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At least 127 records · Page 7

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NASA NTRS1991

Horizontal fields generated by return strokes

Horizontal fields generated by return strokes play an important role in the interaction of lightning generated electric fields with power lines. In many of the recent investigations on the interaction of lightning electromagnetic fields with power lines, the horizontal field was calculated by employing the expression for the tilt of the electric field of a plane wave propagating over finitely conducting earth. The method is suitable for calculating horizontal fields generated by return strokes at distances as close as 200m. At these close ranges, the use of the wavetilt expression can cause large errors.

Cooray, Vernon↗

NASA NTRS1992

Changes in monkey horizontal semicircular canal afferent responses after spaceflight

Extracellular responses from single horizontal semicircular canal afferents in two rhesus monkeys were studied after recovery from a 14-day biosatellite (Cosmos 2044) orbital spaceflight. On the 1st postflight day, the mean gain for 9 different horizontal canal afferents, tested using one or several different passive yaw rotation waveforms, was nearly twice that for 20 horizontal canal afferents similarly tested during preflight and postflight control studies. Adaptation of the afferent response to passive yaw rotation on the 1st postflight day was also greater. These results suggest that at least one component of the vestibular end organ (the semicircular canals) is transiently modified after exposure to 14 days of microgravity. It is unclear whether the changes are secondary to other effects of microgravity, such as calcium loss, or an adaptive response. If the response is adaptive, then this report is the first evidence that the response of the vestibular end organ may be modified (presumably by the central nervous system via efferent connections) after prolonged unusual vestibular stimulation. If this is the case, the sites of plasticity of vestibular responses may not be exclusively within central nervous system vestibular structures, as previously believed.

Correia, M. J.↗

NASA NTRS1957

Effect of Ground Proximity on Aerodynamic Characteristics of Two Horizontal-Attitude Jet Vertical-Take-Off-and-Landing Airplane Models

An investigation has been made to study the effect of ground proximity on the aerodynamic characteristics of two jet vertical-take-off-and-landing airplane models in which the fuselage remains in a horizontal attitude for the take-off and landing. The first model (called the tilt-wing model) had a tilting wing-engine assembly which was set at 90 degree incidence for the take-off and landing. The second model (called the deflected-jet model) had a cascade of retractable turning vanes to deflect the exhaust of the horizontally mounted Jet engines downward for vertical take-off and landing while the entire model remained in a horizontal attitude. With the models at various heights above the ground in the take-off and landing configuration, the llft, drag, and pitching moment were measured and tuft surveys were made to determine the flow field caused by the Jet exhaust. The tilt-wing model experienced a loss of lift of less than 3 percent near the ground. The deflected-Jet model, however, suffered losses in lift as high as 45 percent near the ground because of a low pressure region under the model caused by the entrainment of air by the jet exhaust as it spread out along the ground. This loss in lift for the deflected Jet configuration could probably be reduced to less than 5 percent by the use of a longer landing gear and a high wing location.

Newsom, William A , Jr↗

NASA NTRS1948

Lifting-surface-theory aspect-ratio corrections to the lift and hinge-moment parameters for full-span elevators on horizontal tail surfaces

A limited number of lifting-surface-theory solutions for wings with chordwise loadings resulting from angle of attack, parabolic-ac camber, and flap deflection are now available. These solutions were studied with the purpose of determining methods of extrapolating the results in such a way that they could be used to determine lifting-surface-theory values of the aspect-ratio corrections to the lift and hinge-moment parameters for both angle-of-attack and flap-deflection-type loading that could be used to predict the characteristics of horizontal tail surfaces from section data with sufficient accuracy for engineering purposes. Such a method was devised for horizontal tail surfaces with full-span elevators. In spite of the fact that the theory involved is rather complex, the method is simple to apply and may be applied without any knowledge of lifting-surface theory. A comparison of experimental finite-span and section value and of the estimated values of the lift and hinge-moment parameters for three horizontal tail surfaces was made to provide an experimental verification of the method suggested. (author)

Swanson, Robert S↗

NASA NTRS1923

The Pressure Distribution Over the Horizontal Tail Surfaces of an Airplane I

This work was undertaken to determine as completely as possible the distribution of pressure over the horizontal tail surfaces of an airplane, and to analyze the relation of this pressure to the structural loads and the longitudinal stability. The investigation is divided into three parts, of which this the first. The first part of the investigation is for the purpose of determining the pressure distribution over two horizontal tail surfaces in uniform free flight; the second part to conduct tests of similar tail planes in the wind tunnel; and the third part to determine the pressure distribution on the horizontal tail surfaces during accelerated flight on the full-size airplane.

