Path-Following Control for Thrust-Vectored Hypersonic Aircraft

Launcher guidance and control (G&C) design is a very demanding process, most notably because mission requirements are known to compete against each other and strong couplings between different disciplines exist. These effects become even more impactful when it comes to reusable launch vehicles, many of which are currently under development. The main task of the G&C system is to generate and follow a trajectory to fulfil mission objectives. This is achieved using various actuator types, which typically include the main engine(s), thrust vector control (TVC), aerodynamic control surfaces and cold-gas thrusters of a reaction control system‎(RCS). The motion of these actuators introduces excitations of flexible modes and perturbations through the launchers’ structure which cannot be easily modelled since the mechanical properties are highly time-varying due to the propellant being burnt to generate thrust. External perturbations from aerodynamics or wind reinforce these effects. Furthermore, actuators and other subsystems are subject to faults and failures having multiple potential origins. All of these perturbations must be handled by the G&C system. In the current industrial approach, these multi-physics effects are tackled by separate teams using their own tools while G&C design is usually based on low-fidelity models that simplify the interactions between disciplines. The adoption of multi-physics acausal modelling approaches such as MODELICA and MATLAB Simscape is believed to enable a more efficient and accurate modelling of the multi-disciplinary interactions. This motivates the development of a dedicated multi-physics simulator for multi-actuated vertical take-off vertical landing (VTVL) vehicles based on MathWorks’ Simulink/Simscape. Setting up simulators is a crucial and time-consuming activity in GNC design. The openly distributable Rapid Reusable Launcher Simulation via Multi-physics Modeling (R2M2) tool is a multi-physics simulator framework that aims at reducing this modeling effort and enabling users to quickly and easily set up simulations of VTVL vehicles by only defining the required model parameters. This helps users to save time and resources and enables them to focus their research and development efforts on the GNC system. On the other hand, R2M2 provides the simulation environment to rapidly evaluate GNC approaches. In addition to simplifying the setup process, the R2M2 tool is also highly adaptable and able to simulate a wide range of VTVL mission scenarios, including different vehicle and actuator configurations and environmental conditions. Automated Monte Carlo routines are also provided to facilitate the investigation of the effects of wind disturbances and uncertain parameters. The tool is capable of modeling external influences such as gravitational and aerodynamic effects, as well as internal dynamics from time-varying and moving masses. Modeling of variable-mass dynamics is an essential component for launch vehicle simulations. Mass properties of launch vehicles are changing mainly due to the propulsion causing the ejection of combustion products through the engines’ nozzles. The varying mass influences not only the vehicle’s properties such as the center of mass and moments of inertia but also generates additional forces and moments for instance due to Coriolis effects [R1] [R2]. In addition, the tool can consider common actuator failure cases including the jamming of TVC actuators and aerodynamic control surfaces and degraded engine performance. Future implementations may extend the tool to being capable to consider sloshing effects and structural flexibility. This paper describes the design of the R2M2 tool and provides an overview of its functionalities and applications. The implementation within MathWorks’ physical simulation environments Simscape and Simscape Multibody is shown for all relevant subsystems and physical effects. Challenges and drawbacks using Simscape for flight mechanics modeling are addressed. These main challenges arise from limited Simscape functionalities and its closed-source nature when the interaction of variable mass dynamics and physical effects specific to aerospace applications, such as aerodynamic forces and moments, have to be modeled. Possible solutions and work-arounds, as implemented in the tool, are shown. A benchmark scenario of a two staged launch vehicle ascent is implemented to verify the desired functionality of the R2M2 tool. To enable trajectory tracking the benchmark vehicle is configured with an engine cluster of five throtteable main engines, thrust vector control (TVC), aerodynamic control surfaces (fins) and a reaction control system‎(RCS). A preliminary controller and control allocation design is shown which enables stable flight on the vehicle’s ascent trajectory. The benchmark implementation offers the potential for synthesis and assessment of more sophisticated RLV guidance and control algorithms to improve the overall system performance and robustness. [R1] F. O. Eke; Dynamics of Variable Mass Systems. Technical Report CR-1998-208246, National Aeronautics and Space Administration (NASA); 1999 [R2] B. Gäßler, L.E. Briese, P. Acquatella, P. Simplício, S. Bennani, M. Casasco; Variable-Mass Dynamics Implementation in Multi-Physics Environment for Reusable Launcher Simulations; 9th EUROPEAN CONFERENCE FOR AERONAUTICS AND AEROSPACE SCIENCES (EUCASS), 2022, Lille

