Hedrick T L, Usherwood J R, Biewener A A
Department of Biology, CB 3280 Coker Hall, University of North Carolina, Chapel Hill, NC 27599-3280, USA.
J Exp Biol. 2007 Jun;210(Pt 11):1912-24. doi: 10.1242/jeb.002063.
The reconfigurable, flapping wings of birds allow for both inertial and aerodynamic modes of reorientation. We found evidence that both these modes play important roles in the low speed turning flight of the rose-breasted cockatoo Eolophus roseicapillus. Using three-dimensional kinematics recorded from six cockatoos making a 90 degrees turn in a flight corridor, we developed predictions of inertial and aerodynamic reorientation from estimates of wing moments of inertia and flapping arcs, and a blade-element aerodynamic model. The blade-element model successfully predicted weight support (predicted was 88+/-17% of observed, N=6) and centripetal force (predicted was 79+/-29% of observed, N=6) for the maneuvering cockatoos and provided a reasonable estimate of mechanical power. The estimated torque from the model was a significant predictor of roll acceleration (r(2)=0.55, P<0.00001), but greatly overestimated roll magnitude when applied with no roll damping. Non-dimensional roll damping coefficients of approximately -1.5, 2-6 times greater than those typical of airplane flight dynamics (approximately -0.45), were required to bring our estimates of reorientation due to aerodynamic torque back into conjunction with the measured changes in orientation. Our estimates of inertial reorientation were statistically significant predictors of the measured reorientation within wingbeats (r(2) from 0.2 to 0.37, P<0.0005). Components of both our inertial reorientation and aerodynamic torque estimates correlated, significantly, with asymmetries in the activation profile of four flight muscles: the pectoralis, supracoracoideus, biceps brachii and extensor metacarpi radialis (r(2) from 0.27 to 0.45, P<0.005). Thus, avian flight maneuvers rely on production of asymmetries throughout the flight apparatus rather than in a specific set of control or turning muscles.
鸟类可重构的扑翼使其能够通过惯性和空气动力学两种方式进行重新定向。我们发现，这两种方式在玫瑰凤头鹦鹉（Eolophus roseicapillus）的低速转弯飞行中都起着重要作用。我们利用在飞行走廊中六只玫瑰凤头鹦鹉进行90度转弯时记录的三维运动学数据，根据翅膀的转动惯量和扑动弧度估算值以及叶素空气动力学模型，对惯性和空气动力学重新定向进行了预测。叶素模型成功预测了机动飞行的凤头鹦鹉的重量支撑（预测值为观测值的88±17%，N = 6）和向心力（预测值为观测值的79±29%，N = 6），并对机械功率进行了合理估算。该模型估算的扭矩是侧倾加速度的显著预测因子（r² = 0.55，P < 0.00001），但在无侧倾阻尼的情况下应用时，大大高估了侧倾幅度。需要约-1.5的无量纲侧倾阻尼系数，比飞机飞行动力学中的典型值（约-0.45）大2至6倍，才能使我们根据空气动力学扭矩得出的重新定向估算值与测量的方向变化相符。我们对惯性重新定向的估算在统计学上是翅膀拍动周期内测量的重新定向的显著预测因子（r²从0.2到0.37，P < 0.0005）。我们对惯性重新定向和空气动力学扭矩的估算值的组成部分都与四块飞行肌肉（胸肌、上喙肌、肱二头肌和桡侧腕伸肌）激活曲线的不对称性显著相关（r²从0.27到0.45，P < 0.005）。因此，鸟类的飞行机动依赖于整个飞行器官产生的不对称性，而非特定的一组控制或转弯肌肉。
