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Results for “dynamic operation and stability”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

A study of flight control requirements for advanced, winged, earth-to-orbit vehicles with far-aft center-of-gravity locations

Control requirements of Controlled Configured Design Approach vehicles with far-aft center of gravity locations are studied. The baseline system investigated is a fully reusable vertical takeoff/horizontal landing single stage-to-orbit vehicle with mission requirements similar to that of the space shuttle vehicle. Evaluations were made to determine dynamic stability boundaries, time responses, trim control, operational center-of-gravity limits, and flight control subsystem design requirements. Study tasks included a baseline vehicle analysis, an aft center of gravity study, a payload size study, and a technology assessment.

Hepler, A. K.↗
NASA NTRS1993

Problem reporting management system performance simulation

This paper proposes the Problem Reporting Management System (PRMS) model as an effective discrete simulation tool that determines the risks involved during the development phase of a Trouble Tracking Reporting Data Base replacement system. The model considers the type of equipment and networks which will be used in the replacement system as well as varying user loads, size of the database, and expected operational availability. The paper discusses the dynamics, stability, and application of the PRMS and addresses suggested concepts to enhance the service performance and enrich them.

Vannatta, David S.↗
NASA NTRS2011

Signal Processing Methods for Liquid Rocket Engine Combustion Stability Assessments

The J2X Gas Generator engine design specifications include dynamic, spontaneous, and broadband combustion stability requirements. These requirements are verified empirically based high frequency chamber pressure measurements and analyses. Dynamic stability is determined with the dynamic pressure response due to an artificial perturbation of the combustion chamber pressure (bomb testing), and spontaneous and broadband stability are determined from the dynamic pressure responses during steady operation starting at specified power levels. J2X Workhorse Gas Generator testing included bomb tests with multiple hardware configurations and operating conditions, including a configuration used explicitly for engine verification test series. This work covers signal processing techniques developed at Marshall Space Flight Center (MSFC) to help assess engine design stability requirements. Dynamic stability assessments were performed following both the CPIA 655 guidelines and a MSFC in-house developed statistical-based approach. The statistical approach was developed to better verify when the dynamic pressure amplitudes corresponding to a particular frequency returned back to pre-bomb characteristics. This was accomplished by first determining the statistical characteristics of the pre-bomb dynamic levels. The pre-bomb statistical characterization provided 95% coverage bounds; these bounds were used as a quantitative measure to determine when the post-bomb signal returned to pre-bomb conditions. The time for post-bomb levels to acceptably return to pre-bomb levels was compared to the dominant frequency-dependent time recommended by CPIA 655. Results for multiple test configurations, including stable and unstable configurations, were reviewed. Spontaneous stability was assessed using two processes: 1) characterization of the ratio of the peak response amplitudes to the excited chamber acoustic mode amplitudes and 2) characterization of the variability of the peak response's frequency over the test duration. This characterization process assists in evaluating the discreteness of a signal as well as the stability of the chamber response. Broadband stability was assessed using a running root-mean-square evaluation. These techniques were also employed, in a comparative analysis, on available Fastrac data, and these results are presented here.

Kenny, R. Jeremy↗
NASA NTRS1987

Stability studies of Solar Optical Telescope dynamics

The Solar Optical Telescope (SOT) is designed to operate as an attached payload mounted on the Instrument Pointing System (IPS) in the cargo bay of the Shuttle Orbiter. Pointing and control of SOT is accomplished by an active Articulated Primary Mirror (APM), an active Tertiary Mirror (TM), an elaborate set of optical sensors, electromechanical actuators and programmable controllers. The structural interactions of this complex control system are significant factors in the stability of the SOT. The preliminary stability study results of the SOT dynamical system are presented. Structural transfer functions obtained from the NASTRAN model of the structure were used. These studies apply to a single degree of freedom (elevation). Fully integrated model studies will be conducted in the future.

