In a message dated 11/27/01 10:15:14 AM, [EMAIL PROTECTED] writes:
<< One other thing to be careful of is the difference between stiffness and stiffness-to-weight. The stiffness of most carbon fiber-epoxy per square inch of material is nowhere near as high as that of steel. A 1/8" diameter carbon rod, even with the fibers oriented for torsion, would be torsionally much less stiff than a 1/8" steel rod. However, the stiffness-to-weight ratio of the carbon is much higher than steel. If you replaced a 1/8" diameter steel rod with a torsionally-oriented carbon fiber rod of the same WEIGHT, the carbon fiber rod would be stiffer. However, it would also be more than twice as big in diameter. Whether you could get an improvement from that approach would depend on whether you had enough room for the fatter rod. At that point you might also want to consider a steel tube. For stiffness-critical structures, if space is the limiting factor, its usually best to go with the stiffest material available. If weight is the criteria and space is not a constraint, the best choice is probably the material with the best stiffness-to-weight ratio. For RADS, where the thickness available for the pocket in the control surface is usually the limiting factor (at least in most of our applications), steel is therefore probably the best choice. Don Stackhouse @ DJ Aerotech >> Don, Thanks for your extensive examination of the heat treated drive shaft issue. I think that we have arrived at the same conclusion (hardened tool steel rods are the best choice for the RDS application) with very different approaches. I'm just a machinist, occasionally a blacksmith, and not an engineer. My problem with the tubing approach was the same one you pointed out though. It would have to be a larger tube than most wings could accomidate in order to be strong enough to do the job. I know that Mike Garton is doing some tests on servos and RDS that might contribute some data for this discussion. He told me that the results would be in his February Model Aviation, soaring column. Regards, Walt Dimick I. R. F. Machine Works, Inc. RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
