Hi,

Attached is my idea of a simple fuel system for my Vision low wing aircraft.
Will this work or am I overlooking something?

Regards,

Pierre Swanepoel

Not a bad idea. Looks like it is worth a try. Monitor the tank
quantities when testing to see what happens. I assume there is a bit
of dihedral in the wings.

Paul Lamar



If I may. From what I understand you are running two pumps , at the same
time, or you could run one pump, in one tank, and let the inter drainage
between the tanks equalise as you run. That assume that the inter
drainage will keep up with fuel consumption. That will work , and you
will have one other pump as back up, just switch and it will do the same
thing but from another tank.

However, will one pump fail, and you need to repair it, you need to
disassemble the tank. Or make hatches to be able to get in, already at
construction time.It almost certainly involve a full fuel drainage of
your tanks, and a pretty messy and time consuming affair to get in
there, replace it, close it up and hope you did seal the tank good
enough for no leaks.

Chances of a pump failure is very low, in cars the pumps usually outlive
the vehicle ( heck most are not even aware they have a fuelpump)....but
it has happen, even if it is rare, it is common enough that it is a
possibility to count on.

An external fuel pump installation where you would place the fuel pumps
after point "T" in your drawing, ...at that point and forward, do a
paralell installation with backvalves in such a way that when one pump
runs, it blocks fuel flow through the other pump, and in that way you
can, in case of pump replacement have an easy access to it.

Theoretically that would eleminate the interdrainage pipe, as the pipe
sucking fuel into the "T" will be the interbalance pipe, but I would
keep the interdrainage pipe, as it is impossible to say, in the details
of things , if one side would suck more than another, and thus feed air,
once one tank is depleted quicker than another.

Small things that is impossible to measure....a slighty higher pressure
on one vent tube compared with the one on the other side, or some
geometry in the connection in the "T" ,  etc all that could make you
deplete one tank quicker....The interdrainage pipe will guarantee you to
get fuel as long as you have fuel.

The set up I have described have been used with success. The routine is
usually, to do a check on both pumps at pre flight check time, by
switching to one pump and another, and leave it on an alternate pump for
each flight, in order to have equal run time on both, done with a two
position switch.

Another issue is, maybe not that much of a deal, but you may get just a
little bit more useful fuel out of the tanks in this way, because
...depending on how your pump looks like...usually you will suck up fuel
from not the absolute lowest possible point with an internal pump
arrangement, theyr'e usually pretty good in getting down there, but a
drainage pipe flush to the bottom, you know you can't get any lower than
that.

Roger