Gullapalli, Sarma N.↗
NASA NTRS1985

Dynamic modeling and adaptive control for space stations

Of all large space structural systems, space stations present a unique challenge and requirement to advanced control technology. Their operations require control system stability over an extremely broad range of parameter changes and high level of disturbances. During shuttle docking the system mass may suddenly increase by more than 100% and during station assembly the mass may vary even more drastically. These coupled with the inherent dynamic model uncertainties associated with large space structural systems require highly sophisticated control systems that can grow as the stations evolve and cope with the uncertainties and time-varying elements to maintain the stability and pointing of the space stations. The aspects of space station operational properties are first examined, including configurations, dynamic models, shuttle docking contact dynamics, solar panel interaction, and load reduction to yield a set of system models and conditions. A model reference adaptive control algorithm along with the inner-loop plant augmentation design for controlling the space stations under severe operational conditions of shuttle docking, excessive model parameter errors, and model truncation are then investigated. The instability problem caused by the zero-frequency rigid body modes and a proposed solution using plant augmentation are addressed. Two sets of sufficient conditions which guarantee the globablly asymptotic stability for the space station systems are obtained.

Ih, C. H. C.↗
NASA NTRS1977

Differential multi-MOSFET nuclear radiation sensor

Circuit allows minimization of thermal-drift errors, low power consumption, operation over wide dynamic range, improved sensitivity and stability with metaloxide-semiconductor field-effect transistor sensors.

Deoliveira, W. A.↗
NASA NTRSDate not supplied

Aeroservoelastic Flight Dynamic Modeling of UAM Conceptual Vehicles

This paper presents an aeroservoelastic flight dynamic modeling approach for NASA Lift+Cruise eVTOL aircraft in forward flight. A conceptual aerodynamic analysis for forward flight is performed in CHARM, a rotorcraft aeromechanics unsteady vortex-lattice flow solver. A trim analysis is performed to obtain the steady state aerodynamic information at a trim point to be used for the aeroelastic analysis. A NASTRAN finite element model for the Lift+Cruise vehicle is available. The structural dynamic mode shapes are extracted from the NASTRAN for the aeroelastic analysis. An aeroservoelastic model is developed using the Theodorsen’s theory. A stability and control derivative analysis is performed to formulate a flight dynamic model of the Lift+Cruise vehicle. An aeroservoelastic flight dynamic model is formulated by coupling these two models together. Flight dynamic and flutter analyses are performed to determine vehicle stability and flutter-free operation.

Aeroservoelasticity↗
NASA NTRS1982

An in-flight investigation of pilot-induced oscillation suppression filters during the fighter approach and landing task

An investigation of pilot-induced oscillation suppression (PIOS) filters was performed using the USAF/Flight Dynamics Laboratory variable stability NT-33 aircraft, modified and operated by Calspan. This program examined the effects of PIOS filtering on the longitudinal flying qualities of fighter aircraft during the visual approach and landing task. Forty evaluations were flown to test the effects of different PIOS filters. Although detailed analyses were not undertaken, the results indicate that PIOS filtering can improve the flying qualities of an otherwise unacceptable aircraft configuration (Level 3 flying qualities). However, the ability of the filters to suppress pilot-induced oscillations appears to be dependent upon the aircraft configuration characteristics. Further, the data show that the filters can adversely affect landing flying qualities if improperly designed. The data provide an excellent foundation from which detail analyses can be performed.

Bailey, R. E.↗
NASA NTRS1982

An in-flight investigation of pilot-induced oscillation suppression filters during the fighter approach and landing task

An investigation of pilot-induced oscillation suppression (PIOS) filters was performed using the USAF/Flight Dynamics Laboratory variable stability NT-33 aircraft, modified and operated by Calspan. This program examined the effects of PIOS filtering on the longitudinal flying qualities of fighter aircraft during the visual approach and landing task. Forty evaluations were flown to test the effects of different PIOS filters. Although detailed analyses were not undertaken, the results indicate that PIOS filtering can improve the flying qualities of an otherwise unacceptable aircraft configuration (Level 3 flying qualities). However, the ability of the filters to suppress pilot-induced oscillations appears to be dependent upon the aircraft configuration characteristics. Further, the data show that the filters can adversely affect landing flying qualities if improperly designed. The data provide an excellent foundation from which detail analyses can be performed.