Results are presented from a study of time-optimal attitude reorientation maneuvering for an aircraft with thrust-vectoring capability. A detailed mathematical model for attitude motions of the aircraft is developed. First-order necessary conditions for optimality are applied and a family of extremal solutions obtained for two classes of reorientation maneuvers of practical interest. The thrust-vectoring power is varied parametrically, and thus an estimate of the reduction in maneuvering time due to the thrust-vectoring enhancement of the aircraft is obtained. ARIOUS analyses have shown that emerging trends in missile and radar technologies will have a profound effect on design requirements for air-superiority vehicles. It appears that, in close-in combat, vehicles with the ability to operate at extreme angles of attack will have a decided advantage.1'4 Designing such supermaneuverable aircraft is a complex and challenging task, and future design efforts may well lead to radically new concepts. At present, however, the preferred approach is to provide a form of thrust vectoring in which propulsive power is used to generate control moments.5'6 At high angles of attack a, especially in the post-stall region, the effectiveness of the aerodynamic control surfaces decreases rapidly with increase in a.. Thus, thrust-vectoring generated (propulsive) moments must be used to maintain control of the aircraft at high a. At low a the propulsive moments can supplement the aerodynamic control surfaces and thus increase the agility of the aircraft. In addition, thrust vectoring can be used for control of the aircraft in case of mechanical failure or malfunction of the aerodynamic control surfaces. Several research programs that focus on utilizing thrust-vectoring control are currently under way. Among these is the F/A-18 based High Angle-of-attack Research Vehicle (HARV) program.7 The flight mechanics issues can be divided into two areas: 1) analysis of changes in the velocity vector and 2) analysis of changes in the body attitude. This paper presents some results obtained in a study that focused on understanding the nature of aircraft minimum-time fuselage-reorientation maneuvering. In the study, data for the HARV were used. Accordingly, the numerical results correspond to this aircraft. However, the discussion and methodology in analyzing the results presented in the next sections are quite general. A mathematical model of the aircraft and the interacting environment (the aerodynamic forces and moments) is derived in Sec. II. The basic ideas and assumptions in the development of the mathematical model are discussed in detail. In Sec. Ill a class of optimal control problems of interest is formulated and a set of necessary conditions for optimality derived by using the Minimum Principle.8'10 This set of necessary conditions is cast into a numerical multipoint boundary-value problem (MPBVP). Subsequently, a homotopy method and the related procedure for solving the MPBVPs (and thus generat

The Thrust vector control (TVC) is a method for controlling the angular velocity and attitude of aerial vehicles (AV) by manipulating the thrust direction of propulsion. This technology enhances maneuverability and allows for dynamic aerobatics at low speeds and near-zero airspeeds without stalling at high angles of attack (AOA). As the aerodynamic control surfaces are ineffective for vehicles operating outside the atmosphere, TVC is a suitable technique for these applications. To design a control system for AVs utilizing TVC, an accurate mathematical model is essential to simulate flight parameters and optimize the control gains. This work presents a complete six degrees-of-freedom (6-DOF) high-fidelity simulation model of a thrust vector control aerial vehicle (TVC-AV). The nonlinear model is developed by dividing the mathematical representation into five submodules, including the geometrical model, the actuation model that was experimentally identified, and an aerodynamic model that was validated through semi-empirical techniques, computational fluid dynamics (CFD), and wind-tunnel experiments; in addition, the propulsion model’s characteristics are identified through experimentation, and the atmospheric model is based on International Standard Atmosphere (ISA) values. The integrated model was implemented in MATLAB[Formula: see text] (Simulink) that provides a foundation for designing effective flight controllers and guidance systems.

