Measured Engine Installation Effects of Four Civil Transport Airplanes

INTRODUCTION The Federal Aviation Administration's Integrated Noise Model (INM) is one of the primary tools for land use planning around airports [1]. The INM currently calculates airplane noise lateral attenuation using the methods contained in the Society of Automotive Engineer's Aerospace Information Report No. 1751 (SAE AIR 1751) [2]. Researchers have noted that improved lateral attenuation algorithms may improve airplane noise prediction [3]. The authors of SAE AIR 1751 based existing methods on empirical data collected from flight tests using 1960s-technology airplanes with tail-mounted engines. To determine whether the SAE AIR 1751 methods are applicable for predicting the engine installation component of lateral attenuation for airplanes with wing-mounted engines, the National Aeronautics and Space Administration (NASA) sponsored a series of flight tests during September 2000 at their Wallops Flight Facility [4]. Four airplanes, a Boeing 767-400, a Douglas DC-9, a Dassault Falcon 2000, and a Beech KingAir, were flown through a 20 microphone array. The airplanes were flown through the array at various power settings, flap settings, and altitudes to simulate takeoff and arrival configurations. This paper presents the preliminary findings of this study. Figure 1 below shows an example where lateral attenuation influences the received noise. In situation A, the airplane flies directly over the receiver at slant distance R and an elevation angle of 90 degrees. In situation B, the airplane flies at the same slant distance R from the receiver, but at an elevation angle close to zero. Although the slant distances are the same, the receiver at situation B experiences less noise. Two factors contribute to this reduction in noise; the first factor is the influence of the ground on absorbing some of the propagating sound, the second factor is the influence of the airplane geometry itself on shielding some of the noise. This shielding effect is referred to as " engine installation effects. " This study examined how specific airplane geometry influences engine installation effects. The specific airplane geometries examined were wing-mounted engines and tail-mounted engines.