X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 05 Nov 2007 14:59:52 -0500 Message-ID: X-Original-Return-Path: Received: from dmzmta101.na.baesystems.com ([149.32.252.101] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTPS id 2456969 for lml@lancaironline.net; Mon, 05 Nov 2007 14:43:13 -0500 Received-SPF: none receiver=logan.com; client-ip=149.32.252.101; envelope-from=Christopher.Zavatson@baesystems.com Received: from BLUMS0035.bluelnk.net (blums0035.bluelnk.net [10.40.96.56]) by dmzmta101.na.baesystems.com (Switch-3.2.5/Switch-3.2.5) with ESMTP id lA5JemLL012555 for ; Mon, 5 Nov 2007 14:40:50 -0500 Received: from usdmta002.na.baesystems.com ([10.40.96.58]) by BLUMS0035.bluelnk.net with InterScan Message Security Suite; Mon, 05 Nov 2007 14:42:31 -0500 Received: from GLDMS00005.goldlnk.rootlnka.net ([10.44.64.11]) by usdmta002.na.baesystems.com (Switch-3.2.5/Switch-3.2.5) with ESMTP id lA5Jfs4k014661 for ; Mon, 5 Nov 2007 14:41:56 -0500 Received: from gldms10602.goldlnk.rootlnka.net ([10.64.39.19]) by GLDMS00005.goldlnk.rootlnka.net with Microsoft SMTPSVC(6.0.3790.3959); Mon, 5 Nov 2007 14:42:29 -0500 Received: from GLDMS10607.goldlnk.rootlnka.net ([10.64.39.20]) by gldms10602.goldlnk.rootlnka.net with Microsoft SMTPSVC(6.0.3790.1830); Mon, 5 Nov 2007 11:42:28 -0800 X-MimeOLE: Produced By Microsoft Exchange V6.5 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C81FE3.FEC4A06D" Subject: RE: [LML] LNC2 Hyd Chirp Tim/ Joe/ Brent Question X-Original-Date: Mon, 5 Nov 2007 11:42:27 -0800 X-Original-Message-ID: In-Reply-To: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [LML] LNC2 Hyd Chirp Tim/ Joe/ Brent Question Thread-Index: AcgfxFFm2U3hbFXERfG500xUBWkJeAAGPaEw References: From: "Zavatson, Christopher J (US SSA)" X-Original-To: "Lancair Mailing List" X-OriginalArrivalTime: 05 Nov 2007 19:42:28.0121 (UTC) FILETIME=[FF4B2090:01C81FE3] This is a multi-part message in MIME format. ------_=_NextPart_001_01C81FE3.FEC4A06D Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Larry, All is normal here. =20 <> =20 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 =20 =20 =20 Chris Zavatson N91CZ 360std www.N91CZ.com ------_=_NextPart_001_01C81FE3.FEC4A06D Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable
Larry,
All is=20 normal here.
 
<<On the secret = switch=20 note, I am one of those High pressure leaks to Low pressure side and = sets low=20 pressure switch guys (after some duration + 1 hr).  The opening of = the dump=20 valve, after the switch down does nothing, allows pressure off the low = pressure=20 switch and fires up the pump.  That’s why I keep going back = to the shuttle=20 valve test.  I find mine (once reversed) now in correctly.  = The idea=20 that both switches are set and anyone  CAN NOT get gear extension = is beyond=20 my fathom ability (ok, maybe the dump valve handle could fall = off).  In=20 other words, if the fluid is leaking to the low pressure side, then why = do it=20 not depressurize through the shuttle valve?  The pump would have = been in=20 the ……  (I don’t know?)??? BdBdBdBdBd (finger = lapping against flapping=20 lips)>>
 
I have looked at this = in some=20 detail and the phenomenon is quite reproducible.  Our gear = hydraulics have=20 a few unique design aspects that allow this gear extension problem to=20 occur.  BTW, I am curious if you have pressure gauges so you see = what is=20 happening during these events.  It really has nothing to do with = leaks from=20 high to low as the low side is vented to the reservoir while in = flight.  In=20 my plane, I can almost predict when the gear will refuse to come down = before I=20 hit the switch.  If I descend from very high and cold altitudes = into warmer=20 air the hydraulic pressure rises.  Sometimes even as high as 1,800=20 psi while the low side remains at zero.  All system pressure = is held=20 back by a poppet valve that is pushed off its seat by the spool = valve.  The=20 spool valve is moved via fluid pressure, most often that generated by = the pump=20 motor.  Here though we have unique situation.  With the gear = stowed in=20 the wells we have loaded and cocked three fluid pumps ready to push = fluid back=20 to the pump.  Here is the scenario.  You select gear = down.  The=20 pump starts to turn building pressure internally.  This pushes the = spool=20 valve against the poppet valve.  Now a torrent of pressurized fluid = rushes=20 in.  Remember this fluid is also pressurized by gravity acting much = like an=20 acculmulator with gas pressure.  It will maintain some = level of=20 hydraulic pressure over time while fluid is leaving the=20 system.  We therefore do not see an instant loss of=20 pressure.  The pump cannot remove fluid as fast as the landing gear = is=20 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=20 again.  Now you have a situation where the low pressure = switch can=20 become pressurized, with the gear not deployed.  Oftentimes = the gear=20 will not get stuck, but a very slight hesitation is noticed after = selecting=20 down.  What is observed in the system is a pressure spike in = the low=20 side an instant after the poppet valve is opened by the spool = valve.  If=20 the spike is high enough, the pump stops thinking that the gear is = down. =20 Note that all this happens extremely fast such that you may never = actually know=20 wether or not the pump came on at all.  This spike happens to some = degree=20 on every gear extension.  This can be observed in the cockpit = if=20 pressure gauges are installed (which I highly recommend doing)  = Whether or=20 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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