Propeller Comparisons
Unfortunately, I was able to test 4 different props on the same engine/airframe. I did not plan to do this, but it is working out that way. Hopefully others can benefit from my experience.
Test Procedure
I was careful to test each prop in the same way. I made test runs on 8 different days, to try to average out our mountain winds and wave action, being careful to pick the calmest days I could.. Unfortunately, the weather changed (spring arrived) rather suddenly between the MT and the AC props. I was able to compensate in the speed runs by flying at the same density altitude for both, but I was unable to compensate for the climb portion.
Each time, I would time my climb from brake release to 10,000 ft. (Starting from 7650 ft.) During the MT testing, the O.A.T. was always under 30 degrees. During the AC testing, the temp was always over 40, and often over 50. The best I can say right now is that the two props are approximately the same in climb performance. I am able to find a cool morning, even in the summer, to test the Hartzells under the same conditions.
For the speed testing, I would fly south of the airport where the ground elevation is lower. I flew at 9,000 ft density altitude by compensating for temperature and barometric pressure. I flew 4 legs roughly 90 degrees apart in heading, and recorded ground track and ground speed from my GPS. I then used the spreadsheet from the National Test Pilot School http://www.ntps.edu/HTML/Downloads/ to calculate my true airspeed. Of course I used the same power setting (2500 rpm, wide open throttle, 1300 egt. with LASAR ON) on each run.
Results
Over the 8 runs, the AC averaged 4.4 kts faster than the MT.
Subjectively, the AC is not as smooth as the MT. At a fast idle (1200 rpm) the AC is much rougher than the MT. At 2500 rpm cruise, I can't tell much difference. The AC has a wider comfort range of rpm for cruise, feeling about the same from 2200 to 2700 rpm, where the MT started to vibrate noticeably below 2400. I have not noticed any of the harmonic vibration that Randy Lervold reported with the Hartzell, but my plane has quite a bit of sound damping foam that I installed in an effort to quiet the 4 into 1 exhaust. I can't tell any difference in sound levels through my electronic Dave Clark headset, but I made no effort to measure them. I felt all along the exhaust noise would dominate, and it does.
Hartzell HC-C2YK-1BF/F7666A-2 74" diameter 2-blade
This prop has long been the standard for 180 HP RVs. I found it's vibration characteristics to be similar to the AC prop, except that it is smoother in the 800 to 1800 rpm range. After following the test regimen above, I have been unable to detect any difference in either climb or cruise performance from the 2-blade AC prop. It would seem the only advantage in the AC prop is it's lighter weight, and the difference that makes in handling.
Hartzell HC-C2YR-1BF/F7496 74" diameter 2-blade
This is the new "blended airfoil" prop. I have now (8/21/04) done some speed testing. This prop has averaged 2 kts faster than the other Hartzell. The climb testing will have to wait for cooler temperatures in the fall. After a dynamic balance it is quite smooth for a 2-blade prop, and I am happy with it. I am hoping this will be the last prop on this airplane. I will report more details when the weather cools.
May, 2007
I now have about 200 hours on the BA prop. It has been perfect.