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Message
Lee,
I'm
not sure that I'm hearing an actual maintenance problem with your
hydraulics. Specifically, your nose gear remaining down longer than the
mains is potentially normal because of the gas shock strut's added force.
The entire system pressure (to raise the gear) remains roughly constant at all
times. Therefore, before full gear retraction variable
sequencing is probable due to the greater forces holding the nose gear in
place. My mains come up non-symetrically with a noticable yaw during gear
retraction. However, if further trouble shooting is desired I would
consider 4 possible areas of failure.
1) How do I determine if the nose
cylinder needs rebuilt or replaced? Assess all 6 cylinders and the
free fall vavle for internal leaks (up or down). This is done
fastest by owning 12 AN fitting caps. Troubleshooting is a series of
elimination of offending components individually. The steady pressure
non-chirping pump is a sign of a good internal seals. Internal leaks are
noticed by occasional pump chirp (either up or down). Of course with
hydraulic pressure gauges this can also be assessed rapidly. The original
dump valve supplied in my kit (1996) was rated at 600 psi. The system
running up to 1200 psi caused the dump valve's internal failure.
This failure does not seem related to your symptoms.
2) Several spool valves have
been installed backwards. I would attribute some "quirky" behavior of my
system to this. Such behavior included an occasion gear stuck in the down
position after takeoff for no apparent reason. The system will
however work with the spool valve in backwards but responds better with it in
correctly. The fastest way to trouble shoot this is to raise the gear part
way. At about 80% raised reverse the gear handle to down.
Instantaneous pump reversal denotes a correct installation of the spool
valve. A delay of 8-20 seconds would indicate that it is in
backwards.
3) The up and down pressure switches have been accused
of numerous failures. I don't know that the "new" switches have any
adverse track record. These are quickly removed from the electrical
circuit with a jumper wire. The switch is nromally closed and should open
when adequate pressure is reached, thus turning off the
pump.
4) I suppose physical binding or mechanical
failure should be your first assessment. If something is indeed hanging up
then it'll talk to you. Disconnect the hydraulic cylinders individually
and check for smooth free operation of all the gear.
Larry Henney
LNC2 IO-360
Ft Worth, TX
Ok, new symptom
today. Upon gear retraction after take-off this morning it took
noticeably longer than normal for the nose gear to start retracting (the down
light stayed lit 3-4 seconds longer than normal). Am I losing my
nose gear actuating cylinder? I don't have the log books handy, but it's
my recollection that the nose cylinder was rebuilt about 200 hours ago (by the
previous owner). (Reminder: I didn't build my
plane).
Lee
Metcalfe
N320WH
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