward momentum would cancel out the velocity the rifle is shooting the bullet at.

These are fun things to wrap your brain around though! :)

[AZST]

Imagine Mellow is running on a treadmill at full treadmill speed. What's the windspeed hitting Mellow's face?

Answer: 0 mph, same as the airplane, hence, no lift on the wings.

--Bryan
04ST1300A
:04biker:

[DAS]

Yes, the engines provide the thrust, not the wheels. So as long as the wheels can roll as fast as the plane need for ltake-off speed plus the speed of the conveyor belt - then it will go.

[ST1300 Alicia]

YES, Lift is created by Airspeed over the wings. The wings have no Idea what the ground-speed or wheel speed is. Thrust is what provides the forward motion not wheel torque.

Alicia from the Left Coast

[Caper]

YES, Lift is created by Airspeed over the wings. The wings have no Idea what the ground-speed or wheel speed is. Thrust is what provides the forward motion not wheel torque.

Alicia from the Left Coast

Yes it would take off, air speed is the only thing that matters to an airfoil.

[jaster]

Depends on how think the rubber is on the tires. :)

The engines would provide thrust but for the plane to travel down the runway, the wheels would have to travel faster than the conveyor belt. I would think the engine thrust would overpower the tires' traction and drag them down the runway. One of three thigns woudl happen:

1) The plane would smoke the tires before taking off.
2) The plane would smoke the tires until one blew and the plane crashed.
3) The plane would smoke the tires until it ran out of runway and crashed (it's hard to take off with the brakes on :) ).

Doesn't really matter since I don't think anyone will actually try it. Not sure if it's even possible to build a conveyor of that magnitude and speed.

[IlliniST]

Yes it would take off, air speed is the only thing that matters to an airfoil.
+1 on this (to make the minimum 6 characters).

[Rob Hephner]

It is a question of friction.

If the plane is never able to move forward because of the treadmill it will never be able to break the friction of the Earth's gravity in order to take off. Forward motion is required to create lift. Without that forward motion you get no lift, thus the plane would never take off.

Physics is the key here folks. ;)

Now, add a huge fan to the equation......

[illzoni]

Imagine a plane is sat on the beginning of a massive conveyor belt type
arrangement, as wide and as long as a runway, and intends to take off.

The conveyer belt is designed to exactly match the speed of the wheels
at any given time, moving in the opposite direction of rotation.

There is no wind.

Can the plane take off?

Mellow,

The plane would take off, but parts of your little experiment is impossible. The engine thrust of the plane would propel it down the runway-size conveyor belt at usual takeoff ground and air speed.

It's just not possible for the conveyor to keep up with the wheels. As the plane accelerates, the wheels would start to turn from friction with the belt. Presumably, the conveyor controller would somehow sense this friction and match it. The faster the wheels attmempt to spin, the faster the conveyor would attempt to roll. I suppose if this imaginary conveyor could continue matching speed, the plane tires would explode.

So, would the tires explode before enough ground speed is generated for liftoff?

You also propose there would be no wind. Assuming you mean no air flow over the wings--wrong. That assumes no ground speed and thus no air speed. But the engine thrust would move the plane, regardless of how fast the wheels spun until failing.

Jon

[illzoni]

+1 on this (to make the minimum 6 characters).

ex-m109rider,

Nice avatar.

Jon (aka illzoni)

[Spencer]

What kind of oil is the plane using ?

Spencer :crackup

[MilesFromNowhere]

When the thrust generated by the engine(s) caused the airflow over the wings to generate enough lift to offset the weight of the plane, it would "take off". Likely it would be unstable in the transition.

It would need to wait on the tarmac fully loaded with passengers for 8 hours before being placed on the conveyor.

[wjbertrand]

The plane would accelerate anyway and then take off because the engines will accelerate it relative to air speed, not ground speed. The reverse speed of the tread mill /conveyor thingy would only result in making the wheels spin faster than normal.

[georgeorge]

I'm SO CONFUSED!!!

[Texas]

Has anyone ever run on a treadmill? It gets pretty hot. I don't ever remember the wind blowing through my hair when I was on a treadmill. Wheels spinin, engines burnin.....has nothing to do with planes flyin. It is all about the speed of which air molecules flow over the top of the wing versus the bottom......lift.

A plane does not need even need wheels or a engine to fly. It could just sit on the ground and let mother nature do the rest. Of course mother nature would have to be blowin pretty had to get one of those jets off the ground (usually 100+ mph).

Texas

[MileHigh]

It is a question of friction.

If the plane is never able to move forward because of the treadmill it will never be able to break the friction of the Earth's gravity in order to take off. Forward motion is required to create lift. Without that forward motion you get no lift, thus the plane would never take off.

Physics is the key here folks. ;)

Now, add a huge fan to the equation......

+1

If the plane can overcome the friction of the belt and rollers and, gain enough forward motion to create lift (air flowing past the wings sufficiently) it will take off.

That would have to be one heck of a conveyer belt (and rollers) with zero friction.

Plane is going to take off.

If it don't, invest in that conveyer belt manufacturer quick!!

[sparkinator]

Imagine a plane is sat on the beginning of a massive conveyor belt type
arrangement, as wide and as long as a runway, and intends to take off.

The conveyer belt is designed to exactly match the speed of the wheels
at any given time, moving in the opposite direction of rotation.

There is no wind.

Can the plane take off?

Hypothetically, No it will not take off. We are assuming that the belt will do its job and not allow the plane to move any in relation to the ground. Like others have stated, no lift.

[Hobie]

yes it can

[STPilot]

Oye.... Joe? ***?? Do think of these things in your sleep?? ;)


Forward motion is required to create lift. Without that forward motion you get no lift, thus the plane would never take off.

Bingo... We have a winner.. !!!!!

Have you guys ever run on a treadmill??? Do you move forward?? NO!!! If the Treadmill (conveyer belt) is matching the leg speed of the runner (tires of the airplane) He is not moving. There IS NO lift. What we're talking about here is relative wind, Relative to the wing of the airplane. If you run down the street do you feel wind on your face?? Of course... this is relative wind, relative to YOU moving thru space. Do you feel wind on your face on a tread mill??? No. (not without a fan) The engine/propeller can be running as fast as you like, has NOTHING to do with relative wind over the wings.

[kingprawnokay]

Based on Mellow's criteria, no, a plane could not take off. No wind (air speed)=no Bernoulli Effect=no lift.

Many people here have come up with a "yes" response based on their own criteria.

[Trekker]

Hypothetically, No it will not take off. We are assuming that the belt will do its job and not allow the plane to move any in relation to the ground. Like others have stated, no lift.

+1

The imaginary treadmill will not allow the plane to move in relation to the earth. If there is no relative motion to the earth, there will be no air flowing over the wings and no lift. The engines of a typical aircraft do not generate lift, that is the wings job. A rocket can generate lift without wings because of the enormous thrust it generates.

I like Bryan's proposal... Mellow running on a treadmill will not feel wind on his face!

No air flowing over wingies..... no lift... simple physics. Come on folks! Do we need to get the Mythbusters on this????? :D

[Sink]

My treadmill has fans on it to keep me cool, but it is not big enough for an airplane... or were you talking about a plane used to smooth wood???

No it would not take off if it had no forward motion!

Now I have one for you.... If I said something and my wife didn't hear me, would I still be wrong????

[Sink]

I like Bryan's proposal... Mellow running on a treadmill will not feel wind on his face!



But what if Mellow is running on an obstacle course??? Will he still fall over?

[Trekker]

What if Sink were running on a treadmill... and some bacon were dangled like a carrot in front of him? Would he catch it? :D

[redst05]

I think the plane is a red one this means it's the fastest and as long as the planes were not in motion (brakes applied) then there would be air flow that would allow lift. So the answer would be

YES

But it could have a heat issue!

[thumperjdm]

This question is similar to ones that ask "If you fired a rifle off the back of a train that is traveling at the speed of the exiting bullet, what would the bullet do?"

The answer is, nothing. Foreward momentum would cancel out the velocity the rifle is shooting the bullet at.

These are fun things to wrap your brain around though! :)

O.K., I'll try this one. The bullet would exit the rifle barrel (as the explosion from the powder charge forces the projectile out of the confined area of the rifle barrel), and then appear to drop to the ground.

But, the bullet would drop to the ground at the same rate as a bullet fired from the stationary rifle--it just wouldn't disappear down range at the rate of 3,000 ft/second--and end up a mile or so away.

From the moving train, it would appear to exit the barrel to the extent the barrel had no more outside influence on the path of the bullet, and then drop to the ground.

[illzoni]

The treadmill does not prevent the plane from moving. It only matches the wheel speed. Since the plane doesn't derive it's forward motion from wheel spin, but instead from engine thrust, the wheels are irrelevant.

Mellows assertion of "no wind" is false.

Jon

[Trekker]

Wheel speed is a direct result of thrust acting against the friction of the ground. If the "ground" is moving with the wheels.... the plane will not move relative to the earth, only relative to the treadmill... and no lift will be generated.

[STPilot]

Ok, so the plane has a heat issue, needs risers and then prolly Russel seat with a back rest... oh, then some highway pegs.... I still say no...

Nobody mentioned what kind of tires it has?? Are OEM, Metz?? Pilot Roads(no, then it would never get passed the tar snakes...)


MAYBE...if it was blue.... :D

[Imrubicon]

Props creat air flow

Wonder if it has more of a heat issue that the FJR?

[STPilot]

The treadmill does not prevent the plane from moving. It only matches the wheel speed. Since the plane doesn't derive it's forward motion from wheel spin, but instead from engine thrust, the wheels are irrelevant.

Mellows assertion of "no wind" is false.

