O.S. Engines 60B Carb - 27981010 - Manual

INSTRUCTIONS FOR THE O.S. TYPE 60B CARBURETTOR
The O.S. Type GOB is an entirely new carburettor of sophisticated design that has been developed specifically for the
O.S.MAX-61SX-H and MAX-61RX-H series helicopter engines designed for F.A.I. F3C competition use.
It incorporates a total mixture control system that enables the helicopter expert to fine-tune his engine to suit individual
requirements at different stages, i.e. at idling speeds, in the hovering mode and in high-speed flight. Once the adjustments
have been correctly set, the carburettor automatically controls the fuel/air mixture strength through the entire performance
range.
The Type 608 is also fitted with a special insulating sleeve to minimize the transfer of heat from the engine to the carburettor
body. An excessively hot carburettor preheats the fuel/air mixture and lowers the weight of the charge entering the
combustion chamber, thereby reducing power output. Also, variation in carburettor temperature can have an adverse effect
on throttle response.
Three adjustable mixture controls are fitted to the Type 60B. They
are as follows.
A The High-Speed (Main) Needle-Valve
When set to produce maximum power at full throttle, this
establishes the basic fuel/air mixture strength. This is then
maintained by the carburettor's automatic mixture control
system to cover the engine's requirements at reduced throttle
settings.
B The Idle Mixture Control Screw
This provides the means of manually adjusting the 60B's mixture
control valve. -By setting the Mixture Control Screw for the best
idling performance, the mixture control valve automatically
ensures that fuel is accurately metered to maintain the correct
mixture strength as the throttle is opened.
C The Medium Speed Needle Valve
This is an extra control that can be brought into play, if
necessary, after adjusting A and B above. It provides the means
of fine-tuning mixture strength over that all-important part of
a helicopter's throttle range where the model is flying in, or near,
the hovering mode.
Note: The Type 60B is not fitted
with an adjustable throttle stop
Hiqh Speed Needle Valve
(Main Needle)
screw. The throttle linkage to the
servo should be arranged so that
Medium Speed
the throttle trim lever on the Needle Valve
transmitter can be used to set the
required idling speed. This also Idle Mixture
provides the means of stopping Control Screw
the engine from the transmitter.
Fig. 1
PROVISIONAL SETTINGS
Use a muffler-pressurized fuel feed and, before starting the engine
for the first time, check that the three mixture controls are set up
as follows
1. High-Speed Needle Valve: exactly two turns open from the fuily
closed position. (Note: If a different muffler is used, this setting
may require readjustment.)
2. Idle Mixture Control Screw : exactly two turns open from the
fully closed position.
3. Medium Speed Needle Valve : exactly one turn open from the
fully closed position.
ADJUSTMENT
Existing Position
Please observe the following before
beginning to make any adjustment.
a High-Speed Needle Valve. Turn
this a p p r o x i m a t e l y 30 (3 to 4
clicks) at a time, when making
initial adjustments; then in steps
of •approximately 15° ( 1 to 2
clicks) when making final adjust-
ments.
Desired Position
Richer
b Idle Mixture Control Screw. A special technique is required
here. (see Fig. 2.) If intending to make an adjustment (e.g.
90 s ) in one direction, first turn the screw an extra 90° in the
same direction, before returning it to the new setting. If this
procedure is not followed, movement of the throttle rotor may
become s t i f f , resulting in undue loading of the throttle servo.
c Medium-Speed Needle Valve. Turn approximately 45" (4 to 5
clicks) at a time.
The general course of adjustment procedure is shown in the
ADJUSTING CHART and is correct for a fuel containing 20%
lubricant and a nitromethane content of between 10% and 30%.
Bear in mind that fuels containing relatively large percentages of
power-boosting nitromethane operate at richer mixture settings than
are needed for mild fuels and will, therefore, require the High-
speed Needle Valve to be readjusted accordingly. The type and
percentage of lubricant used is also a factor here, as noted later in
these instructions.