Norton, F H↗

NASA NTRS1952

Experimental Determination of the Effect of Horizontal-Tail Size, Tail Length, and Vertical Location on Low-Speed Static Longitudinal Stability and Damping Pitch of a Model Having 45 Degree Sweptback Wing and Tail Surfaces

Report presents the results of an investigation conducted in the Langley stability tunnel to determine the effects of horizontal tails of various sizes and at various tail lengths (when loaded on the fuselage center line) and also the effects of vertical location of the horizontal tail relative to the wing on the low-speed static longitudinal stability and on the steady-state rotary damping in pitch for a complete-model configuration. The wing and tail surfaces had the quarter-chord lines swept back 45 degrees and had aspect ratios of 4. The results of the investigation showed that, in agreement with analytical considerations, the contribution of the horizontal tail to static longitudinal stability was related directly to the tail size and length; whereas, its contribution to damping in pitch was related directly to tail size and the square of tail length.

Lichtenstein, Jacob H↗

NASA NTRS1947

Stability and control characteristics of an airplane model having a 45.1 degree swept-back wing with aspect ratio 2.50 and taper ratio 0.42 and a 42.8 degree swept-back horizontal tail with aspect ratio 3.87 and taper ratio 0.49

Tests were made of an airplane model having a 45.1 degree swept-back wing with aspect ratio 2.50 and taper ratio 0.42 and a 42.8 degree swept-back horizontal tail with aspect ratio 3.87 and taper ratio 0.49 to determine its low-speed stability and control characteristics. The test Reynolds number was 2.87 x 10(6) based on a mean aerodynamic chord of 2.47 feet except for some of the aileron tests which were made at a Reynolds number of 2.05 x 10(6). With the horizontal tail located near the fuselage juncture on the vertical tail, model results indicated static longitudinal instability above a lift coefficient that was 0.15 below the lift coefficient at which stall occurred. Static longitudinal stability, however, was manifested throughout the life range with the horizontal tail located near the top of the vertical tail. The use of 10 degrees negative dihedral on the wing had little effect on the static longitudinal stability characteristics. Preliminary tests of the complete model revealed an undesirable flat spot in the yawing-moment curves at low angles of attack, the directional stability being neutral for yaw angles of plus-or-minus 2 degrees. This undesirable characteristic was improved by replacing the thick original vertical tail with a thin vertical tail and by flattening the top of the dorsal fairing.

Schuldenfrei, Marvin↗

NASA NTRS1994

Formation of fold and thrust belts on Venus due to horizontal shortening of a laterally heterogeneous lithosphere

An outstanding question relevant to understanding the tectonics of Venus is the mechanism of formation of fold and thrust belts, such as the mountain belts that surround Lakshmi Planum in western Ishtar Terra. These structures are typically long (hundreds of km) and narrow (many tens of km), and are often located at the margins of relatively high (km-scale) topographic rises. Previous studies have attempted to explain fold and thrust belts in various areas of Venus in the context of viscous and brittle wedge theory. However, while wedge theory can explain the change in elevation from the rise to the adjacent lowland, it fails to account for a fundamental aspect of the deformation, i.e., the topographic high at the edge of the rise. In this study we quantitatively explore the hypothesis that fold and thrust belt morphology on Venus can alternatively be explained by horizontal shortening of a lithosphere that is laterally heterogeneous, due either to a change in thickness of the lithosphere or the crust. Lateral heterogeneities in lithosphere structure may arise in response to thermal thinning or extensive faulting, while variations in crustal thickness may arise due to either spatially variable melting of mantle material or by horizontal shortening of the crust. In a variable thickness lithosphere or crust that is horizontally shortened, deformation will tend to localize in the vicinity of thickness heterogeneity, resulting in a higher component of dynamic topography there as compared to elsewhere in the shortening lithosphere. This mechanism may thus provide a simple explanation for the topographic high at the edge of the rise.

Zuber, M. T.↗

NASA NTRS1994

The time-delay spectrum of GX 5-1 in its horizontal branch

Using a cross-spectral technique we investigate time delays between intensity variations of GX 5-1 in 10 X-ray spectral channels. The data were taken during a 1989 Ginga observation during which the source was in its horizontal-branch spectral state. We develope a new method to measure 'time-delay spectra' in fixed Fourier frequency ranges and use it to determine the energy and intensity dependence of time delays in the low-frequency noise (nu less than 2 Hz), the horizontal branch quasi-periodic oscillations (QPO), and the QPO second harmonic. These are the first time-delay spectra of a Z-source in its horizontal branch, and the first detection of time delays in the second harmonic. We consider two mechanisms for the production of the time lags: Comptonization and evolving shots. We perform Monte Carlo simulations of Compton scattering in a homogeneous, isotropic, central corona and show that it qualitatively explain the observed energy and time-delay spectra, but that it cannot explain the differences in the QPO first and second harmomnic time-delay spectra, nor the observed dependence of the QPO fractional rms variability upon energy. We consider implications of our results for millisecond pulsar searches in low-mass X-ray binaries.

