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At least 289 records · Page 16

En route noise test preliminary results

Preliminary results are reported from ground measurements of noise emitted by a full-scale advanced single-rotation turbofan model mounted on the wing of the NASA Lewis Propfan Test Assessment aircraft during test flights in October 1987. The procedures and instruments employed in the test program are described, and the data are presented in tables. The repeatability of the measurements is shown to be good within one test day, with day-to-day variations attributed to cross-wind convection. Fair agreement is found between these measurements and the predictions of ray-tracing models.

Willshire, William L., Jr.↗

Description of the Joint Damping Experiment (JDX)

The overall objective is to develop a small-scale shuttle flight experiment which allows researchers to: (1) characterize the influence of gravity and joint gaps on a small-scale truss model, and (2) evaluate the applicability of low-g aircraft test results for predicting on-orbit behavior. The experiment consists of a three-bay truss and associated hardware for truss excitation and measurement of oscillations. Other aspects of the investigation are presented in viewgraph form.

Folkman, Steven L.↗

Flight test evaluation of precision-code differential GPS for terminal approach and landing

A flight test evaluation conducted at the NASA Ames Research Center of precision-code differential GPS for terminal approach and landing is described. Differential corrections to satellite range and range-rate measurements are computed in a stationary ground reference system, uplinked to the test aircraft, and employed to correct corresponding airborne satellite data. Differentially corrected range and range-rate data, combined with inertial data, are then utilized with satellite position and velocity to compute aircraft position and velocity employing an eight-state extended Kalman filter.

Mcnally, B. D.↗

Experimental and analytical investigations of fuselage modal characteristics and structural-acoustic coupling

Measurements conducted on a DC-9 aircraft test section to define the shell and cavity modes of the fuselage, understand its structural-acoustic coupling characteristics, and measure its response to different types of acoustic and vibration excitations are reported. The data were processed to generate spatial plots and wavenumber maps of the shell acceleration and cabin acoustic pressure field. Analysis and interpretation of the spatial plots and wavenumber maps showed that the only structural-acoustic coupling occurred at 105 Hz between the N=2 circumferential structural mode and the (n=2, p=0) circumferential cavity mode. The fuselage response to vibration excitation was found to be dominated by modes whose order increases with frequency.

Simpson, Myles A.↗

Wake-vortex structure from lift and torque induced on a following wing

A procedure based on vortex lattice theory to interpret the lift and torque measured on a following model in a wind tunnel is developed to retrieve the velocity distribution in the vortex wake that caused the induced forces. It is concluded that the retrieval procedure has a potential for reliably determining the structure of vortex wakes that trail from the wings of subsonic transport aircraft. Tests using idealized theoretical models show that the procedure is highly reliable and accurate. However, certain difficulties are found in the retrieval procedure when applied to actual data measured with following wings of various sizes in a wind tunnel.

Rossow, Vernon J.↗

An operational ASDAR system

The story of the Aircraft to Satellite Data Relay (ASDAR) program began when airline meteorologists realized that B-747's and other commercial jets provided cockpit displays of digital values for outside air temperature and winds. Later, when a few B-747's were used to carry portable air quality monitoring equipment for the Global Air Sampling Program (GASP), scientists at NASA-Lewis explored ways in which these digital values could be used to label data collected during the GASP flights. Digital values of GASP analyses were recorded along with digital values of location and altitude, time, winds, and temperature, obtained by microprocessors from within the host aircraft's avionics. These data suggested a way in which manually recorded in-flight meteorological reports could be replaced by an automatic system, which could record winds and air temperatures as often as desired. NASA's prototype ASDAR showed that automated data relay by meteorological geostationary satellites could be accomplished from an aircraft. Testing of the instruments and analyses of its data are examined.

Sparkman, James K., Jr.↗

High-Temperature Resistance Strain Gauges

Resistance strain gauges developed for use at high temperatures in demanding applications like testing aircraft engines and structures. Measures static strains at temperatures up to 800 degrees C. Small and highly reproducible. Readings corrected for temperature within small tolerances, provided temperatures measured simultaneously by thermocouples or other suitable devices. Connected in wheatstone bridge.

Lei, Jih-Fen↗

The Flowfield Around a STOVL Aircraft Model in Ground Effect

An experimental investigation was conducted to determine the causes of hot gas ingestion of engine inlets in STOVL and V/STOVL aircraft in ground effect. Marker nephelometry was used to establish the interactions between the jets, forward velocity, and ground for a typical aircraft model configuration. The aircraft test model consisted of a two inlet configuration with four low subsonic velocity jets impacting vertically on a flat plate. The vertical distance between the plate and model under-surface was adjustable, and a wind tunnel provided forward air velocities from 0 to 0.1 times the jet velocity to simulate landing into a wind. Single frame pictures of the smoke concentration distribution in the flowfield revealed several vortical features in the interaction region, which were affected variously by the distance between the ground plane and model, the forward wind velocity, and the inlet suction. Some of these vortical features, such as the ground vortex, have been seen before in experiments using single jets. Other vortical features in the flowfield, such as the forward vortex pair, have not been seen before. Frame-averaged experimental smoke concentration profiles compared favorably with numerical time-averaged predictions of temperature distribution carried out at the University of Illinois. However, such predictions did not seem to reveal some aspects of the vortical flow features which should affect instantaneous distortion into the engine inlet.

