New experimental approaches to the biology of flight control systems

Abstract

The great majority of experimental research on animal flight has been done while the animal is tethered, and therefore -strictly speaking -not flying. This somewhat paradoxical situation has arisen because it is often necessary to tether an animal in order to make any measurements at all, but the opportunity that tethering presents for measuring forces and moments directly allows us to make a virtue out of a necessity. Moreover, given that the forces SummaryHere we consider how new experimental approaches in biomechanics can be used to attain a systems-level understanding of the dynamics of animal flight control. Our aim in this paper is not to provide detailed results and analysis, but rather to tackle several conceptual and methodological issues that have stood in the way of experimentalists in achieving this goal, and to offer tools for overcoming these. We begin by discussing the interplay between analytical and empirical methods, emphasizing that the structure of the models we use to analyse flight control dictates the empirical measurements we must make in order to parameterize them. We then provide a conceptual overview of tethered-flight paradigms, comparing classical ʻopen-loopʼ and ʻclosed-loopʼ setups, and describe a flight simulator that we have recently developed for making flight dynamics measurements on tethered insects. Next, we provide a conceptual overview of free-flight paradigms, focusing on the need to use system identification techniques in order to analyse the data they provide, and describe two new techniques that we have developed for making flight dynamics measurements on freely flying birds. First, we describe a technique for obtaining inertial measurements of the orientation, angular velocity and acceleration of a steppe eagle Aquila nipalensis in wide-ranging free flight, together with synchronized measurements of wing and tail kinematics using onboard instrumentation and video cameras. Second, we describe a photogrammetric method to measure the 3D wing kinematics of the eagle during take-off and landing. In each case, we provide demonstration data to illustrate the kinds of information available from each method. We conclude by discussing the prospects for systems-level analyses of flight control using these techniques and others like them. Supplementary material available online at

The influence of sensory delay on the yaw dynamics of a flapping insect

“…This suggests that the role of the haltere may be to provide fast inner-loop feedback, resulting in additional active damping which would allow the slower visual system to operate at higher gain with a faster response for the same level of robustness. The experiments also provide evidence that the large open-loop responses observed in tethered-flight might not be an artefact of the preparation, as previously suggested [43], but are indeed what would be required of a well-tuned flight control system.…”

Vision-based flight control in the hawkmothHyles lineata

“…It is important to note that assuming that tethering has no effect upon the physiological properties of the control system is not the same as assuming that tethering has no measurable effect upon the output of the control system. For example, an integral controller would be expected to saturate in the presence of any persistent non-zero deviation from the insect's commanded state that tethering might impose [20], but this does not appear to be an issue here, because the responses that we have measured are evidently not saturated (see §3).…”

“…Rigidly tethering an insect leaves its controller physiologically intact, but eliminates the flight dynamics that would normally close its feedback loops [19,20]. It is of course possible that the insect might somehow perceive that it was tethered, and that it might alter the physiological properties of its control system to compensate, whether through learning, feedback or neuronal adaptation.…”

Current Application and Technology of Functional Multineuron Calcium Imaging

“…To solve this issue, a sensory-feedback system will be required for future experiments. Closed-loop systems have been developed to analyze tethered insects [189][190][191][192][193] and are now applied to rodents. 194) To simulate more real environments, virtual reality techniques will be a powerful tool for neuroethology.…”