Plane on a treadmill argument...

[Drew Dowdell]

But the wheels cant spin faster than the belt speed, because they must always be the same values, but in opposite directions.

incorrect.

while the belt is moving, the wheels are rolling foward on the belt.

Have you ever walked up a down an "up" escalator? if you tried hard enough, you could eventually make it to the bottom..... if you ever make it to the bottom of an "up" escalator, your legs were moving at a speed faster than, but opposite to the escalator.

[Drew Dowdell]

We're over analyzing the problem???

Are you kidding me? You guys are talking about all

kinds of math here. Check this out:

CB = conveyor belt

AS = air speed

WS = wheel speed

P = aircraft

P pushes itself down the CB... it accelerates using the

thrust of its engines, we all know a plane does not

push itslef down a runway using wheels & axles, I

hope all of us knew that fropm the begining otherwise

how would it sustain air speed once airborne.

Anyway....

AS = 0mph when treadmill is stationary. Other than a

10mph wind or what have you, not relevant to AS.

WS = 100mph

(sensors in the wheel tell the CB to accelerate to 100mph)

AS= 0 since 100mph -100mph = 0 (zero)

so now the plane only has the friction of the wheels

preventing it from pushing itself down the runway &

accelerating to an AS high enough for takeoff...

the force of 2/3/4 turbines easily negates the 100mph

of the CB...

so the plane accelerates to 200 (on the CB not relative to the ground)

(sensors in the wheel tell the CB to accelerate to 200mph)

and this goes on and on and on untill (in theory) infinity.

Either way the plane CAN NOT fly even if the treadmill is

going light speed so long as the aircraft is stationary.

Ropes, rockets, cars in neutral, roller skates and all the

other things yoy can throw at this problem do NOT

change the fact that the CB is preventing AS from

reaching even 1mph nevermind the 120 required for flight.

entirely wrong.

[scharmer05]

Nick changed it halfway.....not sure everyone knows that.....the "treadmill from hell" is moving at the speed of the plain, not the speed of the wheels, so it completely changes the problem

[CaddyXLR-V]

No! That is only the case if the rollerskate wheels are providing the forward motion.  in this case your hand is providing the forward motion. the wheels are just along for the ride.

The wheels still have some friction. And since the belt keeps increasing as the wheel speed increases, friction increases as well. The belt will keep increasing speed until there is enough friction to counter the thrust from the engines.

Lets give the thrust a value of 10. The speed of the belt will keep increasing, until there is friction causing a negative force of 10.

[Newbiewar]

you're trying to tell me, that if you move a rollerskate forward with your hand on a belt moving the same speed in the opposite direction, the rollerskate will stay in place relative to the earth?

You need to go to the grocery store and try it. 

i'm going to have to get a video camera I see....

well the conveyor belt at the grocery store isnt a magical one that matches speed...

No! That is only the case if the rollerskate wheels are providing the forward motion.  in this case your hand is providing the forward motion. the wheels are just along for the ride.

the wheels are more then just along for the ride... there is a tremendous amount of friction that will occur once those wheels get spinning...

after you provide enitial force to the roller skate, the conveyorbelt instantly provides friction to the wheels... and after you get the magical conveyorbelt up to 100+ mph, those tiny wheels on the roller scate wont beable to spin any faster, and its just like trying to slide a rubber shoe, allong a rubber conveyor belt... there is too much friction to acheive an increase in speed...

[Newbiewar]

Nick changed it halfway.....not sure everyone knows that.....the "treadmill from hell" is moving at the speed of the plain, not the speed of the wheels, so it completely changes the problem

the speed of the plane?

ohh, then it can take off... no problem

but if it matches the speed of the wheels we have a large problem...

[Drew Dowdell]

The wheels still have some friction. And since the belt keeps increasing as the wheel speed increases, friction increases as well. The belt will keep increasing speed until there is enough friction to counter the thrust from the engines.

