Figure 3-2: Collective Pitch
Decreasing collective will of course result in the opposite reaction. The primary effect of moving collective will be a change in height, and the secondary effect is a change in yaw.
THROTTLE
A twist grip throttle is mounted on the forward end of the collective. It is used to set the engine and rotor RPM to the normal operating range on piston engine helicopters. Your instructor will demonstrate that in addition to increasing RPM, applying throttle will also cause the manifold pressure to increase, and the helicopter to yaw to the right. Reducing throttle, while causing a decrease in RPM and manifold pressure, will again cause yaw, this time to the left. Your instructor will also demonstrate proper coordination of throttle, and collective movements, to maintain both manifold pressures, engine and rotor RPM in the correct operating ranges.
On most light turbine helicopters, the throttle is used to bring the engine up into the governed range, where precise adjustments of the engine and rotor RPM are made through the engine governor “beep” switch. Once set correctly, RPM will remain relatively constant regardless of collective movement. It is worth mentioning that some helicopters do not have a collective mounted throttle; some have the throttle on the floor, others on a roof console.
TAIL ROTOR PEDALS
The purpose of the pedal controlled tail rotor is to counteract the torque effect of the main rotor, to control the heading of the helicopter during hovering flight, and to initiate turns while in the hover. It is not, however, used to control the heading while in cruise flight, but only to compensate for torque. This puts the helicopter in longitudinal trim so as to maintain co-ordinated flight (Figure 3-3 refers). Some helicopters have a ‘ball’ to assist you to keep in co-ordinated flight. This is a simple spirit level device, if the ball is deflected to the right, apply right pedal until the ball centres and vice versa.
Figure 3-3: Torque Effect
Movement of the pedals will effect a change in the collective pitch of the tail rotor blades. The result of pressure on one pedal will be a yaw in the corresponding direction, i.e.; pressure on the left pedal will cause the nose to yaw left, and vice versa. An increase in pitch will require an increase in power, a decrease in pitch a decrease in power. On North American helicopters the left pedal is the “power” pedal. In other words when you apply left pedal you will require more power.
Your instructor will demonstrate to you that the need for pedal application must be anticipated every time you change power. In fact, any change in collective or cyclic position will require you to adjust the pedals in order to maintain co-ordinated flight.
ANCILLARY CONTROLS
These controls, while not actually used to control the helicopter in flight, are nevertheless vital to the safe and comfortable operation of the helicopter. Depending on helicopter type, ancillary controls may include: carburettor heat, mixture control, engine anti-icing, windshield defogging, rotor brake and heater. Your instructor will demonstrate the correct use of the particular ancillary controls that equip the type of helicopter on which you will be training.
CARBURETTOR HEAT CONTROL AND MIXTURE CONTROL
CARBURETTOR HEAT CONTROL
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