A jet plane on a large treadmill

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Originally Posted by The AD

It seemed to me you were asking if you understood the scenario correctly. Of course, you're Franz Klammer so maybe something got lost in the English to German translation!

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No worries, but I can assure you that Franz Klammer is fluent in plenty of languages ...

This reminds me of the bar joke involving 30 dollars and a bellhop.

You know, the one where you subtract instead of add... I never was told the "real" answer to this one, but anyone who tells the joke must be a genius. C'mon it's cool to be dumb...

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Originally Posted by commonlaw

What happens if you are traveling at the speed of light and you turn on your flash light? What if you point it behind you?

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Originally Posted by flabango

Tiny particles of light will eat your face.

Light speed is independent of motion. The flashlight won't shine in front of you but will shine behind you. Shine it to the sides and it will probably bend toward the rear... and then eat your face.

Actually you won't notice any difference. Time and Distance are not constant.

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Actually according to Einstein and the Theory of Relativity it will shine ahead of you and behind you just as if you where standing still because the speed of light is constant relative to the observer. This also means time is variable and can speed up and slow down.

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Originally Posted by Lurch

Actually according to Einstein and the Theory of Relativity it will shine ahead of you and behind you just as if you where standing still because the speed of light is constant relative to the observer. This also means time is variable and can speed up and slow down.

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Originally Posted by flabango
Actually you won't notice any difference. Time and Distance are not constant.


That's what I meant.

Check out

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


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Conversely, if Manfred has a lot of runway and nothing to hit, and takes off downwind in a 25 mph tailwind, the propeller will have to accelerate the airplane to a zero airspeed, which will be a 25 mph groundspeed, and then on to a 45 mph airspeed, which will have him humming across the ground at 70 mph. The speed over the ground, or a conveyor belt, when an airplane takes off is irrelevant; all that matters is its speed through the air, and unless the pilot sets the brakes, a moving conveyor belt -- under the freely turning wheels -- cannot stop the process of acceleration.

Things eventually calmed down as the number of "it won't fly" folks dwindled as they began to understand that the airplane would take off.

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wow
I can't believe I just found and read this whole thread. I feel dumber and smarter at the same time. Does that mean I'll be stationary if the treadmill is moving beneath me?

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Originally Posted by The Big One

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

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I hope this can help sway the No-Fliers minds:

Think about it this way if you are driving a motorcycle with a side car on it at 50MPH and the conveyor is ONLY on the side car you can still drive the motorcycle at 50MPH, however the sidecars wheel(s) will be rotating at the same RPM as they would if the sidecar were traveling at 100MPH. Same principal applies here. The planes motors providing thrust would be the motorcycle in above analogy and the planes wheels would be the side car. It is very possible for the plane to take off.

This thread made my day :D though parts of it scares me. Hall of fame material either way.

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Originally Posted by Telepath

This thread made my day :D though parts of it scares me. Hall of fame material either way.

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I think Beaver summed it up quite well in regards to the wheels. "Then they will rip off cause no treadmill will stop a jet engine." Taken out of context I think that's funny as hell.

dbp's diagram needs to be posted on every page. It makes me fall out of my chair laughing every time I read the caption above the skater.

http://www.tetongravity.com/forums/a...1&d=1134762033

bump. don't know how i missed this. frickin hilarious.

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However, they cannot spin faster than the speed of light... i.e. the plane cannot go any faster than half the speed of light before taking off.

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OK, the answer isn't immediately apparent to me. What the hell would happen if the planes wheels ended up needing to go (.5c+1)?

Where did this thread come from? This is awesome.

So I did my own experiments: I pulled my hang glider out of the closet and started running on my treadmill at 20mph. Wouldn't you know it, I flew right through my living room window and landed across the street. :rolleyes:

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Originally Posted by huck4bucks

Where did this thread come from? This is awesome.

So I did my own experiments: I pulled my hang glider out of the closet and started running on my treadmill at 20mph. Wouldn't you know it, I flew right through my living room window and landed across the street. :rolleyes:

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Tard. :)

edg

this thread has been very funny but just so you guys know....the plane WILL takeoff.

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Originally Posted by AsheanMT

this thread has been very funny but just so you guys know....the plane WILL NOT takeoff.

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You got that right.

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Originally Posted by AsheanMT

the plane WILL takeoff.

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Bullshit.

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Originally Posted by AsheanMT

this thread has been very funny but just so you guys know....the plane WILL takeoff.

