here's a nice twist:


suppose this same plane is taking off on this same conveyor belt with the same speed sensing equipment controlling the speed of the conveyor belt system. But this time, the plane and the conveyor belt are going in the same direction. The speed of the conveyor continuously matches the speed of the airplane from 0 to take off speed.

Will the landing gear wheels rotate or not, and if so which direction.

 

No, the wheels won't rotate but the plane will take off because it will be able to gain forward momentum. Planes have a minimum speed they must be travelling in order to create enough lift to fly. Below that speed the plane will fall out of the sky like a rock, regardless of how fast the engines or wheels are spinning.

 

Yes the plane will lift up....

 

Yes and the wheels will be going twice the speed.

 

You are saying in your question that the plane actually moves.
If that is the case and the plane needs (say) 200 knots to achieve take off then eventually the plane will reach that speed while the wheels rotate backwards which have no effect on the plane.

Under these circumstances, the plane takes off.

 

I've read through most of the posts... and I say there is not enough information to form a logical answer.

The "conveyor" has nothing to do with the plane's lift, neither do the wheels. What we need to know is the planes velocity relative to the earth (whether this is at an "airport" or on a "aircraft carrier"), and/or any wind that might present.

The plane could be sitting still, engine off, conveyor off, but if a strong enough wind comes along the wings will create lift. It may not be controlled, but the plane will leave the ground/conveyor/runway/shipdeck/etc...

 

yes the plane would take off.

wouldnt matter which way the wheels were spinning, they are just coasters to hold the plane up.

the jet engines will create the same thrust as always which will push the plane forward and create the neccessary lift.

 

I really dont see the debate.

If the forward thrust of the plane is countered by the conveyor belt then no air is moving past the wings and the plane cant take off.

The plane is trying to move forward but cant.

Running on a treadmill doesn't create a breeze on your face but running in general does....same theory...

I don't get it....wheres the confusion.

 

Vader,

I see your point but, say the plane were sitting still and the conveyor were doing like a 100 mph against the plane, the plane could theoretically remain in place if they used thrust of the engines to keep it there. Now, nothing drives the wheels on an airplane, so really, there's nothing for the airplane to overcome when it comes to movement, other than simply going like 11ty kabillion miles per hour and melting the bearings in the wheels or something like that. Even if the conveyor were moving, as stated, all the plane has to do is throttle up, the conveyor could accelerate as fast as it wants, and as long as the bearings don't melt down due to friction the aircraft would still move forward. I guess, to my pea brain, the only way to truly stop this from happening would be to force air down the engines so quickly it would overload the engine, thus rendering it useless, but ofcourse, air that quick would be plenty to lift the plane off the ground anyway, unless there were some way to funnel it directly into the engine intakes... So yes, in the given scenerio, the airplane would lift off the ground, ground speed has nothing to do with air speed.... thus, wheel speed, has nothing to do with wing speed, and that's what matters...

 

Vader, the main discussion going on here is not the "treadmill effect" as you described but more of how a plane works.

Your example of running on the treadmill is slightly different then the plane. A person uses their legs moving against the friction of the ground to gain speed. A plane uses its engines to gain power and the wheels are free to rotate (either frowards or backwards).

I know I really didnt explain it very well but that is what one of the variables is.

31C

 

Well I went out on the net and started looking into this....

I found the following:

http://www.avweb.com/news/columns/191034-1.html

It states the plane will fly. It describes a propeller based plane. I assume it would work the same for jet based planes but I dont know...

So I'sa wrong....and I admit it...dont get it but I accept it...

I'm off to study this more so I can get it...

 

it will take off, read my post again, ground/wheel speed, has absolutely nothing to do with engine thrust/ wing speed...

 

The plane WILL take off because the engine's thrust is against the surrounding air, not the ground. All that would happen is that the wheels will be spinning faster, and that has nothing to do with lift.

MR

 

The wheels dont spin to make the plane take off, so the conveyor does nothing.

 

I don't understand how the plane will take off. The lift that causes an airplane to fly is created by air passing over the wing. Given the curvature of the top surface of the wing, air has to travel farther over the top surface than the bottom as it moves through the atmosphere. As a result, the air pressure on the top of the wing is less than on the bottom. As airspeed increases, there reaches a point where the pressure inequality between lift (or the extent to which the above-wing pressure is lower than the below-wing pressure) and the weight of the plane is such that the plane can leave the ground.

In the conveyor belt example, what generates the lift? I'm not sure the example cited in the link from Vader really is that helpful, because it deals with a model airplane driven by a propeller -- too many variables (e.g., ratio of lift to weigh of plane) that could be different from a real plane.

So what is generating the lift in the conveyor belt scenario?