The Development of Neural Network Based System Identification ...

60 CHAPTER 3 AERIAL PLATFORM AND CUSTOM-BUILT FLIGHT TEST SYSTEM
Forward
Clockwise Rotation
Bell Input
Hiller Input
Main Rotor
Blade
Stabilizer
Bar
β
Stabilizer Bar
Teetering Hinge
Slider
Wash-out Arm
Swash-plate
Roll Servo Input
Pitch Servo Input
Main Rotor
Blade
Stabilizer
Bar
Figure 3.4 The basic cyclic and collective pitch mechanism in the helicopter control system. β
indicates the stabiliser bar flapping with respect to the body coordinate frame attached to the rotor
hub. Symbol ‘◦’ indicates ball joints and fixed joints are shown as ‘•’. Figure adapted from Kim and
Tilbury [2004].
blades is manipulated so that more lift is produced at the aft rather than the front of
the rotor head. This tends to tilt the vehicle forward creating a forward component
of force from the main rotor lift vector and thus creating forward motion. Similarly, a
tilt of the swash-plate to the left causes more lift to be produced on the right than the
left sides of the rotor disc. This asymmetry tilts the vehicle and moves it to the left.
A tilt in any intermediate direction creates motion in that particular direction. The
collective actuator moves the swash-plate up and down the rotor shaft and does not
induce any tilt to the swash-plate. As the swash-plate moves up, the blade angle is
increased by the same amount at all points through the cycle. This creates a uniform
increase in lift across the disc with an overall increase in lifting force. In the TREX600
class helicopter, the motion of the collective actuator is achieved with a combination of
three servomotors (120 ◦ Cyclic/Collective Pitch Mixing type) to push the swash-plate