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<< Lancair Builders' Mail List >>
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In a message dated 9/20/00 0:32:43 AM EST, lancair.list@olsusa.com writes:
<< To me the all electric option is attractive but before I proceed with my
order I would like to ask your opinions.
Is it better?
Is it safer? especially under IFR?
Does the FAA have any problems with one using it under IFR?
Is it costlier?
>>
Man, what a can of worms! But it's a fair question, so here goes.
1) Is it better? It depends. With an all-electric system you eliminate the
problems resulting from a vacuum pump failure, but are now more concerned
about electrical system malfunctions. Which is easier for you -- to build a
fail-safe electrical supply, install a standby vacuum source, or replace the
vacuum pump at regular intervals (say every 1000 hours) and practice partial
panel occasionally? Any of these approaches is sound.
2) Is it safer under IFR? This whole issue is purely an IFR question. The
failure mode you're trying to eliminate by going all-electric is the vacuum
pump failure. In VFR it doesn't matter if your vacuum pump fails. One could
envision a happy outcome with a vacuum system failure in IFR with no backup
vacuum source where you press on by going partial panel. One could also
envision an electrical failure where you press on without a radio (you DO
have a handheld radio and GPS, don't you?). One cannot envision a happy
outcome with loss of electrical power in IFR with only electric gyros. So in
this sense, the backup electricity is key with an all-electric system, but a
backup vacuum system is less important for the standard hybrid system.
3) What does the FAA think? I don't know. Sorry.
4) Is it costlier? Well, that depends. A vacuum pump system costs about
$600 (Rapco system from Varga Aircraft Supply) but you can spend more. A
backup vacuum source, tapping off the intake manifold, will add $430 to that
(if you don't have a turbo -- if you do, you're out of luck because the
intake manifold is at a high pressure). But vacuum gyros cost less than
electric gyros. You can do the shopping and add it up for yourself. The
difference in prices between the two options can be small or large, depending
on whose electric gyros you buy.
There are failure modes associated with either option, but they are
different. The system you ultimately implement needs to be tolerant of those
failure modes by providing adequate functionality in a single-failure
condition. I would accept an argument that a vacuum pump failure which takes
out your primary gyros and leaves you only with a turn needle is not adequate
functionality, in which case you need a backup vacuum source and something to
tell you to turn it on. Same goes for the electric option. The failure
modes are different but need to be addressed. Personally, I can go either
way on this issue. If you have good fault tolerance it doesn't really matter
which option you choose. If you don't have good fault tolerance, either
option can be deadly. So the question is not really "which is better, vacuum
or all-electric" but "Now that I've chosen option this option, how should I
implement it to be fault tolerant?" We know how to do this for the standard
vacuum gyros and electric turn needle. A fault-tolerant all-electric option
can also be implemented but I'd rather you asked one of the other guys for
details.
Now, to open another Pandora's box, if you decide to go all-electric on the
gyros, why not go electric on the ignition system?
- Rob Wolf
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