X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from relay01.roc.ny.frontiernet.net ([66.133.182.164] verified) by logan.com (CommuniGate Pro SMTP 4.3.2) with ESMTP id 965234 for flyrotary@lancaironline.net; Fri, 27 May 2005 10:08:06 -0400 Received-SPF: pass receiver=logan.com; client-ip=66.133.182.164; envelope-from=canarder@frontiernet.net Received: from filter06.roc.ny.frontiernet.net (filter06.roc.ny.frontiernet.net [66.133.183.73]) by relay01.roc.ny.frontiernet.net (Postfix) with ESMTP id 9B0213658A8 for ; Fri, 27 May 2005 14:07:19 +0000 (UTC) Received: from relay01.roc.ny.frontiernet.net ([66.133.182.164]) by filter06.roc.ny.frontiernet.net (filter06.roc.ny.frontiernet.net [66.133.183.73]) (amavisd-new, port 10024) with LMTP id 31722-21-94 for ; Fri, 27 May 2005 14:07:19 +0000 (UTC) Received: from [127.0.0.1] (67-137-69-152.dsl2.cok.tn.frontiernet.net [67.137.69.152]) by relay01.roc.ny.frontiernet.net (Postfix) with ESMTP id 0723A3658EF for ; Fri, 27 May 2005 14:07:18 +0000 (UTC) Message-ID: <42972994.605@frontiernet.net> Date: Fri, 27 May 2005 09:07:16 -0500 From: Jim Sower User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7) Gecko/20040514 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Re: No fuel return for RX-8 six port References: In-Reply-To: Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit X-Antivirus: avast! (VPS 0521-4, 05/27/2005), Outbound message X-Antivirus-Status: Clean X-Virus-Scanned: by amavisd-new-20040701 (2.0) at filter06.roc.ny.frontiernet.net David Staten wrote:


Jim Sower wrote:

I think that makes the sump tank way too "busy".  Submerged pumps are nice but not pivotal.  Returning fuel from the rail to the sump is what got Paul Connor in trouble.
Gravity feed main(s) to sump, return to main(s) ... Jim S.

Dave,
How do we KNOW that the return to the sump is what caused the prob? Are we talking his redesign or the original install?
That was the consensus after looooong discussion.  Paul had a small unvented sump to which he returned fuel from the rail.  When things got hot and he returned vapor, it had no place to go, so it accumulated in the sump, displacing fuel until the inevitible happened. 
If we are talking about his first engine out, if I remember right, he had the pumps mounted high, and his fuel lines were un-sleeved/ un-insulated.
Yes we are.  Yes they were.  But he might well have gotten away with that had he not returned hot fuel (/vapor) to the sump.
The reason I am SO interested in this particular issue is that the Velocity has a sump tank as well, but it holds nearly an hour of fuel at lower power settings.
I am aware of that.  I have a Velocity too.  I've had hideous problems with assymmetric [gravity] feed to the sump from the strakes.  It doesn't take much to disturb that flow (at least with 3/8" lines).  I've had a flame out from the left strake not gravity feeding properly to the point that the 5-gal sump ran dry with a nearly full wing tank.
It HAS the room for an in-sump fuel pump, if desired (even though we've closed it already), and with the volume it lists, I am suspecting that it has enough thermal "inertia" to prevent the sump from over-heating the fuel to the point it would vapor lock.
The fact that it has room for a pump does not in and of itself make it a good idea to put a pump in there.  I'm against submerged fuel pumps on principle.  Just a strong opinion (driven mostly by instalation and maintenance issues).  There are plenty of other places to put fuel pump(s) and lots of injected cars do just that.
My original plan was to return fuel to the sump, but after Paul's first engine out to  also have the sump vent be capable of overflowing into one of the wing tanks (both of which gravity feed into the sump).
I think returning fuel to the sump is a terrible idea.  It's too small to properly cool the fuel, and it's very sensitive to transfer issues.  Paul "solved" his problem by mounting his pumps lower (not the cause of his first failure IMO but a very good idea) and venting his [heretofor unvented] sump to the main tank (a bad idea IMO).  One possible scenario that I can see on his accident is the long (10' - 12') EZ/Cozy-type run of fuel lines from strakes through selector valve to sump could have very well presented more resistance to fuel flow than the vent line back to strake presented to air flow (into sump), causing gradual depletion of sump fuel until he ran out of gas.
Trying to figure this out and follow the data.
Dave
My own (personal) recommendation is:
Large (>1/2") gravity feed from Right ("supply") strake to Sump;
Sump feeds engine; return from rail to Right strake;
Have a facet pump that transfers fuel from Left ("transfer") strake to Right;
Sump vent is capped off (and only uncapped to initially fill the sump);
ONLY fluid path into sump is from "supply" tank;
"Transfer" tank feeds ONLY the "supply" tank.

Dirt simple, as reliable as it can be, does require some fuel management (which if I can't handle, I shouldn't be flying unsupervised :o).  Simple warnings and other simple gizmos can assure more timely fuel management.

 Homepage:  http://www.flyrotary.com/
 Archive:   http://lancaironline.net/lists/flyrotary/List.html