Rotorcraft typically operate near the ground throughout the duration of the operation. For this reason, military rotorcraft are vulnerable to acoustic detection, and public acceptance of civil rotorcraft is limited by annoyance caused by rotor noise radiation. The purpose of this device is to inform the rotorcraft operator of the acoustic impact of rotor noise radiation so that the flight condition of the vehicle can be changed to reduce and/or redirect rotor noise away from noise-sensitive areas.
The magnitude and direction of rotor noise radiation is determined by the aerodynamic operating state of the rotor, commonly referred to as the “Blade-Vortex Interaction” that occurs when the wake vortex trailing from a preceding rotor blade interacts with the front edge of the following rotor blade. The wake vortex causes a rapid change in the blade loading, which results in the generation of high-amplitude, impulsive, and highly directional noise. The occurrence, magnitude, and directionality of Blade-Vortex Interaction noise is very sensitive to the rotor operating state because it is dependent on the relative positions of the rotor and its vortex wake. By providing the rotorcraft pilot with information about annoying noise levels currently being emitted by the rotorcraft and its effects on the ground, corrective action can be taken to change the operating state of the vehicle to minimize or avoid annoyance due to such rotor noise sources.
During operation, the pilot would activate the device before or during operation of the rotorcraft. The device displays the noise abatement information through a display unit, informing the pilot about the current acoustic state of the vehicle and providing guidance on how to change the vehicle performance and acoustic state to avoid objectionable blade-vortex interaction noise. Annoyance footprint information can then be used by the pilot to change the flight path of the vehicle such that the annoyance footprint will not extend into noise-sensitive areas.