O.S. Engines FT-300 Gemini - Manual (Page 8)

PROPELLER
The choice of propeller depends on the size and weight of
the model and on the type of flying envisaged. Determine
the best size after practical experiment.
Suggested propellers are shown in the separate instructions
sheet. For safety, keep your face and other parts of the
body well away from the propeller when starting the engine
or when adjusting the needle-valve while the engine is run-
ning. Remember that the propeller turns through a much
wider arc with the larger sized propellers that this engine is
capable of driving.
Refer to the "Safety Instructions and Warnings" leaflet
enclosed.
IMPORTANT: Use well balanced propellers only. An
unbalanced propeller causes vibration and
loss of power.
The larger displacement O.S. engines were originally
designed so that the propeller could be fixed to the engine
with screws, as weil as the usual nut, in order to prevent
propeller slippage. However, if the propeller nut or screws
are inadequately tightened, this can (due to detonation or
"knocking" if the engine is run too lean or under too heavy
a load) cause the propeller to split and fly off. Obviously,
this can be very dangerous.
It is recommended, therefore, to use the Safety Propeller
Locknut Assembly supplied with the engine to prevent the
propeller from fracturing or flying off, even if it loosens.
(See Figs 3, 4 & 5)
Lockout spacer
Lockout
Propeller nut
Propeller washer
Propeller washer
Lock nut
Propeller nut
Drive hub
Propeller
Drive hub
Fig. 3
Back-plate of spinner
Fig. 4
Drive hub
Propeller washer pig. 5
Locknut
Propeller nut
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