Return-Path: Received: from wb2-a.mail.utexas.edu ([128.83.126.136] verified) by logan.com (CommuniGate Pro SMTP 4.2b5) with ESMTP-TLS id 166302 for flyrotary@lancaironline.net; Thu, 17 Jun 2004 12:06:21 -0400 Received: (qmail 72437 invoked from network); 17 Jun 2004 16:05:49 -0000 Received: from dhcp-191-101.per.utexas.edu (HELO benefits3.mail.utexas.edu) (146.6.191.101) by wb2.mail.utexas.edu with RC4-SHA encrypted SMTP; 17 Jun 2004 16:05:49 -0000 Message-Id: <5.1.1.5.2.20040617104627.028c0e90@localhost> X-Sender: msteitle@mail.utexas.edu@localhost X-Mailer: QUALCOMM Windows Eudora Version 5.1.1 Date: Thu, 17 Jun 2004 11:04:13 -0500 To: "Rotary motors in aircraft" From: Mark Steitle Subject: Re: [FlyRotary] Re: Fuel Delivery - Vapor Lock In-Reply-To: Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="=====================_67086578==.ALT" --=====================_67086578==.ALT Content-Type: text/plain; charset="us-ascii"; format=flowed Kelly, I think you're right, I should have said that avgas is lower than mogas. Mark At 01:36 PM 6/17/2004 +0000, you wrote: >Guys, > > I could be wrong but mogas vapor pressure has been reported as usually > >higher than avgas.IMHO > > > >Kelly Troyer >-- >Dyke Delta/13B/RD1C/EC2 > > > >-------------- Original message from "Russell Duffy" ><13brv3@bellsouth.net>: -------------- > A couple of questions... Your pumps, filters, and regulator is in the > cockpit, not in the tank as in 99.9% of the automobiles today? > >Correct. No good way to put the pumps in an RV wing tank. > > How far are your pumps from the tank fitting, and what size line feeds > the pumps. > >The distance from the pickup, to the fuel pump inlet is less than 2 feet, >and would be gravity fed until about the last 5 gallons or so of the tank. > > Do you run mogas? > >Yes. 87 octane. > > If you do run mogas, do you know the vapor pressure of the fuel you're > running? Do you test it? > >Nope, and nope. > > I have read that mogas has a lower vapor pressure, which means it can > vapor lock easier than 100LL. > >That's what I've always heard as well. I've also heard that they modify >the vapor pressure for temp, so the worst case would be a hot day, in the >winter. I've always wondered if they even bother changing the mixture >here in FL though. > >Have you tested your installation to see if it will re-prime if you >inadvertently run a tank dry? > >I haven't done that particular test, but the first time I ran the pumps >after filling the tanks, the fuel pressure was almost instantaneous. I'll >make a mental note to try this again when I get the tank low enough to >easily drain the remaining fuel. Since I stole Tracy's fuel system, I >only feed from one tank. If I run that dry, I would first have to >transfer fuel (fairly slowly) from the other tank, then worry about >priming the pumps. In other words, I don't plan to run the tank dry when >there's any fuel in the other tank. I realize this is easier said than >done, but that's the plan. > >Cheers, >Rusty (hoping I don't get hit by lightning when I have a fuel leak) --=====================_67086578==.ALT Content-Type: text/html; charset="us-ascii" Kelly,
I think you're right, I should have said that avgas is lower than mogas.

Mark

At 01:36 PM 6/17/2004 +0000, you wrote:

Guys,

I could be wrong but mogas vapor pressure has been reported as usually

higher than avgas.IMHO

Kelly Troyer
--
Dyke Delta/13B/RD1C/EC2

-------------- Original message from "Russell Duffy" <13brv3@bellsouth.net>: --------------
A couple of questions... Your pumps, filters, and regulator is in the cockpit, not in the tank as in 99.9% of the automobiles today?

Correct. No good way to put the pumps in an RV wing tank.

   How far are your pumps from the tank fitting, and what size line feeds the pumps.

The distance from the pickup, to the fuel pump inlet is less than 2 feet, and would be gravity fed until about the last 5 gallons or so of the tank.

   Do you run mogas?

Yes. 87 octane.

   If you do run mogas, do you know the vapor pressure of the fuel you're running? Do you test it?

Nope, and nope.

   I have read that mogas has a lower vapor pressure, which means it can vapor lock easier than 100LL.

That's what I've always heard as well. I've also heard that they modify the vapor pressure for temp, so the worst case would be a hot day, in the winter. I've always wondered if they even bother changing the mixture here in FL though.

Have you tested your installation to see if it will re-prime if you inadvertently run a tank dry?

I haven't done that particular test, but the first time I ran the pumps after filling the tanks, the fuel pressure was almost instantaneous. I'll make a mental note to try this again when I get the tank low enough to easily drain the remaining fuel. Since I stole Tracy's fuel system, I only feed from one tank. If I run that dry, I would first have to transfer fuel (fairly slowly) from the other tank, then worry about priming the pumps. In other words, I don't plan to run the tank dry when there's any fuel in the other tank. I realize this is easier said than done, but that's the plan.

Cheers,
Rusty (hoping I don't get hit by lightning when I have a fuel leak)

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