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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 307 records · Page 17

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NASA NTRS1979

Performance analysis for collector-side reflector systems

The F-Chart method of solar collector performance evaluation is extended to a flat-plate collector system augmented with planar side reflectors. The modified F-Chart evaluations show that the augmentation of the collector has approximately the effect of increasing the collector area by 60%, and the energy supplied by the collector better matches the load. The installed reflector cost of about 10% of the collector cost is shown to be well justified.

Espy, P. N.↗

NASA NTRS1980

A Summery of an In-flight Evaluation of Control System Pure Time Delays During Landing Using the F-8 DFBW Airplane

An in-flight investigation of the effect of pure time delays on low L/D space shuttle type landing tasks was undertaken. The results indicate that the sensitivity of the pilot ratings to changes in pure time delay in pitch is strongly affected by the task and only slightly affected by changes in control system augmentation mode. Low L/D spot landings from a lateral offset were twice as sensitive to pure time delay as normal low L/D landings. For comparison purposes, formation flying was also investigated, and was found to be less sensitive to time delay than the landing tasks.

Berry, D. T.↗

NASA NTRS1980

Space platforms - An evolution from Spacelab payload operations

The evolution of the present Spacelab mode of operation to allow optimal utilization of the newly developing augmentation system is described. The following new systems are considered: the Power Extension Package, the Power System, and the Science and Applications Space Platforms. The projected models are analyzed, showing how each system would be utilized to provide benefits to the users' missions.

Ballance, J. O.↗

NASA NTRS1980

Economic evaluation of flying-qualities design criteria for a transport configured with relaxed static stability

Direct constrained parameter optimization was used to optimally size a medium range transport for minimum direct operating cost. Several stability and control constraints were varied to study the sensitivity of the configuration to specifying the unaugmented flying qualities of transports designed to take maximum advantage of relaxed static stability augmentation systems. Additionally, a number of handling qualities related design constants were studied with respect to their impact on the design.

Sliwa, S. M.↗

NASA NTRS1982

A mathematical model of a single main rotor helicopter for piloted simulation

A mathematical model, suitable for piloted simulation of the flying qualities of helicopters, is a nonlinear, total force and moment model of a single main rotor helicopter. The model has ten degrees of freedom: six rigid body, three rotor flapping, and the rotor rotational degrees of freedom. The rotor model assumes rigid blades with rotor forces and moments radially integrated and summed about the azimuth. The fuselage aerodynamic model uses a detailed representation over a nominal angle of attack and sideslip range of + or - 15 deg., as well as a simplified curve fit at large angles of attack or sideslip. Stabilizing surface aerodynamics are modeled with a lift curve slope between stall limits and a general curve fit for large angles of attack. A generalized stability and control augmentation system is described. Additional computer subroutines provide options for a simplified engine/governor model, atmospheric turbulence, and a linearized six degree of freedom dynamic model for stability and control analysis.

Talbot, P. D.↗

NASA NTRS1983

NASA/FAA experiments concerning helicopter IFR airworthiness criteria

A sequence of ground and flight simulation experiments was conducted as part of a joint NASA/FAA program to investigate helicopter instrument flight rules (IFR) airworthiness criteria. The first six of these experiments are described and the results summarized. Five of the experiments were conducted on large amplitude motion base simulators; V/STOLAND UH-1H variable stability helicopter was used in the flight experiment. Airworthiness implications of selected variables that were investigated across all of the experiments are discussed, including the level of longitudinal static stability, the type of stability and control augmentation, the addition of flight director displays, and the type of instrument approach task. Among the specific results reviewed are the adequacy of neutral longitudinal statics for dual pilot approaches and the requirement for pitch and roll attitude stabilization in the stability and control augmentation system to achieve flying qualities evaluated as satisfactory.

Lebacqz, J. V.↗

NASA NTRS1983

Low cost fluidic sensors

The gyroscopic inertial sensors used in general aviation autopilots and in stability augmentation systems probably contribute more than any other component to the initial cost and to the continuing maintenance costs of these installations. Several fluidic devices which were developed to replace the gyroscopes in the conventional ""wing-leveler'' type autopilots used in small, general aviation airplanes are described. These sensors are characterized by simplicity of design, ease of fabrication, and lack of wearing parts. A unique, fluidic, true airspeed sensor is also described. All these devices are adapted to fabrication by low cost plastic molding techniques, and their lack of wearing parts promises long, maintenance free service lives.