Maclean, Roderick J.↗

An investigation of small scales of turbulence in a boundary layer at high Reynolds numbers

The assumption that turbulence at large wave-numbers is isotropic and has universal spectral characteristics which are independent of the flow geometry, at least for high Reynolds numbers, has been a cornerstone of closure theories as well as of the most promising recent development in the effort to predict turbulent flows, viz. large eddy simulations. This hypothesis was first advanced by Kolmogorov based on the supposition that turbulent kinetic energy cascades down the scales (up the wave-numbers) of turbulence and that, if the number of these cascade steps is sufficiently large (i.e. the wave-number range is large), then the effects of anisotropies at the large scales are lost in the energy transfer process. Experimental attempts were repeatedly made to verify this fundamental assumption. However, Van Atta has recently suggested that an examination of the scalar and velocity gradient fields is necessary to definitively verify this hypothesis or prove it to be unfounded. Of course, this must be carried out in a flow with a sufficiently high Reynolds number to provide the necessary separation of scales in order unambiguously to provide the possibility of local isotropy at large wave-numbers. An opportunity to use our 12-sensor hot-wire probe to address this issue directly was made available at the 80'x120' wind tunnel at the NASA Ames Research Center, which is normally used for full-scale aircraft tests. An initial report on this high Reynolds number experiment and progress toward its evaluation is presented.

Wallace, James M.↗

Helicopter precision approach capability using the Global Positioning System

The period between 1 July and 31 December, 1992, was spent developing a research plan as well as a navigation system document and flight test plan to investigate helicopter precision approach capability using the Global Positioning System (GPS). In addition, all hardware and software required for the research was acquired, developed, installed, and verified on both the test aircraft and the ground-based reference station.

Kaufmann, David N.↗

The Portable Dynamic Fundus Instrument: Uses in telemedicine and research

For years ophthalmic photographs have been used to track the progression of many ocular diseases such as macular degeneration and glaucoma as well as the ocular manifestations of diabetes, hypertension, and hypoxia. In 1987 a project was initiated at the Johnson Space Center (JSC) to develop a means of monitoring retinal vascular caliber and intracranial pressure during space flight. To conduct telemedicine during space flight operations, retinal images would require real-time transmissions from space. Film-based images would not be useful during in-flight operations. Video technology is beneficial in flight because the images may be acquired, recorded, and transmitted to the ground for rapid computer digital image processing and analysis. The computer analysis techniques developed for this project detected vessel caliber changes as small as 3 percent. In the field of telemedicine, the Portable Dynamic Fundus Instrument demonstrates the concept and utility of a small, self-contained video funduscope. It was used to record retinal images during the Gulf War and to transmit retinal images from the Space Shuttle Columbia during STS-50. There are plans to utilize this device to provide a mobile ophthalmic screening service in rural Texas. In the fall of 1993 a medical team in Boulder, Colorado, will transmit real-time images of the retina during remote consultation and diagnosis. The research applications of this device include the capability of operating in remote locations or small, confined test areas. There has been interest shown utilizing retinal imaging during high-G centrifuge tests, high-altitude chamber tests, and aircraft flight tests. A new design plan has been developed to incorporate the video instrumentation into face-mounted goggle. This design would eliminate head restraint devices, thus allowing full maneuverability to the subjects. Further development of software programs will broaden the application of the Portable Dynamic Fundus Instrument in telemedicine and medical research.

Hunter, Norwood↗

Milestones in boundary-layer transition research with infrared imaging

Since its first use in aerodynamic testing in 1967, IR imaging techniques have made distinctive contributions to two major development programs: the configurational design of the Space Shuttle, and the laminar-flow wing program of the Advanced Technologies Testing Aircraft System (ATTAS). In the case of the Space Shuttle, IR imaging was uniquely able to generate transition and heat-transfer data while retaining full control of thermal protection tile-system surface roughness. In ATTAS, much boundary layer transition data was produced with otherwise unobtainable time- and cost-efficiency.

Gartenberg, Ehud↗

Validation of the dynamic response of a blade-element UH-60 simulation model in hovering flight

The dynamic fidelity of an operational blade-element simulation model of the UH-60A helicopter is assessed for the hovering and low-speed flight regimes. Nonparametric frequency-response identification techniques and time-history comparisons are used to determine the validity of vehicle responses. Frequency-domain methods are applied to the model to isolate deficiencies and verify refinements and corrections. A dedicated flight-test program was conducted to provide data used in the analyses. Model deficiencies are also identified by using side-by-side pilot assessments of a motion-based simulation and of a test aircraft. Model refinements are found to improve fidelity significantly in the frequency range of interest to handling-qualities research. The applicability of the model to high-bandwidth flight-control research is also discussed.

