Engineering topics

Hilbert, K. B.

Publications and source records attributed to Hilbert, K. B..

8 records

NASA NTRS1994

Galileo Spacecraft Scan Platform Celestial Pointing Cone Control Gain Redesign

During September and October 1991, pictures of the Gaspra asteroid and neighboring stars were taken by the Galileo Optical Navigation (OPNAV) Team for the purpose of navigation the spacecraft for a successful Gaspra encounter. The star tracks in these pictures showed that the scan platform celestial pointing cone controller performed poorly in compensating for wobble-induced cone offsets.

Gaspar asteroid Galileo Optical Navigation (OPNAV)↗

NASA NTRS1986

Flight investigation of a multivariable model-following control system for rotorcraft

A high-bandwidth, multivariable, explicit model-following control system for advanced rotorcraft has been developed and evaluated on the NASA Ames CH-47B fly-by-wire helicopter. This control system has expanded the in-flight simulation capabilities of the CH-47B to support research efforts directed at the next generation of superaugmented helicopters. A detailed, analytical model of the augmented CH-47B has also been developed to support the flight tests. Analysis using this theoretical model was used to expose fundamental limitations caused by the basic vehicle characteristics and original control system implementation that had affected the performance of the model-following control system. Improvements were made to the nominal control system design to compensate for large time delays created by the higher-orderd dynamics of the aircraft and its control system. With these improvements, high bandwidth control and excellent model-following performance were achieved. Both analytical and flight-test results for the lateral axis are presented and compared. In addition, frequency-domain techniques are employed for documenting the system performance.

Hilbert, K. B.↗

NASA NTRS1986

Flight evaluation of height response characteristics for the hover bob-up task and comparison with proposed criteria

The CH-47B variable-stability helicopter was used to evaluate a range of height-response configurations while performing a precision hover bob-up task. The purpose of the study was to assess the validity of results obtained in previous ground-based and in-flight simulations in the context of a precision bob-up task and to provide additional flight data for inclusion in revisions to specifications for helicopter handling qualities. Height response characteristics were implemented using explicit model-following techniques, and the resulting CH-47B dynamics were validated using time-domain and frequency-domain data-analysis methods. The tests complemented the previous investigations by providing detailed pilot comments and ratings, and performance and control-utilization data that relate exclusively to the hover bob-up task. The results are compared with those from previous investigations and with new criteria that have been proposed for handling qualities requirements for helicopters.

Hindson, W. S.↗

NASA NTRS1986

New capabilities and recent research programs of the NASA/Army CH-47B variable-stability helicopter

The CH-47B is the third in a series of variable-stability helicopters developed and operated by NASA since 1952 to investigate helicopter and VTOL handling qualities. Recently, several new capabilities were added to this helicopter to enable it to better support new and evolving research requirements. The installation of a programmable force-feel system for the evaluation pilot's conventional cyclic stick, and a four-axis side-stick controller permit a range of in-flight investigations concerning manipulator characteristics and augmentation system features that had not been possible with earlier NASA research helicopters. A recently installed color electronic display system with a programmable symbol generator will permit the investigation of display formats for a variety of VTOL and helicopter missions. Finally, a powerful new general-purpose flight computer is now in operation. It is programmable in high-level languages and will provide more efficient support of research programs. In addition to these new hardware capabilities, flight-control software has been developed to improve the in-flight simulation capability of the aircraft. A brief description of the CH-47B's variable-stability research equipment is provided, recent research programs are summarized, and some remarks concerning the potential of the helicopter are presented.

Hindson, W. S.↗

NASA NTRS1984

A mathematical model of the UH-60 helicopter

This report documents the revisions made to a ten-degree-of-freedom, full-flight envelope, generic helicopter mathematical model to represent the UH-60 helicopter accurately. The major modifications to the model include fuselage aerodynamic force and moment equations specific to the UH-60, a canted tail rotor, a horizontal stabilator with variable incidence, and a pitch bias actuator (PBA). In addition, this report presents a full set of parameters and numerical values which describe the helicopter configuration and physical characteristics. Model validation was accomplished by comparison of trim and stability derivative data generated from the UH-60 math model with data generated from a similar total force and moment math model.

Hilbert, K. B.↗

NASA NTRS1984

An investigation of side-stick-controller/stability and control-augmentation system requirements for helicopter terrain flight under reduced visibility conditions

Simulation of the reduced visibility tasks is effected by providing the pilot with a visually coupled, helmet-mounted display of flight-control symbols superimposed upon terrain-board imagery. Forward-flight, low-speed, and precision-hover control modes are implemented, and a method is developed for the blending of control laws between each control mode. An investigation is made of the variations in the level of integration of primary control functions on a single side-stick controller. For most of the flight tasks investigated, separated controller configurations are preferred to a single, fully integrated side-stick device. Satisfactory handling qualities over all controller configurations are attained only for a precision-hover task conducted with a high level of stability and control augmentation. For most tasks flown with the helmet-mounted display significant degradation in handling qualities occurs relative to the identical tasks flown under visual flight conditions.

Landis, K. H.↗

NASA NTRS1984

The design of a model-following control system for helicopters

The design of an explicit model-following control system is described and the results of a ground-based simulation experiment investigating the performance and limitations of this control system for a hingeless-rotor and a teetering-rotor helicopter are reported. The explicit model was a linear, decoupled model such that the pilot commanded pitch attitude with the longitudinal cyclic, roll attitude with the lateral cyclic, yaw rate with the pedals, and earth-fixed vertical velocity with the collective. A new model-following performance criterion was developed to optimize the control-law design and to evaluate the model-following performance. The results of the simulation indicate that the performance of the model-following control system is dependent on the dynamics of the explicit model and on the limitations of the actuating system. Increases in the bandwidth of the explicit model placed higher demands on the control system and resulted in degraded model-following performance. Significant improvements in model-following performance were achieved when a control-law switching feature, which was designed to account for position- or rate-limited actuators, was included in the control system. The excellent overall model-following performance obtained for these two radically different helicopters indicates the flexibility and versatility of this control technique.

Hilbert, K. B.↗

NASA NTRS1984

A piloted simulator investigation of side-stick controller/stability and control augmentation system requirements for helicopter visual flight tasks

A piloted simulator experiment was conducted to assess the effects of side-stick controller characteristics and level of stability and control augmentation on handling qualities for several low-altitude control tasks. Visual flight tasks were simulated using four-window computer-generated imagery depicting either a nap-of-the-earth course or a runway with obstacles positioned to provide a slalom course. Both low speed and forward flight control laws were implemented, and a method for automatically switching control modes was developed. Variations in force-deflection characteristics and the number of axes controlled through an integrated side-stick were investigated. With high levels of stability and control augmentation, a four-axis controller with small-deflection in all four axes achieved satisfactory handling qualities for low-speed tasks.

Landis, K. H.↗