X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sun, 09 Sep 2012 21:50:20 -0400 Message-ID: X-Original-Return-Path: Received: from nm23-vm3.bullet.mail.ne1.yahoo.com ([98.138.91.153] verified) by logan.com (CommuniGate Pro SMTP 6.0c1) with SMTP id 5752566 for lml@lancaironline.net; Sun, 09 Sep 2012 15:02:26 -0400 Received-SPF: none receiver=logan.com; client-ip=98.138.91.153; envelope-from=chris_zavatson@yahoo.com Received: from [98.138.226.177] by nm23.bullet.mail.ne1.yahoo.com with NNFMP; 09 Sep 2012 19:01:50 -0000 Received: from [98.138.87.4] by tm12.bullet.mail.ne1.yahoo.com with NNFMP; 09 Sep 2012 19:01:50 -0000 Received: from [127.0.0.1] by omp1004.mail.ne1.yahoo.com with NNFMP; 09 Sep 2012 19:01:50 -0000 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 200631.11687.bm@omp1004.mail.ne1.yahoo.com Received: (qmail 49768 invoked by uid 60001); 9 Sep 2012 19:01:50 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; 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Sun, 09 Sep 2012 12:01:49 PDT X-Mailer: YahooMailWebService/0.8.121.416 References: X-Original-Message-ID: <1347217309.49605.YahooMailNeo@web121605.mail.ne1.yahoo.com> X-Original-Date: Sun, 9 Sep 2012 12:01:49 -0700 (PDT) From: Chris Zavatson Reply-To: Chris Zavatson Subject: Re: [LML] Re: Accumulators X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="2053635335-97691264-1347217309=:49605" --2053635335-97691264-1347217309=:49605 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Jim,=0AI forgot to add this caution.=C2=A0 If the accumulator volume is gre= ater than the rod-volume of the cylinders it can interfere with the free-fa= ll emergency gear extension.=0AChris=0A=C2=A0=0AChris Zavatson=0AN91CZ=0A36= 0std=0Awww.N91CZ.net=0A=0AFrom: Chris Zavatson = =0ATo: lml@lancaironline.net =0ASent: Saturday, September 8, 2012 3:22 PM= =0ASubject: [LML] Re: Accumulators=0A=0A=0AJim,=0AI like the idea of accumu= lators and tried to incorporate them into the system back in about =E2=80= =9999.=C2=A0 My motivation wasn=E2=80=99t for the thermal expansion issue.= =C2=A0 Rather, I was trying to add some system tolerance for small internal= leaks.=C2=A0=C2=A0 Unfortunately, failure analysis revealed two unacceptab= le failure modes that didn=E2=80=99t have a simple solution and so I shelve= d the idea.=C2=A0 Accumulators work by using a gas charge separated by a pi= ston or bladder.=C2=A0 The first and more critical failure mode was if the = accumulator seal failed while the aircraft was parked on the ground.=C2=A0 = It could unlock and collapse the gear.=C2=A0 =E2=80=93small probability of = occurrence, but catastrophic consequence.=C2=A0 Possible mitigation options= were to disconnect or isolate the =E2=80=98up-circuit=E2=80=99 accumulator= when on the ground or to pin the gear in the down and locked position.=C2= =A0 =E2=80=93like the big boys do.=C2=A0=C2=A0=C2=A0=C2=A0 =0AThe second is= sue comes from the stored energy in the accumulator.=C2=A0 The added potent= ial energy released upon selecting gear-down would contribute to the =E2=80= =9Cextension failure lock-up mode=E2=80=9D by overwhelming the return side = of the pump.=C2=A0 The accumulator will increase the pressure pulse that pr= opagates through the system. =0APage 10 has more detail: http://www.n91cz.c= om/Hydraulics/Lancair%20Hydraulics.pdf=0AThis issue could potentially be mi= tigated by one-way flow restrictor out of the accumulator or by perhaps inc= reasing the down-side operating pressure substantially.=C2=A0 I didn=E2=80= =99t investigate these options because I was still stuck on issue one above= .=0AA number of other options were explored using mechanical energy storage= via heavy springs and pistons that would return to a zero energy state whe= n not in use. =C2=A0=C2=A0All had their drawbacks, size, weight, cost, etc.= =C2=A0Some were theoretically possible though and could be revisited.=C2= =A0=C2=A0=C2=A0 =0AAdjusting the =E2=80=9Cnon-adjustable=E2=80=9D thermal r= elief valves solves the thermal expansion issue, but not the leak sensitivi= ty, so the concept is certainly worth exploring further. The important thin= g is to analytically explore all operating and, in particular, off nominal = failure modes to discover undesirable side effects on paper rather in the p= lane. =C2=A0=C2=A0Unfortunately it is very easy to fix one problem and in t= he process introduce another.=C2=A0 Let me know if you would like to discus= s further.=0AChris=0A=C2=A0=0AChris Zavatson=0AN91CZ=0A360std=0Ahttp://www.= n91cz.net/=0A=0A=0AFrom: Jim Nordin =0ATo: lml@la= ncaironline.net =0ASent: Friday, September 7, 2012 5:10 AM=0ASubject: [LML]= Accumulators=0A=0A=0AI want to employ an accumulator after reading all abo= ut the problems. So I figured someone would know what size to use on the we= e little 320 hydraulic system. =0AI went to the internet to see if there wa= s a formula for doing such. And there is:=0A=C2=A0=0Ahttp://www.accumulator= s.com/sizing.html =0A=C2=A0=0AOf course somebody must know the volume in th= e system. Does anybody know that? My guess is between .15 gallons and .2 ga= llons (19-25 ounces). If this is close the accumulator of 3-7 in3 might be = close too.=0AThe temperature ranges are 10=C2=BAF to 160=C2=BAF (too high I= =E2=80=99m sure). Max pressure 2,000psi initial of 500psi. If the initial p= ressure is 1,000psi or so, the vol of the accumulator rises to about 10 in3= . =0ACan somebody help please? Comments?=0AJim=0A=C2=A0=0A=0A=0A--=0AFor ar= chives and unsub http://mail.lancaironline.net:81/lists/lml/List.html --2053635335-97691264-1347217309=:49605 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Jim,
I forgot to add this= caution.  If the accumulator volume is greater than the rod-volume of= the cylinders it can interfere with the free-fall emergency gear extension= .
Chris
 
