X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 06 Nov 2007 16:28:45 -0500 Message-ID: X-Original-Return-Path: Received: from web54402.mail.yahoo.com ([206.190.49.132] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with SMTP id 2457540 for lml@lancaironline.net; Mon, 05 Nov 2007 22:24:38 -0500 Received-SPF: none receiver=logan.com; client-ip=206.190.49.132; envelope-from=randylsnarr@yahoo.com Received: (qmail 94588 invoked by uid 60001); 6 Nov 2007 03:24:02 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding:Message-ID; b=FaRmxzxiuK1E3EJMZtxkB9/g8hDuZj7p1qkleUzTlGvMC35nEj/vef9XXCC6IZR2H4SIRj225xApNkzM82LmH8ZsKZHO5wev2LusUNqRhgMFj6yP/3KNr9X/WMbLRfY8AXFtsOYoeDpV6tV3aniQcW0gAjt6ffiqruLK28iL8fk=; X-YMail-OSG: VmHw8xwVM1nas6mwQuoNdWhIFVrzF0ogodaQjoE16t6HUrq26QWeHiEhSdw8IVQaBhqpgvAvJ2hhBNTabsjBBZ189gfBCBZpwymalwiORKu9gq0oqg-- Received: from [76.8.220.18] by web54402.mail.yahoo.com via HTTP; Mon, 05 Nov 2007 19:24:02 PST X-Original-Date: Mon, 5 Nov 2007 19:24:02 -0800 (PST) From: randy snarr Subject: Re: [LML] Re: LNC2 Hyd Chirp Tim/ Joe/ Brent Question X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1140161471-1194319442=:93882" Content-Transfer-Encoding: 8bit X-Original-Message-ID: <296025.93882.qm@web54402.mail.yahoo.com> --0-1140161471-1194319442=:93882 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Larry, With Gauges I see the following when decending from cold to warm: Gear down pres starts at 0 high side and 1300 or so at altitude- 17k or so. I might a get 1 bleep from the pump per hour at altitude. Decend to 3500 in the desert of AZ and gear does not extend with the switch. n. The high side is up to 1900 and the low to 600 telling the gear down pres switch to tell the pump to not go. Crack the dump valve and everything starts moving.. This has happened from time to time under similar circumstances. Ideally it would be nice if the 0 pres side of the system vented to the resevoir when the pump is not running like it does when it is running. It does not. When the pump stops the system is sealed up allowing pressures to rise from temp changes as in my case or bleeding from high to low as other have said. Someone come up with a fix for this and my check is in the mail. I plan to at least put in a 3 way dump valve and run a vent line back to the resevoir so you could always zero out the system. I have seen the same thing taking the airplane out of a cold hangar into the warm sun. down side starts at 600 and high is at 0. I have seen the down side get to 1300 or so and the up side around 8-900 after 3 minutes in the summer sun. If that happens you can take off but the gear will not retract cuz the up switch is beyond it's pressure limit. This has happened once but come close on one other occasion as well. There has been much discussion about this. I have a fix for the "ever loosening" nose over center link connection, one of you guys figure this out! Larry/Chris, you are a smart guys.... Come up with something... FWIW Randy... "Zavatson, Christopher J (US SSA)" wrote: v\:* { BEHAVIOR: url(#default#VML) } o\:* { BEHAVIOR: url(#default#VML) } w\:* { BEHAVIOR: url(#default#VML) } .shape { BEHAVIOR: url(#default#VML) } st1\:* { BEHAVIOR: url(#default#ieooui) } @font-face { font-family: Wingdings; } @font-face { font-family: Tahoma; } @page Section1 {size: 8.5in 11.0in; margin: 1.0in 1.25in 1.0in 1.25in; } P.MsoNormal { FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman" } LI.MsoNormal { FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman" } DIV.MsoNormal { FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman" } A:link { COLOR: blue; TEXT-DECORATION: underline } SPAN.MsoHyperlink { COLOR: blue; TEXT-DECORATION: underline } A:visited { COLOR: blue; TEXT-DECORATION: underline } SPAN.MsoHyperlinkFollowed { COLOR: blue; TEXT-DECORATION: underline } SPAN.EmailStyle17 { FONT-WEIGHT: normal; COLOR: blue; FONT-STYLE: normal; FONT-FAMILY: Arial; TEXT-DECORATION: none; mso-style-type: personal-reply } DIV.Section1 { page: Section1 } Larry, All is normal here. <> I have looked at this in some detail and the phenomenon is quite reproducible. Our gear hydraulics have a few unique design aspects that allow this gear extension problem to occur. BTW, I am curious if you have pressure gauges so you see what is happening during these events. It really has nothing to do with leaks from high to low as the low side is vented to the reservoir while in flight. In my plane, I can almost predict when the gear will refuse to come down before I hit the switch. If I descend from very high and cold altitudes into warmer air the hydraulic pressure rises. Sometimes even as high as 1,800 psi while the low side remains at zero. All system pressure is held back by a poppet valve that is pushed off its seat by the spool valve. The spool valve is moved via fluid pressure, most often that generated by the pump motor. Here though we have unique situation. With the gear stowed in the wells we have loaded and cocked three fluid pumps ready to push fluid back to the pump. Here is the scenario. You select gear down. The pump starts to turn building pressure internally. This pushes the spool valve against the poppet valve. Now a torrent of pressurized fluid rushes in. Remember this fluid is also pressurized by gravity acting much like an acculmulator with gas pressure. It will maintain some level of hydraulic pressure over time while fluid is leaving the system. We therefore do not see an instant loss of pressure. The pump cannot remove fluid as fast as the landing gear is trying to push it in. For an instant, the force on the spool valve reverses. If this reversal was long enough, the poppet valve will close again. Now you have a situation where the low pressure switch can become pressurized, with the gear not deployed. Oftentimes the gear will not get stuck, but a very slight hesitation is noticed after selecting down. What is observed in the system is a pressure spike in the low side an instant after the poppet valve is opened by the spool valve. If the spike is high enough, the pump stops thinking that the gear is down. Note that all this happens extremely fast such that you may never actually know wether or not the pump came on at all. This spike happens to some degree on every gear extension. This can be observed in the cockpit if pressure gauges are installed (which I highly recommend doing) Whether or not the gear will actually get stuck depends on many variables acting in together. Chris Chris Zavatson N91CZ 360std www.N91CZ.com __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com --0-1140161471-1194319442=:93882 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Larry,
With Gauges I see the following when decending from cold to warm:
 Gear down pres starts at 0 high side and 1300 or so at altitude- 17k or so. I might a get 1 bleep from the pump per hour at altitude.
Decend to 3500 in the desert of AZ and gear does not extend with the switch. n. The high side is up to 1900 and the low to 600 telling the gear down pres switch to tell the pump to not go. Crack the dump valve and everything starts moving..
This has happened from time to time under similar circumstances. Ideally it would be nice if the 0 pres side of the system vented to the resevoir when the pump is not running like it does when it is running. It does not. When the pump stops the system is sealed up  allowing pressures to rise from temp changes as in my case or bleeding from high to low as other have said.
Someone come up with a fix for this and my check is in the mail. I plan to at least put in a 3 way dump valve and run a vent line back to the resevoir so you could always zero out the system.
I have seen the same thing taking the airplane out of a cold hangar into the warm sun. down side starts at 600 and high is at 0. I  have seen the down side get to 1300 or so and the up side around 8-900 after 3 minutes in the summer sun. If that happens you can take off but the gear will not retract cuz the up switch is beyond it's pressure limit. This has happened once but come close on one other occasion as well.

