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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Practical aspects of on-orbit modal identification using free-decay data

This paper discusses practical aspects of performing on-orbit modal identification using time domain analysis of free-decay data. The effects of environmental constraints, structural characteristics, excitation, and sensing are reviewed. In a recent laboratory application, an on-orbit experiment is simulated using a limited number of excitation and measurement points. The identified modal parameters correlate well, though not uniquely, with those obtained in a complete modal survey. Practical difficulties in performing the correlation are illustrated.

Schenk, Axel↗
NASA NTRS1992

Star trackers, star catalogs, and attitude determination - Probabilistic aspects of system design

Optimizing spacecraft attitude determination systems that use onboard star trackers requires analysis and evaluation of some probabilistic aspects of system design. This paper discusses methods of constructing or compiling optimum star catalogs, which are defined as uniform distributions on a sphere. Both local and global measures of uniformity on a sphere are defined. Application of these methods and measures to a specific problem is also discussed. In addition, Poisson models of star tracker acquisition probabilities are formulated to provide a useful analytical basis for designing and optimizing attitude determination systems. These analytical models and methods lead to rapid and realistic quantitative results, and should therefore facilitate making system performance trades. Use of such methods should also reduce the need for performing tedious computer simulations to obtain analogous results.

Vedder, John D.↗
NASA NTRS1993

Some aspects of the interaction between chemical and dynamic processes relating to the Antarctic ozone hole

Observational and modeling studies have been conducted to examine the interaction between the chemical and dynamical processes that occur during springtime in the lower stratosphere of the Southern Hemisphere. The temporal evolution of the ozone distribution and the circulation during 1987 is contrasted with that for 1988 as an illustrative example of how dynamical processes and the resulting meteorological conditions modulate the ozone depletion. Concurrently with the observational analysis, an effort was initiated to simulate the ozone depletion during austral spring using a 3D chemical/transport model. The model includes a parameterized representation of the heterogeneous processes thought to be important in this region. The simulation indicates that the inclusion of this additional chemistry, which results in the release of free chlorine and the redistribution of odd nitrogen into reservoir species, reproduces many aspects of the observations.

Eckman, R. S.↗
NASA NTRS1956

The Interference Effects of a Body on the Spanwise Load Distributions of Two 45 Degree Sweptback Wings of Aspect Ratio 8.02 from Low-Speed Tests

Tests of two wing-body combinations have been conducted in the Langley 19-foot pressure tunnel at a Reynolds number of 4 x 10(exp 6) and a Mach number of 0.19 to determine the effects of the bodies on the wing span load distributions. The wings had 45 degrees sweepback of the quarter-chord line, aspect ratio 8.02, taper ratio 0.45, and incorporated 12-percent-thick airfoil sections streamwise. One wing was untwisted and uncambered whereas the second wing incorporated both twist and camber. Identical bodies of revolution, of 10:1 fineness ratio, having diameter-to-span ratios of 0.10, were mounted in mid-high-wing arrangements. The effects of wind incidence, wing fences, and flap deflection were determined for the plane uncambered wing. The addition of the body to the plane wing increased the exposed wing loading at a given lift coefficient as much as 10 percent with the body at 0 degrees incidence and 4 percent at 4 degrees incidence. The bending-moment coefficients at the wing-body juncture were increased about 2 percent with the body at 0 degrees incidence, whereas the increases were as much as 10 percent with the body at 4 degrees incidence. The spanwise load distributions due to the body on the plane wing as calculated by using a swept-wing method employing 19 spanwise lifting elements and control points generally showed satisfactory agreement with experiment. The spanwise load distributions due to body on the flapped plane wing and on the twisted and cambered wing were dissimilar to those obtained on the plane wing. Neither of the methods of calculation which were employed yielded distributions that agreed consistently with experiment for either the flapped plane wing or the twisted and cambered wing.

Martina, Albert P.↗
NASA NTRS1991

Practical aspects of on-orbit modal identification using free-decay data

Future large space structures such as Space Station Freedom can be tested as a total structure on Earth. Size, zero g design, and the existing atmosphere conflict with traditional structural dynamic testing. On-orbit modal identification will become necessary. Practical aspects of performing such tests using time domain analysis of free decay data are discussed. The effects of environmental constraints, structural characteristics, and excitation and sensing are reviewed. A recent laboratory application and sensing are reviewed. In this test, an on-orbit experiment is simulated using free decay data and a limited number of excitation and measurement points. The test article is dynamically similar to the truss/solar arrays of Space Station. The identified modal parameters from this simulation correlate well, though not uniquely, with those obtained in a complete modal survey. Practical difficulties in performing the correlation are illustrated. Model parameters are identified with the Eigensystem Realization Algorithm.

