Systems Guide
Table Of Contents
Aerosoft
Twin Otter E
XTENDED
Systems
Vol
2
2-1-6
19 November 2013
PROPELLER GOVERNOR
The propeller governor is mounted on the reduction gearbox and combines the following functions:
• Constant speed governor (regulates the turbine speed by varying the propeller pitch)
• Beta range control valve (controls the propeller angle in the beta range using the power control
levers.
• Fuel governor
On turbo prop aircraft, the pitch (angle between the blade and the relative wind) of the propeller can be
varied. Beta mode is a range of settings that are below the normal flight idle. It is commonly known as the
ground operating range. (With the air operating range named Alpha)
POWER / PROPELLER / FUEL CONTROL LEVERS
The main controls of the engines are located on the overhead panel.
POWER LEVERS
Incorrectly labelled THROTTLE the power levers controls the fuel flow to the engines. There are two ranges
combined in the control, MAX to IDLE and IDLE to REVERSE. The MAX to IDLE range controls the engine
between full power and idle. Moving the power levers beyond the IDLE setting to REVERSE allow the engine to
drive the propellers so thrust is reversed. This allows the aircraft to taxi backwards or reduce speed.
The power lever range goes from full reverse through ground idle (GI) to flight idle (FI) and then on up to full
power. Below flight idle you are operating in the beta range where the power lever directly controls the prop
pitch from -15° to +17°. Above flight idle there is a minimum pitch stop ranging from +10 (flight idle) to +25
(full power) degrees pitch. As you move the power lever from full aft to full forward, more and more fuel is
added to the engine. At low power settings (below approx. 30%), this amount of fuel is not enough to spin the
propeller up to the commanded 1180 RPM at the pitch setting commanded by PL in beta range or at the
minimum pitch stop.