O.S. engine FS-120S-E - Page 3

Note: Slightly smaller or larger props than those shown in the list
can be used. However, it should be noted that propeller noise
will increase if propeller blade tio velocity is increased
(i.e. due to higher engine r.p.m. or a larger prop diameter).
For safety, keep your face and other parts of the body well
away from the propeller when starting the engine or adjust-
ing the needle-valve while the engine is running. Remember
that the propeller turns through a much wider arc with the
large sized propellers that this engine is capable of driving.
Refer to the “Safety Instructions and Warnings” leaflet
enclosed.
IMPORTANT: Use well balanced propellers and spinners only. An
unbalanced propeller or spinner causes vibration and
loss of power.
There is always a danger, especially with nylon pro-
pellers (and depending on engine speed and weather
conditions), of the propeller fracturing and a blade
flying off and, obviously, this could cause serious
injury. Therefore, never crouch over the engine when
it is running and keep all onlookers well back and
behind the model. if a spinner is used, make sure
that the spinner notches are large enough to clear the
propeller blades and so do not cut into and weaken
the blade roots when the propeller nut is tightened.
WARNING:
There is also a risk, particularly with four-stroke engines, of
the propeller flying off if the propeller nut loosens due to
detonation or “knocking” when the engine is run too lean
or under too heavy a load. Obviously this can also be very
hazardous.
To combat this danger, we have developed the special
Safety Propeller Locknut Assembly supplied with the
FS-120S-E. This prevents the propeller from flying off,
even if the propeller itself should slip or loosen.
1. Ream the propeller centre hole to 8mm dia. Make sure
that the propeller is properly balanced.
2. Fit the propeller sleeve-nut and washer to the propeller,
screw onto the shaft and tighten firmly with 17mm
wrench supplied.
3. Finally, insert the Safety Propeller Locknut. Tighten
Locknut firmly (but not with excessive force) using
14mm wrench. (see Fig. 2)
IMPORTANT:
Regardless of the type of propeller
fixing used, make a habit of al-
ways checking the tightness of the
propeller before starting the
engine. Remember that, especially
with wooden propellers, there is a
tendency for the material to
shrink, or for it to be reduced by
the serrated face of the drive hub.
Drive hub
Propeller washer \
STARTING
It is preferable to use a heavy-duty electric starter.
1. Firstly, fit a spinner so
that an electric starter can
be used. The O.S. special
locknut set for spinner,
that is available as an
optional part, enables you
to fit a spinner securely
and easily.
2. Open the throttle so that
the throttle-arm is at one- Starting position
quarter of its full throw. Fig. 3
(see Fig. 3)
(a) lf a silencer pressurized fuel system is employed, set
the needle-valve 2⁄2 turns open from the fully closed
position.
(b) If a silencer pressurized fuel system is not employed,
set the needle-valve 3 turns open from the fully
closed position.
3. Energize the glowplug and apply the electric starter after
making sure that the battery leads are properly connected
for counter-clockwise rotation. If the power of your
starter is insufficient to immediately rotate the engine
freely, turn the propeller clockwise (‘backwards’) until
compression is felt, then, with the propeller in this posi-
tion, try the starter again. This will enable the kinetic
energy of the rotating propeller to assist in carrying the
engine through its compression stroke. Also, make sure
that your starter battery is in good condition and fully
charged.
CAUTION: Never apply an electric starter with the choke closed.
Such an action will cause an excess quantity of fuel to
be drawn into the cylinder and result in an hydraulic
lock that may damage the engine.
4. When the engine starts, keep it running, initially, with
the original needle-valve setting while steadily moving the
throttle to the fully open position. If the engine slows
down because the mixture is excessively rich, close the
needle-valve slowly until the engine runs evenly. Then
disconnect the battery from the glowplug and close the
needle-valve slowly so that revolutions increase. Adjust
the needle-valve gradually. Abrupt adjustment of the
needle-valve may cause the engine to stop.
Note: Excess fuel in the carburettor may drip into the engine com-
partment when the choke valve is reopened. Therefore, it is
advisable to drill a drain hole in the bottom of the engine bay
or cowling and to apply fuelproof paint to the surrounding
surfaces to prevent fuel from penetrating the airframe struc-
ture.
RUNNING-IN (‘‘Breaking-in’’)
All internal combustion engines benefit, to some degree,
from extra care when they are run for the first few times —
known as running-in or breaking-in. This is because the
working parts of a new engine take a little time to settle
down after being subjected to high temperatures and Stress.
However, as O.S. engines are made with the aid of the finest
modern precision machinery and from the best and most
suitable materials, only a very short and simple running-in
procedure is required and can be carried out with the
engine installed in the model.
For running-in, use the same sized propeller as you intend
for flying your model.
Running-in procedure is as follows:
Start the engine and run it for about 5 seconds at around
maximum r.p.m., then open the needle-valve % turn to
produce a rich mixture for cooler, slower running, and run
for ,20 seconds at this setting. Keep the throttle fully open,
using only the needle-valve to reduce speed. Repeat this
procedure, alternately running the engine fast and slow
with the needle-valve, but gradually extending the short
periods of maximum speed running until two full tanks of
fuel are consumed.
Note: Take care to avoid dusty and sandy locations. Dust and grit
drawn into the engine will seriously damage its working parts.
Following the initial break-in on the ground, the engine
should be given a period of moderately rich running in the
air. For the first flights, set the needle-valve rich, consistent
with adequate take-off power and steady level flight and, if
necessary, readjust the throttle trim on the transmitter so
that the engine does not stop when the throttle is fully
closed.
With each successive flight, close the needle-valve slightly,
until, at the end of 10 flights, the needle-valve is set for
maximum power. The carburettor can now be adjusted for
optimum throttle performance following the instructions
given in the next section.
Note: Remember that, while the engine is being run-in and the
needle-valve is set on the rich side, the carburettor cannot be
expected to show its best response. Therefore, avoid abrupt
throttle operation at this stage.