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Sunday, April 17, 2011

Z-8 RC Wheel Brakes

As I test fly, and quickly iterate the GP Yak-55M, one need that became very apparent was a wheel brake solution to operate this big boy out of my FOB.  The 55M lands slow enough, but it was clear after the first touchdown that the relatively high mass of the airplane and slightly larger than stock wheels (2.75") can really roll out, and roll out, and roll out, with very little incentive to slow down.  Add yesterdays mild tail wind to my downhill overrun, and well, I seriously need some brakes.
As is often the case, I looked online and found nothing except a few gold-plated, probably heavy, and needlessly complex/expensive solutions.  So I played with a few ideas of my own, from servo-triggered or applied brake application to electric thrust reversing.  Necessity is the mother of invention, so here is a very simple solution that worked absolutely perfectly on the first outing:
  1. Drill out the wheel hubs to add 1/16" more diameter
  2. Wrap the airplane wheel axles in shrink tubing
    The result is a wheel brake that increases braking action as lift decreases, and decreases braking action as lift increases.  Happily, this shortens both the takeoff (slightly) and landing roll (a whole lot). 

    Landing roll decreased by 75%.  Brake drag was perfectly symmetrical.  Takeoff roll was a bit shorter, due to the lack of much roll during power run up, reduced braking action as lift generation relieves the brake, and there was no tendency at all to nose over even without additional elevator compensation.  Taxi was much safer as well.

    Simple.  Perfect.

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