X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from poplet2.per.eftel.com ([203.24.100.45] verified) by logan.com (CommuniGate Pro SMTP 5.3.7) with ESMTP id 4340785 for flyrotary@lancaironline.net; Tue, 08 Jun 2010 18:01:45 -0400 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from sv1-1.aanet.com.au (mail.aanet.com.au [203.24.100.34]) by poplet2.per.eftel.com (Postfix) with ESMTP id CF4D417369E for ; Wed, 9 Jun 2010 06:01:08 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by sv1-1.aanet.com.au (Postfix) with SMTP id 13686BEC030 for ; Wed, 9 Jun 2010 06:01:03 +0800 (WST) Message-ID: From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: high/low pressure pumps question Date: Wed, 9 Jun 2010 08:01:06 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000D_01CB07A9.EA064CE0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5931 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5931 X-Antivirus: avast! (VPS 100608-1, 06/08/2010), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_000D_01CB07A9.EA064CE0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Steve, How would you assume the small fuel radiator (before header tank) = would work in the circumstances you describe. George (down under)=20 In the reference provided by Ed, there is mention of the fuel = temperature being monitored to allow compensation for changes in fuel = viscosity with changes in temperature. The ECU might be changing = injector pulse width in response to the fuel temperature rather than = changing the fuel pressure in an attempt to avoid vapor lock. When I first assembled my fuel system, I put a section of glass tubing = in the return line after the pressure regulator. I did this because I = saw bubbles in the fuel being returned to the tank and assumed that = there was an air leak somewhere in the system, most likely in the = suction section between the tank and the pumps. I never found an air = leak after many hours of searching. The bubbles I saw were air bubbles = that separated from the fuel during the rapid pressure drop through the = regulator. The formation of the air bubbles takes place quickly whereas = the dissolution back into the fuel is much slower. The solubility of = air in fuel is much greater than the solubility of air in water, and we = all have seen the air bubbles that form on the walls a container of = water as it warms up and the solubility decreases. When returning the = fuel to the tank, eventually the air would be purged from the liquid = fuel and out the vent. I observed the elimination of the air bubbles in = the return line after about 10 minutes of recurculation when using a = vented fuel tank of only a gallon in volume. I don't know how long this = would take in the case of a large wing tank. Returning the fuel from the regulator to the supply line orto a small = header tank feeding the fuel pumps seems to me to have the potential for = problems in at least three ways: 1) from increasing fuel vapor pressure = as temperature rises, 2) decreased solubility of air in the fuel as = temperature rises, 3) the accumulation of air as a result of the = formation of air bubbles in the pressure regulator which occurs even = without an increase in temperature. All of these things could = contribute to vapor lock. =20 These are just my observations. There is also the indisputable = observation of the success of Ed's system for many years of operation. Steve Boese=20 RV6A, 1986 13B NA, RD1A, EC2 -------------------------------------------------------------------------= ----- From: Rotary motors in aircraft [flyrotary@lancaironline.net] On = Behalf Of Al Wick [alwick@juno.com] Sent: Tuesday, June 08, 2010 8:59 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: high/low pressure pumps question Hi Ed. You often make significant contributions that help improve = flight safety. If you share your fuel design, at least do the = calculations and let users know how close this is to vapor lock. We're = talking about life risk here. You are glossing over my point and = changing the topic. Returning fuel to pump inlet is very risky and = should not be done unless you desire to operate on the threshold of = vapor lock. I agree, there is one exception. That's if you have one of the new = fuel pump controllers that measures fuel parameters and alters pump = speed. I looked into that one years ago. Talk about added complexity! On with the good stuff! -al wick ------=_NextPart_000_000D_01CB07A9.EA064CE0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
Steve,
How would you assume the small fuel = radiator=20 (before header tank) would work in the circumstances you = describe.
George (down under) 
 
In the reference provided by Ed, there is mention of the fuel = temperature=20 being monitored to allow compensation for changes in fuel viscosity = with=20 changes in temperature.  The = ECU might be=20 changing injector pulse width in response to the fuel temperature = rather than=20 changing the fuel pressure in an attempt to avoid vapor lock.
 
When I first assembled my fuel = system, I put a=20 section of glass tubing in the return line after the pressure = regulator. =20 I did this because I saw bubbles in the fuel being returned to the = tank and=20 assumed that there was an air leak somewhere in the system, most = likely in the=20 suction section between the tank and the pumps.  I never found an = air=20 leak after many hours of searching.  The bubbles I saw were air = bubbles=20 that separated from the fuel during the rapid pressure drop through = the=20 regulator.  The formation of the air bubbles takes place quickly = whereas=20 the dissolution back into the fuel is much slower.  The = solubility of air=20 in fuel is much greater than the solubility of air in water, and we = all have=20 seen the air bubbles that form on the walls a container of = water as=20 it warms up and the solubility decreases.  When returning the = fuel to the=20 tank, eventually the air would be purged from the liquid fuel and out = the=20 vent.  I observed the elimination of the air bubbles in the = return line=20 after about 10 minutes of recurculation when using a vented fuel tank = of only=20 a gallon in volume.  I don't know how long this would take in the = case of=20 a large wing tank.
 
Returning the = fuel from the=20 regulator to the supply line orto a small header tank feeding the fuel = pumps=20 seems to me to have the potential for problems in at least three=20 ways: 1)  from increasing fuel vapor pressure as temperature = rises,  2)  decreased solubility of air in the fuel as = temperature=20 rises,  3)  the accumulation of air as a result of the = formation of=20 air bubbles in the pressure regulator which occurs even without an = increase in=20 temperature.  All of these things could contribute to vapor = lock. =20
 
These are just = my=20 observations.  There is also the indisputable observation = of the=20 success of Ed's system for many years of operation.
 
Steve = Boese=20
RV6A, 1986 13B NA, RD1A,=20 EC2
 
From: Rotary = motors in aircraft=20 [flyrotary@lancaironline.net] On Behalf Of Al Wick=20 [alwick@juno.com]
Sent: Tuesday, June 08, 2010 8:59 = AM
To:=20 Rotary motors in aircraft
Subject: [FlyRotary] Re: high/low = pressure=20 pumps question

Hi Ed. You often make significant = contributions=20 that help improve flight safety. If you share your fuel design, at = least do=20 the calculations and let users know how close this is to vapor lock. = We're=20 talking about life risk here. You are glossing over my point and = changing the=20 topic. Returning fuel to pump inlet is very risky and should not be = done=20 unless you desire to operate on the threshold of vapor = lock.
 
I agree, there is one exception. = That's if you=20 have one of the new fuel pump controllers that measures fuel = parameters=20 and alters pump speed. I looked into that one years ago. Talk about = added=20 complexity!
 
On with the good stuff!
 
-al wick
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