Mailing List lml@lancaironline.net Message #44729
From: <Sky2high@aol.com>
Sender: <marv@lancaironline.net>
Subject: Re: [LML] LNC2 Hyd Chirp Tim/ Joe/ Brent Question
Date: Mon, 05 Nov 2007 13:50:43 -0500
To: <lml@lancaironline.net>
Larry,
 
Egads man, I forgot about the piston/shaft internal seal.  More later. 
 
First, I should have mentioned what appears to some of us as obvious - The blip-o-monia (leading to chirpaholism) certainly occurs whilst trying to clear the air out of everything.  I still think there is some possibility for a wee amount of air to remain is some of the longer door lines.  After I sent my last wet missive, I realized that the bubble I described in the top of the nose gear actuator would be almost completely diminished on the first retraction after it was formed on the first extension after air introduction.  It can take quite a while for the lines to be cleared of small bubbles.  Terry's point is also well taken - as was pointed out, fluid does not "flow" thru the system but tends to go back and forth, with the main actuators contributing the most displacement.  Thus, filters may not trap particles and deteriorated rubber at the retract end of the cylinder because of the space by the stops pulling it up short.  Upon extension the main actuator piston rests against the end, leaving very little room for fluid (assuming properly rigged).  Also, one must be careful about any oil, other than the final hydraulic fluid, introduced into the cylinders as it may be incompatible with the hydraulic fluid or the seals.
 
The Pistons:
 
(attached are two pictures at 75 dpi and 400 x 600 with 1/2 sized "thumbnails" included in the text as a test)
The door pistons are welded to the shaft, thus no leakage can occur there (upper piston).
The main actuator pistons are bolted to the shaft (just loosely assembled in this pic).
 
 
Here is what it looks like when taken apart:
 
From left to right - nut, washer with bonded o-ring, piston, washer and shaft.  The o-ring rides very close to the cut in where the threads start.  It is not impossible that your "system leak" might occur at this washer area.  HOWEVER, it is hard to believe this would be the cause of chirpaholism for only one direction, especially on the down side.  OK, it might be possible on the high to low pressure direction (up-->down).  I think better positioning of the seal washer could be accomplished by using a thin washer on the shaft side and adding a thin washer between the nut and the sealing washer.  I noticed bits of rubber sticking out under the nut.
 
With respect to the dump valve going directly to the sump.  This seems more correct if (and only if) the sump can handle the excess fluid.
 
Alas, while I have a newer pump,
I retro-fitted the older, smaller sump. 
Chump!
This has been a very good exchange that, along with passages from Chris Z, it should be compiled into a clump.
 
Scott Krueger
 
Goo? Only air turns the fluid to goo.  Hmmmmm....  Some problems do seem to be caused by sticky pressure switches. 
 
 
In a message dated 11/5/2007 9:57:59 A.M. Central Standard Time, LHenney@charter.net writes:

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.

 

 




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