Hedrick Tyson L, Tobalske Bret W, Biewener Andrew A
Concord Field Station, Museum of Comparative Zoology, Harvard University, Old Causeway Road, Bedford, MA 01730, USA.
J Exp Biol. 2002 May;205(Pt 10):1389-409. doi: 10.1242/jeb.205.10.1389.
Birds and bats are known to employ two different gaits in flapping flight, a vortex-ring gait in slow flight and a continuous-vortex gait in fast flight. We studied the use of these gaits over a wide range of speeds (1-17 ms(-1)) and transitions between gaits in cockatiels (Nymphicus hollandicus) and ringed turtle-doves (Streptopelia risoria) trained to fly in a recently built, variable-speed wind tunnel. Gait use was investigated via a combination of three-dimensional kinematics and quasi-steady aerodynamic modeling of bound circulation on the distal and proximal portions of the wing. Estimates of lift from our circulation model were sufficient to support body weight at all but the slowest speeds (1 and 3 ms(-1)). From comparisons of aerodynamic impulse derived from our circulation analysis with the impulse estimated from whole-body acceleration, it appeared that our quasi-steady aerodynamic analysis was most accurate at intermediate speeds (5-11 ms(-1)). Despite differences in wing shape and wing loading, both species shifted from a vortex-ring to a continuous-vortex gait at 7 ms(-1). We found that the shift from a vortex-ring to a continuous-vortex gait (i) was associated with a phase delay in the peak angle of attack of the proximal wing section from downstroke into upstroke and (ii) depended on sufficient forward velocity to provide airflow over the wing during the upstroke similar to that during the downstroke. Our kinematic estimates indicated significant variation in the magnitude of circulation over the course the wingbeat cycle when either species used a continuous-vortex gait. This variation was great enough to suggest that both species shifted to a ladder-wake gait as they approached the maximum flight speed (cockatiels 15 ms(-1), doves 17 ms(-1)) that they would sustain in the wind tunnel. This shift in flight gait appeared to reflect the need to minimize drag and produce forward thrust in order to fly at high speed. The ladder-wake gait was also employed in forward and vertical acceleration at medium and fast flight speeds.
众所周知，鸟类和蝙蝠在扑翼飞行中采用两种不同的步态，慢速飞行时采用涡环步态，快速飞行时采用连续涡旋步态。我们研究了鸡尾鹦鹉（玄凤鹦鹉）和环颈斑鸠在最近建造的可变风速风洞中飞行时，在很宽的速度范围（1-17米/秒）内这些步态的使用情况以及步态之间的转换。通过三维运动学和对机翼远端和近端部分附着环量的准稳态空气动力学建模相结合的方法来研究步态的使用。我们的环量模型估算的升力足以在除最慢速度（1和3米/秒）外的所有速度下支撑体重。通过将我们的环量分析得出的气动冲量与全身加速度估算的冲量进行比较，似乎我们的准稳态空气动力学分析在中等速度（5-11米/秒）时最为准确。尽管机翼形状和翼载荷存在差异，但两种鸟类在7米/秒时都从涡环步态转变为连续涡旋步态。我们发现，从涡环步态到连续涡旋步态的转变：（i）与近端机翼部分从下拍转为上拍时攻角峰值的相位延迟有关；（ii）取决于足够的向前速度，以便在上拍时提供与下拍时类似的机翼气流。我们的运动学估算表明，当任何一种鸟类采用连续涡旋步态时，在整个振翅周期内环量大小存在显著变化。这种变化足够大，表明两种鸟类在接近它们在风洞中能够维持的最大飞行速度（鸡尾鹦鹉15米/秒，斑鸠17米/秒）时都转变为梯形尾流步态。这种飞行步态的转变似乎反映了为了高速飞行而将阻力降至最低并产生向前推力的需求。梯形尾流步态在中速和快速飞行速度下的向前和垂直加速中也会采用。
