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- Sep 13, 2011
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In an idle moment the other day I thought I'd do some calculations along the lines of the thread title.
The fixed pitch "MT" prop on my S1 is quoted as a 68" pitch, so
68"/12" = Theoretically 5.66 feet moved forward per rotation of the prop
@ 2700 RPM = 5.66 X 2700 = 15300 feet per minute
15300 X 60 = 918000 feet per hour
918000' = 173.8 mph
Since all the above was theoretical I was stunned that the above MPH came out virtually spot on my observed figure in the aeroplane.
I always thought the quoted pitch number for a propellor came from a calculation based around the pitch angle of the blade. Now I'm wondering if it is simply based on an "in service" measurement ?
I'd be interested to hear if others come up with similarly accurate calculations, it seems strange that there is no apparent "slip" where the actual speed was slightly lower than the theroretical one ? .... is this a sign of an efficient prop ?.
The fixed pitch "MT" prop on my S1 is quoted as a 68" pitch, so
68"/12" = Theoretically 5.66 feet moved forward per rotation of the prop
@ 2700 RPM = 5.66 X 2700 = 15300 feet per minute
15300 X 60 = 918000 feet per hour
918000' = 173.8 mph
Since all the above was theoretical I was stunned that the above MPH came out virtually spot on my observed figure in the aeroplane.
I always thought the quoted pitch number for a propellor came from a calculation based around the pitch angle of the blade. Now I'm wondering if it is simply based on an "in service" measurement ?
I'd be interested to hear if others come up with similarly accurate calculations, it seems strange that there is no apparent "slip" where the actual speed was slightly lower than the theroretical one ? .... is this a sign of an efficient prop ?.
