Use of Fiber Optics in Digital Automatic Flight Control Systems

Recently, the Plant Input Mapping (PIM) method was proposed as a digital-redesign (or an emulation) approach in digital control system design. This method guarantees stability of a redesigned digital control system for a wide range of sampling periods. In this paper the PIM method is applied to the design of a digital model-matching flight control system. In the model-matching control system design a plant must have no unstable zeros. However, unstable zeros appear for small sampling periods in a step invariance model of a continuous-time (CT) plant with the relative degree greater than two, even if the CT plant has no unstable zeros. Hence, in such a case, the direct-digital approach cannot be applied to the design of a digital model-matching control system. By contrast, the digital-redesign approach such as the Tustin's method or the PIM method is free from the problem. Simulation results for an unstable VTOL aircraft show that the proposed method gives better performance than the conventional design methods.

It is demonstrated that reconfigurable digital multiple model-following flight control systems incorporating fast-sampling error-actuated digital PID (proportional plus integral plus derivative) controllers can be easily designed using directly measurable input/output data. Thus, for example, it is shown in the case of the F-16 aircraft that desired flying qualities with respect to both pitch-rate and angle-of-attack response characteristics can be simultaneously achieved in the absence of sensor failures. In addition, in the case of failure of the angle-of-attack sensor, it is shown that desired flying qualities with respect to pitch-rate response characteristics and satisfactory flying qualities with respect to angle-of-attack response characteristics can still be achieved by reconfiguring the digital controller. >

The DC-DC converters at the Advanced Photo Source at Argonne National Laboratory are over 15 years old. An upgrade to digital control system is being evaluated to resolve the aging and obsolescence issues. These converters supply power to electromagnets that are used to guide high energy beams. Thus a highly accurate control system is required for the DC-DC converters. This paper describes the design and evaluation of a digital control system to regulate the output current. The digital control system is proposed to replace the current analog control system thereby resolving the aging and obsolescence issues. A digital controller is first designed based on the small signal model of the converter. Experimental data of the output current is analyzed. The complete control system is then simulated and results are evaluated.

Purpose – The presented paper aims to describe the general idea, simulations and prototyping process of an assisting flight control system (FCS) for light sport aircraft (LSA). The proposed FCS framework is intended to simplify piloting, reduce pilot workload, and improve system's reliability and handling qualities of manual flying. Design/methodology/approach – Assisting flight control strategy integrates mechanical and digital FCS into a synergic platform, combining the high reliability of mechanical controls with the computation and actuation power introduced through a single line digital FCS. Concepts drawn from classical control theory along with flight envelope protection algorithms have been used throughout the design of the flight control laws. A prototype of the assisting FCS has been subjected to validation trials during series of hardware-in-the-loop simulations. Findings – Despite controversies between the pilots' perception of a modern aircraft and limitations imposed by the legacy airworthiness codes, it has been shown that a pilot assisting and workload reducing control system can be successfully implemented on board of a LSA while satisfying the expectations on a state-of-the-art equipment meeting required level of safety defined by the current legislation. Research limitations/implications – A transition between specific flight modes as well as nonlinearities in the FCS may lead to unfavorable and unpredictable forms of aircraft-pilot interactions. The number of accessible flight control modes should be therefore limited to the most significant ones. Practical implications – Sport aircraft are mostly flown by a single pilot, who could benefit from the pilot assisting FCS as the system has the potential to supervise the aircraft's safe operation in various flight conditions. Originality/value – Introducing an assisting FCS on board of a LSA through an innovative approach which utilizes hidden and unused resources of modern digital automatic FCSs while respecting the limitations imposed through the weight and cost sensitive nature of the LSA market.

Over the past forty years, the number of fighter aircraft controlled flight into terrain (CFIT) accidents per flight hour has not improved despite the addition of multiple manual warning systems. The Air Force Research Laboratory (AFRL) has undertaken a program to develop an automatic system that will take over when the pilot can no longer recover the aircraft, perform an automatic recovery and quickly return control to the pilot. It is called the Automatic Ground Collision Avoidance System or Auto GCAS. This system has been successfully demonstrated on a Block 50 F-16 with a digital flight control system as shown in Figure 1 and is transitioning to operational Block 40/50 F-16s. Until now the technology could not be applied to early model F-16s with analog flight control systems because of the lack of a high authority autopilot needed for the automatic recovery and the absence of a way for the flight control system to ascertain system integrity to insure safe operation. AFRL is now focused on finding a technical solution that will allow the implementation of Auto GCAS on aircraft with analog flight control systems. The effort is called Analog Auto GCAS. The Analog Auto GCAS project has developed an innovative method of adding redundant digital processor modules to the existing analog flight control computers of pre-block 40 F-16's. This will not only allow Auto GCAS to be added to F-16s with analog flight control computer but demonstrates a technical path forward for incorporating Auto GCAS onto other older aircraft with analog flight control computers. This paper provides a description of Auto GCAS, discusses the changes needed to implement Auto GCAS on an analog aircraft, and covers the results to date as well as the future path forward for implementing Auto GCAS on the pre-block 40 F-16 fleet.

