Jae-Sung Bae

As morphing is an emerging topic of interest in aircraft research, the following article provides a review of the subject, with specific focus on modeling and flight control of large-scale planform altering flight vehicles. Our discussion proceeds in a fundamental manner to demonstrate that, although design methods for rigid aircraft have become highly developed, the consideration of morphing necessitates further investigation into the typically disparate fields of dynamic modeling, aerodynamic theory, and flight control theory. To clarify these points, the equations of atmospheric flight are derived in a general form, methods of integrating the aerodynamic forces are examined, and we distinguish between various approaches and methods of flight control.

For a few decades, various methods to suppress the vibrations of structures have been proposed and exploited. These include passive methods using constrained layer damping (CLD) and active methods using smart materials. However, applying these methods to large structures may not be practical because of weight, material, and actuator constraints. The objective of the present study is to propose and exploit an effective method to suppress the vibration of a large and heavy beam structure with a minimum increase in mass or volume of material. Traditional tuned mass dampers (TMD) are very effective for attenuating structural vibrations; however, they often add substantial mass. Eddy current damping is relatively simple and has excellent performance but is force limited. The proposed method is to apply relatively light-weight TMD to attenuate the vibration of a large beam structure and increase its performance by applying eddy current damping to a TMD. The results show that the present method is simple but effective in suppressing the vibration of a large beam structure without a substantial weight increase.

In the present study, a piezo-aeroelastic energy harvester using nonlinear aeroelastic behaviors is proposed, and their characteristics and performance are investigated. The energy harvester is modeled by a two-dimensional typical section airfoil. The nondimensional parameters of the harvester are introduced, and the nondimensional piezo-aeroelastic equations are formulated. For the piezo-aeroelastic analysis, the root-locus method and time-integration method are used, and the present method is verified with experimental and analytical results. The iterative method is introduced to calculate the frequency response functions of a nonlinear piezo-aeroelastic energy harvester. The aeroelastic characteristics of a linear piezo-aeroelastic energy harvester and the effects of parameters are investigated. The results show that the linear piezo-aeroelastic energy harvester can be used to generate electricity only at the vicinity of flutter speed. It is assumed that the nonlinear piezo-aeroelastic energy harvester has free play and cubic hardening in pitch. For free play, nonlinear aeroelastic results show that stable limit cycle oscillations are observed in the wide range of air speed below flutter speed when the frequency ratio is 1.3, and unstable limit cycle oscillations are observed at air speeds over flutter speed when the frequency ratio is 0.3. For cubic hardening, unstable limit cycle oscillations are observed at air speeds below flutter speed when the frequency ratio is 0.3, and stable limit cycle oscillations are observed at air speeds over flutter speed when the frequency ratio is 1.3. Finally, the authors discussed how to use these aeroelastic responses for piezo-aeroelastic energy harvesting.

In this work the benefits of variable span morphing are considered, specifically with regards to the increased maneuverability of bank-to-turn cruise missiles. Along with an increase in range associated with variable span aircraft-in the case where both wings are equally extended-there is also the possibility of an additional advantage of higher control authority over both pitch and roll motions. In the case of roll control, one wing is extended while the other is contracted thus producing a moment about the longitudinal axis of the missile. Compared to conventional tail surface control, this moment can be substantial depending on the flight conditions. There is, however, some complexity involved in flight control of variable span aircraft; namely the shift of the missile’s center of mass and the dependence of the roll producing moment on the angle of attack. The following work attempts to address these complexities through nonlinear control. First, a full nonlinear model of the missile is presented that includes aerodynamic effects and changes in weight distribution. Nonlinear methods are then used to control the trajectory of the missile via the roll angle, angle of attack, and sideslip angle. The results show that, in comparison with conventional missile configurations, the addition of variable span morphing has the capability of increasing overall flight performance.