Prop Blade Loading

Prop blade loading is equal to the BHP divided by the prop blade area (BHP/PBA), as opposed to prop disc loading, which is BHP divided by prop disc area (BHP/PDA).

The Scottish Aviation Twin Pioneer of 1955 vintage has three, high – aspect ratio prop blades, de-iced with a curved leading edge and a trailing edge cuff. It is housed in the RAF Cosford Museum, England.

Prop blade loading =

Prop blade area

Increasing the number of blades can reduce the prop blade loading for a given prop. It is akin to wing loading where the

reduced strength of air circulation and a reduction in the air flow velocity over the prop blades causes a reduction in prop blade loading (or wing loading). The reduced air flow over the prop blades may at first be puzzling when examining Diagram 16, Forces in Cruise Flight, which shows the ‘relative air flow’ to be dependant on the RPM and forward velocity. As the air mass flow approaches the prop disc, the velocity in front of the prop disc increases and then decreases behind the prop disc; with increased blade area (reduced blade loading) the air circulation over the blades is reduced.