Finn Lassen wrote:

I had an experience Sunday which I've been pondering the last couple of
days (had to work yesterday and too cold and windy today).

I'd been having substantial EGT differences (as much as 100F) between
the two rotors; the rearmost (nearest water pump) being the hottest. I
ascribed that to ram air going all the way back to the rear carburetor
and leaning that out. Due to this I'd been weary of running at full
throttles.

Sunday I finally got around to draping a bit of dacron over the rear
carb intake (inside the airbox). That produced more even EGTs and a bit
too rich indication on the O2 sensor (~820mV) but engine running
smoothly. So I took off and flew out over the beach. At 3,500' I shut
off the fuel pump feeding the center carb and used the center throttle
to lean out the mixture. EGTs came up nicely from about 1550F to 1690F
and O2 sensor reading dropped to 600 - 700 mV. I increased to full
throttle on outer carbs and saw about 5900 RPM in a shallow climb. Oil
pressure ok around 70 psi, oil temps 208F and 226F (oil pan). Water temp
about 189F, don't remember if I saw any water pressure.

What happened next is still fuzzy. I think there was an RPM drop, power
loss and a vibration. I reduced throttle (but forgot to turn on the
center carb fuel pump!). Oil pressure and temps still ok. Water temp ok
but noticed zero water pressure. Exhaust noise increased. Increasing
throttles caused engine stumble/roughness, so I concentrated on flying
directly back to the airpark. While gliding back I advanced throttle(s?)
and engine did run at maybe 3000 RPM.

Only when shutting down the engine did I notice that I had left the
center carb fuel pump off. After stepping out of the plane did I see
that my "muffler" was gone - reason for more noise in the cockpit. After
letting the engine cool a bit I checked water level, which was ok (and
so was oil level). I checked for increased re-drive play but didn't feel
any. I briefly ran the engine up to 3600 RPM and didn't notice anything
unusual. It got dark and cold and I went home.

Obviously I mishandled the situation. I should have turned on the center
carb fuel pump and  switched over to the other ignition controller. As
it turned out, I had plenty of altitude to make it back to the airport
and I should have done more trouble shooting while in the air. That
would be a lot safer that having to take off again and loose power
there. I'll print a "engine problems" checklist and post it on the
instrument panel.

It is *possible* that the sequence of event were: "muffler" coming
loose, vibrating against airplane, increased noise and that I then
automatically reduced throttle causing power loss due to center carb
pump being off (way too lean mixture), but I'd like advice on what to
inspect before I again take to the air.

Should the water pump produce water pressure or does that only come up
when coolant gets close to 212F ? Water temp sensor is mounted in engine
block below oil filter pad. Voltage stayed up at 14 volts indicating
that alternator was running and thus water pump moving freely. But if
water pump has failed internally, shouldn't I have seen high water temp?

Do the ignition coils heat up at higher RPM? The initial power loss
"felt" like ignition loss, maybe only on one rotor - thus the vibration.

Here are things I will inspect:
Spark plugs (I did run very rich initially) and cables.
Prop tracking.
Check compression.
Exhaust system for cracks.
Intake manifold for cracks.
E-shaft end play.

Of course I don't want to take things apart if I can avoid it. If the
re-drive had failed, wouldn't it stay failed - something noticeable even
at lower RPMs like 3600?

Again, all comments and suggestions are welcome!

Finn

Chuck wrote:

Hi Finn

I don't get any water pressure until temp get up to about 150, about 2 lbs.
at 160, 8 lbs. at 180.
I don't think the water pump develops enough pressure to register on the
gauge. Come to think of it, the only pressure it could develop would be
between the inlet and outlet of the pump, it wouldn't pressurize the system
relative to atmospheric, which is what your gauge is measuring. I think the
system pressure comes only from expansion of the coolant. Is your gauge
electric or mechanical? Mine is mechanical and it kept plugging up the 1/8"
tubing between the engine and the gauge with debris from the coolant. I
fixed that by installing a small inline bronze filter sold by NAPA as an
inline air filter for air tools. I installed it at the thermostat housing.

It might even be a good idea to put a filter in front of an electric gauge
sender - it could plug up too. Seems like theres a lot of crud in any
(water) cooling system.

If you suspect coil overheating you could get a remote reading digital
thermometer from Radio Shack and stick the remote probe to the coil(s).They
should stay below 160 degrees. I think the coil makes heat in a linear
relationship with RPM.
I bet if you fix your muffler and your gauge you can go flying again.

Chuck Dunlap

 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

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