Integrated Aeroservoelastic Design Optimization of Actively-Controlled Strain-Actuated Flight Vehicles

Journal of Guidance, Control, and Dynamics

2016

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...

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Static and Dynamic Aeroelastic Tailoring with Variable-Camber Control

Journal of Guidance, Control, and Dynamics

2016

“…The analytical sensitivities of these terms, typically required for gradient-based optimization, may also be computed. 5,7,11 For a large-scale structurally-detailed wingbox with complex failure mechanisms, however, accelerations and bending moments may be too simplistic to serve as design constraints. Detailed stress constraints, typically the superposition of 1g cruise stresses and the stochastic gust stresses, introduce two numerical challenges.…”

Section: Introductionmentioning

confidence: 99%

Aeroservoelastic Optimization under Stochastic Gust Constraints

2018 Applied Aerodynamics Conference

2018

This work considers the aeroservoelastic optimization of a highly flexible transport aircraft wingbox with several control surfaces distributed along the trailing edge. The steady deflections of the control surfaces are designed to alleviate static maneuver loads, while the unsteady deflections are designed to alleviate stochastic continuous gust disturbances. Spatially-detailed unsteady stochastic stress and panel buckling constraints are formulated via modal acceleration, and by methods to locate the most-probable failure point along an equal-probability hypersurface. For the case considered here, it is found that the inclusion of such gust constraints during optimization presents a sizable structural mass penalty. In some cases, this mass penalty can be completely recovered with controlled gust load alleviation.

“…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?…”

mentioning

confidence: 99%

Static and Dynamic Aeroelastic Tailoring with Variable Camber Control

15th Dynamics Specialists Conference

2016

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...