Indirect actuation reduces flight power requirements in Manduca sexta via elastic energy exchange

In many insects, wing movements are generated indirectly via exoskeletal deformations. Measurements of inertial and aerodynamic power suggest that elastic recovery of energy between wingstrokes might reduce power requirements of flight. We tested three questions. 1) Can the thorax itself provide significant energy return? 2) Does a simple damped elastic model describe the bulk mechanical behavior? and 3) Are different regions of the thorax specialized for elastic energy exchange? We measured deformation mechanics of the hawkmoth Manduca sexta thorax by recording the force required to sinusoidally deform the thorax over a wide frequency range. Elastic energy storage in the thorax is sufficient to minimize power requirements. However, we find that a structural (frequency-independent) damping model, not a viscoelastic model, best describes the thorax's mechanical properties. We next performed complementary experiments on a structurally damped homogeneous hemisphere. In contrast to the hemispherical shell, we find that mechanical coupling between different regions of the thorax improves energy exchange performance, and that local mechanical properties depend on global strain patterns. Specifically, the scutum region provides energy recovery with low dissipation, while the majority of energy loss occurred in the wing hinge region, highlighting the specificity of thorax regions for flight energetics.

在多数昆虫中，翅的运动通过外骨骼形变间接产生。针对惯性功率与气动功率的测量结果显示，翅击间隙的能量弹性回收或许能够降低飞行的功率需求。我们针对三个问题开展了验证：其一，昆虫胸部自身能否提供可观的能量回收效果？其二，简单阻尼弹性模型能否描述其整体力学行为？其三，胸部的不同区域是否特化用于弹性能量交换？我们通过记录在宽频率范围内以正弦方式形变烟草天蛾（Manduca sexta）胸部所需的作用力，以此测量其胸部的形变力学特性。胸部内的弹性储能足以将功率需求降至最低。然而我们发现，能够最优描述该胸部力学特性的是结构（与频率无关）阻尼模型，而非粘弹性模型。随后我们针对结构阻尼均质半球开展了对照实验。与该半球壳形成对照的是，我们发现胸部不同区域间的力学耦合能够提升能量交换性能，且局部力学特性依赖于整体应变模式。具体而言，盾片区域能够实现低损耗的能量回收，而绝大多数能量损耗发生在翅关节区域，这凸显了胸部不同区域在飞行能量利用上的特化性。