Engine Installation
We strongly advise you to complete the motor
and exhaust installation before the fuel tank
base and the vertical former at the back of the
landing gear mount plate are installed, as it pro-
vides much easier access.
Here we show a DA-150 motor installed, with a
pair of MTW TD110 canisters, and this is an
excellent combination. Another suitable motor
would be the 3W 157cc X1 B2 twin, which is
powerful and very compact - and easily fits
inside the 376mm diameter (14.8”) cowling.
The front surface of the motor-dome and firewall
already has approx. 1.5 degrees of sidethrust
built into it, and the downthrust is nominally set
at 0 degrees. However, due to manufacturing
and assembly tolerances these may vary slight-
ly, and you can check the precise angles of the
firewall in your plane with an inci-
dence meter.
Accurately mark the exact vertical
and horizontal centrelines on the ply-
wood firewall. Cover it with masking
tape and measure from the inside
surface of the circular fuselage, ver-
tically and horizontally. You should
find that the centre will be 188mm
from the inner surfaces.
The Composite-ARF Yak only needs
1 - 1.5 degrees right thrust, so the
motor only needs to be offset to the
(pilots) left by 5mm to have the cor-
rect thrustline and the spinner centrally posi-
tioned. Mark another vertical line 5mm to the
(pilots) left of the fuselage centerline as shown.
The downthrust required is also very small at
approx. 0.5 degrees, so you should offset the
centre of the motor about 1 - 2mm above the
horizontal centreline. Both the DA-150 and 3W
157 Xi require standoffs of 25mm (1”), and the
remaining small adjustments for final thrustline
settings are made by adding the included large
diameter washers between the firewall and the
standoffs.
The mounting plate for the DA-150 has horizon-
Composite-ARF YAK 55SP
(3m span)
23
(above) Centrelines and offsets marked on the
firewall to suit DA-150 mounting.
(below) The DA-150 is fitted on 25mm long
stand-offs, and the final side & down thrust set
using washers between them and the firewall.
You can also seen the ignition unit, secured by
cable ties onto the top of the motor dome.
(below) Another DA-150 view showing the
headers and the location of the hole thru’ the
firewall for the Tygon fuel tube.
