Variable Pitch Propellers for Amazing Aerobatics in Indoor RC Planes

Variable Pitch Propellers for Amazing Aerobatics in Indoor RC Planes

Blade pitch, or simply pitch, describes the turning angle of attack of the blades of a propeller into or out of the air in order to control the production or absorption of thrust. In aircraft, pitch is normally given as either 'coarse', referring to a high angle of attack, or 'fine' for a low angle of attack and acts much like the gearing of a car - fine pitch yields good low-speed acceleration (and climb rate in the aircraft), whilst coarse pitch optimizes high-speed performance. It is because of the need to keep pitch constant along the length of a propeller blade, that the blades are twisted in shape, as this compensates for the fact that the velocity of a blade in motion varies from its centre to its tip.

Aircraft are often designed with the ability to vary the pitch of the propellers, so that performance and economy can be optimized for different stages of flight, such as take-off and cruising. These are known as Variable Pitch Propellers (VPP) and how they work is that the propeller blades are rotated around their long axis to change their angle of attack. If the pitch can be set to negative values, the propeller can create reverse thrust for manoeuvres such as breaking or going backwards, without having to change the direction of revolution of the propeller shaft.

The use of variable pitch propellers on indoor RC planes allows for some fantastic aerobatics displays, which are always the high point of RC tournaments and shows. The four main control elements on an indoor RC plane are the aileron, elevator, rudder and throttle. In normal flight, the pitch of the propeller blades is fixed and throttle is adjusted to vary the thrust. Normal flight applies to conventional flying such as take-off, cruising and landing. However, being able to vary the propeller pitch allows what is referred to as 4D flight where manoeuvres, which until recently had rarely been seen before, include flying backwards, inverted take-offs, reverse spins, nose-down hovering and even bouncing the nose on the floor!