For modern supersonic vehicles, thrust vector control is a conspicuous prerequisite to accomplish high performance aerospace applications. Thrust vector control chiefly falls into a few classifications, for example, mechanical thrust vector control and shock vector control. Shock vector control is outstanding amongst other approaches to achieve this thrust vector control. A bypass mass injection is used to generate shock vectoring in a planar supersonic Convergent-Divergent (CD) propulsion nozzle in this study and a 10×10 square mm bypass channel was used for the injection. This bypass mass injection is kept perpendicular at the diverging section of the studied nozzle. Overexpanded nozzle flow is achieved by carrying out the investigation at Nozzle Pressure Ratio (NPR) of 3.0. The flow conditions and size of the square injection channel ensures the bypass mass flow ratio around 5%. Reynolds-Averaged-Navier-Stokes (RANS) equations with k-ω SST turbulence model have been applied through numerical computations to capture the three-dimensional steady characteristics of the flow field. Results show that the shock structure becomes asymmetric due to the bypass mass injection along with the formation of recirculation zone near the bypass mass injection. Moreover, a considerable thrust vectoring can be achieved due to the asymmetric velocity distribution at the exit plane.For modern supersonic vehicles, thrust vector control is a conspicuous prerequisite to accomplish high performance aerospace applications. Thrust vector control chiefly falls into a few classifications, for example, mechanical thrust vector control and shock vector control. Shock vector control is outstanding amongst other approaches to achieve this thrust vector control. A bypass mass injection is used to generate shock vectoring in a planar supersonic Convergent-Divergent (CD) propulsion nozzle in this study and a 10×10 square mm bypass channel was used for the injection. This bypass mass injection is kept perpendicular at the diverging section of the studied nozzle. Overexpanded nozzle flow is achieved by carrying out the investigation at Nozzle Pressure Ratio (NPR) of 3.0. The flow conditions and size of the square injection channel ensures the bypass mass flow ratio around 5%. Reynolds-Averaged-Navier-Stokes (RANS) equations with k-ω SST turbulence model have been applied through numerical computatio...

Thrust vector control (TVC) methods were developed as an alternative to aerodynamic control surfaces for missiles, which suffered from poor pitch-over characteristics in launching stage. TVC system, can allow the missile to turn quickly and stably in any direction by deflecting the nozzle exhaust gas irrespective of the missile speed. A jet vane is one of such devices, used for thrust vectoring. In conventional approaches, jet vane is connected control surface through a mechanical interface such as wire and link. However, these approaches lead to angular position dependent transmission ratio. In addition, these techniques limit designer to obtain the required hybrid control ratio. In this study, a novel compact electromechanical actuator is proposed to overcome these problems. Constant or variable transmission ratio can be obtained using such actuator. Proposed solution is not only a simple and compact structure, but also being able to provide sufficient control torque for a missile's quick turn.

Thrust Vectoring Applied to Catastrophic Failure Prevention in Jet Transports

The task of achieving a safe and short landing for a flying-wing unmanned aircraft with a three-bearing-swivel thrust vector is highly challenging. The process is further complicated due to the need to switch between multiple control modes, while also ensuring the protection of the flight boundaries from environmental disturbances and model uncertainties to ensure flight safety. To address this challenge, this paper proposes a short-landing strategy that employs mixed control using lift fans, thrust vectors, and aerodynamic control surfaces. The extended state observer (ESO) is integrated into the inner angular rate control and outer sink rate control to account for environmental disturbances and model uncertainties. To ensure flight safety, the attainable linear and angular acceleration is calculated through a trim analysis to determine the command value of velocity and angle of attack during a short landing. Additionally, a flight boundary protection method is employed which includes an additional command value of the angle of attack, resulting in a higher probability of a successful landing. This paper provides a detailed description of the short-landing strategy, including the control objectives for each phase. Finally, a Monte Carlo simulation is conducted to evaluate the effectiveness and robustness of the short-landing strategy, and the landing accuracy is assessed using the circular error probability metric.

