Return-Path: Received: from [199.185.220.220] (HELO priv-edtnes57.telusplanet.net) by logan.com (CommuniGate Pro SMTP 4.3c1) with ESMTP id 726021 for flyrotary@lancaironline.net; Sat, 12 Feb 2005 06:19:36 -0500 Received-SPF: pass receiver=logan.com; client-ip=199.185.220.220; envelope-from=haywire@telus.net Received: from Endurance ([207.81.25.155]) by priv-edtnes57.telusplanet.net (InterMail vM.6.01.04.00 201-2131-118-20041027) with SMTP id <20050212111840.NMRV6731.priv-edtnes57.telusplanet.net@Endurance> for ; Sat, 12 Feb 2005 04:18:40 -0700 From: "Todd Bartrim" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Vapor lock in sump/header tank. Date: Sat, 12 Feb 2005 03:18:05 -0800 Message-ID: <00b201c510f4$86e9efb0$0201a8c0@Endurance> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00B3_01C510B1.78CB4390" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook CWS, Build 9.0.2416 (9.0.2910.0) X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 Importance: Normal In-Reply-To: This is a multi-part message in MIME format. ------=_NextPart_000_00B3_01C510B1.78CB4390 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Hi Paul; Caution this is a long story relating my previous vapour lock issues and how they may relate to yours. Recent comments have differed about the need to vent or not to vent a sump/header tank. As I understand it you have a sump tank in which it is gravity fed from your mains, then pumped up to your engine. However IIRC a previous post in which you said you had copied Ed's system which is a header tank that has boost pumps feeding it. (I may have that incorrect as I couldn't find the post in question) Now I went through a couple different versions of a header tank before scrapping the idea altogether. My first one was always vented, but this required level control, via the boost pumps as it required fuel to be pumped up to the tank, then it gravity fed my FI pumps. If not filled by pumps, it would just drain the tank due to the vent. If pumps were left on it would over fill and fuel would go out the vent lines which were tied via a common header to the main tanks so negative draft would draw most of the fuel back to the feed tank, but not all. I'd planned to use an electronic level control system to help manage this but supplier problems caused me to look closely at what was really an unnecessary failure mode. At this time I decided to use a non-vented system much like Ed's, however I was certain that I could improve upon it by increasing the size of the header tank and having it located on the cool side of the firewall. But I found that it required a vent as there was no other way to purge out the air from the tank which would accumulate there when one would run a tank dry before switching tanks (I have 6 tanks so it is important to completely empty the aux tanks). So I installed a vent with a pilot accessible valve. This allowed the venting of all air out of the tank at which time it would be closed. Then the fuel would draw up from the main tanks to replace the fuel that had been drawn out and not returned through the return line from the fuel reg, without the need for pumps. I had a clear sight tube to see the level of the header tank and another short clear section of hose on the vent line, so that I could see whether I was venting air or fuel. This seemed like a fine system, until it began seeing the heat of flight operations. Ground runs seemed mostly successful and running a tank dry until the header tank was empty resulted in approximately a 20 second delay in getting fresh fuel to restart the engine and completely purging the air within 2-3 minutes. But under flight conditions it was much different. Heat would cause vapour problems that were very difficult to deal with. The pressure would build within the header tank and the sight tube would not always give a true reading as it should. Twice I ran a tank dry while at +10000' above the airport and had a very difficult time in getting fuel back resulting in approx 6000' of glider alt loss each time. Another time I was doing circuits and was on my downwind leg when the pressure in the tank caused a vapour lock even though I had plenty of fuel in the tank(s) feeding the header tank. The pressure had just built up to the point where even the 7 psi boost/transfer pumps couldn't overcome it to keep fuel in the tank. In this case I was able to make an emergency deadstick landing on an intersecting runway and fortunately I even kept my speed up enough to coast all the way to my tie-down spot. That's where the firetrucks met me... kinda embarrassing! In each of these cases, I found that when opening the vent valve to release the pressure, I could see through the clear vent tube section that I was venting a boiling fuel (air/fuel) mixture. And it took an uncomfortably long period of time to relieve that pressure and refill the tank with fresh fuel. I then installed optical fuel level sensors (hi/low) on the header tank, a vacuum/pressure gauge and a temp sensor. I found that it would begin by having