Message-Id: <5.1.0.14.2.20020529205941.04767c70@olsusa.com>
Date: Wed, 29 May 2002 21:01:18 -0400
To: lml@lancaironline.net
From: Brent Regan <Brent@regandesigns.com> (by way of marv@lancaironline.net)
Subject: [Fwd: Re: Vacuum v. all electric]
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IMHO an all electric system is the hands down winner IF you replace the
vacuum system with a standby alternator and battery. If you study the
failure tree you will see that an all electric system with full backup
and cross feed  capability will provide a lot more options than an
electrical and vacuum system together. This is due to the fact that you
can't crossfeed electrons into a vacuum system and sucking on a wire
does you no good either. "Hey Moe! No wonder water won't go through
these pips. They's plugged wit wires!"

Having said that, I did have the opportunity to design a vacuum system
for a friends IV-P. He wanted a flight director so a vacuum system was a
must have. I configured it with a vacuum regulator, filter and a small
sonic venturi so that the system used filtered cabin air and discharged
into the engine compartment. The advantage to this configuration was
that when the vacuum pump failed (not IF) the cabin pressure would run
the system. Free standby vacuum, works great. The bad news is that you
have to watch for a vacuum flag when you transition to unpressurized
flight in case the pump went T.U. in cruise.

Regards
Brent Regan