15 Gallon Fuel Tanks
The MKIII has very little room behind/below
the seats for Stuff, and us Old Poops need to take Stuff with
us when we go aviating. Also, the stock 10 gallons of gas was
not much range with two people. 15 gallons is better.
The gap seal area is now fuel tank, and holds
13 gallons. It weighs about 15 pounds empty and is 5 to 9 plys
thick, depending on the stress areas. It rests on all the upper
fuselage tubes, each of which is covered with a rubber radiator
or heater hose, split and glued to the tubes. It was not very
difficult to make, but very tedious & messy.
The tank is held in place with seat belt webbing
which also secures an aluminum angle that the front gapseal is
attached to. Unpainted areas are marked for fuel level. The front
part of the tank in these pictures had a built up section that
elevated the fuel filler to a higher position. Around this elevated
section was a balsa wood streamline that blended the airflow off
the parachute launcher and then smoothly redirected the airflow
up, over, and around the engine. That has since been cut off,
and redesigned, but I didn't take any pictures while I did that
part. You'll see the current version on another page.
The tank was made by forming it in place around
the upper fuselage tubes. The tubes were wrapped with two thicknesses
of heater hose to allow for the thickness of the tank to increase
as extra plys were added to the outside as it was built up. The
shape of the lower half of the tank was formed in place out of
aluminum flashing from Lowe's, which was covered in duct tape,
and braced with wood. Then the glass cloth and epoxy was laid
up inside the aluminum onto the duct tape covered areas. Neither
epoxy nor polyester resin will stick to duct tape. These pictures
show the mold just before the layup began.
The glass plys were laid up inside and allowed
to cure, then the mold was removed and stripped off. The top edge
of the tank sides were cut to just below airfoil shape and a 1"x1"x1/16"
aluminum angle was attached to the upper inside edge to provide
an attach flange for the upper surface of the tank. The easiest
way to securely bond a metal angle or similar item to a fiberglass
surface is to drill and cleco it, and then when you get ready
to glass it, mix up a batch of flox and epoxy to make a thick
slurry, spread it on both surfaces and then secure everything
with pop rivits. The tank top is flat and was made by covering
a flat table with duct tape, laying the cloth on it, wetting it
out with epoxy, and letting it cure. Then just pull it off and
trim it to size. After the fuel pickups, vent lines and transfer
lines were installed, (the lower surface of the tank divides into
four sections to fit around the fuselage tubes, and you need to
have a way for the front sections to drain into the back ones)
the tank top was drilled, clecoed, slurried and rivited into place.
Then the gas filler neck was glassed on and it was done. Then
the whole tank got two more layers of glass, with extra layers
in high stress areas. Due to the complexity of the plumbing, such
as the fuel transfer lines between the front and rear sections
of the tank, vent lines, and feeder lines, removing the tank is
not something that is undertaken lightly...
The main tank feeds a 2.5 gallon hopper tank
located behind the passenger seat. That area was modified with
the addition of an extra brace tube welded in to give the tank
something more to rest on, and all tubes were covered with split
3/8" fuel hose, glued in place. At left is the area modified
and ready. Center, is the cargo bay floorboard with the Facet
electric fuel pump installed. At right is the tank as seen from
the rear side. The hopper tank is fed from the main tank and vented
to it, making a closed system. The fuel pickup is 2.5" from
the tank bottom, and the sump drain is at the bottom. It takes
more than 1/2 pint of water in the tank before it gets to the
fuel pickup.
The ELT is visible in the picture to the left, attached
to the cargo bay floor behind the pilot's seat. The center picture
shows the tank in place, the right picture shows it strapped in
and plumbed. There is a clear sight tubing running along the left
front edge of the tank for a fuel gauge. The cargo area is 13"
high, as wide as the fuselage, and 15" front to back. The
floor of the cargo area is 3/16" plywood. Between what you
can fit in the cargo area, plus underneath it, there is lots of
room for "Stuff", and it is all right on the center
of gravity.