The separation vortex in the Weis-Fogh circulation-generation mechanism

Journal of Experimental Biology

Pick

2007

100

SUMMARY Flying insects may enhance their flight force production by contralateral wing interaction during dorsal stroke reversal (`clap-and-fling'). In this study, we explored the forces and moments due to clap-and-fling at various wing tip trajectories, employing a dynamically scaled electromechanical flapping device. The 17 tested bio-inspired kinematic patterns were identical in stroke amplitude, stroke frequency and angle of attack with respect to the horizontal stroke plane but varied in heaving motion. Clap-and-fling induced vertical force augmentation significantly decreased with increasing vertical force production averaged over the entire stroke cycle, whereas total force augmentation was independent from changes in force produced by a single wing. Vertical force augmentation was also largely independent of forces produced due to wing rotation at the stroke reversals, the sum of rotational circulation and wake capture force. We obtained maximum (17.4%) and minimum(1.4%) vertical force augmentation in two types of figure-eight stroke kinematics whereby rate and direction of heaving motion during fling may explain 58% of the variance in vertical force augmentation. This finding suggests that vertical wing motion distinctly alters the flow regime at the beginning of the downstroke. Using an analytical model, we determined pitching moments acting on an imaginary body of the flapping device from the measured time course of forces, the changes in length of the force vector's moment arm,the position of the centre of mass and body angle. The data show that pitching moments are largely independent from mean vertical force; however,clap-and-fling reinforces mean pitching moments by approximately 21%, compared to the moments produced by a single flapping wing. Pitching moments due to clap-and-fling significantly increase with increasing vertical force augmentation and produce nose-down moments in most of the tested patterns. The analytical model, however, shows that algebraic sign and magnitude of these moments may vary distinctly depending on both body angle and the distance between the wing hinge and the animal's centre of mass. Altogether, the data suggest that the benefit of clap-and-fling wing beat for vertical force enhancement and pitch balance may change with changing heaving motion and thus wing tip trajectory during manoeuvring flight. We hypothesize that these dependencies may have shaped the evolution of wing kinematics in insects that are limited by aerodynamic lift rather than by mechanical power of their flight musculature.

Section: Significance Of Heaving Motion In Insect Flightmentioning

confidence: 99%

The aerodynamic benefit of wing–wing interaction depends on stroke trajectory in flapping insect wings

Journal of Experimental Biology

Pick

2007

100

“…For example, the damselfly Calopteryx splendens performs the clap-and-fling similar to the motion of the wings described by Weis-Fogh (1973) for the small wasp Encarsia formosa. As the wing reaches the top of the upstroke, the upper wing surfaces meet and then, as the wings rotate and separate, air is drawn into the opening gap, enhancing wing circulation and thus wing lift (Bennett, 1977;Edwards and Cheng, 1982;Ellington, 1975;Lighthill, 1973;Maxworthy, 1979;Spedding and Maxworthy, 1986;Sunada et al, 1993;Weis-Fogh, 1973). In addition to damselflies, the clap-and-fling was found in various other insect species such as various Diptera (Ellington, 1984b;Ennos, 1989), lacewings (Antonova et al, 1981) and a whitefly (Wootton and Newman, 1979).…”

Section: Wing-wake Interaction Between Contralateral Wingsmentioning

confidence: 99%

The fluid dynamics of flight control by kinematic phase lag variation between two robotic insect wings

