trelines; in the case of the DA-50
these are 66mm apart vertically
and 78mm apart horizontally.
Temporarily clamp the 2 ply fire-
walls together, allowing an equal
overlap of about 3mm all around
(see photo page 22), as the inner
plywood is bigger than the front
one, and drill thru’ all 4 mounting
holes with a 6mm drill.
Position the front firewall (only)
on the fibreglass firewall in the
model - with the short straight
parts on both sides exactly 10mm
above the horizontal flanges and
temporarily hold in position with 1
or 2 very small drops of CA. Using the 4 holes in
the plywood as a template, drill all four Ø 6mm
holes thru’ the fibreglass also.
Tip:
At this point it is wise to temporarily bolt
your motor and stand-offs to the firewall, insert
washers to set the sidethrust/upthrust and check
that the spinner is centrally aligned with the
cowling. Small adjustments to the alignment can
be made easily now by slightly moving the posi-
tion of the plywood firewalls on the fibreglass
bulkhead, and redrilling the holes in it, without
having to redrill the holes in the ply firewalls.
When satisfied, remove the front firewall from
the fibreglass bulkhead and rough up and clean
the gluing surfaces of both ply firewalls, and
both surfaces of the black fibreglass.
Now glue both plywood firewalls into position
and temporarily bolt them tightly together, with
the fibreglass bulkhead sandwiched in between
them, using the M6 bolts, washers and T-nuts
included in the kit, while the glue cures. Wax or
oil the bolts first so that you can get them out
easily later! This method ensures that there are
no air pockets in the firewall - especially where
the stand-offs will be positioned. Use a slow (at
least 30 minute) epoxy and microballoons mix-
ture and make a nice smooth fillet all around as
shown in the photos.
For the DA-50 you will need 65mm long stand-
offs, which are mounted to the firewall with the
M6 bolts and large diameter washers provided -
Composite-ARF Yak 55
(2.1m/83”)
23
10mm
(above) The short straight edges on the sides
of the front firewall should be 10mm above
the flanges of the fuselage. Dimensions shown
are for mounting a DA-50.
(below) The inner firewall is larger than the
front one. Align symmetrically, to give an even
overlap all around, when drilling the motor
mounting bolt holes.
Secure firewalls with M6 bolts, washers & T-
nuts provided while the epoxy cures.
