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At least 469 records · Page 26

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NASA NTRS1998

Formal Aspects of Human-Automation Interaction

While new versions of automated control systems such as flight guidance systems are introduced at a rapid pace, it is widely recognized that user interaction with these machines is increasingly problematic. One cause for this difficulty that is commonly cited in the literature, is the discrepancy between the machine's behavior and the operator's (e.g., pilot) expectations. This paper discusses a formal approach to the analysis of operator's interaction with complex automated control systems. We focus attention on the issue of interface correctness; that is, on the question whether the display provides adequate information about the machine's configurations (states, modes, and associated parameters) and transitions, so as to enable the operator to successfully perform the specified set of tasks. To perform the analysis several assumptions are made: (1) A complete formal model of the machine's behavior is available (e.g., as a state transition system, or as a hybrid-machine); (2) A specification of operator's tasks is available and can be formally described (e.g., the reliable and predictable transition between activities involved in executing a climb to a new altitude); (3) The pilot is well trained and has a correct 'mental' model of the machine's response-map. By 'comparing' the machine's model with the set of operator's tasks we formally (i.e., mathematically) evaluate two questions: 1) does the machine's output interface (display) enable the operator to determine, unambiguously, what the current configuration (e.g., mode) of the machine is, and 2) does the display enable the operator to determine, unambiguously, what the next configuration of the machine will be, in response to a specified interaction by the operator (e.g., engaging a mode or changing a parameter such as a speed or target altitude). This paper describes a methodology for conducting such an evaluation using examples from automated flight control systems of modem 'glass cockpit' jetliners. Taxonomy of the different types of discrepancies that lead to pilot inability to resolve the current and next configuration of the machine is suggested. Data from incident reports involving 'mode confusion' is used to corroborate these discrepancies. Finally, means for compensating, either by augmenting the display and/or the operator's 'mental model' are briefly mentioned.

Degani, Asaf↗

NASA NTRS1993

The Mini-Mast CSI testbed: Lessons learned

The Mini-Mast testbed was one of the first large scale Controls-Structure-Interaction (CSI) systems used to evaluate state-of-the-art methodology in flexible structure control. Now that all the testing at Langley Research Center has been completed, a look back is warranted to evaluate the program. This paper describes some of the experiences and technology development studies by NASA, university, and industry investigators. Lessons learned are presented from three categories: the testbed development, control methods, and the operation of a guest investigator program. It is shown how structural safety margins provided a realistic environment to simulate on-orbit CSI research, even though they also reduced the research flexibility afforded to investigators. The limited dynamic coupling between the bending and torsion modes of the cantilevered test article resulted in highly successful SISO and MIMO controllers. However, until accurate models were obtained for the torque wheel actuators, sensors, filters, and the structure itself, most controllers were unstable. Controls research from this testbed should be applicable to cantilevered appendages of future large space structures.

Tanner, Sharon E.↗

NASA NTRS1976

The economic impact of NASA R and D spending

The economic impact of R and D spending, particularly NASA R and D spending, on the U. S. economy was evaluated. The crux of the methodology and hence the results revolve around the fact that it was necessary to consider both the demand effects of increased spending and the supply effects of a higher rate of technological growth and a larger total productive capacity. The demand effects are primarily short-run in nature, while the supply effects do not begin to have a significant effect on aggregate economic activity until the fifth year after increased expenditures have taken place. The short-term economic impact of alternative levels of NASA expenditures for 1975 was first examined. The long-term economic impact of increased levels of NASA R and D spending over a sustained period was then evaluated.

