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 4340311 for flyrotary@lancaironline.net; Tue, 08 Jun 2010 12:30:35 -0400 Received-SPF: none receiver=logan.com; client-ip=129.72.10.31; envelope-from=SBoese@uwyo.edu Received: from ponyexpress-ht2.uwyo.edu (ponyexpress-ht2.uwyo.edu [10.84.60.209]) by willowsprings.uwyo.edu (8.14.2/8.14.2) with ESMTP id o58GTvsh006214 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=FAIL) for ; Tue, 8 Jun 2010 10:29:57 -0600 (MDT) (envelope-from SBoese@uwyo.edu) Received: from ponyexpress-mb5.uwyo.edu ([fe80::9813:248c:2d68:a28b]) by ponyexpress-ht2 ([10.84.60.209]) with mapi; Tue, 8 Jun 2010 10:29:56 -0600 From: "Steven W. Boese" To: Rotary motors in aircraft Date: Tue, 8 Jun 2010 10:29:55 -0600 Subject: RE: [FlyRotary] Re: high/low pressure pumps question Thread-Topic: [FlyRotary] Re: high/low pressure pumps question Thread-Index: AcsHG1o8F+nkMhytQa2APgUJ8TvS3wAA+J1v 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_E1AA3B1AF41D8049B1E3FBD5E225626004D4FE7C74ponyexpressmb_" MIME-Version: 1.0 --_000_E1AA3B1AF41D8049B1E3FBD5E225626004D4FE7C74ponyexpressmb_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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 ________________________________ 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 sa= fety. If you share your fuel design, at least do the calculations and let u= sers know how close this is to vapor lock. We're talking about life risk he= re. You are glossing over my point and changing the topic. Returning fuel t= o pump inlet is very risky and should not be done unless you desire to oper= ate on the threshold of vapor lock. I agree, there is one exception. That's if you have one of the new fuel pum= p 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 --_000_E1AA3B1AF41D8049B1E3FBD5E225626004D4FE7C74ponyexpressmb_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
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
=  
From: Rotary moto= rs in aircraft [flyrotary@lancaironline.net] On Behalf Of Al Wick [alwick@j= uno.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 cont= ributions that help improve flight safety. If you share your fuel design, a= t least do the calculations and let users know how close this is to vapor l= ock. We're talking about life risk here. You are glossing over my point and changing the topic. Returning fuel to p= ump 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 ab= out added complexity!
 
On with the good stuff!
 
-al wick
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