285 research outputs found

    Surface protection

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    The surface protection subproject consists of three major thrusts: airfoil deposition model; metallic coating life prediction; and thermal barrier coating (TBC) life prediction. The time frame for each of these thrusts and the expected outputs are presented. Further details are given for each thrust such as specific element schedules and the status of performance; in-house, via grant, or via contract

    Aeronautical Engineering: A special bibliography with indexes, supplement 51

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    This bibliography lists 206 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System in November 1974

    Aeronautical Engineering: A special bibliography with indexes, supplement 67, February 1976

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    This bibliography lists 341 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1976

    Swimming of a Waving Plate

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    The purpose of this paper is to study the basic principle of fish propulsion. As a simplified model, the two-dimensional potential flow over a waving plate of finite chord is treated. The solid plate, assumed to be flexible and thin, is capable of performing the motion which consists of a progressing wave of given wave length and phase velocity along the chord, the envelope of the wave train being an arbitrary function of the distance from the leading edge. The problem is solved by applying the general theory for oscillating deformable airfoils. The thrust, power required, and the energy imparted to the wake are calculated, and the propulsive efficiency is also evaluated. As a numerical example, the waving motion with linearly varying amplitude is carried out in detail. Finally, the basic mechanism of swimming is elucidated by applying the principle of action and reaction

    Aeronautical Engineering: A special bibliography with indexes, supplement 62

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    This bibliography lists 306 reports, articles, and other documents introduced into the NASA scientific and technical information system in September 1975

    A theoretical analysis of pitch stability during gliding in flying snakes

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    Abstract Flying snakes use their entire body as a continuously morphing 'wing' to produce lift and shallow their glide trajectory. Their dominant behavior during gliding is aerial undulation, in which lateral waves are sent posteriorly down the body. This highly dynamic behavior, which is unique among animal gliders, should have substantial effects on the flight dynamics and stability of the snakes, resulting from the continuous redistribution of mass and aerodynamic forces. In this study, we develop two-dimensional theoretical models to assess the stability characteristics of snakes in the pitch direction. Previously measured force coefficients are used to simulate aerodynamic forces acting on the models, and undulation is simulated by varying mass. Model 1 is a simple three-airfoil representation of the snake's body that possesses a passively stable equilibrium solution, whose basin of stability contains initial conditions observed in experimental gliding trajectories. Model 2 is more sophisticated, with more degrees of freedom allowing for postural changes to better represent the snake's real kinematics; in addition, a restoring moment is added to simulate potential active control. The application of static and dynamic stability criteria show that Model 2 is passively unstable, but can be stabilized with a restoring moment. Overall, these models suggest that undulation does not contribute to stability in pitch, and that flying snakes require a closed-loop control system formed around a passively stable dynamical framework

    Numerical Investigation of Leading-Edge Modifications of a NACA Airfoil

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    A parametric investigation was carried out to understand the flow characteristics of tubercle airfoils and to determine the best approach and parameters for designing a tubercle airfoil. For this purpose, a straight edge base airfoil (NACA 4414) and several tubercle airfoils, by modifying the leading edge of the base airfoil, were created in SolidWorks and tested with Computational Fluid Dynamics (CFD) application software Star CCM+. Alternative tubercle airfoil with elliptical bumps demonstrated superior post-stall performance when compared to their straight edge counterparts; their post-stall lift did not decrease drastically. However, their pre-stall lift coefficients were always lower than the base NACA 4414 airfoil. Alternative tubercle airfoil with spherical bumps at the leading edge showed good agreement with the base NACA 4414 lift curve while providing slightly higher lift coefficients for all tested angles. However, the drag coefficient was also higher for this model which resulted in a poor lift to drag ratio. Tubercle models with varying amplitude suffered drastically at high angles of attack while also stalling earlier. Early flow separation took place at tubercles with high maximum amplitudes. Gradual increase of lift and stall angle were achieved by lowering the maximum amplitude of tubercles. The varying amplitude model 4414_sin_0.015t_0.4_100 with a maximum amplitude of 1.5% of chord length provided a higher lift to drag ratio than the base airfoil at low angles of attack between 0° and 4°. Conventional sinusoidal models were created with various magnitudes of amplitude and wavelength. It was found that low amplitude and long wavelength contribute to the best aerodynamic performance. An additional study found that surface waviness contributes to the enhancement of post stall lift coefficient. Following these parametric studies, an optimal tubercle airfoil (4414_sin_0.6_0.2_100) configuration was identified with a uniform amplitude of 0.6% of chord length and wavelength of 31.4% (0.2 factor) of chord length. Finally, the effect of Reynolds number on the optimal tubercle airfoil was studied by testing the airfoil at three Reynolds numbers: 1x106, 5x106, 10x106. A trend of increasing lift and a 4° increase of stall angle was observed with the increase of Reynolds number
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