a vacuum in the tank as the system would draw in new fuel to replace that which was being consumed, but it would soon begin to build as a pressure as the fuel heated and would then begin to push the level down. Opening the vent relived this pressure but it couldn't be left open, or it would just empty the header tank. Keeping the pump(s) running would over flow the tank. Can you see where all this was going? I surmise that the greater capacity of the header tank (as compared to Ed's) allowed some heat absorption as it took longer to become affected, but once heated it was far less manageable. My pilot workload was too great and became centred around fuel management. I had so much time, effort and $$$ invested in making that header tank work that I didn't want to let go of the idea, but one day I just had enough and tore it out of there. I've now converted to a returnless system with no header tank and I couldn't be happier. What I'm trying to show is that there is more going on with heat in the fuel system than expected. I'm not familiar with your system, but the way I understand it, you have your main tanks draining by gravity into your sump tank. Your FI return line feeds into this tank bringing heat from the engine with it. I surmise that it is bringing enough heat to begin a vapour build-up in your sump tank overcoming the gravity feed. How long after your emergency landing did you restart your engine? If it was immediately and it ran fine, then this theory may not be valid, however if there was sometime elapse (while you kissed the ground & changed your shorts :-), then it could be that the tank had time enough to cool and/or relive the pressure allowing more fuel to enter the tank. One way that I could see overcoming this would be..... A vent line from the top of your sump tank up to the top of both of your main tanks, but not tied into the main tank vent system. This would allow any fuel vapours to immediately flow out of the sump tank, eliminating any chance of vapour build-up, while allowing the cool fuel to continue to be gravity fed to the sump tank. These fuel vapours would then flow into the main tanks where they should immediately condense, preventing the loss of any fuel through a direct atmosphere vent system. This would (may) only work if you have your main tanks located above the sump tank. Having your FI pumps located at or below the sump pump would surely be a help as well. But I would not expect the tank to work without a vent or with a vent to atmosphere. I hope some of this is relevant to you and helps. Todd Bartrim (top posted all the way to the bottom) ------=_NextPart_000_00B3_01C510B1.78CB4390 Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
Hi=20 Paul;
    Caution this is a long story relating my = previous vapour=20 lock issues and how they may relate to yours. Recent comments have = differed=20 about the need to vent or not to vent a sump/header tank. As I = understand it you=20 have a sump tank in which it is gravity fed from your mains, then pumped = up to=20 your engine. However IIRC a previous post in which you said you had = copied Ed's=20 system which is a header tank that has boost pumps feeding it. (I may = have that=20 incorrect as I couldn't find the post in question) Now I went through a = couple=20 different versions of a header tank before scrapping the idea = altogether. My=20 first one was always vented, but this required level control, via the = boost=20 pumps as it required fuel to be pumped up to the tank, then it gravity = fed my FI=20 pumps. If not filled by pumps, it would just drain the tank due to the = vent. If=20 pumps were left on it would over fill and fuel would go out the vent = lines which=20 were tied via a common header to the main tanks so negative draft would = draw=20 most of the fuel back to the feed tank, but not all. I'd planned = to use=20 an electronic level control system to help manage this but supplier = problems=20 caused me to look closely at what was really an unnecessary failure = mode.=20
    At this time I decided to use a non-vented = system much=20 like Ed's, however I was certain that I could improve upon it by = increasing the=20 size of the header tank and having it located on the cool side of the = firewall.=20 But I found that it required a vent as there was no other way to purge = out the=20 air from the tank which would accumulate there when one would run a tank = dry=20 before switching tanks (I have 6 tanks so it is important to completely = empty=20 the aux tanks). So I installed a vent with a pilot accessible = valve. This=20 allowed the venting of all air out of the tank at which time it would be = closed.=20 Then the fuel would draw up from the main tanks to replace the fuel that = had=20 been drawn out and not returned through the return line from the fuel = reg,=20 without the need for pumps. I had a clear sight tube to see the level of = the=20 header tank and another short clear section of hose on the vent line, so = that I=20 could see whether I was venting air or fuel.
