I would think that harmonic RPM could "almost" be eliminated as a cause except in combination with a prop extention or out of balance prop/ spinner ect.. Simply because the crank problems only started when they were put in KRs. I would suspect that the same harmonic ranges that would be of concern would have alreardy been observed in all those aircraft which had corvairs in the past. So what makes KRs different?? I think a hard look has to be in the direction of prop extentions and in the way KR pilots fly them compared to the way others fly corvair aircraft. Are KRs the only group that will sometimes fly WOT or screem across the runway and yank back on the stick and pull 4 plus Gs. I'm sure other corvair aircaft have done the same thing but at what speed and what weight? I would think that as speed and mass increase, other forces which may adversely affect the crank may also increase during any change in direction of mass or speed. I think Wiliam Wayne addresed this in the conversion manual as being hard on the crank. Something to do with angular displacement? How about a hard 5 G landing , what kind off affect does this have on a crank? Please don't take any offense to what I have to say. I'm not an engineer nor have I flown a KR. It's just me asking questions and thinking out loud. I will also nitrate my crank just for a little added safty.
Mike Turner Jackson Missouri Swing the prop and light the fire, dance amoung the stars.........N642MC > Ron Eason wrote: >> Some fan shafts geometries have critical harmonic RPM's that will cause >> failure if the shaft rotates at that RPM for extended time periods. The >> solution is to stay out of this RPM range i.e. above or below. I think >> the >> problem may be fatigue failure due to critical harmonic loading caused by >> the prop. This would require solids modeling the shaft and stress >> analyzing.