Evans, M. K.↗

NASA NTRS2019

Electrochemical, Polarization, and Crevice Corrosion Testing of Inconel X750: A Supplement to the Environmental Control and Life Support System Sustaining Metal Materials Compatibility Study

In previous studies, electrochemical test results were experimentally acquired and then presented for several noble alloys in two specific solutions representative of waste liquids generated or present within the Environmental Control and Life Support System (ECLSS) aboard the International Space Station (ISS). Subsequently, another metal candidate, Inconel X750, has been submitted and was subjected to the same test routines in the same solutions and evaluated with the same statistical/analytical methodologies as those utilized in the earlier studies. Previous studies included three titanium grades, (Commercially Pure, 6Al-4V alloy, and 6Al-4V Low Interstitial alloy), two nickel-chromium alloys (Inconel® 625 and Hastelloy® C276), one high tier stainless steel (Cronidur® 30), and a nickel-titanium alloy (Nitinol 60). Thus far, all candidate alloys have exhibited excellent corrosion protection and galvanic compatibility attributes and have been deemed qualified materials for application within the ECLSS facility. Inconel X750 now joins that group. The titanium alloys gave the best results of all the metal candidates by demonstrating superior nobility and galvanic protection properties. It is worth noting that the corrosion performance properties for the three titanium alloys were essentially indistinguishable. As such and for expediency, this study and all future evaluations will refer only to the comparative properties already documented for Titanium 6Al-4V as this alloy is representative of all three alloys and considered to be more mainstream. Now the measured corrosion properties for Inconel X750 were very similar to those determined previously for Inconel 625 and Hastelloy C276 which were also determined to be very high performers. For the current effort, the results have clearly shown that Inconel X750 possesses exceptional anti-corrosion attributes comparable to metals in the highest tier of the galvanic series. Overall, one can conclude that Inconel X750 is quite noble, highly corrosion resistant and galvanically compatible with the other metal groups from both an electrochemical perspective and a long-term exposure scenario. This was clearly demonstrated after utilizing the same techniques as those applied in previous studies which included linear, Tafel and cyclic polarization, galvanic coupling with each of the other metal candidates, and pitting/crevicing assessments after one full year of immersion in the subject test solutions. Attributes defining the nobility and anti-corrosion capabilities for X750 appear to be on par with all the other candidates thus far and this alloy can now be classified as ‘excellent’ exhibiting very high resistance toward general, localized, and galvanic corrosion in the subject test media.

Lee, R. E.↗

NASA NTRS1990

Performance Data from a Wind-Tunnel Test of Two Main-rotor Blade Designs for a Utility-Class Helicopter

An investigation was conducted in the NASA Langley Transonic Dynamics Tunnel to evaluate an advanced main rotor designed for use on a utility class helicopter, specifically the U.S. Army UH-60A Blackhawk. This rotor design incorporated advanced twist, airfoil cross sections, and geometric planform. For evaluation purposes, the current UH-60A main rotor was also tested and is referred to as the baseline blade set. A total of four blade sets were tested. One set of both the baseline and the advanced rotors were dynamically scaled to represent a full scale helicopter rotor blade design. The remaining advanced and baseline blade sets were not dynamically scaled so as to isolate the effects of structural elasticity. The investigation was conducted in hover and at rotor advance ratios ranging from 0.15 to 0.4 at a range of nominal test medium densities from 0.00238 to 0.009 slugs/cu ft. This range of densities, coupled with varying rotor lift and propulsive force, allowed for the simulation of several vehicle gross weight and density altitude combinations. Performance data are presented for all blade sets without analysis; however, cross referencing of data with flight condition may be useful to the analyst for validating aeroelastic theories and design methodologies as well as for evaluating advanced design parameters.

Singleton, Jeffrey D.↗

NASA NTRS1989

Probability of failure and risk assessment of propulsion structural components

Because of the increasing need to account for the uncertainties in material properties, loading conditions, geometry, etc., a methodology was developed to determine structural reliability and to assess the associated risk. The methodology consists of a probabilistic structural analysis by a probabilistic finite element computer code, numerical evaluation of stochastic structures under stress (NESSUS), and a generic probabilistic material property model. The methodology is versatile and is equally applicable to structures operating at high and cryogenic temperature environments. Results obtained demonstrate that the issues of structural reliability and risk can be formally evaluated by using the methodology developed which is inclusive of the uncertainties in material properties, structural parameters, and loading conditions. The methodology is described in some detail with illustrative examples.

