To generate corrective pitching torques, flies bilaterally modulate their wings' front-most stroke angle, i.e. However, such fluid-impulse methods are difficult to tune, and are thus not ideal for inducing the fast, precise mechanical perturbations that are required for a quantitative understanding of pitch control. Some notable exceptions to this include methods of mechanical perturbation using air-flow vortices ( Combes and Dudley, 2009 Ortega-Jimenez et al., 2013 Ravi et al., 2013) or gusts of wind ( Vance et al., 2013). Significant analysis has been performed on freely flying insects executing voluntary maneuvers ( Bergou et al., 2010 Ennos, 1989 Fry et al., 2003 Ristroph et al., 2011, 2009) or responding to visual stimuli ( Cheng et al., 2011 Muijres et al., 2014 Tammero and Dickinson, 2002 Windsor et al., 2014), but the general challenge of systematically inducing mechanical perturbations on untethered insects has traditionally been a barrier to the study of stabilization reflexes. Thus, free-flight studies are necessary for a comprehensive understanding of pitch control. Moreover, in the case of tethered flies, it has been shown that the wing kinematics are qualitatively different from those in free flight ( Bender and Dickinson, 2006 Fry et al., 2005). However, tethered insects do not constitute a closed-loop feedback system, as changes to their wing kinematics do not affect their body orientation ( Roth et al., 2014). Experimental studies subjecting tethered insects to both mechanical pitching perturbations and visual pitching stimuli ( Dickinson, 1999 Nalbach, 1994 Sherman and Dickinson, 2004, 2003 Taylor and Thomas, 2003 Zanker, 1990) have elucidated stereotyped kinematic responses for pitch correction, including manipulation of wingstroke angle, stroke plane orientation, wingbeat frequency and body configuration. Our work builds upon an already rich corpus of literature on insect flight control, a sizable portion of which addresses the pitch degree of freedom. Mitigating the effects of this instability requires flies to actively adjust their wing motion on time scales faster than the growth of these oscillations. This mechanism results in an undulating instability of the body pitch angle, which doubles over a time scale of ∼9 wingbeats ( Sun, 2014). The fly then begins to move backwards, and oscillation ensues in the opposite direction. Rather than acting as a restoring torque, the drag – together with the body inertia – pitches the fly up, beyond its initial pitch orientation. Because the centers of pressure of the fly's wings are always above the body center of mass during normal flapping, this drag asymmetry generates a torque that pitches the fly up. For example, if a fly pitches down while hovering, its re-directed lift propels its body forward, causing an increased drag on the wings during the forward stroke relative to the backward stroke. This oscillatory instability can be understood as the result of differential drag on the wings due to longitudinal body motion ( Ristroph et al., 2013 Sun et al., 2007). flies), periodic flapping couples with longitudinal body motion to produce rapidly growing oscillations of the body pitch angle ( Chang and Wang, 2014 Ristroph et al., 2013 Sun, 2014 Sun et al., 2007). Analytical and numerical modeling suggest that, for many two-winged insects (e.g. In particular, pitching instability is a prominent obstacle for flight control in flapping insects. Together with previous studies regarding yaw and roll control, our results on pitch show that flies' stabilization of each of these body angles is consistent with PI control. Remarkably, flies can also correct for very large-amplitude pitch perturbations – greater than 150 deg – providing a regime in which to probe the limits of the linear-response framework. Flies initiate this corrective process only 10☒ ms after the perturbation onset, indicating that pitch stabilization involves a fast reflex response. Combining experimental observations and numerical simulation, we found that flies correct for pitch deflections of up to 40 deg in 29☘ ms by bilaterally modulating their wings' front-most stroke angle in a manner well described by a linear proportional–integral (PI) controller. To directly investigate how freely flying Drosophila melanogaster control their body pitch angle against such instability, we perturbed them using impulsive mechanical torques and filmed their corrective maneuvers with high-speed video. Flapping insect flight is a complex and beautiful phenomenon that relies on fast, active control mechanisms to counter aerodynamic instability.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |