3,508 research outputs found

    A piloted simulator investigation of stability and control, display and crew-loading requirements for helicopter instrument approach. Part 2: Supporting data

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    Pilot rating comments and standard deviation measures of flight performance and control use are presented

    A ground-simulator investigation of helicopter longitudinal flying qualities for instrument approach

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    A ground-simulation experiment was conducted to investigate the direct and interactive influences of several longitudinal static and dynamic stability parameters on helicopter flying qualities during terminal-area operations in instrument conditions. Variations that were examined included five levels of static control-position gradients ranging from stable to unstable; two levels of dynamic stability for the long-period oscillation; two levels of the steady-state pitch speed gradient; two levels of angle-of-attack stability and pitch-rate damping; and two levels of stability and control augmentation. These variations were examined initially in calm air and thin in simulated light-to-moderate turbulence and wind shear. Five pilots performed a total of 223 evaluations of these parameters for a representative microwave landing system precision approach task conducted in a dual-pilot crew-loading situation

    A piloted simulator investigation of stability and control, display and crew-loading requirements for helicopter instrument approach. Part 1: Technical discussion and results

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    A ground-simulation experiment was conducted to investigate the influence and interaction of flight-control system, fight-director display, and crew-loading situation on helicopter flying qualities during terminal area operations in instrument conditions. The experiment was conducted on the Flight Simulator for Advanced Aircraft at Ames Research Center. Six levels of control complexity, ranging from angular rate damping to velocity augmented longitudinal and vertical axes, were implemented on a representative helicopter model. The six levels of augmentation were examined with display variations consisting of raw elevation and azimuth data only, and of raw data plus one-, two-, and three-cue flight directors. Crew-loading situations simulated for the control-display combinations were dual-pilot operation (representative auxiliary tasks of navigation, communications, and decision-making). Four pilots performed a total of 150 evaluations of combinations of these parameters for a representative microwave landing system (MLS) approach task

    Results of NASA/FAA ground and flight simulation experiments concerning helicopter IFR airworthiness criteria

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    A sequence of ground and flight simulation experiments was conducted to investigate helicopter instrument-flight-rules airworthiness criteria. The first six of these experiments and major results are summarized. Five of the experiments were conducted on large-amplitude motion base simulators. The NASA-Army V/STOLAND UH-1H variable-stability helicopter was used in the flight experiment. Artificial stability and control augmentation, longitudinal and lateral control, and in pitch and roll attitude augmentation were investigated

    Mechanisms of fast-ice development in the south-eastern Laptev Sea: a case study for winter of 2007/08 and 2009/10

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    Accurate representation of fast ice in numerical models is important for realistic simulation of numerous sea-ice and ocean variables. In order to simulate seasonal and interannual variability of fast-ice extent, the mechanisms controlling fast-ice development need to be thoroughly understood. The objective of this paper is to investigate mechanisms contributing to the advance of fast-ice edge to its winter location in the south-eastern Laptev Sea. The study is based on time series of synthetic aperture radar (SAR) imagery for winter 2007/08 and 2009/10. A detailed examination of SAR-based ice drift showed that several grounded ice features are formed offshore prior to fast-ice expansion. These features play a key role in offshore advance of the fast-ice edge and serve as stabilizing points for surrounding pack ice as it becomes landfast. Electromagnetic ice thickness measurements suggest that the grounded ice ridges over water depths of ca. 20 m water might be responsible for interannual variations in fast-ice edge position. Contrary to previous studies, we conclude that grounding is a key mechanism of fast-ice development in the south-eastern Laptev Sea

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    Paleotethys was a highly mobile oceanic realm pinching into the supercontinent Pangea between Gondwana and Eurasia in the late Paleozoic/early Mesozoic. Published Paleotethyan reconstructions reveal that the time of Paleotethys closure and the position of its suture are highly debated. We present new magmatic and detrital zircon ages, separated from pre-Alpine basement and Permian to Triassic cover rocks exposed in the External Hellenides of Crete. These age data reveal Variscan and Cimmerian docking of microplates along the southern margin of Laurasia and help to constrain the time of Paleotethys closure.46% of detrital zircons from quartzite in the Variscan basement, are Pennsylvanian with concordant ages at 321. ±. 2. Ma, 310. ±. 3. Ma, and 300. ±. 3. Ma. The basement is unconformably overlain by arc-related volcanics of the Tyros Unit, magmatic zircons of which yielded a concordant U-Pb zircon age at 285. ±. 2. Ma. Thus, the metasediments of the basement, interpreted as former trench sediments, were deposited, metamorphosed and exhumed in latest Carboniferous to early Permian times (302-283. Ma). Magmatic activity during this late Variscan phase is also indicated by igneous boulders within Olenekian (meta)conglomerates of the Tyros Unit, which yielded concordant U-Pb zircon ages at 291. ±. 2 and 310. ±. 2. Ma. The late Variscan orogenic phase is attributed to the collision of the Gondwana-derived southern Minoan terrane (SMT) with Laurasia subsequent to northward subduction of Paleotethys lithosphere and Viséan collision of the northern Minoan terrane (NMT).Magmatic activity ceased during the late Permian, but revived in the Lower Triassic as is indicated by felsic volcanics (249. ±. 2. Ma, concordant U-Pb zircon) and by detrital zircons (242. ±. 3, 240. ±. 5. Ma, 237. ±. 3. Ma concordant U-Pb zircon) of the Tyros Unit. At the same time the Variscan chain was exhumed and removed as is shown by the detritus in the Lower to Middle Triassic Tyros sediments, which includes high-grade metamorphic rocks and detrital zircons with U-Pb ages ranging from 280 to 335. Ma.A significant change in the detrital components occurred in the Ladinian when the Variscan basement with its Permo-Triassic cover was thrust on top of clastic sediments, today represented by the Phyllite-Quartzite Unit s.str. The Phyllite-Quartzite Unit s.str. shows Cadomian and older - but no Variscan - detritus because of its position along the northern margin of the Cimmerian ribbon continent. Thus, in the eastern Mediterranean, Paleotethys was closed during the Ladinian and the related suture in the External Hellenides is situated between the Variscan basement (active margin in the north) and the Phyllite-Quartzite Unit s.str (passive margin in the south). Carnian crustal extension led to subsidence of the Variscan/Cimmerian chain, most parts of which merged below sea level. This is the reason why 90% of the detritus of the Carnian Tyros Beds are not related to the Variscan, but to the Cadomian and Grenvillian basement of the E-Gondwana derived Cimmerian ribbon continent

    B2 sequences whose terms are squares

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    6 páginas.Peer reviewe
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