26
L Now adjust the Needle Valve to achieve the best
performance when the model is flying at full
throttle. lf, at full throttle, acceleration is poor, the
exhaust unduly smoky and the model fails to reach
expected straight line speed, the mixture is too rich
and the Needle Valve setting will need to be
reduced. lf, however, after smoothly acceIerating
to satisfactory high-speed straight and level flight,
power is lost when the model is puIled up into a
climb, the mixture is too lean. ln this case, land the
model immediately and readjust Needle Valve to a
richer setting.
M
N For helicopters, good throttle response at medium
r.p.m. (e.g.hovering speeds) is most important,
since this is a power range widely used in
helicopter flight. The optimum fuel/air mixture
strength at medium speeds is dependent on
obtaining balanced adjustment of both the Needle
Valve and the Mixture Controlof both the Needle
Valve and the Mixture Control Valve. lf both
controls are already at their optimum setting, some
modification to these settings may be necessary to
achieve satisfactory mid-range throttle response,
but such readjustments should onIy be made
within the range where idle reliability and high-
speed performance are not unduly compromised.
Readjustments should therefore be carried out as
follows:
After about 10 seconds of idling, open the throttle
to 'float' the model. lf the transition is smooth, the
idle mixture is O.K. If the symptoms of either rich or
Iean running are observed, readjust the Mixture
Control Screw accordingly.
K
When satisfactory hovering flight has been
achieved, land the modeI again and re-check the
engine's idle qualities.
J
Now re-check hovering performance and, if
necessary, fine-tune the mixture for hovering flight.
27
lf, on the other hand, the response to mid-range
throttle movement is too sensitive (indicating a lean
mid-range mixture), turn the Needle Valve 2 or 3
clicks counter-clockwise or turn the Mixture Control
Valve 1-3 degrees counter-clockwise.
Throttle response at hovering speeds is aIso
affected by the reIationship of the main rotor pitch
angle to throttle opening. If the optimum mid-range
throttle response cannot be obtained by the
carburettor adjustments described above, try
adjusting the helicopter's pitch control
characteristics.
Q
P
O lf the mid-range throttle response is not rapid and
positive (indicating a rich mid-range mixture), turn
the Needle Valve 2 or 3 clicks clockwise, or turn the
Mixture Control Valve 1-3 degrees cIockwise.