Shiao, Michael C.↗

NASA NTRS1981

Whys and hows of in-house writing

The combining of requisite technical knowledge with requisite writing ability is addressed. Considerations in the development of in-house writing courses, in-plant training, are presented and evaluated. Specific problems in past methodology are also detailed. It is suggested that teachers of technical writing should be technical people themselves, preferably with working experience in industry or business; the training provided should be user-oriented, not theory oriented.

Lane, J. C.↗

NASA NTRS1983

An overview of the Goldstone Energy Systems study

A systems planning methodology was developed for analyzing and synthesizing Deep Space Network (DSN) energy systems. The resultant product, the Deep Space Network Planning and Analysis Methodology supports DSN energy planning evaluations. It addresses a broad spectrum of tradeoff and dispatching scenarios. It evaluates a variety of energy generation configurations and also includes a capability to evaluate conservation measures.

Rosenberg, L. S.↗

NASA NTRS1983

Uncertainty methodology for in-flight thrust determination

A methodology is proposed for the evaluation of uncertainty in the in-flight determination of aircraft thrust, which provides error traceability to a national standards laboratory, and is independent of the procedure used to calculate or measure thrust in flight, thereby yielding a consistent means for the evaluation of measurement capabilities. Attention is given to the factors of measurement error, precision, bias, uncertainty, error estimation and classification, error propagation, ground testing, and the related problems of model bias error, model precision error, and the uncertainty limit.

Adams, G. R.↗

NASA NTRS1983

Integrated technology rotor/flight research rotor hub concept definition

Two variations of the helicopter bearingless main rotor hub concept are proposed as bases for further development in the preliminary design phase of the Integrated Technology Rotor/Flight Research Rotor (ITR/FRR) program. This selection was the result of an evaluation of three bearingless hub concepts and two articulated hub concepts with elastomeric bearings. The characteristics of each concept were evaluated by means of simplified methodology. These characteristics included the assessment of stability, vulnerability, weight, drag, cost, stiffness, fatigue life, maintainability, and reliability.

Dixon, P. G. C.↗

NASA NTRS1987

Task allocation in a distributed computing system

A conceptual framework is examined for task allocation in distributed systems. Application and computing system parameters critical to task allocation decision processes are discussed. Task allocation techniques are addressed which focus on achieving a balance in the load distribution among the system's processors. Equalization of computing load among the processing elements is the goal. Examples of system performance are presented for specific applications. Both static and dynamic allocation of tasks are considered and system performance is evaluated using different task allocation methodologies.

Seward, Walter D.↗

NASA NTRS1989

Systems analysis for DSN microwave antenna holography

Proposed systems for Deep Space Network (DSN) microwave antenna holography are analyzed. Microwave holography, as applied to antennas, is a technique which utilizes the Fourier Transform relation between the complex far-field radiation pattern of an antenna and the complex aperture field distribution to provide a methodology for the analysis and evaluation of antenna performance. Resulting aperture phase and amplitude distribution data are used to precisely characterize various crucial performance parameters, including panel alignment, subreflector position, antenna aperture illumination, directivity at various frequencies, and gravity deformation. Microwave holographic analysis provides diagnostic capacity as well as being a powerful tool for evaluating antenna design specifications and their corresponding theoretical models.

Rochblatt, D. J.↗

NASA NTRS1990

H-infinity based integrated flight-propulsion control design for a STOVL aircraft in transition flight

Results are presented from an application of H-infinity control design methodology to a centralized integrated flight/propulsion control (IFPC) system design for a supersonic Short Take-Off and Vertical Landing (STOVL) fighter aircraft in transition flight. The overall design methodology consists of a centralized IFPC controller design with controller partitioning. Only the feedback controller design portion of the methodology is addressed. Design and evaluation vehicle models are summarized, and insight is provided into formulating the H-infinity control problem such that it reflects the IFPC design objectives. The H-infinity controller is shown to provide decoupled command tracking for the design model. The controller order could be significantly reduced by modal residualization of the fast controller modes without any deterioration in performance. A discussion is presented of the areas in which the controller performance needs to be improved, and ways in which these improvements can be achieved within the framework of an H-infinity based linear control design.

