Design trade studies and assessment for advanced quiet aircraft concepts

Abstract

(cont.) designed for 4,000nm range, 25,000 to 35,000ft cruise altitude, Mach 0.8 at cruise, and 10,000 to 14,000ft takeoff field length. By identifying the main high-level design drivers of an aircraft design, the mission for a baseline silent aircraft planform and engine was determined. A silent aircraft was designed for a range of 4,000nm and 250 passengers. A noise assessment was conducted on the engine and airframe noise sources of the resulting design. The noise impacts of five engine (jet, fan forward, fan rearward, core, and turbine) and airframe (airfoil, elevator, slat, drag rudder, and undercarriage) noise sources were investigated in terms of their noise footprints and, more specically, the loudest noise caused outside the airport boundary. The greatest noise source was the drag rudder, which was required to offset the idle thrust of the engine during approach. Because of the variable cycle and shielding effects on the embedded engines, engine noise at takeoff was greatly reduced. The main contribution of engine noise was the fan rearward noise. Overall, airframe and engine noise during approach was found to be 12dBA and 9dBA louder than during takeoff respectively. The loudest airframe noise occurred during a 3-degree approach, and was about 6dBA louder than engine noise.

This thesis describes the creation and use of tools to assess the noise impacts of conventional and blended-wing-body aircraft designs. These tools were used to set up trade studies to explore the effects of varying high level design parameters on noise. A framework was also created to conduct a detailed noise audit of various noise sources. The trade studies explored four baseline high-level design parameters: range, cruise altitude and Mach number, and takeoff field length. The results of the trade study were assessed in terms of the change in size of noise contours on the ground predicted using the noise propagation model. The main conclusion from the study on conventional tube-and-wing designs was that the two main drivers for noise are range, followed by takeoff field length, with results showing a trend of noise footprint reduction for an aircraft designed for shorter range and longer takeoff field length. The trends observed in change of footprint areas show correlation to the weight of the aircraft, with a lower weight resulting in less noise. It was also found that as the design moved towards one with higher bypass ratio engines, the savings from design range reduction and takeoff field length increase became less significant. From a baseline silent aircraft conguration that consists of a blended-wing-body air-frame and embedded engine technology, a similar trade study was conducted. The results from the study indicated that compared to a conventional tube-and-wing design, the jet noise footprint area of a blended-wing-body design that incorporates embedded engine technology is much less sensitive to changes in high level design parameters. To minimize the jet noise impacts given the baseline blended-wing-body design, the aircraft should be