A great flight, Al and sounds like every
thing is doing great. Nice cruise speed for the fuel consumption for sure.
When I had a 2.17:1 gear box, I also
noticed that I was “making Oil” in the sump and would have to drain
a bit ever so many hours. I was using a mix of 1 oz/gallon. When I went to ¾
Oz gallon of 2 cycle oil, the oil accumulation ceased.
I appear to “consume” a bit
more oil now that I am using the 2.85 gear box (higher engine rpm) and have not
notice any accumulation at 1 oz/gallon.
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
On Behalf Of Al Gietzen
Sent: Sunday, July 13, 2008 11:48
AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] pre-mix;
great trip
Just returned from about 2500 nm trip.
Engine ran great, including flying over the Rockies west of Denver where I was briefly at about 14,000 ft
with density altitude of 16,500, and still had some throttle to go. Generally
cruising at 165 KTAS, 9.2 – 9.5 gph, about 5600 rpm. Not bad for a
4-place airplane.
OK, now for some technical stuff.
You may recall I converted my 20B over from pan oil injection to using premix.
The main issue is the amount of 2-cycle oil
that is ending up in the oil pan. When mixing 1 oz/gal I found the
pan oil level had gone up by about 1 ½ quarts (from 6 ½ to 8) in about 15
hours of flying; and my nice clear-amber 15-50 synthetic had become the dark
blue-black color of the SuperTech 2-cycle oil. Doing the math suggests that
about 1/3 of the pre-mix oil is ending up in the pan. That seems way out
of line, and although a suspect it is not harmful to the engine, I don’t
think it the best lube for the re-drive. I changed the oil and reduced
the amount of pre-mix to ¾ oz per gallon. I’ll be surprised if
there isn’t still some 2-cycle oil going into the pan.
So. . ; suggestions? Use different
brand 2-cycle? Further reduce pre-mix amount?
I’m wondering if the fact that my
cruise coolant temp is now running around 150F would result in more of the
pre-mix to condense out than if it was running at maybe 180F.
Another thing I notice is a small amount
of fuel is coming out of the fuel vent. The only explanation I can come
up with is foaming/bubbles forming in the return line after the pressure
regulator. This goes into the 3-gallon sump tank and up the ¼” vent
line. This may have been occurring previously, and the fuel evaporated as
it went back along the surface; but now the blue 2-cycle oil is left behind to
be quite visible at the back of the cowl; but I suspect the pre-mix is
exacerbating the foaming.
I notice the plugs have less carbon than
before, and the inside of the exhaust exit is now very light grey.
Al
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