Plane and conveyor belt...

[snico]

BTW how can a plane "move" yet remain stationary?

The planes move on the conveyor belt i.e the wheels will be turning. But the actual plane is stationary.

This is the original question that was asked

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?

In that scenario the plane will be stationary, as its stated a control system is in place to counter act on the belt speed and the planes speed. This would make the plane appear to be standing still.

If that was to happen the plane would not take off, its impossible.

Now if the belt was slowed down and the plane carried on at its given speed, it would eventually take off as it would be moving against the air which will give it lift.

Hope that makes sense to people, and thats the correct answer to the correct question.

 

[Norcon]

In that scenario the plane will be stationary

Wrong. The plane will "move" relative to its surroundings unless anchored or braked and ultimately take off.

 

[Inky Pete]

The plane starts stationary. The wheels aren't turning, and so neither is the conveyor. The engines apply thrust to the AIR which starts to move the plane forwards.

The conveyor control systems senses this and turns the conveyor at the same speed in the opposite direction - but that only affects the FREE-SPINNING wheels, THIS DOES NOT PREVENT THE AIRCRAFT AS A WHOLE FROM MOVING FORWARDS!!! The plane continues to accelerate through the air as more thrust is applied and lift starts to be generated by the airflow over the wings.

At any particular point in time the conveyor is moving backwards at the same speed the plane is moving forwards - so the FREE-SPINNING wheels are rotating at twice the aircrafts speed.

The rolling friction of the wheels spinning at that speed is going to be very small compared to the engines ability to accelerate the aircraft forwards - so the aircraft continues to accelerate.

In the scenario quoted, the plane will take off at it's normal take-off airspeed, at a fractionally higher thrust setting than normal, with its wheels spinning at twice that speed.

 

[snico]

WRONG

The plane moves forward, the belt speeds up....

The question is will the plane take off? and the answer is a simple NO, its impossible without lift from the wings.

I've had enough now

 

[Norcon]

The plane moves forward

Yes its obvious the plane moves forward generating lift and of course eventually takes off.

 

[wotan]

No one is as blind, as those who do not want to see, the plane is going nowhere just like this thread.

Wotan

 

[Norcon]

No one is as blind, as those who do not want to see, the plane is going nowhere just like this thread.

You haven't explained why the aircraft won't move forwards.

Are the brakes on or is the anchor dropped?

If you can explain that then perhaps the thread might move forwards.

 

[wotan]

How many more times, the plane does not move forward..relative to it's surroundings, because the conveyor belt ( the runway) is moving in the opposite direction, matching the speed of the aircraft.
There will be no airflow over the wings so Bernouli's effect will not take place, there will be no lift.

Wotan

 

[Norcon]

How many more times, the plane does not move forward

And whats preventing it from moving forwards?

 

[wotan]

The runway moving in the opposite direction exactly matching its acceleration, it remains static to its relative surroundings.

No airflow over the wings no lift..

Wotan

 

[Norcon]

No airflow over the wings no lift..

But that won't happen. The conveyor only acts on the wheels, not the plane as inkypete has already explained.

If the plane was mounted on a maglev rail and the rail on a conveyor or dragged backwards relative to the plane the same situation would occur. ie the plane would take off.

 

[wotan]

Inkypete has explained nothing to me that I accept'

 

[sooey]

Try this

For every action there is an equal and opposite reaction. (Newtons third law)

So the propellors thrusting backwards will cause the plane to move forwards through the air. The wheels can freewheel as fast as they like, but the plane will take off.

 

[Norcon]

Inkypete has explained nothing to me that I accept'

Then no better quote applies to you...

No one is as blind, as those who do not want to see

 

[wotan]

Why do aircraft take off into the wind?

Wotan