Our flight testing of N304R (IO550G LIV) is progressing and I’ve been using a performance spread sheet to convert test results to standard atmosphere and maximum weight.  My approach is to guess at a propeller efficiency curve and then adjust lift efficiency (.65) and parasite drag (2.15 ft²) to match climb performance test results. I’m assuming that my 3 blade Hartzell (F7490) has the following parabola shaped efficiency curve:                        eff = -.253*(J-1.5)² + .85                                where   peak efficiency = .85 at an advance ratio (J) of 1.5 and a second efficiency of  .7 for J= .73. Is this reasonable for the Hartzell/IO550 combination?  I’d be interested in any propeller performance results that have worked for a spread sheet performance model. Thanks, Carl Scheid