Plans: 1. Integrate the propeller with the engine. I need to do a few things before hooking it up to the engine. I want to verify the bolt hole dimensions needed for the prop extension. I also need to measure the Mass Moment of Inertia of the prop. The propeller flange has a limit of 6000 kgcm^2. Status: I received the propeller from Culver Props yesterday. It is beautiful. I was able to measure the holes no problem. Determining the Mass Moment of Inertia is a little more difficult. Because the math is hard it is easier to measure it than calculate. Measuring it requires the construction of a Bifilar Pendulum jig. Basically you suspend it from 72" long wires spaced 1' apart. Then you rotate 5-10 degrees, release it and measure the period for a cycle. It creates a pendulum in the horizontal plane. The following equation is used:
I=W[rT/(2Pi)]^2/L
Where: I = Inertia in slugs/ft^2 W =Weight in pounds of the test item (propeller) r = Radius of the wires from the center of rotation in feet (6 inches) T = Time in seconds for each oscillation (use average over 30 oscillations) Pi = 3.14 L = Pendulum length in feet (6 ft)
My propeller weight is 8.2 lbs. My oscillation period is 7.4 seconds Calculated I is .478 slugft^2 or 6478 kgcm^2
Unfortunately the result exceeds the rating of the engine's propeller flange. This is a huge problem. Before purchasing the engine I had received assurance from Aeromomentum that it could drive the long wooden Culver Prop. Before purchasing the prop I had Culver props talk with Aeromomentum to verify the correct prop to fabricate. Now the prop turns out not to work. I shouldn't have this problem and feel misled by Aeromomentum. After further consultation with Aeromomentum I am informed that by replacing the engine flywheel with a heavier one I can correct the problem (at my expense). Replacing the flywheel requires some engine disassembly of course as well as my cooling system etc.
