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I think it can be done while complying with everything set out in the question.
The question never states how the conveyor belt is mounted to the ground.
is it even mounted to the ground?
if the conveyor is mounted on wheels and the 747 applies it's wheel brakes, the conveyor will move forward at the same speed as the 747 - the 747 wheels will be doing the same speed as the conveyor ie. 0 while the 747 can achieve liftoff, draging the conveyor with it along the ground.......[bigsmile1]
Scott
The engines generate Trust and the airflow over the wings generate Lift.
If the aircraft is stationary sitting on a conveyer belt regardless of how fast the belt is moving to match the thrust imparted by the engines there will be NO airflow over the wings to lift the aircraft.
So NO it cant get airborne this way.
Nice thinking Scott, that should work!
The thrust or "drive" is coming from the jet efflux and by-pass air flow, so the wheel/belt interface only serves to maintain the aeroplane's body above the ground.
Anyway, since the bottom of the wheel when in contact with the ground (belt) is at zero velocity, it can only - by tiny wheel-bearing friction - "push" the conveyor belt 'forwards' .... thus triggering the fiendish mechanism to match the direction and 'force'... but since we've fooled it... the FORWARD motion of the belt will negate the usual wheel/ground drag, and we'll be up to speed a tiny bit sooner. [biggrin][biggrin][biggrin]
Imagine a plane stationary at the end of the conveyor runway. The conveyor starts moving and the plane starts moving backwards. To counter this movement the captain increases the revs of the engine until the plane is stationary again. The plane is now under positive thrust but not getting any further up the conveyor. If the conveyor could always match the speed of the wheels then even if the engines reach maximum RPM, it still wouldn't be getting any further up the runway.
If there was zero friction between the plane and the runway then it wouldn't matter. The plane could still take off as the conveyor could never move the plane. There is enough friction between the plane and the runway though to pull the plane backwards as the conveyor moves under the plane.
If the plane is stationary there is nil uplift on the wings so it can't take off.
If you imagine this thread could generate enough hot air to obtain lift... check this mob of Pilots !
Airplane on a Conveyor Belt
But if you'd rather not go there...
the question is most commonly posed
“If you put a plane on a conveyor belt, and it matches the speed of the plane as it spins up its engine, would the plane take off?”
sounds simple right? WRONG.
Forget Newton, Forget aerodynamics.. forget that whole longwinded discussion…
The question itself is the problem.. It is missing 1 simple piece of clarification, “the conveyor belt is moving to the rear the same speed as the plane MOVING forward.” that's it.. the PLANE is still moving forward, just it’s wheels are turning twice as fast and the pilot just needs to give a tick more throttle than normal because of the minor resistance on the wheels.. (as we all saw on Mythbusters)
This became clear to me when someone said that the conveyor belt was the length of the runway.. which sounded obsurd for a plane that most thought wasnt moving.
Either way I am going to boycott that airline...they are using way too much fuel and leaving a huge carbon footprint.
And their conveyor belts should be travelators.
Read the question again. You have changed the question. The conveyor is moving at the same speed as the wheels, not the plane.Quote:
Originally Posted by superquag