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Instructions Titan ZG 45PCI-HV
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run decidedly rich. A good setting for the low speed needle is 1 1/4. Both needles are
more sensitive to adjustment with a manifold fitted.
The engine‘s ability to turn larger propellers increases in proportion to the length of
the intake ram tube.
You can only tell from the engine performance in flight whether the carburettor is cor-
rectly adjusted, additionally you should check the colour of the spark plug. To check
the spark plug colour it is essential that the engine be shut off at full throttle after run-
ning for few minutes on full throttle. It is no use to check for colour after the engine
has been running at tickover. The ideal colour is an even soft brown. When the plug
is black and oily it is of course too rich, when whitish or with an appearance of being
glazed over then the mixture is too weak.
Should you have fitted the intake ram tube so that it protrudes through the cowl and
the engine is running rich at full throttle, in horizontal flight and when diving, but on
the ground and when climbing it is running lean, the problem is that the cowl is so
shaped that the air pressure inside the cowl is higher than on the outside where the
intake is. This pressure differential affects the compensating diaphragm in the carbu-
rettor, causing the engine to run rich.
To avoid this you may increase the outlet area of the cowl or reduce the inlet area. A bet-
ter answer is to solder a short piece of brass tube into the small hole on the steel cover
plate above the compensating chamber and bring this tubing out to the same level
as the intake tube bell mouth. The carburettor now reacts to the air pressure present
at the intake and not the pressure inside the cowl. The engine should now run evenly
in flight at every attitude. Should there still be a problem, then the acceleration of the
airflow around the cowl, where the intake ram tube is located, is too intense, causing
the air pressure to drop to much to be compensated by the carburettor.
Sucking the intake air from inside the fuselage
The air flowing over a body is forced to accelerate. The increased velocity will cause a
reduction in air pressure at local areas over the body. It is clear to most that the models
we fly use this same induced difference of air pressure on the wing to achieve flight.
But many modellers do not realize how large the difference in pressure over an engine
cowling can be, especially when the flow is around a very small radius curvature it can
have such a significant effect, as to deprive the engine of sufficient air. With a cowling
like this, you will be forced to fit a 90 degree inlet manifold on the carburettor, so that
it sucks the air out of the fuselage. On an air-tight fuselage this then requires that you
bore two holes about 10 mm diameter opposite each other in the neutral part of the
fuselage i.e. between wing and tail on the left and right fuselage sides. Do not place
the holes anywhere near the wing, the engine cowl or in the firewall.
