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I just completed my 40 hr. exile to the desert and finally returned back to
the workshop and home airport. What a relief and a great feeling. I also
took my wife up for her first ride. Her major complaints were: it sounds
funny, it kinda smells like gas (left over from an old fuel leak), its too
bumpy, and it goes too fast :-).
The last couple flights I took some more turbo data that is interesting.
I went to 7500 (density alt 10800) with the stock waste gate actuator
connected and collected data in level flight. I set a constant MAP and
recorded the RPM and IAS. Then I increased MAP by 1" and waited for steady
state and recorded again. I did this up to max prop RPM (2800), which was
30" MAP, 151 KIAS (173 KTAS), but only 168 Kts on the GPS (193mph). (Based
on multi-direction GPS testing I think my ASI is reading about 5 Kts high).
Anyway, then I disconnected the waste gate actuator and repeated the testing
(waste gate is then always fully open). My theory is that back pressure
from the turbo is making the engine work significantly harder than a n.a
engine, and I hope to see higher RPM for a given MAP
The good news is that I had more RPM and IAS at any given MAP. The
difference was more pronounced at the lower MAPs, but generally there was
about 1" MAP improvement in RPM up to about 26" where the two graphs merged.
I guess this is about where the waste gate would be fully open even with the
actuator. At the lower MAPs there seemed to be improved cooling as well.
Now the bad news. It became very difficult to run lean of peak with the
lack of an automatic waste gate actuator. Since boost is very dependant on
RPM, even the small of pitch changes required to maintain level flight
caused enough variation in RPM to significantly change the boost - i.e. slow
down just a little, boost drops, less RPM, less boost etc.. and in about a
second the engine quits running. Slightly increasing the mixture is not
enough to get it back as by then the RPM s have really dropped. It usually
took a significant increase in mixture to start the engine again. I'm even
starting to get used to the sensation of my engine stopping (watch out Ed,
I'm gaining on you in glider time). It was essentially impossible to run
significantly lean of peak. Even at the higher manifold pressures the
automatic (stock) wastegate controller did a much better job of smoothing
out the variations in boost. With the waste gate actuator attached I can
run WOT at 14.5k 150 deg lean of peak showing about 29" MAP. It is equally
easy to control boost pressure (prevent over boost) with the throttle in
either configuration. Also, when running rich of peak this rapid loss of
power does not occur.
The questions at this point are which configuration is better and is there a
way to fix the leaning issue? Also, how much more improvement could I get
by opening up the waste gate a little more? Perhaps removing the flapper
valve? The answer to the configuration issue is found in the purpose of
each flight. Local flights full of sightseeing and aerobatics would be
better with the actuator off. Cross country would do better with the
ability to aggressively lean at altitude. Perhaps I will eventually make it
cockpit adjustable or better yet, just do it right and put on a huge turbo
and wastegate. I already bought a TO4 from Bill.... Now to just make it all
fit.
Separate e-mail to follow with separate issues.
David Leonard
The Rotary Roster
http://members.aol.com\_ht_a\rotaryroster\index.html
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