Jon

"Where" the energy comes from is irrelvant, prop, wheels.. whatever... As long as the treadmill matches the the rotation of the wheels, the plane cannot move!! Again... Treadmill?? Runner?? No relative wind, no fly...

[kingprawnokay]

Mellows assertion of "no wind" is false.

Mellow's assertion is hypothetical, not false.

The engines don't produce lift, they only produce thrust. If thrust is counter-acted by another force, the plane does not move. If the plane does not move, the plane does not move.

The plane does not move in Mellow's scenario.

If an object is flying it is moving.

[sparkinator]

The treadmill does not prevent the plane from moving. It only matches the wheel speed. Since the plane doesn't derive it's forward motion from wheel spin, but instead from engine thrust, the wheels are irrelevant.

Mellows assertion of "no wind" is false.

Jon

How can you assert a given is false in a hypothetical question? Just curious.

[Trekker]

Or..... it could highside and explode in a hellacious fireball! :22yikes:

[Hashimoto]

In the case of a treadmill, your legs are applying force to the track in one direction. The treadmill is applying equal force in the opposite direction, nullifying motion. :sbike1: In the case of the plane, the engines are applying force to the surrounding air. The planes forward movement is relative to the air around it, the tire speed is irrelevant. I say: The Plane Flies :plane1:

[bmcdonau]

O.K., I'll try this one. The bullet would exit the rifle barrel (as the explosion from the powder charge forces the projectile out of the confined area of the rifle barrel), and then appear to drop to the ground.

But, the bullet would drop to the ground at the same rate as a bullet fired from the stationary rifle--it just wouldn't disappear down range at the rate of 3,000 ft/second--and end up a mile or so away.

From the moving train, it would appear to exit the barrel to the extent the barrel had no more outside influence on the path of the bullet, and then drop to the ground.

I think this is a trick question. He said the bullet was fired out the back of the train didn't he? That means its going in the opposite direction of motion so it'll appear to go twice as fast.

[tommyboy]

Yes, but does the fly inside the plane move? The plane will not take off because the plane is moving on the treadmill. Lets say the take off speed is 250mph ground speed. If the treadmill is adjusted to the same speed, 250 mph east + 250 mph west = 0mph over the wings. I vote for Mythbusters, but only if Buster gets to fly the plane after smoking a cigarette in the toilet full of methane and with it pressurized and a bullet is shot through the windshield to see if Buster get sucked out of the plane. (answer to all of these questions - poor Buster, is no, it won't happen!

[kingprawnokay]

The planes forward movement is relative to the air around it, the tire speed is irrelevant. I say: The Plane Flies :plane1:

The plane isn't moving forward in Mellow's scenario.

[MilesFromNowhere]

The plane isn't moving forward in Mellow's scenario.

I've been in light aircraft in strong headwinds when the groundspeed was almost zero. Not airspeed, but groundspeed. No movement relative to the ground. It can be depressing to see traffic below on the interstate advancing while you are not.

[Hashimoto]

The plane isn't moving forward in Mellow's scenario.
Actually, Mellow's scenario states that the plane intends to take off, which means it will apply force to the surrounding air. It does not state that the plane is not going to move. In fact, that is the question isn't it, whether the plane moves or not?:rolleyes:

[pretbek]

Guys, it is so easy.

The treadmill exits the airplane with a speed equal to the viscosity of the oil in the Metzeler Pilot Road, so yes, the bullet DOES take off.

[georgeorge]

I think my head's about to explode!

[Mark]

:popcorn:
Post number 3...
:D

[Hashimoto]

Ok,, a rifle is fired in a level postion. At the exact moment the bullet leaves the barrel , you drop a bullet from the same height of the rifle barrel. Which bullet hits the ground first?

It's hard to imagine, but they both hit the ground at the same time.

[Highrider]

The question from Mellow's scenario is: Will the plane move forward. The answer is yes, as long as there is no mechanical attachment to the conveyor and the thrust of the planes engine can overcome the friction of the wheel bearings.
No problem here, the plane will take off.

[dteel]

I'm thinking that the movement of this massive conveyor belt will cause enough air movement that the plane may achieve enough lift, once the wheels break contact with the runway, all this talk about how fast the conveyor is going and wheel bearing resistance become moot. I'm thinking it will be the shortest flight in history as the air moving over the conveyor belt is likely to be highly localized.

[sparkinator]

I'm thinking that the movement of this massive conveyor belt will cause enough air movement that the plane may achieve enough lift, once the wheels break contact with the runway, all this talk about how fast the conveyor is going and wheel bearing resistance become moot. I'm thinking it will be the shortest flight in history as the air moving over the conveyor belt is likely to be highly localized.

I'm thinking that is what it would take in order for flight to be possible. It would take a bounce or something in order to cause some difference to airspeed/groundspeed/wheelspeed. If the wheels clear the ground due to bouncing it should slow down the wheels, thus slowing down the conveyor and allow movement of the plane.

Just my guess.

[Liam Comerford]

F = mA

The conveyor belt is decoupled from the aircraft by the aircraft wheel bearings. It doesn't affect anything.

The jet engines are coupled to the airframe so the thrust of the engines causes the mass of the aircraft to accelerate.

It takes off.

Liam

[MLRickards]

So this is what happens to Joe's brain when he doesn't have a model car to work on...:eek:

[Hunter]

Laim is correct. The wheels isolate the airplane from the surface so in effect it doesn’t matter what the conveyer belt is doing; going forward at 100 mph backwards at 100 mph or stationary!!!

Hunter, aka Doug K., P.Eng.

[IlliniST]

Thanks!


ex-m109rider,

Nice avatar.

Jon (aka illzoni)

[IlliniST]

The wheels of the plane are irrelevant. They provide no propulsion of the plane anyway, only reaction force due to friction. The movement of the plane is dictated by the thrust against the atmosphere surrounding (behind) the engines.

Think of it this way... Say the plane was suspended by infinitely small but infinitely strong wires. It would have NO connection to the ground. If those wires were released and the engines simultaneously ignited, the plane would move in the direction AWAY from the thrust of the engines REGARDLESS of the fact it no longer made contact with the wires and did not yet make contact with the ground.

- Jeff

[mshihrer]

Imagine a plane is sat on the beginning of a massive conveyor belt type
arrangement, as wide and as long as a runway, and intends to take off.

The conveyer belt is designed to exactly match the speed of the wheels
at any given time, moving in the opposite direction of rotation.

There is no wind.


Lets take it step by step. Opposite the direction of rotation of forward moving wheels, if I'm getting this right, would look like this:

<------------- plane
O wheel(s)
--------------> belt thingee

the wheels have to be moving for the belt thingee to match the wheel speed.
the wheels cannot move unless there is some forward motion.
So, I see a problem right here. there can be no way to have the conveyer precisely match the speed of the wheels. Because to even get it going, the wheel would have to move first, and since it moved, even the slightest, any speed the conveyer did has to match the speed. But the wheel got a head start. So, over time, and it might be a long time, eventually the plane would build up enough speed ahead of the conveyer, and have enough forward motion to create airflow over the wing, allowing the plane to take off.

That's my guess.

EDIT:
Found the answer on the internet. I was way wrong, but there is someone here who is way right.
Here's the link if you want to see the answer:


http://www.boingboing.net/2006/12/11/airplanetreadmill_pr.html

[Rob Hephner]

F = mA

The conveyor belt is decoupled from the aircraft by the aircraft wheel bearings. It doesn't affect anything.

The jet engines are coupled to the airframe so the thrust of the engines causes the mass of the aircraft to accelerate.

It takes off.

Liam


See, it is a question of friction. ;)

[ST1300 Alicia]

Think about it Guy's. The wheels do not propel the airplane or cause it to move in any way. I don't care what the wheels are doing when the Jet Engine or the Trust from the Propeller exceeds Aerodynamic Drag the Aircraft moves forward. When the minimum required airspeed is reached for Rotation the Plane will lift off of the runway and flight will be achieved. The hypothetical proposition that Mellow is giving you is similar to that of an Airplane with a Tailwind equal to the Stall Speed. That is what you will have when the Aircraft has a ground speed equal to the Stall-Speed and no airflow over the wings. Thats not Ideal and your Ground-Speed would be required to be Twice what it normally would be. However when you reached the minimum Air Speed the airplane would indeed FLY. The Aircraft flies on Air Speed not Ground Speed.

See my Post #8

Alicia from the Left Coast

['04 ST1300A in NJ]

I agree with the 2 other posters---belt goes backwards & wheels spin forward even faster. Plane takes off faster as air causes lift to wings.

Try it with your ST!!!!!! IT FLIES.................

[mshihrer]

well, I missed this part, seems I was almost correct ...
it is a paradox

However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way

http://www.straightdope.com/columns/060203.html

[wjbertrand]

Wheel speed is a direct result of thrust acting against the friction of the ground. If the "ground" is moving with the wheels.... the plane will not move relative to the earth, only relative to the treadmill... and no lift will be generated.

This would be true only if the airplane was wheel driven, when was the last time you saw a wheel-driven airplane?

[ST1300 Alicia]

I think I get it now. We were tricked. I think. But I'm not sure about that anymore either. I don't think well any more. A = A+5 , thats the answer. In order for the plane to have forward motion relative to the air, it's wheels must turn forward faster than the belt is moving backward. That in itself is very do able. However that would cause a speed gradient, or rather a motion gradient that the equations does not allow. In order for the wheels to turn forward only as fast as the belt turns backward, the airplane must remain stationary. This precludes flight, as it has no provisions for airspeed, with static wind conditions. Congratulations on mshihrer :bow1: showing me the light.

Alicia from the Left Coast:confused:

[kingprawnokay]

I thought about this for a while longer and will retract all previous "nay" statements.

