Multiaxis Thrust Vectoring Research Articles

F-16/MATV; Optimal Position Controller Design using Robust and Discrete Linear Quadrature Gaussian [RLQG] Controller

This paper presents the robust controller design for nonlinear F-16/MATV (Multi–Axis – Thrust - Vectoring) position control system. The linearization of nonlinear flight position system is guaranteed by feedback linearization using Taylor series expansion and the optimal LQG controllers are designed to achieve the steady state flight condition. The comparison of the using continuous and discrete LQG is fully discussed for control system. First the continuous optimal LQG controller is designed for continuous time state space represented flight dynamic system based on separation principle. But the designed optimal LQG controller requires a very large controller gain to achieve the design objective, which lacks high sensitivity and leads to highly cost system. This leads to design a controller using discrete LQG controller for discrete time state space represented flight control system. After implementing this controller into the system in MATLAB Simulink environment, using singular value decomposition technique, it is founded that the performance and robustness of the design objective is satisfied.

Nonlinear Flight Control Design Using Constrained Adaptive Backstepping

The design of an adaptive backstepping flight control law for the F-16/MATV (multi-axis thrust vectoring) aircraft is discussed. The control law tracks reference trajectories with the angle of attack a, the stability-axes roll rate p s , and the total velocity V T . Furthermore, the sideslip angle β has to be kept at zero. B-spline neural networks are used inside the parameter update laws of the backstepping control law to approximate the uncertain aerodynamic forces and moments. Command filters are used to implement the constraints on the control surfaces and the virtual control states. The stability of the parameter estimation process during periods of saturation is guaranteed by using a modified tracking error definition, in which the effect of the saturation has been filtered out. The controller and its performance are evaluated on a nonlinear, six-degrees-of-freedom dynamic model of an F-16/MATV aircraft in a number of simulation scenarios.

Demonstration of Fluidic Throat Skewing for Thrust Vectoring in Structurally Fixed Nozzles

The experimental demonstration of a fluidic, multiaxis thrust vectoring (MATV) scheme is presented for a structurally fixed, afterburning nozzle referred to as the conformal fluidic nozzle (CFN). This concept for jet flow control features symmetric injection around the nozzle throat to provide throttling for jet area control, and asymmetric injection to subsonically skew the sonic plane for jet vectoring. The conceptual development of the CFN was presented in a companion paper (Miller et al. [1]). In that study, critical design variables were shown to be the flap length and expansion area ratio of the nozzle, and the location, angle, and distribution of injected flow. Measures of merit were vectoring capability, gross thrust coefficient, and discharge coefficient. A demonstration of MATV was conducted on a 20 percent scale CFN test article across a range of nozzle pressure ratios (NPR), injector flow rates, and flow distributions. Both yaw and pitch vector angles of greater than 8 deg were obtained at NPR of 5.5. Yaw vector angles greater than 10 deg were achieved at lower NPR. Values of thrust coefficient for the CFN generally exceeded published measurements of shock-based vectoring methods. In terms of vectoring effectiveness (ratio of vector angle to percent injected flow), fluidic throat skewing was found to be comparable to shock-based vectoring methods.

The X-31 aircraft: Advances in aircraft agility and performance

The X-31 enhanced fighter maneuverability (EFM) demonstrator has pioneered agile flight in the post-stall flight regime and explored integrated multi-axis thrust vectoring across a broad flight envelope. Its maneuvering achievements include sustained flight up to 70 degrees angle of attack, velocity vector rolls in deep post-stall conditions, and post-stall turns from high entry to exit speeds with ultra low turning/transitional conditions. The concept of post-stall maneuverability was extensively studied in simulations preceding initiation of the X-31 program. These simulations provided a baseline for tactical utility demonstrations and vehicle design requirements. Post-stall maneuverability was not achieved without encountering and mitigating the effects of highly unsteady, asymmetric, vortex-dominated flow-fields associated with post-stall flight. Anomalies in vehicle response to control inputs were observed at high angles of attack, as were differences between simulator and actual flight parameters due to a misrepresentation of the effects of these complex flowfields. Some preliminary force and moment data for the X-31 configuration during dynamic maneuvers are provided to highlight the complex nature of the flowfield. The X-31 aircraft's enabling capabilities, including multi-axis thrust vectoring and integrated flight/propulsion control also provided performance enhancements across the entire flight envelope. In what were known as ‘quasi-tailless’ experiments, conventional aerodynamic control surfaces were used to reduce or eliminate the stabilizing influence of the vertical stabilizer, while the vehicle's multi-axis thrust vectoring capability was used for restabilization. Properly exploited, these technologies can lead to the reduction or elimination of traditional aerodynamic control surfaces, which provides profound improvements in vehicle range, weight, payload, and low observability. This review focuses on some of the principal aerodynamic issues encountered during the course of the X-31 program, the resulting lessons learned, and the derived results concerning the complex aerodynamic effects associated with exploiting this aircraft's unique capabilities. Suggested research and technology development issues which came to light during the X-31 program are also discussed.

High-alpha vectoring characteristics of the F-18/HARV

An investigation was conducted in the Langley 16-Foot Transonic Tunnel (16FTT) to determine the multiaxis thrust vectoring characteristics of the F-18 high-alpha research vehicle (HARV). A 0.10-scale model of the F-18 airplane was modified with hardware to simulate the three-vane thrust vectoring system of the F-18/HARV. This investigation was conducted at Mach numbers ranging from 0.30 to 0.70, angles of attack from 0 to 70 deg, and nozzle pressure ratios from 2.0 to approximately 5.0. Results indicate that the thrust vectoring system of the F-18/HARV can generate useful levels of multiaxis thrust vectoring. During vectoring, resultant thrust vector angles were always less than the corresponding geometric vane deflection angle and were accompanied by large thrust losses. Significant external flow effects that were dependent on Mach number and angle of attack were noted during vectoring.

Maximizing thrust-vectoring control power and agility metrics

A new set of standard agility comparison maneuvers (SACOM) is proposed for testing the maximization of thrust-vectoring control power during post stall, manned, and unmanned flight tests. An innovative approach is presented to help define and simulate agility in a low cost manner by means of unmanned scaled models. Debated agility metrics are reassessed in light of new developments in multiaxis thrust vectoring. A methodology for measuring and maximizing TV-agility under PST conditions has been identified. Excellent controllability and very rapid nose pointing are easily obtainable during PST-TV maneuvers. TV-agility is an interdisciplinary subject involving a revolution in engineering and pilot education.