Sukhoi SU 31—2.75m/2.6m Page|22
It is important to keep your engine cool, regardless of the engine
manufacturer. Keeping your engine cool is good practice, your engine
will love you for it! Another area you must also consider is the fuse-
lage. If you are running canisters or tuned pipes this is a
must!
We will show you how we ducted the air to the DA120 that we used.
Clearly with so many engine choices, it would be impossible to cover
all variations. But the principle is the same, and the following is a
good guideline for you to follow.
Remember, what we are trying to achieve, is to channel all the incom-
ing air from the opening at the front of the cowl directly onto the cylin-
der fins, before it can disburse or be forced to other areas of the cowl.
It s important that your ducting components are close to, but not
touching your engine. About 2mm is sufficient.
We manufactured our ducting components from 0.5mm Alloy, but
4mm balsa and 0.5mm ply will also do the job. The balsa is easily
shaped to your requirements and is also very light. The ply is added
as the top layer when most of the shaping is done to add strength and a tough surface. Use some card to get the basic
shape you require, and then trace the shape onto the balsa. The thin ply can be easily cut with scissors and the final
shape trimmed with a sanding block. We used medium CA to glue the ply to the balsa.
Tack your components in place with some CA and kicker. Make sure you trial fit as you go. It is also a good idea to bolt
the upper part of the cowl in place from time to time just in case the lower cowl is getting slightly pulled out of shape.
When you are satisfied with the fit, epoxy the components in place. While the epoxy is curing, reassemble the cowl and
fit to the fuselage, so as everything stays in shape.
To ventilate the fuselage you will need to cut some cooling slots. The fuselage material is easy to cut out, using your
Dremel. Finishing with a sanding drum will keep the process simple and tidy. Where you place the slots is again de-
pendent on the final fit out and components used.
Keep in mind that you should not cut through the seam line or the fibreglass reinforcement band. Keep your vent slots
about 25mm from the seam line. Use the seam line as a reference to keep your vent slots nice and straight. The shape
of the slots is not that important, but making them oval, and just large enough to accommodate the Dremel sanding
drum makes the process easy.
Engine cooling and vents
