Small unmanned aerial vehicles (UAVs) are becoming increasingly popular as low-cost observation and research platforms. However, these aircraft operate low in the atmosphere, exposed to the turbulent wakes of man-made and natural roughness features. As such, it is important to estimate their unsteady aerodynamic performance. The leading-edge suction parameter (LESP) is one criterion used in vortex methods for predicting flow separation, which can arise in both steady and unsteady flows. The critical LESP represents the maximum suction supported in the leading-edge region, equivalent to the flat-plate behavior of thin airfoil theory. This parameter was investigated at low pitch rates for a NACA0012 airfoil at Reynolds numbers applicable to small UAVs, to examine the hypothesis of a constant critical value existing for an arbitrary motion. It is seen that the critical LESP shows a strong dependence on pitch rate, with a piecewise linear fit being obtained. A higher pitch rate induces a greater pressure-field lag, promoting a higher peak LESP for flow separation, and a lower value for reattachment. These peaks in the LESP agree well with the instances of separation and reattachment. Raising the Reynolds number also acts to raise the critical LESP for a given reduced pitch rate.

小型无人机 (UAV) 作为低成本观测和研究平台正变得越来越受欢迎。然而，这些飞机在低空运行，暴露在人造和自然粗糙度特征的湍流尾流中。因此，重要的是估计它们的不稳定空气动力学性能。前缘吸力参数 (LESP) 是涡流方法中用于预测流动分离的一种标准，它可能出现在稳态和非稳态流动中。临界 LESP 表示前缘区域支持的最大吸力，相当于薄翼型理论的平板行为。在适用于小型无人机的雷诺数下，NACA0012 翼型在低俯仰率下研究了该参数，以检查任意运动存在恒定临界值的假设。可以看出，临界 LESP 表现出对俯仰率的强烈依赖，获得了分段线性拟合。更高的俯仰率会导致更大的压力场滞后，促进更高的流动分离峰值 LESP 和更低的重新附着值。LESP 中的这些峰与分离和重新附着的情况非常吻合。对于给定的降低的俯仰率，提高雷诺数还可以提高临界 LESP。