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After a heck of a lot of study over a couple years I decided to modify the
standard Lancair fuel system to meet my personal objectives. This is not
intended to be a criticism of the standard Lancair fuel system and I'm in no
way suggesting this modification to anyone else. I thought some of you may
find it useful.
The following are the basic components:
1. I added a 3.25 gal. pressurized, aluminum header tank rated to 4 times
line pressure. I located this tank in the far corner of the baggage
compartment. (See the attached picture.)
2. I relocated the continuous duty electric fuel pump to a location next to
the header tank.
3. I added a fuel filter between the fuel pump and the pressure tank.
4. I added an air vent line that would make it highly unlikely for air to
enter the fuel control unit.
The system works like this:
1. Fuel is gravity fed from the wings into the belly tank, through a
fuel selector valve by (2) 1/2" fuel lines (one from each wing) to the 35
gal. belly tank. The belly tank has a fuel probe for indicating fuel
level. This is identical to the Lancair system. In addition I've added
an optical fuel sensor just under the fuel selector valve which will
alert me when there is no longer fuel entering the belly tank from the
wings. I believe this is now standard on the current Lancair fuel
system also.
2. Fuel is picked up from the belly tank by a 1/2" fuel line. This
line travels aft and comes up through the floor just under the baggage
floor. The belly tank overlaps this area. Within a foot or so fuel enters
the continuous duty, electric fuel pump which is within a foot or so of
the header tank. Before it enters the header tank fuel is pushed
through a fuel filter located between the fuel pump and the header tank.
The main fuel filter is still mounted in the engine compartment.
3. Fuel enters the at the top of the vertically mounted header tank and
is picked up in the very bottom of the header tank then goes though the
belly tank to a fitting on the firewall. The belly tank serves as a good
chase for the fuel and vent line. There is a 1/4" air vent line at the
very top of the header tank that is restricted to a very small diameter
hole. This line goes back left wing and into the wing tank through the
exiting fuel return line hole located near the top of the wing root. If you
were to un- port for any reason and suck air into the header tank this
air would vent out of the system. At normal curse you'd have to
un-port for a few minutes before air could enter the system. If that
happens you're probably out of fuel. If air did pocket in the top
of the header tank you'd be alerted by an optical fuel sensor that is
located near the top of the tank. You can see the wires in the attached
picture. You'd at least have a few minutes to change the aircraft's
attitude or correct a slip to get the fuel to flow again. This
fuel vent has a check valve that ensures the system maintains pressure IF
the electrically driven fuel pump were to fail and you had to rely on the
engine driven pump.
The solenoid vent was mentioned in someone's previous post. This valve is
open when there's no power to it (during fueling) and it's closed when there
is power (during flight). It must stay closed because if it were to open
and if the engine demanded more fuel than what can be gravity fed through
the fuel selector valve, air could enter the system at through this vent.
Also there's no way of determining if the valve is actually working except
you can activate it and hear it clicking before engine start. The man who
helped me wire my airplane tells me there is a solenoid vent valve currently
used by the aircraft industry that can improve this condition. He's found
one but it's over 3K and he believes there is something better. If this
happens I'll let you know.
Other points:
- Another builder who used this modification ran his engine with the
electric fuel pump turned off and it had no effect on the engine. The
fuel pump fails in the open position allowing the engine driven fuel pump
to work as intended.
- The fuel pump and fuel filer is accessible through the main gear
door. The pump can also be accessed by removing a panel in the baggage
floor board. Before this pump fails it begins to dribble fuel out from
fitting in the bottom of the pump.
Since the pump is located over the gear door opening part of every
preflight would be to inspect the gear door opening for leaking fuel.
(See the attached picture) I'm planning on building a very light
weight carbon fiber enclosure for the tank.
- I'm hoping this additional and relocated weight toward the rear of
the airplane will help with the CG. It seems some IVPT's are having
some minor forward CG issues unlike the IVP.
- I don't have much to say about the previous comments regarding
flying around with a belly full of fuel except I've been told there are
other aircraft that fly around with fuselage tanks. I've also been told
that tanker truckers are not thrilled with driving around empty
tankers. Apparently the vapors are more explosive than the fuel
although I believe this is more of an issue with gasoline and not jet fuel.
I can say that this modification has flown on at least one airplane and I
believe it will be flying on another within a month or two. The opinions
expressed here are mine and I'm not suggesting anyone to do the same. Quite
frankly the vicious attack by Mr. McDonald was way out of line. I'm very
appreciative to Lancair for this wonderful airplane. I had the pleasure of
flying with Clark Still in his spectacular Propjet a couple weeks ago and
all I can say is... What a ride!
Best regards, Joe Trepicone
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