| Grayhawk, Yes, I neglected to bring in humidity into the calculation, but the reason was that for normal flying it probably represents a small error. For instance, most of the cruise flight temperatures are probably at 60F or lower. Saturated conditions (100% relative humidity, or a dew point of 60) imply that water vapor takes up 1.7% of the air, so it would reduce power by that amount. Its effect on density altitude is less than that since its density is a little more than half that of air so it would reduce density by about 0.8%. Given all the other approximations I was using I felt that humidity could be left out. That would not be true for a takeoff at 100F under very humid conditions when water vapor could make up 6% of the air. Gary
Gary, Try this calculator and see what the dew point does to % power. Grayhawk PS: I have an inexpensive instrument that I stick into the cabin air inlet in flight to measure the dew point or % humidity. Temperature isn't enough. PPS: The sq rt of .75 is .866. 86.6% of 30" is 26" and 86.6% of 2700 is 2300. But since I fly at 2500 rpm, using your adjustment, then a MAP of 24" would approximate 75% power. Since I also like to fly at WOT and anytime I see a MAP that low, I must be at or below 75% power. Normally that would be at or above 6500 MSL. Since I also use ram air induction at around 175 KIAS at that altitude, I have to go up another 1000 feet and fly in the opposite direction (towards O'Hare) in order to conduct the GAMI lean test. Bummer.
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