X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from willowsprings.uwyo.edu ([129.72.10.31] verified) by logan.com (CommuniGate Pro SMTP 5.3.7) with ESMTPS id 4340968 for flyrotary@lancaironline.net; Tue, 08 Jun 2010 21:43:06 -0400 Received-SPF: none receiver=logan.com; client-ip=129.72.10.31; envelope-from=SBoese@uwyo.edu Received: from ponyexpress-ht1.uwyo.edu (ponyexpress-ht1.uwyo.edu [10.84.60.208]) by willowsprings.uwyo.edu (8.14.2/8.14.2) with ESMTP id o591gPTg015556 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=FAIL) for ; Tue, 8 Jun 2010 19:42:27 -0600 (MDT) (envelope-from SBoese@uwyo.edu) Received: from ponyexpress-mb5.uwyo.edu ([fe80::9813:248c:2d68:a28b]) by ponyexpress-ht1 ([10.84.60.208]) with mapi; Tue, 8 Jun 2010 19:42:25 -0600 From: "Steven W. Boese" To: Rotary motors in aircraft Date: Tue, 8 Jun 2010 19:42:24 -0600 Subject: RE: [FlyRotary] Re: high/low pressure pumps question Thread-Topic: [FlyRotary] Re: high/low pressure pumps question Thread-Index: AcsHVkxvqBnf9uApT4exLoQPyLTU1wAHG36U Message-ID: References: In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: multipart/alternative; boundary="_000_E1AA3B1AF41D8049B1E3FBD5E225626004D4FE7C76ponyexpressmb_" MIME-Version: 1.0 --_000_E1AA3B1AF41D8049B1E3FBD5E225626004D4FE7C76ponyexpressmb_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable George, If I understand your question correctly, I would expect that the fuel radia= tor would be useful in keeping the fuel cool and help with respect to the p= otential problems 1 & 2 mentioned below. It would not help much with respe= ct to #3 since the dissolution of the air back into the fuel seems to be re= latively slow. If the header tank is small enough, the air may remain disp= ersed and be drawn into the pump supply as small bubbles to be compressed e= ven smaller and some of them injected with the fuel. Then the air would no= t accumulate in the small header tank like it could in a large one where th= e mixing is not so effective. In other words, Ed's header tank may work we= ll partly because of its small volume. This is just speculation on my part= , though. Steve Boese RV6A, 1986 13B NA, RD1A, EC2 ________________________________ From: Rotary motors in aircraft [flyrotary@lancaironline.net] On Behalf Of = George Lendich [lendich@aanet.com.au] Sent: Tuesday, June 08, 2010 4:01 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: high/low pressure pumps question Steve, How would you assume the small fuel radiator (before header tank) would wor= k in the circumstances you describe. George (down under) In the reference provided by Ed, there is mention of the fuel temperature b= eing monitored to allow compensation for changes in fuel viscosity with cha= nges in temperature. The ECU might be changing injector pulse width in res= ponse 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 t= he return line after the pressure regulator. I did this because I saw bubb= les in the fuel being returned to the tank and assumed that there was an ai= r 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 sear= ching. The bubbles I saw were air bubbles that separated from the fuel dur= ing the rapid pressure drop through the regulator. The formation of the ai= r 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 solub= ility of air in water, and we all have seen the air bubbles that form on th= e 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 fro= m 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 usi= ng a vented fuel tank of only a gallon in volume. I don't know how long th= is would take in the case of a large wing tank. Returning the fuel from the regulator to the supply line orto a small heade= r tank feeding the fuel pumps seems to me to have the potential for problem= s in at least three ways: 1) from increasing fuel vapor pressure as temper= ature rises, 2) decreased solubility of air in the fuel as temperature ri= ses, 3) the accumulation of air as a result of the formation of air bubbl= es in the pressure regulator which occurs even without an increase in tempe= rature. All of these things could contribute to vapor lock. 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 RV6A, 1986 13B NA, RD1A, EC2 --_000_E1AA3B1AF41D8049B1E3FBD5E225626004D4FE7C76ponyexpressmb_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
George,
 
If I understand your question correct= ly, I would expect that the fuel radiator would be useful in keeping the fu= el cool and help with respect to the potential problems 1 & 2 mentioned= below.  It would not help much with respect to #3 since the dissolution of the air back into the fuel seems to be= relatively slow.  If the header tank is small enough, the air may rem= ain dispersed and be drawn into the pump supply as small bubbles to be comp= ressed even smaller and some of them injected with the fuel.  Then the air would not accumulate in the small header= tank like it could in a large one where the mixing is not so effective.&nb= sp; In other words, Ed's header tank may work well partly because of its sm= all volume.  This is just speculation on my part, though.
 
 Steve Boese
RV6A, 1986 13B NA, RD1A, EC2
 
=  
From: Rotary moto= rs in aircraft [flyrotary@lancaironline.net] On Behalf Of George Lendich [l= endich@aanet.com.au]
Sent: Tuesday, June 08, 2010 4:01 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: high/low pressure pumps question

 
Steve,
How would you assume the small fuel radiato= r (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 temperat= ure being monitored to allow compensation for changes in fuel viscosity wit= h 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 attem= pt 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 reg= ulator.  I did this because I saw bubbles in the fuel being returned t= o the tank and assumed that there was an air leak somewhere in the system, most likely in the suction section betwe= en 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 solubi= lity of air in fuel is much greater than the solubility of air in water, an= d we all have seen the air bubbles that form on the walls a container of water as it warms up and the solubility d= ecreases.  When returning the fuel to the tank, eventually the air wou= ld be purged from the liquid fuel and out the vent.  I observed the el= imination of the air bubbles in the return line after about 10 minutes of recurculation when using a vented fuel tank of o= nly a gallon in volume.  I don't know how long this would take in the = case of a large wing tank.
 
Returning the f= uel 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 t= hree 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 o= ccurs even without an increase in temperature.  All of these things could contribute to vapor lock. 
&= nbsp;
These are just = my observations.  There is also the indisputable observation of= the success of Ed's system for many years of operation.
 
Stev= e Boese
RV6A, 1986 13B NA, RD1A, EC2
=  
 
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