The Development of Neural Network Based System Identification ...

3.2 AIR VEHICLE DESCRIPTIONS 57
Table 3.1 The specification of TREX600 ESP helicopter.
Specifications TREX600 ESP
Length
1.16 m
Height
0.4 m
Main Blade Length 0.6 m
Main Rotor Diameter 1.35 m
Tail Rotor Diameter 0.24 m
Weight
3.3 kg
Endurance
15 min
casing and leaves this vehicle less attractive for tight component installation.
The main structure of the helicopter consists of two vertically mounted parallel
main frames made of carbon fibre, battery and gyro mounts (plastic), metal motor
mount and a metal bottom bracket. This simple structure design produces minimum
weight with maximum strength for the helicopter platform. The electric motor and
associated reduction gearing are mounted in between these two carbon fibre main frames,
with various accessories and control components attached where appropriate as shown
in Figure 3.2. The factory also provided a lightweight plastic landing skid which was
connected to the metal bottom bracket via four mounting points.
The RC helicopter usually has a very high rotor speed of around 1500 rpm and fast
dynamic response due to its small inertia value. Shim [2000] had reported that in order
for scaled model helicopters to achieve equilibrium of lift on the rotor disc in less than one
rotor revolution, most of the small size helicopters would require stabilisation response
time to be achieved in less than 40 ms. Without any extra stability augmentation
devices, this is an extremely short time for radio controlled (RC) pilots to control the
helicopter. For this reason, almost all small-size RC helicopters have a mechanism to
artificially introduce damping. In most RC model helicopters, a large control gyro with
an air-foil, referred to as a stabiliser bar or fly-bar is used to improve the stability
characteristic around the pitch and roll axes and to minimise the actuator force required
to control the main rotor cyclic pitch [Kim and Tilbury, 2004]. In addition, an electronic
gyro is also used with the tail rotor input command to further stabilise the yaw axis.
According to Mettler et al. [2002a], the stability augmentation system can be