Maybury

Journal of Experimental Biology

2004

151

124

Functionally four-winged insects such as dragon-and damselflies use a large variety of wingbeat kinematics to produce and control aerodynamic forces for flight (Alexander, 1984;Azuma et al., 1985;Azuma and Watanabe, 1988;Chadwick, 1940;Grodnitsky and Morozov, 1992;Reavis and Luttges, 1988;Rüppell, 1989;Rüppell and Hilfert, 1993;Sato and Azuma, 1997;Somps and Luttges, 1985;Wakeling, 1993;Wakeling and Ellington, 1997;Wang et al., 2003;Weis-Fogh, 1967). The neuromuscular system allows these animals to actively manipulate many aspects of wing motion such as stroke amplitude, stroke frequency, the angle of attack and stroke plane (Norberg, 1975;Rüppell, 1989), but also to actively control the timing between the fore-and hindwing stroke cycles (kinematic phase relationship, Alexander, 1984;Azuma and Watanabe, 1988;Clark, 1940;Grodnitsky and Morozov, 1992;May, 1995;Sato and Azuma, 1997; Simmons, 1977a,b;Wakeling and Ellington, 1997;Wang et al., 2003). Thus dragonflies and damselflies differ significantly from other four-winged insect species such as butterflies, bees, wasps and ants, whose fore-and hindwings always beat in phase, due to a sophisticated joint that mechanically couples the motion of both wings throughout the entire stroke cycle (Gorb, 2001). Other insects of more primitive orders, such as locusts, lie somewhere between both extremes; in locust, the stroke-phase relationship seems to be highly consistent, with little variation during flight control (Chadwick, 1953;Weis-Fogh, 1956;Wilson, 1968;Wortmann and Zarnack, 1993). Cooter and Baker (1977) reconstructed wing motion of freely flying locust Locusta migratoria and found a fixed phase relationship between their fore-and hindwings in which the forewing slightly leads by approximately 61°.In contrast, dragonflies vary the phase relationship between ipsilateral fore-and hindwings with different behaviors (Norberg, 1975;Reavis and Luttges, 1988;Wakeling and Ellington, 1997;Wang et al., 2003). Three categories of phase relationship between fore-and hindwing have been established: phase-shifted stroking, counterstroking and parallel stroking. A highly consistent characteristic for the Insects flying with two pairs of wings must contend with the forewing wake passing over the beating hindwing. Some four-winged insects, such as dragonflies, move each wing independently and therefore may alter the relative timing between the fore-and hindwing stroke cycles. The significance of modifying the phase relationship between fore-and hindwing stroke kinematics on total lift production is difficult to assess in the flying animal because the effect of wing-wake interference critically depends on the complex wake pattern produced by the two beating wings. Here we investigate the effect of changing the fore-and hindwing stroke-phase relationship during hovering flight conditions on the aerodynamic performance of each flapping wing by using a dynamically scaled electromechanical insect model. By varying the relative phase difference between fore-and hindwing stroke cycles we...

“…Despite the lack of direct evidence, studies in the past have emphasised that clap and fling might augment unsteady aerodynamic forces in flapping flight based on kinematic patterns of the small wasp Encarsia formosa. However, these studies solely estimated the benefit of the fling part of wing motion using either two-dimensional analytical models (Edwards and Cheng 1982;Ellington 1975;Lighthill 1973) or a combined approach incorporating measurements of flow velocities (Bennett 1977;Maxworthy 1979) and forces (Spedding and Maxworthy 1986;Sunada et al 1993) in simple robotic wings, but ignored any aerodynamic alterations due to the clap part of wing motion at the end of the up-stroke, including wake history. The overall benefit of the clap and fling thus remains uncertain in many studies of insect wing kinematics as well its robustness against changes in the angular distance between both wings (near clap condition) during dorsal wing excursion or changes in stroke shape.…”

Section: Added Mass Effects and Analytical Modelsmentioning

confidence: 99%

The mechanisms of lift enhancement in insect flight

2004

Naturwissenschaften

157

Recent studies have revealed a diverse array of fluid dynamic phenomena that enhance lift production during flapping insect flight. Physical and analytical models of oscillating wings have demonstrated that a prominent vortex attached to the wing's leading edge augments lift production throughout the translational parts of the stroke cycle, whereas aerodynamic circulation due to wing rotation, and possibly momentum transfer due to a recovery of wake energy, may increase lift at the end of each half stroke. Compared to the predictions derived from conventional steady-state aerodynamic theory, these unsteady aerodynamic mechanisms may account for the majority of total lift produced by a flying insect. In addition to contributing to the lift required to keep the insect aloft, manipulation of the translational and rotational aerodynamic mechanisms may provide a potent means by which a flying animal can modulate direction and magnitude of flight forces for manoeuvring flight control and steering behaviour. The attainment of flight, including the ability to control aerodynamic forces by the neuromuscular system, is a classic paradigm of the remarkable adaptability that flying insects have for utilising the principles of unsteady fluid dynamics. Applying these principles to biology broadens our understanding of how the diverse patterns of wing motion displayed by the different insect species have been developed throughout their long evolutionary history.