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Composite-ARF Extra 330L (2 x 2m)
techsupport@composite-arf.com
The main firewall should be installed at approx.
3° sidethrust, but perpendicular to the cowling
flanges (which are at 0° incidence). If using the
standard DA stand-offs (65mm/2.5" long) you
can set the approx. sidethrust for the DA-50 with
the front face of the firewall (pilots left side) is
151mm from the front of the fuselage lip, and the
right side is 157mm. Fine tuning of the sidethrust
and upthrust is set by using an incidence meter
and adding washers between the plywood fire-
wall and the stand-offs.
4 small holes have been milled in the firewall to
give you a reference point for setting the correct
position of your engine. Mark accurate lines
between these holes to use for setting your
engine position. The photo shows where the
6mm Ø holes must be drill for mounting the DA-
50, to give the correct sidethrust, and still have
the spinner central with the radiused top of the
fuselage. The dimensions shown on the firewall
in this photo suit the DA-50 and 3.5" spinner,
with 3.5° sidethrust and 0.75° upthrust - adjust
for spinner diameter of your choice.
The stand-offs should be mounted to the firewall
with M6 bolts and large diameter washers. Fit
the spinner backplate to the motor to set final
position, so that the outside edge of the spinner
is exactly in the middle of the radiused curve on
the top of the fuselage.
You will need to make a cut-out in the bottom of
the cowl as the DA-50 cylinder head sticks out a
little, but this gives excellent cooling and no
internal baffles are needed in the cowling.
With the DA-50 and a carbon 23 x 8 Mejzlik prop
we needed 3.5° right thrust and almost 1°
upthrust for correct tracking, but this will vary a
little depending on your motor/prop combination.
A TD75K mini-pipe and header from MTW is
shown fitted, and these are available as an
option from Composite-ARF, with the DA-50.
This set-up gives the engine a nice throttle
response, a perfect mid-range, and also increas-
es top end power slightly.
You can see from the photos here how to cut out
the exhaust support bulkhead for a MTW
TD75K mini-pipe, and make a steel strap and
spring to retain the mini-pipe to the bulkhead
with a little flexibility. It just fits with about 5mm
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