Chris Zavatson
N91CZ
360std

From:= Chris Zavatson <chris_zavatson@yahoo.com>
To: lml@lancaironline.net
Sent: Saturday, September 8, 2012 3:= 22 PM
Subject: [LML] Re:= Accumulators

Jim,
I like the idea of accumulato= rs and tried to incorporate them into the system back in about =E2=80=9999.=   My motivation wasn=E2=80=99t for the thermal expansion = issue.  Rather, I was trying to add some system tolerance= for small internal leaks.   Unfortunately, failure = analysis revealed two unacceptable failure modes that didn=E2=80=99t have a= simple solution and so I shelved the idea.  Accumulators= work by using a gas charge separated by a piston or bladder.  <= /SPAN>The first and more critical failure mode was if the accumulator seal = failed while the aircraft was parked on the ground.  It c= ould unlock and collapse the gear.  =E2=80=93small probability of occurrence, but catastrophic consequence.  Possible mitigation options were to disconnect or isolate the =E2=80=98up= -circuit=E2=80=99 accumulator when on the ground or to pin the gear in the = down and locked position.  =E2=80=93like the big boys do.=     
The second issue comes from = the stored energy in the accumulator.  The added potentia= l energy released upon selecting gear-down would contribute to the =E2=80= =9Cextension failure lock-up mode=E2=80=9D by overwhelming the return side = of the pump.  The accumulator will increase the pressure = pulse that propagates through the system.
Page 10 has more detail: http://www.n91cz.com/Hydraulics/Lancai= r%20Hydraulics.pdf
This issue could potentially= be mitigated by one-way flow restrictor out of the accumulator or by perha= ps increasing the down-side operating pressure substantially.  <= /SPAN>I didn=E2=80=99t investigate these options because I was still stuck = on issue one above.
A number of other options wer= e explored using mechanical energy storage via heavy springs and pistons th= at would return to a zero energy state when not in use.   <= /SPAN>All had their drawbacks, size, weight, cost, etc.  = Some were theoretically possible though and could be revisited.  =  
Adjusting the =E2=80= =9Cnon-adjustable=E2=80=9D thermal relief valves solves the thermal expansi= on issue, but not the leak sensitivity, so the concept = is certainly worth exploring further. The important thing is = to analytically explore all operating and, in particular, off nominal failu= re modes to discover undesirable side effects on paper rather in the plane.=   Unfortu= nately it is very easy to fix one problem and in the process introduce anot= her.  Let me know if you would like to discuss further.
Chris
 
Chris Zavatson
N91CZ
360std

From: Jim Nordin <panel= maker@earthlink.net>
To:<= /B> lml@lancaironline.net
Sent: Friday, September 7, 2012 5:10 AM
Subject: [LML] Accumulators

I want to employ an accumulator after reading= all about the problems. So I figured someone would know what size to use o= n the wee little 320 hydraulic system.
I went to the internet to see if= there was a formula for doing such. And there is:
 
http://www.accumulators.com/sizing.html
&n= bsp;
Of course somebody must know the volume in th= e system. Does anybody know that? My guess is between .15 gallons and .2 ga= llons (19-25 ounces). If this is close the accumulator of 3-7 in3 might be close too.
The temperature ranges are 10=C2=BAF to 160= =C2=BAF (too high I=E2=80=99m sure). Max pressure 2,000psi initial of 500ps= i. If the initial pressure is 1,000psi or so, the vol of the accumulator ri= ses to about 10 in3<= /B>.
Can somebody help please? Comments?
Jim
&n= bsp;


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For archives and unsub http://mail.lancaironline.net:81/lists= /lml/List.html


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