Optimization of Flexible Wings with Distributed Flaps at Off-Design Conditions

Abstract

An efficient process to aerodynamically optimize transport wings while addressing static aeroelastic effects is presented. The process is used to assess the aerodynamic performance benefits of a full-span trailing-edge flap system on a generic transport aircraft at off-design conditions. To establish a proper baseline, a transport wing is first aerodynamically optimized at a midcruise flight condition. The optimized wing is then analyzed at several offdesign cruise conditions. The aerodynamic optimization is repeated at these off-design conditions to determine how much performance is lost by the wing optimized solely for the midcruise condition. The full-span flap system is then adapted to maximize performance of the midcruise-optimized wing at each off-design condition. The improvement due to the trailing-edge flaps is quantified by examining the degree to which the flaps can recover the performance of a wing designed specifically for the off-design condition. To evaluate the repercussions of aeroelasticity on the effectiveness of the flap system, this entire process is performed on both a conventional stiff wing and a modern, more flexible wing. The impact of the choice of flap layout is also explored. The results indicate that the flap system allows for significant improvement in performance throughout cruise and that it can be advantageous even for wings with increased flexibility. Moreover, the flaps appear to provide a means for active wave drag reduction during flight.

Distributed-Flap Layout Trade Study on a Highly Flexible Common Research Model

“…The aerodynamic analysis and design tools used to complete the trade study of the distributed flap system are identical to those used in past work. 4 In this section, the static aeroelastic analysis method 12 previously developed by the authors is summarized. This method was then incorporated within a proven optimization framework 13 to allow for aerodynamic design that includes aeroelastic effects.…”

“…While the method has mostly been applied to rigid geometries, the authors have extended the framework to accommodate static aeroelastic effects. 4 With some minor enhancements, the aeroelastic analysis algorithm described in Figure 1 has been used to perform aerodynamic shape optimization of flexible wings with a fixed structural layout. The loosely-coupled analysis method was wrapped within an iterative loop as shown in Figure 2.…”

“…Modern airplanes such as the Boeing 787 and Airbus A350 employ cruise flaps to improve performance. Exploiting the same principles, a related concept is the Variable-Camber Continuous-Trailing-Edge Flap (VCCTEF) system proposed by Nguyen 1 and further studied by Nguyen et al, 2 Urnes et al, 3 and Rodriguez et al 4 This concept consists of an array of multi-segmented, rigid flaps that are distributed along most of the span of the wing. It is a subset of the variable camber concept described by Spillman 5 and is similar to that presented by Szodruch and Hilbig.…”

“…The GTM wing was analyzed assuming a modern composite structure which resulted in greater wing deformation than the nominal design. This "softened" GTM wing was redesigned using previous developed tools 4,12 at the mid-cruise point of a notional mission profile. The deflections of the VCCTEF system were then optimized at three off-design conditions to evaluate the flap system's effectiveness in improving performance.…”

Improved aerostructural performance via aeroservoelastic tailoring of a composite wing

“…It has been shown that Variable Camber Continuous Trailing-edge Flaps (VCCTF) (25) can be rotated to optimal patterns for load relief (and thus achieving a lighter-weight wingbox) at The Aeronautical Journal symmetric and roll manoeuvres (26) , and/or to improve fuel burn and to mitigate flutter (27,28) of an all-metallic variant of the NASA Common Research Model (29) subjected to stresses, buckling, flutter and actuator constraints. There has also been interest in evaluating potential benefits of trailing-edge control devices for minimum drag (30,31) , particularly in cruise and in off-design conditions (32,33) .…”