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In other words; Those of you who think the plane will not take off are pretty damn stupid. Its one thing to think it won't take off as you began reading this thread but after having read it and truly taking the time to think about it.....if you still think it won't take off you're fucking retarded. If you think your physics is correct than that would mean that if said treadmill where in motion as a plane came in for landing that it would become completely stationary immediately upon landing:eek: . The wheels are free rolling!!! AKA damn near frictionless and frictionless is exactly what the plane needs in order for the jets to propell it forward!!! You don't even need "jets" as a regular prop plane will take off as well.

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Originally Posted by AsheanMT

You don't even need "jets" as a regular prop plane will take off as well.

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Now that's just crazy talk.

The only question that should be asked is "Is there any snakes on that motherfuckin plane?".

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Originally Posted by Dantheman

Bullshit.

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Dumbshit!

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Originally Posted by AsheanMT

Dumbshit!

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fkna, dumb as a rock.

Shall we?
http://www.tetongravity.com/forums/a...1&d=1134762033

Best I've seen for explaining this..

wow wtf, how did I miss this.

that motorcycle analogy is incorrect because the force is not transmitted through the skater but directly to the ground. I havent read everything in this massive thread but;

Heres how I read the problem
Plane is standing still on the treadmill to start, with 0 air and ground speed.
Plane fires its turbines and instantly, the treadmill matches to maintain this 0 velocity condition. The treadmill will always match the speed and the plane will never move.

Sure there is air moving through the turbines, and if you were to drop the landing gear, the plane would jut forward a little bit, but since the plane has mass, and is not moving, it will fall to the ground. If the engines had infinite thrust, the plane would take off. The impulse is just not enough to take the plane from 0 velocity to takeoff airspeeds of around 200mph.

Seriously folks, this is exactly the same as saying that a rope is tied to the back of the plane when the turbines are at full thrust. Cut the rope and what happens? There is no lift to keep the plane up in the air. The thrust of a passenger jet is NOT greater than the plane itself, so it will not just be held stationary in the air. The plane has mass, and has inertia, and will not just magically take off. It would either take a JETO-Pack or something with enough impulse to raise the thrust-weight ratio of the plane above 1 so it jets off.

thats it folks
it doesnt go anywhere.
seriously.

edit
as an fyi, a similar scenario actually occurs on carrier take off.
planes wheels are locked into a track, plane fires engines to 100%, track slingshots the plane from 0-150mph in 1.5 seconds, and because of the delta V imparted to the plane by the track, it is able to take off. Some fighter jets actually do have T-W ratios greater than 1, but need this extra velocity for aero stability as well. Otherwise id have the feeling the planes engine might just whip around on it, similar to a RWD car in the snow.

oh fuck it, I'll play.

Of course the rollerblader will get pulled off the treadmill. Of course the plane will fly.

All you need to assume is that the friction in the wheels is much much smaller than the force pulling the said rollerblader or pushing the said plane.

The initial problem is wrongly worded - in that friction cannot in the real world counteract the jet engine thrust - and hence the treadmill will be unable to move as fast as the plane but in the opposite direction. At some point the threadmill won't keep up using real-world assumptions about friction. This assuming of course that we can't build a treadmill moving at lightspeed.

But IF it could, which is what the thought experiment is asking us to contemplate, then the rollerblader would NOT move forward, and the plane would NOT fly.

Those of you answering that the plane would fly are talking about the real world. In the real world, the force of a jet engine or that of a motorbike pulling a rollerblader is hundreds of times higher than friction. Hence the initial thought experiment CANNOT be reproduced in reality. (You're simplifying this by talking about zero friction, which could be considered a reasonable assumption in the real world).

Slam on the brakes and suddenly things become more interesting. Rollerblader gets all mangled up but might well not move forward (rope might break though), and the plane won't fly. Yet this is just a special case of the first question. You've brought two previously imbalanced forces closer and now you can see how they affect the plane.

for fucks sake!!! WRONG WRONG WRONG! It would be NO different than a plane with skis on a snow field. The landing gear is simply there to keep the plane off the ground it does not matter if its on a treadmill or on water or on snow or flying off a moving fuckin aircraft carrier.

The only plane that's leaving this treadmill is this one:
http://www.ussyorktown.com/yorktown/harrier.jpg

As for everyone that mentions the word 'friction' in this thread, you're not paying attention to the correct principle: lift.

On an airplane wing (and even a helicopter wing) lift is created when the pressure above the wing is lower than the pressure below the wing dues to it's shape and wind speed. When a plane relative to the ground is motionless because the treadmill counteracts any forward motion from the plane with it's own counterbalancing reverse motion, there's never any wind over the wings. With no wind, the wings cannot create lift. Without lift, the plane will never leave the ground. Unless it's a Harrier jump jet or some other VTOL (Vertical Take-off or Landing) vehicle, or a helicopter with creates it's own lift by rotating it's wings in a circle.

