OK, Thinking-Cap Time...

2) In steady-state flight, both of us hear a "woo--woo--woo..." softly in
the headphones. It sounds just like strobes that aren't grounded properly.

3) The noise slows down -- or speeds up -- in synch with the prop RPM. At
2300 RPM, it's going a bit faster than once per second -- maybe around three
times every two seconds.

4) I switch our digital voltage/amperage meter to AMPs, and watch as it
oscillates in time with the noise. It's alternating from 5 amps to 10-11
amps, in time with the "woo--woo--woo"... Voltage appears to be pretty
steady at around 13.8-ish volts.


Jay,

Is this not the "Cherokee oscillating Ammeter" thing? Mine has it. Exact
same symptoms. Had it for 11 years and 4 different alternators. Either
the split master switch (alternator side) or the alternator breaker
having a high resistance connection (either the wires or the
switch/breaker itself).

Google it. You should see lots of hits. A common problem if I recall.

Mike

Is this not the "Cherokee oscillating Ammeter" thing? Mine has it. Exact
same symptoms. Had it for 11 years and 4 different alternators. Either the
split master switch (alternator side) or the alternator breaker having a
high resistance connection (either the wires or the switch/breaker
itself).

Google it. You should see lots of hits. A common problem if I recall.

It may be -- but it just started happening in mine. *Something* had to
change, and the fact that my mechanic was digging around in the magnetos
last week seems to point to the all-to-common "mechanic-induced" squawk.

Or, it could be the sudden, severe cold? Or, it could be coincidence.

Next nice day I'm going to de-cowl the engine and tighten all electrical
connections. That has cured other electrical gremlins for us...and it's
cheap!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay - If you get desperate, you might be able to create this problem on
the ground using a hand held or jury rigged electric motor to spin the
alternator rather than having to run the engine. This would allow
better diagnostic capability using an oscilloscope.

However, if the problem only occurs only at higher amperage loads, a
fractional hp electric motor won't be able to spin the alternator.
Likewise the RPM may be a problem. Alternators spin pretty fast at
cruise - like over 10,000 rpm.

nrp wrote:
Jay - If you get desperate, you might be able to create this problem on
the ground using a hand held or jury rigged electric motor to spin the
alternator rather than having to run the engine. This would allow
better diagnostic capability using an oscilloscope.

If you try this, keep a fan blowing on the alternator. Even in cold
temperatures, it will need cooling air.

George Patterson
If a tank is out of ammunition, what you have is a sixty ton portable
radio.

Jay Honeck wrote:
last week seems to point to the all-to-common "mechanic-induced" squawk.

It's not just mechanics. Any good troubleshooter knows you always look
"where the human being was last".



--
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Jay and Teresa Masino ___(_)___
http://www2.ari.net/jmasino ! ! !
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