We are finding it a bit difficult to set the mixture using
   Tracy's computer on the dyno. In an aircraft at low altitude there is
   a much simpler set of situations where intake manifold pressure
   is strictly a function of throttle opening. On a dyno
   the load can be varied over a wide range. Tracy's in the air method
   of setting the map works quite well but it is less well suited
   to a dyno situation.

   Never the less we got one useful data point where the throttle
   was 3/4 open at 5250 and intake air temp of 84 degrees F.
   The HP was 148. BSFC was .53 and EGTs were 1402 and 1477.
   EGTs were down about 100 F from peak 1532 and 1580
   The air:fuel mixture was about 15:1
   Unfortunately the mixture knob was set to full rich at that point.
   We were using the default mixture settings.

   Frankly I am not entirely sure what we are going to do next.

   Paul Lamar



Having done my share of dyno work, I offer you the following
suggestions. Unfortunately I don't know anything about how to program
Tracy's controller, so some of this may not be directly of benefit.

Since you are primarily concerned with a prop curve, you should do your
first settings along that line. Most dynos can be run in either speed
control or load control mode. You would set it on speed control, then
set the dyno controller for the desired speed, say 4000 rpm. The dyno
will continuously vary the applied resistance to keep the speed constant
at 4000 rpm regardless of the throttle setting. You will use the
throttle to set the desired power, say 100 hp. When you are below WOT,
you will probably want to optimize the mixture and timing for best BSFC.
You will have to vary the throttle opening to maintain your target HP as
you tweak the mixture and timing. If you have a good fuel flowmeter
setup, you can read BSFC directly, and simply tweak the knobs to
optimize BSFC. Once you have a few points along the prop curve
established, you can "guess" (mental interpolation) at the settings you
will need inbetween and around those points -- put those guesses into
the map offline, and you will have a broader range of the map that will
run the engine reasonably well. Then you can go back to the dyno to
refine your guesses and expand the map and so forth. I always leave the
WOT curve (torque curve) for last, that way I know that I am approaching
it from settings that I have already determined to be safe. Of course
the WOT curve should be tuned for maximum power, not best BSFC. How
gradually you ramp up the mixture from best BSFC to best power is up to
you. Hope this helps. Feel free to contact me on or offline if you want
to discuss anything.

If you can't get enough injection pulse width to run the fuel flow you
want, you might want to increase the fuel pressure.

Jon

Thanks for the tips Jon.


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