Header tank, venting, flow, low fuel levels

The header tank - and more specifically the header tank level indication - have been giving me problems.

On the first flight, the header tank warning went off.  Landed quickly, and tore the entire system apart and made it better.  

4 hours of trouble free flying after that.

Then the low fuel header warning started going off again - but it always cleared, usually within 30 to 60 seconds.

I am not going to live with this, so investigation into why.

I know the fuel system can keep up with the demands of the engine.

Through a bunch of smart fellas on the forum and fellow UL builders, we have been scratching our heads.

The suggestion came up to look for something on the suction side that is tight enough to not leak, but not tight enough to not let air into the pump / injectors.  He also suggested del rings (available at spruce) that provide a better seal on AN fittings.  But then I found it.

On the input to the pumps, the clamps were not tight.  And the hose barb fittings on the other side of the hose had no clamps.

Before

After:

Time will tell if this solves the problem... but the current working theory is air was coming in through the return line into the header.  The air would build up, and it would take time for there to be enough pressure for the air to make its way up the vent and 'burp' the tank.  Then everything would be fine for awhile.

Header tanks are a real head scratcher in their design, specifically the vents (in high wing aircraft).  I think I am slowly ironing out the kinks.

Update:  This did not solve the problem, and now the problem is worse.  I started putting some pieces of the puzzle together a few days ago.

I started of running ethanol free 89 octane fuel, and used boostane to bring it up to 94 octane.  Around hour 5, I switched to ethanol 94 octane, which I can get locally (have to go to Blaine, WA for ethanol free).  The problems started (again) when I switched fuels.  I did not put these two things together until about hour 19.

So the problem started again after switching to ethanol fuel, and it has been getting worse the as the outside air temps have risen.

I started googling 'ethanol fuel', 'injection systems', and 'header tank'.

And then add this (below) from the UL installation manual.

What I make from all this.

• I had 5 trouble free hours running non-ethanol fuel
• My header tank design had a flaw, in that my return was on the top of the tank.
• Ethanol fuel is more prone to frothing
• I've been having more problems since the weather started warming.

I now have a tube / stand pipe for the return that is 5" below the top of the tank.

This should fix or at least help the frothing problem.  I may be dealing with vapour as well.

The vents are capable of clearing the air... it's been doing that for 14 hours of issues.

I have replaced a section of the vent line on the A pillar with translucent tubing.

The hope is I will be able to see bubbles.  I plan on having a camera face the vent tube to capture what is going on.

I am going to go back to ethanol free fuel.  I may start off with a 2/3'rds mix as I have to get rid of the ethanol 94.  1 part ethanol, 2 parts non ethanol.

Cameras on the panel and the vent tube.

Ground run first to shake out any issues.  If that is successful, will stay over the airport for at least an hour to shake it out more. 

So fast forward months... 

I've upgraded the vent line to a 6 mm ID all the way out to the wing tips.

I moved the header vent line to be AFTER the check valve (not before).

The problem is virtually gone... it will happen every once in awhile, and you need to drop a wing and go into uncoordinated flight for 30 seconds to get the bubbles moving from the header up to the tips.  Seems to happen about every 2 hours of flight.

I think I have a bit of a P trap in a climb... but it doesnt always happen in a climb.  So I dont know.  Its FAR FAR FAR better than it was.