Amiga.Org users encouraged to help debate

[blobrana]

Hum,
If we assume that there is air and that the aircraft uses jets  (or the propellers do not push air past the wings) the airspeed relative to the aircraft is zero.

The plane cannot takeoff.... (the answer in  av web.net is wrong!)

You canna change the laws of physics.

[JLF65]

People are getting confused, but an airplane is not a car - the thrust doesn't come from the wheels. Took me less than a second to decide the correct answer is yes, the jet takes off.

[blobrana]

Lol.
Took me less than a second to decide the correct answer is No.

It’s simple physics.

There is no forward motion. (It does not matter if it comes form wheels, jets, magnets or rubber bands etc)

No forward motion  = no air flow = no lift...

[JLF65]

blobrana wrote:
Lol.
Took me less than a second to decide the correct answer is No.

It’s simple physics.

There is no forward motion. (It does not matter if it comes form wheels, jets, magnets or rubber bands etc)

No forward motion  = no air flow = no lift...

Wow. You flunked physics, obviously. A plane's motion is due to thrust from the engine/propellor against the frame, not from the motion of the wheels.

The jet engine applies force to the plane, which starts to move. The conveyor belt starts to move the opposite direction at the same speed, but all it's doing it TURNING THE WHEELS! The wheels have NO EFFECT on the speed of the plane (assuming the brake isn't set). The jet engine keeps thrusting the plane forward faster while the conveyor belt keeps turning the wheels faster WITH NO EFFECT ON THE FORWARD MOTION OF THE PLANE! The plane reaches take off speed and takes off.

[blobrana]

Hum,
whoops...
thinking about it further...the plane does move forward...
Assuming that the wheels have no or little friction.

And if it moves forward then there is air flow.

[a1200]

I think all forums (this one, aw.net & others) are now concluding that the plane WILL TAKE OFF! This has been awesome and I am in agreement now the plane is outta there!

[uncharted]

Hmmmn, I misread the question, I could of sworn it said stationary in there.

[blobrana]

LOL
me too...
My first thought was to add up the two (opposite) vectors to give zero speed.
But the ground vector is a red herring,  there is only one vector (the plane)

Doh!

[JLF65]

That's what made me pause a second when I first read it. It's deliberately misleading in an effort to make you think about it in the wrong manner to provoke an incorrect answer. They state the problem in a manner to make people think about a jogger on a treadmill whose net velocity with respect to the ground is 0. That's not what it is, though. This problem would be more like a jogger on a treadmill wearing a jet pack and roller skates. The treadmill would simply turn the wheels of the roller skates while the jet pack blasted the person forward irrespective of the treadmill's speed.  :-D  :lol:

[blobrana]

Hum,
i hate

[ameegah]

The plane will take off because it's a harrier jump jet.

[whabang]

lol

[Vincent]

:lol:

[FluffyMcDeath]

The plane takes off, and it takes off slightly sooner than it otherwise would have.

The runway will go backwards as fast as the plane moves forwards. The vast length of the moving runway will naturally entrain some air and will drag said air past the plane thus slightly increasing the planes airspeed over what it would have been with a static rnuway.

The runway can only move backwards if the plane is moving forwards.

Imagine the question is asked but the plane does not touch the ground. The plane flies over the runway at 600 km/h. The runway moves backwards at 600 km/h. Does the plane fall out of the sky? Of course not. Wheels down, wheels up, ground speed is irrelevant.

Now, imagine the same question but with a car and ask does the car move? Or just as much fun, does the road move?

Imagine that the car starts to move at 1 km/h. The road starts to move backwards at 1 km/h. Now the car is spinning it's wheels to stay in one place. But now it's velocity is zero. Ergo the runway matches that and the car starts to move. So the road ...
etc

[Agafaster]

I believe I can state this better:

its all down to a pressure difference between the air above the wing, and beneath the wing - this is the bernoulli principle: the shape of the wing is such that the topside path is longer than the underside path. the airflow over the top is therefore travelling faster to get past the wing than the air under, so the air pressure is lower, causing lift. in order to best get this, the plane must be moving relative to the body of air. this is also why planes take off into the wind.

therefore, a 'conveyor belt' runway moving in a direction to negate the motion of the aircraft will prevent takeoff - except for this small omission: the wheels dont generate the motion, they just allow free motion: the drive is purely air-based - either a jet or a prop !

Helicopters do exactly the same thing, its just that the 'wings' rotate to produce this pressure difference.

Harriers just do VTO/L by sheer use of thrust. :-)

PS: that was all physics - I did a degree for 3 years, and still like to dabble.

[Agafaster]

Now, imagine the same question but with a car and ask does the car move? Or just as much fun, does the road move?

err - how do you think rolling roads work ? those things uised by the automotive industry for measuring such things as power output, and the accuracy of speedometers ?

although I will concede the nitpick that rolling roads are just passive rollers, and not conveyer belts...