Motor Installation - Desert Aircraft DA100-I Owner's Manual

Motor Installation

• Mount the motor using high grade 1/4" or 6mm dia. bolts with washers and locking nuts on the rear
of the firewall. Make sure your firewall is structurally sound. The crankshaft centerline is in the exact
center of the rear mounting plate bolt pattern.
• The throttle linkage ha a 4-40 thread. Make sure the carburetor's idle set screws are removed or set
so that the carbs can be fully closed by the servo at low trim. Use a high quality servo for the
throttle. A poor quality servo or linkage will not provide accurate and repeatable throttle settings.
Don't use metal to metal linkages.
• You can un-hook, but don't remove, the throttle return springs if the motor is not going to be bench
run. The spring helps to limit shaft wear due to vibration.
• The carburetors should have at least 1/2" (13mm) of clearance between the intake and the inside of
the cowl. If there is less than ½", make an opening in the cowl at least as large as the carb intake
diameter.
• Since the carburetors must often be adjusted differently with the cowl on as compared to off, we
recommend small access holes be made in the cowl for adjusting the needle valves with a long,
narrow, screw driver. Sometimes the needles can be reached through the cowl's openings for the
exhaust system.
• A 32 oz. (or larger) fuel tank is recommended. The tank must be vented. The carb has a strong
pump, so the tank can be mounted almost anywhere. The fuel line and tank stopper must be gas
compatible. Do not use any silicone sealers on the fuel system. Gas can break it down and carry it
into the carb. A single pick up line with clunk can be used in the tank. A "T" fitting is then used close
to the carburetors to run a fuel line to each carb. The inner diameter of the fuel tubing should be the
same or larger than the carburetor's fuel inlet fitting's inner diameter. 1/8" I.D. is recommended.
Make sure all fuel line connections are secure. Small nylon zip ties work well to keep the fuel line on
the metal fittings. Make sure the fuel line is secure and not touching the exhaust or cylinder fins. An
inline fuel filter can be used. We recommend filtering the gas entering the fuel tank from your field
container.
• Cooling is critical to motor performance and longevity. Allow as much cooling air as possible in
through the front inlets of the cowl. All cowls, round or narrow, must have ducting to direct the air
equally through the front and rear cylinder fins. Air must flow through the cylinder fins, not just inside
the cowl, to properly cool the motor. Don't let the air take the easy way out! Make it go through the
fins with ducting. The preferred method of ducting the 2 cylinder inline engine, is a vertical plate on
the centerline of the engine that "silhouettes" the shape of the engine. Air entering the cowl is
directed to the "positive pressure" side of the engine (Normally the carb side) then flows through the
fins to the "negative" side and then out of the cowl. You want to establish a side to side flow across
the engine and through the fins, not a front to back flow. This way the cylinders get equal cooling.
Allow an outlet opening approximately 2 1/2 times larger than the intake at the bottom rear of the
cowl for the hot air to escape.
• Air ducts can be made from thin plywood, balsa, fiberglass, or aluminum sheet to guide and force air
from the front inlets to and through the cylinder fins.
• Keep components like the ignition system, fuel tank, fuel lines, receivers, etc, shielded from heat
generated by canister and tuned pipe exhaust systems. Hot fuel tanks and fuel lines can cause
frustrating tuning issues, and over heated electronic components can have intermittent problems or
total failures.
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