Why is my throttle 3/4 closed at cruise?

All this is why I advocate a manifold pressure gage for even fixed
pitch aircraft. It is ridiculous how little full scale error in a
tachomenter can influence such important things like fuel consumption
and engine evaluation. I've never tried the flourescent light trick at
1800 RPM. Does it work in practice?

Any audio measurements using a computer as a timebase would have to be
made in the aircraft or with the aircraft sitting still on the ground,
to eliminate sonic velocity errors. Even a musician who allows a
quarter step error to creep in would have a 2 1/2 percent error. Maybe
if he carried the tuning fork (or whatever) in the aircraft?

nrp wrote:
: All this is why I advocate a manifold pressure gage for even fixed
: pitch aircraft.
Absolutely... I put on in my Cherokee as part of a previous engine upgrade.
Even with fixed pitch it's tremendously useful for setting power before the speed
settles. Climb to altitude, nose over, speed up to about where you should be, then
pull MP back to what it should be... the RPM will follow... eventually. Since it's
not adjustable and changes with altitude, the 23/23=65% and 24/24=75% doesn't quite
work. If you average the two, however, it's still pretty close:
1000' MSL: 24", 2200 RPM = 65%
8000' MSL: 21", 2500 RPM = 65%


It is ridiculous how little full scale error in a
: tachomenter can influence such important things like fuel consumption
: and engine evaluation.
I figured out my tach read 50 RPM low because my fuel burn was about 1/2 gph
higher and TAS was 2-3 mph more than book values. I checked it with a calibrated
strobe, and sure enough... 50 RPM off.

I've never tried the flourescent light trick at
: 1800 RPM. Does it work in practice?
Yes, but it works better the closer you can get to the light (with it behind
you). You might even want to try putting a small piece of tape on the same place on
each blade of the prop. It's quite likely to come off at that RPM, though.

: Any audio measurements using a computer as a timebase would have to be
: made in the aircraft or with the aircraft sitting still on the ground,
: to eliminate sonic velocity errors. Even a musician who allows a
: quarter step error to creep in would have a 2 1/2 percent error. Maybe
: if he carried the tuning fork (or whatever) in the aircraft?
I recorded sound from a laptop inside the aircraft. It was horribly clipped
(loud in there!), but the fundamental frequency is still preserved. It worked
reasonably well.

-Cory

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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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