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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Development of a Rotor-Body Coupled Analysis for an Active Mount Aeroelastic Rotor Testbed

At the Langley Research Center an active mount rotorcraft testbed is being developed for use in the Langley Transonic Dynamics Tunnel. This testbed, the second generation version of the Aeroelastic Rotor Experimental System (ARES-II), can impose rotor hub motions and measure the response so that rotor-body coupling phenomena may be investigated. An analytical method for coupling an aeroelastically scaled model rotor system to the ARES-II is developed in the current study. Models of the testbed and the rotor system are developed in independent analyses, and an impedance-matching approach is used to couple the rotor system to the testbed. The development of the analytical models and the coupling method is examined, and individual and coupled results are presented for the testbed and rotor system. Coupled results are presented with and without applied hub motion, and system loads and displacements are examined. The results show that a closed-loop control system is necessary to achieve desired hub motions, that proper modeling requires including the loads at the rotor hub and rotor control system, and that the strain-gauge balance placed in the rotating system of the ARES-II provided the best loads results.

Wilbur, Matthew L.↗
NASA NTRS1960

Effect of Afterbody Terminal Fairings on the Performance of a Pylon-Mounted Turbojet-Nacelle Model

An investigation of the effect of afterbody terminal fairings on the performance of a pylon-mounted turbojet-nacelle model has been conducted in the Langley 16-foot transonic tunnel. A basic afterbody having a boattail angle of 16 deg was investigated with and without terminal fairings. The equivalent boattail angle, based on the cross-sectional area of the afterbody and terminal fairings, was 8 deg. Therefore, a simple body of revolution with a boattail angle of 8 deg was included for comparison. The tests were made at an angle of attack of 0 deg, Mach numbers of 0.80 to 1.05, jet total-pressure ratio of 1 to approximately 5, and an average Reynolds number per foot of 4.1 x 10(exp 6). A hydrogen peroxide jet simulator was used to supply the hot-jet exhaust. The results indicate that addition of terminal fairings to a 16 deg boattail afterbody increased the thrust-minus-drag coefficients and provided the lowest effective drag of the three configurations tested.

Willis, Conrad M.↗
NASA NTRS1959

Transonic Aerodynamic Characteristics of a 45 deg Swept Wing Fuselage Model with a Finned and Unfinned Body Pylon Mounted Beneath the Fuselage or Wing, Including Measurements of Body Loads

An investigation of a model of a standard size body in combination with a representative 45 deg swept-wing-fuselage model has been conducted in the Langley 8-foot transonic pressure tunnel over a Mach number range from 0.80 to 1.43. The body, with a fineness ratio of 8.5, was tested with and without fins, and was pylon-mounted beneath the fuselage or wing. Force measurements were obtained on the wing-fuselage model with and without the body, for an angle-of-attack range from -2 deg to approximately 12 deg and an angle-of-sideslip range from -8 deg to 8 deg. In addition, body loads were measured over the same angle-of-attack and angle-of-sideslip range. The Reynolds number for the investigation, based on the wing mean aerodynamic chord, varied from 1.85 x 10(exp 6) to 2.85 x 10(exp 6). The addition of the body beneath the fuselage or the wing increased the drag coefficient of the complete model over the Mach number range tested. On the basis of the drag increase per body, the under-fuselage position was the more favorable. Furthermore, the bodies tended to increase the lateral stability of the complete model. The variation of body loads with angle of attack for the unfinned bodies was generally small and linear over the Mach number range tested with the addition of fins causing large increases in the rates of change of normal-force coefficient and nose-down pitching-moment coefficient. The variation of body side-force coefficient with sideslip for the unfinned body beneath the fuselage was at least twice as large as the variation of this load for the unfinned body beneath the wing. The addition of fins to the body beneath either the fuselage or the wing approximately doubled the rate of change of body side-force coefficient with sideslip. Furthermore, the variation of body side-force coefficient with sideslip for the body beneath the wing was at least twice as large as the variation of this load with angle of attack.