 There  has been much discussion about this. I have a fix for the "ever loosening" nose over center link connection, one of you guys figure this out!

Larry/Chris, you are a smart guys....
Come up with something...
FWIW
Randy...


"Zavatson, Christopher J (US SSA)" <Christopher.Zavatson@baesystems.com> wrote:
Larry,
All is normal here.
 
<<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)>>
 
I have looked at this in some detail and the phenomenon is quite reproducible.  Our gear hydraulics have a few unique design aspects that allow this gear extension problem to occur.  BTW, I am curious if you have pressure gauges so you see what is happening during these events.  It really has nothing to do with leaks from high to low as the low side is vented to the reservoir while in flight.  In my plane, I can almost predict when the gear will refuse to come down before I hit the switch.  If I descend from very high and cold altitudes into warmer air the hydraulic pressure rises.  Sometimes even as high as 1,800 psi while the low side remains at zero.  All system pressure is held back by a poppet valve that is pushed off its seat by the spool valve.  The spool valve is moved via fluid pressure, most often that generated by the pump motor.  Here though we have unique situation.  With the gear stowed in the wells we have loaded and cocked three fluid pumps ready to push fluid back to the pump.  Here is the scenario.  You select gear down.  The pump starts to turn building pressure internally.  This pushes the spool valve against the poppet valve.  Now a torrent of pressurized fluid rushes in.  Remember this fluid is also pressurized by gravity acting much like an acculmulator with gas pressure.  It will maintain some level of hydraulic pressure over time while fluid is leaving the system.  We therefore do not see an instant loss of pressure.  The pump cannot remove fluid as fast as the landing gear is trying to push it in.  For an instant, the force on the spool valve reverses.  If this reversal was long enough, the poppet valve will close again.  Now you have a situation where the low pressure switch can become pressurized, with the gear not deployed.  Oftentimes the gear will not get stuck, but a very slight hesitation is noticed after selecting down.  What is observed in the system is a pressure spike in the low side an instant after the poppet valve is opened by the spool valve.  If the spike is high enough, the pump stops thinking that the gear is down.  Note that all this happens extremely fast such that you may never actually know wether or not the pump came on at all.  This spike happens to some degree on every gear extension.  This can be observed in the cockpit if pressure gauges are installed (which I highly recommend doing)  Whether or not the gear will actually get stuck depends on many variables acting in together.
Chris
 
 
 
Chris Zavatson
N91CZ
360std
www.N91CZ.com


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