The belt would have no effect other than doubling the speed of the wheels. Planes don't need wheels to take off, but they help with safety, cost of repair, etc. Thrust isn't produced by the wheels.

Clever trick question. The belt is a distraction. It reminds me of the joke, "If a rooster lays an egg on the peak of a roof, which way does it roll?"

Plane takes off. Roosters don't lay eggs.

[Mellow]

LOL... a friend of mine, mechanical engineer asked this question a couple years ago on a private site... I said the plane won't fly... he said it would.

Shortly after that, Trailace posted it on advrider but I can't find it, it only had something like 33 replies I think so we've already beat that...

The answer is supposed to be 'Yes' but I'm not sure I believe it until I see it..

[Schavlan]

I'm afraid that Alicia and all the others who say the plane won't fly are absolutely correct.
The premise of the question, a conveyor belt big enough and strong enough, etc is a totally hypothetical situation.
To then discuss real life factors, such as bearing friction and control system time lag is inappropriate. It's like trying to make sense out of a horror movie. Why doesn't the young scantilly clad teen simply outrun the mummy, instead of always getting trapped in a corner?
We either accept the hypothetical or we don't.
If the conveyor belt itself has no motion relative to the earth, then it follows that the belt motion cancels the motion of the plane. If it's not moving relative to the earth then no lift is generated.
Somebody call Mythbusters.

[Kevin_56]

I'm afraid that Alicia and all the others who say the plane won't fly are absolutely correct.
The premise of the question, a conveyor belt big enough and strong enough, etc is a totally hypothetical situation.
To then discuss real life factors, such as bearing friction and control system time lag is inappropriate. It's like trying to make sense out of a horror movie. Why doesn't the young scantilly clad teen simply outrun the mummy, instead of always getting trapped in a corner?
We either accept the hypothetical or we don't.
If the conveyor belt itself has no motion relative to the earth, then it follows that the belt motion cancels the motion of the plane. If it's not moving relative to the earth then no lift is generated.
Somebody call Mythbusters.

Lets go with the no drag on bearings and all of the other pitfalls. Planes wheels turn only if you apply engine thrust. If you now put said plane on a moving belt, the plane will move at the speed of the belt. If you "could" reach out and hold the plane, you would now stop the movement of the plane. Remember we do not have any bearing drag. Start said engine and throttle up, guess what. Plane moves forward and then you have air flow over the wings and the next thing you have is an airplane in the sky.

A wheel driven vehicle would seem to stand still with Mellow's scenario.

Great mind puzzle.

[Trekker]

We need to apply basic physics theory to this hypothetical test.

Remember that we have a rule of Conservation of Energy. The energy of thrust is equaled by the imaginary treadmill, therefore there is no forward movement of the wings relative to the surrounding air to create lift. (this imaginary treadmill as stated instantly matches the wheel speed, therefore it is powered and reactive to the thrust of the airframe).

If we completely ignore the effects of the wheels on any aircraft... then why don't they simply immediately fly when thrust is applied from the engines? Because lift is not generated by thrust alone.... air MUST flow around the wing.

[Marshal_Mercer]

Imagine a plane is sat on the beginning of a massive conveyor belt type
arrangement, as wide and as long as a runway, and intends to take off.

The conveyer belt is designed to exactly match the speed of the wheels
at any given time, moving in the opposite direction of rotation.

There is no wind.

Can the plane take off?
Yes, if the 'plane is a vectored thrust device, or a rotary wing aircraft, allowing for flight upward without the need for a differentiated surfaces' airspeed in a horizontal plane. Otherwise, no.

The speed of the air passing over differentiated surfaces (the tops and bottoms of the wings) provides the lift in fixed wing aircraft. As there is no difference (zero sum) in the relative speed of the belt and the wheels (only the direction is different), there is no airspeed. No airspeed equates to no lift. No lift equates to no take off -- but a perfect landing.

BTW: the problem never stated that the 'plane had an engine; only that the conveyor belt moved at the rate of the 'plane's wheels. If one uses a glider to test the problem, and given that there is no motive force, the wheels' -- and belt's -- speed should be zero at all times as the belt matches exactly the wheels' speed.

Asking the same question a different way: If a boat lies in the water two meters above its water-line, and the tide rises one meter, how high in the water now will be the boat?

Marshal
PS For another take on this, please see #147 of this thread.

[Mellow]

Hey... I don't agree but the answer is supposed to be yes... It don't make no sense to me... and obviously, there are probably some things a mechanical engineer knows that are not part of the questions, basic stuff that is left out maybe because it's intended for that audience.. I don't know.. I don't believe it but then again.. there are so many other variables which might justify both sides.

[Sink]

So, if the treadmill EXACTLY matches the speed of the wheels, how would the wheels EVER go faster than zero? The wheels would have to START rolling FIRST... BUT the treadmill won't allow this. Only way it would take off is if it dragged the wheels across the treadmill... brakes locked..... does that make sense to anyone? Or maybe if it was a Harrier.....

[Kevin_56]

We need to apply basic physics theory to this hypothetical test.

Remember that we have a rule of Conservation of Energy. The energy of thrust is equaled by the imaginary treadmill, therefore there is no forward movement of the wings relative to the surrounding air to create lift. (this imaginary treadmill as stated instantly matches the wheel speed, therefore it is powered and reactive to the thrust of the airframe).

If we completely ignore the effects of the wheels on any aircraft... then why don't they simply immediately fly when thrust is applied from the engines? Because lift is not generated by thrust alone.... air MUST flow around the wing.

Upon rereading of the original question, Trekker seems to be right. It stated that the belt will match the wheel speed. Once the wheels start to turn forward the belt turns also, negating the forward motion of the wheel and forward motion of the plane.

However, you do not need an airfoil on a wing to make a Radio Controlled airplane fly. You just need thrust. Guys make planes using the plastic corrugated material you see signs made out of. A simple sheet cut to look like a wing in shape. Some sort of a fuselage and tail feathers of the same material. Balance the weight and give her power. Now they do not glide very well though. That seems to need an airfoil, but under power they fly well.

Kevin

[Txrebel]

I'm torn...
I think the thrust of the planes engine will move the plane forward in relation to the aerodynamic drag of the airframe, nothing to do with the wheels on the ground since the wheels are not providing the force to move forward. Yes the wheels will certainly turn faster since the treadmill is matching the wheel speed in the oposite direction but the engines will move the plane in realtion to airflow regardless of the speed the wheels are turning.
Now take the thrust and put it on an airboat, in a river... if the river is flowing as fast as the max thrust speed of the propeller then the airboat will be stationary in relation to the ground that the river is flowing over.
I think the key to the difference here is the drag of the airframe of a plane related to the air and the drag of the hull of an airboat related to the water.

[DAS]

I thought this would fit nicely in this thread. You only think I guessed wrong! That's what's so funny! I switched glasses when your back was turned! Ha ha! You fool! You fell victim to one of the classic blunders! The most famous is never get involved in a land war in Asia, but only slightly less well-known is this: never go in against a Sicilian when death is on the line! Ha ha ha ha ha ha ha! Ha ha ha ha ha ha ha! Ha ha ha...

[Skywriter]

Imagine a plane is sat on the beginning of a massive conveyor belt type
arrangement, as wide and as long as a runway, and intends to take off.

The conveyer belt is designed to exactly match the speed of the wheels
at any given time, moving in the opposite direction of rotation.

There is no wind.

Can the plane take off?

*********
My approach to answering the theoretical is with a view to enlighten and instruct...

Not too show anyone up...

Here goes..
************

The aircraft MIGHT be able to take-off if the aircraft is a classic VTOL ( Vertical Take-Off and Landing)

(1) the AV-8 Harrier series.... or any other theoretical airplane with vectored thrust greater than 1:1 thrust/weight ratio

(2) Or possible the new STOVL version of the new JSF fighter ( the F-35B remains in test flight phase --
The F-35B is supposed to be a Short Take-Off...(requires a minimum forward rolling distance)
...and then capable of vertical landing at lighter weights.

It is my opinion that only the AV-8 Harrier series could take-off from this hypothetical scenario.

**********
BASIC AERODYNAMICS:

(1) Lift is generated and the aircraft controlled by the acceleration and movement of the airfoil surfaces THROUGH THE SURROUNDING AIRMASS at adequate speed and correct angles of attack with the relative wind...

(2) The takeoff maneuver is basically an accelerated ground run that terminates at lift-off -- transitioning from the ground run to airborne flight by controlling the aerodynamic lifting forces generated during the take-off run.

(3) This aircraft in order to take-off -- Assuming a classic (CTOL (Conventional Take-Off & Landing) configuration must accelerate to Vr (Minumum rotation AIRSPEED) and maintain at least Vmc (Minimum controllable AIRSPEED for a multi-engine airplane) or Vs (Minmum stall AIRSPEED for a single-engine airplane)

(3) Mellow's setup permits the aircraft to ROLL FORWARD in relation to the magic/matching/opposite direction conveyor belt... while REMAINING STATIONARY to the surrounding airmass...

(4) The theoretical aircraft at Maximum Takeoff Power/Thrust would be able to move forward in relation to the conveyor belt at phenomal relative ground speed (...To the surface of the belt...) but would not generate any relative airspeed due to the landing gear/conveyor belt arrangement.

CONCLUSION....

A lot of noise & exhaust...

A lot of shake-rattle & roll through the undercarriage/conveyor arrangement

Negligible airflow over the wings from which to generate aerodynamic lifting forces

Negligible airflow over the control surfaces from which to generate the aerodynamic forces that are needed to rotate the aircraft into a sufficient angle of attack in order to generate said lift

No conventional flying today...

