A New State Observer and Flight Control of Highly Maneuverable Aircraft

In this paper, a new nonlinear observer (θ-D observer) is proposed to estimate the feedback states for optimal control of a highly maneuverable aircraft. This observer is derived by constructing the dual of a recently developed nonlinear optimal control technique-known as the θ-D technique. The θ-D optimal control approach provides an approximate closed-form solution to the Hamilton-Jacobi-Bellman (HJB) equation. An optimal flight controller using this technique is designed for a highly maneuverable aircraft operating at high angle of attack where the θ-D observer is employed to estimate the states for feedback. The structure of this observer is similar to the State Dependent Riccati Equation Filter (SDREF). However, the new method provides a closed-form observer gain and does not need time-consuming online computations of the algebraic Riccati equation at each instant as the SDREF. The theoretical results about this new observer are given. The simulation shows that the θ-D control and observer exhibit excellent performance for this flight control problem

Feedback control laws for highly maneuverable aircraft

During this year, we concentrated our efforts on the design of controllers for lateral/directional control using mu synthesis. This proved to be a more difficult task than we anticipated and we are still working on the designs. In the lateral-directional control problem, the inputs are pilot lateral stick and pedal commands and the outputs are roll rate about the velocity vector and side slip angle. The control effectors are ailerons, rudder deflection, and directional thrust vectoring vane deflection which produces a yawing moment about the body axis. Our math model does not contain any provision for thrust vectoring of rolling moment. This has resulted in limitations of performance at high angles of attack. During 1994-95, the following tasks for the lateral-directional controllers were accomplished: (1) Designed both inner and outer loop dynamic inversion controllers. These controllers are implemented using accelerometer outputs rather than an a priori model of the vehicle aerodynamics; (2) Used classical techniques to design controllers for the system linearized by dynamics inversion. These controllers acted to control roll rate and Dutch roll response; (3) Implemented the inner loop dynamic inversion and classical controllers on the six DOF simulation; (4) Developed a lateral-directional control allocation scheme based on minimizing required control effort among the ailerons, rudder, and directional thrust vectoring; and (5) Developed mu outer loop controllers combined with classical inner loop controllers

Lessons learned from the developmental flight testing of the Terrain Awareness Warning System

The Ground Proximity W aming System (GPWS) currently fielded on the F/A-18A/B/C/D/E/F and AV-8B aircraft is a great safety-backup system that alerts the pilot of an impending Controlled Flight Into Terrain (CFIT) condition. However, it does have one major limitation: the reliance on the look-down radar altimeter, which results in little or no CFiT protection in rising terrain. The Terrain Awareness Warning System (TAWS) is the generational evolution of GPWS that provides the predictive, or look-ahead, capability sorely missing \u27rrom the current system. Utilizing aircraft positioning from the Global Positioning System (GPS) and an onboard Digital Terrain Elevation Data (DTED), TA WS computes recovery trajectories and presents a combination of aural and visual warnings when necessary to cue the pilot to avoid a CFiT condition. TA WS, without being solely reliant on the radar altimeter, has the ability to calculate and present appropriate warnings regardless of aircraft position or attitude. Ultimately, TA WS has to walk a fine line between providing timely warnings that allow the pilot to conduct maximum performance maneuvering during all mission roles, without the impedance of nuisance cues. At the heart of TA WS is a generic algorithm that can be tailored to specific aircraft performance and mission characteristics. This thesis examines all aspects of the flight test of TA WS: the history of GPWS and TA WS in aviation, the conundrum of how to plan a flight test of a terrain avoidance system in close proximity to the ground without endangering aircrew or aircraft, the use of simulation, additional safety precautions, results, lessons learned for program managers and test pilots, and future applications

Piloted simulation of one-on-one helicopter air combat at NOE flight levels

A piloted simulation designed to examine the effects of terrain proximity and control system design on helicopter performance during one-on-one air combat maneuvering (ACM) is discussed. The NASA Ames vertical motion simulator (VMS) and the computer generated imagery (CGI) systems were modified to allow two aircraft to be independently piloted on a single CGI data base. Engagements were begun with the blue aircraft already in a tail-chase position behind the red, and also with the two aircraft originating from positions unknown to each other. Maneuvering was very aggressive and safety requirements for minimum altitude, separation, and maximum bank angles typical of flight test were not used. Results indicate that the presence of terrain features adds an order of complexiaty to the task performed over clear air ACM and that mix of attitude and rate command-type stability and control augmentation system (SCAS) design may be desirable. The simulation system design, the flight paths flown, and the tactics used were compared favorably by the evaluation pilots to actual flight test experiments

Compensation of distributed delays in integrated communication and control systems

The concept, analysis, implementation, and verification of a method for compensating delays that are distributed between the sensors, controller, and actuators within a control loop are discussed. With the objective of mitigating the detrimental effects of these network induced delays, a predictor-controller algorithm was formulated and analyzed. Robustness of the delay compensation algorithm was investigated relative to parametric uncertainties in plant modeling. The delay compensator was experimentally verified on an IEEE 802.4 network testbed for velocity control of a DC servomotor

A Comparison of the Strengths and Weaknesses of Small-Format Aerial Photography Platforms

The demand for small-format aerial photography continues to grow in large part due to the rapid adoption of unmanned aerial vehicles (UAVs). Prior to the explosion of UAV use, this kind of photography was collected using older technologies such as tethered kites and blimps. Due to the increased demand for aerial imagery, this article looks at four platforms commonly used to collect small-format aerial imagery: multi-rotor UAVs, fixed-wing UAVs, kites, and blimps. Practical use considerations are explored, including characteristics of flight and operation, atmospheric and site factors, imaging sensors and costs, and regulatory limitations. Each of the four categories of lifting platform have their strengths and limitations, and they often complement one another. UAVs tends to be more maneuverable and able to cover more ground, but they have limited flight times due to battery technology limitations. They also have clearly defined regulatory requirements for use, whereas the tethered platforms have very few legal restrictions on use. In some cases, a tethered platform may be the only legal option for gathering small-format aerial imagery at a location. There is no one perfect option that will fill all needs, but rather multiple solutions that are better suited to some situations than others. The ways in which some of these strengths and limitations may change in the future in regards to technology and regulations is also discussed

Ride quality systems for commuter aircraft

The state-of-the-art in Active Ride Augmentation, specifically in terms of its feasibility for commuter aircraft applications. A literature survey was done, and the principal results are presented here through discussion of different Ride Quality Augmentation System (RQAS) designs and advances in related technologies. Recommended follow-on research areas are discussed, and a preliminary RQAS configuration for detailed design and development is proposed

Design of Flight Control Systems for a Hypersonic Aircraft Using sliding-PID Control

The paper presents the application of sliding-PID control to the design of robust flight control system for a hypersonic aircraft. The proposed controller uses an approach that combines the high-order PID controller with high-order sliding mode (HOSM) control. The PID uses high-order time-derivative (HOTD) function of the sliding mode variable while the HOSM uses the signum function of the HOTD function. HOTD is built using the relative degree nonlinear dynamics of multivariable systems driven by affine control inputs. A displacement autopilot is designed for pitch control of an air-breathing hypersonic vehicle model. Numerical simulation demonstrates the effectiveness of the proposed controller and shows its advantages as compared to the quasi-homogenous HOSM controller