X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 06 May 2014 12:38:22 -0400 Message-ID: X-Original-Return-Path: Received: from [107.14.166.226] (HELO cdptpa-oedge-vip.email.rr.com) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTP id 6860981 for lml@lancaironline.net; Tue, 06 May 2014 12:22:24 -0400 Received-SPF: none receiver=logan.com; client-ip=107.14.166.226; envelope-from=Wolfgang@MiCom.net X-Original-Return-Path: Received: from [74.218.201.50] ([74.218.201.50:3479] helo=lobo) by cdptpa-oedge01 (envelope-from ) (ecelerity 3.5.0.35861 r(Momo-dev:tip)) with ESMTP id 7C/F8-16163-F1C09635; Tue, 06 May 2014 16:21:51 +0000 X-Original-Message-ID: <8C361629041546EDBFD428FDB4D0A607@lobo> From: "Wolfgang" X-Original-To: "Chris Zavatson" , References: Subject: Re: [LML] Re: Gear Down...INOP X-Original-Date: Tue, 6 May 2014 12:21:53 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0151_01CF6925.C3A1C8E0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5512 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5512 X-RR-Connecting-IP: 107.14.168.118:25 X-Cloudmark-Score: 0 This is a multi-part message in MIME format. ------=_NextPart_000_0151_01CF6925.C3A1C8E0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Chris, you are clearly pationate about what you do but I still say here = you're not the only, let alone the final answer. I think it improper and do not appreciate you make assumptions on what = others have experienced without first hand knowledge (Lorn) and what I = have or not said in the past (You had asked what their purpose was.) As I have said before, you go to great lengths to support yourself but = give only passing support to the "other side". This is "fair and = balanced" ? Wolfgang ----- Original Message -----=20 From: Chris Zavatson=20 Sent: Monday, May 05, 2014 7:14 AM Subject: Re: [LML] Re: Gear Down...INOP Wolfgang, The concept I have trying to describe here and in my hydraulics = write-up is nothing new. It is however difficult, if not impossible, to = identify without instrumentation. Most often this phenomenon simply = causes what is perceived as a hesitation during gear extension. Sort of = a quick Start-Stop-Start with the gear continuing all the way down. It = becomes quite clear what is happening if one looks at the system = pressures when gear-down is selected. Analog gauges are best for = catching the interaction. What you=EF=BF=BDll see is a pressure pulse = just as the gear starts to fall. The magnitude of the pulse is made = greater by a few factors: =20 1.. Warm/hot hydraulic fluid (lower viscosity) 2.. Outback gear (adds gear down force) 3.. High-side pressure well above nominal (descending into = significantly warmer air) 4.. Original, lower volume gear pump When the landing gear is in the retracted position, it stores a lot of = potential energy. This is from the mass of the landing gear, the = pressure on the high side circuit and, with the outback gear, the aero = loads trying to pull the gear down. It is useful to look at Figures 9 and 10 in the hydraulics write-up = when trying understand the chain of events. =20 http://www.n91cz.com/Hydraulics/Lancair%20Hydraulics.pdf In Figure 9, you=EF=BF=BDll see state of the pump while the gear is = retracted. When beginning the extension cycle, the pump builds up = pressure behind the spool (right side) and pushes it against the poppet = valve on the left as seen in Figure 10. Opening the high side poppet = valve opens a path for fluid from the high side circuit to return back = to the pump. It is not just the pump moving fluid though. All the = stored energy in the system is released and the falling gear, now also = pushing fluid back to the pump. Given the fixed volume nature of the = gear pump, it can only absorb fluid at a certain rate. If the gear = pushes the fluid back faster than the pump can absorb it, back pressure = builds up in the high side circuit. With enough back pressure the spool = is pushed back to the right. As this happens, the high side poppet = starts to close off again. Pressure begins to rise and propagates = backwards through the system. As soon as the low side pressure rises = above the pressure switch set point, the pump is shuts down. =20 Most of the time, the shut-down is momentary. This is because the = pump takes time to spool down and it is still moving fluid as it does = so. At the same time, the falling gear is losing energy. If the = pressure spike was small, the pump side will win, the spool will again = open the poppet all the way and the gear comes down. If the spike was = large, the pump will remain off and you will see equal pressure in the = high and low side, just like in Lorn=EF=BF=BDs photo. Pressure will be = just above the set-point of the low side pressure switch and the gear = will be partially extended. Mitigation simply involves raising the low = side pressure set-point so that the pressure spike can no longer affect = the switch and pump. I really don=EF=BF=BDt expect you to be convinced. I post these = details for the benefit everyone. For many years now, I have been publishing all kinds of reports, = studies, diagrams, maintenance guides and videos of Lancair systems is = to promote a better understanding and safe operation of the LNC2. If I = have made errors somewhere, please point them out. But don=EF=BF=BDt = just say it is wrong or that you don=EF=BF=BDt agree. Please provide = some legitimate, logical reasoning, some data or something that makes = the point. =20 To be honest, I found many of your posts to be a bit worrisome. They = left me with the impression you did not have a full understanding of the = pump operating environment or its operation.