Scott,
As with most of which I speak, 90% was
lost in my inability to articulate in a language perceptible to the soberness
of my readers. My point regarding the air in lines being an accumulator was
missed. I believe you dissected it below by pointing out the various
natural paths by which air makes it’s way back to the pump. I
believe your premise was that all of the air gets back to the pump. This
would then make my premise that the air would act as an accumulator initially
but thereafter work it’s way out. Thus, one would have longer time
between chirps (TBC) until the air worked it’s way out. Then, ops
normal (occasional chirpage ) would resume.
However………….
I rebuilt two main cylinders Friday and flew all weekend. The results of
much air introduced into the system were quite contrary to my theory. It
was pure chirpaholism for the first hour. Thereafter, I ran the pump for
about 30 seconds (dump valve open) upon each gear extension. Now after 6
such cycles it seems to be “better”. I need more cycleage to
tell for sure. Or maybe more cylinders rebuilds.
BTW, does it bother only me that the HC-06
cylinder rebuild kit does not come with a thread seal? I think a cylinder
rebuild kit should include all the O rings and seals that the cylinder entails.
Especially, since our leak headache discussion is internal
High/Low. The seal is for the shaft at the piston. It was
only a minor set back (90 mile drive and two hours at American Hydraulics
with help from Rose). Help us here Tim O., Joe B.???? HC-06
no thread seal. Is it the kit supposed to have one? Mine haven’t
several times.
On the secret switch note, I am one of
those High pressure leaks to Low pressure side and sets low pressure switch
guys (after some duration + 1 hr). The opening of the dump valve, after
the switch down does nothing, allows pressure off the low pressure switch and
fires up the pump. That’s why I keep going back to the shuttle
valve test. I find mine (once reversed) now in correctly. The idea
that both switches are set and anyone CAN NOT get gear extension is
beyond my fathom ability (ok, maybe the dump valve handle could fall off).
In other words, if the fluid is leaking to the low pressure side, then why do
it not depressurize through the shuttle valve? The pump would have been
in the …… (I don’t know?)??? BdBdBdBdBd (finger lapping
against flapping lips)
On a parallel solution, my Berkut buddy
(James Redmond) and all his Berkut friends use a different dump valve
concept. They say, yeah those little cylinders leak bad but we don’t
care. They dump both high and low pressure to a common line that returns
through the center port in the pump. I have such a port in my pump and
wonder if this would be a safer Free Fall system. He says the port is directly
common to the jug and thus is a more guaranteed dump to ambient pressure.
BTW, he bought a very nice little panel
mounted valve. The installation is soo much more professional than our
knee knocker under sided Al flox blobbed chunk of workmanship.
The Berkut guys do several other little
cutes like using Dexron III instead of 5606 and MOV’s on the pump wires.
I wonder sometimes about the shear stickiness of 5606 in my low pressure switch.
Is goo the problem?
Your secret wire with switch is
interesting but perhaps I’d only have it on the down switch. But,
free fall works great. Maybe with a three port dump valve, the secret
wire to override a failed down pressure switch would be excessively redundant
(like extra wings, prop blades, or prop bolts- you only need one, right?).
Still head scratch’n,
But at least my Catto Prop is soon to ship (RPM to follow). Look out
Bruce Hammer J
Larry Henney
Race 36
252 mph Memphis 100 (wind enhanced)
PS: And Brent, if photographing tail
wind enhanced groundspeeds is analogous to standing on a pile of books, why
does one arrive earlier as compared to the guy stepping off the books
subsequently being his original height? Flame suit worn out but ready
anyway.
From: genemartin
[mailto:genemartin@enid.com]
Sent: Sunday, November 04, 2007
9:28 PM
To: lml@lancaironline.net
Subject: Re: [LML] Re: FW: [LML]
LNC2 Hyd Chirp Alternative Mousetrap
I have such a secret override
switch...top secret unmarked don't ask don't tell.
----- Original Message -----
Sent: Saturday, November 03, 2007 9:06 AM
Subject: [LML] Re: FW: [LML] LNC2 Hyd Chirp Alternative Mousetrap
Air is good if your breathing and bad if
leaking into your brain. OK, I'll go out and rebuild one this am and
report back. Oh, but wait, I guess the rebuild of the leaker will have an
affect on our test.
I love spirited discussions leading to
one's spirit sipping spirits during contemplation of the
metaphysical. I thought more about all the problems reported over the
years and the possible effect of air. Let's see if we can work thru
this by picking the system apart. But first, I said you should only
introduce air into the system as a test of your theory, not rebuild a
cylinder.
4 of the six cylinders, those associated
with the main gears and doors, can be eliminated because they are oriented
horizontally with all ports pointed upward so the air will not remain in
those actuators.
