Systems Guide
Table Of Contents
Aerosoft
Twin Otter E
XTENDED
Systems
Vol
2
2-1-5
19 November 2013
ENGINE TEMPERATURE (T
5
)
Engine temperature is measured at 8 locations in the gas stream between the gas generator turbine and the
power turbine. An average of the temperature is send to the instrument panel and the gauge requires 26 volts
to operate.
GAS GENERATOR RPM (NG)
Gas Generator RPM is measured at the accessory gear and is send to the instrument panel in percentage of
maximum design RPM.
FUEL FLOW
See Fuel System section.
OIL PRESSURE / OIL TEMPERATURES
See Oil System section.
PROPELLERS
The Twin Otter comes with either 3 bladed or a 4 bladed propellers with similar performance. The 4 bladed
propellers make less noise and are therefore better suited in some conditions. The propellers are of the
constant speed type, which means that blade pitch is set to keep a certain propeller RPM.
Normally when the engines are stopped, the propeller blades will feather due to loss of oil pressure. On some
floatplanes there are devices called “start locks” which prevents the propeller blades from feathering. This is
done to prevent any thrust to be produced during startup, which can be troublesome on floatplanes.
The Twin Otter has an auto feather system, which will automatically will feather the propeller if an engine
should fail. It senses if there is too large a difference of torque between the two engines.
Below the power levers flight idle range the propellers are operated in ‘beta range’. In beta range the blades
are controlled directly by the power lever and can also be set to zero pitch as well as reverse. While not
certified to be used when flying, reverse power can still be applied.
During the run-up check certain functions of the auto feather and beta range controls are checked to ensure
their proper function. The testing of the beta control system include the beta range backup system, which
prevents the propeller blades to run into an unacceptable low pitch if the beta control system should fail. A
micro switch that senses when reverse power is applied is tested during run-up.
The two constant speed propellers (3 or 4 bladed) have a propeller reverse cam mechanism to control the
blades between its 17° and -15° (beta) range. It features an overspeed protection, auto feathering and an
optional blade latch system. The rotational speed is indicated on a propeller tachometer on the engine
instrument panel
PROPELLER BETA RANGE
The propeller beta range is the pitch range that is controlled by the power levers (+17° to -15°). Propeller
speed in the beta range is controlled by the propeller governor fuel section together with the engine fuel
controllers.