O.S. Engines 61LX-H - Manual (Page 18)

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, theexhaust
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 the Needle Valve
to a richer setting.
Now re-check hovering performance and, if
necessary, fine-tune the mixture for hovering flight.
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
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achieve satisfactory mid-range throttle response,
but such readjustments should onIy be made
within the range where idling reliability and high-
speed performance are not unduly compromised.
O Readjustments should therefore be carried out as
follows:
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 Screw 2-3 degrees cIockwise.
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
Screw 2-3 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
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