ABSTRACTIn general, an airship is equipped with hybrid-heterogeneous actuators: the aerodynamic surfaces, the vectored propellers and the buoyant ballonets. The aerodynamic surfaces have high efficiency in attitude control at high speed. However, vectored propellers are also introduced here for attitude control under the special working condition of low airspeed. Due to the lower thrust-to-weight ratio, the composite control of hybrid-heterogeneous actuators is the primary object in controller design for an airship. In composite attitude control, first the attitude moment allocation between aerodynamic control surfaces and vectored propellers is designed according to different dynamic airspeed, to achieve the smooth motion transition from low to high airspeed, then the weighted generalised inverse (WGI) is used to design the reconfigurable actuator allocation among the homogeneous multi-actuators, where the authority of every actuator can be decided by setting the corresponding value of the weight matrix, thus the control law is unchanged under different actuator configurations. Taking the mid-altitude airship as an example, the simulations of position control, trace tracking and altitude control are provided. Simulation results demonstrate that the attitude moments allocation obtains moment distribution between the aerodynamic surfaces and the vectored propellers under different airspeeds; the reconfigurable actuator allocation achieves a good distribution and reconfiguration among homogeneous actuators, thereby enhancing the reliability of the control system.

Thrust vector control technology is widely used in modern advanced aircrafts, space shuttles and unmanned aerial vehicles, etc. An accurate thrust vector mathematical model is of great significance to enhance the thrust vector control effect. In this paper, the P200 micro-turbine engine with an axisymmetric thrust vector nozzle placed at the rear is taken as an example, A hybrid thrust vectoring dynamics modeling method consisting of engine speed model, engine thrust model, actuator dynamics model, airflow angle model and thrust loss coefficients is proposed. The engine speed model is of Linear Parameter Varying (LPV) model with each segment is characterized by a First Oder Plus Dead Time (FOPDT) model. The engine thrust model is characterized as a cubic polynomial function of engine speed. The actuator’s dynamic model is a FOPDT model. The nozzle airflow deflection angle is proportional to the airflow deflection angle. the thrust loss coefficient is approximated by a cosine relationship with the airflow deflection angle. The experimental results show that the established model can well characterize the dynamics of the thrust vector system.

In this research, the effects of some liquid side injection from nozzle wall into exhaust gas of combustion chamber are studied. The side injection against main flow is as elliptical solid thing that change the symmetric of flow field on nozzle wall and causes some different pressure distribution on wall, and finally causes thrust vector deviation. Flows interaction causes some physical phenomena as bow shock wave in front of injection region. This paper explain the effects of this wave and variation velocity & pressure distribution at different cross sections of flow field and comparison results of air and other liquid fluid in thrust vector control system. The results are compared with experimental data and have well agreement with them. The results show that Freon is one of best injection liquid for this type of thrust vector control. Performance of Injection is optimum in relative position 35 to 40% nozzle divergence length.

A potential concept that can offer an alternate method for thrust vector control of the Space Shuttle Solid Rocket Booster is the use of a cylindrical probe that is inserted (on demand) through the wall of the rocket nozzle. This Probe Thrust Vector Control (PTVC) concept is an alternate to that of a gimbaled nozzle or a Liquid Injection Thrust Vector (LITVC) system. The viability of the PTVC concept can be assessed either experimentally and/or with the use of CFD. A purely experimental assessment can be time consuming and expensive, whereas a CFD assessment can be very time- and cost-effective. Two key requirements of the proposed concept are PTVC vectoring performance and the active cooling requirements for the probe to maintain its thermal and structural integrity. An active thermal cooling method is the injection of coolant around the pheriphery of the probe. How much coolant is required and how this coolant distributes itself in the flow field is of major concern. The objective of the work reported here is the use of CFD to answer these question and in the design of test hardware to substantiate the results of the CFD predictions.

