Advertisement
Composite-ARF SuperXtra 330L (3.1m span)
The twin mini-pipes seat on a steel strap (supplied with a
template for bending), and are held in place with 2 springs.
The springs are hooked over three M3 bolts that are
screwed into 2.5mm Ø holes drilled in the 3 small plywood
blocks that are securely glued to the front of this bulkhead.
The photos here should make the construction very clear.
You will find that the mufflers must be angled downwards at
the back to make sure that they clear the wing spars when
the wings are in the forward (3D) position, and you may
need to bend the headers very slightly to achieve this,
which is easily done by hand. You might need to enlarge
the 2 semi-circular cut-outs in the bulkhead slightly, as we
have in the photo above, to get this angle.
If you don't have any suitable springs to retain the mini-
pipes it is very easy to make them. Just clamp a length of
1.0mm piano wire and an old screwdriver (about 5mm Ø
shaft) into a battery drill, and hold the other end of the wire
in a glove while spinning it on slow speed. Bend 2 hooks in
the ends to finish the job. Please take care doing this.
To be really sure that the mini-pipes cannot more back-
wards and touch the spar, we install a couple of 'stops'
made from scrap 6mm (1/4") plywood, with a small piece of
teflon joiner held onto it with an M3 bolt. Glue these behind
the mufflers, against the carbon-composite bulkhead.
This simple mini-pipe retaining system has proven very reli-
able for several years in all our planes, and holds the pipes
securely enough, while still being flexible enough to prevent
them breaking under normal vibrations. If using internal
mini-pipes, C-ARF recommend that you protect the top sur-
face of the moulded carbon-fibre main landing gear legs by
covering them with a thin sheet of 1mm plywood, attached
with silicone adhesive. No other heat protection is neces-
sary to the fuel tank base, when using the DA-150 and mini-
pipes as shown.
The last job to do, an important one, is to cut out the 2 slots
in the bottom of the fuselage to let the warm air from the
exhaust system escape from the fuselage. These slots
should be 50mm (2") wide and 150mm (6") long, and it is
best if you make nice rounded corners to reduce any
chance of tearing in the composite skin.
Depending on your motor, you may need to make a simple
3mm thick balsa baffle plate inside the cowling to make
sure that enough cooling air is directed around the engine
cylinder heads, instead of just going directly out of the
opening in the bottom of the cowling. See photo here for an
example of the baffle, which improves the cooling consider-
ably. In any case, check that your motor is not overheating
techsupport@composite-arf.com
(above) View of the muffler mount-
ing from the front, taken through
the firewall.
(below) View of the twin muffler
mounting from behind.
(above and below) For additional
security, you can fit 'stops' behind
both mufflers, so that they cannot
move backwards. These are easily
made from teflon tube and 6mm
plywood blocks as shown.
28
Advertisement
