Stability analysis of digital linear flight controllers subject to electromagnetic disturbances

High intensity electromagnetic radiation has been demonstrated to be a source of computer upsets in commercially available digital flight control systems. Such upsets can degrade the quality of the control signal ranging from a perturbation error over a few sample periods to a permanent error mode or computer failure. Under these conditions, the primary concern of the control engineer is to insure that the closed-loop system remains stable. A stochastic disturbance model and a set of associated stability assessment tools are introduced for determining stability robustness of a nominal closed-loop system subject to electromagnetic disturbances. The focus is primarily on night control applications, but the methodology is suitable for any application where highly reliable digital control is needed. The technique is demonstrated on a simple test example and on a stabilizing controller for the longitudinal dynamics of the AFTI/F-16 aircraft.     

Optimal Aircraft Go?Around and Flare Maneuvers

This paper analyzes in detail two of the critical aircraft maneuvers associated with approach and landing: the go-around maneuver and the flare maneuver. Optimal solutions that include state and control variable constraints are obtained for both problems. Two algorithms are given for computation of the minimum and maximum altitude loss associated with the pilot-controlled go-around maneuver. A matrix operator is obtained that can be used for in-flight computation of the altitude loss on a small general-purpose digital computer. The flare optimization presented is for a cost functional that includes both the longitudinal touchdown dispersion and the normal acceleration. A closed-loop mechanization is given that approximates the optimal trajectory. A second matrix operator which can be used for prediction of the longitudinal touchdown point is obtained. Uncertainties are also obtained for the purpose of establishing a prediction confidence level. It is proposed that these prediction techniques should be incorporated into a decision making performance monitor. This monitor could provide the pilot with a continuous assessment of the approach and could generate a preflare decision on whether or not to commit the aircraft to the flare maneuver.     

Evaluation on novel architecture for harmonizing manual and automatic flight controls under atmospheric turbulence

Pilot uncertainty in aircraft response under automatic flight control has triggered aircraft accidents/incidents in the past. This uncertainty compels a pilot to disengage autopilot and switch to manual control. However, the decision to disengage autopilot and when to do it can be difficult: especially if there is not enough time to monitor the cockpit displays, for instance while countering atmospheric turbulence. Against this background, we proposed the “human as a control module” architecture for harmonizing pilot and autopilot controls. The architecture blends pilot maneuver with autopilot control instead of switching between them when simultaneous inputs are given to the aircraft. By automatically adjusting pilot and autopilot control inputs, the architecture avoids overlaps of both control authorities and helps to circumvent the effect of conflicting actions. This paper applies the architecture to the situations of past aircraft incidents which had been caused by the transfer from autopilot control to pilot maneuver after encountering atmospheric turbulence. The effectiveness of the architecture is evaluated via simulation study for the specific incident examples. Furthermore, this paper extends the architecture with an Extended Kalman Filter (EKF) based observer and evaluates its robustness under errors in wind estimation.     

过失速机动飞机的鲁棒非线性控制律设计

 采用非线性动态逆和结构奇异值综合方法设计了过失速飞行条件下飞控系统控制律,解决了飞控设计中面临的非线性和鲁棒性问题。应用非线性动态逆的目的就是对过失速机动飞行条件下高度非线性的飞机动力学进行线化;从而围绕线性的快逆回路应用结构奇异值综合方法设计相应的鲁棒控制器,以提供对驾驶员指令的鲁棒跟踪。所设计的飞控系统将达到期望的飞行品质,确保系统对过失速机动飞行过程中因非定常气动力效应引起的系统参数摄动鲁棒性良好。高逼真度、非线性的仿真验证了这一点。     

机动增强及阵风减缓飞行控制系统设计

本文以CCV—YF—16飞机为背景,阐述了机动增强/阵风减缓这一直接力控制模态的构成及设计思想;以数字仿真进行功能验证与评价;提出以C飞行品质指标为目标函数的参数优化设计法,从而有效地解决该模态的参数设计问题。     

Augmented flight dynamics model for pilot workload evaluation in tilt-rotor aircraft optimal landing procedure after one engine failure