Regarding the enhanced technical capabilities of today’s tactical aircraft, high-agility maneuvering always draws attention. Agility should ensure enhanced controllability and maneuverability of the aircraft which generally necessitates redirection of the thrust by means of thrust vectoring control. The enhancement of airframe agility also entails assurance of on-board safety and improvements of mission effectiveness. Hence, automated maneuvering assistance can be proposed to assist the cockpit crew in achieving highly-agile maneuvers under emergency or combat circumstances. This study focuses on automated maneuvering controller design for a tactical aircraft equipped with thrust vectoring controls. It specifically concentrates on automated controllability and maneuverability demonstration by design of body pointing and velocity vector pointing maneuver controllers. The modeling and the design of the controllers are presented in detail and their performance and implementation alternatives are demonstrated with synthetic simulations. An automatic tailchase acquisition maneuver is implemented using the designed nose pointing controller. Also, with the proposed velocity vector pointing controller, an automatic velocity vector roll maneuver is implemented.

Attitude stability during the reentry phase of hypersonic flight vehicle (HFV) relies heavily on aerodynamic control surfaces. Any failure in these components can severely compromise mission safety. However, the acquisition of fault data is prohibitively expensive, and the types of faults are diverse. Existing methods show suboptimal diagnostic performance under these conditions. This article proposes a contrastive learning-based approach for diagnosing faults in aerodynamic control surfaces. The diagnosis task is defined as a multi-class classification problem using multivariate state time series. To this end, a dilated attention temporal network (DAT-Net) is developed within the contrastive orthogonal-center framework (COC-Framework), forming the COC-DAT-Net. The proposed network combines dilated convolutions with attention mechanisms for feature extraction. It employs an orthogonal-center contrastive learning strategy to optimize the structure of the feature space. In addition, a dynamic sampling mechanism is introduced to improve the quality of sample pair construction. Simulation experiments demonstrate that the proposed method performs well in fault diagnosis of aerodynamic control surfaces. It achieves an average F1-Score of 94.04% and a silhouette score of 81.43%. These results confirm the effectiveness of COC-DAT-Net in multi-class and small-sample scenarios. The method provides methodological support for enhancing the safety of HFV reentry.

Two controllers are developed to provide attitude control of a spinning rocket that has a thrust vectoring capability. The first controller has a single-input/single-output design that ignores the gyroscopic coupling between the control channels. The second controller has a multi-input/multi-output structure that is specifically intended to account for the gyroscopic coupling effects. A performance comparison between the two approached is conducted for a range of roll rates. Each controller is tested for the ability to track step commands, and for the amount of coupling impurity. Both controllers are developed via a linear-quadratic-regulator synthesis procedure, which is motivated by the multi-input/multi-output nature of second controller. Time responses and a singular value analysis are used to evaluate controller performance. This paper describes the development and comparison of two controllers that are designed to provide attitude control of a spinning rocket that is equipped with thrust vector control. 12 refs., 13 figs., 2 tabs.

Future space missions may use Nuclear Thermal Rocket (NTR) stages for human and cargo missions to Mars and other destinations. The vehicles are likely to require engine thrust vector control (TVC) to maintain desired flight trajectories. This paper explores requirements and concepts for TVC systems for representative NTR missions. Requirements for TVC systems were derived using 6 degree-of-freedom models of NTR vehicles. Various flight scenarios were evaluated to determine vehicle attitude control needs and to determine the applicability of TVC. Outputs from the models yielded key characteristics including engine gimbal angles, gimbal rates and gimbal actuator power. Additional factors such as engine thrust variability and engine thrust alignment errors were examined for impacts to gimbal requirements. Various technologies are surveyed for TVC systems for the NTR applications. A key factor in technology selection is the unique radiation environment present in NTR stages. Other considerations including mission duration and thermal environments influence the selection of optimal TVC technologies. Candidate technologies are compared to see which technologies, or combinations of technologies best fit the requirements for selected NTR missions. Representative TVC systems are proposed and key properties such as mass and power requirements are defined. The outputs from this effort can be used to refine NTR system sizing models, providing higher fidelity definition for TVC systems for future studies.