James E. Bluman

Wing-wake interaction destabilizes hover equilibrium of a flapping insect-scale wing

Wing-wake interaction is a characteristic nonlinear flow feature that can enhance unsteady lift in flapping flight. However, the effects of wing-wake interaction on the flight dynamics of hover are inadequately understood. We use a well-validated 2D Navier-Stokes equation solver and a quasi-steady model to investigate the role of wing-wake interaction on the hover stability of a fruit fly scale flapping flyer. The Navier-Stokes equations capture wing-wake interaction, whereas the quasi-steady models do not. Both aerodynamic models are tightly coupled to a flight dynamic model, which includes the effects of wing mass. The flapping amplitude, stroke plane angle, and flapping offset angle are adjusted in free flight for various wing rotations to achieve hover equilibrium. We present stability results for 152 simulations which consider different kinematics involving the pitch amplitude and pitch axis as well as the duration and timing of pitch rotation. The stability of all studied motions was qualitatively similar, with an unstable oscillatory mode present in each case. Wing-wake interaction has a destabilizing effect on the longitudinal stability, which cannot be predicted by a quasi-steady model. Wing-wake interaction increases the tendency of the flapping flyer to pitch up in the presence of a horizontal velocity perturbation, which further destabilizes the unstable oscillatory mode of hovering flight dynamics.

Balancing the Efficiency and Stability of the Coupled Dynamics and Aerodynamics of a Flapping Flyer

Many studies in recent years have analyzed the stability and control of flapping wing micro air vehicles (FWMAVs). Because of its small size, low operating speed, and complex wing kinematics, the aerodynamics and flight dynamics are inherently coupled. The objective of this study is to simultaneously examine both the stability and efficiency implications of important design parameters: the chordwise location of the wing’s pitch axis, the duration of wing rotation, and the wing mass. A key feature is that the FWMAV is trimmed to an equilibrium state prior to evaluating the effect of changing each parameter, ensuring that the tradeoffs discussed truly lie in the space of feasible configurations. All simulations are performed based on bumblebee morphological parameters. Both simplified quasi-steady and Navier-Stokes solvers are used to model the aerodynamic forces and moments. The flapping power predictions between the two methods are similar across a wide range of input parameters, showing an increase with the pitch axis location and wing mass. The agreement in the predictions for pitching power was not as good, but pitch power is minimized when the pitch axis is near the quarter-chord. Also, the quasi-steady and Navier Stokes models predict significantly different stability characteristics. The primary driver of this difference is amount of lift created during wing rotation. Since this lift is generated while the wing’s position creates a significant moment arm from the body center of mass, the pitch stability demonstrates sensitivity to the amount and timing of the rapid wing rotation. Vehicle pitch instability increased with increasing pitch axis location (toward the mid-chord), increased with longer pitch durations, and increased once wing mass exceeded 1% of body mass.

Jump-starting a senior-level capstone project through hands-on laboratory exercises

Many universities incorporate either a senior-level thesis research requirement or a senior-level capstone design experience for their engineering majors. One of the biggest challenges in advising such projects is providing a means for students to make meaningful progress early in the project timeline, very often due to the steep learning curve associated with the technical details of the projects. This paper reports on a technique that requires students to complete a series of laboratory exercises designed to give them an operational awareness of the technical issues associated with small wind turbines. The three main efforts required of students were characterizing the efficiency of small generators, characterizing the efficiency of different wind turbine designs, and determining the charging characteristics of lead-acid batteries. This technique has been found to be much more effective than classroom-style instruction or pure literature review, most likely because it appeals to active, visual, and sequential learning styles. This technique, which is based on earlier work in this area, is broadly applicable to many engineering capstone design efforts. Survey data and project performance data will be presented and the effectiveness of the method is evaluated.

Chordwise wing flexibility may passively stabilize hovering insects

Insect wings are flexible, and the dynamically deforming wing shape influences the resulting aerodynamics and power consumption. However, the influence of wing flexibility on the flight dynamics of insects is unknown. Most stability studies in the literature consider rigid wings and conclude that the hover equilibrium condition is unstable. The rigid wings possess an unstable oscillatory mode mainly due to their pitch sensitivity to horizontal velocity perturbations. Here, we show that a flapping wing flyer with flexible wings exhibits stable hover equilibria. The free-flight insect flight dynamics are simulated at the fruit fly scale in the longitudinal plane. The chordwise wing flexibility is modelled as a linear beam. The two-dimensional Navier–Stokes equations are solved in a tight fluid–structure integration scheme. For a range of wing flexibilities similar to live insects, all eigenvalues of the system matrix about the hover equilibrium have negative real parts. Flexible wings appear to stabilize the unstable mode by passively deforming their wing shape in the presence of perturbations, generating significantly more horizontal velocity damping and pitch rate damping. These results suggest that insects may passively stabilize their hover flight via wing flexibility, which can inform designs of synthetic flapping wing robots.

Achieving bioinspired flapping wing hovering flight solutions on Mars via wing scaling

Achieving atmospheric flight on Mars is challenging due to the low density of the Martian atmosphere. Aerodynamic forces are proportional to the atmospheric density, which limits the use of conventional aircraft designs on Mars. Here, we show using numerical simulations that a flapping wing robot can fly on Mars via bioinspired dynamic scaling. Trimmed, hovering flight is possible in a simulated Martian environment when dynamic similarity with insects on earth is achieved by preserving the relevant dimensionless parameters while scaling up the wings three to four times its normal size. The analysis is performed using a well-validated 2D Navier-Stokes equation solver, coupled to a 3D flight dynamics model to simulate free flight. The majority of power required is due to the inertia of the wing because of the ultra-low density. The inertial flap power can be substantially reduced through the use of a torsional spring. The minimum total power consumption is 188 W kg-1 when the torsional spring is driven at its natural frequency.