Bailey, R. E.↗
NASA NTRS1986

Active suppression of compressor instabilities

A strategy is proposed for controlling aerodynamic instabilities which limit the useful range of both axial and centrifugal turbomachines. Both local and global instabilities (incipient rotating stall and surge) are analyzed. A theory is developed which shows how an additional disturbance, driven from real time data measured within the machine, can be generated so as to realize a device with characteristics fundamentally different from those of the turbomachine without control; for the particular compressor analyzed, the control led to a 20 percent increase in the extent of the stable operating range. The use of structural dynamics to enhance stability is also discussed.

Epstein, A. H.↗
NASA NTRS1972

V/STOL tilt-rotor study, task 1. Volume 1: Conceptual design

A conceptual design study was conducted to define a representative military and/or commercial tilt-propeller aircraft for short takeoff and landing operation. The level of structural technology selected for the operational aircraft was based on aluminum, steel, titanium, and adhesive bonded structures. The data describe the following: (1) aircraft weight, (2) performance and stability, (3) aerodynamic noise, (4) dynamic characteristics, (5) maintainability and reliability, and (6) operating economics.

Source record↗
NASA NTRSDate not supplied

Development of Data Reduction Methods for Dynamic Stability Tests in a Magnetic Suspension and Balance System

The NASA/ODU 6-inch Magnetic Suspension and Balance System (MSBS) is operational in a “free-to-yaw” configuration in a subsonic wind tunnel. The MSBS hardware has been heavily modified over recent years to utilize a transverse magnetization scheme, with mixed electromagnetic and motion tracking camera position sensors and a relatively sophisticated control system. The project aims to provide a unique test capability for dynamic stability testing of planetary entry capsules, free from support interference. Aerodynamic tests are being conducted, with a focus of validation of the data reduction methods used to extract dynamic stability parameters. The unique complication is the existence of magnetic, aerodynamic, and mass centers, where magnetic, aerodynamic, and inertia forces respectively are resolved. The paper will report on tests of a family of EEV-like geometries, where the conical half-angle varied between 45 and 60 degrees in steps of 3.75 degrees. The paper will present experimental results from the parametric family of EEV-like geometries. Simulation results will also be presented, based on a two or three degree-of-freedom Simulink model. The model allows the exploration of the effects of non-coincident centers and the sensitivity of results arising from uncertainties in location.

Entry Systems Modeling↗
NASA NTRS1991

Controls for space structures

Assembly and operation of large space structures (LSS) in orbit will require robot-assisted docking and berthing of partially-assembled structures. These operations require new solutions to the problems of controls. This is true because of large transient and persistent disturbances, controller-structure interaction with unmodeled modes, poorly known structure parameters, slow actuator/sensor dynamical behavior, and excitation of nonlinear structure vibrations during control and assembly. For on-orbit assembly, controllers must start with finite element models of LSS and adapt on line to the best operating points, without compromising stability. This is not easy to do, since there are often unmodeled dynamic interactions between the controller and the structure. The indirect adaptive controllers are based on parameter estimation. Due to the large number of modes in LSS, this approach leads to very high-order control schemes with consequent poor stability and performance. In contrast, direct model reference adaptive controllers operate to force the LSS to track the desirable behavior of a chosen model. These schemes produce simple control algorithms which are easy to implement on line. One problem with their use for LSS has been that the model must be the same dimension as the LSS - i.e., quite large. A control theory based on the command generator tracker (CGT) ideas of Sobel, Mabins, Kaufman and Wen, Balas to obtain very low-order models based on adaptive algorithms was developed. Closed-loop stability for both finite element models and distributed parameter models of LSS was proved. In addition, successful numerical simulations on several LSS databases were obtained. An adaptive controller based on our theory was also implemented on a flexible robotic manipulator at Martin Marietta Astronautics. Computation schemes for controller-structure interaction with unmodeled modes, the residual mode filters or RMF, were developed. The RMF theory was modified to compensate slow actuator/sensor dynamics. These new ideas are being applied to LSS simulations to demonstrate the ease with which one can incorporate slow actuator/sensor effects into our design. It was also shown that residual mode filter compensation can be modified for small nonlinearities to produce exponentially stable closed-loop control. A theory for disturbance accommodating controllers based on reduced order models of structures was developed, and stability results for these controllers in closed-loop with large-scale finite element models of structures were obtained.

