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Chris,
I don't believe I missed anything, just focusing on
the more likely problem. The items you cited are more a one-of condition but the
thermal soaking causing gear failure is more frequent.
With that in mind, I would be inclined to come up
with a simple test scenario to validate one's pump without having to remove it
from the aircraft. It does sound from your comments on the springs that my
original suspicion of the spool coming off it's end point (with the help of
springs and airframe vibration) is in fact what's causing the problem. The
module I came up with powers up the pump when necessary and forces the spool
back into position in spite of the springs.
Wolfgang
----- Original Message -----
Sent: Friday, February 24, 2012 4:36
PM
Subject: Re: [LML] Re: 320/360 Hydraulic
Pressure Switch
Wolfgang,
I think you
missed the point of my last post. I was describing the benefits of
having momentary switches Angier suggested to
jumper across the pressure switches. The three examples cited are not in
any way related to hydraulic lock-up nor are they addressed by your
module. Designing another circuit to detect, identify and
properly respond to component failures is a tad complex. The
pressure switch failure I described is a perfect example. In those
situations, having more information along with more options available to the
pilot is a good thing?
Regarding the pumps Lancair
currently sells, both Oildyne and Lancair have already acknowledged that the
pump currently sold can lock up when used in a stock 320/360. The reason
for not offering the proper pump configuration for the 320/360 is purely financial
- very low volume. Lancair did suggest that they could include a
warning regarding the lock up potential each time they ship a pump as a
replacement for a 320/360. This leaves the aircraft owner in an awkward
position. The ironic thing is that a properly
configured pump can be obtained directly from a Parker distributor for much
less.
My concern with misconfigured
pumps trickling out into the fleet is that it will eventually catch pilots
unaware of the technical issues off-guard.
Chris Zavatson
N91CZ
360std
We can keep this up for the next year but I
believe talking it to death will not fix the problem. My preference is to have
a system that takes care of itself. You seem to want to be "involved" in the
anomalies of flight. If most people wanted to be "involved", we wouldn't have
things like FADEC's and auto pilots. The module I provide can help keep flight
a bit more self sufficient and safer. If you could convince Oildyne and
Lancair that they have a problem with the pumps as used in Lancairs, and fix
the problem, then more power to you and the Lancair owners. But in the mean
time. I still like my gear module.
Wolfgang
----- Original Message -----
Sent: Tuesday, February 21, 2012 9:01
AM
Subject: Re: [LML] Re: 320/360
Hydraulic Pressure Switch
" . . . you can only override one pressure switch at a time or
overload the system.
You need one switch each for the up and down. In the
event of a problem you have to make sure you push the right
switch"...
Overload what exactly? The gear selector determines which
pressure switch is powered. If you jumper across an unpowered switch, nothing happens.
While I do not advocate putting in switches to mask a pump
problem that should really be investigated and fixed at the source,
momentary switches have other benefits.
1. Checking the relief valve settings in the pump. By
holding down the switch, one can see the relief valve setting of the
pump.
2. Back-up for a failed pressure switch. This was
more common with the VEP switches, but current version is not immune.
3. Recharging the system on demand - The hysteresis loop on
the pressure switches is quite large. The gear can start to sag before
the pressure switch
recharges the system. This is more of an issue for the
Outback Gear due to the higher aerodynamic loads pulling on the
gear.
With automation and complexity come new failure
modes. Give the pilot enough information about the state of the
aircraft systems to figure out what happened and enough controls to solve
the problem.
Last summer when the high pressure switch went out, the pump
shut off before the gear was all the way up. Higher than normal air
noise was the first clue. A quick look at the pressure gauges revealed
the high side at only 800 psi. The momentary switch pulled the
gear the rest of the way up. Examination of the
pressure switch uncovered intermittent electrical contact within the
switch when pressurized.
Chris Zavatson
N91CZ
360std
Yes, that would
be easy . . . except . . . you can only override one pressure switch at a
time or overload the system.You need one switch each for the up and
down. In the event of a problem you have to make sure you push the right
switch.If you come up with some more complicated wiring, you could make
it work with only one switch for both up and down but you still have to push
the button if something isn't working as required.. . . or . . . you
could put in a completely automatic system . .
.Wolfgang----- Original Message ----- From: "Greenbacks,
UnLtd." <N4ZQ@VERIZON.NET>To:
<lml@lancaironline.net>Sent:
Friday, February 17, 2012 1:07 PMSubject: Re:320/360 Hydraulic Pressure
SwitchSeems to me the simplest and least expensive option
would be to install a momentary on switch in the cockpit to override and
close the open pressure switches.Just my 2 cents.Angier
AmesN3ZQ --For archives and unsub http://mail.lancaironline.net:81/lists/lml/List.html
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