Return-Path: Received: from [24.25.9.101] (HELO ms-smtp-02-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.3c1) with ESMTP id 726030 for flyrotary@lancaironline.net; Sat, 12 Feb 2005 08:01:02 -0500 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.101; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-185-127.carolina.rr.com [24.74.185.127]) by ms-smtp-02-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id j1CD0Ded012823 for ; Sat, 12 Feb 2005 08:00:13 -0500 (EST) Message-ID: <003301c51102$cf127fb0$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Vapor lock in sump/header tank. Date: Sat, 12 Feb 2005 08:00:20 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0030_01C510D8.E5FE5D40" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0030_01C510D8.E5FE5D40 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Good post, Todd. Certainly any vapor lock is a dangerous situation, whether in a Lycoming = or Auto conversion installation. As Todd mentioned I do use a = ventless, very small header tank mounting on my lower firewall. The two = EFI pumps are plumbed to the bottom of this header tank made out of an = 8" length of 3x1 1/2" rectangular tube with plates welded across both = ends and fittings - including separate feed for each pump, return from = pressure regulator, inlet from wing tanks and a sump drain. I also have = plates inside the header tank with numerous 1/8" holes drilled in them. = The theory is that as he hot bubbly return fuel plashes down on the = plashes upon returning from the injector fuel rails, the bubbles will = have a better chance to collapse and return to liquid form. I found when doing runs on my test stand that the two EFI pumps produced = a tremendous pressure differential inside the sump. On one occasion, I = had a heavy duty marine plastic fuel tank sitting on the ground 24" = below the EFI fuel pumps, I notice the engine began to run roughly and = checking around discovered I had forgotten to open the vent on the = plastic tank. The pressure differential created was sufficient to = collapse this heavy duty tank. I was impressed!. After than I knew = there would be sufficient pressure to pull fuel from my wing tanks = without a boost pump. But, I installed a boost pump (6 psi) never the = less. The boost pump is located between my wing tanks and sump and = produces approx 6 psi. My first encounter with a possible vapor lock problem was when doing = high powered stalls (high engine power/low cooling airflow) on a hot = summer day during my test phase. The engine started to surge and I = noticed my fuel pressure fluctuating and dropping as low as 20 psi in = its swings. I turned on the boost pump and the pressure stabilized and = back to flying. After that - I did three things which may account for = why I now have 260+ hours of flying in the Southeast and have had not = further problems. =20 1. I shielded the header tank, pumps and filters from exposure to = radiant exhaust heat by enclosing them in a foiled covered fiberglass = box.=20 2. I routed a 1 1/2" dia blast tube from a NACA duct to this fiberglass = box for cooling air.=20 3. I used 100LL avgas which has a much less tendency for vapor lock (I = started using 100LL for a completely different reason than vapor = lock..another story). The only thing I would do differently had I to do it over, is to mount = the header tank is a cooler place like in the wing root area. = Understand I am not advocating this system - the potential for problems = if you overlook some factor is there - make no doubt of it. I do agree with Todd that my use of a very small header tank may reduce = the vapor lock problem. True, due to the small amount of fuel, it could = get heated to the vapor point quicker - however, I believe that since = the volume is small I am replacing that quantity of fuel with fresh wing = tank fuel quickly and frequently which would tend to preclude too much = of a heat build up as the fuel is quickly gone. If you have a much = large tank then it would take longer for the fuel to be heated to that = point - but, then also longer for the problem to be overcome. I believe someone, Jim S?, mentioned that if there is a vapor lock = problem it is almost certainly occurring before the EFI pumps, and I = agree. Many EFI automobiles today are using a "no-return" fuel system. = But in those systems the fuel system is pressurized to high pressure = all the way from the in-tank pump to the engine - so with 20-40 psi fuel = pressure in the lines it considerably reduces the probability of vapor = forming. Although if you heat any fuel sufficiently (like a line next = to an exhaust header pipe) you can get vapor bubbles. Todd's experience would indicate that no or very small header tank = eliminates or considerably reduces the problem. IF anyone should decide to use a set up similar to mine (which again, I = am not advocating), I would strongly recommend: 1. Use a small header tank, less than a quart - perhaps around a pint. 2. Place it in a cool location 3. Ensure that cooling air is routed to the fuel system components = (pumps/filters) 4. Have a boost pump between tanks and header tanks (turned on for all = take-offs and landings) In Paul's case, I am not certain it was vapor lock since he mentioned = he found the his header tank cool to the touch. Certainly not a = definitive temperature sensor - but a reasonable one. Certainly not to = be discounted as a possible source of the problem and it possibility = needs to be confirmed or eliminated. FWIW Ed A ----- Original Message -----=20 From: Todd Bartrim=20 To: Rotary motors in aircraft=20 Sent: Saturday, February 12, 2005 6:18 AM Subject: [FlyRotary] Re: Vapor lock in sump/header tank. 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=20 snip 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_0030_01C510D8.E5FE5D40 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Good post, Todd.
 