NOTES:

Typical tire failure speeds on transport category jets are +/- 190- 200 knots tire rotation speed...
(Much lower speeds for smaller propeller driven civil aircraft)

Aft-mounted engines like the DC-9/MD-80 series typical ingest tire fragments on take-off roll...

This could be a real crowd-pleaser before it's all said & done..


All Harrier pilots.... have a nice flight...

Hope this helps....

Skywriter:

31 years in the cockpit...
+/- 2000 hrs F-4 Phantom series USMC included 100+ carrier landings
+/- 17000 hrs major carrier flight time... B-727, DC-8, L-1011, MD-88/90, B757/767 series

ATP MEL B-727, DC-9, B-757/767
COMM PRIVS SEL
CFII/ME over 20 years

[MilesFromNowhere]

We need to apply basic physics theory to this hypothetical test.

Remember that we have a rule of Conservation of Energy. The energy of thrust is equaled by the imaginary treadmill, therefore there is no forward movement of the wings relative to the surrounding air to create lift. (this imaginary treadmill as stated instantly matches the wheel speed, therefore it is powered and reactive to the thrust of the airframe).

If we completely ignore the effects of the wheels on any aircraft... then why don't they simply immediately fly when thrust is applied from the engines? Because lift is not generated by thrust alone.... air MUST flow around the wing.

Engines develop thrust which moves air across the wing. Air moving across the wing creates lift. When there is sufficient lift from engine thrust to offset the weight of the aircraft, it will rise or take off.

Forward movement of the aircraft (wing) is just one way to move air across the wing to generate lift. Lift is generated on a wing in a wind tunnel even though the wing is stationary. Air is still moving past the wing creating lift.

[MileHigh]

Is this an African or European airplane?

[Trekker]

While on the ground, the vehicle is a truck. It becomes an aircraft once it leaves contact with the "ground". As a truck, it don' make no difference how it be moved forward. It's on wheels and it's a truck.

[dr1954]

This is one of those time I'm glad I a did not attend college. I can truthfully say that I am ignorant of the question and stand back and leave the debate to those of higher learning!

[Spencer]

Bridgekeeper: What... is the air-speed velocity of an unladen swallow?

Mellow: What do you mean? An African or European swallow?

Bridgekeeper: Huh? I... I don't know that. [he is thrown over] Auuuuuuuugh.

Sir Bedevere: How do know so much about swallows?

Mellow: Well, you have to know these things when you're a king, you know.

[Mark]

I thought this would fit nicely in this thread. You only think I guessed wrong! That's what's so funny! I switched glasses when your back was turned! Ha ha! You fool! You fell victim to one of the classic blunders! The most famous is never get involved in a land war in Asia, but only slightly less well-known is this: never go in against a Sicilian when death is on the line! Ha ha ha ha ha ha ha! Ha ha ha ha ha ha ha! Ha ha ha...

You forgot the 'thud' at the end of that soliloquy...
:-)
Great movie.

Mark

[GRN]

Bridgekeeper: What... is the air-speed velocity of an unladen swallow?

Mellow: What do you mean? An African or European swallow?

Bridgekeeper: Huh? I... I don't know that. [he is thrown over] Auuuuuuuugh.

Sir Bedevere: How do know so much about swallows?

Mellow: Well, you have to know these things when you're a king, you know.

So which way will the bike go if I press left :rolleyes:

[MileHigh]

Bridgekeeper: What... is the air-speed velocity of an unladen swallow?

Mellow: What do you mean? An African or European swallow?

Bridgekeeper: Huh? I... I don't know that. [he is thrown over] Auuuuuuuugh.

Sir Bedevere: How do know so much about swallows?

Mellow: Well, you have to know these things when you're a king, you know.

Mellow: "It's good to be the king"

[CrashTestDanny]

There is only one way for the conveyer belt to match the speed of the wheels - if the wheels are stuck to the conveyer belt and the belt spins in reverse to match the forward velocity of the aircraft - as if the brakes were locked (or the wheels are bolted to the conveyer). Clearly the aircraft will be propeled forward. Will it reach liftoff speed? Barring mechanical failures and design flaws - sure. Will it take off? If the brakes are applied, yes. If it is bolted to the conveyer? Maybe, maybe not.

By the by, the radio-controlled airplanes mentioned by another poster do have airfoils. Some bend the cardboard around a spar to create a conventional-shaped airfoil. Others make use of a "flat-plate" airfoil (which has a lift coefficient of 2*pi).

[adamk]

The plane takes off. As Jeff B stated, the wheels just spin faster. <if> the plane had no wheels, but had skids like bush planes in Alaska, then it <might> be possible to actually move the plane backwards fast enough to cancel out the jet force. But in this case there is a mechanism to transfer force to the plane.

Think about it this way, if the engines weren't running, you could hold the plane in place quit easily as the belt started to move backwards. The only force required would be to overcome the friction of the wheel bearings. If you then started the engines, the plane would start to move forward, the wheels would spin even faster, and the plane would take off when it reached takeoff velecity relative to the air over the wings.

[Putt]

O.K., I'll try this one. The bullet would exit the rifle barrel (as the explosion from the powder charge forces the projectile out of the confined area of the rifle barrel), and then appear to drop to the ground.




But, the bullet would drop to the ground at the same rate as a bullet fired from the stationary rifle--it just wouldn't disappear down range at the rate of 3,000 ft/second--and end up a mile or so away.

From the moving train, it would appear to exit the barrel to the extent the barrel had no more outside influence on the path of the bullet, and then drop to the ground.

Not quite,
To the shooter on the train, the bullet would "appear" to leave the
barrel of the rifle at 3000 fps. (remember, the train is moving in
the opposite direction of the fired bullet)
To an observer watching the train go by, the bullet would appear to
leave the barrel at zero velocity and drop to the ground. It's all relative..
Putt

[Putt]

Ok,, a rifle is fired in a level postion. At the exact moment the bullet leaves the barrel , you drop a bullet from the same height of the rifle barrel. Which bullet hits the ground first?

both at the same time....

Putt

[Trekker]

"Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... now you tell me what you know." - Groucho Marx

[STPilot]

*********
My approach to answering the theoretical is with a view to enlighten and instruct...

Not too show anyone up...

Here goes..
************

31 years in the cockpit...
+/- 2000 hrs F-4 Phantom series USMC included 100+ carrier landings
+/- 17000 hrs major carrier flight time... B-727, DC-8, L-1011, MD-88/90, B757/767 series

ATP MEL B-727, DC-9, B-757/767
COMM PRIVS SEL
CFII/ME over 20 years

Skywriter...

Nicely said !! :bow1:

Tim
ATP MEL
Comm SEL
CFII/ME
10 years
6000 hrs
I'm gettin there.... :D

[tommyboy]

The question is related to gound speed until the plane is up. Since the plane will always have zero ground speed, you will not have any air moving over the wings. No air over the wings, no lift. I think it would be fun get the plane's thrust to supersonic and see what happen when we stop the treadmill, though. (not that I want to be on THAT plane).

[Sink]

Quantum physics says that NOW isn't really NOW because Now was said before you heard it...... the wheels couldn't move because the threadmill couldn't start at precisely the same time as the wheels started to roll.

Not many aircraft have enough power to overcome friction enough to make the plane take off with the wheels not moving. The engine does not provide air for lift, but rather it provides THRUST for forward movement through the air producing lift by the forward movement, not the air over the wings.

Someone shoot me down on this please!!!!! I say it couldn't happen.... unless the treadmill was made of ICE.... or like I said before... Harrier.

[Liam Comerford]

Sorry, the plane takes off as usual.

This is a simple physical system. A jet engine is attached to an airframe. It exerts force on the airframe by reaction (see Newton's laws).

The airframe also rests on wheels. The wheels rotate freely with respect to the airframe. They must. Consider what would happen if they didn't rotate freely when the plane lands.

The wheels rest on the conveyor belt. When the conveyor belt turns, however fast it turns, the wheels spin at the same speed in the opposite direction. Because the wheels spin freely, essentially no force is coupled from the belt to the airframe. (OK OK there is an insignificant friction in the bearings so an insignificant force is coupled to the airframe through the wheel strut.)

This means the reaction force from the jet engine is unbalanced and results in accelleration. A = F/m

There are also wings on the airframe. As the airframe accelerates forward air flows over the wings causing lift.

The plane flies.

Liam

[pretbek]

I can't believe this thread is 10 pages long and people still don't agree whether the plane takes off or not! :22yikes: It is entertaining, though. :D


The plane takes off.

The correct answer has been given several times already. Here it is again in a slightly different form:

The only function of the wheels is to hold the plane up, to keep its belly from touching the ground.
Here is the crux:
The wheels do not propel the plane, nor do they hold the plane back!!
The wheels exert only an upward force on the plane, any horizontal force on the wheels (moving conveyor for example) is decoupled from the plane thanks to the (near frictionless) wheel-bearings.
The plane couldn't care less if the wheels are on the runway, on a fast moving conveyor belt or on blue eggshells, as long as they carry the weight of the plane.
(If you want, this system is equivalent to the plane standing on skates on ice, and the ice moves forward or backward under those skates. As you can imagine, it doesn't matter to the plane...)

What does exert force on the plane in a horizontal direction is the jet engines or the propellor, which pushes against the air behind it, thus moving the plane forward until it takes off.
Again, there is no correlation between the plane and the wheels or the conveyor belt, those are irrelevant to the system.

Also, the speed of the plane relative to the air surrounding it is the only thing that counts. Speed of the plane relative to the moving conveyor belt (whichever direction it is moving in) does not matter. The moving force is against the air (jet engine) and lift is generated by the plane moving through the air.



Of course I took too long posting this, so now I say exactly the same as Liam, who posted 4 minutes quicker. :rolleyes:

[Trekker]

Perhaps this is only a test post and not a real hypothesis?

