On Mon, 10 May 2004 16:15:48 GMT, "Richard Kaplan"
wrote:

snip

Very few piston general aviation airplanes have dual alternators and you
could not even begin to consider a non-vacuum-system airplane without both
dual alternators and dual electrical buses. Even dual electrical buses can
fail and that is why business jets often have an emergency battery-powered
gyro which completely self-contained; these backup gyros can easily cost
over $7,000.

At those prices, it seems a lot more practical or at least economical in a
GA airplane to simply have a conventional vacuum AI backed up by a
conventional electric AI.

I would be interested in the maintenance requirements for a couple of
the new "electric" aircraft. Another thread was asking about the
batteries keeping the engine turning on the Liberty XL2. My totally
uninformed guess is that on the Liberty, when the batteries quit, the
engine does as well. This was indeed the case with the certified
Porsche-powered Mooney.

Having maintained a few turbine aircraft & "business jets", periodic
maintenance and inspection/cap check of the various batteries and
specific DC generator life limits (one specific example has three
primary DC buses, six batteries, and three generators installed) are
an important factor in maintaining the "normal" and "emergency"
systems.

I would like to think that this same matter (periodic cap check and
alternator life limts) is specifically addressed in the new GA
designs.

BTW, I've also thought that it curious that cap checks on the main
ship's battery (which is the sole source of emergency electricity) on
"classic" GA designs seems to be a non-issue.

Regards;

TC