The Development of Neural Network Based System Identification ...

3.2 AIR VEHICLE DESCRIPTIONS 59
Main Rotor
Rotation Plane
Stabilizer Bar
Rotation Plane
Stabilizer Bar
Teetering Hinge
β
Wind Gust
Figure 3.3 The stabilising effect of the stabiliser bar. Figure adapted from Kim and Tilbury [2004].
The TREX600 class helicopter uses a standard Bell-Hiller actuation system to
control the angle of the main rotor blade. In contrast to fixed wing aircraft propeller,
the blade angle of a helicopter’s main rotor blade varies as it moves around the rotation
plane in each cycle. The blade angle may be at a maximum at one point in its cycle
around the mast and fall to a minimum value 180 ◦ later in the cycle. The main rotor
blade angle is controlled through the action of the swash-plate. The swash-plate is a pair
of plates, one rotating and the other fixed, positioned surrounding the rotor shaft that
can be tilted in any direction by the control actuators as shown in Figure 3.4. Figure
3.4 shows two linkage arms coming from the swash-plate denoted as the Bell input and
the Hiller input. The tilting motion of the swash-plate is accomplished by two cyclic
actuators indicated as pitch servo input and roll servo input. The swash-plate is tilted
fore and aft by the pitch servo input, and left and right by the roll servo input. The
blade angle of the main rotor blades is manipulated by the combination of the Bell input
from the swash-plate and the Hiller input from the stabiliser bar. The collective pitch
input to the main rotor blade is achieved by lowering or raising the swash-plate. The
washout arm with the slider prevents the collective input from affecting the stabiliser
bar. The slider slides only when the collective input is applied and it remains stationary
if only a cyclic input is applied.
If the swash-plate is tilted forward, for example, the blade angle of the main rotor