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 5.4.1) with ESMTPS id 5087473 for flyrotary@lancaironline.net; Tue, 09 Aug 2011 22:12:37 -0400 Received-SPF: none receiver=logan.com; client-ip=129.72.10.31; envelope-from=SBoese@uwyo.edu Received: from ponyexpress-ht5.uwyo.edu (extlb.uwyo.edu [172.26.4.4]) by willowsprings.uwyo.edu (8.14.4/8.14.4) with ESMTP id p7A2C008015156 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=FAIL) for ; Tue, 9 Aug 2011 20:12:00 -0600 (MDT) (envelope-from SBoese@uwyo.edu) Received: from ponyexpress-m10.uwyo.edu ([fe80::60dd:cb9e:6f71:3d48]) by ponyexpress-ht5.uwyo.edu ([fe80::addc:5ab0:b0f8:ab9e%13]) with mapi id 14.01.0289.001; Tue, 9 Aug 2011 20:11:59 -0600 From: "Steven W. Boese" To: "flyrotary@lancaironline.net" Subject: vapor lock Thread-Topic: vapor lock Thread-Index: AcxXApt59tUy/hK8SCSWbRvfyMT0pw== Date: Wed, 10 Aug 2011 02:12:00 +0000 Message-ID: <3E8191F276108F4481AB0721BBA9269E05A5E008@ponyexpress-m10.uwyo.edu> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [75.220.120.247] Content-Type: multipart/alternative; boundary="_000_3E8191F276108F4481AB0721BBA9269E05A5E008ponyexpressm10u_" MIME-Version: 1.0 --_000_3E8191F276108F4481AB0721BBA9269E05A5E008ponyexpressm10u_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ed, Do you think your fuel system is somewhat unique with the use of the small = header tank? It seems to me that running two high pressure pumps simultaneously to deal = with the possibility of failure of one pump increases the likelyhood of vap= or lock in the supply to the pumps due to the doubled fuel flow requirement= compared to running only one pump. This increased susceptibility to vapor = lock would only exist during the critical phases of flight when both pumps = would be running. The procedure used would depend on the operators judgemen= t of which failure mode (pump failure or vapor lock) would be most likely. = Like everything else, a compromise. This may not have anything to do with Sam's system, operating procedure, or= problem, just something to consider. Steve Boese On Tue, Aug 9, 2011 at 8:06 AM, Ed Anderson > wrote: Further discussion with Sam leads me to believe that the highest probably c= ause was a "vapor lock" of some type in the fuel line. Sam stated the engin= e never stopped running (correction to my earlier report - where I stated i= t had quit), but just continued to sputter and failed to produce power. The ignition checked out OK as did the rest of the system back in the hanga= r. The symptom of sputtering engine and no power would put a fuel system pr= oblem high on my list of suspects and given the high ambient temps (98F) an= d the run up before take off -- would leave me to believe those conditions = could have lead to diminished fuel flow. Sam is going to inspect his coarse filter to ensure it was not partially ob= structed. One item of note is that Sam does not have any sort of boost pump between t= anks and his EFI pumps. In my early days of testing while doing power-on st= alls (high power low cooling airflow) on a hot day, my engine started to sp= utter (unlike Sam I had plenty of altitude when it happened) and I noticed = my fuel pressure fluctuating between 20 - 35 psi. I turned on my Facet boos= t pump (puts out approx 6 psi pressure) and it immediately squelch the prob= lem. So I now take off/land with boost pump on and have never since had tha= t problem. We know that any obstruction in a fuel line produces at least a small press= ure drop down stream - Given the suction of the EFI pumps and even minor re= striction of the coarse filter - a lower pressure region would exist betwee= n filter and EFI pumps - elevated temperatures could be enough to cause som= e of the fuel in this area to flash into a gaseous state - which of course = is not pumped very well. Its my opinion that a boost pump is a worthwhile a= ddition in keep pressure in the low pressure part of the fuel system suffic= iently high to prevent the fuel from percolating - particularly on HOT ambi= ent days. However, make certain that the boost pump is of a type that does = not obstruct fuel flow during a malfuction or when off. --_000_3E8191F276108F4481AB0721BBA9269E05A5E008ponyexpressm10u_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Ed,

 

Do you think your fuel system is somewhat unique wi= th the use of the small header tank?

 

It seems to me that running two high pressure pumps= simultaneously to deal with the possibility of failure of one pump increas= es the likelyhood of vapor lock in the supply to the pumps due to the doubl= ed fuel flow requirement compared to running only one pump. This increased susceptibility to vapor lock woul= d only exist during the critical phases of flight when both pumps would be = running. The procedure used would depend on the operators judgement of whic= h failure mode (pump failure or vapor lock) would be most likely. Like everything else, a compromise.

 

This may not have anything to do with Sam's system,= operating procedure, or problem, just something to consider.

 

Steve Boese
On Tue, Aug 9, 2011 at 8:06 AM, Ed Anderson <eanderson@caroli= na.rr.com> wrote:
Further discussion with Sam leads me to believe that t= he highest probably cause was a "vapor lock" of some type in the = fuel line. Sam stated the engine never stopped running (correction to my ea= rlier report - where I stated it had quit), but just continued to sputter and failed to produce power.
The ignition checked out OK as did the rest of th= e system back in the hangar. The symptom of sputtering engine and no power = would put a fuel system problem high on my list of suspects and given the h= igh ambient temps (98F) and the run up before take off -- would leave me to believe those conditions could hav= e lead to diminished fuel flow.
Sam is going to inspect his coarse filter to ensu= re it was not partially obstructed.
One item of note is that Sam does not have any so= rt of boost pump between tanks and his EFI pumps. In my early days of testi= ng while doing power-on stalls (high power low cooling airflow) on a hot da= y, my engine started to sputter (unlike Sam I had plenty of altitude when it happened) and I noticed my fuel press= ure fluctuating between 20 - 35 psi. I turned on my Facet boost pump (puts = out approx 6 psi pressure) and it immediately squelch the problem. So I now= take off/land with boost pump on and have never since had that problem.
We know that any obstruction in a fuel line produ= ces at least a small pressure drop down stream - Given the suction of the E= FI pumps and even minor restriction of the coarse filter - a lower pressure= region would exist between filter and EFI pumps - elevated temperatures could be enough to cause some of the= fuel in this area to flash into a gaseous state - which of course is not p= umped very well. Its my opinion that a boost pump is a worthwhile addition = in keep pressure in the low pressure part of the fuel system sufficiently high to prevent the fuel from percola= ting - particularly on HOT ambient days. However, make certain that the boo= st pump is of a type that does not obstruct fuel flow during a malfuction o= r when off.
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