Static and Dynamic Aeroelastic Tailoring with Variable-Camber Control

Abstract

This paper examines the use of a Variable Camber Continuous Trailing Edge Flap (VCCTEF) system for aeroservoelastic optimization of a transport wingbox. The quasisteady and unsteady motions of the flap system are utilized as design variables, along with patch-level structural variables, towards minimizing wingbox weight via maneuver load alleviation and active flutter suppression. The resulting system is, in general, very successful at removing structural weight in a feasible manner. Limitations to this success are imposed by including load cases where the VCCTEF system is not active (open-loop) in the optimization process, and also by including actuator operating cost constraints. I. IntroductionDistributed control surfaces along the trailing-edge of a wing structure can have a substantial impact upon the aeroelastic stiffness, mass, and damping properties of that structure [1]. The quasi-steady and unsteady deflection patterns/history of these control surfaces may be optimized during an aeroelastic tailoring procedure, alongside more traditional design variables such as structural thicknesses of the skins, spars, ribs, and stringers. Designing both sets of design variables at once allows the optimizer to take full advantage of the strong synergies that exist between the two. Quasi-steady flap deflections may be optimized for maneuver load alleviation and cruise drag (or fuel burn) reduction [2][3]. Unsteady flap deflections (where each control surface oscillates about its mean quasi-steady position) may be used for active flutter control, gust alleviation, ride quality control, etc. [4]- [7].Despite the efficacy of control surface rotations for aeroelastic optimization, two important considerations should be included in the process, in the form of design constraints. The first is rooted in certification concerns: will the aeroelastic response of the wing be sufficiently safe in the unlikely event that the control surfaces are inactive? This risk may be mitigated by increasing the level of importance of open-loop load cases (where control surfaces are not actuated/included) relative to closed-loop cases (where they are) during the optimization process. As is often the case with aerospace systems [8], there is a strong trade-off between this form of risk reduction and overall structural performance (weight, e.g.). Design constraints attached to open-loop cases will dilute the effectiveness of the control surface actuation design variables.A second consideration may be the cost to actuate the control surfaces, measured in terms of the work done by applied hinge moments, or controller cost metrics. Distributed control surfaces are adept at maneuver load alleviation, for example, but maintaining large deflections under strong aerodynamic loading may increase the overall operating costs of the airplane. As above, one may expect a trade-off between these actuation cost metrics and the aeroelastic performance of the control surfaces. In addition to actuation cost metrics, constraints which recognize actuation limitatio...

Improved aerostructural performance via aeroservoelastic tailoring of a composite wing

“…Since NASTRAN solution 144 performs a trim analysis, additional lift is then necessary for trimming the aircraft, which is achieved by giving the inner wing controls an upward displacement. This control deflection pattern is close to the one previously found by Stanford (26,27) . Intuitively, this loading shape is preferable from a structural perspective because the centre of pressure is shifted inboard, therefore reducing the root bending moment which, in turn, allows for more material to be removed from the wing skins and spars without any structural constraint violation.…”

“…Moreover, a number of recent studies have explored active aeroelastic adaptations as a means to improve aircraft overall performance. 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) .…”

Flow and Mechanical Characteristics of a Modified Naca Wing Geometry

“…Guo [32] optimized a wing's weight and aeroelastic response together and was able to achieve similar aeroelastic behaviour with 40% less weight without the use of reinforcements. Stanford [33] studied the aeroservoelastic response of one edge of the wings prepared with various camber shapes and focused on minimizing weight while avoiding buckling, hinge moments, flutter. Szollosi and Baranyi [34] examined the control performance for a 2D airfoil with 3 degrees of freedom and provided performance improvement by using different models in their parametric analysis.…”

Synthesis Of Robust Control Systems With Dynamic Actuators And Sensors Using A Static Output Feedback Method

“…With the development of more sophisticated technology and equipment, it tends to become increasingly relevant to consider the dynamics of sensors and actuators in modern control problems. For instance, sensors, actuators, control law, and control surfaces could affect the stability and performance of modern lightweight aircraft (Yang et al, 2018;Al-Jiboory et al, 2017;Stanford, 2016), due to aeroservoelasticity, a design characteristic inherent of such airplanes (Botez et al, 2008). In fact, the negative impact of neglecting of sensor and actuator dynamics has been long known (Young and Kokotovic, 1982;Leitmann et al, 1986).…”