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In my Sonex-A (aka The Tool Shed) refurbish project I've been scratching my head about the fuel system, specifically sumping the fuel tank for water. So, I'm just thinking out-loud looking for the latest group think. I'll consider wisdom and non-sense as well.

Seems installing a gascolator is frowned upon. It also seems that making a nice continuous fuel path run from the tank to the carburetor is important. I believe keeping the fuel line an insulated 3/8's hose sloping from the tank will aid in gravity feed as well as allow any formed air gas bubbles flow up stream back to the tank and not into the carb.

Now, for potential fuel contamination. I'm too much of a mechanic/engineer to build a fuel system without a way to sump the tank. The fuel pickup is not at the bottom of the tank but close. That means that the potential exists for there to be water in the tank that is unable to get to the fuel pickup until the tail is raised (conventional gear) during take-off. A potentially bad scenario.

I wish the fuel pickup was on the bottom of the tank so that "all" fuel was drainable thus water contamination would be discovered on taxi and run-up. If I don't install some sort of low point in the fuel run to trap water I must have a fuel drain the lowest part of the sump. So I'm thinking of installing an OOPS Fitting at the lowest point of the tank and installing a conventional fuel drain. Probably an Andair DV125 as they don't seem to be as leak prone as other designs. This too is a problematic solution as it's bad form to put a fuel drain in the the cockpit. Just gotta be certain it's drip free before flight. I don't like it but it's the best I've come up with so far.

What is the latest thought on this subject?

Thanx,
-brs

My builder came out the low point of the tank and firewall forward removed the gascolator and fitted an inline filter. With everything well insulated - he never completely solved slow running with everything hot. I put a NACA scoop on the underside of the cowl with a blast tube of outside air to the air intake filter. That was a major factor in resolving the stumbling at idle when hot.

I was similarly concerned about inspecting fuel. The builder of my aircraft had removed his gascolator and incorporated an in-line filter so keeping the crud out was good. But inspecting it meant cowl removal and insulation removal and wrenching.....

So I put a gascolator back in. Observing keeping the run smooth as you note. I also wrapped the exhaust pipes with insulating wrap - almost all the way to the tips (which helps the smoke system I fitted) and by some careful folding, taping and safety wiring - I insulated the gascolator body and bowl with aluminized fiberglass tape. The fuel lines themselves are insulated with insulated silicone sleeves and then wrapped with aluminized fibreglass tape.

The Gascolator I used was the ACS High Pressure Gascolator from Aircraft Spruce. It is a little larger than the one on the plans and has a higher flow rate.
https://www.aircraftspruce.com/catalog/ ... ators1.php

Not in front of my notes - but in the fuel flow test I got a slightly better result with the gascolator than the original in-line filter.

Not sure which factor (insulating it, the exhaust or the air blast tube on the intake) but it hasn't hesitated - even on a hot day with everything well heat soaked.

Hey BRS,

Let me try to address a couple of your comments/concerns:

The fuel pickup for the Sonex tank *is* at the lowest point when the aircraft is in flight attitude.

As for sumping the tank: the consensus is that it isn’t a concern *if* you are using an Aerocarb/Aeroinjector (or similar throttle-body injector / slide-carb). The reason is twofold-

• Since there is no bowl and float, you won’t get a big “pool” of water built up that will cause the intake system to see only atomized water (no fuel) for an extended time. Nor will the float (calibrated for fuel’s density) get all messed up and meter the fuel/water incorrectly. A slide carb will allow the water to pass into the engine freely, then continue to pass fuel. As long as it isn’t a huge amount of water, the claim is that the engine will stumble a bit but then carry on running.
• The Sonex fuel tank does not use the aircraft skin as part of the tank. Thus the tank does not see the same day/night heating cycle and condensation risk that wing tanks see. Unless you buy contaminated gas, it’s considered unlikely that the Sonex will collect much water in the tank.

Now nothing I’ve said is a guarantee, but I hope it addresses your concerns - along with the fact that there are a great many Sonexes flying with no sump points and little to no reports of water in the tanks or engine failures due to water ingestion.

Take care,

—Noel
Sonex #1339 - getting painted!

NWade wrote:Hey BRS,

....,,,

The fuel pickup for the Sonex tank *is* at the lowest point when the aircraft is in flight attitude.
.....
.......

Take care,

—Noel
Sonex #1339 - getting painted!

