Top Flite TOPA0415 - Manual (Page 26)

Mount the engine
The instructions show a U.S. Engines 41cc engine
and a Great Planes Isolation Mount. Other engines
are suitable, provided they are within the
recommended range, but may require a different
engine mount. Keep in mind that you can rotate the
engine to conceal the muffler inside the cowl and to
aim the engine exhaust where you want (the engine
doesn’t have to be mounted exactly inverted). Just
make sure the mount is centered on the reference
lines on the firewall and that the orientation you have
chosen will allow sufficient air flow over the head
and cylinder.
❏
1. Use 30-minute epoxy to glue the die-cut 1/8"
plywood forward firewall (FW) to the 1/4" x 6-1/8" x
5-1/2" plywood aft firewall. From now on this
assembly will be referred to as the firewall.
❏
2. Drill four 19/64" (or 5/16") holes through the
outer punch marks in the firewall only if you are
using a Great Planes Isolation Mount. If you are
using another engine mount, use a ballpoint pen and
a straightedge to draw lines connecting the four
inner punch marks. Center the engine mount on the
cross marks, then mark and drill the appropriate size
holes for the engine mount.
❏
3. Tap blind nuts into the back of the firewall
through the holes you drilled. Secure the blind nuts
to the back of the firewall with CA.
❏
4. Use the drawing of the Isolation Mount on the fuse
plan to mark the location of the mounting holes for
mounting your engine. Trim the bottom of the mount
along the lines. Drill 1/4" holes through the iso plate and
temporarily mount your engine with 1/4-20 x 1-1/4"
bolts and flat washers (not included with this kit).
❏
5. Temporarily mount the iso plate with the engine
to the firewall to confirm that the mounting holes
align. Make adjustments if necessary.
❏
6. Glue together both sets of die-cut 1/8" plywood
parts that make up the right and left fuse
crutch doublers.
❏
7. Test fit the doublers to the crutches in the fuse,
then test fit the firewall. Be certain the firewall will fit
all the way into the notches of the crutches. If it
doesn’t, trim the forward edges of the crutch
doublers as necessary.
❏
8. After adjustments have been made, glue the
crutch doublers to the crutches with 30-minute epoxy.
❏
9. Remove the iso plate from the firewall. Glue the
firewall into position with 30-minute epoxy. Use
masking tape or clamps to hold the firewall in place
until the epoxy cures. If you don’t have clamps that
are big enough, use #2 x 1/2" or 3/8" screws to hold
the crutches to the firewall. We used flat head screws
on our prototype and countersunk them into the
crutches. Work neatly and don’t build up a large fillet
of epoxy behind the firewall because we’re going to
add reinforcing triangle stock in the next step.
❏
10. Use the 1/2" x 24" basswood triangle stick
to reinforce the glue joint between the four sides of
the firewall and the inside of the fuse crutches and
the tank roof and floor. Glue the sticks into position
with epoxy.
❏
11. Further reinforce the glue joint by drilling 3/32"
holes through the crutches, tank floor and tank roof
into the edges of the firewall. “Pin” it all together with
round toothpicks glued in place with epoxy.
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