Fuel System Musings, comments encouraged

On Oct 20, 5:45*pm, wrote:
On Oct 20, 6:43*am, flybynightkarmarepair wrote:

RE the Ercoupe example: I don't like header tanks from a crash safety
standpoint, and another vent, and a return line souunds like MORE
plumbing to me. *Plus, this is a VW conversion, and if I used a
mechanical fuel pump it would be on the TOP of the engine, plus they
are not sealed like aircraft mechanical fuel pumps are, so this is a
no-go.

The Ercoupe design has worked safely and well for over fifty years.
The lack of a header tank does not guarantee crash safety - nor does
it's presence necessarily increase the danger.

I've read an accident report where 2 POB died in an otherwise
survivable Ercoupe crash due to the fuel tank splitting and soaking
them in gas. Ignition happened, and they became human wicks.

Others have noted ways of mitigating this via fuel cells, and while
you make a pretty good argument, I'm not convinced. Fred Weick, the
designer of the Ercoupe (although perhaps not this part of it...) also
had significant input to the most numerous low wing production design,
the Piper Cherokee, and it DOES NOT use a header tank. Strictly
circumstantial, to be sure, but draw your own conclusions.


The one pump in that design can either be mechanical or electric, it
matters not. There are no vents involved in the design. The float
gauge holes in the caps provide adequate venting. If you are forced to
park outside in the rain, you simply put a cap over the cap.

I don't like this at all. I don't like relying on the nut between the
headphones to keep me safe from a significant hazard (water in the
gas) in an airplane with as small a fuel capacity as the one I'm
building. I want a screened vent of at least 3/8 in. dia. that exits
the BOTTOM of the wing, but vents the TOP of the tank.

There is
one line connecting the two tanks which are located at the wing roots.
If one wing is parked, or flown, a little low it makes no difference.
There is a tee in the line that leads to the inlet of the pump.

I recall a LONG argument on this forum (or maybe it was on a Zenith
601 forum - LOTS of that design fly with a system VERY much like
you're advocating) about unporting a tank at low fuel levels and
sucking air, that I don't want to rehash, but I'll just note that I'm
firmly in the LEFT/RIGHT/OFF fuel selector camp for low wing planes
with wing tanks.

Gravity flow to a
carburated engine is the safest and most reliable fuel feed possible,

I agree, I agree, to the extent that I'd rather build a high wing
airplane if plans for one that meets my mission requirements were
available when I was first looking. The Aerosport Quail is the only
HIGH wing all metal VW powered single place homebuilt aircraft I'm
aware of, and it's not clear you can actually get plans, although a
source iin Oregon is rumored.

For a low wing plane with fuel in the wings, which I'm well convinced
is safer than fuel in the fuselage, pumps are a necessary evil, and
since they can fail, I'll take two please. William Wynne has done
more engine installations by far than I have, and he's going this way;
so am I.

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Anybody have anything to say about the fittings? That was my initial
interest. Should I ditch the pumps I have and just bite the bullet
and go with AN fittings per the exemplar? Do all those unions make
sense?(heavy little suckers! Think of a ball of solid brass the
diameter of a quarter for the 1/8" NPT size, and the diameter of a
Susan B. Anthony dollar for the 1/4" NPT size, and they lighten the
wallet to the tune of $13-20 per at the same time they increase empty
weight) - given that NPT fittings don't seal anyway metal-to-metal,
and you can "clock" them with SOME degree of freedom as long as
they're at least slightly more than finger tight, relying on Loctite
Pipe Sealant to keep them leak free?