Except when it is inverted, or in a looping... :-)

Couldn’t resist, Noel

Cheers
Carlos

Hi Graeme, that newer ACS gascolator sounds promising. Would you please share the details of your complete fuel system (fuel flow sender or not?) as well as the results of your fuel of fuel flow tests with that new gascolator in place. I'm currently flying without a gascolator but never have complete peace of mind in doing so.

Thanks,

Art.............Sonex taildragger #95............Jabiru 3300 #261

Carlos Trigo wrote:Except when it is inverted, or in a looping... :-)

Couldn’t resist, Noel

Cheers
Carlos

Except if you are doing positive G acro - it's still at the low point. Sorry - couldn't resist.....

builderflyer wrote:Hi Graeme, that newer ACS gascolator sounds promising. Would you please share the details of your complete fuel system (fuel flow sender or not?) as well as the results of your fuel of fuel flow tests with that new gascolator in place. I'm currently flying without a gascolator but never have complete peace of mind in doing so.

Thanks,

Art.............Sonex taildragger #95............Jabiru 3300 #261

Art - no fuel flow sender in the system - though I am considering a RED cube.

Attached is a PDF of my schematic. And a couple of shots showing the gascolator installed and insulated and the tailpipes on the exhaust insulated. Clamps to secure fuel line to firewall and engine mount not yet installed in these shots. Bit of an optical illusion in the picture of the fuel pipe after the gascolator - it doesn't loop uphill. Very shallow downhill all the way to the carb.

As long as I orient the drain correctly - I can "reach" it with a Gats jar through the air exit when the cowl is on.

--

Fuel Flow at carburetor inlet point:

With inline filter in place - 5 US Galls of fuel in 5min and 45 sec
With Gascolator in place of inline filter - 5 US Gall of fuel in 5 min and 25 sec

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To the other point about
"Sonex not having a water history"

I had a solid 1,100 hours in a C150 with not a scrap of water at the Gascolator - till the day I got a Gats jar full of water - traced to bad gas picked up at an airport.

Sonex have gone down with engine failures - for not obvious reasons. Even if the AeroInjector is "tolerant" of water - I don't want mine to be "tolerating" water at a mission critical moment. If I can arrange clean fuel - I want clean fuel.

Call it the ex-ship captain in me where ships have been killed by contaminated fuel - especially when stirred up out the tanks in bad weather.

--

I'm also mindful of folks who have had vapor lock in gascolators and might have a different experience. I've tried to do my best to work around this possibility.

This set up has been on the plane since March 2000 and I've put 75 hours on this fuel system with gascolator - through some decent heat of the summer of 2020 as well.

YMMV

Graeme, thanks for taking the time to post all the information regarding your Sonex. I was curious as to whether or not you currently had a fuel flow sender in the system and I read the answer is no. My experience has been that with the red cube installed I have to remove the Usher gascolator and go with a filter to eliminate all of the "burps". And that's with the gascolator contained in a shroud with a cold air blast tube to keep the bowl cool. When fuel flow tests are done either with the gascolator or the filter in place, the results aren't that much different from each other, and that's puzzeling.

What was the pitch attitude and the amount of fuel in the tank while doing your fuel flow tests? You're showing a rate about double of the highest I've ever observed on any tests I've done on my Sonex.

Thanks again, Art

Just 5 gallons in the tank - tail picked up and pitched "level" for cruise flight.

Wonder what would happen if the Red Cube was immediately below the tank pickup on the "cool side" - rather than forward of the firewall on the engine side?...

Graeme, my red cube is installed just downstream of the on-off valve at the exit of the tank. Last 2 fill ups were within 0.1 gallon so that seems to be a good location for the cube despite it not being a recommended location.

Thinking about where you installed the gascolator. .....it's really located where a filter might be installed rather than down lower on the firewall which is more typical and where mine was installed. But your location could be a good compromise where one gets much of the benefits of having a gascolator but without all the additional plumbing involved with a lower position. I may try what you have done and see how that works on my Sonex.

Regarding the fuel flow tests.....they're usually done with the aircraft pitched up to simulate a climb under full power. On my initial tests I used a pitch angle of 21 degrees as well as additional tests in the 3 point stance (taildragger). When I run additional tests at this time I generally compare the results in the 3 point stance as its more easily done.

Art...............Sonex taildragger #95,,,,,,,,,,,,,,,,,Jabiru 3300 #261