X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.121] verified) by logan.com (CommuniGate Pro SMTP 5.4.1) with ESMTP id 5087920 for flyrotary@lancaironline.net; Wed, 10 Aug 2011 09:30:08 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.121; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=1.1 cv=SOlsIBN44tkg4MqIq+y2aLZdhoA3kHpmiRsLue6rfnM= c=1 sm=0 a=rPkcCx1H5rrOSfN0dPC7kw==:17 a=ayC55rCoAAAA:8 a=ufqdMB3fjkCzCWvEs6oA:9 a=b2oz_CiamsFruL7a8J4A:7 a=wPNLvfGTeEIA:10 a=JFZkHGrfbi1iwdFg:21 a=TRhVb_YfcsOqrfFF:21 a=Ia-xEzejAAAA:8 a=TBsngjUD4CxeroG7VewA:9 a=JH69OfR_OQNWwdUSJs8A:7 a=tXsnliwV7b4A:10 a=EzXvWhQp4_cA:10 a=0ItGI39Bn1_7-YgI:21 a=vYSs9UTGTy2Vaxh9:21 a=rPkcCx1H5rrOSfN0dPC7kw==:117 X-Cloudmark-Score: 0 X-Originating-IP: 174.110.167.5 Received: from [174.110.167.5] ([174.110.167.5:59900] helo=EdPC) by cdptpa-oedge01.mail.rr.com (envelope-from ) (ecelerity 2.2.3.46 r()) with ESMTP id 40/7B-15242-DB7824E4; Wed, 10 Aug 2011 13:29:34 +0000 Message-ID: <6703E4B1487F4326A131A1590A27C608@EdPC> From: "Ed Anderson" To: "Rotary motors in aircraft" References: In-Reply-To: Subject: Re: [FlyRotary] vapor lock Date: Wed, 10 Aug 2011 09:28:22 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00F1_01CC573F.D91F3900" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8117.416 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8117.416 This is a multi-part message in MIME format. ------=_NextPart_000_00F1_01CC573F.D91F3900 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Some excellent points, Steve, as always.=20 Each system is different and as we know even "small" details can made a = big difference if operating close to a critical point. =20 =20 I agree the pressure in front of the pump inlet with two pumps running = would be less than with only one pump drawing the fuel. I guess the = question is how much less. I suspect the effect is not linear but = related to the square of the flow volume/velocity. =20 Heating of the fuel seems to be the major factor in why a system seems = to operate fine one day - until perhaps the hottest days/conditions and = then problems occur. =20 In my case, I do have a small (1/2 pint) header tank on the firewall = side which I return the Pressure regulator line to. In the early days = before I shielded and added a blast tube to my set up, there were = occasions on hot days when I noticed the fuel pressure start to wobble - = turning on the boost pump stopped in in every case. =20 Now if I took off with only one EFI running - would I need the boost = pump - don't know- not inclined to find out {:>). Actually, there have = been a few occasions when I neglected to turn on my boost pump, but they = were not on the hottest days - so not a true test. My greatest concern is this regard - is pump failure on take off - if = only one pump is on and fails, then it is going to take x amount of time = to detect, recognize and take corrective action - and my reaction time = is not improving with age {:>). Yes, I could set up some sort of = automatic pressure sensor to turn on the second pump, but I dislike = complicating my set up anymore that it is. So as you point out - you = evaluate the scenario and make your choices. The output of the two pumps would still be regulated to whatever = pressure you have set in your regulator - but with two pumps pumping = that would indicate that more fuel is flowing through the system and the = excess is being dumped back into the return line (because no more fuel = is being used by the engine). =20 So would this increased flow of cooler fuel through the system increase = or decrease the probability of creating low enough pressure (with the = cooler fuel) to cause vapor? Ah, the devil is in the details. Basically, it would seem that anything you do to lessen the pressure = drop and/or keeping the fuel cool (perhaps turning off one EFI, removing = the coarse filter, increasing pressure in the line through a boost pump, = fuel cooler, etc) reduces the risk of fuel turning to vapor. My = assessment is that the positive effects of the boost pump can be relied = upon with more confidence than most other "fixes" or preventive measures = - but that assessment is not based on any testing, just my opinion. =20 The one I potential preventive measure/fix I have not looked into is the = vapor by-pass/dump that I know a few folks are using. I search the = archive but could not find a description of this method - anyone care to = provide one? Since I always take off with my boost pump on (produces approx 6 psi) = whatever adverse effect running with two EFI pumps might have on the = possibility of vapor lock appears to be alleviated by the addition line = pressure on the EFI pump intake line.=20 Now if I took off with only one EFI running - would I need the boost = pump - don't know- not inclined to find out {:>). Actually, there have = been a few occasions when I neglected to turn on my boost pump, but they = were not on the hottest days. My greatest concern is this regard is pump failure on take off - if only = one pump is on, then it is going to take x amount of time to detect, = recognize and take corrective action - and my reaction time is not = improving with age {:>). Yes, I could set up some sort of automatic = pressure sensor to turn on the second pump, but I dislike complicating = my set up anymore that it is. So like most problems we wrestle with - it's a trade off.=20 FWIW Ed From: Steven W. Boese=20 Sent: Tuesday, August 09, 2011 10:12 PM To: Rotary motors in aircraft=20 Subject: [FlyRotary] vapor lock 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 vapor 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 judgement 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 =20 =20 On Tue, Aug 9, 2011 at 8:06 AM, Ed Anderson = wrote: Further discussion with Sam leads me to believe that the highest = probably cause was a "vapor lock" of some type in the fuel line. Sam = stated the engine never stopped running (correction to my earlier report = - where I stated it had quit), but just continued to sputter and failed = to produce power.=20 The ignition checked out OK as did the rest of the 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 high ambient = temps (98F) and the run up before take off -- would leave me to believe = those conditions could have lead to diminished fuel flow.=20 Sam is going to inspect his coarse filter to ensure it was not = partially obstructed.=20 One item of note is that Sam does not have any sort of boost pump = between tanks and his EFI pumps. In my early days of testing while doing = power-on stalls (high power low cooling airflow) on a hot day, my engine = started to sputter (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 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 produces at least a small = pressure drop down stream - Given the suction of the EFI 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 pumped 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 = percolating - particularly on HOT ambient days. However, make certain = that the boost pump is of a type that does not obstruct fuel flow during = a malfuction or when off. ------=_NextPart_000_00F1_01CC573F.D91F3900 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Some excellent points, Steve, as=20 always. 
 
