Standby Vacuum?

Scott Moore wrote:
: I agree with most of what you say, but this mystical belief by pilots that because
: VAC is a "different" system than electrical it is more secure to have both.
: Electrical systems can be made fully redundant, with separate generator, battery
: and even distribution system and breakers. The fact that your airplane is not
: comletely redundant may or may not degrade its reliability to LESS than the
: inferior reliability of a vac pump.

Even without full redundancy, single point failures must still be eliminated.

: For my own part, I'll be glad to see the vac components go. I'm tired of worrying
: about the low replacement times on the vac pump, the posibility of contamination,
: the lower general reliability of the components, etc.

I've done a number of systems designs where critical components, failure
modes, and redudancy were of major concern, so I am familiar with what goes into such
a system. I'm not saying that a fully redundant electrical system can be done... it
certainly can. My point is that for your average single-engine spam-can, fully
redundant electrical systems are generally overkill. Both financially and from
additional weight, a single-engine plane is not the right platform for a fully
redundant electrical system.

A vacuum pump, regulator, and a few feet of tubing provide relatively
inexpensive, completely redundant attitude information. Yes it's much less sexy and
less reliable than a fully redundant electrical system, but it's *MUCH* simpler,
cheaper, and lighter.

-Cory

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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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