Showing papers by "William A. Crossley published in 2006"

Morphing Airfoil Design for Minimum Aerodynamic Drag and Actuation Energy Including Aerodynamic Work

Abstract: Recently, there has been great interest in developing technologies that may enable a morphing aircraft. Such an aircraft can change shape in flight, which would make it possible to adjust the wing to the best possible shape for any flight condition encountered by the aircraft. However, there is an actuation cost associated with making these shape changes that must be included in the optimization process. A previous effort investigated a simple strain energy model to account for the actuation cost for a morphing airfoil, and a multiobjective optimization found tradeoff solutions between low-energy, high-drag and highenergy, low-drag morphing airfoils. Building upon the previous effort, the main purpose of this paper is to formulate the aerodynamic contribution to work on the morphing airfoil. This aerodynamic work term can be added to the strain energy model to compute the total energy required for changing the shape of a morphing airfoil. With this formulation, a beneficial contribution of aerodynamic work could reduce the morphing actuation energy from that associated solely with deformation of the aircraft structure, or an unfavorable contribution of aerodynamic work could increase the morphing actuation energy. Studies presented in this paper illustrate how the aerodynamic work is computed and how the aerodynamic work can be either beneficial or unfavorable. The effect of the morphing airfoil’s relative stiffness on the multi-objective solutions is also presented. Nomenclature i d C = Coefficient of drag at design condition i i l C = Coefficient of lift at design condition i m C = Coefficient of pitching moment f C = Coefficient of skin friction p C = Coefficient of pressure c = Airfoil chord length e K = Unit vector from State 1 to State 2 a f = Actuator force s f = Internal force in spring

Building Surrogate Models for Capability-Based Evaluation: Comparing Morphing and Fixed Geometry Aircraft in a Fleet Context

Abstract: Recent advances in adaptive structures and advanced compact actuators have renewed interest in variable geometry aircraft that can change shape in flight to obtain better performance during dissimilar flight conditions. These new morphing aircraft may allow for shape changes beyond the current variable sweep and variable camber available in the F-111 or F-14 aircraft. Because of the potential for a wider range of shape changes, significant effort has been put forth to develop strategies for the conceptual sizing of such vehicles, including the “morphing as an independent variable” sizing approach that allows the use of continuous optimization techniques to size the morphing aircraft. Although these previous aircraft sizing studies have predicted advantages for variable geometry in performance and weight by conventional design comparisons, this paper extends the evaluation by investigating the effectiveness of a morphing aircraft design in a fleet of aircraft. A key feature of this work involves creating surrogate models to approximate the capability of an aircraft or a fleet of aircraft as a function of parameters describing the aircraft design mission. These capability surrogate models, coupled with similarlyconstructed cost models, enable the design of a best fleet in which the number of aircraft and the design parameters of the aircraft may be determined simultaneously. The approach here uses some initial simplifications to the approach and relies upon enumerating a number of discrete choices, but it suggests that more formalized approaches could be used for this kind of aircraft fleet design problem. For the morphing aircraft application, comparisons of the best fleet of morphing aircraft offer improvements in capability and cost over the best fleet of fixed-geometry aircraft for an example search-and-find concept of operations.

On Synergetic Extremal Control for Aerospace Applications

Abstract: This paper presents an exposition to synergetic control method. The method itself is derived from a special class of functional optimization commonly addressed in the calculus of variations. Using an Euler-Lagrange equation, a closed-form of extremizing solution which yields to extremizing control function is obtained. It turns out that such control is tightly connected to a special class of LQR as well as variable structure control. This paper presents proper design guidelines for using synergetic control so that the resulting closed loop solution is stable. Numerical explorations show promising results for this approach to be applied on other aerospace problems. Nomenclature t time t0 initial time

Aerodynamic Optimization of a Morphing Airfoil Using Energy as an Objective

Abstract: significantly change shape during flight. The research discussed in this paper focuses upon the shape design of morphing airfoil sections. In the efforts herein, the relative strain energy needed to change from one airfoil shape to another is presented as an additional design objective along with a drag design objective, while constraints are enforced on lift. Solving the resulting multi-objective problem generates a range of morphing airfoil designs that representthebesttradeoffsbetweenaerodynamicperformanceandmorphingenergyrequirements.Fromthemultiobjective solutions, a designer can select a set of airfoil shapes with a low relative strain energy that requires a small actuation cost and with improved aerodynamic performance at the design conditions.