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Z-14 implementation for SDS

 
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nuckolls.bob(at)aeroelect
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PostPosted: Tue Jan 28, 2020 5:53 am    Post subject: Z-14 implementation for SDS Reply with quote

Quote:
If the injector bus loses power for whatever reason, the engine dies.

Trying to decide which architecture is the most reliable.

But what might be the reason? 99.999% of the time,
when a bus looses power, it's because the source of
power for that bus was lost . . .not because of
any catastrophic failure of wiring and/or
bus structure.

This is a good topic for conducting an
artful FMEA. I posed the question earlier:

Assume all injectors are powered from
the z-14 aux bus. What failure of a device
would bring down the bus in a manner that
had no handy mitigation i.e. a plan-B?


Bob . . .


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echristley(at)att.net
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PostPosted: Tue Jan 28, 2020 7:04 am    Post subject: Z-14 implementation for SDS Reply with quote

On Tuesday, January 28, 2020, 6:10:55 AM EST, Krea Ellis <krea.ellis(at)gmail.com> wrote:


If the “injector bus” loses power for whatever reason, the engine dies.

The Wright brother had an engine that dripped fuel into a bowl at the intake. That method doesn't give a lot of control, but it still works. If you can gravity feed fuel, you might consider running a line to someplace on the intake and control it with a needle valve.


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ceengland7(at)gmail.com
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PostPosted: Tue Jan 28, 2020 8:04 am    Post subject: Z-14 implementation for SDS Reply with quote

On 1/28/2020 5:08 AM, Krea Ellis wrote:
Quote:


I’ve tried to register to log in, but no luck - so I have to post a new thread. Sorry.

Z14 architecture. As with John Bright, the issue is powering the injectors. All other components are redundant (ECU, fuel pump, 6 cylinder coil pack) and can be powered by an individual hot battery bus - protected by CB’s and controlled by a Honeywell TL switch.

My dilemma for the injectors is whether or not to power them from a Schottky diode protected “injector bus”, fed by each hot battery bus - or power them through a double pole triple throw switch. Normal position - 3 injectors powered by their respective hot battery bus, or all injectors powered by either “A” or “B” hot battery bus - with all power running through the TL switch.

If the “injector bus” loses power for whatever reason, the engine dies.

Trying to decide which architecture is the most reliable.
Well, most safety related analysis techniques I've read about tend to

assign 'reliable' to stuff we can't make redundant or for which we can't
supply an alternative, like wings and other structure.

If it's reasonably possible to provide an alternative for a safety of
flight item, we *assume* that it can fail, *regardless of its
reliability*, and provide an alternative (ex: pitch trim backs up direct
pitch control from the stick).

If you route all power for the injectors through a single multi-section
switch, a mechanical failure of the switch (no matter how 'reliable')
can take out all power to all injectors. In my opinion, it fails failure
mode analysis, since there's no 'plan B' for a mechanical switch failure.

Charlie


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