Can scalable design of wings for flapping wing micro air vehicle be inspired by natural flyers?

Lift production is constantly a great challenge for flapping wing micro air vehicles (MAVs). Designing a workable wing, therefore, plays an essential role. Dimensional analysis is an effective and valuable tool in studying the biomechanics of flyers. In this paper, geometric similarity study is firstly presented. Then, the pw−AR ratio is defined and employed in wing performance estimation before the lumped parameter is induced and utilized in wing design. Comprehensive scaling laws on relation of wing performances for natural flyers are next investigated and developed via statistical analysis before being utilized to examine the wing design. Through geometric similarity study and statistical analysis, the results show that the aspect ratio and lumped parameter are independent on mass, and the lumped parameter is inversely proportional to the aspect ratio. The lumped parameters and aspect ratio of flapping wing MAVs correspond to the range of wing performances of natural flyers. Also, the wing performances of existing flapping wing MAVs are examined and follow the scaling laws. Last, the manufactured wings of the flapping wing MAVs are summarized. Our results will, therefore, provide a simple but powerful guideline for biologists and engineers who study the morphology of natural flyers and design flapping wing MAVs

Of hummingbirds and helicopters: Hovering costs, competitive ability, and foraging strategies

Wing morphology and flight kinematics profoundly influence foraging costs and the overall behavioral ecology of hummingbirds. By analogy with helicopters, previous energetic studies have applied the momentum theory of aircraft propellers to estimate hovering costs from wing disc loading (WDL), a parameter incorporating wingspan (or length) and body mass. Variation in WDL has been used to elucidate differences either among hummingbird species in nectar-foraging strategies (e.g., territoriality, traplining) and dominance relations or among gender-age categories within species. We first demonstrate that WDL, as typically calculated, is an unreliable predictor of hovering (induced power) costs; predictive power is increased when calculations use wing length instead of wingspan and when actual wing stroke amplitudes are incorporated. We next evaluate the hypotheses that foraging strategy and competitive ability are functions of WDL, using our data in combination with those of published sources. Variation in hummingbird behavior cannot be easily classified using WDL and instead is correlated with a diversity of morphological and physiological traits. Evaluating selection pressures on hummingbird wings will require moving beyond wing and body mass measurements to include the assessment of the aerodynamic forces, power requirements, and power reserves of hovering, forward flight, and maneuvering. However, the WDLhelicopter dynamics model has been instrumental in calling attention to the importance of comparative wing morphology and related aerodynamics for understanding the behavioral ecology of hummingbirds

Experimental Studies Towards Understanding the Aeromechanics of a Flexible Robotic Hummingbird Wing in Hover

This study investigated the aeroelastic mechanics of a flexible flapping wing designed and implemented on a two-winged, flapping wing, robotic hummingbird capable of hovering. The investigation focused first on measuring aerodynamic and inertial forces and using these results to quantify efficiency; second, on measuring vertical inertial forces on the flexible flapping wing for the first time using Digital Image Correlation; and three, on quantifying the flowfield using Particle Image Velocimetry at the 70% spanwise location of the wing. The purpose of these experiments was to optimize the lift generation and increase the efficiency of the hover-capable robotic hummingbird. A bench-top experimental setup was designed and developed which flapped a duplicate of the wing used in the actual flying vehicle, and utilized the same flapping kinematics. This setup allowed for the variation of flapping parameters, as well as measurement of performance metrics through sensors which measured the instantaneous lift, torque, flap angle, and current draw. The results found that 108° flapping amplitude at 20 Hz was the most power efficient. This is the first time instantaneous vertical force and torque measurements have been successfully conducted on a flexible, hover capable flapping wing used on a flying vehicle. Additionally, this study calculates vertical inertial loads for the same type of wing using deflection measurements. Results from this investigation can be used for further refinement and structural tuning of flexible flapping wing design for hovering flight