=20 For example, when discussing spool movement, you claimed the pump = could be subjected to 70 g=EF=BF=BDs. The actual environment is much = more benign. Vibration peaks are more on the order of 0.1 G=EF=BF=BDs. = Below is a link to a vibration study that looks at airframe vibration = in different phases of flight. The study was done while looking into an = engine isolator issue, but is a useful environmental baseline for = anything mounted to the structure. =20 http://www.n91cz.net/Vibration/Vibration_Summary.pdf Another example was a question regarding the ball and spring in the = return line. You had asked what their purpose was. This would normally = a very legitimate question. My concern was that you had already = designed a circuit to alter pump operation without being aware of or = understanding the function of all the internal parts.=20 Innovation is a good thing, but on an aircraft the level of required = due diligence is quite high. Lorn=EF=BF=BDs pump definitely had issues. Mounting the pump behind = the baggage bulkhead is not ideal. It discourages good maintenance = practices, just as it did in this case. Being unwilling to remove it = from the aircraft to investigate the internals because it was = =EF=BF=BDso hard to get to=EF=BF=BD simply makes it impossible to = properly investigate a problem. When I offered to examine the pump, the = response was that these airplanes were built to fly and two weeks of = down-time was too much of a burden. That was unfortunate. Based on = Lorn=EF=BF=BDs description of the pumps behavior I strongly suspected = the root cause of its problems would have been immediately obvious upon = examination. I have disassembled more pumps that I can remember. All = were made to operate normally once configured and adjusted correctly. =20 Chris Zavatson N91CZ 360std www.N91CZ.net On Monday, April 28, 2014 4:59 AM, Wolfgang = wrote: Chris, I remain unconvinced with your theory. You have suggested that the = pump will somehow shut down immediately after it has started up due to = some pressure pulse. The mechanisim of which you have yet to clarify, = let alone demonstrated. I'm tired of your kibitzing and since you have proven that you can't = let it go, I will and leave you to humor yourself. Wolfgang ----- Original Message -----=20 From: Chris Zavatson=20 To: lml@lancaironline.net=20 Sent: Saturday, April 26, 2014 1:28 PM Subject: Gear Down...INOP Wolfgang, <<=EF=BF=BDI believe in redundancy and it looks like you = don't=EF=BF=BD.=EF=BF=BD>> I am a big proponent of redundancy. That is redundancy defined as a = true back-up to an otherwise trouble-free system. First, I have redundant switches to power the pump solenoids. This = allows me to raise and lower the gear in case of the failure of either = of the pressure switches. It doesn=EF=BF=BDt happen very often, but it = does happen - twice in 17 years of flying my 360. =20 I also have redundant gear down indications. Two completely = separate systems, separate switches, separate wires and separate = indicators. The second set of switches is mounted directly on the = over-center links.=20 I even carry two iPads and a iPhone - just in case <<=EF=BF=BDThe pressure pulse you're talking about will subside = (glad you agree) and as it does, because the cylinder is only partially = extended, the cylinder will continues to extend, the low switch will = close again, and enable the pump to continue . .=EF=BF=BD>> The part you seem to be missing here is that the momentary pulse is = not directly turning off the pump. Thus when the pulse subsides, the = pump doesn=EF=BF=BDt just spring back to life. The pulse pushes the = spool in the wrong direction -against the pump flow. This locks the = poppet that the pump just opened up a fraction of a second earlier. = When this happens, the high side begins to pressurize along with the low = side. As soon as both sides reach the low side pressure setting, the = pump is turned off. This is why you see both high and low circuits = pressurized to the same value in Lorn=EF=BF=BDs photo. To prevent this, the low side pressure settings should be raised. = 800 psi has proven sufficient. The high volume gear pump will reduce = the size of the pulse since the higher volume pump is able to absorb = incoming fluid at a higher rate. I highly recommend pressure gauges for both high and low circuit be = installed in a location visible to the pilot. The state of the system = can always be verified. One can immediately diagnose any in-flight = problem. Leaks can be caught early. And adjusting pressure settings is = no longer guess work. Chris Zavatson N91CZ 360std www.N91CZ.net ------=_NextPart_000_0151_01CF6925.C3A1C8E0 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable =EF=BB=BF
Chris, you are clearly pationate about = what you do=20 but I still say here you're not the only, let alone the final=20 answer.
 