Schenk, Axel↗
NASA NTRS1993

Operational and research aspects of a radio-controlled model flight test program

The operational and research aspects of a subscale, radio-controlled model flight test program are presented. By using low-cost free-flying models, an approach was developed for obtaining research-quality vehicle performance and aerodynamic information. The advantages and limitations learned by applying this approach to a specific flight test program are described. The research quality of the data acquired shows that model flight testing is practical for obtaining consistent and repeatable flight data.

Budd, Gerald D.↗
NASA NTRS1993

Practical aspects of transfer from GTO to lunar orbit

This paper is a presentation of some practical aspects of orbital transfer from Geosynchronous Transfer Orbit (GTO) to close, near-circular orbits of the Moon. The intent is to identify the important parameters affecting the problem and to bound (approximately) the range of required delta V for a spacecraft that has been placed in GTO. The basic geometric relationships are described and the dynamics are simulated by use of the Zero-Sphere-of Influence Patched Conic method. It is found that the inclination of the transfer orbit to the Earth-Moon plane is relatively unimportant while the position of the line of apsides with respect to the Moon's orbit is the main geometric parameter of interest. It is shown that this parameter can be controlled by selecting the time of day for launch and that two launch windows of approximately 45 minutes duration are available each day of the year if use is made of the recommended phasing orbit transfer. The phasing orbit transfer not only provides twice-daily launch windows, but also provides a mechanism for efficacious correction of GTO injection errors. Delta V penalties for out-of-plane transfer and for late launch are evaluated and the method is recommended for use as an affordable means of achieving lunar orbit.

Uphoff, Chauncey↗
NASA NTRS1992

The Fifth Symposium on Numerical and Physical Aspects of Aerodynamic Flows

This volume contains the papers presented at the Fifth Symposium on Numerical and Physical Aspects of Aerodynamic Flows, held at the California State University, Long Beach, from 13 to 15 January 1992. The symposium, like its immediate predecessors, considers the calculation of flows of relevance to aircraft, ships, and missiles with emphasis on the solution of two-dimensional unsteady and three-dimensional equations.

Source record↗
NASA NTRS1990

High-Reynolds-Number Test of a 5-Percent-Thick Low-Aspect-Ratio Semispan Wing in the Langley 0.3-Meter Transonic Cryogenic Tunnel: Wing Pressure Distributions

A high Reynolds number test of a 5 percent thick low aspect ratio semispan wing was conducted in the adaptive wall test section of the Langley 0.3 m Transonic Cryogenic Tunnel. The model tested had a planform and a NACA 64A-105 airfoil section that is similar to that of the pressure instrumented canard on the X-29 experimental aircraft. Chordwise pressure data for Mach numbers of 0.3, 0.7, and 0.9 were measured for an angle-of-attack range of -4 to 15 deg. The associated Reynolds numbers, based on the geometric mean chord, encompass most of the flight regime of the canard. This test was a free transition investigation. A summary of the wing pressures are presented without analysis as well as adapted test section top and bottom wall pressure signatures. However, the presented graphical data indicate Reynolds number dependent complex leading edge separation phenomena. This data set supplements the existing high Reynolds number database and are useful for computational codes comparison.

Chu, Julio↗
NASA NTRS1993

Operational and research aspects of a radio-controlled model flight test program

The operational and research aspects of a subscale, radio-controlled model flight test program are presented. By using low-cost free-flying models, an approach was developed for obtaining research-quality vehicle performance and aerodynamic information. The advantages and limitations learned by applying this approach to a specific flight test program are described. The research quality of the data acquired shows that model flight testing is practical for obtaining consistent repeatable flight data.

Budd, Gerald D.↗
NASA NTRS1991

Design aspects and comparison between high Tc superconducting coplanar waveguide and microstrip line

The high T sub c superconducting microstrip line and coplanar waveguide are compared in terms of the loss characteristics and the design aspects. The quality factor Q values for each structure are compared in respect to the same characteristic impedance with the comparable dimensions of the center conductor of the coplanar waveguide and the strip of the microstrip line. Also, the advantages and disadvantages for each structure are discussed in respect to passive microwave circuit applications.