Certainly any vapor lock is a dangerous = situation,=20 whether in a Lycoming or Auto conversion installation.  =  As Todd=20 mentioned I do use a ventless, very small header tank mounting on my = lower=20 firewall.  The two EFI pumps are plumbed to the bottom of this = header tank=20 made out of an 8" length of 3x1 1/2" rectangular tube with plates = welded=20 across both ends and fittings - including separate feed for each = pump,=20 return from pressure regulator, inlet from wing tanks and a sump = drain.  I=20 also have plates inside the header tank with numerous 1/8" holes drilled = in=20 them.  The theory is that as he hot bubbly return fuel plashes down = on the=20 plashes upon returning from the injector fuel rails,  the bubbles = will have=20 a better chance to collapse and return to liquid form.
 
I found when doing runs on my test = stand that the=20 two EFI pumps produced a tremendous pressure differential inside the = sump. =20 On one occasion, I had a heavy duty marine plastic fuel tank sitting on = the=20 ground 24" below the EFI fuel pumps, I notice the engine began to run = roughly=20 and checking around discovered I had forgotten to open the vent on the = plastic=20 tank.  The pressure differential created was sufficient to collapse = this=20 heavy duty tank.  I was impressed!.  After than I knew there = would be=20 sufficient pressure to pull fuel from my wing tanks without a boost = pump. =20 But, I installed a boost pump (6 psi) never the less.  The boost = pump is=20 located between my wing tanks and sump and produces approx 6 = psi.
 
My first encounter with a possible = vapor lock=20 problem was when doing high powered stalls (high engine power/low = cooling=20 airflow) on a hot summer day during my test phase.  The engine = started to=20 surge and I noticed my fuel pressure fluctuating and dropping as low as = 20 psi=20 in its swings.  I turned on the boost pump and the pressure = stabilized and=20 back to flying.  After that - I did three things which may = account for=20 why I now have 260+ hours of flying in the Southeast and have had not = further=20 problems. 
 
1.  I shielded the header tank, = pumps and=20 filters from exposure to radiant exhaust heat by enclosing them in a = foiled=20 covered fiberglass box. 
 
2.  I routed a 1 1/2" dia blast = tube from a=20 NACA duct to this fiberglass box for cooling air. 
 
3.  I used 100LL avgas which has a = much less=20 tendency for vapor lock (I started using 100LL for a completely = different reason=20 than vapor lock..another story).
 
The only thing I would do differently = had I to do=20 it over, is to mount the header tank is a cooler place like in the  = wing=20 root area. Understand I am not advocating this system - the potential = for=20 problems if you overlook some factor is there - make no doubt of=20 it.
 