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Originally Posted by huck4bucks

As for everyone that mentions the word 'friction' in this thread, you're not paying attention to the correct principle: lift.

On an airplane wing (and even a helicopter wing) lift is created when the pressure above the wing is lower than the pressure below the wing dues to it's shape and wind speed. When a plane relative to the ground is motionless because the treadmill counteracts any forward motion from the plane with it's own counterbalancing reverse motion, there's never any wind over the wings. With no wind, the wings cannot create lift. Without lift, the plane will never leave the ground. Unless it's a Harrier jump jet or some other VTOL (Vertical Take-off or Landing) vehicle, or a helicopter with creates it's own lift by rotating it's wings in a circle.

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Correct.

I can hook my bike up on my trainer and pedal as fast as I want, but still will never create any wind in my face. No wind, no lift, the plane does not take off.

Lift is obviously needed. What you no brainers fail to see is that the plane WILL move forward as usual and therefore create lift as usual. In this scenario a prop plane could take off, you don't even need it to be a jet. The motion of the treadmill is not going to prevent the plane from moving forward. If the plane were a car THEN you would be correct to think that the car would not be able to move forward but the plane can because its not dependent on power through the wheels!

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Originally Posted by huck4bucks

The only plane that's leaving this treadmill is this one:
http://www.ussyorktown.com/yorktown/harrier.jpg

As for everyone that mentions the word 'friction' in this thread, you're not paying attention to the correct principle: lift.

On an airplane wing (and even a helicopter wing) lift is created when the pressure above the wing is lower than the pressure below the wing dues to it's shape and wind speed. When a plane relative to the ground is motionless because the treadmill counteracts any forward motion from the plane with it's own counterbalancing reverse motion, there's never any wind over the wings. With no wind, the wings cannot create lift. Without lift, the plane will never leave the ground. Unless it's a Harrier jump jet or some other VTOL (Vertical Take-off or Landing) vehicle, or a helicopter with creates it's own lift by rotating it's wings in a circle.

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100% agree, except that you can have something with an obscene amount of thrust that will just horizontally launch something to takeoff speed in the same time that the plane would fall to the ground.

however, it would probably be so much thrust, it would shear the wings straight off the plane or crumple the fuselage as in a JETO-Pack

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Originally Posted by pechelman

wow wtf, how did I miss this.

that motorcycle analogy is incorrect because the force is not transmitted through the skater but directly to the ground. I havent read everything in this massive thread but;

Heres how I read the problem
Plane is standing still on the treadmill to start, with 0 air and ground speed.
Plane fires its turbines and instantly, the treadmill matches to maintain this 0 velocity condition. The treadmill will always match the speed and the plane will never move.

Sure there is air moving through the turbines, and if you were to drop the landing gear, the plane would jut forward a little bit, but since the plane has mass, and is not moving, it will fall to the ground. If the engines had infinite thrust, the plane would take off. The impulse is just not enough to take the plane from 0 velocity to takeoff airspeeds of around 200mph.

Seriously folks, this is exactly the same as saying that a rope is tied to the back of the plane when the turbines are at full thrust. Cut the rope and what happens? There is no lift to keep the plane up in the air. The thrust of a passenger jet is NOT greater than the plane itself, so it will not just be held stationary in the air. The plane has mass, and has inertia, and will not just magically take off. It would either take a JETO-Pack or something with enough impulse to raise the thrust-weight ratio of the plane above 1 so it jets off.

thats it folks
it doesnt go anywhere.
seriously.

edit
as an fyi, a similar scenario actually occurs on carrier take off.
planes wheels are locked into a track, plane fires engines to 100%, track slingshots the plane from 0-150mph in 1.5 seconds, and because of the delta V imparted to the plane by the track, it is able to take off. Some fighter jets actually do have T-W ratios greater than 1, but need this extra velocity for aero stability as well. Otherwise id have the feeling the planes engine might just whip around on it, similar to a RWD car in the snow.

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What you said is true if the treadmill matches the speed of the wheels.

It doesn't though, it matches the plane. Which means the wheels spin twice as fast as normal, but otherwise everything is the same.

edit: Imagine if this plane is on skis in antarctica, and the conveyer belt is made of snow. Then what happens?

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Originally Posted by TacomaLuv

Correct.

I can hook my bike up on my trainer and pedal as fast as I want, but still will never create any wind in my face. No wind, no lift, the plane does not take off.