Wornom, Dewey E.↗
NASA NTRS1998

Performance of Surface-Mount Ceramic and Solid Tantalum Capacitors for Cryogenic Applications

Low temperature electronics are of great interest for space exploration programs. These include missions to the outer planets, earth-orbiting and deep-space probes, remote-sensing and communication satellites. Terrestrial applications would also benefit from the availability of low temperature electronics. Power components capable of low temperature operation would, thus, enhance the technologies needed for the development of advanced power systems suitable for use in harsh environments. In this work, ceramic and solid tantalum capacitors were evaluated in terms of their dielectric properties as a function of temperature and at various frequencies. The surface-mount devices were characterized in terms of their capacitance stability and dissipation factor in the frequency range of 50 Hz to 100 kHz at temperatures ranging from room temperature (20 deg. C) to about liquid nitrogen temperature (-190 deg. C). The results are discussed and conclusions made concerning the suitability of the capacitors investigated for low temperature applications.

Patterson, Richard L.↗
NASA NTRS1998

Fluids and Materials Science Studies Utilizing the Microgravity-vibration Isolation Mount (MIM)

Canada's Microgravity Sciences Program (MSP) is the smallest program of the ISS partners and so can participate in only a few, highly focused projects in order to make a scientific and technological impact. One focused project involves determining the effect of accelerations (g-jitter) on scientific measurements in a microgravity environment utilizing the Microgravity-vibration Isolation Mount (MIM). Many experiments share the common characteristic of having a fluid stage in their process. The quality of the experimental measurements have been expected to be affected by g-jitters which has lead the ISS program to include specifications to limit the level of acceleration allowed on a subset of experimental racks. From finite element analysis (FEM), the ISS structure will not be able to meet the acceleration specifications. Therefore, isolation systems are necessary. Fluid science results and materials science results show significant sensitivity to g-jitter. The work done to date should be viewed only as a first look at the issue of g-jitter sensitivity. The work should continue with high priority such that the international science community and the ISS program can address the requirement and settle on an agreed to overall approach as soon as possible.

Herring, Rodney↗
NASA NTRS1998

Optimal Controller Design for the Microgravity Isolation Mount (MIM)

H2 controllers, when designed using an appropriate design model and carefully chosen frequency weightings, appear to provide robust performance and robust stability for Microgravity Isolation Mount (MIM). The STS-85 flight data will be used to evaluate the H2 controllers' performance on the actual hardware under working conditions. Next, full-order H-infinity controllers will be developed, as an intermediate step, in order to determine appropriate H-infinity performance weights for use in the mixed-norm design. Finally the basic procedure outlined above will be used to develop fixed-order mixed-norm controllers for MIM.

Hampton, R. David↗
NASA NTRS1999

The Microgravity Isolation Mount: A Linearized State-Space Model a la Newton and Kane

Vibration acceleration levels on large space platforms exceed the requirements of many space experiments. The Microgravity Vibration Isolation Mount (MIM) was built by the Canadian Space Agency to attenuate these disturbances to acceptable levels, and has been operational on the Russian Space Station Mir since May 1996. It has demonstrated good isolation performance and has supported several materials science experiments. The MIM uses Lorentz (voice-coil) magnetic actuators to levitate and isolate payloads at the individual experiment/sub-experiment (versus rack) level. Payload acceleration, relative position, and relative orientation (Euler-parameter) measurements are fed to a state-space controller. The controller, in turn, determines the actuator currents needed for effective experiment isolation. This paper presents the development of an algebraic, state-space model of the MIM, in a form suitable for optimal controller design. The equations are first derived using Newton's Second Law directly; then a second derivation (i.e., validation) of the same equations is provided, using Kane's approach.

