Maximum whole-body force production can influence behavioral outcomes for volant taxa, and may also be relevant to aerodynamic optimization in microair vehicles. Here, we describe a new method for measuring maximum force production in free-flying animals, and present associated data for the wandering glider dragonfly. Flight trajectories were repeatedly acquired from pull-up responses by insects dropped in mid-air with submaximal loads attached beneath the center of body mass. Forces were estimated from calculations of the maximum time-averaged acceleration through time, and multiple estimates were obtained per individual so as to statistically facilitate approximation of maximum capacity through use of the Weibull distribution. On a group level, wandering glider dragonflies are here estimated to be capable of producing total aerodynamic force equal to ∼4.3 times their own body weight, a value which significantly exceeds earlier estimates made for load-lifting dragonflies, and also for other volant taxa in sustained vertical load-lifting experiments. Maximum force production varied isometrically with body mass. Falling and recovery flight with submaximal load represents a new context for evaluating limits to force production by flying animals.

Bionic micro air vehicles are currently being popularized for military as well as civilian use and dragonflies display a wealth of skill in their remarkable flight capabilities. This study designs an asymmetric motion flapping-wing mechanism inspired by the dragonfly, using a single actuator to achieve the coupling of stroke and pitch motion. This study simulates the motion of the dragonfly’s wings using the designed mechanism and experimentally validates the motion laws and aerodynamic characteristics of the mechanism. The analysis focuses on the asymmetry in the wing’s stroke and pitch motion and their aerodynamic implications. The flapping-wing mechanism accurately replicates the wing motion of a real dragonfly in flight, and the maximum lift-to-weight ratio can reach up to 230.2%, demonstrating significant aerodynamic benefits. This mechanism provides valuable guidance for the structural design and kinematic control of future flapping-wing vehicles.

This study presents a model experiment method that can accurately reproduce the flapping motion of insect wings and measure related unsteady aerodynamic data in real time. This method is applied to investigate the aerodynamic characteristics of inclined hovering, which distinguishes it from normal hovering by having asymmetric wing rotation during the two half strokes. In the study of the aerodynamic influence of the downstroke rotational angle, it is found that the rotational angle affects lift generation by changing the angle between the wing surface and the horizontal plane in the mid-downstroke. When the wing is almost parallel to the horizontal plane in the mid-downstroke, the vortex structure can maintain structural integrity and a large magnitude, which is conducive to the generation of high lift. In the study of the aerodynamic effect of the upstroke rotational angle, the windward conversion mechanism is proposed to explain the influence of the upstroke rotational angle on the direction and magnitude of thrust. Obtaining the rotational angle that is most conducive to maintaining the flight state of hovering in the present study can provide guidance for the structural design and kinematic control of micro aerial vehicles.

To investigate the influence of initial instability waves on the secondary atomization of a rotating conical liquid sheet, this study adopted a numerical simulation method. By varying the initial velocity of the liquid sheet to simulate the initial instability waves, the effects of sinusoidal fluctuating velocities under different frequencies and amplitudes on secondary atomization were investigated. The research demonstrates that the characteristic parameters of secondary atomization undergo regular changes with increases in the frequency and amplitude of the initial velocity fluctuations of the liquid sheet. Furthermore, the direction of these changes (increase or decrease) periodically reverses depending on the axial position or the moment of observation. The initial velocity fluctuations of the liquid sheet form ring-shaped droplet-dense regions along the axis of the spray field. Variations in frequency and amplitude lead to changes in the droplet number distribution within each droplet-dense region, as well as alterations in the droplet distribution on the inner and outer sides of the spray cone in the radial direction. In addition, the influence of the velocity fluctuation frequency on the secondary atomization characteristics and the spatial distribution characteristics of the droplets is significantly greater than that of the amplitude. This study provides insights for regulating the droplet size and spatial distribution characteristics of the spray field, contributing to reliable prediction and control methods for the design of high-performance advanced combustion chamber nozzles.