Header tank venting...

Well, I have backed myself into a corner.

Further to the last post about the header tank vent(s)... current design (T'ed into the vent for the pillar header and to each main tank) is not going to work.  This will lead to cross feed and an ineffective fuel valve.

What are the 'truths'.  Things that I know are facts:

1. The header needs to be vented to allow air out so there is room for fuel to enter
2. The vent point should be higher than the highest fuel level
3. The current configuration will allow bypassing of the fuel valve, and cross feed on the tanks

Options:

1. Check valves on the header vent between the pillar header and the main header.  This will stop fuel from the main tank / pillar header from each side entering the header.  It will allow air to escape IF the air pressure is greater than the head pressure from the fuel.
2. Mast vent on the center line with the exit above the wing level.  This presents an opportunity for fuel siphoning out the vent.  No bueno.
3. Using Paul's method run a new vent line out to one wing tip.  This is problematic, but doable.  In theory this solves all problems.

Option 1 is easy and cheap to try.

Option 2 scares me

Option 3 is more work but most likely the best solution.

4th option:  Modification on option 3... run a vent line out and T into the outboard vent on the main tank.  This is more doable, but assumes I have access through the forward spar to fish the new vent line through and T it in.  Need to look at old pictures to see if this is possible.

Yesterday (February 22) I installed a check valve on the starboard header vent.  Aircraft spruce check valve that has no spring, gravity only.  Arrow points towards the main tank to let the air out.  I was going to install the port side, and realized I only ordered enough fittings for one side (ordered 2, needed 4).  So those are now ordered.

Prior to installing, I wanted to get the fuel out of the vent lines.  After grounding the aircraft and draining all the fuel from the belly low points and header, closed the main fuel selector to OFF, and pushed compressed air into the header from the firewall fuel line fitting.  That did the trick... when cutting the vent line, there was no fuel.  WIN!

Now waiting for the other fittings to arrive to do the starboard side.

I am very concerned about fuel delivery.  This needs to work and work well.  No compromises here.

2nd check valve installed (Feb 28).  Fuel ready to go in the tanks... first will be a leak check, and then a fuel delivery check.  See how much I can actually deliver.

I am getting more stoked / positive on option 1.  In theory, when the pumps are drawing fuel from the header, it will create suction... which will pull the check valves closed... and actually draw fuel faster.  At least that is my theory.  Will see if it holds true.  Stay tuned...