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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Preliminary characterization of a one-axis acoustic system

The acoustic fields and levitation forces produced along the axis of a single-axis resonance system were measured. The system consisted of a St. Clair generator and a planar reflector. The levitation force was measured for bodies of various sizes and geometries (i.e., spheres, cylinders, and discs). The force was found to be roughly proportional to the volume of the body until the characteristic body radius reaches approximately 2/k (k = wave number). The acoustic pressures along the axis were modeled using Huygens principle and a method of imaging to approximate multiple reflections. The modeled pressures were found to be in reasonable agreement with those measured with a calibrated microphone.

Oran, W. A.↗
NASA NTRS1977

A dual-loop model of the human controller

A representative model of the human controller in single-axis compensatory tracking tasks that exhibits an internal feedback loop which is not evident in single-loop models now in common use is presented. This hypothetical inner-loop involves a neuromuscular command signal derived from the time rate of change of controlled element output which is due to control activity. It is not contended that the single-loop human controller models now in use are incorrect, but that they contain an implicit but important internal loop closure, which, if explicitly considered, can account for a good deal of the adaptive nature of the human controller in a systematic manner.

Hess, R. A.↗
NASA NTRS1977

The effect of a visual/motion display mismatch in a single axis compensatory tracking task

The frequency response of visual systems is typically unity from 0 to 20 rad/sec, while that of motion systems typically falls off in the vicinity of 6 rad/sec. The question arises as to what effect, if any, such a difference in servomechanism performance has on the simulation. Is pilot performance reduced by the conflict between displays? Would a more realistic simulation occur if the visual servomechanisms were degraded to match the motion servomechanisms? Does the pilot need and use the higher frequency information present in the visual display? The purpose of the experiment is to take a step forward toward answering these questions. Work already in the literature which bears on these questions is outlined. A description is then given of an experiment used to check for the effects of a difference in the performance of the visual and motion servomechanisms (the experiment uses a single-axis, compensatory, roll-tracking task). The results of the experiment are then presented and analyzed.

Shirachi, D. K.↗
NASA NTRS1978

In-flight gyro drift rate calibration on the Viking Orbiters

The drift rates of the attitude control gyros on the Viking Orbiters were calibrated several times in flight. The process by which these rates were estimated as functions of time is novel for a space flight project, although relatively standard estimation techniques were used. The process is described fully and the results obtained from the twelve Viking single-axis gyros are analyzed. Although the possibility was explored, no significantly repeatable function of drift rate vs time or temperature was discovered; the overall mean was found to predict drift rate with acceptable accuracy.

Breckenridge, W. G.↗
NASA NTRS1979

Preliminary study of pilot lateral control of two light airplanes near the stall

For two representative light, single-engine airplanes the single-axis piloting task of controlling bank angle with combined aileron and rudder, and a two-axis task of controlling bank angle with aileron and sideslip with rudder have been studied. For these tasks existing divergence criteria have been applied to determine conditions for closed-loop stability for selected flight conditions near the stall; in addition closed-loop stability characteristics and airplane response to bank angle command were calculated. Results obtained from applying the divergence criterion and from calculations of airplane responses to bank angle command indicate that aileron-alone bank angle control is marginally acceptable at high angle of attack. Of the two rudder control techniques considered, rudder used with the aileron in controlling bank angle increasd stability and produced satisfactory responses; the combined bank angle and sideslip control task does not warrant further consideration because of the task difficulty and the small improvement indicated in airplane closed-loop response with this technique.

Moul, M. T.↗
NASA NTRS1980

Dual-frequency bidirectional antenna

Simultaneous two-way communication at 20 and 30 GHz is possible with versatile paraboloid-dish antenna. Developed for two-way communications between Space Shuttle and ground station, antenna includes parabolic reflector, feed horn, waveguide network, and single-axis gimbal mounting. System resolution and accuracy are better than 1 percent.

Kummer, W. H.↗
NASA NTRS1981

Aircraft control-display analysis and design using the optimal control model of the human pilot

The use of the optimal control model (OCM) of the human pilot as a design tool is discussed. A novel procedure for the assignment and selection of model parameters in the absence of experimental data is proposed. A technique for partitioning a weakly coupled, multiaxis task into approximate state-uncoupled, single-axis tasks is introduced. The resulting modeling technique is utilized in the design and analysis of an aircraft flight-director system. This flight-director design technique differs from previous related work using the OCM in that considerable effort is devoted to ensuring that the OCM-designed director exhibits the desirable frequency-domain characteristics associated with experimentally verified classical designs (e.g., K/s 'effective vehicle' characteristics, noninteracting controls). The implications of the technique in the design of automatic flight control systems which employ the human pilot as a performance assessor and failure detector are briefly discussed.