Lets give the thrust a value of 10. The speed of the belt will keep increasing, until there is friction causing a negative force of 10.

friction is such a minimal force in this case. If the wheels were actually cement bricks, then it would be a factor.

the thrust of a single jet engine is about 20,000 pounds.

the force of friction is in the range of 1,000 pounds.

a 747 can rip it's landing gear off if it wants to.

[Newbiewar]

incorrect.

while the belt is moving, the wheels are rolling foward on the belt.

Have you ever walked up a down an "up" escalator?  if you tried hard enough, you could eventually make it to the bottom..... if you ever make it to the bottom of an "up" escalator, your legs were moving at a speed faster than, but opposite to the escalator.

but the escalator doesnt match your speed... if it did, you'd never get anywhere...

an escalator that matches your speed would be called a stair stepper, and as fast as you go, you wont go anywhere...

they have that design already

[Newbiewar]

friction is such a minimal force in this case. If the wheels were actually cement bricks, then it would be a factor.

the thrust of a single jet engine is about 20,000 pounds.

the force of friction is in the range of 1,000 pounds.

a 747 can rip it's landing gear off if it wants to.

but we were talking about a magical tredmill from hell...

friction is not a mimumal force when we change the runway...

[Flybrian]

I don't see what the speed or friction or E=MC^2 has to do with any of this. The plane will not fly unless lift can be generated and if the plane is not moving in relation to the earth AROUND the treadmill, it will not attain lift.

[Nick]

First off, I didnt edit it half way through, I edited 10 posts down from the first post...

Secondly, here are the other threads that I got the original question from for reference...

http://answers.google.com/answers/threadview?id=428718

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

[CaddyXLR-V]

friction is such a minimal force in this case. If the wheels were actually cement bricks, then it would be a factor.

the thrust of a single jet engine is about 20,000 pounds.

the force of friction is in the range of 1,000 pounds.

a 747 can rip it's landing gear off if it wants to.

Is it still minimal when the wheels are spinning +1000mph, and the conveyor is moving -1000mph? The conveyor will keep spinning faster until the point where friction is no longer minimal. At a certain speed(who knows what that speed is, it could be 1000mph, or 100,000mph) the force of friction will be pulling against that plane at 20,000 pounds of thrust to counter the thrust from the engine. Edited June 26, 2006 by CaddyXLR-V

[Sixty8panther]

incorrect.

while the belt is moving, the wheels are rolling foward on the belt.

Have you ever walked up a down an "up" escalator?  if you tried hard enough, you could eventually make it to the bottom..... if you ever make it to the bottom of an "up" escalator, your legs were moving at a speed faster than, but opposite to the escalator.

The speed of an escalator at the mall is a constant. You, I

and most athletic people can overcome a constant of like

4mph. But if you started running at 4mph up the escalator

and it accelerated to 8mph then you'd still be moving at 4

mph in REVERSE.

At no point in Nick's example or anywhere on the net was

it established that the conveyor belt tops out at a certain

speed or that it is a constant.

[Newbiewar]

I don't see what the speed or friction or E=MC^2 has to do with any of this. The plane will not fly unless lift can be generated and if the plane is not moving in relation to the earth AROUND the treadmill, it will not attain lift.

well E=MC^2 is completely irrelevent

but if the speed of the conveyor belt is based on the plane's speed...

you have the plane is going 40 mph --->

and the conveyorbelt is going 40mph <----

the wheels are going 80 mph, and the plane is still going 40 mph ---->

if the speed of the conveyor belt is based on the wheels speed

the plane is going 40 mph --->

the wheels are spinning at a rate of... lets just say infinity

because, if what is above is true, the plane is going 40 mph ---->

the wheels are going double in speed consistantly until that plane goes back down to 0 mph while the wheels continue to move....

A.) the plane gets up to 150 mph hour

or

B.) the friction of the wheels going infinity rotations per minute slows the plane down enough such that it cannot attain 150 mph marker...

[ocnblu]

Will somebody please park a Piper Cub across two check-out lanes at Safeway so we can get the hell out of here?

The treadmill itself is not powered, it is actually moved by the plane's wheels, which are in turn rolled indirectly by the plane's engines (thrust pulls the plane and rolls the wheels)... you're not getting anywhere unless something is not equal!