Balas, Mark↗
NASA NTRS1972

Experimental evaluation of a 600 lbf spacecraft rocket engine.

Experimental results are presented for a long-duration-capability (1000-sec), space-storable, bipropellant liquid rocket motor burning fluorine/hydrazine or FLOX/monomethylhydrazine. The interrelationship between injected mixture ratio and the per cent film cooling on vacuum specific impulse performance and chamber heat transfer is given. Experimental sea level measurements are used to predict space vacuum performance based upon simplified JANNAF reference procedures. Dynamic combustion stability is demonstrated over a wide range of operating conditions. Analytical results of char penetration, erosion, and ablative wall temperature distributions are presented for prototype chamber designs.

Hoehn, F. W.↗
NASA NTRS1987

A flight investigation of helicopter low-speed response requirements

A flight experiment has been conducted using the Canadian National Aeronautical Establishment's variable-stability airborne simulator to define the dynamic response requirements for operations at hover and low speeds. Fourteen Attitude Command/Attitude Hold, Rate, and Rate Command/Attitude Hold configurations were evaluated by six pilots using both conventional controls and a four-axis integrated sidestick over a low-speed course consisting of precision hover, landing, sidestep, and dash/quickstop tasks. The results indicate that with conventional controls all three response-types were acceptable as long as their response bandwidth was sufficiently high, and higher bandwidths were required in roll than in pitch. With the four-axis sidestick, there was a preference for the Rate systems. The range of acceptable bandwidths was lower, and the spread in pilot ratings smaller, than were found in a similar ground-based simulation.

Mitchell, David G.↗
NASA NTRS1960

An Examination of Handling Qualities Criteria for V/STOL Aircraft

A study has been undertaken to define hand-ling qualities criteria for V/STOL aircraft. With the current military requirements for helicopters and airplanes as a framework, modifications and additions were made for conversion to a preliminary set of V/STOL requirements using a broad background of flight experience and pilots' comments from VTOL and STOL aircraft, BLC (boundary-layer-control) equipped aircraft, variable stability aircraft, flight simulators and landing approach studies. The report contains a discussion of the reasoning behind and the sources of information leading to suggested requirements. The results of the study indicate that the majority of V/STOL requirements can be defined by modifications to the helicopter and/or airplane requirements by appropriate definition of reference speeds. Areas where a requirement is included but where the information is felt to be inadequate to establish a firm quantitative requirement include the following: Control power and damping relationships about all axes for various sizes and types of aircraft; control power, sensitivity, d-amping and response for height control; dynamic longitudinal and dynamic lateral- directional stability in the transition region, including emergency operation; hovering steadiness; acceleration and deceleration in transition; descent rates and flight-path angles in steep approaches, and thrust margin for approach.

Anderson, Seth B.↗
NASA NTRS1980

Effects of primary rotor parameters on flapping dynamics

The effects of flapping dynamics of four main rotor design features that influence the agility, stability, and operational safety of helicopters are studied. The parameters include flapping hinge offset, flapping hinge restraint, pitch-flap coupling, and blade lock number. First, the flapping equations of motion are derived that explicitly contain the design parameters. The dynamic equations are then developed for the tip-path plane, and the influence of individual and combined variations in the design parameters determined. The steady state flapping response is examined with respect to control input and aircraft angular rate which leads to a feedforward control law for control decoupling through cross feed, and a feedback control law to decouple the steady state flapping response. The condition for achieving perfect decoupling of the flapping response due to aircraft pitch and roll rates without using feedback control is also found for the hover case. It is indicated that the frequency of the regressing flapping mode of the rotor system can become low enough to require consideration in the assessment of handling characteristics.

Chen, R. T. N.↗