will it take off?

[Iplayfarmer]

[[[ I dont recall anyone saying that. I doubt that those who understand what is involved here would say it.]]] Actually tho, magical wheels would be wonderful and would assure that the magical conveyor could keep the plane on the ground forever. -- just so the wheels magicalness did not include causing them to be massless, or causing them to have a moment of inertia of zero.
larry

I'm referring to the implication that the conveyor is able to accelerate infinately assuming that it overcomes the phenomenal friction of it's own bearings but the wheels are not able to overcome the consequent friction on their bearings and somehow the drag pulls the plane backwards overcoming the force of the thrust.

I'm still waitin for the backlash as to how this question is so much different from the "Rooster's Egg" or "Where do you bury the survivors" http://www.tractorbynet.com/forums/owning-operating/90325-will-take-off-82.html#post132104

 

[Egon]

All night I have been lying awake. Sleep would not come. Mayhaps it was the incoming rain. Anyways lots of time to think.

Here we have a solution to the worlds shortest runway. Instead of a conveyor belt we use rollers like on a dyno. Run them up to the takeoff rotational speed and then open all the throttles. The plane should instantly raise into the air and fly away. This should really alleviate some of the congestion at real busy airports!

I'm on my way to the patent office, fortunes must await me.

 

[Tororider]

I haven't read the whole thread, but just wanted to make sure that you all saw that the Mythbusters did a show on this myth.

The plane will fly. It will take off like normal. The reason being the plane gets no thrust from its wheels like a car. If you put a car on a treadmill and match the forward speed of the car to the treadmill the car will stay in one spot.

Do the same thing with a plane, try to match the forward speed of a plane to a treadmill and the plane will continue on at the normal speed. Unlike a car a plane gets its thrust from its propeller/jet. I am not sure about the wheels speed, but I would guess the wheels would spin twice as fast as normal until the moment of liftoff. But as proved on Mythbusters, the plane WILL take off.

 

[SPYDERLK]

I'm referring to the implication that the conveyor is able to accelerate infinately assuming that it overcomes the phenomenal friction of it's own bearings but the wheels are not able to overcome the consequent friction on their bearings and somehow the drag pulls the plane backwards overcoming the force of the thrust.

I'm still waitin for the backlash as to how this question is so much different from the "Rooster's Egg" or "Where do you bury the survivors" http://www.tractorbynet.com/forums/owning-operating/90325-will-take-off-82.html#post132104

Inevitably some of the counterforce will be due to friction, but actually the counterforce Pat and I have described comes from inertia - the resistance that the wheel mass has to being rotationally accelerated.

As for the others, Icant see any relation to physics in them, but with the rooster you are dealing with a probabilistic situation. Everything stated is improbable, and if improbability had inertia, a train of astounding events that long may drive the result. Hence the egg would never fall. -- The survivors would be buried in the ground.
larry

 

[kozak]

Plane is stationary therefore.......is NOT fly !! The simple answer is normally correct so......I must be right !!

Vic

 

[Redbug]

Oh Gawd!!! This thread came back to life!!!! I'ma sufferin'...Just shoot me!!!!

 

[Runner]

It is....ALIVE....

I couldn't wait for this thread to be brought back, just so I, as a licensed pilot, could give my opinion that the plane will take off.

 

[David Cockey]

The plane will take off.

Speed relative to air is what matters for lift and thrust, not speed relative to the ground. The airplane accelerates due to the thrust of the jet engines and/or propellers, and when the lift exceeds the weight of the airplane it will lift off. Lets call that air speed Vto. When the plane reaches Vto the conveyor/runway will be moving relative to the airplane with speed 2 X Vto.

Any boundary layer effects from the moving ground (and on an actual airplane designed for normal takeoffs they would be small at the height of the wing) would only increase the speed of the air relative to airplane similar to a light headwind. This actually means the airplane will lift off at a slower speed relative to a fixed reference.

The rolling resistance (force) of tires increases only slightly with speed. So with the runway speed twice normal the power consumed by the tires would be only twice that of a normal takeoff. The power required to overcome the rolling resistance of the tires is very small compared to the power required to overcome the aerodynamic of the lifting wing. Assuming the airplane is "real" there will be plenty of power to overcome the added resistance of the rolling tires. And once the airplane lifts off the rolling resistance vanishes.

I didn't bother to read all the messages in this string, so I may have missed some claimed nuance. But the basic physics are as above.

Qualifications upon request.

 

[RobS]

I didn't bother to read all the messages in this string, so I may have missed some claimed nuance. But the basic physics are as above.

Qualifications upon request.

Welcome to the board David. As you might imagine, it's all those nuances that have kept this thread alive for as long as it is! Interesting reading, if nothing else.

 

[SPYDERLK]

The plane will take off.

Speed relative to air is what matters for lift and thrust, not speed relative to the ground. The airplane accelerates due to the thrust of the jet engines and/or propellers, and when the lift exceeds the weight of the airplane it will lift off. Lets call that air speed Vto. When the plane reaches Vto the conveyor/runway will be moving relative to the airplane with speed 2 X Vto.

Any boundary layer effects from the moving ground (and on an actual airplane designed for normal takeoffs they would be small at the height of the wing) would only increase the speed of the air relative to airplane similar to a light headwind. This actually means the airplane will lift off at a slower speed relative to a fixed reference.

The rolling resistance (force) of tires increases only slightly with speed. So with the runway speed twice normal the power consumed by the tires would be only twice that of a normal takeoff. The power required to overcome the rolling resistance of the tires is very small compared to the power required to overcome the aerodynamic of the lifting wing. Assuming the airplane is "real" there will be plenty of power to overcome the added resistance of the rolling tires. And once the airplane lifts off the rolling resistance vanishes.

I didn't bother to read all the messages in this string, so I may have missed some claimed nuance. But the basic physics are as above.

Qualifications upon request.

Welcome to the thread David. Nothing wrong with what youve deduced. However, there is another way of looking at this which makes more complete use of the physics. It is essentially an extrapolation of the conveyors effect on the situation. I believe it came up to counter the false claim that the conveyor could have no inhibiting effect on the thrust of the plane. The physics of this counter thrust via rotational acceleration of the wheels is described pretty well starting about 1/3 of the way in the thread in the 300's. I dont believe many understand it.
larry