Dave Butler wrote in message ...
Matt Young wrote:
Ok, a curious question just popped in my mind. Say that one was flying
IFR in a piston single, maybe a 172 or 182. While enroute, either in
actual or above a cloud layer, the engine fails. Will the windmilling
prop keep the vacuum pump going enough to make the AI and DG usuable
during descent through the clouds, or will the gyros keep spinning fast
enough long enough to make the vacuum pump irrelevant?

No and no.

No and maybe.

Especially with a constant speed prop, you will wish to pull the
prop pitch to low rpm to get the longest glide. Your pump will be doing
about nothing -- tho the wet ones will make some vacuum even as you crank.

The gyros will typically run for ~ 5 min, but they lose the erection
function caused by the vacuum loss.

But heck, unless you are REALLY high, they will run at least sort
of until you contact the earth. It's not that many minutes.

Bill Hale