An augmented flight dynamics model is developed to extend the existing flight dynamics model of tilt-rotor aircraft for optimal landing procedure analysis in the event of one engine failure.Compared with the existing flight dynamics model, the augmented model involves with more pilot control information in cockpit and is validated against the flight test data. Based on the augmented flight dynamics model, the optimal landing procedure of XV-15 tilt-rotor aircraft after one engine failure is formulated into a Nonlinear Optimal Control Problem(NOCP), solved by collocation and numerical optimization method. The time histories of pilot controls in cockpit during the optimal landing procedure are obtained for the evaluation of pilot workload. An evaluation method which can synthetically quantify the pilot workload in time and frequency domains is proposed with metrics of aggressiveness and cutoff frequencies of pilot controls. The scale of the pilot workload is compared with those of the shipboard landing procedures, bob-up/bob-down and dash/quickstop maneuvers of UH-60 helicopter. The results show that the aggressiveness of pilot collective and longitudinal controls for the tilt-rotor aircraft optimal landing procedure after one engine failure are higher than those for UH-60 helicopter shipboard landing procedures up to the condition of sea state 4, while the pilot cutoff frequency of collective control is lower than that of the bob-up/bob-down maneuver but the pilot cutoff frequency of longitudinal control is higher than that of the dash/quick-stop maneuver. The evaluated pilot workload level is between Cooper–Harper HQR Level 2 and Level 3.     

有侧风时某验证机着陆品质分析

以刚体系动力学理论为基础,建立飞机、起落架六自由度全量非线性方程,根据有侧风时着陆过程中驾驶员的操纵特点,提出比较符合实际情况的操纵逻辑,以及用3个单轴操纵的驾驶员模型,通过采用分时采集、分时处理飞行状态信息和分时操纵的方式,将它们有机地综合成~个同时做三轴操纵时的驾驶员模型。最后,对所建立的人-机闭环系统模型编制了相应的仿真软件,并对某验证机进行了着陆品质分析,其结果与试飞情况比较吻合。     

基于深度确定性策略梯度算法的战机规避中距空空导弹研究

飞机规避中距空空导弹的逃逸机动策略对于提高战斗机的生存力至关重要。针对深度确定性策略梯度算法训练智能体学习飞机规避导弹的逃逸机动策略进行研究。以飞机导弹相对态势参数等作为智能体的输入状态,飞机控制指令作为智能体的输出动作,导弹飞机追逃模型作为智能体的学习环境,设计由相对态势和飞行参数构成的成型奖励以及由交战结果组成的稀疏奖励,实现从状态参数到控制量端到端的逃逸机动策略。通过与四种基于专家先验知识的典型逃逸机动攻击区仿真验证对比,结果表明：智能体实现的逃逸策略攻击区仅次于置尾下降攻击区,该策略对飞机规避导弹先验知识的依存度最低。     

计算机辅助的低空风切变改出优化控制

介绍了动态系统的计算机辅助直接优化方法的原理及其在低空风切变改出飞行中的应用，利用较真实的风切变工程化模型，选择适当的控制函数模型，性能准则及其约束条件，通过计算机直接地，系统地和迭代地探寻最优条件，对飞机改出低空风切变控制进行了优化，获得了最佳改出性能飞行参数曲线，并与没有优化的改出引导策略结果作了比较，结果表明，通过优化，飞机改出低空风切变的性能获得了明显的改善。     

飞机亚跨声速飞行操纵特性分析

针对中等展弦比、中等后掠角机翼布局的超声速飞机在亚跨声速飞行时遇到的操纵特性异常现象,通过估算飞机在海拔5 km高空的气动特性,获得了飞机的纵向平衡性能和静操纵性的变化规律.通过数值计算,得到了飞机在低空跨声速飞行时的操纵特性;分析了造成飞机在某些飞行速度下操纵跟随性较差、大速度飞行时俯仰操纵过于灵敏、不同速度下杆力变化大等现象的原因.针对亚跨声速区的飞行与操纵特点,给出了飞行操纵建议,以提高飞行安全.     

