In article . net,
"Jimmy B." wrote:

Dan Luke wrote:
"Jimmy B." wrote:

As some of you know, I'm plane sitting for a friend. It is a 1983
172RG. Over the past couple of weeks, it seems to have picked up an
electrical issue. Occasionally, the "low voltage" light will flicker.
So far, I've seen this happen 3 times in about 5 weeks. Once, I
happened to be looking at the engine instrument panel when it happened
and both of the fuel gauges pegged to empty and then recovered during
the event. It happens so fast, if you are not looking at the panel
when it happens, you would miss it. So, I'm not sure how many times
this has happened without me knowing it.

Has anyone seen a similar problem and can point me in the right
direction?


Oddly enough, this is may be a hydraulic problem. The symptoms you are
seeing are most likely from the voltage spike produced by the landing
gear hydraulic pump starting and stopping. The pump only needs to run
for a second to restore pressure. Both 172RGs I've flown (mine and a
renter) do it. I've only seen it on the takeoff roll, perhaps because
the hydraulic gear actuators unload as the weight comes off the wheels.

It's a problem only if it does it frequently, indicating a continual
loss of pressure from a leak of some kind.

For my own curiosity, what TAS do you get from that Cutlass at around
6,000'?


I was reading the POH and it mentions that why the pump will cycle
during the take-off roll is because the nose gear squat switch
deactivates the power pack. So, when you lift the nose, the pump cycles
to repressurize the system, which has bled off a little sitting on the
ground.

Now that you mention it, last couple of times that I flew it, when I
pull the gear up the low voltage light comes on for a few seconds just
as the gear is completing the cycle.

Maybe I need to get the power pack overhauled? The one that is in there
is about 15 years old.

This one seems to cruise around 135 knots.


A couple of other possibilities:

1. Check for corrosion at the grounding points for the battery and for
the hydraulic pack.

2. Check for loose positive connections at the power pack and the main
bus bar,

3. Master solenoid could be dying (they do this).