Airplane physics question

I've spent five minutes mulling this over-- the only conclusion I came to is that I now hate you.

 

maybe i'm missing something (i'm barely reading at this stage ) but if there's no turbulence over the wings what's gonna make it want to defy gravity?

edit: oops, i'm using the assumption that the wheels are the driving force. but still 'no', because no matter how much thrust is applied rearward the position of the aircraft will be the same. the only thing that could happen is that there's some weird effect that comes about from a gazillion pounds of thrust going out the back and it spontaneously develops VTOL abilities do to ground effects or something

 

Plane won't take off.

Why I get tired running on a treadmill is another story...

 

If I understand your poser correctly, it is a treadmill for an airplane. So just as you would feel no "wind in your face" on a treadmill, there is no "relative wind" in your scenario. Hence the airplane can't fly.

This is contrasted to an aircraft carrier like situation, where the plane sits still but the underlying surface is in relative motion versus the air even prior to the catapaults being engaged. In this situation a low take-off speed aircraft (like a Citabria) could possibly take off without even rolling or being launched by the catapault. Between the aircraft carrier moving at 20+ knots into a headwind of 30+ knots, this could achieve a relative wind of 50+ knots.

I'm not sure why this should take 8 pages to discuss.

 

Great minds think alike Yin! -

 

I've heard that somewhere before...

 

I would imagine, NO!

Wheelspeed wouldn't help create the airflow needed for flight.

Just a guess.

 

i'll chime in here, the forward thrust of the plane is generated by the turbine engines not the wheels. so if the speed of the wheels is matched by the "treadmill" the forward motion of the plane would still occur and hence the plane would still lift off.

not convinced? try this, if you have a treadmill take a toy car and with your hand push the car forward while the treadmill is on. does the car move forward? yes, why? becouse the force moving the car is external to the wheels. and even pushing the car forward the belt matches the speed of the tires otherwise the car would stop/accelerate depending which is going faster/slower.

 

you're making it out to be a trick question like on fake mensa tests. i just believe it's a poorly werded question without enough parameters given which is why it's been given like 50 pages of discussion on physicsdork/aeronut forums.

in other werds, the speed of the earth exactly matches the speed at which i drive my car, but the way the question comes across is that the conveyor will actually match the speed of the wheels in exactly negative, if this actually occurs, the plane CANNOT move forward without talking about too many random things like my ground-effect theory above and stuff like tyre slip-angles and frictional efficiency.

stoopid question, the plane stays still and the passengers get pissed off coz they can't make their connecting flight. it's saturday night and i have no beer.

 

The plane absolutely takes off.....

SMG2 has it perfectly correct and well explained!!!

The engines thrust the air back, the plane will move forward...once enough forward speed is achieved where enough lift developes under the wings to overcome gravity, the planes takes to the air. This all happens IRREGARDLESS of wheel rotation.

The only thing the treadmill will do is cause the wheels to spin excessively.

15 minutes after the plane is airborn Lamour does the big-titty blonde stewardess in the bathroom.....

No idea what the in-flight movie is....

 

i know i'm an idiot but explain the bit how the plane moves forward if not on the tyres.

 

The real question is.....when will they make a huge rolling platform that can roll down the runway at high speeds and match the planes location over the runway.....that way planes with malfunctioning landing gear can just keep their gear up and simply land on it?

yeah...word to the FAA

 

Plane does not take off. Definitionally if the conveyor speed equals wheel speed then the plane can not get any ground speed. Simple as that.

However, some very astute people have noticed that planes aren't wheel driven and therefore the plane will still accelerate. True, but that just means that the wheel speed and conveyor speed both accelerate to a ridiculously high number until the bearing friction force equals the thrust force and no acceleration occurs.Then the wheel speed & conveyor speed are going to be be like 1000000mph but the plane will not take off.

If people start arguing the practically of the a tire that goes 1000000mph, then just assume the plane ends as a fiery wreck at the side of the conveyor.

 

Okay.....let's use terms you can relate to:

Take a keg of beer and strap it to a skateboard. Put it on a treadmill. Borrow a page from the book of the Coyote who chases the road runner: strap an ACME rocket atop the keg. Light the rocket....MEEP MEEP!!!!!

Rocket ignites and pushes the keg forward. No matter what the treadmill does the wheels of the skateboard will just roll along.

We green????

 

You are right, don't let them bother you. Definitionally the plane can not take off. Now, if the problem statement is an impossible situation - that's another question entirely.

 

it is a trick question. think of the forward motion of a hovercraft, or a pontoon plane.

 

Then it fails the condition of the wheel speed equaling the conveyor speed.

 

No chance. Would basically be the same as having a car on a dyno, and none flew away.
Planes need lift form the wings to take off, and if there is no air/wing speed difference, it won't take off, unless of course it has en engine strong enough no to use any wings. But none of them has it, otherwise they would never "stall".

 

Put your hand out the car window @ 60mph.

Put your hand out the window of a car on a dyno @ 60mph.

Jet engine creates thrust, moves the wheels, moves the plane and therefore forces airflow over wings creating lift.

A jet-powered automobile on a dyno would do exactly the same thing.

 

DING DING DING we have a winner!!!

whilst i like the beer keg theory the dyno one is the best analogy for us car nuts.

 

Then it fails the condition of the conveyor moving at the same speed as the wheels.

 

Sorry dude....doesn't work that way.

Think of the wheels and the treadmill like 2 bearings, that's all. The engines will direct their thrust backwards and the plane will move forward PERFECTLY. The treadmill will merely cause the wheels to turn twice as fast....nothing more. No warp-speed or breaking of the sound barrier.

 

Dude, explain how a plane can have *any* ground speed when wheel speed equals conveyor speed. This is a constraint in the problem statement.

 

guys it really is simple. the confusion is that the question has you focusing on the one thing that has no relation to forward movement or thrust on a planes ability to fly.

cars use thier wheels for propulsion. planes use jet,prop,rocket propulsion systems. external to the landing gear.