X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao03.cox.net ([68.230.241.36] verified) by logan.com (CommuniGate Pro SMTP 4.3.4) with ESMTP id 1000321 for flyrotary@lancaironline.net; Mon, 13 Jun 2005 11:48:44 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.36; envelope-from=ALVentures@cox.net Received: from BigAl ([68.7.14.39]) by fed1rmmtao03.cox.net (InterMail vM.6.01.04.00 201-2131-118-20041027) with ESMTP id <20050613154757.GIBA26972.fed1rmmtao03.cox.net@BigAl> for ; Mon, 13 Jun 2005 11:47:57 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: Fuel System Date: Mon, 13 Jun 2005 08:48:07 -0700 Message-ID: <000001c5702f$4b520f10$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C56FF4.9EF5A810" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C56FF4.9EF5A810 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Do you have a number that represents a minimum head pressure to prevent vapour lock, some suggestions for a filter and the pressure altitude I should limit my flying to =20 Ian; =20 I know you asked this of the =93other=94 Al, but here=92s my $.02 worth. =20 We know that there are fractions in auto fuel that have (partial) vapor pressures at ambient conditions that are =BD - 2/3 of atmospheric = (absolute). This suggests that we don=92t have to draw the pressure down very far = below atmospheric (negative gauge pressure, psig) for incipient bubble = formation. And as temp goes up, or our altitude goes up, the margin decreases. So reiterating what Leon pointed out, we should have a system which = maintains some positive gauge pressure at the pump inlet; enough so even at = altitude we have a something around zero guage or better. =20 Remember, we are talking =91at the pump inlet=92. If you have some = line, and/or some filtering before the pump, that loss has to be accounted for. I = have about 18=94 of level 3/8 line from the bottom of my sump tank to the = pump, so I want a minimum of about 1 ft head of fuel to the pump inlet (that=92s = only about 0.5 psig) when I=92m down to that last gallon of gas (which should = never happen except when I=92m testing on the ground). I=92ll have over 2 ft = of head with full tanks. Generally something less than could be OK, but we want margin for those hot days, time on the taxiway; whatever. =20 BTW; speaking of the other Al, Al Wicks, I would only comment that statistical failure analysis requires statistically significant numbers = of cases, which for much of what we are doing doesn=92t exist. But there = were good points buried in there about determining root causes; and measuring and/or calculating whatever unproven aspects we can to verify function = PRIOR to taking to the air. It was disappointing to see rude and even vulgar remarks here. We can look for what can be of value and either ignore, = our simple say we disagree and why, for stuff we don=92t agree with. =20 Al G. ------=_NextPart_000_0001_01C56FF4.9EF5A810 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message

Do you have a number that = represents a minimum head pressure to prevent vapour lock, some suggestions for a = filter and the pressure altitude I should limit my flying to

 

Ian;

 

I know you asked this of the = “other” Al, but here’s my $.02 worth.

 

We know that there are fractions = in auto fuel that have (partial) vapor pressures at ambient conditions that are = =BD - 2/3 of atmospheric (absolute). =A0This suggests that we don’t have to = draw the pressure down very far below atmospheric (negative gauge pressure, psig) = for incipient bubble formation. And as temp goes up, or our altitude goes = up, the margin decreases.=A0 So reiterating what Leon pointed out, we should have a system which maintains some = positive gauge pressure at the pump inlet; enough so even at altitude we have a = something around zero guage or better.

 

Remember, we are talking = ‘at the pump inlet’.=A0 If you have some line, and/or some filtering = before the pump, that loss has to be accounted for.=A0 I have about 18” of = level 3/8 line from the bottom of my sump tank to the pump, so I want a minimum of = about 1 ft head of fuel to the pump inlet (that’s only about 0.5 psig) = when I’m down to that last gallon of gas (which should never happen except when = I’m testing on the ground). =A0I’ll have over 2 ft of head with full = tanks.=A0 Generally something less than could be OK, but we want margin for those hot days, = time on the taxiway; whatever.

 

BTW; speaking of the other Al, Al = Wicks, I would only comment that statistical failure analysis requires = statistically significant numbers of cases, which for much of what we are doing = doesn’t exist.=A0 But there were good points buried in there about determining = root causes; and measuring and/or calculating whatever unproven aspects we = can to verify function PRIOR to taking to the air.=A0 It was disappointing to = see rude and even vulgar remarks here. =A0We can look for what can be of value = and either ignore, our simple say we disagree and why, for stuff we don’t agree = with.

 

Al G.

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