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Old 12th November 2009 | 22:46
  #17 (permalink)  
awblain
 
Joined: Dec 2007
Posts: 633
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From: Pasadena
Re: Wheel spin up energy loss

Cough - I've used this as a first-year physics example.

Spinning up the wheels should soak up about 0.6% of the kinetic energy when landing a 747 at M = 300 tons. This is equivalent to 0.3% of the speed, so less than a knot is right.

I assumed a moment of inertia of about I = 45 Kg-square-meter for a 747 tire, a mass of M_W = 200 Kg (guess) and a radius of R_W = 66cm.

The 0.6% number should be almost independent of R_W, but scales with the mass ratio M_W/M, and the moment of inertia to mass-radius-squared scaling value of I/(M_W * R_W * R_W), which I took to be 0.5. It's independent of landing speed. Landing light soaks up more of the total energy to spin the wheels.
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