发动机喘振裕度自适应控制

本文研究飞行 /推进系统一体化控制中的发动机喘振裕度自适应控制。通过一定的控制作用 ,使发动机在所有飞行条件和工况下都保持一定的喘振裕度 ,从而充分发挥发动机的潜力。将发动机大偏差模型、进气道及飞机模型综合在一起 ,构成飞机 /推进系统一体化数学模型 ,以进行发动机自适应控制的仿真。计算机仿真表明 ,发动机自适应控制具有很好的性能效益 ,例如在飞行高度 H=10公里 ,飞机由 Ma=0 .65加速到 Ma=0 .90 ,在采用自适应喘振裕度控制后 ,双发动机推力提高 16 ,飞机加速时间缩短 2 3 ,大大提高了飞机性能。     

E-CATS: First time demonstration of embedded training in a combat aircraft

Air Forces are facing difficulties in training pilots effectively for their missions. Due to a reduction of defense budgets, fewer resources can be made available for training. In addition, airspace available for training is limited, especially in Europe, and this is aggravated by the increase in the range of advanced weapon systems. Moreover, only few Surface-to-Air Missile (SAM) sites are available for suitable training.Embedded Training (ET) is considered to be a potential solution for these problems. ET for fighter aircraft is a capability installed in an operational fighter to train the pilot while operating the aircraft in a situation it was designed for, but which is not available in everyday life. Thereto, the ET capability generates simulated threats and feeds them into the various avionics systems of the aircraft. This allows pilots to train against a virtual force, or a virtually augmented real force. Benefits of employing ET include cost reduction (fewer real aircraft are needed to act as enemy), use of smaller training airspace (simulated threats may move outside this space), and the potential to train anywhere, at any time.NLR, Dutch Space, and the Royal Netherlands Air Force (RNLAF) have jointly developed an ET system to demonstrate the feasibility of current technology for implementing an ET capability in fighter aircraft. The system, installed in an RNLAF F-16B, supports training for ground-to-air and (one-versus-two) air-to-air engagements. It consists of two units; one unit executes the ET simulations and provides most of the required interfaces with aircraft systems, while the other unit is dedicated to interfacing with the radar processing chain.The system was evaluated by demonstrating it to a group of pilots and engineers and collecting their expert opinions. It was concluded that embedded training has considerable value for a variety of training objectives related to Beyond Visual Range tactics, and it is expected that embedded training will play an important role in the future mission training of fighter-aircraft pilots.     

F/A-18E/F全自动着舰飞行特性分析

以F/A-18E/F舰载机为对象,针对航迹精确控制和安全性要求,分析了舰载机全自动着舰飞行特性。首先,基于自动着舰控制系统,建立了全自动着舰飞行控制系统的动力学模型;然后,对下滑轨迹纠偏与控制能力、控制器指令响应特性、变换下滑道机动特性进行了仿真分析。仿真结果表明,在全自动着舰安全边界范围内,舰载机能在较短时间内将航迹控制在理想下滑线附近;控制器具有良好的高度变化率、俯仰角、俯仰角速度等状态指令响应特性及控制面指令响应特性;F/A-18E/F变换下滑道机动则需要配合油门完成,说明仅通过平尾控制实现该机动并非安全着舰的必要条件。     

刚弹耦合飞行器的机动载荷减缓

针对飞行器刚体/弹性模态耦合作用下的机动载荷减缓问题,运用亚音速非定常空气动力学理论以及分析力学原理,建立了柔性飞机机动载荷分析及控制的气动弹性模型,分析了飞机作纵向机动飞行时结构弹性对机动飞行参数的影响。数值分析结果表明,结构弹性模态对飞机机动过程的影响不容忽视。为了有效减缓机动载荷,运用最优控制理论,采用多组控制面联合偏转的作动方案,设计机动载荷减缓最优控制律,实现了对飞机纵向机动载荷的控制。研究结果表明,提出的机动载荷减缓控制方案是有效的。     