I still say this is a truck when on the ground and not going to move forward. Funny thing is, so many engineers and pilots have voted no....:D

[Schavlan]

This IS getting a little silly, but the answer still is no. The plane does not take off.

The only way the conveyor belt can turn at the exact same speed of the wheels is if the conveyor belt applies a force on the plane equal to the thrust of the engine cancelling out the forward thrust.

A much simpler way to think of this is a seaplane trying to take off travelling upriver. If the plane can generate a 30 knot forward speed, and the river current is 30 knots in the opposite direction, the plane will not take off. (Yes, I know a 30 knot current is unlikely, and the plane would probably have thrust available to create more than 30 knots of forward speed, but just work with me)

In mellow's example, the conveyor belt replaces the river, but exerts a similar force.

Does anybody have any idea which are the best tires, and what is the best oil ?

[pretbek]

If the plane can generate a 30 knot forward speed, and the river current is 30 knots in the opposite direction, the plane will not take off.

Sorry, not true.

The water has no bearing on the speed of the plane relative to the air. The plane pushes itself forward against the air. The plane's speed relative to the water does not matter.

Your assumption is only true if the plane propels itself by pushing against the water, using an outboard motor or something.
But it doesn't.
The plane glides over the water on floaters, with presumably negligable friction. Just like the wheels on its bearings from the previous example.


Recurring theme:
We are interested in the speed of the plane relative to the air, NOT relative to whatever surface it moves on.

[Trekker]

Recurring theme:
We are interested in the speed of the plane relative to the air, NOT relative to whatever surface it moves on.

Nope... it's not an airplane until it is not acted on by contact with the ground, (or water). It is a car or boat. Forces (including friction) must ALL be accounted for.

Regarding the speed of the plane relative to the air... that's what some of us have been saying. The aircraft will NOT have any speed relative to the air.

This hypothetical is totally dependent on the imaginary treadmill exactly matching the attempted forward motion of the craft, thus negating the forward motion, thus negating any speed relative to the air.

[Bones]

Will the plane take off? Let's consult the cockpit crew:

"Roger, Oveur. What's our vector, Victor? Do we have clearance, Clarence?"

"Surely you don't think the plane will take off."

"Of course it can't take off. And don't call me Shirley."

[Rob Hephner]

This hypothetical is totally dependent on the imaginary treadmill exactly matching the attempted forward motion of the craft, thus negating the forward motion, thus negating any speed relative to the air.


You are missing the point that the treadmill is not attached to the plane.

The engines are......

Put the same plane on floats in a stream and what do you get?

[Txrebel]

You are missing the point that the treadmill is not attached to the plane.

The engines are......

Put the same plane on floats in a stream and what do you get?

I know the answer to this one... A float plane...

[Sink]

BUT the wheels would be spinning, (not the way I see it), and sliding so fast that they would fail, applying more friction to the plane so it wouldn't get enough speed to get airborne... that is if it didn't have enough power... consider an ultralight as opposed to the huge freaking turbines you are assuming here...

I understand this is all hypothetical, but the friction IS a big part of it! Can't gain enough airspeed to rotate..... no flying today boys! Probably not many airplanes could take off with that much friction. Remember, the treadmill is going as fast as the wheels are, so the wheels would have to be sliding on it to gain airspeed. Otherwise, the wheels would be traveling FASTER than the treadmill. The wheels ARE the problem in this equation..... They are what holds it off the ground and reduces the friction enough to let the plane gain speed!

[Trekker]

You are missing the point that the treadmill is not attached to the plane.

The engines are......

Put the same plane on floats in a stream and what do you get?

No, I'm not missing that point. I'm accounting for it. Put same aircraft w/ floats (boat) on a stream moving at a certain speed, face the aircraft (boat) into that current and apply the exact amount of thrust to counteract the drag (friction) of the moving water, and the airplane (boat) does not move relative to the shore or surrounding air.

How about- put an airboat in a river current and apply just enough thrust so as to negate the friction of the current so it is "apparently" stationary on the river. It has an engine (propeller) applying thrust and does not move relative to the shore. Now put wings on it. Will it fly? No. That's what this hypothetical situation is.

The current is the treadmill, and if we assume it can do the same as the magic treadmill, it can increase in speed to match the thrust of the aircraft (boat) and keep the aircraft (boat) in place relative to the shore and surrounding air.

[wefcisco]

Clever trick question. The belt is a distraction. It reminds me of the joke, "If a rooster lays an egg on the peak of a roof, which way does it roll?"

Plane takes off. Roosters don't lay eggs.

+1. Regardless of what the question asks or what facts it states, the purpose of the question is to see if your thinking. The real answer is that wheels don't make the plane move forward, thrust from the propeller does! Just like Roosters don't lay eggs, hens do!

[Coop]

Roosters don't lay eggs? Well what are they crowing about then?

[Computer Nerd]

The treadmill does not prevent the plane from moving. It only matches the wheel speed. Since the plane doesn't derive it's forward motion from wheel spin, but instead from engine thrust, the wheels are irrelevant.

Mellows assertion of "no wind" is false.

Jon

The jet thrust would compell the aircraft foreward. Causing the wheels to turn, and move the aircraft along the ground. If the tarmac was moving under the aircraft like a conveyor belt, the aircraft would not be moving foreward, thus, the wings would not experience airflow over the wings.

The wheels would be spinning, and the engines thrusting, but the energy of the movement of the tarmac under the aircraft would absorb the energy of the thrusting engines.

No airflow over wings, no lift. The aircraft would hold it's position over the tarmac.

Should the tarmac slow, then lift would begin to be generated.

Wonder what kind of tires the aircraft is using?? :)

[Computer Nerd]

BTW,

It is within the realm of possibility to test this.

I used to fly model airplanes, and they don't need a whole lot of speed to take off. You could, I suppose, make a treadmill that could go really really fast.

Set the model plane upon the treadmill, and start matching the speed of the plane.

Of course, for what this would probably cost, I'd rather spend the money on a new motorcycle.

[Rob Hephner]

Wonder what kind of tires the aircraft is using?? :)

The real question is what oil and filter the plane is using. ;)

[dmulk]

My gawd man.... this thread is on a tread mill.... I can't catch up to the end of it.... it's updating faster than I can read!!!


<D>

[dmulk]

Anyway... my physics guy here at work says the answer is "yes".... if it is a harrier Jet.


<D>

[Rob Hephner]

Or a F-35

[4INer]

It's all about Bernoulli’s principle. As air is accelerated, pressure is decreased. A wing is shaped the way it is shaped (an airfoil) so that the air flowing over the wing has to accelerate around the curved surface in order to keep up with the air that flows under the wing. The greater the difference in the airspeed above the wing and the airspeed below the wing, the more lift you have. Now back to Mellows question. If the aircraft power is such that the engine does not increase airflow over the wing, then the aircraft has to have forward motion relative to the earth to get the airflow needed for lift. The treadmill may be attempting to keep up with wheel speed but since the wheels are connected to nothing except bearings (think the front tire of your ST) the aircraft accelerates normally until the wheels are spinning so fast that the heat generated by the bearings cause bearing failure. On the other hand if the aircraft has an engine configuration that causes air to flow over the wing surface, the aircraft will take off as soon as lift is greater than the aircraft weight. If we were talking a float plane in a river, the aircraft could appear to be stationary until the engine provided enough airflow for lift. Then as soon as the drag from the water was no longer a factor (the airplane is now flying) the aircraft would accelerate forward and produce even more lift. And this cycle would continue until drag became greater than forward thrust.
And of course the red one would fly higher and faster than the rest of them even if it had dinosaur oil in it's oil tank and ethanol in its fuel tank.......

[mshihrer]

they should send this thread to someone at "Mythbusters"

[huxtablejones]

When you people run on a treadmill does yer hat fly off in the wind?


If you are standing on the tarmac next to this contraption, the net speed of the plane relative to you - and the air surrounding you - is nada. Nothing.

so no speed = no air over the wing = no lift = no takeoff.

All you are doing is moving the surface underneath the airplane. Just like you running on a treadmill.

/high school diploma ;)

[Rob Hephner]

When you people run on a treadmill does yer hat fly off in the wind?



No, but my feet move me.

If I put a jet pack on my back I would move forward regardless of what my feet did.....


Get it yet?

[huxtablejones]

No, but my feet move me.

If I put a jet pack on my back I would move forward regardless of what my feet did.....


Get it yet?

they only move you in relation to the belt's surface. Not to the air surrounding you. All the jet pack would do is provide thrust to counteract the movement of the belt. The air doesn't move with the belt. You'd never exceed the speed of the treadmill and the air surrounding it/you - which is zero. Zero airspeed = zero lift.

yall are killing me here LOL

[DixieFlyer]

Flight will not happen in Mellow's hypothetical, but supersonic flight would occur if you factored in airflow from Mellow laughing his a** off at all of us having a serious discussion at his instigation!!! Lot's of folks having too much fun and time on their hands -- including moi.......

[MileHigh]

Just to have fun and see if this thread can set a record, changed a few key words in Mellows orig post.

Imagine a ST1300 (standard or ABS, any color) is sat on the beginning of a massive conveyor belt type
arrangement, as wide and as long as a highway, and intends to take off.

The conveyer belt is designed to exactly match the speed of the wheels
at any given time, moving in the opposite direction of rotation.

There is no wind.

Can the ST1300 take off?

:rolleyes:

[Computer Nerd]

Imagine an ST1300 is sitting in a shop about to get an oil change...

[huxtablejones]

wait wait wait - synthetic or dino juice?

