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From: "Rumburg, William" <william.rumburg@cdicorp.com>
To: "'Ian B. Crowe'" <ian.crowe@sympatico.ca>, lancair.list@olsusa.com
Subject: RE: 320  Landing gear
Date: Wed, 31 May 2000 14:25:47 -0400
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Ian -
Thanks for the quick response, I didn't even know the current LNN had been
mailed! 
Six years ago, I also was determined to build the perfect gear and hydraulic
system and thought that I had. I even discarded the cad-plated steel
fittings and stiff hydraulic hose supplied with the kit and spent $ 500. for
stainless fittings and premium stainless-braided teflon hose. The fittings
had to be crimped by a local shop, after I determined each required hose
length. During gear operation, both mains retracted and extended in perfect
unison, not only under power but during free-fall as well. With a lot of
micro and work, the door fit up was perfectly faired in when closed.
However, over the years, problems crept in one by one.
So, you've experienced this same failure to retract problem, but under more
benign circumstances. As an engineer, you learn not to rule out any
possibility. You could make a list of possible causes; however, I don't
believe it's electrical. Rather, I believe it's due to a "hydraulic lock"
phenomonea which causes the high pressure switch contacts to remain open. My
pressure switches are circa 1994 and I had considered replacing them with
new ones as a troubleshooting step. Since you've experienced the same
problem, it's unlikely they are at fault. For whatever reason, I believe the
high pressure switch sometimes remains pressurized and it's open contacts
then prevent retraction. 
As I noted in the LNN, a temporary solution that will "get you back on the
road" is to open the pressure release valve and jog the hydraulic pump by
using a pair of pliers to short either the UP or DOWN solenods.

Bill Rumburg
N403WR  (Sonic bOOm)  


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