I do agree with Todd that my use of a = very small=20 header tank may reduce the vapor lock problem.  True, due to = the small=20 amount of fuel, it could get heated to the vapor point quicker - = however, I=20 believe that since the volume is small I am replacing that quantity of = fuel with=20 fresh wing tank fuel quickly and frequently which would tend to preclude = too=20 much of a heat build up as the fuel is quickly gone.  If you have a = much=20 large tank then it would take longer for the fuel to be heated to that = point -=20 but, then also longer for the problem to be overcome.
 
I believe someone, Jim S?, mentioned = that if there=20 is a vapor lock problem it is almost certainly occurring before the EFI = pumps,=20 and I agree.   Many EFI automobiles today are using a = "no-return" fuel=20 system.  But in those systems the fuel system is pressurized to = high=20 pressure all the way from the in-tank pump to the engine - so with 20-40 = psi=20 fuel pressure in the lines it considerably reduces the probability of = vapor=20 forming.  Although if you heat any fuel sufficiently (like a line = next to=20 an exhaust header pipe) you can get vapor bubbles.
 
Todd's experience would indicate that = no or very=20 small header tank eliminates or considerably reduces the = problem.
 
IF anyone should decide to use a set up = similar to=20 mine (which again, I am not advocating), I would strongly=20 recommend:
 
1.  Use a small header tank, less = than a quart=20 - perhaps around a pint.
2.  Place it in  a cool=20 location
3.  Ensure that cooling air is = routed to the=20 fuel system components (pumps/filters)
4.  Have a boost pump between = tanks and header=20 tanks (turned on for all take-offs and landings)
 
 
 In Paul's case, I am not certain = it was vapor=20 lock since he mentioned he found the his header tank cool to the = touch. =20 Certainly not a definitive temperature sensor - but a reasonable = one. =20 Certainly not to be discounted as a possible source of the problem and = it=20 possibility needs to be confirmed or eliminated.
 
FWIW
 
Ed A
----- Original Message -----
From:=20 Todd = Bartrim=20
Sent: Saturday, February 12, = 2005 6:18=20 AM
Subject: [FlyRotary] Re: Vapor = lock in=20 sump/header tank.

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=20 you have a sump tank in which it is gravity fed from your mains, then = pumped=20 up to your engine. However IIRC a previous post in which you said you = had=20 copied Ed's system which is a header tank that has boost=20
 
 
 
snip
 
 
    Can you see where all this was going? I surmise that the = greater=20 capacity of the header tank (as compared to Ed's) allowed some heat = absorption=20 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=20 with no header tank and I couldn't be happier.
    What I'm trying to show is that there is more = going on=20 with heat in the fuel system than expected. I'm not familiar with your = system,=20 but the way I understand it, you have your main tanks draining by = gravity into=20 your sump tank. Your FI return line feeds into this tank bringing heat = from=20 the engine with it. I surmise that it is bringing enough heat to begin = a=20 vapour build-up in your sump tank overcoming the gravity feed. How = long after=20 your emergency landing did you restart your engine? If it was = immediately and=20 it ran fine, then this theory may not be valid, however if there was = sometime=20 elapse (while you kissed the ground & changed your shorts :-), = then it=20 could be that the tank had time enough to cool and/or relive the = pressure=20 allowing more fuel to enter the tank.
    One way that I could see overcoming this = would=20 be.....
A=20 vent line from the top of your sump tank up to the top of both of = your=20 main tanks, but not tied into the main tank vent system. This would = allow any=20 fuel vapours to immediately flow out of the sump tank, eliminating any = chance=20 of vapour build-up, while allowing the cool fuel to continue to be = gravity fed=20 to the sump tank. These fuel vapours would then flow into the main = tanks where=20 they should immediately condense, preventing the loss of any fuel = through a=20 direct atmosphere vent system. This would (may) only work if you = have=20 your main tanks located above the sump tank. Having your FI pumps = located at=20 or below the sump pump would surely be a help as well. But I would not = expect=20 the tank to work without a vent or with a vent to=20 atmosphere.
 
    I hope some of this is relevant to you and = helps.
 
Todd=20 Bartrim  (top posted all the way to the=20 bottom)
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