Reply-To: Sky2high@aol.com
Reply-To: lancair.list@olsusa.com
From: "Scott Krueger" <sky2high@hotmail.com>
To: lancair.list@olsusa.com
Cc: Sky2high@aol.com
Bcc: 
Subject: LNC2 Hydraulic System - More information
Date: Fri, 08 Jun 2001 10:01:42 -0500
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Message-ID: <F53MxvgTdHVUbTXwKto0001a16a@hotmail.com>

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Last week I flew over to Romeo Michigan and visited with Ed de Chazal (he 
has pressure gauges installed)- With his plane on jacks, the outback main 
gear is raised with 400 psi, the nose gear (against the gas spring) with 500 
psi and the pump stops after hitting 1200 psi.  In ten minutes, the pressure 
had dropped to 1100 psi and he noted that the pump won't start again until 
about 800 psi.  In cracking the dump valve, the
doors didn't start to open until the pressure dropped to about 500 psi and 
the gear began to drop down at about 400 -- note that the nose gear door had 
not quite opened completely when the nose gear began to drop.  By this time 
the sequence valve stem extended, probably influencing the rate at which 
fluid is returned to the high pressure side.  The door was brushed aside by 
the wheel.  This may be why we get scratches on the door from the wheel - it 
could be the wheel is also turned by having to push the door out of the way. 
  Think about the guy (like me) who installs a new gas spring -- more 
pressure to raise the nose against the spring and a snappier powered 
extension of the nose gear - maybe so fast it starts to beat the door and 
"closes" the sequence valve which slows the return fluid.  Or it may be that 
the return fluid from the nose gear is under higher return pressure than the 
fluid from the door.  Think about it (remember the sequence valve is marked 
for in and out).

Additionally, I had a conversation with Mike Reinath (also has pressure 
gauges) and he had a problem with the pump internal relief valves -- He 
pointed me to Oildyne and I got a fax copy of how to adjust them -- they 
must be set 200 psi higher than the pressure switch.  Imagine if the springs 
weaken with age or are set low enough to allow the hydraulic circuit to 
reach its shut-off pressure, but then the relief valve quickly drains the 
pressure off!  My next experiment will to set the relief valve to a higher 
value.

I also flew to Florida and back pulling the center console mounted 50 amp 
pump/relay breaker and running a timer.  If I closed the breaker in 5 
minutes, the merest blip restored the pressure (remember that the pressure 
switch would have already closed in the absence of any current across the 
contacts) with no radio noise.  If I ran to ten minutes, the blip was longer 
and I felt a change in cabin pressure (ears).  I think a relaxation on the 
doors had the famous Mister Bernoulli trying to suck me out the door gaps!  
I am going to try and find my Lagacy pressure switch and swap that in for 
the next test.

Scott Krueger
LNC2 N92EX
Lagacy Kit #2

PS.  Remember the North Central Lancair Fly in at KJOT - 23,24 June -  
Contact Doug McCallister at Mcgoose@mediaone.net
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