Fuel filtration

Thanks Jeff,

I have "finger screens" in both wing tanks (yet to install wings) that have been pressure tested & washed out with fuel (never quite get everything).

Wing tanks 30 L x 2 feed, via transfer pump, into a 40 L in fuselage header tank (no finger screen).

I have been doing engine runs, to fine tune cowling air flow/cooling, with fuel from header tank. Have been a bit surprised by the amount of gunk that has mostly been caught by the gascolator with only a few flecks ending up in the carby float bowls.

As you rightly point out the finger screens are a very course mesh, that pretty well just keep the odd fly out or whatever that goes into the tank when refiling.

In my view the system needs a 120 micron (or similar) between the transfer pump & the wing tanks and a similar filter between the boost pump and its supply tank. By doing this, I would hope,  a 74 micron screen in the gascolator will bring the fuel "quality" to Rotax standard.

Is there guidance on this from Sonex or other Sonex builders?  

"...........guidance on this from Sonex or other Sonex builders?"

Not that I am aware of.

# Sonex has only quite recently recognised Rotax engines in its suggested/approved/supported engine line up - so unlikely to have advice that varies from Rotax manuals.

# The problem (if there is one) is nothing to do with the airframe - its about delivering appropriate (Rotax specification) fuel to the engine.

# My Sonex is definitely not a standard airframe - amongst its several  "adjustments" is the two wing tanks  feeding into a large header tank - Sonex have a single fuselage tank.

# I will have to find an effective/safe way of introducing,  what I consider to be appropriate, fuel filtration into the existing system. This will almost certainly be the cutting of the existing aluminium fuel lines and the introduction of an in line filter where appropriate. 

# If I am to conform to the general advice - a dedicated filter on each tank, I will need to adapt a 10mm OD aluminium fuel line down to an 8mm OD fuel filter and then back up again - is there a way of shrinking/squeezing aluminium fuel line down?

You might talk with the folks at Andair, they specialize in light aircraft fuel system components and design. They have a few sample fuel system configurations on their website and one of them uses filters at the root of each wing tank. 

https://www.andair.co.uk/

Jeff,

My fuel system is already installed, however I am not happy with the lack, level and location of filters.

In my circumstance it will be most time/ effective to cut into the existing fuel supply lines and , using rubber hose, introduce a suitable inline filter for each wing tank.

I will probably use Hengst H102 WK filters as I have experience with them and have a small supply on hand. I also intend to change the existing gascolator filter screen (which I suspect is 120 mu) to a 74 mu.

The alternative is to leave the existing fuel reticulation untouched  (including the 120mu gascolator screen) and put a single large area in line filter of 75 mu (Baldwin BF7863) between gascolator and Rotax pump. Although this is by far the simplest "fix" it has the disadvantage of using a plastic filter within the engine bay/cowling, no separate filter for each wing tank and no filtration before pumps.