I think it improper and do not = appreciate you make=20 assumptions on what others have experienced without first hand knowledge = (Lorn)=20 and what I have or not said in the past (You had asked what their = purpose=20 was.)
 
As I have said before, you go to great = lengths to=20 support yourself but give only passing support to the "other side". This = is=20 "fair and balanced" ?
 
Wolfgang
 
----- Original Message -----
From:=20 Chris=20 Zavatson
Sent: Monday, May 05, 2014 7:14 = AM
Subject: Re: [LML] Re: Gear=20 Down...INOP

Wolfgang,
The = concept I have=20 trying to describe here and in my hydraulics write-up is nothing = new.  It is however difficult, if = not=20 impossible, to identify without instrumentation.  Most often this phenomenon = simply=20 causes what is perceived as a hesitation during gear extension.  Sort of a quick = Start-Stop-Start with=20 the gear continuing all the way down.  It becomes quite clear what = is=20 happening if one looks at the system pressures when gear-down is=20 selected.  Analog gauges = are best=20 for catching the interaction. =20 What you=EF=BF=BDll see is a pressure pulse just as the gear = starts to=20 fall.  The magnitude of = the pulse=20 is made greater by a few factors: =20
  1. Warm/hot = hydraulic=20 fluid (lower viscosity)
  2. Outback = gear (adds=20 gear down force)
  3. High-side = pressure=20 well above nominal (descending into significantly warmer = air)
  4. Original, = lower volume=20 gear pump
When the landing gear = is in the=20 retracted position, it stores a lot of potential energy.  This is from the mass of the = landing=20 gear, the pressure on the high side circuit and, with the outback = gear, the=20 aero loads trying to pull the gear down.
It=20 is useful to look at Figures 9 and 10 in the hydraulics write-up when = trying=20 understand the chain of events. =20
http://www.n91cz.com/Hydraulics/Lancair%20Hydraulics.pdf
In = Figure 9,=20 you=EF=BF=BDll see state of the pump while the gear is retracted.  When beginning the extension = cycle,=20 the pump builds up pressure behind the spool (right side) and pushes = it=20 against the poppet valve on the left as seen in Figure 10.  Opening the high side poppet = valve=20 opens a path for fluid from the high side circuit to return back to = the=20 pump.  It is not just = the pump=20 moving fluid though.  = All the=20 stored energy in the system is released and the falling gear, now also = pushing=20 fluid back to the pump.  = Given the=20 fixed volume nature of the gear pump, it can only absorb fluid at a = certain=20 rate.  If the gear = pushes the=20 fluid back faster than the pump can absorb it, back pressure builds up = in the=20 high side circuit.  With = enough=20 back pressure the spool is pushed back to the right.   As this happens, the = high side=20 poppet starts to close off again. =20 Pressure begins to rise and propagates backwards through the=20 system.  As soon as the = low side=20 pressure rises above the pressure switch set point, the pump is shuts=20 down. =20
Most of the time, the = shut-down=20 is momentary.  This is = because the=20 pump takes time to spool down and it is still moving fluid as it does = so.  At the same time, the = falling gear is=20 losing energy.  If the = pressure=20 spike was small, the pump side will win, the spool will again open the = poppet=20 all the way and the gear comes down. =20 If the spike was large, the pump will remain off and you will = see equal=20 pressure in the high and low side, just like in Lorn=EF=BF=BDs = photo.  Pressure will be just above = the=20 set-point of the low side pressure switch and the gear will be = partially=20 extended.  Mitigation = simply=20 involves raising the low side pressure set-point so that the pressure = spike=20 can no longer affect the switch and pump.
I really = don=EF=BF=BDt expect you to be=20 convinced.  I post these = details=20 for the benefit everyone.
For = many years=20 now, I have been publishing all kinds of reports, studies, diagrams,=20 maintenance guides and videos of Lancair systems is to promote a = better=20 understanding and safe operation of the LNC2.  If I have made errors = somewhere,=20 please point them out.  = But don=EF=BF=BDt=20 just say it is wrong or that you don=EF=BF=BDt agree. Please provide = some legitimate,=20 logical reasoning, some data or something that makes the point.  =
To be honest, I found = many of=20 your posts to be a bit worrisome. =20 They left me with the impression you did not have a full = understanding=20 of the pump operating environment or its operation.
For = example, when=20 discussing spool movement, you claimed the pump could be subjected to = 70 g=EF=BF=BDs.=20  The actual environment = is much=20 more benign.   = Vibration=20 peaks are more on the order of 0.1 G=EF=BF=BDs. =20 Below is a link to a vibration study that looks at airframe = vibration=20 in different phases of flight.  = The study was done while looking into an engine isolator issue, = but is=20 a useful environmental baseline for anything mounted to the = structure.   =20
http://www.= n91cz.net/Vibration/Vibration_Summary.pdf
Another example was a = question=20 regarding the ball and spring in the return line.  You had asked what their = purpose=20 was.  This would = normally a very=20 legitimate question.  My = concern=20 was that you had already designed a circuit to alter pump operation = without=20 being aware of or understanding the function of all the internal = parts.=20
Innovation is a good = thing, but=20 on an aircraft the level of required due diligence is quite = high.
Lorn=EF=BF=BDs pump=20 definitely had issues.  = Mounting=20 the pump behind the baggage bulkhead is not ideal. It discourages good = maintenance practices, just as it did in this case.  Being unwilling to remove it = from the=20 aircraft to investigate the internals because it was =EF=BF=BDso hard = to get to=EF=BF=BD=20 simply makes it impossible to properly investigate a problem.  When I offered to examine = the pump,=20 the response was that these airplanes were built to fly and two weeks = of=20 down-time was too much of a burden. =20 That was unfortunate.  = Based on=20 Lorn=EF=BF=BDs description of the pumps behavior I strongly = suspected the root=20 cause of its problems would have been immediately obvious upon=20 examination.  I have = disassembled=20 more pumps that I can remember. =20 All were made to operate normally once configured and adjusted=20 correctly. =20
Chris = Zavatson
N91CZ
360std
www.N91CZ.net
 
