矩形截面型材拉弯成形

针对铝合金矩形中空截面挤压型材进行了不同预拉和补拉的拉弯成形试验研究,获取了预拉和补拉对成形精度的影响规律.截面畸变是影响成形精度最主要的因素,由弯曲过程中的径向压力引起.试验表明,型材靠模弯曲即发生截面畸变,主要表现为上腹板的塌陷,沿型材长度方向截面畸变量不同,最大畸变量并不位于型材中间对称截面处;增大预拉和补拉,截面畸变增大.弯曲卸载回弹是影响零件贴模度的主要因素,其大小受多种因素影响,规律复杂.增大预拉和补拉,回弹减小;当预拉和补拉增大到一定值时,增大拉伸量减小回弹的效果不再明显.     

A Hazard Analysis-based Approach to Improve the Landing Safety of a BWB Remotely Piloted Vehicle

The BUAA-BWB remotely piloted vehicle (RPV) designed by our research team encountered an unexpected landing safety problem in flight tests. It has obviously affected further research project for blended-wing-body (BWB) aircraft configuration characteristics. Searching for a safety improvement is an urgent requirement in the development work of the RPV. In view of the vehicle characteristics, a new systemic method called system-theoretic process analysis (STPA) has been tentatively applied to the hazardous factor analysis of the RPV flight test. An uncontrolled system behavior "path sagging phenomenon" is identified by implementing a three degrees of freedom simulation based on wind tunnel test data and establishing landing safety system dynamics archetype. To obtain higher safety design effectiveness and considering safety design precedence, a longitudinal "belly-flap" control surface is innovatively introduced and designed to eliminate hazards in landing. Finally, flight tests show that the unsafe factor has been correctly identified and the landing safety has been efficiently improved.     

动力增升对翼身融合飞机沉降特性的改善

翼身融合体飞机起降阶段的“沉降问题”是影响该类布局飞行安全的典型问题，为此提出了一种将动力风扇竖直嵌入机翼中的动力增升方案。分析了动力增升系统对飞行的气动影响，提出了动力增升系统的匹配设计和评价方法，探讨了动力增升系统布局的主要约束。在综合考虑动力增升系统推质比、俯仰力矩配平以及操稳特性等限制因素基础上，基于示例翼身融合体无人机，匹配设计了动力增升系统及其布局方案，针对过渡飞行状态设计了姿态稳定控制律。飞行试验表明:使用动力增升能缓解进近阶段升降舵操纵所引起的下沉率突增与高度沉降现象，同时可将验证机的起、降速度降低20%以上，且该方案易于在小型翼身融合体飞机上实现。