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Yesterday I had a brief loss of engine power. I'm 26
hours into my Phase I testing and was doing fuel flow/airspeed tests at
various altitudes while playing around with the leaning function on my new
Dynon SkyView. The attached 'full flight log' file shows the entire 1.7
hour flight. I was on the right tank for the first 30 minutes, then
switched to the left tank for the next hour. You can see this in the third
graph down from the top, which shows the 'Fuel R' level dropping steadily
then leveling off when I switch tanks. I
have EI fuel probes with output a frequency proportional to fuel level.
They feed Princeton frequency-to-voltage converters which in turn talk to
the EFIS. The f-to-v converters have a considerable amount of damping.
When combined with the filtering in the EFIS' fuel readout, we determined
that it takes nearly 2 minutes for a fuel level change to register on the
display. As we'll see, that's good for long flights, not so good when
maneuvering. The second attachment, 'flight
detail' zooms in on the last 15 minutes of the flight. It starts with a
calibration of the Dynon AOA probe. That requires a series of pitch
oscillations followed by a full stall. Once that was finished it was time
to head home. I was at 10,000', 9 miles north of my home field, which is
at 81' MSL. I turned towards the airport and pointed the nose downhill.
With the throttle set to 10" MAP and the prop lever most of the way
back I was screaming downhill at 220 KIAS and 2000 RPM. What a blast! I'll
be able to enter the pattern at the correct altitude and the prop isn't
driving the engine. What could possibly go wrong? When I shallowed out the descent, the engine gave a brief increase in
power. I hadn't changed any control settings, so that meant it wasn't
running prior to that. I hadn't detected the power loss earlier because
the engine was configured to provide essentially zero thrust. I opened the
throttle to test the engine and got no response. You can see the manifold
pressure briefly go to 25" at the 45 minute mark when I add
throttle. That's when I noticed the fuel pressure was zero. I then tried
increasing the prop RPM but all that did was add braking action. I put the
prop lever back to its original position, switched tanks and turned on low
boost. The engine started running again. I was now 3 miles north of the
airport so I entered the pattern and landed normally. Once I landed and allowed the fuel levels to
stabilize, I showed 10 gallons in the left tank and 16 in the right (which
agreed with my totalizer). Right now I'm thinking that the left fuel
pickup unported during the descent. I surmise that the fuel pickups are
positioned to stay immersed during high angle climbs, but if the fuel
sloshes forward all bets are off. You can also
see that the the fuel level indications are all over the place. It appears
that the reading is sensitive to pitch angle and increases dramatically
during descent. That combined with the 2 minute lag reduces the usability
of these gauges. Thoughts? Thanks, Adam Molny
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