:)

[4INer]

My ST is seatless for the next week and a half or so while I wait on the shipping gods to get it to Spence and back. You think I could ride it on a treadmill anyway????:biker: Will it fly without a seat???:biker:

[tommyboy]

I am going to see if the best man at my wedding (23 years ago) will get me a definitive answer. He is a flight test engineer at the NASA Dryden test center at Edwards AFB. He was the lead engineer for the AFTI F-16 for 10 years. He is now busy playing with the Predator remote controlled plane. He puts every type of armament on "his" toy and see what he can blow up withought destroying everything that may be around his target. (about as much fun as one can have!)

[loving it]

I say no because its like running on a treadmill. You are running but going no where. So the plane is not moving so it cannot create lift.

[ST1300 Alicia]

If the question was, could the airplane take off on a treadmill that was running backward the answer is yes. Thrust propels the airplane forward not wheel torque. The treadmill and the wheels would be a Red Hearing in that case.

However, the question states that a relationship exists between the treadmill and the wheels. The qualifier is, that the treadmill BELT will be running backward at exactly the same speed as the airplane wheels are turning forward. This would indicate no movement relative to that which surrounds the treadmill frame work. Are you still with me. The airplane would have no problem advancing its position on the treadmill or planet earth, however it could not do that, with a positive wheel speed equal to the negative wheel speed of the conveyor belt. In order for forward motion to exist the wheels have to turn forward faster than the treadmill is turning backward and that is prohibited from happening under the parameters set forth in the Question. Are you still with me. Yes the plane can take off from the treadmill with no problems. It cannot however take off with no movement and that is what you would have if you added -X with +X . Like this +5 -5 = 0. PLUS five mph, MINUS five mph, = 0 mph. No forward motion = no airspeed. It really has noting to do with the wheels. It's about the ratio of positive wheel speed and negative conveyor-belt speed, Zero Sum Game. I hope I have simplified that enough for everyone.

Now let the flames begin!!!!!!!!!!!

Alicia from the Left Coast

[kingprawnokay]

-X with +X . Like this +5 -5 = 0. PLUS five mph, MINUS five mph, = 0 mph. No forward motion = no airspeed. It really has noting to do with the wheels. It's about the ratio of positive wheel speed and negative conveyor-belt speed, Zero Sum Game. I hope I have simplified that enough for everyone.

Now let the flames begin!!!!!!!!!!!

Alicia from the Left Coast

Nope.

This scenario is not a zero sum game. If the plane's wheels turn at 5 mph in the forward direction and the treadmill turns at 5 mph in the reverse direction the wheels will now be turning in the forward direction at 10mph.

[zombiebritts]

The wheel and treadmill speed doesnt matter as they are not the source for movement. The jet engine will move the plane whether the ground is moving or not.

my .02 :03biker:

[Old Git Ray]

I gotta go with the A = A+X thing in an uncontrollable instantaneous loop.

The speed of the spinning wheels has little to do with the lift as they are only connected by the friction from the wheel bearings so if the plane could move forward it would take off.

The problem is the wheels.

As the plane started to move - due to thrust not the wheels - the wheels would turn and also the conveyor. As it moved a little faster, again so would the conveyor until you quickly reached an uncontrollable runaway situation which would instantly destroy the wheels hence stopping the plane from gaining sufficient (if virtually any) forward speed to take off.

So the plane, hardly moving would just drop the thickness of the tyres and not take off.

No it would not take off - nor would I get in it.

[Putt]

It's a secret.......

Putt...

[ST1300 Alicia]

Nope.

This scenario is not a zero sum game. If the plane's wheels turn at 5 mph in the forward direction and the treadmill turns at 5 mph in the reverse direction the wheels will now be turning in the forward direction at 10mph.

Thats why in order for the speed between the wheels and the conveyor belt to be the same, there can be no forward movement of the airplane. Thats what makes the scenario unsuitable for flight, which would require forward motion.

Alicia from the Left Coast

[illzoni]

Alicia is on the trail....

It's like one of the optical illusion drawings. You know, with three columns/pillars on the top, but only two at the bottom. It just doesn't add up.

The engine thrust is what propels the aircraft forward, creating air speed, and thus lift. The wheel speed is just incidental to moving across the ground. However, in this case, it's given that the treadmill will match the wheel speed exactly. That's just not possible.

If the only real question is aimed at asking if wheel speed is important to the liftoff process, then "Yes" the aircraft will take off, as wheel speed is not important.

Note: In a previous response, I misunderstood the given "there is no wind" as a summary of the situation of the treadmill, when in fact it's just another given.

Jon

[Liam Comerford]

Let Fe = force exerted by engine on airframe.
Let Fr = residual force coupled by wheel bearings from the wheel tread to airframe via strut.

Fe >> Fr or aircraft couldn't take off from conventional static runways.

Let A = acceleration of aircraft.
Let m = mass of aircraft.

F = mA
F = Fe - Fr since they act in opposite directions

A = (Fe - Fr) / m until/unless lift adds an additional force vector.

Fe - Fr ~= Fe - 0

so the plane accelerates.

BUT

Do the problem conditions allow it to accelerate to liftoff or is the conveyor - wheel system going to self destruct before liftoff?

Ignoring the "instantanious" matching of rotational velocities (not realizeable in a physical system) we can ask if there is an system state which will meet the condition that the rotational velocity of the belt and wheel are equal at the same time the tangential velocities (as forced by friction) are equal.

It should be inuitively clear that if the plane is standing still then the tangential and rotational velocities are zero for both the wheel and the belt and that this is the only such state.

Now we need to ask whether there are transient or unstable conditions which allow the system to survive long enough to permit the accelerating plane to reach liftoff velocity.

Lets look at systems that can be realized.

As the plane begins to role forward (recall it is acted on by an unbalanced force = Fe - Fr) a difference exists between the wheel velocities and the belt velocities. This difference has to be compensated by the feedback control system operating the conveyor. [I don't know of any engineering method beside feedback control to implement a system with objective of matching two speeds. Open loop systems can't do that.]

Feedback control systems operate in four domains:
1. Overdamped (slow to catch up with the approximate target value)
2. Underdamped (overshoots the critical target value, then undershoots by less, repeating this until it eventually settles at approximately the target value.
3. Critically damped (actually, in effect a fast settling overdamped system)
4. Unstable (Oscillates or accelerates without approximating the target value.)

We don't know the parameters of the physical system so we can't say which domain it operates in or whether:

1. The amount of error allow in the aproximation of the target is large enough to hide the error introduced by the forward motion induced rotation of the wheels (when that becomes a second or higher order contributor to the wheel speeds),

or, for each case,

1,3. the response of an underdamped case is slow enough to avoid destruction before liftoff,
or
2,4. the relative negative excursions and frequency of oscillation of belt system save it from destruction.

In a hypothetical system the belt could survive the runaway (sorry) condition of ever increasing belt speed. The problem doesn't specify a failure speed for the belt. In a real physical system the belt will show damping and error. The fate of the plane depends on those values.


Liam

[huxtablejones]

of course, if this was happening in Newark it would be moot anyways. You'd just sit there for a couple hours regardless of any of it.

[pretbek]

Mellow's hypothetical question has instigated another question in my mind:

Had the question been posed by anyone other than Mellow, would this thread have been this long? :confused: :rolleyes:

This is -and will forever remain- a hypothetical question, because with this precedent we cannot objectively test the case of "thread not started by Mellow".

Due to the same effect on thread length by an earlier posting of a certain title, I propose to call this the "I Have A Secret"-effect, or Mellow's IHAS.

[sparkinator]

Yeah,
Starts this thread, and then leaves for the weekend. Kind of like keep the kids busy and they won't get into any mischief.

Gee thanks, Dad!!!!!

[Phil]

Let Fe = force exerted by engine on airframe.
Let Fr = residual force coupled by wheel bearings from the wheel tread to airframe via strut.

Fe >> Fr or aircraft couldn't take off from conventional static runways.

Let A = acceleration of aircraft.
Let m = mass of aircraft.

F = mA
F = Fe - Fr since they act in opposite directions

A = (Fe - Fr) / m until/unless lift adds an additional force vector.

Fe - Fr ~= Fe - 0

so the plane accelerates.

BUT

Do the problem conditions allow it to accelerate to liftoff or is the conveyor - wheel system going to self destruct before liftoff?

Ignoring the "instantanious" matching of rotational velocities (not realizeable in a physical system) we can ask if there is an system state which will meet the condition that the rotational velocity of the belt and wheel are equal at the same time the tangential velocities (as forced by friction) are equal.

It should be inuitively clear that if the plane is standing still then the tangential and rotational velocities are zero for both the wheel and the belt and that this is the only such state.

Now we need to ask whether there are transient or unstable conditions which allow the system to survive long enough to permit the accelerating plane to reach liftoff velocity.

Lets look at systems that can be realized.

As the plane begins to role forward (recall it is acted on by an unbalanced force = Fe - Fr) a difference exists between the wheel velocities and the belt velocities. This difference has to be compensated by the feedback control system operating the conveyor. [I don't know of any engineering method beside feedback control to implement a system with objective of matching two speeds. Open loop systems can't do that.]

Feedback control systems operate in four domains:
1. Overdamped (slow to catch up with the approximate target value)
2. Underdamped (overshoots the critical target value, then undershoots by less, repeating this until it eventually settles at approximately the target value.
3. Critically damped (actually, in effect a fast settling overdamped system)
4. Unstable (Oscillates or accelerates without approximating the target value.)

We don't know the parameters of the physical system so we can't say which domain it operates in or whether:

1. The amount of error allow in the aproximation of the target is large enough to hide the error introduced by the forward motion induced rotation of the wheels (when that becomes a second or higher order contributor to the wheel speeds),

or, for each case,

1,3. the response of an underdamped case is slow enough to avoid destruction before liftoff,
or
2,4. the relative negative excursions and frequency of oscillation of belt system save it from destruction.

