【作者】 王刚；

【导师】 宋笔锋；

【作者基本信息】 西北工业大学 ， 飞行器设计， 2016， 博士

【摘要】 固定翼飞机的纵向静稳定性、纵向配平与飞行性能对飞机的设计要求是相矛盾的,无尾飞机由于缺少平尾,使该矛盾对其影响尤为显著。因此,无尾飞机设计需要在纵向稳定性、平衡和性能之间做更多的协调和折衷。相比于常规布局,设计性能较好的无尾飞机难度更大。在飞机概念设计阶段,其外形参数以及实际的飞行状态往往存在着一定的随机不确定性。特别地,针对无尾布局,某些不确定性因素对飞机的飞行性能和稳定性影响较为敏感。如果在无尾飞机总体设计时不考虑这些不确定性因素,就极有可能无法达到飞机的设计要求。针对以上两个问题,本文提出了一种利用螺旋桨动力配平纵向力矩(propeller thrust trimming,PTT)的飞机布局方案,力图通过螺旋桨动力产生抬头力矩,来提高无尾飞机的最大升力系数和升阻特性,以改善无尾飞机的飞行性能。围绕该布局,以一架小型电动无尾无人机为研究对象,开展了PTT布局性能收益及纵向稳定性研究,并进行了PTT小型无尾无人机航时稳健性优化设计工作。本文主要完成了以下几方面工作:(1)提出了PTT布局方案,并对PTT小型无尾无人机进行了总体方案初步设计。首先,从改善无尾飞机性能的角度,阐述了PTT布局的方案原理。其次,研究了PTT小型无尾无人机的总体布局。然后,进行了无人机初始外形参数设计,从稳定性、纵向配平以及性能方面,定性地分析了机翼、翼梢小翼以及舵面几何参数的选择。(2)为评估PTT小型无尾无人机的气动性能收益,对采用常规升降副翼配平和采用PTT的两种小型无尾无人机进行了风洞实验。测试结果显示:在满足纵向配平条件下,倘若PTT布局的翼身轴线偏移量设计合理,那么相比于常规升降副翼配平的无尾无人机,PTT布局的最大升阻比可以提升15%左右,最大升力系数可以提升16%左右。此外,风洞实验数据还对本文的无人机气动力计算方法进行了验证。(3)为评估无人机续航性能,建立了PTT小型电动无人机总体设计计算模型。针对PTT布局以及电动无人机存在的特殊性,重点研究了以下四个方面:其一,计入推力线偏移、重心偏移以及螺旋桨矢量推力等影响,建立了PTT布局的纵向稳定性与纵向配平计算模型;其二,建立了存在来流攻角的螺旋桨以及无刷电机模型,为电动无人机设计出了高效的推进系统;其三,建立了恒功率放电条件下锂离子电池放电时间计算模型,并基于该模型推导出了电动无人机航时公式;其四,根据飞机外形尺寸,通过叠加全机各部件重量来评估无人机结构重量,进而建立了电动无人机重量计算模型。(4)基于前文建立的总体设计计算模型,对PTT小型电动无尾无人机进行了总体参数优化,研究PTT带来的无人机续航性能收益。优化结果表明:在满足指定任务目标要求下,PTT无尾无人机具有更轻的重量和更高的升阻比,相比于采用正弯度翼型和反弯度翼型的常规升降副翼配平无尾无人机,PTT布局的航时分别提升了24.2%和40.4%。通过对一架2.5kg级别的样机进行多次飞行测试,证明了本文提出的PTT改善无尾飞机飞行性能这种方案的可行性,以及建立的小型电动无人机总体设计计算模型的有效性。(5)以优化得到的PTT小型电动无尾无人机为基准,探究了总体参数对PTT无尾无人机纵向静稳定性、纵向配平以及纵向动稳定性的影响。分析结果显示:重心下移对纵向静稳定性影响非常显著,它增加了PTT无尾飞机的纵向静稳定性,并使纵向静安定裕度随升力系数呈非线性变化。重心下移量越大,纵向静稳定性越好,但同时会增加配平力矩,降低无人机性能。另一方面,引入的螺旋桨推力线偏移和矢量推力则对纵向静稳定性影响较小,但它们增加了长周期的振荡周期,减小了长周期的阻尼,并且分别决定着PTT无尾无人机的零升俯仰力矩大小和纵向配平能力。(6)开展了PTT小型电动无尾无人机航时稳健性优化设计。通过Sobol’全局灵敏度分析,筛选出了对PTT小型电动无尾无人机航时和约束影响较大的13个几何设计变量和飞行状态参数,并将其划分为5类不确定性问题。然后基于代理模型,利用多目标遗传算法对这5类不确定性问题进行了稳健性优化。与确定性优化结果相比,经过稳健性优化得到的无人机总体参数,在损失较小航时均值的条件下,可以显著降低无人机几何设计变量和飞行状态参数变化对航时的影响,大幅度提升无人机设计过程中满足约束的概率。最后基于稳健性优化设计结果,总结出了PTT小型电动无尾无人机航时和约束稳健性设计准则。更多还原

