Mailing List flyrotary@lancaironline.net Message #65521
From: Charlie England ceengland7@gmail.com <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Fuel System Design for High wing Aircraft
Date: Mon, 20 Jan 2020 16:59:16 -0600
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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It's obviously do-able, but there are several issues that make what you're proposing....complicated. It just can't be done truly returnless with gerotor or roller vane pumps. They pump far more fuel than the engine (variably) needs, and because they are positive displacement pumps, they will either stall or break something else in the fuel system due to excess pressure. You can make the system 'dead head' at the injectors, but there must be some form of bypass regulator somewhere between pump output and injectors. Bypassing excess flow back to the input of the pump will *sometimes* work, but it's too unpredictable for most to trust it in an a/c. If the system ever sucks air for any reason (or vaporized fuel after shutdown manages to push back through the pump to the inlet), the pump will airlock and just recirculate air because air is easier to move than fuel. Add to that the fact that pressure invariably varies with flow, and if pressure varies at the injector, injector flow varies with the same open time, which will make tuning an...adventure.

Cars are returnless by using some variation of the technique shown in the product that Steve linked earlier, combined with in-tank *turbine style* pumps. So, intank turbine pump, pressure controlled by a MAP sensing controller, and you're done. Except, now you need another intank pump and controller for reduncancy. Two tanks? Two more pumps and two more controllers, plus switching. Or a switching array that would make a single pump look reliable and safe.

A high wing a/c with a sump (header) tank would make life simpler, since only one pair of injection pumps would be needed in the sump tank.

Charlie

On Mon, Jan 20, 2020 at 4:33 PM Ernest Christley echristley@att.net <flyrotary@lancaironline.net> wrote:
Does the fuel necessarily have to be returned?  What is the benefit of returning it?  Injectors can take 50lbs of pressure.  In fact, they make a better spray with the higher pressure, and atomize even better if the fuel is sprayed hot.  Many modern cars don't have a return.  As long as you keep the pumps  and the gas going to them cool, you won't get vapor lock. 

Keep the fuel pump below the injectors and behind the firewall.  It'll draw cool fuel and then pressurize it to keep it liquid until it is sprayed.  On shutdown, the fuel in the line firewall forward will get hot and vaporize, pushing liquid back to the pump.  But, as soon as the pump is flipped on the vapor gets compressed and liquified again for the rest of its time in the line.

I could be wrong. . .

On Monday, January 20, 2020, 10:43:07 AM EST, Jeff Whaley jwhaley@datacast.com <flyrotary@lancaironline.net> wrote:


Hi Bobby, yes Ed used a small (1 qt) can attached to the engine-side of the firewall, to accept main fuel IN, return fuel and parallel outputs to his fuel pumps.  This system would work regardless of wing arrangement but I'm not too sure how it performed at keeping LOW fuel temperatures.

My high-wing has a 2 gallon header tank on the cabin-side of the firewall, so I Tee'd my fuel return into one of its two vent lines that connect back to the wing tanks.  This is a gravity-fed system until it passes through the firewall to the pumps ... the vent lines assist in draining the tanks evenly.
Jeff

What is the best method for handling return fuel in a high wing? Fuel return to a small header tank sized to keep fuel temperatures low? I think Ed Anderson may have used a small header in his RV6.

Asking for a friend with an airplane addiction.

Bobby

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: January-20-20 6:01 AM
To: Rotary motors in aircraft
Subject: flyrotary Digest #4865

        Rotary motors in aircraft Digest #4865

1) Re: Mufflers
2) Re: Mufflers

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