On Monday, April 28, 2014 = 4:59 AM,=20 Wolfgang <Wolfgang@MiCom.net> wrote:
Chris,
 
I remain unconvinced with your = theory. You have=20 suggested that the pump will somehow shut down immediately after it = has=20 started up due to some pressure pulse. The mechanisim of which you = have yet to=20 clarify, let alone demonstrated.
 
I'm tired of your kibitzing and since = you have=20 proven that you can't let it go, I will and leave you to humor=20 yourself.
 
Wolfgang
 
-----=20 Original Message -----
From:=20 Chris=20 Zavatson
To:=20 lml@lancaironline.net =
Sent:=20 Saturday, April 26, 2014 1:28 PM
Subject:=20 Gear Down...INOP

Wolfgang,

<<=EF=BF=BDI=20 believe in redundancy and it looks like you=20 don't=EF=BF=BD.=EF=BF=BD>>

I=20 am a big proponent of redundancy.  That is = redundancy=20 defined as a true back-up to an otherwise trouble-free=20 system.

First, I have redundant switches to power the pump=20 solenoids.  This allows me to raise and lower the = gear in=20 case of the failure of either of the pressure switches. =20 It doesn=EF=BF=BDt happen very often, but it does happen - = twice in 17 years=20 of flying my 360. 

I=20 also have redundant gear down indications.  Two = completely=20 separate systems, separate switches, separate wires and separate=20 indicators.  The second set of switches is mounted = directly on the over-center links.

I=20 even carry two iPads and a iPhone - just in case

<<=EF=BF=BDThe=20 pressure pulse you're talking about will subside (glad you agree) = and as it=20 does, because the cylinder is only partially extended, the = cylinder=20 will continues to extend, the low switch will close again, and = enable the=20 pump to continue . .=EF=BF=BD>>

The=20 part you seem to be missing here is that the momentary pulse is not = directly=20 turning off the pump.  Thus when the pulse = subsides, the=20 pump doesn=EF=BF=BDt just spring back to life.  = The pulse pushes=20 the spool in the wrong direction -against the pump flow.  = This locks the poppet that the pump just opened up a fraction = of a=20 second earlier.  When this happens, the high side = begins=20 to pressurize along with the low side.  As soon as = both=20 sides reach the low side pressure setting, the pump is turned=20 off.  This is why you see both high and low = circuits=20 pressurized to the same value in Lorn=EF=BF=BDs = photo.

To=20 prevent this, the low side pressure settings should be = raised. =20 800 psi has proven sufficient.  The high = volume=20 gear pump will reduce the size of the pulse since the higher volume = pump is=20 able to absorb incoming fluid at a higher rate.

I=20 highly recommend pressure gauges for both high and low circuit be = installed=20 in a location visible to the pilot.  The state of = the=20 system can always be verified.  One can = immediately=20 diagnose any in-flight problem.  Leaks can be = caught=20 early.  And adjusting pressure settings is no = longer guess=20 work.
Chris=20 Zavatson
N91CZ 360std www.N91CZ.net
=
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