9,919 research outputs found
Simple method for forming thin-wall pressure vessels
Application of internal hydrostatic pressure to seam-welded circular cylindrical tanks having corner-welded, flat, circular ends forms large thin-walled high quality tanks. Form limits expansion of cylindrical portion of final tank while hemispherical ends develop freely; no external form or restraint is required to fabricate spherical tanks
FLEXSTAB: A computer program for the prediction of loads and stability and control of flexible aircraft
Capabilities of the FLEXSTAB Computer Program System are described and illustrated. Aeroelastic analysis of a wide variety of aircraft configurations is performed. The aerodynamic theory used in FLEXSTAB is applicable to both steady and unsteady, subsonic and supersonic flow for multiple wing-body tail nacelle configurations with a plane of symmetry. For unsteady flow calculations, an unsteady aerodynamic theory is used which is appropriate for the low reduced frequencies associated with aircraft flight dynamics. The aircraft is modeled as either a rigid or flexible structure. The computer trims the aircraft in steady reference flight and computes both static and dynamic stability and control derivatives and the stability behavior about the trim condition. The airplane lifting pressure distribution, aerodynamic and inertia loads and deflected shape are also computed
Studies of interstellar vibrationally-excited molecules
Several molecules thus far have been detected in the ISM in vibrationally-excited states, including H2, SiO, HC3N, and CH3CN. In order for vibrational-excitation to occur, these species must be present in unusually hot and dense gas and/or where strong infrared radiation is present. In order to do a more thorough investigation of vibrational excitation in the interstellar medium (ISM), studies were done of several mm-wave transitions originating in excited vibrational modes of HCN, an abundant interstellar molecule. Vibrationally-excited HCN was recently detected toward Orion-KL and IRC+10216, using a 12 meter antenna. The J=3-2 rotational transitions were detected in the molecule's lowest vibrational state, the bending mode, which is split into two separate levels, due to l-type doubling. This bending mode lies 1025K above ground state, with an Einstein A coefficient of 3.6/s. The J=3-2 line mode of HCN, which lies 2050K above ground state, was also observed toward IRC+10216, and subsequently in Orion-KL. Further measurements of vibrationally-excited HCN were done using a 14 meter telescope, which include the observations of the (0,1,0) and (0,2,0) modes towards Orion-KL, via their J=3-2 transitions at 265-267 GHz. The spectrum of the J=3-2 line in Orion taken with the 14 meter telescope, is shown, along with a map, which indicates that emission from vibrationally-excited HCN arises from a region probably smaller than the 14 meter telescope's 20 arcsec beam
Static and dynamic stability analysis of the space shuttle vehicle-orbiter
The longitudinal static and dynamic stability of a Space Shuttle Vehicle-Orbiter (SSV Orbiter) model is analyzed using the FLEXSTAB computer program. Nonlinear effects are accounted for by application of a correction technique in the FLEXSTAB system; the technique incorporates experimental force and pressure data into the linear aerodynamic theory. A flexible Orbiter model is treated in the static stability analysis for the flight conditions of Mach number 0.9 for rectilinear flight (1 g) and for a pull-up maneuver (2.5 g) at an altitude of 15.24 km. Static stability parameters and structural deformations of the Orbiter are calculated at trim conditions for the dynamic stability analysis, and the characteristics of damping in pitch are investigated for a Mach number range of 0.3 to 1.2. The calculated results for both the static and dynamic stabilities are compared with the available experimental data
Centaur Propellant Thermal Conditioning Study
A wicking investigation revealed that passive thermal conditioning was feasible and provided considerable weight advantage over active systems using throttled vent fluid in a Centaur D-1s launch vehicle. Experimental wicking correlations were obtained using empirical revisions to the analytical flow model. Thermal subcoolers were evaluated parametrically as a function of tank pressure and NPSP. Results showed that the RL10 category I engine was the best candidate for boost pump replacement and the option showing the lowest weight penalty employed passively cooled acquisition devices, thermal subcoolers, dry ducts between burns and pumping of subcooler coolant back into the tank. A mixing correlation was identified for sizing the thermodynamic vent system mixer. Worst case mixing requirements were determined by surveying Centaur D-1T, D-1S, IUS, and space tug vehicles. Vent system sizing was based upon worst case requirements. Thermodynamic vent system/mixer weights were determined for each vehicle
Livestock herds, overgrazing and range degradation in Zimbabwe: How and why do the herds keep growing?
This paper looks at African livestock herds in Zimbabwe over the period 1890-1980. The focus is on the livestock system in the tribal areas where, under communal land use, there has been long-term concern with environmental deterioration Zimbabwe was chosen because it is one of the few African countries for which reasonably accurate historical data are available regarding African (common range) as opposed to Europen (closed range) herd development. In this paper, African owned cattle in Zimbabwe, African and European cattle holdings, African and European cattle and African smallstock African and European cattle drought, and African population, cattle and cultivation are illustrated
Hypersonic test facility Patent
Hypersonic test facility for studying ablation in models under high pressure and high temperatur
Recognition map analysis and crop acreage estimation using Skylab EREP data
There are no author-identified significant results in this report
Laboratory tests of field crop seeds as indicators of seeding value
Laboratory analysis and tests of seed samples were originally undertaken by governmental agencies in the United States and other countries to inform farmers concerning the weed seed content and plant producing capacity of seed lots. The determination of seed purity and the detection of seeds of noxious weeds have not proved difficult provided that representative samples of seed are submitted. Illustrations of weed seeds in bulletins and books, together with the use of herbarium specimens, have made it possible\u27 to identify with some degree of certainty foreign seeds found in crop seeds. Efforts to measure the plant producing capacity of seed lots have been less successful than to identify weed and crop seeds, because of (a) a lack of knowledge as to the factors affecting the viability and germination of many kinds of seeds, (b) difficulty of interpreting what constitutes normal germination and (c) inability to interpret the value of impermeable legume seeds in obtaining and maintaining field stands
Recognition map analysis and crop acreage estimation
There are no author-identified significant results in this report
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