Quote:
Originally Posted by Jim Huseby
I have more layman's questions concerning the energy the flywheel must store and release. At firing impulse on a stock A, the crankshaft flexes torsionally from the energy imparted at the journal and must then "snap back" (and vibrate somewhat torsionally). When it snaps back (primary return pulse), it tries to impart more spin to the flywheel and it also tries to push the rod and piston backwards. Am I right so far? This un-even rotation of the rotating mass (it was already uneven because of uneven rod angularity during each rotation, pressure cycling, etc.) results in another character in the vibration signature. What is the duration of the primary pulse/return pulse? The point in crankshaft angularity when the return pulse will occur increases as rpm rises and will not only change the vibration signature, but will also change the magnitude and timing of the pulses in relationship to the crank's natural frequency. (Harmonics implied.) One of many new thoughts to me, as already stated in this thread, is that the counterweight's mass performs another important function in addition to "counterweighting". (You can't completely counterweight a mass that is part unevenly-reciprocating and part rotating with a purely rotating mass.) That other important function is to reduce crank flex.
It seems to me that the vibration signature would be different for any point it could be measured along the length of the crankshaft. This thread has moved my "theoretical wall" either past my present view or I am against the wall.
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A good point Jim. If you take the reverse impulse moment and apply Chlomondely's grillage coefficient you will see that the forward strake force is cancelled and the engine will run like a top.