[scharmer05]

i was dead set on it flying....still kinda am....but after 6 pages....it seems that there are too many things that could change depending on the way you think about it.....so now im way too confused....i'm on both sides.....and i'm done

[zhawk]

OK, lets look at this.

The problem is the part about the treadmill moving at the speed of the aircraft. If this means that the treadmill is moving at the speed of the aircraft in relation to an external object, IE the ground or the surrounding air then yes, the aircraft will eventually take off.

In this case an aircraft with about a 50MPH ground speed as measured by an outside source would have the treadmill also moving at 50MPH in the opposite direction. The wheel speed would be 100MPH.

Now, in this case, the aircraft would still need the same amount of thrust from the engine(s) and distance to take off since the air is independent from the treadmill and that creates the lift. The engines themselves create forward movement only.

On the other hand, if the treadmill is moving at the same velocity as the aircraft as measured with a closed system then the aircraft is not moving in relation to the air as the forces of forward movement by the aircraft is negated by this treadmill. The wheels may be spinning at 50MPH but the foward movement of the aircraft is 0. In this case the aircraft cannot take off since their is not sufficient air passing around the wing.

It doesn't really matter that the wheels are not used for propulsion. They spin. As the aircraft spools up and takes a minute to gain momentum the treadmill starts to turn. If the treadmill gains speed at half of the aircraft acceleration schedule then the aircraft can take off. If the treadmill gains speed at the same rate as the aircraft then the aircraft remains stationary. (Or at least until the tires massively overheat and blow)

Any of the thoughts of catapults (as used on aircraft carriers) as outside this argument since they are an external force being used. A catapult will pull the aircraft forward no matter if the aircraft is on stationary ground or a treadmill. Its purpose is to provide the initial speed needed for the aircraft's wings to provide lift as the engine will not do so in such a short space (area of an aircraft carrier).

I run engines all of the time at work (I am an C17 engine mechanic with flying crew chief qualifications), even at full power the force of the engines needs a bit to move the plane and our engines put out over 40,000 pounds of thrust each at takeoff rated thrust and we have 4 of those. Let's not get into the new GE engine that is rated at over 100,000 pounds of thrust.

All aircraft engines provide thrust with the same basic principle, Newton's Third Law of Motion which states for every action there is an equal and opposite reaction. The air being pushed behind the engine forces the engine to move forward. Since the aircraft is attached to the engine, it moves as well.

Rocket engines, jet engines, turbojet engines, turbofan engines, turboprop engines, rotary aircraft enginces, it doesn't matter. they all use the same principle.

As I said at the beginning, the problems has 2 potential correct answers based on the interpretation of the given conditions.

[Nick]

An interesting read that may put this debacle to rest...

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

[NOS2006]

An interesting read that may put this debacle to rest...

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

Yay, we win.

[zhawk]

Great explanation.

Thanks for finding it and clearing this up.

[ocnblu]

I wish we could ask Tattoo, he knew a lot about planes.

[NOS2006]

Who is Tattoo?

[Sixty8panther]

Who is Tattoo? 

Damn I feel old!

NOS: download a few episoes of Fantasy Island...

Tattoo was the Mini-Me to the guy who did those ads

for the Chrysler Cordoba... you know: "CoRinthiaan

LeaTHer"

What was his name... Ricardo Montelbaum or

something like that...

Edited June 27, 2006 by Sixty8panther

[Cory Wolfe]

You guys are ridiculous... heh...

[76ChevyTrucker]

All right, lemme throw a little reality into the situation. If any aircraft, in particular a commercial jetliner were strapped to a treadmill, and the engines were run up to full power, then the treadmill would disintegrate. I've seen the Pratt & Whitney and General Electric engine tests where they run their commercial jetliner engines up to full speed and they behind to rip the asphault and concrete of the runway up behind them.....

[ocnblu]

Dude, we're talking about an Ultralight here, not a 747.

