无人机新型水动力弹射动力学特性

针对现役无人机气压、液压弹射方式结构复杂、功率受限等问题，提出一种新型无人机水动力弹射方案，利用高压水高速喷射产生的反推力作为弹射动力，实现无人机加速起飞。综合弹射器气室状态方程和水室动量方程、喷管能量方程和动量方程、弹射负载力平衡方程等建立高压水高速喷射与弹射负载运动耦合的非线性弹射动力学模型，数值解析了弹射速度与位移、喷管喷射速度和反推力、弹射器气室压力等变化规律，以及弹射器直径、喷管直径和充气压力对弹射性能的影响。结果表明：随着弹射时间增加，弹射速度与位移分别近似呈对数曲线状、指数曲线状增大，喷管喷射速度和反推力、弹射器气室压力呈抛物线状显著下降；当弹射器直径为200 mm、弹射器长度为2 400 mm、 喷管直径为20 mm、充气压力为31.5 MPa时，能够将150 kg无人机在16.62 m内加速至25.03 m/s；增大弹射器直径对弹射性能影响不利；增大喷管直径对弹射速度影响不大，但会显著缩短弹射时间和距离、增大弹射过载；在弹射过载满足要求前提下适当增大弹射器充气压力，可减小弹射时间和距离并有助于增大弹射速度。

New Hydrodynamic Ejection Dynamic Characteristics of Unmanned Aerial Vehicles

For the complicated structure and limited power of pneumatic ejection of active unmanned aerial vehicles(UAV)，a hydrodynamic ejection scheme is proposed，in which the reverse thrust generated by high-pressure water jets as power is used to take off the VAU quickly.A non-linear ejection dynamics model is established, which couples the air chamber state equation and water chamber momentum equation of ejector，the energy and momentum equations of jet，and the force balance equation of catapult load. The variations of ejection speed and displacement，spurt speed and reverse thrust，ejector air chamber pressure，and the influences of ejector diameter，jet diameter and inflation pressure on catapult performance are numerically analyzed. The results show that, as the catapult time increases，the catapult speed and displacement increase approximately in a logarithmic curve and an exponential curve, respectively，and the ejection speed，the reverse thrust of jet and the air chamber pressure decrease significantly in a parabolic state. When the ejector diameter is 200 mm，the ejector length is 2 400 mm，the jet diameter is 20 mm，and the inflation pressure is 31.5 MPa，the 150 kg UAV can be accelerated to 25.02 m/s in the range of 16.62 m. Increasing ejector diameter adversely affects ejection performance.The increase in jet diameter has little effect on the maximum ejection speed，but it significantly shortens the catapult time and distance，and increases the catapult overload.Under the premise of catapult overloaded，an appropriate increase in inflation pressure can reduce catapult time and distance，and help to increase catapult speed.