Ballin, Mark G.↗

Configurable Hardware And Software For Multiple Related Uses

Control Monitor Unit (CMU) is system of configurable hardware and software undergoing development for use in controlling and monitoring complex systems of equipment. Provides comprehensive array of capabilities for such functions as processing equipment-test data for calibration and diagnosis, controlling operation of equipment in real time, simulating operation of equipment, and processing large streams of scientific-measurement data. Automates many of ground operations involved in preparing and testing spacecraft prior to launch. Also useful in variety of similar applications; for example, testing aircraft, ships, power plants, and automated production lines.

Uhrlaub, David R.↗

The Joint Damping Experiment (JDX)

The Joint Damping Experiment (JDX), flown on the Shuttle STS-69 Mission, is designed to measure the influence of gravity on the structural damping of a high precision three bay truss. Principal objectives are: (1) Measure vibration damping of a small-scale, pinjointed truss to determine how pin gaps give rise to gravity-dependent damping rates; (2) Evaluate the applicability of ground and low-g aircraft tests for predicting on-orbit behavior; and (3) Evaluate the ability of current nonlinear finite element codes to model the dynamic behavior of the truss. Damping of the truss was inferred from 'Twang' tests that involve plucking the truss structure and recording the decay of the oscillations. Results are summarized as follows. (1) Damping, rates can change by a factor of 3 to 8 through changing the truss orientation; (2) The addition of a few pinned joints to a truss structure can increase the damping by a factor as high as 30; (3) Damping is amplitude dependent; (4) As gravity induced preloads become large (truss long axis perpendicular to gravity vector) the damping is similar to non-pinjointed truss; (5) Impacting in joints drives higher modes in structure; (6) The torsion mode disappears if gravity induced preloads are low.

Folkman, Steven L.↗

Two-Dimensional Fourier Transform Applied to Helicopter Flyover Noise

A method to separate main rotor and tail rotor noise from a helicopter in flight is explored. Being the sum of two periodic signals of disproportionate, or incommensurate frequencies, helicopter noise is neither periodic nor stationary, but possibly harmonizable. The single Fourier transform divides signal energy into frequency bins of equal size. Incommensurate frequencies are therefore not adequately represented by any one chosen data block size. A two-dimensional Fourier analysis method is used to show helicopter noise as harmonizable. The two-dimensional spectral analysis method is first applied to simulated signals. This initial analysis gives an idea of the characteristics of the two-dimensional autocorrelations and spectra. Data from a helicopter flight test is analyzed in two dimensions. The test aircraft are a Boeing MD902 Explorer (no tail rotor) and a Sikorsky S-76 (4-bladed tail rotor). The results show that the main rotor and tail rotor signals can indeed be separated in the two-dimensional Fourier transform spectrum. The separation occurs along the diagonals associated with the frequencies of interest. These diagonals are individual spectra containing only information related to one particular frequency.

Santa Maria, Odilyn L.↗

Application of a Two Camera Video Imaging System to Three-Dimensional Vortex Tracking in the 80- by 120-Foot Wind Tunnel

A description is presented of two enhancements for a two-camera, video imaging system that increase the accuracy and efficiency of the system when applied to the determination of three-dimensional locations of points along a continuous line. These enhancements increase the utility of the system when extracting quantitative data from surface and off-body flow visualizations. The first enhancement utilizes epipolar geometry to resolve the stereo "correspondence" problem. This is the problem of determining, unambiguously, corresponding points in the stereo images of objects that do not have visible reference points. The second enhancement, is a method to automatically identify and trace the core of a vortex in a digital image. This is accomplished by means of an adaptive template matching algorithm. The system was used to determine the trajectory of a vortex generated by the Leading-Edge eXtension (LEX) of a full-scale F/A-18 aircraft tested in the NASA Ames 80- by 120-Foot Wind Tunnel. The system accuracy for resolving the vortex trajectories is estimated to be +/-2 inches over distance of 60 feet. Stereo images of some of the vortex trajectories are presented. The system was also used to determine the point where the LEX vortex "bursts". The vortex burst point locations are compared with those measured in small-scale tests and in flight and found to be in good agreement.

Meyn, Larry A.↗

Two-Dimensional Fourier Transform Analysis of Helicopter Flyover Noise

A method to separate main rotor and tail rotor noise from a helicopter in flight is explored. Being the sum of two periodic signals of disproportionate, or incommensurate frequencies, helicopter noise is neither periodic nor stationary. The single Fourier transform divides signal energy into frequency bins of equal size. Incommensurate frequencies are therefore not adequately represented by any one chosen data block size. A two-dimensional Fourier analysis method is used to separate main rotor and tail rotor noise. The two-dimensional spectral analysis method is first applied to simulated signals. This initial analysis gives an idea of the characteristics of the two-dimensional autocorrelations and spectra. Data from a helicopter flight test is analyzed in two dimensions. The test aircraft are a Boeing MD902 Explorer (no tail rotor) and a Sikorsky S-76 (4-bladed tail rotor). The results show that the main rotor and tail rotor signals can indeed be separated in the two-dimensional Fourier transform spectrum. The separation occurs along the diagonals associated with the frequencies of interest. These diagonals are individual spectra containing only information related to one particular frequency.

SantaMaria, Odilyn L.↗