20
On starting from cold, with the needle-valve
set at the rich starting position:
Take note of this position of the needle-valve.
This will produce the practical best
(i.e. optimum)rpm setting
(lower than maximum rpm).
A light grey exhaust emission may be observed.
Now, re-open needle-valve 20-30 degree
maximum rpm is reached and will fall off
(or engine will stop) if needle -valve is closed
any further. Exhaust gas will be very light.
Finally:
rpm will increase and exhaust
smoke will be reduced.
Further needle-valve closure:
Exhaust smoke will be less dense and
grey in color.
As the needle-valve is closed and the r.p.m. increases
a good deal of white smoke is emitted.
Once the optimum needle-valve setting has been
established (see "Needle-valve adjustment-
Summary") the procedure for starting is simplified as
follows:
1) Open the needle-valve one half-turn (180˚) from
the optimum setting.
2) Open the throttle fully, place your finger over the
carburettor intake and rotate the propeller through
two revolutions to prime the engine.
3) Set the throttle one-third open from the fully closed
position, energize the glowplug and apply the
starter. When the engine starts, re-open the
throttle and re-adjust the needle-valve to the
optimum setting.
Subsequent starting procedure
16
Note: When re-starting the engine on the same
day, provided that atmospheric conditions have
not changed significantly, it may be practicable to
re-start the engine on its optimum (running)
setting. Also, if the engine is being re-started
immediately after a run (i.e.hot), priming should
not be necessary.
21
17
How to stop the engine
Close the throttle to reduce to the lowest possible r.p.m.
Close
With the transmitter throttle trim lever fully retarded, adjust the
throttle servo linkage so that the throttle rotor is fully closed
(i.e.engine stopped) when the stick is fully retarded.
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 stresses. However, because 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.The process is as follows:
1) Start the engine and, with the throttle fully open,
open the needle-valve an extra half turn (180˚)
from the optimum setting. This will produce a rich
mixture that will result in cooler running. Allow the
engine to run out a full tank on the ground. (Avoid
dusty surroundings.)
2) Now fly the model with the needle-valve re-set 20 -
30 degrees open from the optimum setting ( i.e.
40 - 60˚ from the highest rpm setting ).
3) Close the needle-valve very slightly on successive
flights so that the engine is running on its optimum
needle setting at the fifth or sixth flight.
RUNNING-IN ("Breaking-in")