Hampton, R. David↗
NASA NTRS1995

Vertical Scales of Turbulence at the Mount Wilson Observatory

The vertical scales of turbulence at the Mount Wilson Observatory are inferred from data from the University of California at Berkeley Infrared Spatial Interferometer (ISI), by modeling path length fluctuations observed in the interferometric paths to celestial objects and those in instrumental ground-based paths. The correlations between the stellar and ground-based path length fluctuations and the temporal statistics of those fluctuations are modeled on various timescales to constrain the vertical scales. A Kolmogorov-Taylor turbulence model with a finite outer scale was used to simulate ISI data. The simulation also included the white instrumental noise of the interferometer, aperture-filtering effects, and the data analysis algorithms. The simulations suggest that the path delay fluctuations observed in the 1992-1993 ISI data are largely consistent with being generated by refractivity fluctuations at two characteristic vertical scales: one extending to a height of 45 m above the ground, with a wind speed of about 1 m/ s, and another at a much higher altitude, with a wind speed of about 10 m/ s. The height of the lower layer is of the order of the dimensions of trees and other structures near the interferometer, which suggests that these objects, including elements of the interferometer, may play a role in generating the lower layer of turbulence. The modeling indicates that the high- attitude component contributes primarily to short-period (less than 10 s) fluctuations, while the lower component dominates the long-period (up to a few minutes) fluctuations. The lower component turbulent height, along with outer scales of the order of 10 m, suggest that the baseline dependence of long-term interferometric, atmospheric fluctuations should weaken for baselines greater than a few tens of meters. Simulations further show that there is the potential for improving the seeing or astrometric accuracy by about 30%-50% on average, if the path length fluctuations in the lower component are directly calibrated. Statistical and systematic effects induce an error of about 15 m in the estimate of the lower component turbulent altitude.

Treuhaft, Robert N.↗
NASA NTRS2000

Metrology Mount and Optics Mandrels

This document is the Final Report for NASA Grant NAG8-1198 from NASA Marshall Space Flight Center (MSFC) to the Smithsonian Astrophysical Observatory (SAO). The Grant is entitled "Metrology Mount and Optics Materials." This final report is required by the terms of the Grant. The period of performance was from September 15, 1995 through January 14, 1999. Total funding received by SAO from MSFC for this effort was, $254,000. Mr. Lester Cohen carried out most of the work at SAO, but received limited support from other engineers, technicians, and designers. Dr. Harvey Tananbaum, the Principal Investigator for the grant provided overall direction and work- assessment. The Grant has had two funding augmentations to its basic amount and has, over time, emphasized three different research areas - each of which has been an extension of earlier research. The research activity was in 2 areas: (1) Expert opto-structural studies related to separation mechanics and effects of electro formed nickel X-ray mirrors. and (2) Design, fabrication and evaluation of a low force metrology and assembly station for light weight full shell electroformed X-ray mirrors.

Tananbaum, H.↗
NASA NTRS2000

Evaluation of Helmet Mounted Display Alerting Symbology

Proposed helicopter helmet mounted displays will be used to alert the pilot to a variety of conditions, from threats to equipment problems. The present research was performed under the NASA Safe All-weather Flight Operations Research (SAFOR) program supported by a joint Army/NASA research agreement. The purpose of the research was to examine ways to optimize the alerting effectiveness of helmet display symbology. The research used two approaches to increasing the effectiveness of alerts. One was to increase the ability of the alert to attract attention by using the entire display surface. The other was to include information about the required response in the alert itself. The investigation was conducted using the NASA Ames Research Center's six-degree-of-freedom vertical motion simulator (VMS) with a rotorcraft cockpit. Helmet display symbology was based on the AH-64's pilot night vision system (PNVS), cruise mode symbology. A standardized mission was developed, that consisted of 11 legs. The mission included four tasks, which allowed variation in the frequency of alerts. The general trend in the data points to a small benefit from both the full-screen alert and the partial information alert.

DeMaio, Joe↗
NASA NTRS1995

Helmet-Mounted Display Research Capabilities of the NASA/Army Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL)

The Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL) is a UH-60A Black Hawk helicopter that is being modified by the US Army and NASA for flight systems research. The principal systems that are being installed in the aircraft are a Helmet Mounted Display (HMD) and imaging system, and a programmable full authority Research Flight Control System (RFCS). In addition, comprehensive instrumentation of both the rigid body of the helicopter and the rotor system is provided. The paper will describe the capabilities of these systems and their current state of development. A brief description of initial research applications is included. The wide (40 X 60 degree) field-of-view HMD system has been provided by Kaiser Electronics. It can be configured as a monochromatic system for use in bright daylight conditions, a two color system for darker ambients, or a full color system for use in night viewing conditions. Color imagery is achieved using field sequential video and a mechanical color wheel. In addition to the color symbology, high resolution computer-gene rated imagery from an onboard Silicon Graphics Reality Engine Onyx processor is available for research in virtual reality applications. This synthetic imagery can also be merged with real world video from a variety of imaging systems that can be installed easily on the front of the helicopter. These sensors include infrared or tv cameras, or potentially small millimeter wave radars. The Research Flight Control System is being developed for the aircraft by a team of contractors led by Boeing Helicopters. It consists of a full authority high bandwidth fly-by-wire actuators that drive the main rotor swashplate actuators and the tail rotor actuator in parallel. This arrangement allows the basic mechanical flight control system of the Black Hawk to be retained so that the safety pilot can monitor the operation of the system through the action of his own controls. The evaluation pilot will signal the fly-by-wire actuators through the flight computer from electrical sidearm controllers located in the right hand cockpit. The system will have very substantial input/output capacity and impressive computational power. These systems are installed in the aircraft using predominantly a MIL-STD 1553B data bus architecture. Sensor data from the RFCS, the basic aircraft and rotor system instrumentation including navigation information, and the HMD system are easily exchanged among user systems, or are available at the systems operator station located in the cabin for real time monitoring or data recording.

