I had originally replied to Dave personally but decided to share our
posts as there might be some things others should consider when
designing their systems.
Larry Flesner
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On 7/17/2019 2:22 PM, Dave McCauley via KRnet wrote:
Larry,
What I want to be "automatic" is to have my electric fuel pump shut
off if I'm disabled due to a crash. If the fuel system is compromised
the chances of being roasted to death increase greatly. If I'm flying
and the engine stops, I'll switch to the backup fuel pump and
distributor points, both are wired to a single double pole switch (run
off the backup battery). Then I'll go through my emergency check list.
I know that the more pieces you add, the greater the chance for a
failure but having the fuel pump shut off when there is no oil
pressure means bad things have happened or bad things are going to
happen.
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Dave,
I share your concern about fire in a crash. That's why I put all my
fuel in the outer wing panels and eliminated the header tank. My other
concern was rollover. I added a windshield and turtle deck bow to
hopefully keep the cockpit from crushing.
I refer back to Mark's comment on shutting off the fuel if oil pressure
drops to zero. That happened to him but he was able to make it another
20 miles with many more options rather then land on whatever is below
you. I'm more inclined to go with information systems like an idiot
light if oil pressure is lost and then you decide your actions. You
might throttle back to low idle for a longer run time or use what power
is left to execute a successful off field landing. If you have a
failure in the "auto shutoff" setup it may put you down with an
otherwise perfectly flyable airplane. Not good.
I had a similar problem when part way through a race my oil temp gauge
read zero. I considered the situation and, with still good oil
pressure, I assumed it was a gauge or sensor failure and not an engine
problem. If an "automatic" system that took over and shut off fuel I'd
have been down in a field somewhere. My only concern was that the gauge
might be reading zero if there was a massive oil leak. But my pressure
was reading "normal" so I continued and landed safely. It turned out to
be the oil temp sensor.
I like your system of flipping a switch if the engine quits. If that
keeps the engine running fine, if not you could then also shut off the
fuel. We're assuming these failures happen at altitude when you have
time to react and not at lift off when you only have seconds to land
straight ahead. I prefer "information" systems that alert you to a
problem and then lets you decide what actions to take. I don't know
their mode of operation so I'd be concerned that a switch to shut off
fuel in a crash might be activated somehow in "extreme turbulence".
Anyway, just some things to think about. Go with what you're
comfortable with.
One last thought, if the engine stops the oil pressure goes to zero. If
that cuts off the fuel will the engine start again when you flip the
switch? Consider all possibilities when designing the system.
Larry Flesner
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