Investigation of the application of hybrid laminar flow control and variable camber wing design for regional aircraft

Abstract

Approximately 65% of the world's commercial jet fleet consists of narrowbody, single-aisle aircraft with a capacity of 70 to 170 seats. The trend since deregulation in the US has been towards hub-and-spoke networks and a reduction in average aircraft size. The liberalization of the European market could exacerbate this trend. Because of congestion and the competitive environment the airlines are forced to buy technology and competitive aircrafts at low cost and to ask to the manufacturers to provide more operational flexibility, without drastic performance losses. In the feasibility phase of an Advanced Technology Regional Aircraft (ATRA) family, a combined HLFC-VCW (Hybrid Laminar Flow Control - Variable Camber Wing) concept was investigated to improve the overall efficiency, flexibility and reduce weight as the weight-growth factor is a critical issue. A methodology of a conceptual design and wing design incorporating a combined HLFC-VCW concept for regional transport aircraft was developed. For the purpose of this study, SWEPTDES was used to initially design the aerofoil sections for ATRA’s wing. RAMPANT was used to analyse ATRA wing aerodynamic performance in the transonic speed regime for both turbulent and laminar flows. A simple transition prediction method was used, based on assumptions that extended regions of favourable pressure gradient would correspond to extended regions of laminar flow. The boundary layer transition is expected to be just in the front of the recovery point. To identify the drag reductions by the applications of combined HLFCVCW system, a simple drag prediction method was used, to show an initial comparison with a turbulent datum design. Relative to a baseline aircraft, with current state-of-the-art technology, a cruise drag improvement potential of more than 10 % was identified. This drag reduction leads to MTOW reductions up to 4 % or increased range by more than 7 %. Variable camber (VC) offers an opportunity to achieve considerable improvements in operational flexibility, buffet boundaries and performance and enable the use of one wing for a regional aircraft family. Although in this work the design lift requirement was not achieved, but the results showed that using VCW the wing lift could be increased or decreased and could be optimized to produce the desired lift range. The introduction of VC could set off a new generation of intelligent airliners which will optimize their camber schedule automatically throughout the entire mission. Variable Camber is a prerequisite for HLFC wing to control the pressure gradients and the off-design behaviour. Before HLFC and VCW technology can be applied to the transport aircraft, a large multidisciplinary research effort is needed in order to master the technology and demonstrate it on flying test-beds and in-service operational tests.