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Composite-ARF Yak-55 SP (2.6m span)
need to offset the motor mounts 4.5mm to the left (pilots
view) and 3mm up to make sure that the centre of the spin-
ner is central in the cowling. Mark the offsets on the firewall
carefully, and then mark the positions of the 4 motor mount-
ing holes using a 90° square. In the case of the DA-100 the
mounting bolt holes are 80mm vertical, and 70mm horizon-
tal centres.
Drill all 4 holes 7.5mm diameter, and glue the M6 blindnuts
to the inside face of the firewall with 30minute epoxy. Bolt
the engine and stand-offs in place using the M6 x 30mm
bolts and 13mm washers supplied. Depending on which
motor and stand-offs you are using, you may need to pack
the stand-offs equally away from the firewall a little, with
thick washers, to prevent the propeller touching the cowl-
ing. Try to maintain a clearance of about 5 - 6mm.
Small adjustments to sidethrust and downthrust after the
first flights, if needed, can be made by adding or removing
washers between the back of the engine mount and the ply-
wood firewall.
Standard Mufflers: We do not recommend the use of
standard mufflers, do the higher noise levels.
Tuned pipes: A tuned-pipe installation is a little more com-
plicated than the use of a standard muffler, but sometimes
you don't have any choice, especially if you have noise
problems at your club field. In Europe noise is always a
problem, so Composite-ARF had to find a quiet and power-
ful solution. Especially if using a DA-100 motor we highly
recommend the # KS1060 tuned pipes, because the shape
of the fuselage and the separate compartment under the
cockpit area makes it easy, safe and reliable with excellent
cooling. This set-up gives the engine a nice throttle
response, a perfect mid-range, and also increases the top
end power noticeably.
The pair of tuned-pipes, with the headers, teflon joiners and
clamps are all available from C-ARF as optional parts. The
support bulkhead for the tuned-pipes will be included in the
kits shipped from mid-2004. Alternatively you can download
a full-size template of it from our website, or purchase it
from Desert Aircraft (the retailer for KS and MTW products).
The photographs on this page should make the installation clear. They show the special support
bulkhead fitted at the back of the exhaust compartment, under the cockpit area, complete with
the 8 small silicone tubes that soft-mount the pipe, and protect the milled plywood from the heat.
Mini-pipes: The second example of the 2.6m Yak shown in the lower photos shows the instal-
lation of a pair of MTW mini-pipes (part# DT75K), which are also available from C-ARF as an
optional part. There is plenty of space for these, although you must be careful to keep at least
6mm clearance between the headers and the fibreglass sleeves for the main landing gear, which
techsupport@composite-arf.com
(above) A view of the plywood
bulkhead for supporting the full-
length tuned-pipes (# KS1060).
(above) Shows the exits of the pair
of # KS1060 tuned-pipes from the
bottom of the fuselage. Make the
exit holes at least 35mm wide x
120mm long for adequate cooling
air to exit the fuselage.
(below) Alternatively you can fit a
pair of mini-pipes and headers
such as these #DT75K from MTW.
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