Ronald A. Hess

Unified Theory for Aircraft Handling Qualities and Adverse Aircraft-Pilot Coupling

A unie ed theory for aircraft handling qualities and adverse aircraft ‐pilot coupling or pilot-induced oscillations is introduced. The theory is based on a structural model of the human pilot. A methodology is presented for the prediction of 1 ) handling qualities levels, 2 ) pilot-induced oscillation rating levels, and 3 ) a frequency range in which pilot-induced oscillations are likely to occur. Although the dynamics of the force-feel system of the cockpit inceptor is included, the methodology will not account for effects attributable to control sensitivity and is limited to single-axis tasks and, at present, to linear vehicle models. The theory is derived from the feedback topology of the structural model and an examination of e ight test results for 32 aircraft cone gurations simulated by the U.S. Air Force/CALSPAN NT-33A and Total In-Flight Simulator variable stability aircraft. An extension to nonlinear vehicle dynamics such as that encountered with actuator saturation is discussed.

A Model of Driver Steering Control Behavior for Use in Assessing Vehicle Handling Qualities

The resulting model is shown capable of producing driver/vehicle steering responses which compare favorably with those obtained from driver simulation. The model is simple enough to be used by engineers who may not be manual control specialists. The model contains both preview and compensatory steering dynamics. An analytical technique for vehicle handling qualities assessment is briefly discussed. Driver/ vehicle responses from two driving tasks evaluated in a driver simulator are used to evaluate the overall validity of the driver/vehicle model

Generalized technique for inverse simulation applied to aircraft maneuvers

Inverse simulation techniques are computational methods that determine the control inputs to a dynamic system that produce desired system outputs. Such techniques can be powerful tools for the analysis of problems associated with maneuvering flight. An algorithm is developed that serves as an efficient inverse simulation tool for analyzing maneuvering flight. As opposed to current inverse simulation methods, which require numerical time differentiation in their implementation, the generalized technique offered is essentially an integration algorithm. Examples of inverse solutions for a large-amplitude aircraft maneuver and a nap-of-the-Earth helicopter maneuver are presented.

Flight control system design with rate saturating actuators

Actuator rate saturation is an important factor adversely affecting the stability and performance of aircraft flight control systems. It has been identified as a catalyst in pilot-induced oscillations, some of which have been catastrophic. A simple design technique is described that utilizes software rate limiters to improve the performance of control systems operating in the presence of actuator rate saturation. As described, the technique requires control effectors to be ganged such that any effector is driven by only a single compensated error signal. Using an analysis of the steady-state behavior of the system, requirements are placed upon the type of the loop transmissions and compensators in the proposed technique. Application of the technique to the design of a multi-input/multi-output, lateral-directional control system for a simple model of a high-performance fighter is demonstrated as are the stability and performance improvements that can accrue with the technique.

Model for human use of motion cues in vehicular control

A feedback model for human use of motion cues in tracking and regulation tasks is offered. The motion cue model is developed as a simple extension of a structural model of the human pilot, although other equivalent dynamic representations of the pilot could be used in place of the structural model. In the structural model,it is hypothesized that proprioceptive cues and an internal representation of the vehicle dynamics allow the human to create compensation characteristics that are appropriate for the dynamics of the particular vehicle being controlled. It is shown that an additional loop closure involving motion feedback can improve the pilot/vehicle dynamics by decreasing high-frequency phase lags in the effective open-loop system transfer function. Data from a roll-attitude tracking/regulation task conducted on a moving base simulator are used to verify the modeling approach.

Multi-Input/Multi-Output Sliding Mode Control for a Tailless Fighter Aircraft

A frequency-domain procedure for the design of sliding mode controllers for multi-input/multi-output systems is presented. The methodology accommodates the effects of parasitic dynamics, such as those introduced by unmodeled actuators through the introduction of multiple asymptotic observers and model reference hedging. The design procedure includes a frequency-domain approach to specify the sliding manifold, the observer eigenvalues, and the hedge model. The procedure is applied to the development of a flight-control system for a linear model of the Innovative Control Effector fighter aircraft. The stability and performance robustness of the resulting design is demonstrated through the introduction of significant degradation in the control effector actuators and variation in vehicle dynamics.

Robust flight control design with handling qualities constraints using scheduled linear dynamic inversion and loop-shaping

A technique for obtaining a full-envelope decoupled linear flight control design is presented. The methodology begins with a reduced-order linear dynamic-inversion technique that is scheduled over the flight envelope. The reduced order dynamic inverter can offer a significant reduction in the number of state variables to be sensed or estimated as compared to typical applications of inverse dynamic control. The technique can provide desired input-output characteristics including control decoupling. The required gain scheduling of the reduced order dynamic inversion is straightforward. Uncertainty is introduced by perturbing the stability derivatives in the vehicle model at each of the flight conditions considered. The effects of uncertainty are then reduced by additional feedback loops involving a diagonal compensation matrix obtained through application of a loop shaping procedure based upon a quantitative feedback theory predesign technique. The tendency of quantitative feedback theory to produce high-bandwidth conservative designs is mitigated by the scheduling and decoupling associated with the dynamic inversion. Finally, handling qualities and pilot-induced oscillation tendencies are evaluated using a structural model of the human pilot implemented in an interactive computer program that can include the effects of nuisance nonlinearities such as actuator saturation. The proposed methodology is applied to the design of a lateral-directional flight control system for a piloted supermaneuvarable fighter aircraft.

Assessment of Flight Simulator Fidelity in Multiaxis Tasks Including Visual Cue Quality

A technique for analytical assessment of flight simulator fidelity is presented as an extension of a methodology previously introduced in the literature. The assessment is based on a computer simulation of the pilot and vehicle and is inherently task dependent. A simple model of visual cue quality is introduced that is based on the classical concept of human operator visual remnant. The complete assessment procedure now includes proprioceptive, vestibular, and visual cue modeling. Inverse dynamic analysis is employed that allows the use of compensatory models of the human pilot in multiaxis tasks. The methodology is exercised by considering a simple rotorcraft lateral and vertical repositioning task in which visual and motion cue quality is varied.

Analytical Assessment of Flight Simulator Fidelity Using Pilot Models

A simplified approach for modeling pilot pursuit control behavior is adopted for use in assessing the fidelity of flight simulators. The model includes proprioceptive, visual, and vestibular cueing. The model differs from previous simulator fidelity applications in that pursuit, as opposed to compensatory pilot behavior, is modeled. In approximate fashion, the model can account for the effects of task interference, degraded motion and visual cues, vehicle modeling errors, differing levels of pilot control aggressiveness, and to a limited extent, pilot skill level. A fidelity metric similar to one previously discussed in the literature is exercised with three vehicles and tasks: a fighter aircraft in a tail-chase tracking task, a small rotorcraft in a near-hover repositioning task, and a large rotorcraft in acceleration/deceleration and departure/abort tasks. The fidelity assessment procedure is shown to be sensitive to changes in vehicles, tasks, and simulator limitations in these disparate examples.

Inverse simulation of large-amplitude aircraft maneuvers

Inverse simulation techniques are computational methods that determine the control inputs to a dynamic system that will produce desired system outputs. Such techniques can be useful tools for the analysis and evaluation of problems associated with maneuvering flight. As opposed to current inverse simulation methods that require numerical time differentiation in their implementation, the proposed technique is essentially an integration algorithm. It is applicable to cases where the number of inputs equals or exceeds the number of constrained outputs. The algorithm is exercised in determining the trim conditions and then the control inputs that force a nonlinear model of an F-16 fighter to complete large-amplitude maneuvers.