Charlie,Thanks for sticking with this discussion. I, for one, really appreciate you letting us 'take advantage' of your expertise.
Did he tell you what (if anything) he was using for dampers when he was breaking the gearsets? What the low freq tuning was? Or whether, as Ross mentioned, he might have been running metal props at the time? I'm no genius (but not completely stupid either) and have no training/expertise in this field. But when approaching the data logically, we've got:
1. an inherently low torque engine
2. peak torque that has to be less than 1/2 that of an equivalent HP 4 cyl 4 stroke piston engine, since rpm is over twice as high and the net torque never goes negative like it does with a 4 cyl engine
3. 2 per rev power impulses, like a 4 cyl 4 stroke (but with no torque reversals; see #2)
3. a gearset designed for 600 lbs/ft average torque from a diesel V-8; I assume that it isn't a 2 stroke, so 4 per rev power impulses that will be significantly higher than 600 lbs/ft
So, please help me wrap my mind around the processes that could result in resonance when driving a prop. Everett obviously had problems, but where? Metal prop? Grossly misdesigned dampers? misalignment in assembly? Allowing the system to operate 'unloaded' for extended periods? Too low an idle, causing gear slap?
All the failures were running an un-damped system. Once the pendrulous damper was designed the system ran perfectly. There are some torque reversals BTW they are of course worst at idle. The peak torque has little to do with the worst aspect of torsional vibration. Somebody linked a great video on the main forum, I believe it follows Billski's original TV post. (not in auto engines) It shows a super simple oscillating spring and actuator system. There are 2 springs and a weight, plus the actuator which can be tuned, (changing the rate of pulses), to input from 0 to about 60Hz. The movement of the actuator is about 3/8". he starts the system up and the weight moves about 3/8". When he tunes the system to get amplification it goes crazy and the weight starts bottoming the springs in both directions. The amplitude of the actuator never changes, the movement is the same. The force is minimal. The only change is frequency. That is what we are talking about here. It isn't the AMOUNT of torque, it is the frequency of the pulses that causes the problem. If you hit a frequency that isn't dampened or cancelled through WHATEVER means you use you will break parts.