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Here are some details on the Gear Fix Module - - -
- -
There is a potential for the landing gear to fail
to operate in the LNC2.
The spool in the hydraulic pump can come off it's
end position and seal the fluid volume in the lines. When the system incurs a
large temperature rise, the trapped fluid expands raising the pressure in the
lines, tripping both pressure switches open and making the hydraulic
pump inoperable.
A module to fix this gear operation failure in
the LNC2 using the standard hydraulic system is now available. It is installed
across the pressure switches and monitors their operation. If both switches
are tripped open by high pressure, the pump is made to run in the direction
set by the gear switch re-seating the spool in it's end position restoring
normal pump operation and relieving pressure in the offending side. This happens
automatically without pilot intervention.
The module is 2.5" x 1.5" x .75", weighs 2.3
oz. and has two pairs of leads that connect directly to each pressure
switch with 1/4" spade terminals. No other wiring is necessary. Price is $250.00
each. Simple installation instructions included.
----- Original Message -----
Sent: Saturday, April 16, 2011 8:24
PM
Subject: Re: [LML] Re: LNC2 Gear
Hydraulics
Wolfgang,
What is your gear fix module?
Bryan
On Fri, Apr 15, 2011 at 10:11 AM, Wolfgang <Wolfgang@micom.net> wrote:
From a design point of view, I still have a big
concern about relying on the friction from an O-ring to keep the landing
gear functioning properly. Vibration levels can exceed 70 G's. I would be
much happier with a spring loaded ball detent or something
similar.
That's why I came up with the gear
fix module.
Wolfgang
----- Original Message -----
Sent: Wednesday, April 13, 2011 8:25
AM
Subject: Re: [LML] Re: LNC2 Gear
Hydraulics
A symmetric back-pressure circuit and spool will eliminate the
possibility of installing the spool backwards as happened with pumps
manufactured in about the '96 through '98 time frame. The spool must
still remain in place after the pump shuts down to prevent both high and
low circuits from locking up simultaneously.
Using o-ring 013-70 requires 30 g's to move the spool.
Using o-ring 013-90 requires 70 g's to move the spool.
This
includes the return force generated by the poppet springs (410462).
The difference between the two o-rings is durometer. I have
been using the softer one without any problems. The stiffer o-ring
(intended for pumps with back pressure circuits) should leave no
doubt. The first thing to do with a pump that has a history of
locking up both sides is to measure the return force for the spool and
make sure it has an o-ring installed.
Chris Zavatson
N91CZ
360std
From: Wolfgang
<Wolfgang@MiCom.net>
To: lml@lancaironline.net
Sent: Mon, April 11, 2011 4:56:57
AM
Subject: [LML] Re:
LNC2 Gear Hydraulics
When I first got into this problem with the
hydraulic pumps last year, I had a few conversations with the product
manager of the Oildyne 108 pump. There have been many changes in it's
production life and one of them was to make the spool symmetrical and have
the relief circuit the same both ways.
Wolfgang
Wolfgang,
Yes, I have considered this. The spool with O-ring is a very
tight fight. While I have not tried to measure the force to move it,
I would estimate something over 50 g's to move it (I'll measure this the
next time I have a pump opened up) Could it be that a pump somehow
ended up mounted such that it was subjected to some resonant frequency?
Seems like a remote possibilty given all the variables and the mass
of the pump. How about wear and
tear? Perhaps sitting dry and idle for ten
years would do it. A missing O-ring or a spool that doesn't utilize
an O-ring would allow the spool to move very easily. Parker does
make spools that don't even have O-rings. Did these end up getting
installed by chance?
Based on reports from the LML, the behavior seems to be rather
binary. On the one hand we have planes with over 1000 hours and more
than ten years of service that have never once had the spool move off the
poppet. On the other hand, we have planes with circuits that lock up
right out of the box (put into service).
This leads me to believe there is a difference in
configuration. The easiest way to verify this is to simply open up a
pump that is known to lock up hi and low circuits
simultaneously.
While I have opened up several pumps (primarily to flip around spool
valves), I have not yet worked on one that had this lock up issue. I
am optimistic the difference will be quite obvious upon inspection.
Chris Zavatson
N91CZ
360std
Sent from my iPad
Chris, have you considered what effect
airframe vibration has on the position of the spool in the pump and the
problem in general ?
Wolfgang
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I would like to extend the offer to the whole group. I
think the entire community would benefit from understanding why
some pumps are allowing the system to lock up. If anyone has
a pump that exhibits this behavior and could part with it for a
week, I am willing to check it out on the test stand and examine
the internal configuration.
Chris Zavatson
N91CZ
360std
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GearFix2s.jpg
GearSw1s.jpg
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