Hess, R. A.↗
NASA NTRS1982

Performance evaluation of a kinesthetic-tactual display

Simulator studies demonstrated the feasibility of using kinesthetic-tactual (KT) displays for providing collective and cyclic command information, and suggested that KT displays may increase pilot workload capability. A dual-axis laboratory tracking task suggested that beyond reduction in visual scanning, there may be additional sensory or cognitive benefits to the use of multiple sensory modalities. Single-axis laboratory tracking tasks revealed performance with a quickened KT display to be equivalent to performance with a quickened visual display for a low frequency sum-of-sinewaves input. In contrast, an unquickened KT display was inferior to an unquickened visual display. Full scale simulator studies and/or inflight testing are recommended to determine the generality of these results.

Jagacinski, R. J.↗
NASA NTRS1981

Spacecraft attitude calibration/verification baseline study

A baseline study for a generalized spacecraft attitude calibration/verification system is presented. It can be used to define software specifications for three major functions required by a mission: the pre-launch parameter observability and data collection strategy study; the in-flight sensor calibration; and the post-calibration attitude accuracy verification. Analytical considerations are given for both single-axis and three-axis spacecrafts. The three-axis attitudes considered include the inertial-pointing attitudes, the reference-pointing attitudes, and attitudes undergoing specific maneuvers. The attitude sensors and hardware considered include the Earth horizon sensors, the plane-field Sun sensors, the coarse and fine two-axis digital Sun sensors, the three-axis magnetometers, the fixed-head star trackers, and the inertial reference gyros.

Chen, L. C.↗
NASA NTRS1982

The effects of the delays on systems subject to manual control

Results are presented of an experimental study to determine the effects of time delays in manual control systems. A simple, fixed-base laboratory simulation facility is used for determining pilot dynamics and tracking performance in a series of single-axis, compensatory tracking tasks. In these tasks, three time-delay values and three controlled-element dynamics are used. The delays are chosen to encompass values encountered in experimental and operational aircraft. It is noted that the controlled-element dynamics replicate those found in many previous manual control studies, that is, the classical displacement, rate, and acceleration control systems. The experimental effort is complemented with an analytical pilot modeling study where the parameters of a structural model of the human pilot are adjusted so as to provide excellent matches to the experimentally determined pilot dynamics. The experimental and analytical studies both indicate that time delays cause significant changes in pilot equalization requirements.

Hess, R. A.↗
NASA NTRS1981

A comparison of tracking with visual and kinesthetic-tactual displays

Recent research on manual tracking with a kinesthetic-tactual (KT) display suggests that under appropriate conditions it may be an effective means of providing visual workload relief. In order to better understand how KT tracking differs from visual tracking, both a critical tracking task and stationary single-axis tracking tasks were conducted with and without velocity quickening. On the critical tracking task, the visual displays were superior; however, the KT quickened display was approximately equal to the visual unquickened display. Mean squared error scores in the stationary tracking tasks for the visual and KT displays were approximately equal in the quickened conditions, and the describing functions were very similar. In the unquickened conditions, the visual display was superior. Subjects using the unquickened KT display exhibited a low frequency lead-lag that may be related to sensory adaptation.

Jagacinski, R. J.↗
NASA NTRS1982

Development of a magnetic acquisition and attitude control system for spinning rocket payloads

An attitude control system capable of pointing the roll principle axis of a spinning payload to within one degree of the magnetic field vector was flown successfully in 1981-82 aboard three Black Brant X payloads and one Terrier Malemute payload, and additional flights with the system have been requested. Using a filtered linear combination of signals provided by a single-axis rate gyro and a two-axis magnetometer, and control actuation from two cold-gas thrusters, the system can be assembled from standard rocket components and fitted to any payload size.

Olney, D. J.↗
NASA NTRS1983

Compensation for time delay in flight simulator visual-display systems

A piloted aircraft can be viewed as a closed-loop, man-machine control system. When a simulator pilot is performing a precision maneuver, a delay in the visual display of aircraft response to pilot-control input decreases the stability of the pilot-aircraft system. The less stable system is more difficult to control precisely. Pilot dynamic response and performance change as the pilot attempts to compensate for the decrease in system stability, and these changes bias the simulation results by influencing the pilot's rating of the handling qualities of the simulated aircraft. Delay compensation, designed to restore pilot-aircraft system stability, was evaluated in several studies which are reported here. The studies range from single-axis, tracking-task experiments (with sufficient subjects and trials to establish statistical significance of the results) to a brief evaluation of compensation of a computer-generated-imagery (CGI) visual display system in a full six-degree-of-freedom simulation. The compensation was effective - improvements in pilot performance and workload or aircraft handling-qualities rating (HQR) were observed. Results from recent aircraft handling-qualities research literature which support the compensation design approach are also reviewed.

