|
Message
Now, the Subie guys are contemplating a re-design of their fuel
systems. I'm wondering now if I should make any changes to my fuel system
(2 wing tanks, 6-port Andair valve, dual EFI pumps mounted on f/w)?
Comments would be welcome, especially from those that have been flying for a
while.
Mark S.
Hi
Mark,
We're
basically copying the fuel system that's used on the cars, and you just can't go
wrong with the basic design. Where we get into trouble is
when we make changes, even though we may not realize it.
After reading
your message, the primary thing that sticks in my mind is- keep your pump and
lines relatively cool. I
think a little common sense goes a long ways here. In a car, the pump is
usually in the tank, or very close to the tank, so it's effectively at
OAT. There's a long line between it and the engine compartment, so even if
you boil fuel in the engine compartment, the pump is still submerged, and will
blow the air right through the regulator and back to the tank. As
long as you don't do something silly like run the fuel lines next to the
exhaust, the only time you should have a problem with fuel boiling is after
shutdown.
I have to
admit that I'm not personally comfortable with having the EFI pumps on the hot
side of the firewall, unless you build a box around them, and supply lots
of cool air. I have mine in the cockpit, along with the filters, and
regulator. The only thing in the engine compartment is the lines that
absolutely have to be there.
At
first glance, it would seem dangerous to have high pressure fuel in the
cockpit, but not when you think about it. First, it's extremely
unlikely that a line is just going to blow apart (I don't
use automotive rubber lines anywhere). If there's a leak, it's going
to start small, and you'll smell it when it's still just a tiny leak.
If this were on the hot side of the firewall, it would have to be a big
leak before you smell it, and a fire might actually be your first sign of
trouble. Even if you had a big leak in the cockpit, what's going to
start the fire? You can have all the gas you want, as long as you don't
light it with something.
The pumps, filters, and regulator are all cool, so the heated
fuel is minimized. I run both EFI pumps in flight, so there's a
ton of flow as well. In this configuration, there's absolutely no chance
of vapor lock.
I realize
that opinions vary on fuel systems, so take the above comments for what they're
worth.
Cheers,
Rusty
|