Garg, Sanjay↗

NASA NTRS1990

Digital-flutter-suppression-system investigations for the active flexible wing wind-tunnel model

Active flutter suppression control laws were designed, implemented, and tested on an aeroelastically-scaled wind-tunnel model in the NASA Langley Transonic Dynamics Tunnel. One of the control laws was successful in stabilizing the model while the dynamic pressure was increased to 24 percent greater than the measured open-loop flutter boundary. Other accomplishments included the design, implementation, and successful operation of a one-of-a-kind digital controller, the design and use of two simulation methods to support the project, and the development and successful use of a methodology for online controller performance evaluation.

Perry, Boyd, III↗

NASA NTRS1990

Design, implementation, simulation, and testing of digital flutter suppression systems for the active flexible wing wind-tunnel model

Active flutter suppression control laws were designed, implemented, and tested on an aeroelastically-scaled wind-tunnel model in the NASA Langley Transonic Dynamics Tunnel. One of the control laws was successful in stabilizing the model while the dynamic pressure was increased to 24 percent greater than the measured open-loop flutter boundary. Other accomplishments included the design, implementation, and successful operation of a one-of-a-kind digital controller, the design and use of two simulation methods to support the projet, and the development and successful use of a methodology for online controller performance evaluation.

Perry, Boyd, III↗

NASA NTRS1991

Approximate factorization with source terms

A comparative evaluation is made of three methodologies with a view to that which offers the best approximate factorization error. While two of these methods are found to lead to more efficient algorithms in cases where factors which do not contain source terms can be diagonalized, the third method used generates the lowest approximate factorization error. This method may be preferred when the norms of source terms are large, and transient solutions are of interest.

Shih, T. I.-P.↗

NASA NTRS1992

Advanced life support systems in lunar and Martian environments utilizing a higher plant based engineering paradigm

The paper describes a higher-plant-based engineering paradigm for advanced life support in a Controlled Ecological Life Support System (CELSS) on the surface of the moon or Mars, called the CELSS Breadboard Project, designed at John F. Kennedy Space Center. Such a higher-plant-based system would use the plants for a direct food source, gas exchange, water reclamation, and plant residuals in a complex biological resource recovery scheme. The CELSS Breadboard Project utilizes a 'breadboard' approach of developing independent systems that are evaluated autonomously and are later interconnected. Such a scheme will enable evaluation of life support system methodologies tested for their efficiency in a life support system for habitats on the moon or Mars.

Chamberland, Dennis↗

NASA NTRS1992

Application of damage tolerance methodology in certification of the Piaggio P-180 Avanti

The Piaggio P-180 Avanti, a twin pusher-prop engine nine-passenger business aircraft was certified in 1990, to the requirements of FAR Part 23 and Associated Special Conditions for Composite Structure. Certification included the application of a damage tolerant methodology to the design of the composite forward wing and empennage (vertical fin, horizontal stabilizer, tailcone, and rudder) structure. This methodology included an extensive analytical evaluation coupled with sub-component and full-scale testing of the structure. The work from the Damage Tolerance Analysis Assessment was incorporated into the full-scale testing. Damage representing hazards such as dropped tools, ground equipment, handling, and runway debris, was applied to the test articles. Additional substantiation included allowing manufacturing discrepancies to exist unrepaired on the full-scale articles and simulated bondline failures in critical elements. The importance of full-scale testing in the critical environmental conditions and the application of critical damage are addressed. The implication of damage tolerance on static and fatigue testing is discussed. Good correlation between finite element solutions and experimental test data was observed.

Johnson, Jerry↗