_____ From: Don Baker [mailto:[email protected]] Sent: Saturday, March 21, 2009 11:19 AM To: 'Maynard Smith' Subject: RE: [ercoupe-tech] Propellers Hey Guys - A friend of mine here had a McCauley 71/53 prop that he had taken off his Alon. It was skinned up a bit but he is a good mechanic and he was able to smooth out the leading edges without too much effort. He then repainted it for me and rebalanced it. My prop installed with the engine STC measures 68 1/8" and had been repitched by Tiffen Aire to 52". I've been comparing them in a test of ground speed at 2400 and 2500 rpm. The test was done on two clear relatively calm days with altimeter setting of 30.25 and air temp. 60deg. The flights were at 2000 ft. There were numerous thermals both days. I flew over and back between two waypoints (STF and M83). I was simply comparing ground speeds. I was not trying to measure airspeed. I made 12 records of ground speed each way at each rpm and with each prop. The results presented in the attachment are a bit disappointing. The raw data show speed variations due to thermals. The summary table shows that going from 2400 to 2500 gains only 2-4 mph. What is disappointing is that the 71/53 prop is are only about 5 mph faster than the 68/52 prop. Checking fuel consumption, I used about half a gallon more/hour with the 71753 prop. Takeoff distance, I believe, is about the same, but and climb performance increased 200 to 300 ft/min! Don _____
Propeller.xls
Description: MS-Excel spreadsheet