A digital flight control system (DFCS) for a highly maneuverable fighter aircraft is described and evaluated in this paper. The aircraft and DFCS exhibit uniform handling qualities over the entire velocity-angle of attack-roll rate regime encountered in air combat maneuvering (ACM). This is verified by the use of a nonlinear six-degree-of-freedom aircraft simulation and an ACM pilot model. Comparison of the tracking accuracy of the DFCS-aircraft to that of a conventionally controlled aircraft indicates that the DFCS provides better tracking and reduces the likelihood of control-induced departure.

Beginning with process controls in the mid fifties, digital control systems have seldom met all the claimed advantages and in many cases have been outright failures. Airborne digital computers have just begun to appear in the commercial jet transport market after several years of experimental and military development. The success of these systems in meeting user expectations has not been overwhelming, which leads to the question: Why change from known analog flight control technology to digital? This paper examines that question by reviewing the state of the art in analog flight control system technology and evaluating this against current airline problems. A realistic means of evaluating claimed advantages for new technology is thus established. The advertised solutions of digital technology to analog problems are examined and, in some cases, debunked. However, consideration of the real problems and the capabilities of digital systems leads to the conclusion that there is a real payoff. Evidence from background studies at Boeing is offered to support this conclusion. A description of the digital flight control system electronics (FCSE) development program for the new Boeing 7×7 airplane is also provided. This program is currently in progress, and its specific objective is to assure that the real payoff is achieved for the subsequent production system.

This paper discusses implications of digital flight control system design for rotorcraft and illustrates the analysis of the resulting handling qualities obtained with the Advanced Digital Optical Control System demonstrator in the context of the proposed new handling-qualities specification for rotorcraft. Topics covered are digital flight control design and analysis methods, flight testing techniques, handling-qualities evaluation results, and correlation of flight test results with analytical models and the proposed handling-qualities specification. The evaluation of the demonstrator system indicates desirable response characteristics based on equivalent damping and frequency, but undersirably large effective time delays (exceeding 240 ms in all axes). Piloted handling qualities are found to be desirable or adequate for all low, medium, and high pilot gain tasks, but handling qualities are inadequate for ultrahigh gain tasks such as slope and running landings. Correlation of these results with the proposed handling-qualities specification indicates good agreement for the bandwidth boundaries, but suggests the need for more stringent limits on allowable phase delay. Analytical models based on emulation (s-plane) techniques compare favorably with flight-extracted frequency-domain characteristics of the overall (end-to-end) system responses.

In this paper a longitudinal output feedback tracker is developed for an aircraft and is shown to produce excellent performance for three different flight conditions without change of the control law matrices. The aircraft utilizes flight propulsion control coupling to provide greater control and responsiveness to command inputs. The singular perturbation method is applied to obtain an output-feedback digital multivariable control. Each flight condition has three command modes: positive pitch pointing, vertical translation, and straight climb. Decoupling of the outputs is demonstrated. A sensitivity study is performed to validate the robustness of the design and to illustrate design parameter influences on system response. The paper contains a summary of the control law design method. Since the CB matrix of the aircraft model does not have full rank, the use of a modified output feedback is used to obtain the required tracking performance.

The insertion of communication networks in closed-loop of digital control systems makes the system synthesis and analysis complex. In this paper, we consider the combination of classical reliability, risk and safety evaluation with typical control system through digital networked control systems. The main purpose is to study the influence of transmission delays and packet dropouts on the reliability of digital networked control systems by using a modified statistical method-Monte Carlo simulation. The behaviors of two types of fault are modelled by different statistical distribution. The control strategies we apply for digital control systems are Proportion Integration Differentiation control strategies, generated by Genetic Algorithm. In terms of a realistic system model, we evaluate and compare the influences on the reliability of digital networked control systems with different control strategies from quantitative aspect. Numerical examples are presented to illustrate the effectiveness and correctness of the approach.

