Return-Path: Received: from ms-smtp-02.southeast.rr.com ([24.93.67.83] verified) by logan.com (CommuniGate Pro SMTP 4.1) with ESMTP id 2504901 for flyrotary@lancaironline.net; Sun, 27 Jul 2003 20:34:23 -0400 Received: from o7y6b5 (clt78-221.carolina.rr.com [24.93.78.221]) by ms-smtp-02.southeast.rr.com (8.12.5/8.12.2) with SMTP id h6S0V8qQ024162 for ; Sun, 27 Jul 2003 20:31:10 -0400 (EDT) Message-ID: <001401c354a1$2bd12320$1702a8c0@WorkGroup> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Fuel Header tank Date: Sun, 27 Jul 2003 20:42:48 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0011_01C3547F.A3E54FC0" 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 This is a multi-part message in MIME format. ------=_NextPart_000_0011_01C3547F.A3E54FC0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Todd, Its normal to find some pressure in your sump when the ambient = temperature is that high even without the engine running.. And you are = correct - that passing throught the fuel lines and fuel rails, the fuel = does pick up heat. If your high pressure pumps feeds are located on the = bottom of your sump, you should have minimum problems with percolation. = Extend runs on the ground will cause heat to build up in your fuel to = some extent. Normally, the warm fuel is replaced with cooler fuel from = your wing/fuselage tanks, however, when the engine is operated long = enough and the fuel gets warm enough, you will experience some heat = build up in the fuel. That tends to be aggrevated when the fuel flow = is reduce to say idle. Then you do not have as much of the cool fuel = being drawn into the header tank as you are using less of it out of your = header tank. =20 With the location of your header tank, I would be very surpised that = you would see any signs of percolation while flying for two reasons. 1. = you will have less heat under the cowl as the cooling air flows through = and 2. the fuel consumption rate is much higher than at idle so the = fuel does not have as much time to pick up heat and return to the sump = and that fuel does not stay in the sump very long which also tends to = keep the heat build up down. =20 However, I think it wise you installed a boost pump. I would attempt = to make the situation as bad as you can on the ground (within reason = {:>)) to try to get it to percolation and then confirm the operation of = your boost pump will supress the percolation - before flying. Once = flying, I doubt you will have any problem. I have flow in 100F weather = with my sump tank on the forward of the firewall and once I have climbed = to altitude I turn off the boost pump. As you say, you would not want = to be dependent on the boost pump continiously while flying. Ed Anderson ----- Original Message -----=20 From: Haywire=20 To: Rotary motors in aircraft=20 Sent: Sunday, July 27, 2003 3:51 PM Subject: [FlyRotary] Fuel Header tank Due to my addition of auxiliary fuel tanks, I installed a header tank = to return fuel to. After reading Ed's chronicles of his tank and = exchanging a few e-mails with him, I decided to build a tank large = enough to provide a usable reserve and locate it aft of the firewall. I = had concluded that the larger fuel volume and cooler location would = preclude the percolation problems that Ed has experienced. Well it seems that most of the heat is picked up as the fuel runs = through the system, as I'm seeing some signs of heated fuel. It has been = warm here (30C+) and problems didn't start showing up until after = extended taxi runs (40min), but I'm trying to take care of worst case = scenario. Turning on a boost pump does help, but I don't want to have to = run one continuously. I'm hoping this will not be necessary while = in-flight. I did equip this header tank with a vent valve to purge the air = out before starting engine. This valve would normally never be open = during operation as I expected the tank to be under a vacuum as it draws = fuel up from wing tanks, but when I did crack it open, I was surprised = to see it was under pressure. If this continuous, I may add a press = gauge to monitor this.=20 S. Todd Bartrim Turbo 13B RV-9Endurance C-FSTB http://www3.telus.net/haywire/RV-9/C-FSTB.htm "Whatever you vividly imagine, Ardently desire, Sincerely believe = in, Enthusiastically act upon, Must inevitably come to pass".=20 ------=_NextPart_000_0011_01C3547F.A3E54FC0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Todd,
 
    Its normal to find = some pressure=20 in your sump when the ambient temperature is that high even without = the=20 engine running.. And you are correct - that passing throught = the fuel=20 lines and fuel rails, the fuel does pick up heat.  If your high = pressure=20 pumps feeds are located on the bottom of your sump, you should have = minimum=20 problems with percolation.  Extend runs on the ground will cause = heat to=20 build up in your fuel to some extent.  Normally, the warm fuel is = replaced=20 with cooler fuel from your wing/fuselage tanks, however, when the engine = is=20 operated   long enough and the fuel gets warm enough, = you will=20  experience some heat build up in the fuel.   That tends = to be=20 aggrevated when the fuel flow is reduce to say idle.  Then you do = not have=20 as much of the cool fuel being drawn into the header tank as you = are using=20 less of it out of your header tank. 
 
  With the location of your header = tank, I=20 would be very surpised that you would see any signs of percolation while = flying=20 for two reasons.  1.  you will have less heat under the cowl = as the=20 cooling air flows through and 2.  the fuel consumption rate is much = higher=20 than at idle so the fuel does not have as much time to pick up heat and = return=20 to the sump and that fuel does not stay in the sump very long which also = tends=20 to keep the heat build up down. 
 
  However, I think it wise = you installed=20 a boost pump. I would attempt to make the situation as bad as you = can on=20 the ground (within reason {:>)) to try to get it to percolation = and then=20 confirm the operation of your boost pump will supress the percolation - = before=20 flying.  Once flying, I doubt you will have any problem.  I = have flow=20 in 100F weather with my sump tank on the forward of the firewall and = once I have=20 climbed to altitude I turn off the boost pump.  As you say, you = would not=20 want to be dependent on the boost pump continiously while=20 flying.
 
Ed Anderson
 
 
----- Original Message -----
From:=20 Haywire
Sent: Sunday, July 27, 2003 = 3:51 PM
Subject: [FlyRotary] Fuel = Header=20 tank

Due = to my addition=20 of auxiliary fuel tanks, I installed a header tank to return fuel to. = After=20 reading Ed's chronicles of his tank and exchanging a few e-mails with = him, I=20 decided to build a tank large enough to provide a usable reserve and = locate it=20 aft of the firewall. I had concluded that the larger fuel volume and = cooler=20 location would preclude the percolation problems that Ed has=20 experienced.
    Well it seems that most of the heat is picked up as the fuel = runs=20 through the system, as I'm seeing some signs of heated fuel. It has = been warm=20 here (30C+) and problems didn't start showing up until after extended = taxi=20 runs (40min), but I'm trying to take care of worst case scenario. = Turning on a=20 boost pump does help, but I don't want to have to run one = continuously. I'm=20 hoping this will not be necessary while in-flight.
    I did equip this header tank with a vent valve to purge the = air out=20 before starting engine. This valve would normally never be open during = operation as I expected the tank to be under a vacuum as it draws fuel = up from=20 wing tanks, but when I did crack it open, I was surprised to see it = was under=20 pressure. If this continuous, I may add a press gauge to monitor this. =

S. Todd Bartrim
Turbo 13B = RV-9Endurance
C-FSTB
http://www3.telus.net/haywire/RV-9/C-FSTB.htm

=   =20 "Whatever you vividly imagine, Ardently desire, Sincerely believe in,=20 Enthusiastically act upon, Must inevitably come to pass".

 
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