Topic 2 About the Technology

This section relates specifically to multi-rotor or copter drones. Several models of fixed-wing drones are also used in the agricultural and mining sector. The aerodynamics and flight control systems of these systems are like larger fixed-winged aircraft and not covered here However the general aeronautical terminology used here is common to both.

Like all rotor-powered flights, Drones use airfoils or propellers to apply an upwards force that offsets the weight of the aircraft. This is force is referred to as lift. The force that opposes movement through the air is referred to as drag. The movement of air over aerofoils such as wings on a fixed-wing plane or propellers on a helicopter or Drone produces areas of low and high static pressure. It’s these variations of pressure that produce lift. In a fixed-wing aircraft lift, is controlled by the angle of attachment of the curved surface of the wing. The height of the aircraft and the direction are controlled by stabilisers, flaps, and rudders. Helicopters do this by altering the angle of the central rotors and opposing force from the spinning tail rotor. On a drone, all lift and direction are controlled by the amount of power or (Revolutions Per Minute) applied to any of the 4 motors at any one time. For the Drone to remain stable, the aircraft is designed so the propellers rotate in pairs in opposite directions to each other. This opposing rotating motor configuration manages the torque generated by the spinning motors. By applying different RPMs (Revolutions Per Minute) to specific pairs of motors the aircraft will use the resulting torque to change direction.

Image sourced from DJI Authorised Retail Store

This is important to understand as each propeller is designed specifically for its place on the aircraft. Unlike a helicopter, the angle of attack of the propellers is fixed so variations in revolutions (RPM) manage the flight.

AOT (Angle of attack) is the angle of the blades of the center rotor. A steep angle of attack gives more lift but takes more power to move through the air and can cause the aircraft to stall. A shallow angle of attack moves the blade through the air easier but will require more RPMs and power to move the aircraft. If the AOT is too small the aircraft will not produce enough lift and not fly.

The small grey ring around the centre of each rotor determines which of the four motors they belong to.

For the RPA to lift and manoeuvre the pilot sends signals to the RPA via the controller. These commands primarily control the amount of power applied to each motor. For the device to rise the 4 motors increase power or Revolutions Per Minute (RPM) all at the same time.