December, 1988

Not everything we are told is so: For example: We are often told "It is motor torque, and gyroscopic action, that causes an aircraft to want to turn lift when power is applied."

I suspected these forces were insignificant, and that the spiral propwash pushing on the rudder was the over-riding force at play - so I devised a little test. Take a North Pacific type rubber model. Assemble, and fly. It will fly in lift turn circles. Now cement the stab in with CA. and then extend the rudder slot from top to bottom. Put the rudder on facing down. It will fly in right turn circles. Replace the rudder with a longer parallel sheet that you can slide up or down, and you will be able to find a position where the top forces and bottom forces are balanced, and the model will fly straight. Conclusion—the "authorities" were just plain wrong·

A second popular belief that just isn't so: "Reducing the crankcase volume of a 2 cycle model airplane motor will improve its power." My observations didn't jibe with this theory. so I devised a test. I fitted all unported cylinder and piston into a rear cover so I could pull the piston in or out while the motor was running, thus varying the crankcase volume. Result: A very slight increase in R.P.M. as the crankcase volume was increased. This I didn't expect, so the test was repeated with several other Fox motors - and a couple if brand X motors. In every case maximum R.P.M. was achieved with somewhat greater case volume than stock. Conclusion: The "authorities" on hopping up a motor were just plain wrong.

Extracted from a Fox Manufacturing infomercial, Model Airplane News, December 1988, p122.


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