Ron Eason wrote: >I have been reading some of these emails with interest from an engineer > stand point and find that flight testing is laborious way to test. > Why not simply test the cranks in a physical lab where gradual eccentric > dynamic loads can be placed on the shafts and record loaded failure?
Do you have any idea how expensive this "simple test" would be? And it still would not come close to replicating the real-world environment of an airplane in flight. > 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. I'm a CAD kinda guy, and use solid modeling to solve a lot of my problems before they ever crop up. We even solid modeled our house before we built it....but solid modeling a crankshaft and replicating the dynamic forces and their reactions on an entire engine/propeller system installed on an airplane are two different things. In my view, engines are simply too complicated to model all of the complex dynamics of all the reciprocating and rotating parts, at least with software mere mortals can afford (even Nastran/Patran). We have Nastran/Patran at work, and if I thought there was a prayer of getting useful info out of it, I'd have done it already. Ford and GM may have something like that, but even those guys have to do real world testing on a new engine and test and fine tune it after prototyping... Mark Langford, Harvest, AL see homebuilt airplane at http://www.N56ML.com email to N56ML "at" hiwaay.net
