螺旋桨飞机俯仰力矩特性改进方法

螺旋桨滑流对飞机各部件的气动干扰造成飞机的俯仰力矩特性恶化，危害飞行安全。开展螺旋桨滑流对螺旋桨飞机俯仰力矩特性的影响机理研究和螺旋桨滑流作用下螺旋桨飞机俯仰力矩特性改进方法研究十分重要。采用动态重叠多块结构网格，通过求解非定常雷诺平均可压缩Navier-Stokes方程，数值模拟了某螺旋桨飞机不同拉力系数下降落构型的绕流流场。结果显示螺旋桨滑流对机翼、平尾的气动干扰是导致飞机俯仰力矩特性恶化的主要原因，改进螺旋桨飞机俯仰力矩特性的关键是改进其平尾的升力特性。以拉力系数等于0.4时的降落构型为优化对象，开展了俯仰力矩特性的改进方法研究，包括降低平尾高度、改变平尾上反角、抬高螺旋桨轴线等方法。研究发现在不增大机翼对平尾整体下洗强度的前提下，减小平尾和螺旋桨轴线的垂向距离，可以明显地改善螺旋桨飞机的俯仰力矩特性。

Methods for improving pitching moment characteristics of a propeller airplane

The aerodynamic disturbance caused by propeller slipstream on various parts of a propeller airplane results in the deterioration of pitching moment characteristics of a propeller airplane, and endangers flight safety. It is very important to study the influence mechanism of propeller slipstream on pitching moment characteristics and methods for improving pitching moment characteristics with propeller slipsteam for a propeller airplane. Numerical simulation of the flow field around a propeller airplane with different pull coefficients is carried out by using multi-block structured grids which are dynamically overlapped. The governing equation is unsteady Reynolds average compressible Navier-Stokes equations. The results show that the aerodynamic interference of propeller slipstream on wings and flat tails is the main reason of the deterioration of pitching moment characteristics of a propeller airplane. The key to improve pitching moment characteristics of a propeller airplane is to improve lift characteristics of its flat tails. Using the falling configuration when its thrust coefficient is 0.4 as the optimization object, methods for improving pitching moment characteristics of a propeller airplane are studied, in terms of lowering the height of flat tails, changing the dihedral angle of flat tails, and raising the axis of propellers. It is found that pitching moment characteristics of a propeller airplane can be significantly improved by reducing the vertical distance between the flat tails and the axis of propellers without increasing the overall downwash strength of the wings.