I'm enjoying your adventure Mike!Hope I'm not boring too many of you but I thought I'd keep everyone up to
date on my progress. Especially since I keep getting such great ideas and
comments.
58 degrees outside this morning, in October, and here I am stuck at work! I
don't think I mentioned it before but on the day of my first flight my prop
controls weren't working. But the prop was at fine pitch and I decided to
go anyway. Pretty stupid now that I know how bad a prop with too fine a
pitch can be. A little ignorance can get you into a world of trouble.
Anyway, I think I finally figured out what was wrong. The wires that
control the prop connect to brushes with crimp on paddle connectors. For
some reason, the connectors I was able to get locally fit quite loosely.
For that reason I added solder to the connectors then ground them down until
they fit tightly. Unfortunately, the solder fell off on one connector. I
knew I couldn't trust them to stay put so I slathered silicon around them to
keep them in place. I must have used the wrong kind of silicon because it
never hardened up. But the connectors were still in place. Why didn't the
prop work? I pulled the connectors out and cleaned off all of the silicon.
While fiddling with them one of the connectors broke off with very little
pressure applied. I wonder if applying the solder heat treated the metal
and made it brittle. Perhaps it was ready to break already and wasn't
making a good connection. I'm going to try to find new connectors that fit
better today. Then I'll apply Household GOOP which I've used before for
stuff like this. I know it will harden up and stay put.
Heating and cooling metal in air normally removes heat treating. It's
the fast cooling in oil or water that usually hardens metal. For tricky
stuff the new solders seem to have much better fluxes in them than my
20+ year old rosin solder. I like the PIDG series of connectors from
AMP. Mostly I just crimped them but they do solder easily. The push on
ones lock onto spade terminals very well.
9.7 is exactly the CR of the soob as well and it is fine on regularI cleaned off the spark plugs and ran the engine again yesterday. I was
able to get it started easier but it still seemed like it was loading up,
running too rich, even when I leaned until I got an RPM reduction and EGT
increase. Could be my imagination but I'm going to fiddle with things a bit
more. I may get new spark plugs one number hotter.
My calculations for compression ratio comes out to 9.7 to 1. I wonder if I
should be running higher octane fuel? I am using regular unleaded right
now. I don't know much about how much compression ratio is too much for
regular unleaded. I don't detect any detonation or pre-ignition. No
knocking at low RPM or during my first flight running high power settings.
Despite high EGT the engine seemed to be running smooth as silk.
mogas which it was designed to run on but with a knock detector that
will retard the ignition if needed. So far the knock sensor has not
activated. Some 9.7 engines will require high octane fuel as combustion
chamber design and things like ignition timing have significant effect.
Some guys put the original knock sensor in and measure its output with a
voltmeter or dedicated display. Lots of guys just put high octane in
whether there is a need or not and I'd probably do the same with a
modified engine without other's experience to draw on or a knock sensor.
With regular gas it probably makes sense not to advance the ignition
timing too far and not to emply vacuum advance. I might also go easy on
the throttle when the temps are high but that is intuitive for operating
any engine.
I did see some indications that I loaded up the cylinders a bit duringI had to re-read Ken's note about high EGT with a too rich mixture since
it's contrary to what usually happens with mixture and EGT. Normally, as
you lean, EGT rises, and as you enrichen, EGT decreases. But I hadn't
thought about the condition Ken describes about an excessively rich mixture
causing unburned fuel (not burned in the combustion chamber) to continue
burning in the exhaust increasing EGT. That does seem like a reasonable
possibility.
The engine quitting on the landing roll-out was definitely my throttle stop.
I was able to reproduce it. Simple fix.
Mike
044SR
ground running but all has been fine since I started flying it. A very
cheap oxygen sensor and voltmeter will also confirm that you can adjust
the mixture back and forth across the 14.7:1 range but you need a
reasonable length exhaust stack to use one. The plugs don't lie though,
if they continue to carbon up you know it is too rich.
Ken
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