Refer to figures.
Firstly, the blade trim tabs which are located on the trailing edge of each blade generate a corrective force which indirectly provokes the blades pitch angle to change and produce the intended lift result. Also makes the blades fly in the same Tip Path Plane (TPP) and produces a twisting moment making them fly smoother. Thus, trim tabs serve different purposes. Therefore, trim tabs do not adjust the centre of pressure.

Secondly, the Centre Of Gravity is the point around which all moments arising from gravity are equal to zero,where an object’s weight passes through, or where its mass is concentrated.

Thirdly, the Aerodynamic Centre is the fixed point on the chord line about which moments are constant when the angle of attack changes.

In addition, the Centre of Pressure is a theoretical point on the blade chord line through which the resultant of all forces act. Considering C of P on two types of aerofoils:

• Is (more or less) fixed because the lift on the upper and lower surfaces act through points opposite each other, so its position is independent of the angle of attack below the stall, regarding symmetrical aerofoils.
• It moves forward along the chord line as the angle of attack is increased, until just before the stalling angle where it moves rapidly backwards behind the C of G, regarding asymmetrical aerofoils.

Moreover, the distance between the C of G and the C of P produces a twisting moment that can distort the blade and introduce stress. Any kind of movement of the C of P related to the C of G can affect stability.

For this reason, chord-wise balancing is implemented in order to stop unwanted twisting moments on a blade. The C of G, C of P and the aerodynamic centre must be as close to one another as possible, chord -wise. To achieve this, internal weights are placed on the leading edge spar by the manufacturer so as to stop blade oscillations too.