Propeller Blade Passing Frequency & Tonal Noise Calculator

The Blade Passing Frequency (BPF) is the rate at which rotor blades sweep past a fixed observation point, creating periodic pressure pulses perceived as distinct tonal hums.

Propeller noise dominates the acoustic signature of turboprop aircraft, multirotor drones, and HVAC ventilation fans.

Steady thrust and torque forces acting on the fluid rotate with the blades, producing dipole Gutin loading noise.

The displacement of air by the physical volume of the rotating blade blades produces monopole thickness noise, which grows rapidly as tip Mach number approaches 1.0.

BPF is the primary tonal frequency in Hertz.

Harmonics at 2·BPF and 3·BPF also carry significant acoustic energy.

Tip Mach number should ideally stay below 0.70 to avoid harsh transonic thickness noise.

• Blade count: Increasing blade count spreads thrust across more blades, shifting BPF to higher, more easily attenuated frequencies.
• Tip speed: Noise rises dramatically with tip speed; reducing RPM is the most effective way to quiet drones and propellers.

• FAA / EASA aircraft propeller noise certification compliance.
• Designing quiet drone propellers and computer cooling fan blades.

• Evaluates free-field propeller noise without interaction effects from airframe struts or wing surfaces.