In a hypothetical system the belt could survive the runaway (sorry) condition of ever increasing belt speed. The problem doesn't specify a failure speed for the belt. In a real physical system the belt will show damping and error. The fate of the plane depends on those values.


Liam

Ok here is the REAL answer:

Plane accelerates, slips off treadmill, explodes

no survivors

[Bones]

What if it's not a treadmill but a NordicTrak? Will the plane gather dust and become a convenient place to hang laundry and stack boxes?

[Trekker]

What if it's not a treadmill but a NordicTrak? Will the plane gather dust and become a convenient place to hang laundry and stack boxes?

:chrfl1: Hey! You've been in my basement!

[ChipSTer]

If it was a vehicle that is propelled by drive wheels, then I would say that it probably wouldn't go anywhere... but it is a plane.... So my guess is that it would take off... eventually...
:cool:

[Putt]

It won't fly... Youse guys are making this more compllicated than it has to be.
treadmill self destructing, wheel bearing failure etc.. It's a hypothetical question, nothing self destructs.. As long as the conveyor belt can dissipate
all the power generated by the engines, the plane will just sit there...
In this case, the conveyor belt is acting as a brake.... All the thrust of the
engines is being transferred through the tires, bearings, etc. to the belt...
30,000 HP being developed by the engines, 30,000 HP being dissipated by
the conveyor... No different than setting the brakes and cranking up the
power, until you develop enough power to overcome the friction of the brakes
(conveyor belt) you ain't going nowhere..


Putt...

[cheezewhizz]

Is this a 747 or 737 and do they serve drinks and roasted peanuts?

[4INer]

I'm thinking its a balsa wood toy with a rubber band prop. So yes the guy walking the treadmill passes gas and the plane flys....:butt1:

[jholder]

Thank you Liam. You tok the words right out of my mouth. The wheels speed and the conveyor belts speed is irrelevant. The wheels will just spin faster to match the relative speed of the conveyor belt and plane will merrily fly off. The engine, is exerting force independent of any friction or motion between the wheels and the conveyor belt.

Ride safe,

Sorry, the plane takes off as usual.

This is a simple physical system. A jet engine is attached to an airframe. It exerts force on the airframe by reaction (see Newton's laws).

The airframe also rests on wheels. The wheels rotate freely with respect to the airframe. They must. Consider what would happen if they didn't rotate freely when the plane lands.

The wheels rest on the conveyor belt. When the conveyor belt turns, however fast it turns, the wheels spin at the same speed in the opposite direction. Because the wheels spin freely, essentially no force is coupled from the belt to the airframe. (OK OK there is an insignificant friction in the bearings so an insignificant force is coupled to the airframe through the wheel strut.)

This means the reaction force from the jet engine is unbalanced and results in accelleration. A = F/m

There are also wings on the airframe. As the airframe accelerates forward air flows over the wings causing lift.

The plane flies.

Liam

[MileHigh]

Yeah,
Starts this thread, and then leaves for the weekend. Kind of like keep the kids busy and they won't get into any mischief.

Gee thanks, Dad!!!!!

Hey, I found some synthetic oil in the garage and some matches in the kitchen drawer.

Next, we can even build a ramp and jump an ST over a row of used tires!

Let's go have some fun, Dad won't be back for a while.

[Mellow]

Yeah,
Starts this thread, and then leaves for the weekend. Kind of like keep the kids busy and they won't get into any mischief.

Gee thanks, Dad!!!!!

LOL.. hey, I told you the answer.. even if my feeble mind can't comprehend it.. the plane is supposed to fly... :clap2:

[Sink]

Imagine a plane is sat on the beginning of a massive conveyor belt type
arrangement, as wide and as long as a runway, and intends to take off.

The conveyer belt is designed to exactly match the speed of the wheels
at any given time, moving in the opposite direction of rotation.

There is no wind.

Can the plane take off?

First thing... I don't see anything about jet engines here...... that is an asumption on some of your parts....... Second, it says "exactly match the speed of the wheels".... it doesn't say there is no forward motion... IF the plane has enough trust and the wheels can take the draging across the belt and get airborne before they disintegrate, it WILL fly..... but not if the wheels fail..... It also states no wind so STOL wouldn't make much difference. The amount of trust available is definatly the key here..... A rocket flys without horizontal motion..... It's all about the thrust!

The question can't be answered without more information..... It's as simple as that!

[Trekker]

Let it go Sink...... take a deep breath...... there.... all better now?

Trust me on this..... let it go. :D

[Marshal_Mercer]

Imagine a plane is sat on the beginning of a massive conveyor belt type
arrangement, as wide and as long as a runway, and intends to take off.

The conveyer belt is designed to exactly match the speed of the wheels
at any given time, moving in the opposite direction of rotation.

There is no wind.

Can the plane take off?
I said "no" that the 'plane cannot take off, but I was wrong. Here's why.

Given that "take off" has nothing to do with continuing to fly once the 'plane has taken off, the turbulent airmass (boundary layer) movement generated by the conveyor belt will be sufficient to lift the 'plane. The faster the speed of the belt, the greater will be the height of the boundary layer. At some point, the boundary layer will touch the lifting surfaces of the 'plane, and up it goes. Not very much 'up', but up. Then backward and splat. But that's another story.

If one takes a piece of tissue paper and holds it close to a moving treadmill-belt, the effect will become apparent; more so as the treadmill belt's speed increases. It's easy to see this happen at 5 mph and greater.

I feel like a 'donkey' for not concluding this the first time. My intuition got in the way of my reason.

Marshal

[Sink]

Let it go Sink...... take a deep breath...... there.... all better now?

Trust me on this..... let it go. :D

:o4: I need some BACON!!!!!

GEESH Mr. Obvious..... I never made the connection! Boundry layer..... ground effect...... now I remember! German experiments and all.....

AHEM!!!! nevermind......

[Phil]

Is this a 747 or 737 and do they serve drinks and roasted peanuts?

Is this a transatlantic flight? Very important to know because this means:
1-If it is, free booze and you get blasted on the flight
2-If it isn't, no free booze so you get tanked before lift off

[mshihrer]

boy, this thread is still going! It sure beats those "just testing" threads to bits.

[George]

The plane will not take off. The engine provides forward thrust but doesn't provide lift. If the plane is not movign (forward speed offset by the conveyor belt), there is no air movement over the wing, no lift, no fly.

[Putt]

The plane will not take off. The engine provides forward thrust but doesn't provide lift. If the plane is not movign (forward speed offset by the conveyor belt), there is no air movement over the wing, no lift, no fly.

Yup... If you take the question just as it is asked, don't add to it,
the plane will not fly.. there will be NO forward motion..
As a previous poster stated, a sea-plane is an excellent example,
it is is taking off against a 5mph current, at rest it will be going
a -5mph (downstream) it will have to increase it's speed by 5 mph
just to remain stationary... Now, if this river is flowing 100 mph,
it will have to increase its ground speed (over the river) to 100 mph
just to stay stationary... Replace the river with the conveyor belt....


Putt...

[ST1300 Alicia]

Thank you Liam. You tok the words right out of my mouth. The wheels speed and the conveyor belts speed is irrelevant. The wheels will just spin faster to match the relative speed of the conveyor belt and plane will merrily fly off. The engine, is exerting force independent of any friction or motion between the wheels and the conveyor belt.

Ride safe,

However, for the wheel speed to be equal and opposite of that of the treadmill, it would indicate that the airplane is not advancing it's position on the tread mill. It would need to advance its position on the treadmill to gain airspeed. If the treadmill were going two hundred miles an hour backward and you did not care what the relationship was between treadmill speed and airplane wheel speed, it would take right off. It's not a question of if it would fly, its a question of whether or not the airplane is moving. If the wheels are going 80 mph forward and treadmill is going 80 mph backward, the plane is setting still. Unless the plane moves forward on the treadmill (wheels turn forward faster than treadmill turns backward) there will be no airspeed. The airplane only knows about, or responds to airspeed. It could care less what the wheels do. They only turn so that there are no sparks when it lands.

Alicia from the Left Coast

[Skywriter]

Thats why in order for the speed between the wheels and the conveyor belt to be the same, there can be no forward movement of the airplane. Thats what makes the scenario unsuitable for flight, which would require forward motion.

Alicia from the Left Coast

You've got it Alicia...
They might not listen... but your analyasis is correct!

See my #76 --
Same thesis... just more words...

[Essteeguy]

Ha Ha. Can't believe I just read through 16 pages of this!
I work for an airline, I showed this thread to the aircraft mechanics and they went out and tried it. The aircraft did take off.
Unfortunately, the next departure will now be delayed due to a shortage of landing gear parts.
They also said that a loaded 767 has enough thrust in 1 engine to take off without wheels so I guess the treadmill is a mute point.:)

Tony

[zombiebritts]

OMG ... tell me what airline ! :eek:

Also , show me a treadmill that will hold an aircraft .

:worthless

[Don-STOC237]

I can't believe this thread is still going after 16 pages.

Everyone knows the plane won't fly. If it moves, it'll fall off the end of the treadmill and crash.

Sheesh...

[ST1300 Alicia]

You've got it Alicia...
They might not listen... but your analysis is correct!

See my #76 --
Same thesis... just more words...

This is the Fifth time I've posted this same basic statement and I guess some people just don't get it. An airplane sends no power, whatsoever, through the wheels. Its not about propulsion, it's about relativity.

Alicia from the Left Coast

[jholder]

However, for the wheel speed to be equal and opposite of that of the treadmill, it would indicate that the airplane is not advancing it's position on the tread mill. It would need to advance its position on the treadmill to gain airspeed. If the treadmill were going two hundred miles an hour backward and you did not care what the relationship was between treadmill speed and airplane wheel speed, it would take right off.

