Message-Id: <3.0.3.32.19981024065301.0073e748@mail.digital.net>
Date: Sat, 24 Oct 1998 06:53:01 -0400
To: lancair.list@olsusa.com
From: John Cooper <heyduke@digital.net>
Subject: Hydraulic power pack location
Mime-Version: 1.0

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The hydraulic pump and relays are behind the baggage bulkhead on my L-235.
It's a very difficult place to get to, so make sure everything is working
properly prior to installing it there.

In my case, I built a little "mule" cart with everything mounted on it,
which I used to cycle the main gear prior to installing the upper stub-wing
skins. So I knew the pressure switches were set properly before installing
the unit in the plane. (My pressure switches are mounted on the pump package.

Re: the 50A relay will in *no way* protect your pump motor from burning up
if it stays on too long - it will only protect against a dead short
somewhere. I have measured the current draw of those pumps, and it is about
12A while the gear is being cycled, then spikes up to about 30A just as the
gear tightens up and stops. What I am saying is that if your pump runs on,
it will just sit there and draw 10-15 Amps until it burns up and fills the
cockpit with smoke. That 50A CB will not open under this scenario.

What ever rating you decide to use, the "disconnecting means" must be
accessible. In my case, I used a 30-A automotive-type "Maxi-Fuse" from
Digi-Key and located it next to the hydraulic bypass valve where I can
reach it. I wrapped a tie-wrap around it and left the tail sticking up to
make it easy to pull the fuse should I ever have to. 

***Note on fuse rating. I found the 30-A fuse would blow after about 5
rapid gear cycles, so I have a 40-A fuse installed right now. I will
probably leave it that way for my test-flight period, then switch back to
30-A eventually.***

I'm sure this will spark some controversy, but I wired my hydraulic pump
*directly* to the battery through the 30-A fuse using #10 wire, and the
control relays to the master bus via a 1-A circuit breaker mounted on the
panel next to the gear switch. My reasoning is as follows:

1. The fuse should *only* have to be pulled in case of a confirmed
hydraulic pump run-on *due to a stuck relay*. (Unlikely, since I used the
Bosch relays designed for inductive loads with MOVs across the contacts.)

2. It kept those big, noisy, hi-current wires off of the main buss behind
the panel. The hydraulic motor current doesn't pass thru the master relay
either.

3. The pump can't come on with the master switch off, unless a relay
contact fails closed. I suppose there is a "possiblity" that a contact
could decide to weld itself shut while the plane was unattended in the
hangar and the pump come on momentarily, but I can't think of any physical
process that would cause this - earthquake? lightning strike?. If I'm
missing something here, please let me know.