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Good recovery from what could been a bad situation,
Gaylen. Having made a 12 mile glide myself, I can emphasize with what must
have been going through your head at the time.
Actually, I did not have a circuit breaker failure - but a
pin in my Molex electrical connector carrying power to my coils had become
corroded and pitted to the point it no longer made adequate contact. This
condition possibly from not sizing the pin adequately to carry the current
load. But, whether pin or fuse holder or circuit breaker - all can
fail.
However, those details aside, I am in
full agreement with you. With two coils either
of which will support flight, I think it wise to have each coil powered by its
own circuit, be it circuit breaker or fuse. Same applies to our dual
fuel pumps also.
Again, congratulations on good airmanship. I found
that for my Rv-6A that 87 MPH gave me the minimum sink rate. Had to do a
360 and two hard "S" turns after my 12 mile glide to make the airport - started
out at 9500 MSL.
Ed
----- Original Message -----
Sent: Wednesday, August 01, 2007 11:27
PM
Subject: [FlyRotary] Redundant
systems
A few
weeks ago Ed Anderson reported a failed circuit breaker feeding both
coils. He urged that we make our
systems redundant where possible, with separate circuits and circuit
protection to each. I second his
plea and share my recent experience as reinforcement.
I have
about 60 flight hours and about 15 ground hours on my RV8. It is powered by a 13B with the stock
Mazda coils.
Tracy recently updated my
EC2 and I installed it Saturday.
After a half hour ground run adjusting the MAP table I shut down and
installed the cowl. Taking
Tracy’s advice I took off, stayed
near the airport and did the Mode 9 programming at altitudes of 7,000’ to
10,000’ AGL. I did several
simulated approaches and landings at altitude enjoying the smoother running
engine compared with the previous iteration of the program. Also spent time among the puffy clouds
and cooler air above the haze layer!
After 1.5 hours I began simulating another approach but when I pulled
the power to idle the engine quit.
Emergency procedures were fruitless. Even shutting down the entire system
and attempting a power-up didn’t result in an engine start. I was several miles from the field at
about 7,000 AGL. I set up an 85
KT glide, and decided to land on a runway with a six KT tailwind to avoid
flying over a residential area or over a lake on the approach to an alternate
runway. I arrived over the
approach end of the runway on a crosswind leg with 1500’ to lose so I began a
tight pattern flying a descending left turn to lose altitude and position
myself for the landing. I lost
500 feet in the first 180 degrees and about the same in the second 180
degrees. I rolled out on final
high and hot, shut off all the electrics, landed long but without
incident. It all went pretty well
other than the fact I forgot to roll in flaps when I could have used the drag
to get me down sooner.
I use
fuses for circuit protection so the first troubleshooting step was to check
the fuses – all were OK! I
suspected the coils were involved because the tachometer was reading zero even
though the engine was windmilling.
The tach is driven by a signal from the trailing coil. Using the new diagnostic
features, the injectors were
clicking OK but there was no spark.
Tracy reminded me of Ed
Anderson’s post about the failed breaker feeding both coils. Upon close examination the fuse had
not blown but apparently it has been warm because it had warped. It was in the fuse holder but somehow
was not making contact. Replacing
the fuse cured the problem.
I am now a firm advocate of redundancy! I have added a circuit to power the
coils separately and plan to replace the essential bus fuse panel with circuit
breakers. I share this experience
to urge those of you who use a single circuit to power your coils, your fuel
pumps, your EC2 or any other critical systems to modify your wiring so a
single circuit failure doesn’t place you in a dangerous position. Mine ran for about 75 hours. It was just a stroke of good fortune
that the failure occurred while near the airport at an altitude higher than I
usually fly.
Here
are a couple of data points that may be of interest:
The fixed pitch wood prop windmilled at a 100 KT glide, rate of descent
about 1000 FPM.
The prop stopped at about 90 KT.
Fly
safe!
Gaylen Lerohl
RV8
Alexandria, Minnesota
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