Herbert Boks wrote:

Dear fellow rrrrrrrotarians,

I want to ask for your thoughts/comments on the following.

I am building a Cozy MK IV and will install a 3rd gen. 13B. I've spent some
time trying to understand fuel systems for EFI engines, noting that with 2
main tanks, the need for return lines adds a lot of complexity to the
system. I'm thinking about electrically controlled fuel valves on the
firewall (2 valves and 1 solenoid or motor per tank). Since with EFI we
must have electricity to run the engine in the first place, the inability
to switch tanks in case of a power outage is not really an issue. In my
opinion an EFI demands a backup electrical system in any case. I see great
advantages in placing the fuel valves on the firewall:
- shorter fuel lines
- no need for a sump tank
- less fuel heat, because it runs back to the main tanks
- no fuel lines inside the cockpit

There is the added risk of not being able to shut the valves when power
fails due to engine fire. I'm not sure how to address that yet.

My understanding of EFI is rather superficial, so I may be overlooking
things. I may also be overlooking other side effects. What do you think?

Herbert

Building PH-CZY (Ch.10)
Cozy MK IV #0769

herbert@datamax.nl
The Netherlands

Herbert, I've built a Velocity and my friend built a Cozy. Because a Cozy has 2
strake tanks (no sump tank) they have a fuel selector valve near the pilot in
the center of the fuselage. It requires running fuel lines from the tank to the
valve and back to the engine. By using EFI, you will need a dual selector valve
(avail used on several fuel injected planes) which requires you run twice the
number of lines (6 vs 3). This will allow the excess return fuel to return to
the tank it came from.  Do not even think about transfer pumps because you will
run out of fuel at the worst possible time. This has already happened. Fuel
pumps are constant flow and return lots of fuel, especially at low power
settings ( descents and landing), so it must go back to the originating tank.

The other alternative is to do it like a Velocity which uses no valves, but has
a sump tank (min 2 gallons) in the bottom of the plane fed continuously by the
strake tanks. You'll need dual electric fuel pumps which are positive
dispacement, so shutting them off acts as a valve, so that fuel will not flow
into the engine compartment. Mount the fuel pumps low on the engine firewall
(because fire/heat goes up) and they will always have a positive head. Puting a
fuel selector valve on the firewall is how John Denver got killed in a Long
EZ-not a good idea.

Chuck Harbert

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