**2.1.1 Modified RC helicopter**

ServoHeli-20 aerial vehicle is a high quality helicopter which is changed by us using a RC model helicopter operating with a remote controller. The modified system allows the payload of more than 5 kilograms, which is sufficient to carry the whole airborne avionics box and the communication units. The fuselage of the helicopter is constructed with sturdy ABS composite body and the main rotor blades are replaced by heavy-duty carbon fibre reinforced ones to accommodate extra payloads. The vehicle is powered by a 90-class glow plug engine which generates 3.0hp at about 15000 rpm, and practical angular rate ranging from 2,000 to 16,000 rpm. The full length of the fuselage is 1260mm and the full width of it is 160mm. The total height of the helicopter is 410mm, the main rotor is 1600mm and the tail rotor is 260mm.

The overall rotorcraft UAV control system comprises: the aerial vehicle platform, the onboard avionics control system, and the ground monitoring station. The UAV helicopter itself is able to operate with the independent control computer system and onboard sensors.
