riddle The Best Way to Explain to Someone How the Plane Takes Off

[Big Lex]

 

Not exactly, the engines turn the propeller or vanes which creates motion of the plane relative to the air around it. The wheels just spin around underneath the plane. The fact that there is a conveyor belt just means the wheels spin faster.

duh

[CR McDivot]

Air speed over the wings (airfoil) is what creates lift.

Neither a prop nor jet engine can produce enough air movement over the entire surface of the airfoil to produce consistent lift sufficient to lift the aircraft, let alone to sustain such.

Thrust has no bearing, wheel speed has no bearing (both cancelled by the conveyor) - only the speed of the air mass through the airfoil has the capability to produce lift.

The air mass is relatively stationary, the airfoil is relatively stationary.

The aircraft is on the ground as there is no effective lift!

Simple "hillbilly" aerodynamics!

[Missouri Swede]

Air speed over the wings (airfoil) is what creates lift.

Neither a prop nor jet engine can produce enough air movement over the entire surface of the airfoil to produce consistent lift sufficient to lift the aircraft, let alone to sustain such.

Thrust has no bearing, wheel speed has no bearing (both cancelled by the conveyor) - only the speed of the air mass through the airfoil has the capability to produce lift.

The air mass is relatively stationary, the airfoil is relatively stationary.

The aircraft is on the ground as there is no effective lift!

Simple "hillbilly" aerodynamics!

I'm not sure if you're trying to be satirical or not...  I hope it's just satire

[jamo]

From a free-body and forces standpoint, this is the best way I can think to describe it:

Think of an airplane on a treadmill. Now, think of a rope tied from the end of each wing to a big pillar some distance away from the wing, perpendicular to the fuselage. The engines are killed. The treadmill starts up and reaches equilibrium, as the backwards movement from the treadmill is braced by the ropes.

The forces on the airplane include:

• A rolling friction force between the treadmill and the wheel tending to move the plane backwards. (Ft)
• Friction forces in the wheel assembly tending to slow the plane down. (Ff)
• Reaction forces in the ropes tending to keep the plane in its original position. (Fr)

Summing the forces gives you Ft = Ff + Fr

Ff is small. It's just the friction losses in the bearings, which I'll assume have friction coefficients less than .1. There is the potential for this to increase with wheel speed based on the coefficients of friction in the bearings, but it won't be by much.

Ft is also going to be small. It's just the friction between the wheel and treadmill the allows the wheel to grip. This does not increase with wheel speed.

Which means that Rr, the force required simply to hold the airplane in place against the treadmill, is also small.

Because Fr is small, the plane's engines only have to generate whatever small force was represented by the reaction forces in those ropes did (to maintain the airplane in equilibrium), plus whatever it takes to get it to the speed required for takeoff. The wheels will be moving no matter what, so you're only adding a little extra friction loss in the bearings vs. the no-conveyor belt state. 

Edited October 18, 2015 by jamo