Correction: page 504.

"Jon Woellhaf" wrote in message
...
"Tman,"

Congratulations for asking an excellent question!

I'm not qualified to give you an authoritative answer myself, but I found
a good explanation in the FAA's AC 65-15A, The A&P Airframe Handbook (page
5040. I think it's available on-line. Search this document or Google for
"pendulous vanes."

Jon

"Tman" x@x wrote in message
. ..
OK, I get that the thing has a gyro in it which remains rigid as the
airplane banks and pitches around it. But how does it get "reset" to the
correct orientation?

Is it dependent upon gravity to orient it when it spools up, and the
plane is on the ground?

Conversation started when I was talking to a pilot on a dual-vacuum pump
powered 172. One vac pump is shot, and it did not build up sufficient
vacuum to spool up the gyros until airborne.

Well he was VFR only, but still...