FPV Propeller Engineering: Disc Loading, Blade Pitch & Aerodynamic Drag

multirotor propellers generate lift by pushing air downwards. The thrust $T$ generated is mathematically defined by the momentum theory equation:

$$T = 2 \cdot \rho \cdot A \cdot v_i^2$$

Where $\rho$ is air density, $A$ is the disc area, and $v_i$ is the induced velocity of the airflow.

2.1 Propeller Pitch

Pitch defines the theoretical distance a propeller moves forward in one revolution.

• Low Pitch (e.g. 5x4.3): High efficiency, quick acceleration, low current draw, but lower top-end speed.
• High Pitch (e.g. 5x4.8 or 5x5.1): High top-end speed, but requires significant motor torque, draws extreme current, and suffers from heavy aerodynamic drag at low throttle.

2.2 Bi-Blade vs Tri-Blade Dynamics

• Bi-Blade: Lowest drag, highest thermodynamic efficiency. Ideal for ultra-light long range.
• Tri-Blade: Balanced grip, high thrust, linear throttle response. Standard for freestyle and racing.

High disc loading occurs when a heavy multirotor uses small propellers (e.g. 3-inch cinewhoops). High disc loading leads to severe aerodynamic instability in descents, forcing the PID controller to work in highly turbulent vortex states.