[tmp]

I guess I am not getting this one- to me, the magic treadmill negates forward motion of the plane, whether the wheels are powered or not. Forward motion of the plane through the air is what generates lift that allows the plane to become airborne. No forward motion, no lift, no flight.

[zhawk]

ocnblu-the type of aircraft was never specified. The principles are the same no matter what size, its just that the larger aircraft would not be able to be supported.

tmp-The aircraft creates its forward movement by the engines moving air. The pushing of the air backwards makes the airplane move forward (Newton's Third Law of Motion) The wheels just turn. As the airplane starts to accelerate forward the treadmill starts its reverse motion. The plane still moves forward but the wheels spin at twice the rate of the moving aircraft due to the treadmill.

It will take the same approximate distance for the aircraft to reach takeoff velocity. The wheels will just wind up spinning at twice the speed, putting greater stress on the landing gear.

Since the pilots use an indicated airspeed to guage takeoff speed the increased wheelspeed would never be known to them. In fact, our pilots on C17s never know wheelspeed. Our wheelspeed sensors only give them information in case the antiskid system senses a difference between the 12 main landing gear tires.

I know my explanation to tmp is a reversal of what I previously thought but the articled linked in the Fly/No Fly thread was very informative and correct. I also found some great information at work in our technical manuals.

[ocnblu]

I was just playing, zhawk. :AH-HA_wink:

[zhawk]

I was just playing, zhawk. :AH-HA_wink:

OK, its cool. Although I would love to do the power run at edge of the treadmill. The other night I really got to play. I was doing acceleration checks on the engines. Let them stabilize and snap them to the wall as fast as you can. Plance was loud and bouncing. Oh and this was at 4 AM. Making noise and waking the neighbors.

[aaaantoine]

So now that we have apparently decided on a solution (you guys are still certifiably insane), I have another question.

If you take that same scenario, except that the plane's engines and brakes are off and the treadmill is moving backwards like 25 mph, does the plane stay put relative to the ground or does it move backwards?

Because if it stays in place, that would be cool to watch.

No? Ah well.

[zhawk]

So now that we have apparently decided on a solution (you guys are still certifiably insane), I have another question.

If you take that same scenario, except that the plane's engines and brakes are off and the treadmill is moving backwards like 25 mph, does the plane stay put relative to the ground or does it move backwards?

Because if it stays in place, that would be cool to watch.

No?  Ah well.

If the planes engines are not running then it will move with the treadmill.

[capriceman]

I have already stated my reason in the Poll thread and ill post it again....

I thought i wasnt going to comment on this but now i have actually thought about it and now listening to some people my ears are bleeding.

The plane will not fly How ever if we put it into a Wind tunnel it will.

if convyer goes <--- this way and plane ---> and the jets are on the plane will take off under own thrust and fly away.

If convyer goes<-- this way and plane is facing--> this way with no thrust the plane goes <--that way no flying happening

If convyer goes --> that way and plane facing --->that way the plane lets say Cessna 170 If i remeber achives Flight a 63 knots of airspeed under the wings. So if the Convyer can drag the plane to reache the 63 knots of airspeed the plane will shortly fly then lose airspeed and stall crash on to Convyer and the FAA has to file the most strangest accident report in history.

If I acomplished anything but confusion i will be happy. There need to be movement of Air under the wings to cause the change in pressures to create lift to make the plane fly. Airspeed is the Key factor in this problem. The Convyer speed and wheel speed have nothing to do to make the plane fly.

and

heres a diagram since we all need pictures.

there needs to be air flowing under the wings. +

QUOTE

and the airflow over the top of the wings needs to be going faster than the airflow underneath, since the topside of the wing arcs up in front.

Thanks forgot that Turbojett

and

model airplanes arent scale though. Since they can create Extreme amounts of lift and be light as hell. The plane would have to be made of Depleated Urainum (sp) for it to be scale.

I think im right. But I also think im

[76ChevyTrucker]

I had one of my friends in the engine department at the 187th Fighter Wing down here in Montgomery shell out a GE F110 on their "engine dyno" down there....that was one hell of a video to watch. So much exploding and flying metal, so much fire...