ADJUSTMENT PROCEDURE
As a safety measure, first check the transmitter controls, including
the throttle stick and trim lever positions, and hold the main rotor
securely before starting the engine.
1. Warm the engine by allowing it to idle for about 30 seconds. If
the engine stops, advance the throttle trim lever slightly to
Fig. 2
increase the idling rpm. Then open the throttle sufficiently
to 'float' the model above the ground.
If, at this time, the engine is slow to pick up and produces an
excess of exhaust smoke, the mixture is too rich. Correct this
condition by turning the Mixture Control Screw clockwise.
If the mixture is extremely rich, engine rpm will become
unstable: opening the throttle will produce a great deal of smoke
and rpm may drop suddenly or the engine may stop. . This
condition may also be initiated by an excessively prolonged
warming-up period.
If, on the other hand, the mixture is too lean, this will be indi-
cated by a marked lack of exhaust smoke and a tendency for
the engine to cut out when the throttle is opened. In this
case, turn the Mixture Control Screw counter-clockwise to
enrich the mixture.
Needle Valve too far open
High Speed Needle Valve
Setting varies according
to the curve
Adjustment range of Idle Mixture Control Screw
Fully Closed
Throttle Opening
Fully Open
Fig. 3
Needle Valve too far closed
Adjustment range of
Medium Speed
Needle Valve
2. Having provisionally set the idle mixture, the next step is to
adjust the mixture for hovering flight.
Hover the model and actuate the throttle to observe response
over the medium speed range. If the engine smokes excessively
and throttle response is poor, the mixture is too rich: in which
case, land the model and turn the High-Speed Needle Valve
clockwise. Do not close the High-Speed Needle Valve more
than the recommended initial adjustment (3 to 4 clicks) at a
time, keeping it a little on the rich side at this stage. DO NOT
touch the Medium Speed Needle Valve.
If, on the other hand, hovering is not stable and response to the
throttle is over-sensitive, or if the engine tends to overheat,
this indicates that the mixture is too lean and should be correct-
ed by turning the High-Speed Needle Valve counter-clockwise.
When satisfactory hovering flight has been achieved, land the
model again and re-check the engine's idling qualities. After
about 10 seconds of idling, open the throttle to 'float' the
model. If the transition is smooth, the idle mixture is O.K.
If the symptoms of either rich or lean running are observed,
readjust the Idle Mixture Control Screw accordingly.
Note: With this carburettor, neither the Idle Mixture Control
Screw adjustment, nor the Medium Speed Needle Valve adjustment
has any effect on mixture strength when the throttle is fully (or
almost f u l l y ) open.
3. Now adjust the High-Speed Needle Valve to achieve the best
performance when the model is flying at full throttle. If, at full
throttle, acceleration is poor, the exhaust is unduly smoky and
the model f a i l s to reach expected straight line speed, the mixture
is too rich and the High-Speed Needle Valve setting will need to
be reduced.
If, however, after smoothly accelerating to satisfactory high-
speed straight and level flight, power is lost when the model is
pulled up into a climb, the mixture is too lean. In this case,
land the model immediately and readjust the High-Speed Needle
Valve to a richer setting.
4. Having now found the optimum setting for the High-Speed
Needle Valve, re-check the engine's idling performance, fine-
tuning the Idle Mixture Control Screw, if necessary, to perfect
the idle.
5. Now re-check hovering performance. It may be found that
(with the High-Speed Needle Valve now set for optimum full-
throttle performance) hovering will reveal symptoms of slightly
lean running at medium speeds. DO NOT touch the High-Speed
Needle Valve.
It is at this point that the Medium Speed Needle Valve,
previously kept one turn open, may be brought into operation.
Open the Medium Speed Needle Valve 45°, or 4-5 clicks, then
fine tune until the optimum hovering performance is obtained. If
on the other hand. hovering reveals rich running, close the
Leaner