Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Tue, 31 Dec 2002 16:47:02 -0500
Message-ID: <redirect-1942650@logan.com>
From: "Larry Henney" <LHenney@dellepro.com>
Subject: RE: [LML] lml  LNC2  Hyd. Power Pack and Dump valve
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Importance: Normal
In-Reply-To: <list-1942380@logan.com>

D,

Numerous vintage 1996 hyd units (I believe these to be the "New" unit)
have their spool valve inserted backwards.  I am unaware of any
difficulties with the "Old" units.  Perhaps Lancair could tell you why
they changed to the newer unit.

The dump valve originally included in LNC2 kits was rated at 600 psi.
The system runs up around 1100 psi.  Many have begun leaking internally.
Mine lasted about 200 hours before needing replacement.  This is
evidenced by the occasional cycling of the pump.  Although the other 6
cylinders could also be the culprit, the dump valve has had a higher
failure rate on my plane. (1 of 7 <G>) Vern will sell you the new appox.
2200 psi (I think) valve or you could get one from WW Granger.

The electric portion of the pressure switches has been accused of
failing more than once.  I was somehow convinced to aquire a spare low
pressure down switch.  It's still new in the box (does anybody want it?)
I personnaly am more inclined to suspect internal cylinder leakage, a
faulty dump valve, or a reversed spool valve prior to getting worked up
over the pressure switches.  A genuine failure of one these switches
would be an inconvenience but it wouldn't prevent a return flight home
(I would use a switch to momentarily jumper the pressure switch to get
the gear up).

It should be noted that the initial Lancair wiring diagram could be
considered flawed in that it might cause an unweary pilot to burn up his
non-continuous duty relays.  To be precise consider pulling  the 50 amp
circuit for a gear free fall test for example.  The opening of the dump
valve as designed will cause the relay to engage without pump actuation.
This continuous use of a non-continuous duty relay will cause it to
fail.  Therefore, many LNC2 wiring designs include a CB for the "control
power" in addition to the hyd power pack power (or you could wire
control power down stream of your 50 amp breaker).

Finally, there are no system failures (or AD's or upgrades that I'm
aware of) listed above that should cause any crisis in flight.  Fly
yours and wring it out.  If you have difficulty freefall the gear, land,
and troubleshoot the situation.

The largest mechanical risk in the gear systems I'm aware of is when hyd
cylinders fail to bottom out internally resulting in force in the
linkages.  You don't want several hundred psi pushing your linkages
beyond there normal down and locked position.  Nor should there be force
smashing your gear doors into the up position.  Positive contact just
prior to cylinder stoppage is challenging but mandatory.

The largest risk in landing gear systems is the pilot to switch
interconnect.

Hope that wasn't too terribly verbose.  I've been off the list for
awhile and the wife was sick of hearing me try to explain hydraulics to
her.

Larry Henney
N360LH IO-360
Ft Worth, TX