The nose gear door cylinder, vertically
oriented cannot hold much air in the bottom after extension because the air
would have to fit in a donut cylinder volume 5/32 high with the inside
1/2" diameter and the outside 5/8 diameter - a volume of .017 cubic
inches. This space is inside of the extension piston stop that allows
fluid to be passed in and out of the cylinder. Upon retraction, even
though the piston does not tightly reach the top, the fluid exit is at the top
and air would be expelled. The .017 ci of air could be trapped at the
piston that is pushed in by the hi pressure retraction activity and the bubble
could rise to the bottom of the piston.
The nose gear cylinder is somewhat
vertically oriented and the cylinder cannot hold any air in the bottom beyond
the piston at full extension since it is stopped tightly against the
forward bulkhead (if properly rigged). However, retraction is limited by
the external stop and the fluid exit is at the aft lower side of the
cylinder. I forgot to check how vertically oriented the cylinder gets on
retraction, but let's say the whole remaining space can retain air.
That is a cylinder approximately 3/4" high with a diameter of 9/8"
for a volume of about .75 cubic inches. Of course, at retraction this
pocket would not be under pressure since it is the other side of the piston
that is under pressure. So, it is on extension that some of this pocket
could be compressed although it would seem that some of the air would come out
at each retraction.
There also are short pieces of Easton flexible line that
feeds into 1/4" hard Al lines. Let's discuss how much volume
these lines can hold. For the Easton
line (I could not find a sample), assume it has an interior cross section
of 1/4". That is 20.37 inches of tube per 1 cubic inch of
fluid volume. The 1/4" hard lines have a wall thickness of .035,
thus the interior diameter is .18" or 39.3 inches of tube per cubic inch
of volume.
Door actuators move about .9 ci of fluid
in when extended and .7 ci in when retracted. The nose gear cylinder (I
forgot to measure the length, say 4.5" of movement) moves about
4.5 ci of fluid in when extended and 4 ci in when retracted.
Since the opening of doors requires fluid
passage thru sequence valves, those lines might not be completely cleared
because of the hard line length may hold more fluid than is transferred to and
from the actuator. One could consider a small
bubble remaining in those lines. The retraction side moves more
fluid thru shorter lines so it is less likely that air is trapped in those
lines. The large actuators move much more fluid and it is hard to believe
any air remaining in those lines.
The dump valve body can't hold air
once it has been opened. Perhaps the teed vertical lines leading to the
pressure switches retain air.
For those that suspect that heated
trapped air raises the system pressure quite a bit should note that when the
volume is held constant, the pressure increases as the temperature ratio, in
Kelvin, increases. A rise from 50F to 80F is 299K/283K or approximately
a 5% increase - Hardly accounting for a rise of several hundred psi. I
await an engineer to evaluate effects of the differing expansion factors for
aluminum, Easton
lines, cylinders and the fluid itself.
On the converse, if the air is compressed
(so far this looks like a problem that is possible solely on the down side
at the nose gear actuator), I would finally have to agree that more volume
of fluid under pressure from the air would have to pass
through the system leak to activate the pressure switch than that from
incompressible fluid on its own. Maybe. That these air pockets may
work themselves out so that the chirp rate increases is interesting.
So I can see where an accumulator could
delay pump activation. No problem as long as other parts of the system
are working properly. It is hard to see where any air bubbles could
influence the up side of the system other than those trapped in the
sequence valve circuits.
As to some of the other
contentions.................
You said: "You're an electrics
guy. Does that little chirp every 20 seconds not bother you just a
little? You know, arcing and corrosion in the relays, airborne fire,
alternator shorting, etc?"
You are correct, the wiring is
correct. Thus, arcing and corrosion are not a problem -
intermittent relays are operating intermittently . Airborne fire and
alternator shorting are not a problem from the pump blips for the small
percentage of block time that the gear is down, nor is anything
else associated with the hydro-electric gear system. However,
"etc." does indeed bother me, although it is not related to this
situation.
One of the risks you may add is that the
accumulator on the high pressure side may lock up the low pressure side if you
have a failure like that sometimes described by other Lancairites and not yet
fully understood. This is the case where opening the dump valve does not
resolve the peculiarly built system pressure present on both sides
and that trips both pressure switches. There may be an electrical solution
- perhaps bring duplicate wires from the pressure switches forward to
secret over ride switches operable by the captain. Forced activation of
the pump may free the lockup if it is the case of a stuck shuttle
valve. Of course the captain's hearing has to be good enough to
perform an "undo" if the pump is straining as the
captain becomes the acting pressure switch.
Scott
Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL
(KARR)
Darwinian culling phrase: Watch This!