3W 3W-55Xi Manuel d'utilisation - Page 7

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Operation manual

Baffling

Deflecting of the air (baffling) to and over the cylinder(s) is highly recommended for engine cooling.

The idea is to get all of the cool air that is coming through the air intake opening(s) to hit the middle

of the cylinder(s) directly, and then be forced over the cylinder(s), creating turbulent air moving

through the cylinder(s) fins. The freely flowing, but directed and turbulent air between the fins

provides the maximum cooling for an air cooled engine. Without baffling (meaning wood or

composite dampers that direct the airflow) the air will take the path of least resistance. Some

incoming air will bounce off the cylinder(s) and the rest will escape around the cylinder(s) without

coming into contact with the cylinder(s).

Engine in pusher operation:

Important note! When engines are used operating in pusher configuration cooling gets critical and

special attention has to be given to an effective cooling method. A good cooling system layout

depends on the actual location (position) of the engine in the fuselage.

Operating temperature

To be able to check the cylinder head temperature ( CHT ) a thermo element has to be installed which fits

under the spark plug ( M 10 thread ). Optimum operating temperature range : 180° C - 220° C. In this

range piston, spark plug and combustion chamber will be free of remains. Maximum temperature of

270° C should not be exceeded. During a certain time at full speed the temperature could be 250° C.

Colour of the spark plug should be : light or middle brown. A grey / gray colour is a typical sign for over

heating. Temperatures above 270° C are critical and over 300° C, piston can seize and could completely

damage the engine.

Temperatures below 180° C create remains ( carbon ) on the piston crown. Increasing remains hit the

cylinder and cause abnormal running noises ( knocking ) which will increase the load of the needle

bearings and can destroy them. Under extreme conditions the crankshaft can break and a complete

damage of the engine will be the result.

Rear induction

Carburetors, whether front or rear, require a steady supply of fresh air. The best way to supply

air to a rear carburetor is by installing an air scoop. Some have thought to drill holes into the

fuselage near the carburetor area rather than creating an air scoop for the carburetor. This does

not work, in fact it will create a vacuum effect that will draw the air away from the carburetor! Again,

you should install an air scoop into the front of the plane which will supply air into the fuselage.

This air will then need to flow out of the fuselage. Drill exit holes into the rear area of the fuselage

for this purpose. Important: The interior of the fuselage must be sealed to prevent damage from

gasoline that sprays from the carburetor. Use a thin epoxy or other appropriate fuel proofing

method. Do not overlook this step as gasoline will melt some materials like Styrofoam very quickly.

3W Modellmotoren GmbH, Hasswiesenstrasse 22, 63322 Rödermark