"Andreas Maurer" wrote in message
...

How many times have you praised yourself for having instruments on
board that do not need electricity to work properly?

I did that dozens of times - electricity is definitely not a reliable
thing in gliders.



Bye
Andreas

This amazes me. Electricity not reliable? I know this is "conventional
wisdom" but, I have never had an electronic device fail in flight but many,
many mechanical instruments have failed me. In fact, even when an
electronic device seemed to fail, it was always a mechanical switch or
battery contact that failed and not the device itself. (Hint: Use the best
electrical hardware money can buy.)

I sit here typing on an incredibly complex device called a Personal
Computer. The CPU alone has over 10 million transistors in it. If the PC
ever fails, the reason will almost certainly be the mechanical hard drive.
If the power grid fails to provide electricity, the UPS will keep it running
long enough for a graceful shutdown.

In just the last month, we have had a mechanical altimeter fail. The only
way we knew was that it couldn't be set to local field elevation. We had an
airspeed indicator fail to work at all. I had mechanical altimeter suddenly
lose 2000 feet as it became unstuck. The Winter mechanical vario in one
glider spends most of the time stuck at +10 Kts. so we rely on the only
reliable one - the Cambridge L-Nav. (If I ask, "Why the mechanical vario",
I hear, "For backup".) Mechanical instruments are neither rugged nor
reliable.

Mike Borgelt makes an excellent case for using his B40 with it's internal 9V
battery as a backup. Unlike the Winter, it has audio even while running on
the internal battery.

As for readability, I don't think you will find a "three hand" altimeter in
an airliner anymore. They have had drum-type digital displays since
sometime in the 1960's. Many studies have shown the digital readout is
harder to mis-read. Although, today these are likely to be just the back-up
to the digital "glass cockpit".

Bill Daniels