Method to Calculate Behind Start of Takeoff Roll Noise Level Adjustments
This document describes a method to calculate noise level adjustments at locations behind an airplane (described by an angular offset or directivity) at the start of takeoff roll (SOTR). This method is derived from empirical data from jet aircraft (circa 2004), most of which are configured with wing-mounted engines with high by-pass ratios (Lau, et al., 2012). Methods are also described which apply to modern turboprop aricraft.
This AIR describes a method to calculate noise level adjustments at locations behind an airplane at the start of takeoff roll (SOTR) for the purposes of aircraft noise prediction modeling.
This method replaces the methods found in paragraph 3.3.1 (Sound Exposure Level Behind the Start-of-Takeoff Roll) of AIR1845A "Procedure for the Calculation of Airplane Noise in the Vicinity of Airports". Specifically, the calculations presented in 3.1 and 3.2 of this document replace the calculations in Step 3 of paragraph 3.3.1 of AIR1845A. It adheres to the basic approach described in AIR1845A and is based on measurements from modern jet and turboprop aircraft (circa 2004). The behind start of takeoff roll noise directivity method found in AIR1845A is based on measurements of older-generation (circa 1980), low by-pass ratio aircraft, primarily configured with fuselage-mounted engines. The new method described herein for modeling the noise directivity behind start of takeoff roll is derived from empirical data from modern jet aircraft, most of which are configured with wing-mounted engines that tend to have higher by-pass ratios as well as operate at higher thrust levels. Additionally, this AIR version includes a separate directivity adjustment for propeller-driven aircraft. Comparison of directivity adjustments computed from the method described herein and the AIR1845A method are presented in Appendix A.