POH Charts: What am I doing wrong?
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I am not a RL pilot, or even a student pilot (thought I did get an online ground school for Christmas...), so while I'd like to think I've learned how to handle the aircraft competently, flight planning other than just picking waypoints and filling fuel to 100% is a mystery. I've done some light research into it, so now I have some general idea what these newfangled charts in the POH are for.
I looked at the cruise power chart on p10 of the Warrior II Operations Manual. My pressure altitude was 6500ft (close enough I thought, 6500ft at 30.12 giving a PA of about 6300, I just used 6500), OAT was 0 degrees C. I'm not 100% sure how to pick out power setting; I thought I was at 75%+ given that I was at 2400 RPM (leaned for max power, which I think is 50 degrees rich of peak EGT), but the chart shows my TAS should be 122knots. ASI showed about 105KIAS, and using the inner wheel to align a 6500ft PA with the 0 temp gave me maybe 110, 113KTAS.
So where's the rest of my airspeed? DME was showing about 99kts groundspeed, which I think matches about 110KTAS because there was some headwind.
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@jmarkows Hi, one of the things I did wrong for a long time with the GA aircraft was think that 75% is a throttle setting. I don't know if that's your issue, but 75% is 75% of the engine's rated power, at 8000' or above, you are pretty much always at 100% throttle to get 75% power. Don't know if that helps. At 6500' and 0 degrees C, you should be close to 100% throttle, at around 2600 RPM to get 75% power.
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Here are two pages out of my Warrior POH. I think maybe you are only looking at one of them.
As katchalpin says 75% means 75% of the rated engine HP. To achieve that as you gain altitude (without a turbo) you need more throttle, and also more RPM.
According to the Engine Performance page of the POH 2400RPM will only get you about 60% power at 6500ft and 0º. At that density altitude you need about 2630rpm to get 75%
According to the "Best Power Cruise Performance" page 60% power should get you about 107KTAS which is pretty close to what you were seeing
EDIT: One more thing I forgot to mention - if you are trying to debug stuff like this the tablet actually shows you your exact TAS so you don't need to try to use the ASI or your ground speed + wind correction to work that out. Obviously IRL you wouldn't have a tablet with your TAS so for realism absolutely the way you worked it out is best
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@nickd27 Yeah, that's the kind of chart I was missing. That will help immensely, thank you for posting it. I did look up the leaning procedure again and saw that you're supposed to rich 100 degrees, not 50, so maybe I was cheating myself out of a little power there. EGTs seemed to be on the way lower side of the gauge, though, but that could be because I'm finding out I was underpowered.
@Martyn, I noticed that's not in either the manual or the ODM; I can use this one (or look it up myself), but is there a chance we can get updated manuals for the Pipers that include the power chart?
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