Garner, H. D.↗

NASA NTRS1983

Effects of control saturation on the command response of statically unstable aircraft

Hanson and Stengel (1981) have described the effects of saturating controls on the initial-condition response of statically unstable aircraft. In an analysis of the stability augmentation system, consideration was given to maximizing the region of stable response. The present investigation is concerned with an extension of the control saturation analysis to the problem of command response, taking into account the main problem of control design for satisfactory flying qualities (as perceived by the pilot). A model for examining the effects of control saturation on longitudinal stability and command response is developed and applied to an aircraft with a static instability. Three parameters prescribing longitudinal flying qualities are examined with respect to their ability to identify proper flying qualities in the presence of control saturation. The presented analysis provides also satisfactory guidelines for establishing command saturation/stability boundaries.

Hanson, G. D.↗

NASA NTRS1984

Body-freedom flutter of a 1/2-scale forward-swept-wing model, an experimental and analytical study

The aeroelastic phenomenon known as body-freedom flutter (BFF), a dynamic instability involving aircraft-pitch and wing-bending motions which, though rarely experienced on conventional vehicles, is characteristic of forward swept wing (FSW) aircraft was investigated. Testing was conducted in the Langley transonic dynamics tunnel on a flying, cable-mounted, 1/2-scale model of a FSW configuration with and without relaxed static stability (RSS). The BFF instability boundaries were found to occur at significantly lower airspeeds than those associated with aeroelastic wing divergence on the same model. For those cases with RSS, a canard-based stability augmentation system (SAS) was incorporated in the model. This SAS was designed using aerodynamic data measured during a preliminary tunnel test in which the model was attached to a force balance. Data from the subsequent flutter test indicated that BFF speed was not dependent on open-loop static margin but, rather, on the equivalent closed-loop dynamics provided by the SAS. Servo-aeroelastic stability analyses of the flying model were performed using a computer code known as SEAL and predicted the onset of BFF reasonably well.

Chipman, R.↗

NASA NTRS1984

A preliminary look at the effects of coupled lateral modes on aircraft handling qualities

Analytic and six-degree-of-freedom motion base simulator studies have been conducted to better understand how the coupled roll-spiral and coupled roll-aileron actuator modes affect aircraft handling qualities. The results reported herein are preliminary and are subject to change until other aircraft and several more data points can be examined. The results obtained thus far indicate that when the roll-spiral coupled mode is brought about by unusual values of an aircraft's stability and control derivatives, the lateral-directional handling qualities will invariably be degraded. However, when the roll spiral coupling is brought about by a roll-rate command/roll-attitude hold stability and control augmentation system (SCAS), the requirements for satisfactory handling qualities can be correlated to the natural frequency and the damping of the coupled mode. Satisfactory handling qualities were also achieved when the lateral SCAS brought about a coupling of the roll mode with the aileron actuator mode. In this case, the pilot ratings indicate that the handling qualities may be correlated to the natural frequency of the coupled roll-aileron mode.

Ruflin, S. J.↗

NASA NTRS1984

Demonstration of relaxed static stability on a commercial transport

Increasing jet aircraft fuel costs from 25 percent to nearly 60 percent of the aircraft direct operating costs have led to a heavy emphasis on the development of transport aircraft with significantly improved aerodynamic performance. The application of the concept of relaxed static stability (RSS) and the utilization of an active control stability augmentation system make it possible to design an aircraft with reduced aerodynamic trim drag due to a farther-aft cg balance. Reduced aerodynamic parasite drag and lower structural weight due to a smaller horizontal tail surface can also be obtained. The application of RSS has been studied under a NASA-sponsored program to determine ways of improving the energy efficiency in current and future transport aircraft. Attention is given to a near-term pitch active control system, an advanced pitch active control system, and an operational overview.

Rising, J. J.↗

NASA NTRS1986

Directional handling qualities requirements for nap-of-the-earth tasks

A piloted similator experiment designed to investigate directional axis handling qualities requirements for low-speed and hover tasks conducted by a scout/attack helicopter is described. Included were the directional characteristics of various candidate light helicopter family (LHX) configurations. The test also focused on conventional single main/tail rotor configurations where the first-order effects that contribute to the loss of tail rotor control experienced by the OH-58 series aircraft were modeled. Two types of yaw stability and control augmentation systems were implemented: washed-out yaw rate feedback and shaped control input, and a yaw rate command, heading-hold system. The results of the experiment indicate that rotorcraft configurations with high directional gust sensitivity require more yaw damping to maintain satisfactory handling qualities during nap-of-the-earth (NOE) flying tasks. It was also determined that both yaw damping and control response are critical handling qualities parameters in performing the air-to-air target acquisition and tracking task. The lack of substantial yaw damping and larger values of gust sensitivity increased the possibility of loss of directional control at low airspeeds for the tail rotor configurations.