Implementation of tactical maneuvers with maneuver libraries

This study creates and combines the general maneuver libraries for fixed-wing aircraft to implement tactical maneuvers. First, the generalized maneuver libraries are established by analyzing the characteristics of tactical maneuvers required in battlefields. The 7th order polynomial is applied to both the creation of the maneuver libraries and the generation of the trajectories or flight paths for modal inputs. To track the desired trajectory, we design the Attitude Command Attitude Hold (ACAH) system and the Rate Command Rate Hold (RCRH) system using Model Following Controller (MFC). Moreover, the Line-of-Sight (LOS) guidance law is designed. In particular, the CONDUIT® is employed to optimize the gains so that the control systems meet the aircraft Handling Qualities (HQ) criteria. Finally, flight simulations are performed for the longitudinal loop, immelmann-turn, and climb-slalom-descent maneuvers to verify that tactical aggressive maneuvers are realizable via the combination of maneuver libraries. This study can contribute to the development of flight techniques for aircraft tactical maneuvers and to the revision of air force operational manuals.     

Some vortical-flow flight experiments on slender aircraft that impacted the advancement of aeronautics

This paper highlights the three aerodynamic pillars of aeronautics; namely, theory/CFD, wind-tunnel experiments and flight tests, and notes that at any given time these three are not necessarily at the same level of maturity. After an initial history of these three pillars, the focus narrows to a brief history of some vortical-flow flight experiments on slender aircraft that have impacted the advancement of aeronautics in recent decades. They include the F-106, Concorde, SR-71, light-weight fighters (F-16, F/A-18), and F-16XL. These aircraft share in common the utilization of vortical flow and have flown at transonic speeds during a part of the flight envelope. Due to the vast amount of information from flight and CFD that has recently become available for the F-16XL, this aircraft is highlighted and its results detailed. Lastly, it is interesting to note that, though complicated, vortical flows over the F-16XL aircraft at subsonic speeds can be reliably and generally well-predicted with the current CFD flow solvers. However, these solvers still have some problems in matching flight pressure data at transonic speeds. That this problem has been highlighted is both an advancement in aeronautics and a tempting prize to those who would seek its solution.     

Aircraft flight control system design under state and controlbounds

Sophisticated control configurations are needed to meet the mission and pilotage requirements for advanced aircraft. The required vehicle performance during low altitude, low speed and high angle of attack flight, all-weather, day and night operations must be achieved, and new control technologies should be developed. This work presents a systematic control design philosophy for flight control systems when the state variables and control inputs are bounded by the prespecified constraints. The design procedure uses the dynamic programming concept. The fundamental idea involves minimization of nonquadratic functionals. A new representation of constraints is proposed using the smooth functions. The advantages of the synthesis approach are presented. To illustrate the design methodology the longitudinal control configuration for the F-18 fighter is synthesized     

对歼八某型飞机机体改型的探讨

探讨歼八某型机体改型的可能性,使歼八某型机体由二代战机平台提升至三代战机平台.主要的改进有:飞行过载由7 g提升至8 g或更大,以提高飞行机动性能;作战半径由×××km提升至××××km以上;机翼下表面导弹挂点增加到8个.由于机体结构修改范同不大,因而,继承原歼八某型飞机已有可用成果,可以做到省力、省钱、省时,使歼八某型飞机在短时间内挤入第三代战机的行列.     

MMAE-based control redistribution applied to the VISTA F-16

A novel control technique, termed control redistribution, is presented and applied in conjunction with multiple model adaptive estimation (MMAE) to the variable in-night stability test aircraft (VISTA) F-16, to detect and compensate for sensor and/or actuator failures. This ad hoc method redistributes control commands (that would normally be sent to failed actuators) to the nonfailed actuators, accomplishing the same control action on the aircraft. Dither is considered to help disambiguate failures in the longitudinal and lateral-directional channels. Detection of both single-actuator and single-sensor failures is considered. Failures are demonstrated detectable in less than 1 s, with an aircraft output nearly identical to that anticipated from a fully functional aircraft in the same environment