This is a very important topic for all of us. A gear failure is certainly an expensive and likely dangerous situation in any Lancair. While building this was an area I paid a great deal of attention to since I had witnessed hang ups while swinging the gear (140 times!)
I guess I was fortunate in a way that I did see these hang ups and set about eliminating as many of the failure modes that I could nail down. I think what flushed out many of my problems were due to the fact that i had the asymmetric spool installed the wrong way and the pump had sat for at least 3 years in oil without any cycling which led to what I think we're weak O rings
I swapped the spool orientation and I was still able to demonstrate hangups albeit a good deal less.
So, my next step was to read all of the related posts (shout out Chris for the great drawings and description of how the pump is supposed to work) on LML and gather all of the drawings for the pump mechanism and then get on the horn with the manufacturer. My experience was that there is very little detailed institutional knowledge remaining in Parker about the Lancair application. So after describing the system in detail to a seasoned tech I took their advice and installed a new pump body with a symmetrical spool. I could have used the original pump but I wanted to upgrade to 2x speed which works great by the way. The spool I chose has 2 heavy rings instead of one.
Since replacing all this equipment I have not had a single issue. But since i had witnessed earlier hang ups that could not be cleared using the original dump valve I decided to install a three way dump that allows pressure to be relieved across both pump ports to tank. This is a scenario that can happen due to heating and leakage (See other posts) The three way dump was implemented in the legacy by the way. In addition, I wanted the extra piece of my mind that if the flow of electrons into the pump motor could not be energized for any reason (total electrical failure, control circuit failure, breaker failure, solenoid failure, motor failure, porting issue inside the pump) that I would be guarantied the gear would fall and lock. (make sure you test the emergency dump system once a month or so, friction is a nasty thing that can suddenly appear for one reason or another)
By the way on a lighter but related note. Last week I flew a trip of about an hour or so with my foot on the rudder because I could not keep the ball caged. I thought I lost my rudder tab. On inspection I noticed the set screw for the inner gear door valve was missing. Emm well that explains that, problem solved plane now flys straight!
Tom
Sent from my iPad
It's a matter of cost effectiveness. I'm still
waiting for positive evidence of what exactly is causing the failure so your fix
can be validated.
Again, I have come up with a fix that WILL fix that
problem . . . for less than what it costs to "fix" the pump, not to mention down
time . . . assuming that springs and vibration is what's causing the
problem. But you have said that vibration can't do that ? ?
Your "fix" could be the answer but there is no way
to know for sure what is inside a particular pump without a dissection because
part numbers are not reliable.
I'm thinking the springs are the culprit but that
needs to be demonstrated. The springs with the help of vibration are the only
thing that I can think of that can move the spindle off it's end position
against O-ring friction. I'm thinking that no springs and maybe harder O-rings
could be the answer. That scenario makes sense to me.
You have the test rig you made up so why don't you
simulate the supposed problem and implement the supposed fix and document for
all what the "correct" answer is ?
Let us know if your approach WILL fix the
problem.
I have already done that with my electric
module.
Assuming the pump modification is a valid
fix,
which is more cost
effective, remove, dissect, re-assemble, replace the pump
or simply add the electric module using it's
push-on connectors ?
Wolfgang
----- Original Message -----
Sent: Monday, March 05, 2012 8:21
AM
Subject: Re: [LML] Re: 320/360 Hydraulic
Pressure Switch
Wolfgang,
If a mechanic were to install a new cylinder
on my plane using incorrect rings that subsequently led to oil consumption of
2 qt/hr, I could theoretically design a system that refills the sump to assure
I don’t run out of oil during long flights. The more customary
approach would be to remove the cylinder and install the correct
rings.
The ‘problem’ here is not that oil needs to
be replenished. The problem is
the installation of incorrect parts.
The ‘fix’ is not to add a system to keep the sump replenished. The fix is to use the correct
rings.
Chris Zavatson
N91CZ
360std
Chris,
Life is complicated enough so
when I fly, I like to enjoy it. Being a slave to the system like a cog in a
flying machine is not my idea of "enjoyment". Don't get me wrong, I like
getting into technicals up to my eyebrows, but I prefer to do that at my
choosing, not while tending to a malfunction in flight. That's why I cane up
with the gear module.
After you detailed the
presence of springs in the pump to help center the spool and popets, I see
that my original supposition that the spool is coming off it's end position is
confirmed. It looks like the springs are in fact, capable of overcoming the
friction of the O-rings. You keep measuring the forces in G's but that does
not give us an actual force measurement that is what the springs are operating
against.
It remains that some pump
installations have the problem of the spool not maintaining the required
position for safe flight operations. You have come up with many details that
go toward esplaining the problem and a possible fix (take out the springs). I
have come up with a module that WILL fix that problem.
Wolfgang
----- Original Message -----
Sent: Friday, March 02, 2012 7:54
AM
Subject: [LML] Re:
320/360 Hydraulic Pressure Switch
Wolfgang,
It is a sad
day when removing a pump from the aircraft is too much effort to investigate
an anomaly.
Wolfgang wrote:<<We
would all like to get at the root cause of the problem but, as yet, that
hasn't happened. Likely because it's too much work to track down the actual
cause and fix it. …>>
As aircraft
owners we are responsible for knowing the configuration of the aircraft
systems. If something is out of the ordinary, investigate.
We know a lot about what the configuration should be and how it works and
behaves. We also know of configurations that do not
work. You may very well be holding the key to
a new, as of yet, unidentified failure mode, but we may never
know.
Wolfgang
wrote:
<<So far we only have a good plausible theory missing only
demonstratable proof.>>
If my tire has a flat and
I see a nail sticking through the side wall, I am rather confident in
assuming the nail was the source of my leak. Likewise, if
I open up a lock-up prone pump and find return springs, I will have a high
degree of confidence I have found the source of the problem.
Could there be a second cause? Possibly, but as of
yet, none have been
documented.
Wolfgang
wrote:<<…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.>>
Springs
definitely - that is what they were designed to do.
Oildyne started adding springs to center the spool to the
Legacy pump in ~2003. Our system will eventually fail if
these springs are installed. Fortunately the vast majority of our
pumps do not have them. If you have springs installed,
simply remove them.
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