Force generation and wing deformation characteristics of a flapping-wing micro air vehicle ‘DelFly II’ in hovering flight

Abstract

The study investigates the aerodynamic performance and the relation between wing deformation and unsteady force generation of a flapping-wing micro air vehicle in hovering flight configuration. Different experiments were performed where fluid forces were acquired with a force sensor, while the three-dimensional wing deformation was measured with a stereo-vision system. In these measurements, time-resolved power consumption and flapping-wing kinematics were also obtained under both in-air and in-vacuum conditions. Comparison of the results for different flapping frequencies reveals different wing kinematics and deformation characteristics. The high flapping frequency case produces higher forces throughout the complete flapping cycle. Moreover, a phase difference occurs in the variation of the forces, such that the low flapping frequency case precedes the high frequency case. A similar phase lag is observed in the temporal evolution of the wing deformation characteristics, suggesting that there is a direct link between the two phenomena. A considerable camber formation occurs during stroke reversals, which is mainly determined by the stiffener orientation. The wing with the thinner surface membrane displays very similar characteristics to the baseline wing, which implies the dominance of the stiffeners in terms of providing rigidity to the wing. Wing span has a significant effect on the aerodynamic efficiency such that increasing the span length by 4 cm results in a 6% enhancement in the cycle-averaged X-force to power consumption ratio compared to the standard DelFly II wings with a span length of 28 cm.

Flow Visualization around a Flapping-Wing Micro Air Vehicle in Free Flight Using Large-Scale PIV

“…The wings move further apart in the outstroke (compare Figure 7d to Figure 6d), which is a logical consequence of the flapping-wing configuration (see Figures 1 and 2). This notwithstanding, comparing Figure 7b to Figure 6b allows us to conclude that the peeling of the wings has advanced to a further stage at the more outboard position, which has also been observed in static high-speed visualizations [19]. Regarding the generated flow structures, these are consistent with the observations for the S1 plane.…”

“…The white arrows have been inserted to indicate the relative motion of the wings with respect to each other, and it can be seen that shortly after stroke reversal, the wing flexibility results in an apparent rotation of the wings, with the wing LE and TE moving in opposite directions (see t* = 0.6, a similar behavior occurs near t* = 0.1). Also, in the early phase of the outstroke (see t* = 0.2) the visualization gives clear evidence of the "clap-and-peel" effect [14,19], where the rear part of the wings remain connected during much of the initial phase of the outstroke. As soon as the peel ends and the wing gap is opened, a strong downward flow between the wings is established, as can be seen at t* = 0.4, and which is maintained until the end of the instroke phase, see t* = 0.8.…”

“…The wings are constructed from 15 µm thick transparent Mylar foil, with carbon-fiber leading edge spars and wing stiffeners completing the wing structure. The leading edge spars are driven by a single motor through a gear-pushrod mechanism (see Figure 1) in a periodic, quasi-sinusoidal flapping motion, during which the wing surfaces undergo appreciable passive deformation [14,19]. Figure 2 defines the wing kinematics nomenclature based on the leading edge motion, with the outstroke being the phase in the flapping cycle where the wings move away from each other, and the instroke being the phase where they move towards each other.…”

Large-scale volumetric flow visualization of the unsteady wake of a flapping-wing micro air vehicle

“…1) is a flapping-wing MAV concept with a tip-to-tip wingspan of 28 cm and a nominal mass of around 20 g. It features a biplane configuration, with wings moving alternately towards and away from each other when flapping (see Fig. 2) to generate both thrust and lift, taking advantage of the clap-and-fling wing-wing interaction effect, which in the case of flexible deforming wings is rather to be interpreted as a "clap-and-peel" (De Clercq et al 2009;Armanini et al 2016;Percin et al 2016Percin et al , 2017. of a DelFly model, flapping at 13 Hz in a quiescent environment representing a hover flight configuration, in a plane at 75% semi-span.…”

Effects of asymmetrical inflow in forward flight on the deformation of interacting flapping wings

“…6 Elastic forces built up over the stroke can lead to extended rotation of the wing trailing edge at the stroke end, while aerodynamic forces act as damping. 7 In this study, the specific interaction of the flappingwing micro air vehicle (MAV) "DelFly II," 8 henceforth simply called "DelFly," is investigated. This MAV features two wing pairs in an X-wing configuration, which "clap-and-peel" 5 on each side.…”