Haitham E. Taha

Aerodynamic-Dynamic Interaction and Longitudinal Stability of Hovering MAVs/Insects

The dynamic stability of flapping micro-air-vehicles is mainly dictated by the contribution of the body motion to the aerodynamic loads driving this motion. This contribution is, in general, relatively small when compared to that of wing flapping. As such, it is usually neglected in aerodynamic/aeroelastic analysis and optimization. However, it is essential in assessing the dynamic stability of the body motion. In this work, we derive a complete nonlinear aerodynamic-dynamic model for the longitudinal flight of micro-air vehicles that accounts for the effects of the body motion on the aerodynamic loads. The averaging theorem is then used to assess the dynamic stability of such nonlinear time periodic system. The stability of five insects is characterized. The effects of the vehicle design parameters, such as flapping frequency; amplitude; and hinge location, on the flight stability are discussed.

Experimnetal Investigations of the Lift Frequency Response at High Angels of Attack

In comparison to the numerous theoretical research reports on the unsteady nonlinear aerodynamics, there has been very few experimental data available for validation purposes; particularly, at high angles of attack (40◦ and higher). We perform experiments on an oscillating two-dimensional NACA 0012 airfoil at various reduced frequencies (0.1 ≤ k ≤ 0.9) and mean angles of attack (0◦ ≤ α0 ≤ 65◦) that undergoes a plunging motion. For each case of the mean angle of attack, the plunging motion is performed with a small amplitude at different frequencies to determine the frequency response of the dynamics. The objective is to assess the effects of the mean angle of attack on the flow dynamics and determine specific aspects associated with unsteady motions at high values of the angle of attack and the reduced frequency.

Investigation on the Effectiveness of a Nonlinear Energy Sink on an Aeroelastic System

The effectiveness of a passive control system, namely, the Nonlinear Energy Sink (NES) in the control of the response of a nonlinear aeroelastic system is investigated. The system consists of a rigid airfoil elastically mounted on linear and nonlinear springs. The structure equations are derived using Lagrange’s equations. The quasi steady aerodynamics are used to model the aerodynamic loads. The NES having linear damping is attached to the aeroelastic system. The parameters of the passive controller are varied in order to investigate the efficiency in supressing undesirable aeroelastic behavior. The results suggest that the nonlinearity of the NES influences the nonlinear dynamic behavior of the aeroelastic system and may yield undesirable responses. Nomenclature h Plunge motion θ Pitch motion y2 Nes motion α0 Preset angle of attack αeff Effective angle of attack m1 Mass of the airfoil m2 Mass of the nes e Position of the center of gravity relatively to the elastic axis d Position of the nes relatively to the elastic axis Icg Mass moment of inertia of the airfoil relatively to the center of gravity kh0 Airfoil linear plunging stiffness kh1 Airfoil quadratic plunging stiffness kh2 Airfoil cubic plunging stiffness Ch Airfoil plunging motion viscous damping coefficient kθ0 Airfoil linear pitching stiffness kθ1 Airfoil quadratic pitching stiffness kθ2 Airfoil cubic pitching stiffness Cθ Airfoil pitching motion viscous damping coefficient kn0 Nes linear plunging stiffness kn1 Nes quadratic plunging stiffness kn2 Nes cubic plunging stiffness Cy2 Nes plunging motion viscous damping coefficient L Aerodynamic Lift Force M Aerodynamic Moment b Semi-chord Clα Lift coefficient ∗Department of Engineering Science and Mechanics, MC 0219, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA. Email:mhajj@vt.edu, Phone number:+15402314190 Fax:+15402314574 1 of 13 American Institute of Aeronautics and Astronautics Cmα Moment coefficient cs Nonlinear aerodynamic coefficient U Freestream velocity ρ Air density

A Combined Geometric-Control-Averaging to Optimum Trim of Hovering FWMAVs and Insects

In this work, a combined geometric-control-averaging approach is proposed to formulate performance optimization problems of flapping-wing micro-air-vehicles (FWMAVs) accounting for its flight dynamics. Moreover, in such a framework, the two major simplifying assumptions (neglecting the wing inertial effects and averaging the dynamics over the flapping cycle) usually adopted in the analysis of flapping flight dynamics are relaxed. The formulated problem is to balance/trim FWMAVs at hover with minimum actuating torque amplitudes.

Minimum-Time Transition of FWMAVs from Hovering to Forward Flight

Unlike conventional airplanes, flapping-wing micro-air-vehicles (FWMAVs) move their wings continuously with respect to the body. These new degrees of freedom for the wings (wing kinematics) provide more room for optimal design of these miniature vehicles that are prone to stringent weight and power constraints. However, very few attempts have aimed to provide maneuverability-optimum wing kinematics. In general, the shapes of the kinematic functions are assumed from the outset and their level of control authority is assessed at a later stage. In this work, we formulate a minimumtime optimal control problem to steer the FWMAV dynamical system from hovering configuration to forward flight with a prescribed forward speed. Assuming horizontal stroke plane and a piece-wise constant variation for the wing pitching angle, only the waveform of one degree-of-freedom for the wing is optimized (back and forth flapping). Since the flapping angle is periodic, we represent it via a truncated Fourier series. The number of Fourier terms is discussed. The optimal control problem is formulated such that the cost functional is the final time, the slowly time-varying Fourier coefficients of the flapping angle are the inputs to be optimized along with the angles of attack (i.e., design variables), and the goal is to steer the averaged dynamics from the hovering configuration (origin) to a prescribed forward speed.