Jacobsen, R. A.↗
NASA NTRS1995

Color Helmet-Mounted Display System for In-Flight Simulation on the RASCAL Research Helicopter

A high performance color helmet mounted display (HMD) system for in-flight simulation and research has been developed for the Rotorcraft Aircrew Systems Concepts Laboratory (RASCAL). The display system consists of a programmable display generator, a display electronics unit, a head tracker, and the helmet with display optics. The system provides a maximum of 1024 x 1280 resolution, a 4:1 contrast ratio, and a brightness of 1100fL utilizing currently available technologies. This paper describes the major features and components of the system. Also discussed are the measured performance of the system and the design techniques that allowed the development of a full color HMD.

Edwards, Tim↗
NASA NTRS1995

Binocular Convergence and Errors in Judged Distance While Using Head-mounted See-through Displays

Previous observations have shown that optical superposition of a physical backdrops at the judged depth of a stereoscopic virtual image moves the judged depth closer to the observer. This effect was more pronounced for slowly moving physical backdrops and was not enhanced when the virtual image was rendered as a flat shaded solid object rather than a open wire-frame. Since this change in rendering making the virtual image more completely occlude the backdrop did not effect its judged depth and since the motion of the backdrop which would have attracted visual attention and binocular convergence did Increase its perceptual displacement, it was concluded that the change In Judged depth was not due to the perceived occlusion. Rather it was concluded to be due to an increase in binocular convergence. An experimental test of this hypothesis using a unobtrusive nonius technique to detect absolute and relative convergence has confirmed the presence of convergence correlated with the magnitude of the change in judged position of this virtual Image. The practical implications of this cause are demonstrated by a second study using monocular, biocular and stereoscopic viewing conditions and the consequences for the design of head-mounted see-through displays for near work are discussed.

Ellis, Stephen R.↗
NASA NTRS1997

High Speed Rotor Head Mounted Instrumentation System

NASA Ames Research Center has been investigating the air flow of a rotor blade on a UH-60 Blackhawk helicopter in-flight. This paper will address the hardware problems and solutions used to design and fabricate an instrumentation system on top of a UH-60 main rotor head. The instrumentation system consisted of 10 data systems operating in parallel and collected data from 370 sensors that are mounted in four rotor blades and on the rotating rotor head. The data was recorded on board the aircraft and simultaneously down linked to the ground station at 7.5 MHz.

Hee, Leonard↗
NASA NTRS2002

Stability and Control Estimation Flight Test Results for the SR-71 Aircraft With Externally Mounted Experiments

A maximum-likelihood output-error parameter estimation technique is used to obtain stability and control derivatives for the NASA Dryden Flight Research Center SR-71A airplane and for configurations that include experiments externally mounted to the top of the fuselage. This research is being done as part of the envelope clearance for the new experiment configurations. Flight data are obtained at speeds ranging from Mach 0.4 to Mach 3.0, with an extensive amount of test points at approximately Mach 1.0. Pilot-input pitch and yaw-roll doublets are used to obtain the data. This report defines the parameter estimation technique used, presents stability and control derivative results, and compares the derivatives for the three configurations tested. The experimental configurations studied generally show acceptable stability, control, trim, and handling qualities throughout the Mach regimes tested. The reduction of directional stability for the experimental configurations is the most significant aerodynamic effect measured and identified as a design constraint for future experimental configurations. This report also shows the significant effects of aircraft flexibility on the stability and control derivatives.