 Each system is different and as we know = even "small"=20 details can made a big difference if operating close to a critical=20 point.  
 
 I agree  the pressure in front of the = pump=20 inlet with two pumps running would be less than with only one pump = drawing the=20 fuel.  I guess the question is how much less.  I suspect the = effect is=20 not linear but related to the square of the flow volume/velocity. =20
 
Heating of the fuel seems to be the major factor = in why a=20 system seems to operate fine one day - until perhaps the hottest = days/conditions=20 and then problems occur.  
 
In my case, I do have a small (1/2 pint) header = tank on=20 the firewall side which I return the Pressure regulator line to.  = In the=20 early days before I shielded and added a blast tube to my set up, =  there=20 were occasions on hot days when I noticed the fuel pressure start to = wobble -=20 turning on the boost pump stopped in in every = case.  
 
 Now if I took off with only one EFI = running - would=20 I need the boost pump - don't know- not inclined to find out = {:>). =20 Actually, there have been a few occasions when I neglected to turn on my = boost=20 pump, but they were not on the hottest days - so not a true=20 test.
 
 
My greatest concern is this  regard - = is pump=20 failure on take off - if only one pump is on and fails, then it is going = to take=20 x amount of time to detect, recognize and take corrective action - and = my=20 reaction time is not improving with age {:>).    Yes, = I could=20 set up some sort of automatic pressure sensor to turn on the second = pump, but I=20 dislike complicating my set up anymore that it is.  So as you point = out -=20 you evaluate the scenario and make your = choices.
 
The output of the two pumps would still be = regulated to=20 whatever pressure you have set in your regulator - but with two pumps = pumping=20 that would indicate that more fuel is flowing through the system and the = excess=20 is being dumped back into the return line (because no more fuel is being = used by=20 the engine). 
So would this increased flow of cooler fuel = through the=20 system increase or decrease the probability of creating low enough = pressure=20 (with the cooler fuel) to cause vapor? Ah, the devil is in the=20 details.
 
Basically, it would seem that anything you do to = lessen=20 the pressure drop and/or keeping the fuel cool (perhaps turning off = one=20 EFI, removing the coarse filter, increasing pressure in the line through = a boost=20 pump, fuel cooler, etc) reduces the risk of fuel turning to vapor.  = My=20 assessment is that the positive effects of the boost pump can be relied = upon=20 with more confidence than most other "fixes" or preventive measures - = but that=20 assessment is not based on any testing, just my opinion.  =
 
The one I potential preventive measure/fix I = have not=20 looked into is the vapor by-pass/dump that I know a few folks are = using.  I=20 search the archive but could not find a description of this method - = anyone care=20 to provide one?
 
Since I always take off with my boost pump = on =20 (produces approx 6 psi) whatever adverse effect running with two EFI = pumps might=20 have on the possibility of vapor lock appears to be alleviated by the = addition=20 line pressure on the EFI pump intake line. 
 
 Now if I took off with only one EFI = running - would=20 I need the boost pump - don't know- not inclined to find out = {:>). =20 Actually, there have been a few occasions when I neglected to turn on my = boost=20 pump, but they were not on the hottest days.
 
My greatest concern is this regard is pump = failure on take=20 off - if only one pump is on, then it is going to take x amount of time = to=20 detect, recognize and take corrective action - and my reaction time is = not=20 improving with age {:>).    Yes, I could set up some = sort of=20 automatic pressure sensor to turn on the second pump, but I dislike = complicating=20 my set up anymore that it is.
 
So like most problems we wrestle with - it=92s a = trade off.=20
 
 
FWIW
 
Ed

From: Steven W. Boese
Sent: Tuesday, August 09, 2011 10:12 PM
To: Rotary motors in = aircraft
Subject: [FlyRotary] vapor lock

Ed,

 

Do you think your fuel system is = somewhat unique=20 with the use of the small header tank?

 

It seems to me that running two high = pressure=20 pumps simultaneously to deal with the possibility of failure = of one=20 pump increases the likelyhood of vapor lock in the supply to = the=20 pumps due to the doubled fuel flow requirement compared to = running=20 only one pump. This increased susceptibility to vapor lock = would=20 only exist during the critical phases of flight when both = pumps=20 would be running. The procedure used would depend on the = operators=20 judgement of which failure mode (pump failure or vapor lock) = would=20 be most likely. Like everything else, a = compromise.

 

This may not have anything to do with = Sam's=20 system, operating procedure, or problem, just something to=20 consider.

 

Steve=20 Boese

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