Vaughan, B.↗

NASA NTRS1999

Instrumentation and Methods to Measure Dynamic Forces During Exercise Using the Horizontal Exercise Machine

It is hypothesized that bone loss experienced by astronauts in zero gravity conditions may be curtailed by appropriate exercise. According to Wolf's law, bone regenerates when muscles produce stresses by pulling on the bone during daily activity and/or exercise on Earth. To use this theory to prevent or decrease bone loss, one needs to quantify musculoskeletal loads and relate them to bone density changes. In the context of the space program, it is desirable to determine musculoskeletal loads during exercise so that one may make similar measurements on Earth and in space. In this manner, load measurements on Earth may be used as reference to generate similar loads during exercise in space. A research project to investigate the effects of high-resistive exercise to decrease bone density loss underzero-gravity conditions is being carried out in Life Sciences Research Laboratories at NASA JSC. The project consists of a bed-rest study whereby subjects remain in horizontal position for seventeen weeks. During the study, a subset of those subjects executes a regime of resistive exercises in the horizontal exercise machine (HEM). The HEM was designed so that subjects remain horizontal while exercising to minimize gravity loading even during exercise. Bone density of each subject is measured throughout the duration of their participation. The objective of the study is to determine if the resistive exercises are effective in diminishing or eliminating bone loss. My participation in this project relates to instrumentation, measurement, and processing of signals from displacement sensors (optical encoders) and load-cells. Measurement of displacements will be used to determine the motion of the body during exercise, and load measurements will be used (along with displacement data) to determine forces and torques exerted on each section of the body during exercise. Further, I have assisted in specifying new sensors to be added to the HEM and to a new prototype resistive exercise machine called the Interim Resistive Exercise Device (IRED). New load cells and encoders should be mounted in these devices to obtain more complete kineto-dynamic information. This report includes a description of the instrumentation that was built to perform measurements in the HEM and the IRED, along with the software that was developed to collect the measurements. It also includes examples of measurements taken in the HEM. Finally, a plan is laid out that describes how these measurements may be used to determine forces exerted by muscles for each exercise.

Figueroa, Fernando↗

NASA NTRS1998

A Simple Model of Cirrus Horizontal Inhomogeneity and Cloud Fraction

A simple model of horizontal inhomogeneity and cloud fraction in cirrus clouds has been formulated on the basis that all internal horizontal inhomogeneity in the ice mixing ratio is due to variations in the cloud depth, which are assumed to be Gaussian. The use of such a model was justified by the observed relationship between the normalized variability of the ice water mixing ratio (and extinction) and the normalized variability of cloud depth. Using radar cloud depth data as input, the model reproduced well the in-cloud ice water mixing ratio histograms obtained from horizontal runs during the FIRE2 cirrus campaign. For totally overcast cases the histograms were almost Gaussian, but changed as cloud fraction decreased to exponential distributions which peaked at the lowest nonzero ice value for cloud fractions below 90%. Cloud fractions predicted by the model were always within 28% of the observed value. The predicted average ice water mixing ratios were within 34% of the observed values. This model could be used in a GCM to produce the ice mixing ratio probability distribution function and to estimate cloud fraction. It only requires basic meteorological parameters, the depth of the saturated layer and the standard deviation of cloud depth as input.

Smith, Samantha A.↗

NASA NTRS1999

Horizontal Wavenumber Spectra of Winds, Temperature and Trace Gases During the Pacific Exploratory Missions: Gravity Waves, Quasi-Two-Dimensional Turbulence, and Vortical Modes - 2

We examine the horizontal wavenumber spectra of horizontal velocity and potential temperature collected by aircraft above the Pacific Ocean to determine whether gravity waves, quasi-two-dimensional (Q-2-D) turbulence, or vortical modes dominate atmospheric fluctuations at scale sizes of 1-100 km and altitudes of 2-12 km. We conclude from the study of Doppler-shifting effects that Q-2-D turbulence and/or vortical modes are more prevalent than gravity waves over the ocean, except in the equatorial zone. The results are consistent with recent numerical simulations of Q-2-D turbulence, which show that the characteristic inverse cascade of energy is greatly facilitated by the presence of background rotation. Furthermore, a Stokes-parameter analysis reveals the general paucity of coherent wavelike motions, although specific cases of gravity-wave propagation are observed. Finally, a case study of a long flight segment displays a k(sup -3) horizontal velocity variance spectrum at scales longer than about 100 km. A Stokes-parameter analysis indicates that these large-scale fluctuations were likely due to vortical modes rather than inertio-gravity waves.

