|
|
Oh he has a kit he will sell you that does something to the hydraulic system. I'd have to go through the archives to see what it is. Might be worth it for your plane since this seems to be a recurrent problem.
Dan
On Fri, Sep 7, 2012 at 11:13 AM, Ralph Love <ralphlove@stanfordalumni.org> wrote:
Robert, Do you see a solution here? R
I have said it before, removing a pump and taking
it apart to fix a supposed design problem, putting the aircraft down for the
duration, is not always the best solution. After it's apart, you're still
looking to verify your supposition. Installing a fix like mine guarantees a
solution in about 30 minutes. Pilot's choice. 30 minutes is a small price to
pay.
Wolfgang
----- Original Message -----
Sent: Thursday, September 06, 2012 8:15
AM
Subject: Re: [LML] Re: Thermal influence
on Hydraulic Pressure
Wolfgang,
The
‘failure to retract’ issue, to which you refer, sounds like a pump
configuration issue.
For example, the current pump sold by Lancair
for the 320/360/Legacy contains spool return springs. This configuration has the
potential to lock up due to thermal heating. This configuration is simply not
compatible with the design of the Lancair two-seat hydraulic systems.
With personnel turn-over at both companies,
neither side knows why the return springs were added. However, both Parker and Lancair agree
that a lock up on the ground is possible with the springs installed. This lock-up has been experienced by
some, including the factory Legacy.
It just has not been reported enough to drive an engineering change at
Lancair.
Parker
has graciously supplied parts to revert currently sold “CZZ” pumps back to the
original 320/360 configuration with respect to spool operation. I have been forwarding these parts
free of charge to anyone who needs them.
I applaud your ingenuity in devising your
circuit. Unfortunately your
energy seems to be a little misplaced. I would prefer to investigate
and fix the root cause of any out of the ordinary behavior-especially on an
airplane! If my engine was
burning a quart of oil per hour, the fix would not to design a gadget
that would pump oil from an onboard supply into the sump and replenish the
lost oil. The solution, albeit
painful in the short term, would be to open up the engine, find and
fix the problem and then fly like other engines.
I understand that removing a pump, in
particular those mounted behind the baggage bulkhead is no fun. Poor access is a real deterrent for
any maintenance activity. That is
simply human nature. In the grand
scheme of things, it is a small price to pay.
My offer still stands to examine your
(Lorn’s) pump or any other that is able to lock-up both circuits. I have not yet come
across one that did not have an obvious cause-like the springs mentioned
above, so any such reported behavior of great interest to me and is worth
investigating.
Chris
Zavatson
N91CZ
360std
Let's not forget this thermal influence causing
non-function can also happen in reverse. It has been reported that a thermal a
soak on the ground after a cold night can and has caused a failure to retract
after take off.
A while back I offered a solution of bumping the
pump automatically whenever both pressure switches, HI and LO, are open due to
high pressure. This would put the system back in normal operation mode
without the need for pilot intervention
Wolfgang
----- Original Message -----
Sent: Tuesday, September 04, 2012 7:53
PM
Subject: Re: [LML] Re: Thermal
influence on Hydraulic Pressure
Fred,
I wish we had an easy way of bleeding just a wee bit of pressure
without momentarily dumping the gear in cruise.
The
320/360 pumps use a non-adjustable thermal relief valve rated at 2,500
psi. The actual cracking pressure is 2,500 to 2,900 psi. This is
the lowest set-point Parker has available. 2,900 psi is a lot of
pressure for a system that nominally operates at 1,200 psi. Hopefully
the design margin for the cylinders etc. was chosen large
enough.
The
first time I saw a 2,000+ excursion was on the test bench. I was leak
checking a cylinder. The test stand was near the hangar door.
The sun swung around and hit the pressurized clyinder. I dont'
know what the max pressure was since that gauge only went to 2,000
psi.
Chris
Chris
Zavatson
N91CZ
360std
|
<SENDER_EMAILfrederickmoreno>
I have an MPV-50 engine monitor that includes continuous
reading of the hydraulic system pressure on my Lancair IV/
I have seen the same thing, particularly on a flight that
started on a cool morning departure from my home drome and took us to
the desert for a 110+F day. On descent, pressure rose from its
customary 1250 to 1500 psi at which point Bitching Betty started to
complain so I bumped my speed brakes which are hydraulic, and
lowered pressure back down to my customary range.
Same thing sometimes happens in reverse, a hot soak on the ground,
then a climb to 10-11,000 feet for a cool soak, and at some point
the hydraulic pump kicks on to restore pressure to the desired
level. My TR-182 used to the the same thing routinely when
departing Phoenix in the summertime.
It is a real effect, and makes one wonder about very high
pressure events arising from FL 270 (say) cold soak terminating in
Phoenix on a July afternoon. Hmmmm....
Fred
-------Original
Message-------
-took this photo after a descent from 16.5k to 1,500
ft.
OAT went from 42 to 94 degrees.
High Pressure gauge is pegged at 2,000+ psi
-Didn't get a photo, but the opposite happened on the ramp in
Spokane. After sitting for an hour, the low pressure gauge was
pegged at 1,200 psi+. Spokane might not be the warmest spot in
the country, but at 85 deg F, it was 55 degrees warmer than the cold
soak on the previous leg.
Temperature changes have a big impact on system
pressure.
Chris Zavatson
N91CZ
360std
|
|
|
|
|