Fuel System Design Review

[flyvans.com]

steve,

sorry, we did not weigh the components...
our pump package looks a lot more complex than it actually is.
we riveted two pieces of angle to the floor longerons. on these pieces are 4 nutplates each. now the fuel pump assembly plate is laid onto these angles and attached to the angles using screws.
we also took great care to attach the fuel filter adel clamps using an-3 nutplates and run the various fuel lines for easy serviceability later on.
compared to the standard vans/afp mount, we added some aluminum tubing for the return (really lightweight), the dual selector is probably twice as heavy as the standard andair selector, which is again heavier than the default van's el cheapo part. but even that isn't that bad, as a large part of the body is made from composites/plastic.
The piano hinge by the way is intended for the mounting of a cover.
And this is a picture from an earlier stage of construction:
but it shows the approximate location nicely. The package is even a bit closer to the spar in the final location.

the selector sits low on the floor, about level with the tank supply lines, which is another feature positively affecting the head pressure to the fuel pump/probability for vapour lock.
since we plan to build a center console between the flap channel, the point where van's default fuel selector is located and the panel, we will integrate the fuel selector knob with the extension, all from andair. www.andair.co.uk

regards, bernie

[AlexPeterson]

Originally Posted by flyvans.com

Hi,

our thinking really goes this way:

avgas is gonna go sooner than later...
even if the return line might only be used for purging at this point in time (current plans are for a tmx-iof-360), constant return systems will be required to run automotive gasoline. SNIP[/url]

There is an ongoing confusion between what the Airflow Performance purge valve line's and what classical return lines' in some FI systems functions are. Their functions are unrelated.

This thread started with a question about a method to plumb an AFP purge valve. All that tubing and a duplex valve are not needed to get the benefit of a purge valve. My advice is to plumb it in exactly as AFP has outlined in their manual for RV's. As has been pointed out in earlier posts in this thread, hazards to creative fuel system design have been identified.

Please, this is not a flame, but fuel system in-flight design testing is not something to take lightly.

Regarding where to put the flow sensor, I have had no issues with mine between the AFP fuel servo and the flow divider. It is mounted on the firewall, horizontally with the wires pointing up.

[rickmellor]

Originally Posted by AlexPeterson

There is an ongoing confusion between what the Airflow Performance purge valve line's and what classical return lines' in some FI systems functions are. Their functions are unrelated.

Unrelated functions but compatible requirements. The purge line must NOT be returned to the fuel inlet. AFP recommends either returning it to the tank or dumping it into the fuel tank vent line. The purge valve allows you to remove hot fuel and vapors from the fuel system so a full return of some sort is required.

AFP's default configuration essentially gives you a duplex selector by requiring you to select a specific tank (left) while you're purging so that the purge output can discharge to the opposite tank. With a duplex selector you don't have to worry about that. Fewer checklist items are good.

For me the deal maker with the duplex selector is that I already have the Andair. I was originally planning an ECI fuel system, which uses a return, but have since settled on the AFP setup. Since I've already spent the money why not take advantage? I understand that there are simpler/cheaper ways to get the same result but this one works for me. Also, a nice bonus that the Andair + fuel tank return gives you over the vent line returns is that you don't risk dumping gas (small amount as it may be) out on the ground.

As for the pressure relief line running to the Andair ... Don pointed out that this is not such a good idea. You won't run the pump with the selector set to off in any case other than a mistake, but why risk the torture on a critical component? Much better to stick with the plans on that bit.

[rickmellor]

I've modified my original diagram to show the flow sensor between the fuel servo and the purge valve. I've also corrected the relief valve output to return to the pump inlet. I'm posting the updated diagram for posterity.

Originally Posted by AlexPeterson

Regarding where to put the flow sensor, I have had no issues with mine between the AFP fuel servo and the flow divider. It is mounted on the firewall, horizontally with the wires pointing up.

Alex or others who have mounted the flow sensor in front of the firewall, would you guys mind posting a picture of your setup? I could use some ideas to get the wheels turning.

-Rick

[az_gila]

Originally Posted by flyvans.com

......
with our setup, we're pretty much ready for whatever may come down the road. at least no hassle in removing the wings, installing a return line etc...
it's a bit of extra cost (fuel selector $$$, very little added weight), but peanuts compared to the overall tab :-( the AFP FI setup we need anyway for the fuel injected engine.)

regards, bernie
www.flyvans.com

Ahh... a different design requirement not mentioned before...

That makes more sense now....

gil in Tucson

[flyvans.com]

@AlexPeterson

we're fully aware of the "creative fuel system inflight testing" risks...
i would just like to remind you that, if you mentally get rid of all the return system parts, you end up exactly as per AFP on the supply side of things! So nothing creative there. The one thing that needs change/was overlooked/not fully taken into account, has been brought up by don from AFP in this thread. We will replumb the pressure relief right back to the pump inlet instead of the return line.
Aren't these forums simply awesome?

regards, bernie

[RVbySDI]

Bernie,
Thanks for the posts. Please keep them coming. I would like to ask anyone who has pictures of your installs to please post them if at all possible. Many of us out here are interested in the fuel flow issues associated with FI as we are planning for our own systems. This thread has been very helpful.

[SvingenB]

Originally Posted by flyvans.com

Hi,
...

avgas is gonna go sooner than later...
even if the return line might only be used for purging at this point in time (current plans are for a tmx-iof-360), constant return systems will be required to run automotive gasoline. and the various fadec's and related systems coming to market all have their individual requirements as well.
how diesel/jet-a systems will look like is not yet quite clear, but chances are that they will need some form of return line as well. in any case, expect to see changes firewall forward within the next 10 years.
also, avgas is way more expensive over here in europe, so motivation to move to alternative fuels is even bigger when the time comes...

...

I am planning for FI and auto fuel. Why would I need a constant return system? Vapour lock?

[rickmellor]

It's my understanding that a constant return system is meant to reduce the effects of heat-soak and thus, vapor lock issues but they're not strickly required. Although, for conventional auto fuel vapor issues may be as much myth as anything. Auto fuels with ethanol are a different story.

-Rick

[mgomez]

I bought my pump kit 2nd hand, and the only doc it came with was a drawing by Van's. No AFP installation manual (I'll buy one from AFP soon.) So please forgive the dumb questions.

By staring at the intestine-like snarl of tubing I got, I figured out which is the relief valve and which is the bypass valve. So:

1) Is the purpose of the bypass valve to allow fuel to flow to the mechanical pump when the electric pump is off?

2) Is the purpose of the relief valve to set the fuel pressure to some fairly high value (i.e. a bit more than the FI servo wants?) What is that value? I assume the valve cracks above that pressure, and the excess fuel goes back to the T in the inlet line?

3) What's the flow rate in that relief line when the engine is drawing small amounts of fuel?

Thanks,
Martin