I am not saying the comparison is correct, but what about...

 

It can if it's a harrier jet :reechy:


And in my opinion, I don't think it can, and here's why. Yes, we all know that the wheels are disconnected from the engine. BUT, once the plane's engine generates just enough thrust to lift the wheels off the moving tarmac, it will still be generating next to no air intake (because it's not moving) to power the engines, meaning it can't sustain its weight long enough to get up to a speed where the amount of air intake is enough to keep the weight of the jet in mid air.

 

It seems like everyone's stating variations of the same two things. I think the problem is that the original question's description isn't specific enough.

Group 1: People who assume the plane does NOT change position
Forget the idea that the airplane will move forward anyway, the idea is that this is an imaginary conveyor that can somehow magically keep the plane in the same place. The airplane doesn't change position AT ALL. Not changing position at all means no air flow which means no lift. I think this is what the original question assumed.

Group 2: People who assume that the plane DOES change position
The idea here is that realistically, a conveyor belt won't keep a plane in the same position because it doesn't rely on it's tires for thrust. It is assumed that the airplane will eventually overcome the opposite speed of the conveyor belt, reach a takeoff speed, and take off.


Personally, I belong to group 1 because I think that the original question makes certain assumptions. I think it is written simply enough to assume that the airplane was to be stationary with respect to the air around it. But I guess it all comes down to how literal you want to be about it.

 

not necessarily, a conveyor of that size, moving at the speeds required to keep a jet on the ground in this manner will be moving a shit load of air in the direction required to genrate lift against the wings. as the lift increases, the effect of the conveyor on the airplane will decrease proportionally.

 

so ... if we have a conveyor belt (to keep the plane stationary) and a gigantic gust generator blowing against the plane, we'd rule the world?

I like it. :thumbup:

 

Doubtful, the kinematic viscosity for most gases is very low, so you're not going to get enough shear flow to build up velocity higher than maybe 1-2" above ground. Even if there is some entrainment, it's not going to be very fast.

As far as the plane lifting off, given that the conveyor moves exactly opposite the aircraft's speed, meaning that the plane's airspeed velocity is 0, the wings will not generate lift.

 

The conveyor belt is an irrelevant factor in the whole equation. The only thing that happens is the wheels will be spinning twice as fast in relation to a predetermined runway speed. With this said, the wheels have nothing to do with lift. What creates lift is the resistance of some type of medium (air or liquid) against a wing and/or rudder. Submarines use wings & rudders to move up/down/left/right through the water just like aircraft in the air; we'll leave bouyancy control of this for simplicity's sake. For aircraft, they need a certain amount of speed through the air to create a particular amount of wind resistance against their wings to get their weight off the ground. Keep in mind that wing size, shape, and design can affect the speed required for takeoff; not including payload.

The only way an aircraft will create lift while stationary is inside a wind-tunnel.

 

after 2 years of physics...it's not too difficult to figure that everyone here is correct *or at least the first few that i read* is that it can not take off...technically the plane is 100% stationary so therefor there is no wind resistance or pressure anywhere around it....it's like the plane doing a big burnout...the speed it's "going" doesn't mean anything...if there was a big enuff wind tunnel that could produce that kind of pressure...then yes but just on a bigass dyno...it wont work....

 

and anyone saying that the plane moves by thrust not wheel speed can't be right because in the initial post it said that the belt was moving the same speed in the opposite direction....try going up the down escalator at the same speed as it....u wont get anywhere...so if the plane magically hit light speed on that belt theoretically, the belt would be moving light speed backwards.....so there would still be no motion

 

that doesn't mean that the airplane is going to move backward, that means the wheels are going to spin forward. the airplane's negative acceleration will be equal to the resistance in the airplane's wheels.