PurposeThe purpose of this paper is to describe the general idea, design, and implementation of control system for general aviation aircraft which reduces pilot workload.Design/methodology/approachProposed indirect flight control system framework is intended to simplify piloting, reduce pilot workload, and allow low‐end general aviation aircraft to operate under deteriorated meteorological conditions. Classical control theory is used for the design of the flight control laws. Although not inherently robust, controllers with classical control logic are made sufficiently stable using a correct and updated controller structure.FindingsDespite controversies between perception of a modern manned aerial vehicle and limitations imposed by legacy airworthiness codes it is shown that a pilot workload reducing system can be successfully implemented onboard of a low‐end general aviation aircraft.Research limitations/implicationsHi‐level control laws and optimization of handling qualities can lead to unfavourable and unpredictable forms of man‐machine interactions, e.g. pilot‐induced oscillations.Practical implicationsGeneral aviation aircraft are mostly flown by a single pilot, who could benefit from an intelligent system or “virtual copilot” assisting in or supervising the aircraft's safe operation under any conditions. Aircraft with this capability represents a next step in the evolution that might ultimately lead to trajectory‐based free‐flight concept of aircraft operations.Originality/valueThe paper introduces a safety enhanced digital flight control system on board small general aviation aircraft.

Aiming at the problem of MIG welding and considering the existing analog control wire feed system has the disadvantages of low response speed, low control accuracy and poor stability. This thesis designs a set of digital control wire feed system based on LPC2132 microprocessor and introduces the control principle of wire feed motor, CAN bus interface circuit and PID control algorithm. Under the condition of power grid voltage fluctuation and load change, we do a lot of experiments. The results show that: the wire feed change rate of designed system is very small, which not only meets the requirements of JB/T-1998.MIG/MAG arc welding standard, but also greatly improves the accuracy and stability of control system.

Rotorcraft flight control systems present design challenges which often exceed those associated with fixed-wing aircraft. First, large variations in the response characteristics of rotorcraft result from the wide range of airspeeds of typical operation (hover to over 100 kts). Second, the assumption of vehicle rigidity often employed in the design of fixed-wing flight control systems is rarely justified in rotorcraft where rotor degrees of freedom can have a significant impact on the system performance and stability. Proposed herein is a methodology for the design of robust rotorcraft flight control systems utilizing Quantitative Feedback Theory (QFI'), a technique which accounts for variability in the dynamic response of the controlled element in the design of robust control systems. It was developed to address a Multiple-Input-Single-Output (MISO) design problem, but was extended to the address the Multiple-Input-Multiple-Output (MIMO) flight control system (FCS) design problem of a UH-60 Black Hawk Helicopter. Inherent conservatism in this design technique leads to limitations in its utility. A modified QFI' approach proved a viable method for designing robust MIMO flight control systems. An analysis of the two flight control system design methodologies is presented.

From the early 1970s conventional digital and analogue electronic systems have gradually been superseded by microprocessor-based designs. Subsequent experience shows that their reliability rarely exceeded that of earlier designs, due mainly to software errors. The root cause was the lack of design formality and rigour in producing software. Yet in spite of this the micro has been tremendously successful in real-time systems. Clearly, the effects of software problems have been overstated. However, the one area which couldn’t tolerate such error rates is that of safety-critical software. Consequently work was put in hand to investigate this, especially in the aerospace field. One early study was that started in 1976 by Elliott Brothers, London, ‘the study of the design, development, analysis and testing of high integrity software for digital flight control systems’. This concluded that the most promising way forward was based on the semi-formal methods described in chapter 4. These proved to be very effective; yet error rates can still be unacceptably high. Better techniques are needed.

This paper presents a now method of optimal digital PID feedback control for a linear multivariate system by using a, parameter optimization technique. The most difficult points for the design of optimal digital PID feedback control system by the modern control theory are : (1) the control structure of it is specified in advance, (2) unless all the state variables are fed back, the optimal control cannot be obtained by dynamic programming or the maximum principle. However, the optimal digital PID feedback gains are determined by using the parameter optimization technique in this paper. When there are some states which are not fed back in the control system, the optimal feedback gains depend on the initial states. First, the optimal solution is presented in the case where all the initial Btates are known. Next, it is extended to the case where the initial states are random variables and their statistical properties are known,