【Abstract】 For the fixed-wing aircraft,flight performance is traded for longitudinal static stability and trim.Without an empennage,this is especially true for a tailless configuration.As a result,in the tailless aircraft design process,more trade-offs are needed among longitudinal stability,balance and performance.In comparison with a conventional aircraft,a well-designed tailless aircraft is difficult.In the conceptual design,there are many aleatory uncertainties encountered in both aircraft shape and its flight condition.Especially for a tailless configuration,some uncertain factors are sensitive to flight performance and stability.If these uncertainties are not considered in the conceptual design process,the design requirements of aircraft could not probably be satisfied.To deal with these two problems,a new tailless configuration using propeller thrust trimming(PTT)is proposed in this thesis.It is expected that propeller thrust can help to provide a nose-up pitching moment and improve the flight performance of tailless aircrafts.Focusing on this configuration,a small electric-powered tailless unmanned aerial vehicle(UAV)is taken as a case study.The performance benefits and longitudinal stability are studied for the PTT configuration.In addition,the endurance robust optimization is implemented for a small tailless UAV using PTT.The main research issues and achevements in this dissertation are as follows:(1)The PTT configuration is proposed,and the preliminary design is studied for the small tailless UAV using PTT.Firstly,the principle of PTT that improves the flight performance of tailless aircrafts is illustrated.Then,the aerodynamic configuration of the small tailless UAV using PTT is investigated,and the parameter selections of the wing,winglet and control surface are qualitatively analyzed on the base of stability,trim and aerodynamic performance.(2)To evaluate the aerodynamic benefits of the small tailless UAV using PTT,an experimental study is conducted using the wind tunnel.For comparison,two tailless configurations,namely the conventional configuration trimmed by the elevon and the PTT configuration trimmed by propeller thrust are tested.The wind tunnel data indicate that with the help of PTT,the lift to drag ratio and maximum lift coefficient are increased by 15% and 16% in case a moderate pylon height is achieved.Moreover,the aerodynamic computational method for the small UAV is also verified by the wind tunnel test.(3)To evaluate the endurance performance,the conceptual design model of a small electric-powered UAV using PTT is established.Considering the particularity of the PTT configuration and electric-powered UAV,the following four aspects are focused.Firstly,taking into account the effects of the thrust line offset,center of gravity(CG)offset and propeller thrust vectoring,the mathematical models of longitudinal stability and trim are developed for the PTT configuration.Secondly,in accordance with the models of the brushless motor and propeller at angles of attack relative to the propeller axis,the electric propulsion system is designed with a high efficiency.Thirdly,the mathematical model of battery discharge time is established assuming a constant power consumption.The endurance formula of the electric-powered UAV is deduced based on this model.Fourthly,according to the aircraft dimension,the structural weight is estimated by the sum of all components,and then the weight model of the electric-powered UAV is builded.(4)To determine the endurance benefits of PTT configuration,the conceptual parameters of a small electric-powered tailless UAV using PTT are optimized based on the conceptual design model.Two other conventional tailless configurations which are trimmed by the elevon are designed for comparison.One employs a cambered airfoil and the other employs a reflexed airfoil.The optimization results suggest that using propeller thrust to trim the pitching moment,the tailless aircraft is lighter weight and achieves higher lift to drag ratio under the condition that satisfies the design specifications.The PTT tailless configuration results in 24.2% and 40.4% endurance increase compared with the two other conventional tailless UAVs.Flight tests of a 2.5kg built aircraft demonstrate the aerodynamic feasibility of the PTT configuration as well as the validity of the conceptual design model for small electric powered UAVs.(5)According to the optimal geometry of the small tailless electric-powered UAV,the effects of conceptual parameters on the longitudinal static stability,longitudinal trim and longitudinal dynamic stability are explored for the PTT configuration.The analysis results show that the CG offset has significant influences on longitudinal static stability.When the CG location is lowered below the aircraft neutral point,the longitudinal static margin of PTT configuration is increased and varies nonlinearly with respect to the lift coefficient.While increasing the CG offset results in an increased longitudinal static margin,it increases a nose-down pitching moment with the associated performance penalty.The thrust line offset and propeller thrust vectoring have negligible impacts on longitudinal static stability.However,these two factors increase the period of phugoid mode and decrease the damping of phugoid mode.Meanwhile,they also determine the zero-lift pitching moment and longitudinal trim of PTT configuration,respectively.(6)The endurance robust optimization is presented for the small electric-powered tailless UAV using PTT.Through Sobol’ global sensitivity analysis,13 geometric design variables and flight condition parameters that have notable effects on endurance and constraints are selected.These parameters are divided into 5 uncertain problems for the small electric powered tailless UAV using PTT.Based on the surrogate models,the robust design optimization theory is applied to solving 5 uncertain problems through multi-objective genetic algorithm.After an optimization considering the uncertainties,the UAV endurance is insensitive to the variations of geometric design variables and flight condition parameters.The constraints in the UAV design process are also satisfied with much higher probabilities.Finally,according to the robust optimization results,the design principle of endurance and constraints robustness is summarized for the small electric-powered tailless UAV using PTT.更多还原