This is only if the wheels were not free-rolling. The wheels on a plane will roll to whatever their maximum is as the plane throttles forward.

Let me put it a different way. The engine of the plane provides (assuming it's a jet) thrust forward, in order for it to stay in one place, something must counteract that force. In the scenario given, that force would have to be counteracted by the friction of the free-rolling wheels. Not enough to do so.

Or, same plane traveling at 100 mph and lands on our theoretical conveyor belt that is running backwards at 100 mph. By the logic that syas the plane will not go, this plane will come to an immediate stop upon touching down on the conveyor.

I think you are forgetting that the plane gets it's acceleration not from friction with the ground, which is what would cause the conveyor belt to affect it significantly, but from thrust from the air through the engine.

And the seaplane analogy does not work because the skids on a seaplane are not freerolling, they are fixed to the fuselage. Big difference.

By the way, I understand what you are saying, that if the wheel speed is the same as the treadmill it will stay motionless, but I think the question is poorly phrased. There is no way once the engine throttles up that the conveyor can keep the plane in place if the wheels are free-rolling. The question says that it will maintain the same speed, but it really can't. I think part of the problem here is th e way it's phrased.

Ride safe,

[Mellow]

The guy that originally asked ME this question was referring to a Jet plane even if it wasn't stated in the original scenario.

[Sink]

Oh... so now you change the entire thing Joe?????:22yikes:

I suppose it was equipped with a flux capacitor also????:crackup

[jholder]

Here is the way I've seen it posted before "If an airplane is on a large conveyor belt and is trying to take off by exerting the thrust needed to move it forward at 100 knots, and the conveyor belt starts moving backwards at 100 knots, will the plane be able to take off, or will it just sit stationary relative to the ground, with the backwards speed of the conveyor belt counteracting the forward thrust of the plane?".

The point of the exercise, or argument, from my point of view is whether the plane can take off on the conveyor belt. To point out that wheel speed, or conveyor belt speed is irrelevant.

Yes, if the conveyor belt can counteract the forward momentum of the plane it will remain still. But there is no way it could do that. Of course, there is also no conveyor belt so...

In the scenario I quoted above, the plane would take off regardless of what the conveyor belt did. It being phrased to indicate the conveyor belt could counteract the thrust is where our problem lies. (Beyond the whole scenario, that is... :rolleyes:

Ride safe,

[George]

Funny to me that this now has 163 posts when #s 1 & 2 ask and answer the question. ;)

[Bones]

Can someone kindly explain how a fixed wing aircraft flies without lift?

[jholder]

Can someone kindly explain how a fixed wing aircraft flies without lift?

Let me phrase your question back in a sense...

When the engine is throttled up, it creates thrust, not through wheels but directly through airflow essentially. In order for the plane to remain stationary, that force must be balanced by an opposing force. In the scenario given what force balances the thrust to keep it stationary? Not the conveyor, because wheels are free-rolling.

The question is phrased to create an impossible (and I hate to use that word since the whole thing is wildly improbable if not impossible) situation in which the conveyor belt cannot possibly maintain the plane in one position due to the thrust of the engine, but if you assume it can then the plane cannot move.

Newton's 3rd Law, for every action there is an equal and opposite reaction. In this case the conveyor cannot balance the force, cannot be equal and opposite, therefore the plane will move, which is the equal and opposite reaction to the thrust. Otherwise, someone please show me where the equal and opposite force is in this scenario. :confused:

Ride safe,

[Ashrack]

>>Can someone kindly explain how a fixed wing aircraft flies without lift?

Red bull?
Superman?

[Sink]

TRUST MAN! You can make a barn door fly if you have enough THRUST!!!!!

If the answer is supposed to be yes, then I'm thinking this ground affect thing might have a lot to do with it too... IF this situation could occur, the airflow caused by the speeding belt would create a cushion of air to lift the aircraft..... that is until it gets too high and it would come back down. Saw a popular mechanics for kids last night, (son got it from the library), and it showed a ground affects float plane. It was obvious when it was out of ground affect as it would settle back down until it was "flying" again. Short little wings. Let's build one!!!!

I still don't believe the wheels would have a chance to ever start turning becuase the belt EXACTLY matches the speed of the wheels... It would ALWAYS be zero... cause the wheels and belt couldn't start at the same time. No way.

But then again if there was BACON involved.... who knows???

[Sink]

HEY! You are all wrong... the real answer is.................







ready for this?????







Here it comes......

















42!

[jholder]

HEY! You are all wrong... the real answer is.................



42!

Isn't that the answer to what is the meaning of life? Or does it being the answer to life make it the answer to everything? :cool:

Ride safe,

[travlr_45]

lift-off is controlled by forward motion right? just because the conveyer belt is goin in the opposite direction as the wheels, that doesnt negate the forward motion of the plane, it just doubles the speed of the wheels at take-off......................right?

[clmixon]

OK,

I actually sat here and read all of this again (it was on ST.N too) and we all used built in assumptions that made it hard to visualize. All the aviation types were focused on the lift of the wings and the need to exceed drag. All the physics types were visiting Dr. Issac again. I was in the no fly camp until near the end when I sat, looked out the window and pondered (tm) for a few minutes.

I finally saw it and agree that the plane will fly, the wheels will simply spin at whatever the multiple of treadmill and rotational speed they add up to. So our plane, Jet or prop begins to move when thrust is greater than drag, air begins to flow over the wing generating lift, at the same time the wheels spin and the plane translates along the length of the treadmill until lift is greater than weight and then the plane flies.

Hey Timmy!

What about the old control airspeed with elevator, altitude with thrust chestnut?

Chris PPL, SEL,STO, PDQ

[Sink]

Like someone before said, the motion of the treadmill takes air with it creating a "cushion" of air beneath the wings. It's really not a cusion but for those that are interested.....this (http://www.aerospaceweb.org/question/aerodynamics/q0130.shtml) is what is actually happening. Very cool stuff.

Take a look at some of the pictures at the bottom of the page. The Russians did a lot of experimenting with this and there are actually some planes that you can buy out there.

[Sink]

OK,

I actually sat here and read all of this again (it was on ST.N too) and we all used built in assumptions that made it hard to visualize. All the aviation types were focused on the lift of the wings and the need to exceed drag. All the physics types were visiting Dr. Issac again. I was in the no fly camp until near the end when I sat, looked out the window and pondered (tm) for a few minutes.

I finally saw it and agree that the plane will fly, the wheels will simply spin at whatever the multiple of treadmill and rotational speed they add up to. So our plane, Jet or prop begins to move when thrust is greater than drag, air begins to flow over the wing generating lift, at the same time the wheels spin and the plane translates along the length of the treadmill until lift is greater than weight and then the plane flies.

Hey Timmy!

What about the old control airspeed with elevator, altitude with thrust chestnut?

Chris PPL, SEL,STO, PDQ

No one has told me how the wheels can move faster than the treadmill (creating forward motion) if they are moving at the same speed as the treadmill..... I'm voting for the ground effects myself.

[dmulk]

Then how come when I run faster on a treadmill I still don't feel any air moving over my face?

The answer is simple: Unless there is wind, I am not passing through the air. It's stagnant air. With no wind, forward momentum (through the air) is required to create "air speed". If you have no air speed, you don't get any lift.

The plane won't fly.

But then again... I have read else where on this board that you are the "bringer of storms"....:cool:


<D>


OK,

, the wheels will simply spin at whatever the multiple of treadmill and rotational speed they add up to. So our plane, Jet or prop begins to move when thrust is greater than drag, air begins to flow over the wing generating lift, at the same time the wheels spin and the plane translates along the length of the treadmill until lift is greater than weight and then the plane flies.

Hey Timmy!

What about the old control airspeed with elevator, altitude with thrust chestnut?

Chris PPL, SEL,STO, PDQ

[Trekker]

Seems to me this "discussion" keeps going 'round & round'...... without any liftoff ! :D

[jholder]

No one has told me how the wheels can move faster than the treadmill (creating forward motion) if they are moving at the same speed as the treadmill..... I'm voting for the ground effects myself.

The wheels won't create forward motion via interaction with the treadmill, the unbalanced thrust from the engine will create forward motion in spite of the treadmill. You use the term "creating forward motion" but the forward motion has nothing to do with the wheels. The wheels turning is a byproduct of the forward motion, not the cause of it.

In order for the plane to remain stationary you have to accept the premise that the conveyor can keep the plane motionless even with the engine throttled up. Not possible, but I know the question is worded that way. The scenario is just being misquoted.

Newton's Law of Motion require that the plane move forward unless you have a balancing force to counteract the engines thrust.

Ride safe,

[jholder]

Then how come when I run faster on a treadmill I still don't feel any air moving over my face?
<D>

Because you are not moving relative to your surroundings, you have no true speed. You're making the mistake of seeing a plane and your feet in the same light. You move forward by interacting witht the ground beneath your feet and this requires friction. A plane does not require ground friction to get moving. The thrust comes from the engine expelling a fluid (air) so it does not matter if the conveyor goes backwards.

Ride safe,

[Putt]

No airspeed= no lift = no flight
The treadmill would have to be able to dissipate all the
power being generated by the engines in order for the
airplane to be stationary... This is a HYPOTHETICAL question,
so we must (uh-oh) assume that it can.. It does not matter
if the thrust is applied to the air or is applied to the
wheels, if there is not any airflow over the wings,
and there will NOT be if the treadmill always matches
the wheel speed, the wings will not develop any lift...
Airflow caused by the moving belt, probably not enough
to even come close to providing enough lift...


Putt...

[Sink]

Putt,

If we build it... they will come!