HedenstrOM A, Sunada S
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
J Exp Biol. 1999 Jan;202(1):67-76. doi: 10.1242/jeb.202.1.67.
During the moult, birds sequentially replace their flight feathers and thus temporarily have gaps in their wings. These gaps will vary in size and position(s) during the course of the moult. We investigated the aerodynamic effects of having moult gaps in a rectangular wing by using a vortex-lattice (panel) approach, and we modelled the effect of moult gap size at the wing moult initiation position, of gap position in the primary tract and of two simultaneous gaps (as occurs during secondary feather moulting in many birds). Both gap size and gap position had a detrimental effect on aerodynamic performance as measured by lift curve slope, effective aspect ratio and the aerodynamic efficiency of the wing. The effect was largest when the moult gap was well inside the wing, because the circulation declines close to the wing tip. In fact, when the gap was at the wing tip, the performance was slightly increased because the lift distribution then became closer to the optimal elliptical distribution. The detrimental effect of moult gaps increased with increasing aspect ratio, which could help to explain why large birds have relatively slow rates of moult associated with small gaps.
在换羽期间，鸟类会依次更换飞羽，因此翅膀会暂时出现缺口。在换羽过程中，这些缺口的大小和位置会有所不同。我们采用涡格（面板）方法研究了矩形翅膀上存在换羽缺口时的空气动力学效应，并模拟了换羽起始位置的缺口大小、初级飞羽区域的缺口位置以及两个同时出现的缺口（许多鸟类次级羽毛换羽时会出现这种情况）的影响。通过升力曲线斜率、有效展弦比和机翼空气动力学效率衡量，缺口大小和缺口位置对空气动力学性能都有不利影响。当换羽缺口位于机翼内部较深处时，这种影响最大，因为靠近翼尖处的环量会下降。事实上，当缺口位于翼尖时，性能会略有提高，因为此时升力分布更接近最优椭圆分布。换羽缺口的不利影响随着展弦比的增加而增大，这有助于解释为什么大型鸟类换羽速度相对较慢且缺口较小。