Moes, Timothy R.↗
NASA NTRS1997

Head-Mounted and Head-Up Display Glossary

One of the problems in head-up and helmet-mounted display (HMD) literature has been a lack of standardization of words and abbreviations. Several different words have been used for the same concept; for example, flight path angle, flight path marker, velocity vector, and total velocity vector all refer to the same thing. In other cases, the same term has been used with two different meanings, such as binocular field-of-view which means the field-of-view visible to both left and right eyes according to some or the field-of-view visible to either the left or right eye or both according to others. Many of the terms used in HMD studies have not been well-defined. We need to have a common language to ensure that system descriptions are communicated. As an example, the term 'stabilized' has been widely used with two meanings. 'Roll-stabilized' has been used to mean a symbol which rotates to indicate the roll or bank of the aircraft. 'World-stabilized' and 'head-stabilized' have both been used to indicate symbols which move to remain fixed with respect to external objects. HMDs present unique symbology problems not found in HUDs. Foremost among these is the issue of maintaining spatial orientation of the symbols. All previous flight displays, round dial instruments, HDDs, and HUDs have been fixed in the cockpit. With the HMD, the flight display can move through a large angle. The coordinates use in transforming from the real-world to the aircraft to the HMD have not been consistently defined. This glossary contains terms relating to optics and vision, displays, and flight information, weapons and aircraft systems. Some definitions, such as Navigation Display, have been added to clarify the definitions for Primary Flight Display and Primary Flight Reference. A list of HUD/HMD related abbreviations is also included.

Newman, Richard L.↗
NASA NTRS1947

Drag Measurements at Transonic Speeds of NACA 65-009 Airfoils Mounted on a Freely Falling Body to Determine the Effects of Sweepback and Aspect Ratio

Drag measurements at transonic speeds on rectangular airfoils and on airfoils swept back 450 are reported. These airfoils, which were mounted on cylindrical test bodies, are part of a series being tested in free drops from high altitude to determine the effect of variation of basic airfoil parameters on airfoil drag characteristics at transonic speeds. These rectangular and swept-back airfoils had the same span, airfoil section (NACA 65-009), and chord perpendicular to the leading edge. The tests were made to compare the drag of rectangular and sweptback airfoils at a higher aspect ratio than had been used in a similar comparison reported previously. The results showed that the drag of the swept-back airfoil was less than 0.15 that of the rectangular airfoil at a Mach number of 1.00 and less than 0.30 that of the rectangular airfoil at a Mach number of 1.17. A comparison of these swept-back airfoils with similar airfoils of lower aspect ratio previously tested by the same method indicated that in the investigated speed range reduction in aspect ratio results in increased drag. In the highest part of the investigated speed range, however, the drag coefficient of the high-aspect-ratio swept-back airfoils showed a tendency to approach that of the lower-aspect-ratio swept-back airfoils. A similar comparison for the rectangular airfoils showed that delay in the drag rise and a reduction in drag at supercritical speeds can be realIzed through reduction in aspect ratio. These results confirm those reported in NACA ACR No. L5J16.

Mathews, Charles W.↗
NASA NTRS2003

Overview of Mount Washington Icing Sensors Project

NASA, the FAA, the Department of Defense, the National Center for Atmospheric Research and NOAA are developing techniques for retrieving cloud microphysical properties from a variety of remote sensing technologies. The intent is to predict aircraft icing conditions ahead of aircraft. The Mount Washington Icing Sensors Project MWISP), conducted in April, 1999 at Mt. Washington, NH, was organized to evaluate technologies for the prediction of icing conditions ahead of aircraft in a natural environment, and to characterize icing cloud and drizzle environments. April was selected for operations because the Summit is typically in cloud, generally has frequent freezing precipitation in spring, and the clouds have high liquid water contents. Remote sensing equipment, consisting of radars, radiometers and a lidar, was placed at the base of the mountain, and probes measuring cloud particles, and a radiometer, were operated from the Summit. NASA s Twin Otter research aircraft also conducted six missions over the site. Operations spanned the entire month of April, which was dominated by wrap-around moisture from a low pressure center stalled off the coast of Labrador providing persistent upslope clouds with relatively high liquid water contents and mixed phase conditions. Preliminary assessments indicate excellent results from the lidar, radar polarimetry, radiosondes and summit and aircraft measurements.

Ryerson, Charles C.↗