REFLECTOR: Ground Testing Update
Brian Michalk
michalk at awpi.com
Thu Feb 14 22:09:45 CST 2013
It's been quiet here, so here's something to fill the void.
I've been on the cusp of my second first flight for almost four months
now. Man, it's been a long time. My primary problem is that I just
haven't been able to make rated horsepower, and it's been due to three
reasons.
1. The impulse coupler spring on my magneto broke.
I ordered a spare alternator, and it was about 40 days from ordering to
delivery. I continued to do ground testing with the bad coupler,
knowing that the timing was anywhere between 0TDC and 32 TDC.
2. The mixture was too rich.
I spent about four hours tuning the engine in November, starting over
from scratch on the electronic tables that map RPM and manifold pressure
to a fuel flow. If you recall, my first flight four years ago was due
to an over-rich condition. Well, I tuned to 50F ROP. After I got the
magneto in, I still couldn't make power. I brought the plane back and
ran static at full throttle, leaning out the mixture. Sure enough, the
RPM's came up, so I tuned to max RPM, then richened until the RPMS
dropped slightly. This should be a safe mixture for the first flight.
It turns out that I have my engine monitor set for Celsius instead of
Fahrenheit.
3. The turbo is seized.
This is the final discovery made this weekend. It's either spark, fuel
or air, and this was the final problem I hope. About 20 engine hours
ago I put a restriction in the oil line to the turbo to keep from
blowing oil through the seals. Apparently my calculations for the
restriction are wrong. I pulled the turbo and sent it out for repair,
estimated to be about $350.
It's been very frustrating. I have been set up for my "first flight" on
about four different occasions, only to shut her down in the takeoff
roll because of not accelerating through 80 knots. I've had the plane
very light on the wheels. Nose up, one or the other mains up, but no
acceleration through rotation. I bet I've gone through 15 to 20 high
speed taxis like this, and I'm ready to just fly the airplane. This
turbo problem better be the solution. I'm out of ideas if it's not. On
the first flight four years ago, there was plenty of power. Same fuel
system, induction and ignition, so I know the engine is capable of
making the power.
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