Originally Posted by
Connedrod
So what prop speed is it 2000rpm 1586 1833. So megans difference is nearly 25% ish. Thats a large difference is it not. Why is that important. Because one is in prop gov range and the other is not basically. This is an indication of the power being produced by that engine. Case in point you really cannot make any expectation of prop speed with out detail measurements this includes airspeed at inpact. If its slower than expected the inpact marks will be closer and vice versa.
The normal rpm control range of the primary governor, the green arc, is from 1,600 rpm to 2,000 rpm. I estimate that the average prop speed across the first five prop strikes to be 1833 rpm, megan has estimated it to be 1586 rpm; the difference between the two estimates is about 15%. megan's estimate is within 14 rpm (0.875%) of the lower green arc range, my estimate is on the the upper side of the middle of the range. By any reasonable assessment you'd say that the left prop was rotating in the normal range at impact.
Power is clearly a different story but the difference between the first and last sets of five strikes may be instructive; the average prop speed slowed by less than 4% after 11 increasingly deep strikes. That might suggest that the engine was producing power.
The shape of the strikes certainly indicates that the left propeller was not feathered so it is reasonable to infer that the left engine was producing more than 200 foot-pounds of torque otherwise the auto-feather system would have opened the dump valve and feathered the prop.
As has been explained to you previously airspeed is irrelevant to the calculations; the prop strikes are on an object fixed to the
ground and we have the
ground speed at impact from the ADS-B data as 108 knots.