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George,
This is the perfect question for you. Can you tell us how much the thetaPP is retarded based on an RPM reduction. That is, Flying at 9,500 ft at 2,500 RPM vs 2,400, 2,300 2,200 and 2,100. If you don't know the answer, although it doesn't seem to be in your nature, can you venture a guess?
I have been flying at 15,500 ft at full throttle indicating about 130 KTS. I have then reduced the RPM to 2,300 waited 15 minutes and saw no decrease in airspeed. Could this be from effectively advancing the spark by reducing the RPM and therefore keeping the HP the same?
If Bill and I are not thinking correctly, please let us know.
Lorn
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Seems to me that rpm changes effectively adjust ignition timing. For example, if you're running at 2500 rpm and the spark occurs at 25 btc, the flame propagates at a rate that produces max pressure at some point after tdc, lets just say 15 degrees. If you reduced the rpm to 2200 and the spark occurred at 25 btc the flame would propagate at the same rate as before but the piston is moving slower. Seems to me that the max pressure would occur at somewhere less than 15 after tdc, effectively advancing the ignition.
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Bill Harrelson
5zq@cox.net
N5ZQ 320 1,100+ hrs
N6ZQ IV 4.239%
--
Lorn H. 'Feathers' Olsen, MAA, DynaComm, Corp.
248-345-0500, mailto:lorn@dynacomm.ws
LNC2, O-320-D1F, 1,100 hrs, N31161, Y47, SE Michigan
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