Mailing List flyrotary@lancaironline.net Message #63178
From: Andrew Martin <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] fuel system peer review
Date: Tue, 21 Mar 2017 09:51:50 +0800
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Charlie, I think that would work. probably better to re-route the lines though, so fuel from Aux tanks naturally wants to go through the regulator rather than to the fuel rail. eventually you will leave a transfer pump on and suck air.
In effect you've got 4 efi pumps, maybe just a little bit extreme, especially if someone turns them all on.

Andrew
(currently replacing entire fuel system from tanks to rail. previous just too complex and heavy. sump tank, 2 pumps & 4 valves are coming out)

On Tue, Mar 21, 2017 at 5:26 AM, Charlie England <flyrotary@lancaironline.net> wrote:
1st, let me define my delivery architecture. I like Tracy's idea of feeding the engine from one tank, and transferring aux tanks to the main tank. I understand the downside of being unable to switch tanks, but many a/c (including turbines) supply from one tank, so that's my choice. It avoids the need for a duplex fuel selector, which I like. Effectively, I have 3 'aux' tanks, and I'm using the stock (3 inlet) Van's RV fuel selector to feed redundant transfer pumps in parallel. 

I know that most have a separate return port in their tank(s) for regulator return. With my need for aux transfer, my original plan was to 'T' the aux transfer line into the regulator return line, which I'm pretty sure has been done before.

I'm currently working on installing both injection pumps in the fuel tank, conceptually similar to standard auto practice for the last couple of decades: no risk of vapor lock with the added bonus of a very clean installation. The regulator will be in the wingroot, just outside the tank, with the manifold pressure line running to that location for pressure control. (Deadheading fuel to the fuel rail has been done on both cars and a/c successfully; I believe it's an option on the new SDS system being marketed to Lyc drivers now.)

The recent thread on fuel pressure changes while running both injection pumps got me thinking. If it's typical to see only a couple of PSI change when running both pumps, has anyone considered running the transfer line into the regulator? The reason I'm considering this is twofold. It provides a 'final option' for short term fuel delivery if both injection pumps are lost, and, because the regulator is in the wingroot, I would need to run only one fuel line to the supply tank.

I'll be using gerotor style transfer pumps (positive displacement) and the aux selector has an 'off' position, so backflow won't be an issue.

A quick & dirty sketch is attached, diagramming the idea.

There would never be more than 2 pumps running at any time, since transfers would only happen in cruise flight. Can anyone poke holes in this arrangement? 

Charlie

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