Cho, John Y. N.↗

NASA NTRS2001

The Variability of the Horizontal Circulation in the Troposphere and Stratosphere: A Comparison

The variability of the horizontal circulation in the stratosphere and troposphere of the Northern Hemisphere (NH) is compared by using various approaches. Spatial degrees of freedom (dof) on different time scales were derived. Modes of variability were computed in geopotential height fields at the tropospheric and stratospheric pressure levels by applying multivariate statistical approaches. Features of the spatial and temporal variability of the winterly zonal wind were studied with the help of recurrence and persistence analyses. The geopotential height and zonally-averaged zonal wind at the 50-, 500- and 1000-hPa level are used to investigate the behavior of the horizontal circulation in the lower stratosphere, mid-troposphere and at the near surface level, respectively. It is illustrated that the features of the variability of the horizontal circulation are very similar in the mid-troposphere and at the near surface level. Due to the filtering of tropospheric disturbances by the stratospheric and upper tropospheric zonal mean flow, the variability of the stratospheric circulation exhibits less spatial complexity than the circulation at tropospheric pressure levels. There exist enormous differences in the number of degrees of freedom (or free variability modes) between both atmospheric layers. Results of the analyses clearly show that the concept of a zonally symmetric AO with a simple structure in the troposphere similar to the one in the stratosphere is not valid. It is concluded that the spatially filtered climate change signal can be detected earlier in the stratosphere than in the mid-troposphere or at the near surface level.

Perlwitz, Judith↗

NASA NTRS1960

Effect of Ground Proximity on Aerodynamic Characteristics of Two Horizontal-Attitude Jet Vertical-Take-Off-and-Landing Airplane Models

An investigation has been made to study the effect of ground proximity on the aerodynamic characteristics of two jet vertical-take-off-and-landing airplane models in which the fuselage remains in a horizontal attitude for the take-off and landing. The first model (called the tilt-wing model) had a tilting wing-engine assembly which was set at 90 deg incidence for the take-off and landing. The second model, called the deflected-jet model) had a cascade of retractable turning vanes to deflect the exhaust of the horizontally mounted jet engines downward for vertical take-off and landing while the entire model remained in a horizontal attitude. With the models at various heights above the ground in the take-off and landing configuration, the lift, drag, and pitching moment were measured and tuft surveys were made to determine the flow field caused by the jet exhaust. The tilt-wing model experienced a loss of lift of less than 3 percent near the ground. The deflected-jet model, however, suffered losses in lift as high as 45 percent near the ground because of a low pressure region under the model caused by the entrainment of air by the jet exhaust as it spread out along the ground. This loss in lift for the deflected-jet configuration could probably be reduced to less than 5 percent by the use of a longer landing gear and a high wing location.

Newsom, William A., Jr.↗

NASA NTRS2004

Note on the Effect of Horizontal Gradients for Nadir-Viewing Microwave and Infrared Sounders

Passive microwave and infrared nadir sounders such as the Advanced Microwave Sounding Unit A (AMSU-A) and the Atmospheric InfraRed Sounder (AIRS), both flying on NASA s EOS Aqua satellite, provide information about vertical temperature and humidity structure that is used in data assimilation systems for numerical weather prediction and climate applications. These instruments scan cross track so that at the satellite swath edges, the satellite zenith angles can reach approx. 60 deg. The emission path through the atmosphere as observed by the satellite is therefore slanted with respect to the satellite footprint s zenith. Although radiative transfer codes currently in use at operational centers use the appropriate satellite zenith angle to compute brightness temperature, the input atmospheric fields are those from the vertical profile above the center of the satellite footprint. If horizontal gradients are present in the atmospheric fields, the use of a vertical atmospheric profile may produce an error. This note attempts to quantify the effects of horizontal gradients on AIRS and AMSU-A channels by computing brightness temperatures with accurate slanted atmospheric profiles. We use slanted temperature, water vapor, and ozone fields from data assimilation systems. We compare the calculated slanted and vertical brightness temperatures with AIRS and AMSU-A observations. We show that the effects of horizontal gradients on these sounders are generally small and below instrument noise. However, there are cases where the effects are greater than the instrument noise and may produce erroneous increments in an assimilation system. The majority of the affected channels have weighting functions that peak in the upper troposphere (water vapor sensitive channels) and above (temperature sensitive channels) and are unlikely t o significantly impact tropospheric numerical weather prediction. However, the errors could be significant for other applications such as stratospheric analysis. Gradients in ozone and tropospheric temperature appear to be well captured by the analyses. In contrast, gradients in upper stratospheric and mesospheric temperature as well as upper tropospheric humidity are less well captured. This is likely due in part to a lack of data to specify these fields accurately in the analyses. Advanced new sounders, like AIRS, may help to better specify these fields in the future.