Crane, D. F.↗
NASA NTRS1983

A comparison of visual and kinesthetic-tactual displays for compensatory tracking

Recent research on manual tracking with a kinesthetic-tactual (KT) display suggests that under certain conditions it can be an effective alternative or supplement to visual displays. In order to understand better how KT tracking compares with visual tracking, both a critical tracking and stationary single-axis tracking tasks were conducted with and without velocity quickening. In the critical tracking task, the visual displays were superior, however, the quickened KT display was approximately equal to the unquickened visual display. In stationary tracking tasks, subjects adopted lag equalization with the quickened KT and visual displays, and mean-squared error scores were approximately equal. With the unquickened displays, subjects adopted lag-lead equalization, and the visual displays were superior. This superiority was partly due to the servomotor lag in the implementation of the KT display and partly due to modality differences.

Jagacinski, R. J.↗
NASA NTRS1983

Description of the containerless melting of glass in low gravity

A brief description is given of a single-axis, acoustic levitator/furnace apparatus used to position, heat, melt, and quench multicomponent oxide, glass-forming compositions in low gravity. This apparatus is capable of processing eight approximately spherical samples (about 6 mm diameter) at temperatures up to 1550 C in a dry air atmosphere. Results are also presented for a containerless melting experiment conducted on SPAR VI where a ternary CaO-Ga2O3-SiO2 composition was levitated and quenched to a glass. Selected properties of the glass prepared on SPAR VI are compared with the properties of glass samples of identical composition prepared on earth.

Ray, C. S.↗
NASA NTRS1961

Predicted Performance of On-Off Systems for Precise Satellite Attitude Control

An investigation has been made of the use of on-off reaction jets for precision attitude control of a satellite. Since a symmetrical vehicle is assumed, only single-axis control needs to be considered. The responses to initial disturbances and also limit-cycle characteristics for several systems have been evaluated. Calculated results indicate that realistic values of settling time and fuel consumption for the example considered can be obtained. The performance of a given system depends on the characteristics of the error detector used. In cases where the detector output was saturated for a relatively low error input, the settling time deteriorated when a lead network was used to provide damping. This deterioration could be eliminated if a separate rate signal to produce vehicle rate limiting were available. As an alternate approach, two systems were investigated which used a timed sequence of torques and could operate with a detector output of very small linear range. Although the performance of these systems was poorer than that of the lead network system without detector saturation, the performance was better than that of the lead network system with low values of detector saturation. The effects on limit-cycle characteristics of hysteresis, lead network constants, dead zone, and thrust time delays were also investigated.

Brown, Stuart C.↗
NASA NTRS1965

Human Tracking Performance in Uncoupled and Coupled Two-Axis Systems

This report presents tile results of an experimental and analytical study of human performance in uncoupled and coupled control systems. Human pilot performance in single and two-axis systems was mathematically modeled by linear second-order describing functions. Model parameters were determined using model matching techniques. Analysis of the models showed that the amplitude ratio and phase lead of the describing function increased with training indicating an increase in open loop bandwidth. The phase margin also decreased with training. Increasing the plant lag time constant resulted in an increase in the model lead time constant and a decrease in the zero frequency gain. No significant difference was found to exist in the normalized tracking error per axis between the two-axis tasks and the single-axis tasks. However tile model lead time constant was significantly greater in two-axis tracking. Manual tracking of two-axis systems with cross-coupling was studied experimentally and analytically. Approximate methods for modeling two-axis performance were developed and checked using a precise spectral analysis approach. Coupled and uncoupled, symmetrical and asymmetrical two-axis performance was compared. The results show that modeling of cross-coupled systems is feasible and that trained subjects are capable of decoupling the axes of some systems. A methodology study compared the identification performance of continuous, iterative, and extrapolation model matching techniques. An iterative technique employing sensitivity equations for the generation of influence coefficients was found to be the best technique due to its excellent identification accuracy and ease of implementation. Convergence in iterative techniques can be improved substantially by equalizing the parameter adjustment rates and limiting the maximum correction per iteration.

Todosiev, E. P.↗