Andrew Gideon wrote in message gonline.com...
Dan Truesdell wrote:
Thanks for the heads-up on those. I was figuring on about $2K, but $4K
would mean asking the other 4 owners to kick in $1000 for an item that
they won't use. For a 172, it's probably just as good then to get a
manifold-driven backup vacuum. Too bad the electronic AI's are not
certified for IFR (the $1500 ones, not the $6000 ones.)

Well, I'd kind of like to know whether people other than NewPS's
shop have had trouble with the RC Allen electrical AIs. I
know several pilots who have them, IIRC there are several pilots
on these groups who have them, and this is the first I've heard
that they're so incredibly shoddy that the majority of them are
useless. The people I know who have them seem to find them OK.

As far as manifold-driven backup vacuum, my issue is: between us,
DH and I have about 1000 hrs. Our collective tally is:
AI failure (new instrument, less than 1 yr old) --- one
DG failue (overhauled instrument, age 4 yrs) --- one
vacuum pump failue (about 700 hrs best guess) --- one

So backup vacuum would have helped with only 1/3 failures. Whether
this is typical overall I can't say -- wish ASF or someone would do
a survey. Hmmm, maybe I'll start on on that avionics swap Yahoo
group.

One of our club airplanes has something like this. But someone told me that
it works least well under full throttle...which means down low executing a
missed approach.
Was I told correctly?

Pretty much, but it still may be useful.

It depends upon the differential between atmospheric pressure and
manifold pressure to work. For your gyros to function happily, they
need about
4" of pressure. So if you're powered back, *shooting* an approach, it
should be helpful. If you're at 8,000 ft with atm. pressure about
22",
you may not be able to throttle back enough to get it to work
adequately
and maintain altitude. Likewise full throttle, going around on a
missed
approach, it may not work well at all (but, it may give you a better
chance to shoot an approach you can land from).

IIRC part of the installation (and the later AD) is to establish a
chart of power settings for adequate operation in the plane in which
its installed. Your club plane should have this lurking around in the
paperwork, and it should give you a good understanding of when and
to what degree it's likely to be helpful.

HTH,
Sydney