Joiner, J.↗

NASA NTRS1946

Wind-Tunnel Investigation of the Horizontal Motion of a Wing Near the Ground

By the method of images the horizontal steady motion of a wing at small heights above the ground was investigated in the wind tunnel, A rectangular wing with Clark Y-H profile was tested with and without flaps. The distance from the trailing edge of the wing to the ground was varied within the limits 0.75 less than or = s/c less than or = 0.25. Measurements were made of the lift, the drag, the pitching moment, and the pressure distribution at one section. For a wing without flaps and one with flaps a considereble decrease in the lift force and a,drop in the drag was obtained at angles of attack below stalling. The flow separation near the ground occurs at smaller angles of attack than is the case for a great height above the ground. At horizontal steady flight for practical values of the height above the ground the maximum lift coefficient for the wing without flaps changes little, but markedly decreases for the wing with flaps. Analysis of these phenomena involves the investigation of the pressure distribution. The pressure distribution curves showed that the changes occurring near the ground are not equivalent to a change in the angle of attack. At the lower surface of the section a very strong increase in the pressures is observed. The pressure changes on the upper surface at angles of attack below stalling are insignificant and lead mainly to an increase in the unfavorable pressure gradient, resulting in the earlier occurrence of separation. For a wing with flaps at large angles of attack for distances from the trailing edge of the flap to the ground less than 0.5 chord, the flow between the wing end the ground is retarded so greatly that the pressure coefficient at the lower surface of the section is very near its limiting value (P = 1), and any further possibility of increase in the pressure is very small. In the application an approximate computation procedure is given of the change of certain aerodynamic characteristics for horizontal steady flight near the ground.

Serebrisky, Y. M.↗

NASA NTRS1945

Wind-Tunnel Tests of a 1/6-Scale Model of Republic XF-12 Vertical Tail with Stub Fuselage and Stub Horizontal Tail

A 1/6-scale model of the Republic XF-12 vertical tail with stub fuselage and stub horizontal tail was tested in the Langley stability tunnel to determine the aerodynamic characteristics of the model, The investigation included a study of the effects of boundarylayer thickness, rudder area, and cover-plate alinement on the aerodynamic characteristics. Tuft studies were made in the vicinity of the junction of the vertical and stub horizontal tails. The results of the investigation indicated that the flow in the vicinity of the junction of the vertical and stub horizontal tails was only slightly improved by the addition of a fillet. An increase in boundary-layer thickness produced a slight decrease in rudder effectiveness. The increase in lift of the combined rudders over that of the upper rudder alone was not proportional at low deflections and was approximately proportional at high deflections to the increase in rudder area. When the balance-chamber cover plates were bowed out, the change in rudder hinge moment with rudder angle was less negative. The variation of the lift coefficient with angle of attack and the variation, at small values of angle of attack, of rudder hinge-noment coefficient with angle of attack was approximately the same for all model configurations tested. The upper rudder used in conjunction with a tab was found to satisfy the Army specifications regarding asymmetric power on a multiengine airplane.

MacLachlan, Robert↗

NASA NTRS2005

Collection Efficiency and Ice Accretion Characteristics of Two Full Scale and One 1/4 Scale Business Jet Horizontal Tails

Collection efficiency and ice accretion calculations have been made for a series of business jet horizontal tail configurations using a three-dimensional panel code, an adaptive grid code, and the NASA Glenn LEWICE3D grid based ice accretion code. The horizontal tail models included two full scale wing tips and a 25 percent scale model. Flow solutions for the horizontal tails were generated using the PMARC panel code. Grids used in the ice accretion calculations were generated using the adaptive grid code ICEGRID. The LEWICE3D grid based ice accretion program was used to calculate impingement efficiency and ice shapes. Ice shapes typifying rime and mixed icing conditions were generated for a 30 minute hold condition. All calculations were performed on an SGI Octane computer. The results have been compared to experimental flow and impingement data. In general, the calculated flow and collection efficiencies compared well with experiment, and the ice shapes appeared representative of the rime and mixed icing conditions for which they were calculated.

Bidwell, Colin S.↗