The potential for aircraft noise reduction through active suppression from a ground-based system

The feasibility of devising ground-based active noise suppression systems for aircraft which are on the ground and in the air is considered. Detailed numerical calculations are given for various geometries involving an aircraft, sound cancelling sources, reference microphones as well as correction microphones. The calculations are for broadband noise based on a frequency spectrum typical of a jet aircraft. For an aircraft on the ground (during engine run-up and during takeoff from a runway), calculations indicate that noise suppression is both feasible and practical. For an aircraft in the air, while noise suppression is feasible, it is not necessarily practical due to the fact that the most advantageous locations for the suppressing control sources are midway between the ground and the flight path. However, this may not preclude a limited application for very confined areas and for aircraft at relatively low altitudes.