Bivens, C. C.↗

NASA NTRS1985

Flight test trajectory controller synthesis with constrained eigenstructure assignment

The design of a maneuver autopilot for flight test trajectory control using constrained eigenvalue/eigenvector assignment is examined. The aircraft considered was a high-performance fighter with a command augmentation system engaged in all three axes. Attention is given to difficulties encountered in the generation of the desired eigenvalues and eigenvectors. It is found that this approach demands several iterations to converge to a satisfactory result, and does not appear to easily yield suitable insight for the output feedback design of high-order multivariable systems which will be used at other operating points. It is concluded that this technique could be made more attractive by generating gradients of the eigensystem between flight conditions, and including this information in the single-point design technique.

Menon, P. K. A.↗

NASA NTRS1985

Directional handling qualities requirements for nap of the earth (NOE) tasks

A piloted simulator experiment has been conducted to ascertain the directional axis handling requirements of hover and below 40-kt tasks of a scout/attack helicopter, with attention to such light helicopter configurations as those being considered for the 'LHX' program. Two types of yaw stability and control augmentation system were implemented: one consisted of a washed-out yaw rate feedback and shaped control unit, while the other involved a yaw rate command heading-hold system. Experiment results indicate that rotorcraft configurations with high directional gust sensitivity require greater minimum yaw damping to maintain satisfactory handling qualities in nap of the earth flight. Yaw damping and control response are critical handling qualities parameters in air-to-air target acquisition and tracking.

Bivens, C. C.↗

NASA NTRS1988

Analytical sensor redundancy assessment

The rationale and mechanization of sensor fault tolerance based on analytical redundancy principles are described. The concept involves the substitution of software procedures, such as an observer algorithm, to supplant additional hardware components. The observer synthesizes values of sensor states in lieu of their direct measurement. Such information can then be used, for example, to determine which of two disagreeing sensors is more correct, thus enhancing sensor fault survivability. Here a stability augmentation system is used as an example application, with required modifications being made to a quadruplex digital flight control system. The impact on software structure and the resultant revalidation effort are illustrated as well. Also, the use of an observer algorithm for wind gust filtering of the angle-of-attack sensor signal is presented.

Mulcare, D. B.↗

NASA NTRS1989

Making Displaced Holograms At Two Wavelengths

Two-wavelength holographic system augmented with pair of prisms to introduce small separation between holograms formed simultaneously at two wavelengths on holographic plate. Principal use in study of flows. Gradients in index of refraction of fluid caused by variations in temperature, concentration, or both. Holography at one wavelength cannot be used to distinguish between two types of variations. Difference between spacings of fringes in photographs reconstructed from holograms taken simultaneously at two different wavelengths manipulated mathematically to determine type of variation.

Witherow, William K.↗

NASA NTRS1989

Results of an A109 simulation validation and handling qualities study

The results for the validation of a mathematical model of the Agusta A109 helicopter, and subsequent use of the model as the baseline for a handling qualities study of cockpit centerstick requirements, are described. The technical approach included flight test, non-realtime analysis, and realtime piloted simulation. Results of the validation illustrate a time- and frequency-domain approach to the model and simulator issues. The final A109 model correlates well with the actual aircraft with the Stability Augmentation System (SAS) engaged, but is unacceptable without the SAS because of instability and response coupling at low speeds. Results of the centerstick study support the current U.S. Army handling qualities requirements for centerstick characteristics.

Eshow, Michelle M.↗

NASA NTRS1987

Sensor systems testbed for telerobotic navigation

A testbed has been developed for the study of sensor systems to be used in telerobotic operations. The program, conducted in conjunction with Johnson Space Center of NASA, addresses the navigational problems associated with target acquisition and rendezvous for teleoperated robotic work stations. The program will utilize a mobile platform which will support various sensor systems during their development and testing in an earth-based environment. The testbed has been developed in support of a program to develop sensor systems that will aid in rendezvous and docking operations to be conducted as a part of the space station program. A mobile platform has been used to permit testing of these components in a conventional laboratory environment with consequent savings in cost and complexity. The sensor systems, while representative of devices currently in use for robotic applications, are not considered prototypical of the ones that will be used in the final applications. The test program provided information that will support the design of system augmentations and will lead to a comprehensive test program for sensor development.

Thiele, A. W.↗