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Composite-ARF Yak-55 SP (2.6m span)
Engine and Exhaust Installation
We strongly recommend that you complete the motor and
exhaust installation before the fuel tank base and rudder
servo plate are permanently installed.
In the prototype we used a a Desert Aircraft DA-100 and a
pair of tuned-pipes (MTW part # KS1060), which is a high-
ly recommended combination with lots of power and light-
weight. In the new 'Shulman 2000' scheme plane, also
shown here in some photos, we fitted a pair of mini-pipes
(MTW part # DT75K), instead of the tuned-pipes, and this
is also a fabulous set-up with more than adequate perform-
ance for any manoeuvres you might want to fly.
Headers for both set-ups are available, and the aluminium
types can be easily bent by hand, so that they clear the
main undercarriage legs. Of course many other engines in
the 80 - 100 cc range are suitable for this plane as well.
The moulded motor dome is reinforced inside with plenty of
carbonfibre and does not require any additional strengthen-
ing. If using a DA-100 and 2-bladed carbon propeller the
sidethrust required for our Yak-55 is very small at only
about 1 - 1.5°, with 0.5° - 1° downthrust. The fibreglass
motor dome is accurately offset in the moulding process,
using a precision jig, and the plywood firewall is glued
directly to this in the factory, which already gives you very
close to the ideal thrustlines when the motor is mounted in
the centre of the motor dome.
You can check the incidence of the firewall easily by setting
the assembled model on a flat table, and setting the wings
at 0° (measured with an incidence meter). Then check the
incidence of the firewall, which should already have approx.
1° downthrust and 1.5° sidethrust built into it.
To make sure that the centre of the spinner is in the centre
of the cowling, you only need to offset the motor from the
centre of the firewall, which is easily done as the fuselage
is exactly circular at this position. Cut 2 strips of scrap ply-
wood, about 25mm wide and 335mm long, and adjust
lengths so that they both fit inside the fuselage exactly,
against the surface of the firewall. Mark the exact middle of
each piece and drill a small hole through both. Using them
as shown in the photo, you can mark and drill a small hole
in the centre of the firewall as your reference point. Then
mark a horizontal line through the centre point, across the
firewall with a steel ruler, using the moulded lines in the
motor dome as a reference.
If using 1° downthrust and 1.5° sidethrust on a DA-100 you
techsupport@composite-arf.com
Finished in 4 -5 hours
(above) Engine alignment is simple
as the firewall is already offset for
you in a precision jig at the factory.
Here you can see the centre and
offset marks on the firewall.
(below) Use 2 equal length strips
of plywood to find the exact cen-
tre of the firewall.
(below) In this view you can also
see the nice direct throttle linkage
under the cockpit floor.
25
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