Interesting (and thorough) analysis... No wonder your SAX parser worked so
well...
OK now I have another problem with this. Shouldn't this depend on the
propeller? For example, I believe the limitation on static rpm (for maximum
throttle setting) on the plane I fly is less than the 2480 number you
mention, so I would guess all of the numbers will be different for me.
However, my POH seems to show the power curves up to 2700 rpm, and does not
mention the type of propeller (maybe it's the "standard" prop?).
What's with your maximum static rpms? Can you really spin your prop up much
higher than 2480 (e.g., without damaging it)?
"David Megginson" wrote in message
...
"Marty Ross" writes:
You seem to use percentage power as a primary input. How do you
judge that?
For a fixed-pitch prop, you can judge it using the RPM directly, or
the IAS indirectly. Both need to be confirmed: you need to check the
RPM with an optical tach (mine indicates about 25 rpm high), and you
need to check your actual IAS at the proper power setting to see what
your plane does, in case it's draggier than it's supposed to be. For
my Warrior, 110 kias is pretty close for 75% power. If you want to be
more specific, I reverse-engineered these numbers from the true
airspeeds in the POH Performance section for 75%, and this is what
you're supposed to get:
0 ft DA: 113 ktas, 113 kcas, 115 kias
1000 ft DA: 114 ktas, 113 kcas, 115 kias
2000 ft DA: 116 ktas, 113 kcas, 115 kias
3000 ft DA: 117 ktas, 112 kcas, 114 kias
4000 ft DA: 119 ktas, 112 kcas, 114 kias
5000 ft DA: 120 ktas, 111 kcas, 113 kias
6000 ft DA: 121 ktas, 111 kcas, 113 kias
7000 ft DA: 123 ktas, 111 kcas, 113 kias
8000 ft DA: 124 ktas, 110 kcas, 112 kias
9000 ft DA: 126 ktas, 110 kcas, 112 kias
Speeds might be lower, of course, if they plane has old paint or is
badly rigged. I think I'm 2-3 knots slower than these numbers, but I
need to confirm now that I've had my tach rechecked.
In order to target a desired airspseed, I try to recall my
performance chart and just pick the appropriate RPM, without
thinking about "percentage power"; I'm interested to know if you
find that thinking about "percentage power" has some advantage.
It lets me know how much fuel I'm going to burn, how hot/hard I'm
running my engine, and whether my engine is running properly (if the
IAS and RPM are too far out of whack, something is wrong).
I've only seen engine performance charts that give percentage power
from pressure altitude and rpm. Do you really do that calculation
in order to set desired percentage power from RPM, or are you just
estimating?
A combination of both. You always need to know your density altitude
to set power with a fixed-pitch prop anyway, so I'll assume you've
already got that info handy. Then all you have to do for 75% power in
the Warrior II is start at 2480 rpm for sea level, and add 25 rpm for
every 2000 ft of density altitude -- it's an easy calculation to do in
your head.
All the best,
David
--
David Megginson, , http://www.megginson.com/