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If half the people in this thread were standing in front of the treadmill arguing about it, there would be no shortage of airflow across the wings.

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Originally Posted by huck4bucks

The only plane that's leaving this treadmill is this one:
http://www.ussyorktown.com/yorktown/harrier.jpg

As for everyone that mentions the word 'friction' in this thread, you're not paying attention to the correct principle: lift.

On an airplane wing (and even a helicopter wing) lift is created when the pressure above the wing is lower than the pressure below the wing dues to it's shape and wind speed. When a plane relative to the ground is motionless because the treadmill counteracts any forward motion from the plane with it's own counterbalancing reverse motion, there's never any wind over the wings. With no wind, the wings cannot create lift. Without lift, the plane will never leave the ground. Unless it's a Harrier jump jet or some other VTOL (Vertical Take-off or Landing) vehicle, or a helicopter with creates it's own lift by rotating it's wings in a circle.

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Exactly! You need lots of air moving over the wing... the air moving thru the engine and the thrust only provides forward proplusion to GET the lift. If the treadmill negates this, then there is no lift!! no lift= no fly

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Originally Posted by AsheanMT

Lift is obviously needed. What you no brainers fail to see is that the plane WILL move forward as usual and therefore create lift as usual. In this scenario a prop plane could take off, you don't even need it to be a jet. The motion of the treadmill is not going to prevent the plane from moving forward. If the plane were a car THEN you would be correct to think that the car would not be able to move forward but the plane can because its not dependent on power through the wheels!

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DUDE

the plane generates thrust
sure
100% agree

BUT, its not moving on a treadmill. ever. the wings relative to the ground and relative to the air are not moving. wings are stationary. 0. no velocity.

either im really really dense today, or theres something others are assuming thats not in the problem statement

inertia cant just magically be overcome

if you did have enough thrust to propell the plane to takeoff AIRSPEED velocity before it hit the ground, then yes, the plane would take off.
However like I said, its very unlikely this would ever work

It would take the normal amount of thrust it always takes. the only difference is that in this scenario when the plane reaches its 220 mph the wheels and the treadmill will then be rotating exraordinarily fast.

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Originally Posted by pechelman

DUDE

the plane generates thrust
sure
100% agree

BUT, its not moving on a treadmill. ever. the wings relative to the ground and relative to the air are not moving. wings are stationary. 0. no velocity.

either im really really dense today, or theres something others are assuming thats not in the problem statement

inertia cant just magically be overcome

if you did have enough thrust to propell the plane to takeoff AIRSPEED velocity before it hit the ground, then yes, the plane would take off.
However like I said, its very unlikely this would ever work

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Treadmill is to car as wind tunnel is to airplane.

Maybe that will help.

Plane would just jump off the front of the treadmill. That is unless if the treadmill were spinning fast enough to provide enough drag in the landing gear's bearings to counter the thrust of the engines.

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Originally Posted by MeatPuppet

If half the people in this thread were standing in front of the treadmill arguing about it, there would be no shortage of airflow across the wings.

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Bingo. Take a look at this. There's nothing in there that mentions wheels speed, jet packs, prop planes, snow-covered treadmills in Antarctica, fruit booters tied to motorcycles, or any other jackassery.

Planes fly because of lift. Not thrust, not Magnum V12 engines, not magical friction-less wheels. The Wright Brothers had none of that. What they had was a plane with a propeller that could push the plane fast enough to create lift under the wings. A 747 and any other plane today works from that same model.

Jesus Christ -- this is back, and even most of you who say the plane will take off don't really get it.

If the plane generated all its take-off speed by transmitting power through the wheels, it would STILL be able to take off, assuming the motor(s) driving the wheels can push them at at least twice the required take-off speed.

How do we define the plane's speed? Is anybody really going to make a case that the plane's speed is truly measured by how fast the wheels are spinning? If not, shut up about friction, frictionless platforms, and planes not taking off.

now THINK about this: the treadmill is stationary unless the plane is moving forwards. If the plane is moving forwards at 1 mph, the treadmill is moving backwards at 1mph. If the plane is moving forwards at 100mph, the treadmill is moving backwards at 100mph. If the plane is not moving forwards, the treadmill IS NOT MOVING BACKWARDS. The wheels will always spin at twice the forward speed of the plane.

gah
thrust has nothing to do with it, other than it gets the plane to a specific airspeed.

that analogy doesnt help MeatPuppet.

If ConveryVelocity = Plane Velocity then shits not moving anywhere except the air through the turbines...which as I said, is not a sufficient force to accelerate the plane to takeoff airspeed velocity in the time the plane would hit the ground if it dropped its landing gear.