    This seemed like a fine system, until it began = seeing the=20 heat of flight operations. Ground runs seemed mostly successful and = running a=20 tank dry until the header tank was empty resulted in approximately a 20 = second=20 delay in getting fresh fuel to restart the engine and completely purging = the air=20 within 2-3 minutes. But under flight conditions it was much different. = Heat=20 would cause vapour problems that were very difficult to deal with. The = pressure=20 would build within the header tank and the sight tube would not always = give a=20 true reading as it should. Twice I ran a tank dry while at +10000' above = the=20 airport and had a very difficult time in getting fuel back resulting in = approx=20 6000' of glider alt loss each time. Another time I was doing circuits = and was on=20 my downwind leg when the pressure in the tank caused a vapour lock even = though I=20 had plenty of fuel in the tank(s) feeding the header tank. The pressure = had just=20 built up to the point where even the 7 psi boost/transfer pumps couldn't = overcome it to keep fuel in the tank. In this case I was able to make an = emergency deadstick landing on an intersecting runway and fortunately I = even=20 kept my speed up enough to coast all the way to my tie-down spot. That's = where=20 the firetrucks met me... kinda embarrassing!
    In each of these cases, I found that when = opening the vent=20 valve to release the pressure, I could see through the clear vent tube = section=20 that I was venting a boiling fuel (air/fuel) mixture. And it took an=20 uncomfortably long period of time to relieve that pressure and refill = the tank=20 with fresh fuel. I then installed optical fuel level sensors (hi/low) on = the=20 header tank, a vacuum/pressure gauge and a temp sensor. I found that it = would=20 begin by having a vacuum in the tank as the system would draw in new = fuel to=20 replace that which was being consumed, but it would soon begin to build = as a=20 pressure as the fuel heated and would then begin to push the level down. = Opening=20 the vent relived this pressure but it couldn't be left open, or it would = just=20 empty the header tank. Keeping the pump(s) running would over flow the = tank.=20
    Can you see where all this was going? I surmise = that the=20 greater capacity of the header tank (as compared to Ed's) allowed some = heat=20 absorption as it took longer to become affected, but once heated it was = far less=20 manageable. My pilot workload was too great and became centred around = fuel=20 management. I had so much time, effort and $$$ invested in making that = header=20 tank work that I didn't want to let go of the idea, but one day I just = had=20 enough and tore it out of there. I've now converted to a returnless = system with=20 no header tank and I couldn't be happier.
    What I'm trying to show is that there is more = going on with=20 heat in the fuel system than expected. I'm not familiar with your = system, but=20 the way I understand it, you have your main tanks draining by gravity = into your=20 sump tank. Your FI return line feeds into this tank bringing heat from = the=20 engine with it. I surmise that it is bringing enough heat to begin a = vapour=20 build-up in your sump tank overcoming the gravity feed. How long after = your=20 emergency landing did you restart your engine? If it was immediately and = it ran=20 fine, then this theory may not be valid, however if there was sometime = elapse=20 (while you kissed the ground & changed your shorts :-), then it = could be=20 that the tank had time enough to cool and/or relive the pressure = allowing more=20 fuel to enter the tank.
    One way that I could see overcoming this would=20 be.....
A vent=20 line from the top of your sump tank up to the top of both of your = main=20 tanks, but not tied into the main tank vent system. This would allow any = fuel=20 vapours to immediately flow out of the sump tank, eliminating any chance = of=20 vapour build-up, while allowing the cool fuel to continue to be gravity = fed to=20 the sump tank. These fuel vapours would then flow into the main tanks = where they=20 should immediately condense, preventing the loss of any fuel through a = direct=20 atmosphere vent system. This would (may) only work if you have your = main=20 tanks located above the sump tank. Having your FI pumps located at or = below the=20 sump pump would surely be a help as well. But I would not expect the = tank to=20 work without a vent or with a vent to atmosphere.
 
    I hope some of this is relevant to you and=20 helps.
 
Todd=20 Bartrim  (top posted all the way to the=20 bottom)
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