After first trimming flights we added a single thin 6mm ID
washer behind the left side stand-offs and the motor dome,
to increase the sidethrust very slightly - and also a thin
washer behind both lower stand-offs which actually gave
the very slight upthrust (0.25 degree) required for
perfect neutrality.
Tuned Pipe.
Although a bit more complicated to install than a canister
muffler, we fitted a tuned pipe as it gives some increased
power, improved throttling characteristics and reduced
noise levels - especially important in Europe where we
have quite strict laws on this.
The pipe is supported at the front and back on 2 cnc milled
plywood tuned-pipe mounts which are included in the kit (to
suit Ø 49mm pipes), together with enough of the hard sili-
cone tube to make the isolation mounts. Cut the silicone
tube into 20mm lengths and insert in the milled slots as
shown in the photos below/right. The front pipe mount is
secured to the front face of the plywood landing gear mount
with 2 sheetmetal screws (Ø 3.5 x 18mm), access is with a
long X-head screwdriver thru’ the 2 small holes seen lower
right side in the photo above and P16.
The rear mount must be secured to a 3mm thick plywood
reinforcing plate glued onto the side of the fuselage, as
shown - and you can use two of the M3 bolts and T-nuts
included in the spare hardware pack for this. We reinforced
the fuselage at this point with a few carbon rovings, but in
retrospect this was not necessary with the relatively low
vibration levels experienced. Maintain at least 6mm (1/4”)
clearance between the bottom of the tuned pipe and the
fibreglass sleeve around the wing tube, and check to make
sure you can still access the front M6 plastic nuts used to
secure the wings to the fuselage.
Make sure that the tuned pipe cannot move forward (or
backwards) and touch against the end of the manifold, as
the metal-to-metal contact could cause terminal R/C inter-
ference! 2 small sheet metal screws through the teflon join-
ers and pipe/manifold side walls prevent this. The 3W instructions include a full-scale drawing of
the engine mount positions and carburettor which is very useful when making the mounting plate
and carb cut-out.
You can see in photos P20 and P24 that we installed a thin balsa-composite plate against the
left side of the fuel tank, & also above the left hand rudder phenolic servo arm, to prevent any
possibility of heat damage.
Canister mount
Depending on your header, you should find that a single canister (MTW TD110K shown here)
will fit in front of the wing tube sleeve, but you will probably need put the canister on the oppo-
Composite-ARF Extra 300SX
(2.6m span)
26
(above) Prevent the canisters or
tuned pipe moving forwards or
backwards with 2 small sheetmetal
screws thru’ the teflon coupler(s).
Screwdriver is for tightening sheet-
metal screws in front mount.
(below) Rear pipe mount is
secured to a 3mm thick scrap ply-
wood plate glued securely to the
fuselage side.
