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1. 12:50 PM - In-flight CHTs (Gary L Vogt)
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Last Sunday my wife, Clytie, and I flew N626FT back to Auburn from Salt Lake City.
It has a fairly new engine; less than 20 hours on it. The engine is a tricked
out engine from LyCon. It also has a Power Flow Exhaust System.
Getting to SLC was at full throttle and richened to keep the CHTs under 430 on
an EDM 800. We got terrible gas mileage.
Coming back, we went up to 12,500 feet (set the heading and altitude with an S-Tec
30) and I played with the mixture, throttle, and carb heat settings to see
what I could get. The interesting observation was that I could quite easily
get the engine to run smooth lean-of-peak. The odd thing was, at full throttle,
it wouldnt stay there. I can only think it had something to do with local temps
and pressures.
What I observed was: #1 & #2 were always the coldest (by about 10 to 20 degrees)
and I never thought much of them. Between #3 & #4, #3 was the first to go lean
of peak and was very predictable. #4, however, would go lean, run smooth for
a while, then it would richen enough to raise the CHTs. I left the setting
alone and just observed the outcome. The CHT would go from 405 to 415 and back
(plus or minus 10 degrees). Then, occasionally, keep getting hot to 450 and
then go lean again and the temp would go down; one time to as low as 397.
If I leaned slightly more to keep #4 cooler, it would run OK for a while, go lean
enough to run rough for a while. I tried carb heat to see if it had any effect.
Minimal effect at best.
Then I tried pulling the power back to 50% (well, between 50% and 55%) and various
lean settings. The lean-of-peak setting was a lot more sensitive. I aimed
for a maximum CHT of 415. As before, the engine would run great for a while
and then the CHTs would move up or down for no apparent reason; i.e., no RPM
change, no throttle, mixture, altitude or speed change.
In all of this experimentation, only one time did the settings produce CHTs & EGTs
(by-the-way, EGTs were in the 1500 range at max lean) that were steady for
over 15 minutes. Reproducing the setting was fruitless.
Only one time did the #4 CHT go above 450. This was during a full power lean-of-peak
setting. Gradually pulling the power back (no change in mixture setting)
stopped the increase at 465 and all cylinders began getting cooler. When #4
got to 400, I went back to full power and the CHT went back up to 455 and then
back down to 430. Very weird.
When I think of all the cross country flights (or local flights) without an engine
analyzer, I wonder how many times the engine was really running over maximum
temps.
Gary
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