Kong, K. S.↗
NASA NTRS1993

Computational study of a conical wing having unit aspect ratio at supersonic speeds

A study was conducted to identify and assess a computational method as a preliminary analysis and design tool for advanced military aircraft designs. The method of choice for this study was the Euler Marching Technique for Accurate Computation (EMTAC). Computational and experimental results were compared for a thick unit aspect ratio delta wing at Mach 2.8 and 4.0. This geometry along with the associated flow physics is representative of advanced aircraft designs. The comparisons of the lift and drag coefficients show that the computations agree with experimentally obtained data at Mach 2.8 and 4.0. Further, comparison between EMTAC and experiment shows that the computations accurately predict the overall shape and levels of the surface pressure distributions at Mach 2.8 and 4.0. Qualitative assessment of the computed flow-field properties shows that EMTAC captures the basic flow-field characteristics representative of advanced aircraft designs. The study further suggests that EMTAC can be successfully used in the preliminary analysis and design of advanced military aircraft.

Mcgrath, Brian E.↗
NASA NTRS1993

Numerical simulation and physical aspects of supersonic vortex breakdown

Existing numerical simulations and physical aspects of subsonic and supersonic vortex-breakdown modes are reviewed. The solution to the problem of supersonic vortex breakdown is emphasized in this paper and carried out with the full Navier-Stokes equations for compressible flows. Numerical simulations of vortex-breakdown modes are presented in bounded and unbounded domains. The effects of different types of downstream-exit boundary conditions are studied and discussed.

Liu, C. H.↗
NASA NTRS1928

Corrosion Embrittlement of Duralumin I Practical Aspects of the Problem

Since aircraft design is tending toward all-metal construction, the strong heat-treatable light aluminum alloy, duralumin (a generic name for a class of heat-treatable alloys containing Cu, Mg, Mn, and Si), is finding increasing application. Doubt has been expressed concerning the reliability and permanence of these materials. Information is given on the effect of corrosion on the tensile properties of 14-gauge sheet duralumin, heat treated by quenching in hot water after being heated for 15 minutes in a fused nitrate bath at 500 to 510 C. Intercrystalline corrosion and practical aspects of intercrystalline embrittlement are discussed with respect to duralumin.

Rawdon, Henry S↗
NASA NTRS1933

Aerodynamic tests of a low aspect ratio tapered wing with various flaps, for use on tailless airplanes

Wind tunnel tests were made of a model wing having an aspect ratio of 3 and a tapered plan form with a straight trailing edge. The model had the Clark Y airfoil section throughout it's entire span and had no washout, depending on a trailing-edge flap for longitudinal balance and control. The flap had a constant chord and was divided into four equal portions along the span. The tests were made with the entire flap deflected to obtain longitudinal control and balance, and also with the inner portions deflected alone, and with the outer portions deflected alone. It was found that the simple wing with no washout or change of basic section along the span has aerodynamic characteristics well suited for use on tailless airplanes. A higher lift coefficient was obtained with the full-span flap deflected as a unit to give longitudinal balance than was obtained with either the inner or the outer portions of the flap deflected.

Weick, Fred E↗
NASA NTRS1951

Effect of Taper Ratio on the Low-speed Rolling Stability Derivatives of Swept and Unswept Wings of Aspect Ratio 2.61

Results of tests conducted in the 6-foot-diameter rolling-flow test section of the Langley stability tunnel to determine the effects of varying taper ratio on the rolling and static stability characteristics of a swept wing are presented; results are also given for the effects of varying taper ratio on an unswept wing and for the effects of sweep on a tapered wing. All the models were of aspect ratio 2.61 and had NACA 0012 sections normal to the quarter-chord line. Taper ratios of 1.00, 0.50, and 0.25 and sweep angles of 0 degrees and 45 degrees were investigated.

WINGS, COMPLETE - SWEEP↗
NASA NTRS1954

Some Aspects of the Helicopter Noise Problem

Some aspects of the helicopter noise problem are briefly discussed. These discussions deal with the nature of the problem, some tentative criteria for use in evaluating it, and the physical characteristics of noise from helicopters. Overall noise data are presented for a reciprocating-engine helicopter along with discussions of the characteristics of noise from its various components such as the engine, gearing, and rotors. Some consideration is also given to the noise from tip jet rotor systems

Harvey H Hubbard↗
NASA NTRS1957

Investigation at Low Speeds of Deflectors and Spoilers as Gust Alleviators on a Model of the Bell X-5 Airplane with 35 Degree Swept Wings and on a High-aspect-ratio 35 Degree Swept-wing-fuselage Model

Results of an investigation at low speeds to determine the gust-alleviation capabilities (reduction in lift-curve slope) of spoilers and deflectors on a 35 degree swept-wing model of high aspect ratio and on a 1/4-scale model of the X-5 airplane with 35 degree swept wings indicate that deflector and spoiler-deflector types of controls can be designed to provide considerable gust alleviation for a swept-wing airplane while still maintaining stability and control.

CONTROLS, SPOILER - COMPLETE WINGS↗