SERVICE
LETTER #22
October
21, 1992
SUBJECT:
Header Tank and Fuel Line Routing
TO:
All Kitfox™ Builders and Owners (using a header tank)
FROM:
SkyStar Aircraft Corporation
In
keeping with SkyStar Aircraft policy of informing our customers of
important technical information, this Service Letter is being issued
as an advisory which needs your attention. While advising in nature,
the subject of this letter should be considered carefully and a
Service Bulletin will be issued in the near future with specific
instructions regarding maintenance action you will need to perform.
SkyStar
has received reports of header tanks being drained and not refilling
(potentially causing fuel starvation), while there is still plenty of
fuel in the wing tanks. This has occurred in aircraft with both front
and rear mounted header tanks.
We
have been able to recreate this fuel starvation in a special test rig.
In our test the fuel lines were routed out of the wing tanks to the
valve on the head rack, then across to the opposite side, down and
back to the rear mounted header tank, or down under the door, forward
to the firewall and up to the front mounted header tank. In each
situation the header tank was vented and only one wing tank valve
was turned to the “on” position. (It is feasible that this
situation could occur with both wing tank valves turned on). The fuel
flow to the header tank from the wing tank stopped when the wing tank
was un-ported (as in a “slip” with low fuel) and did not resume
because of the air introduced into the fuel line.
Further
testing has shown that when the fuel line is routed directly forward
out from the wing tank, above the door, then down along the diagonal
brace to the front mounted header tank, or out of the tank and
directly back to the rear mounted header tank, fuel flow would resume
on its own to the header
tank from the wing tank after un-porting.
NOTE:
Those
Kitfox's with the standard nose tank and wing tanks should be aware of
this situation, but because of the fuel’s visibility in the standard
nose tank there should be little possibility of fuel starvation.
(1)
The highest point in the main fuel line routing should be the wing
tank outlet. Tube routing should decline as rapidly as possible with
no risers (high points). This will allow air to flow out of the tubing
as quickly as possible. Check to make sure the fuel line coming out
of each wing tank is configured in the most direct (in flight)
down hill route to the header tank.
(2)
If you have a wing tank installed in each wing, fly with Both
fuel valves in the
“open” position.
(3)
Avoid “slips” when fuel in the wing tanks is less than 1/2
full.
(4)
If you have not installed a clear vent line from the header tank to
the wing tank you need to do so (SkyStar offers a retro-fit vent line
and nipple into the right wing tank). The Tygon tubing vent line from
the header tank back up to the right wing tank allows the fuel to be
monitored by observing the level and behavior of the fuel in the vent
line (fuel seeks a common level). Prior to take-off, this tube should
be inspected. Any fuel level noted in the vent tube below the level of
the outlet from the wing tank is a concern. This would mean that
either there is no fuel in the wing tanks or fuel flow has stopped
flowing to
the header tank.