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  • 1
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    Neural Network Prediction of New Aircraft Design Coefficients (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This paper discusses a neural network tool for more effective aircraft design evaluations during wind tunnel tests. Using a hybrid neural network optimization method, we have produced fast and reliable predictions of aerodynamical coefficients, found optimal flap settings, and flap schedules. For validation, the tool was tested on a 55% scale model of the USAF/NASA Subsonic High Alpha Research Concept aircraft (SHARC). Four different networks were trained to predict coefficients of lift, drag, moment of inertia, and lift drag ratio (C(sub L), C(sub D), C(sub M), and L/D) from angle of attack and flap settings. The latter network was then used to determine an overall optimal flap setting and for finding optimal flap schedules.
    Keywords: Aeronautics (General)
    Type: NASA-TM-112197 , A-976719 , NAS 1.15:112197
    Format: application/pdf
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  • 2
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    Reducing Wind Tunnel Data Requirements Using Neural Networks (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The use of neural networks to minimize the amount of data required to completely define the aerodynamic performance of a wind tunnel model is examined. The accuracy requirements for commercial wind tunnel test data are very severe and are difficult to reproduce using neural networks. For the current work, multiple input, single output networks were trained using a Levenberg-Marquardt algorithm for each of the aerodynamic coefficients. When applied to the aerodynamics of a 55% scale model of a U.S. Air Force/ NASA generic fighter configuration, this scheme provided accurate models of the lift, drag, and pitching-moment coefficients. Using only 50% of the data acquired during, the wind tunnel test, the trained neural network had a predictive accuracy equal to or better than the accuracy of the experimental measurements.
    Keywords: Aerodynamics
    Type: NASA-TM-112193 , NAS 1.15:112193 , A-976463
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  • 3
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    Experimental Study of Lift-Enhancing Tabs on a Two-Element Airfoil (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The results of a wind-tunnel test are presented for a two-dimensional NASA 63(sub 2)-215 Mod B airfoil with a 30% chord single-slotted flap. The use of lift-enhancing tabs (similar to Gurney flaps) on the lower surface near the trailing edge of both elements was investigated on four nap configurations. A combination of vortex generators on the flap and lift-enhancing tabs was also investigated. Measurements of surface-pressure distributions and wake profiles were used to determine the aerodynamic performance of each configuration. By reducing flow separation on the flap, a lift-enhancing tab at the main-element trailing edge increased the maximum lift by 10.3% for the 42-deg flap case. The tab had a lesser effect at a moderate flap deflection (32 deg) and adversely affected the performance at the smallest flap deflection (22 deg). A tab located near the flap trailing edge produced an additional lift increment for all flap deflections. The application of vortex generators to the flap eliminated lift-curve hysteresis and reduced flow separation on two configurations with large flap deflections (greater than 40 deg). A maximum-lift coefficient of 3.32 (17% above the optimum baseline) was achieved with the combination of lift-enhancing tabs on both elements and vortex generators on the flap.
    Keywords: Aerodynamics
    Type: NASA/TM-95-207303 , NAS 1.15:207303 , AIAA Paper 94-1868 , Applied Aerodynamics Conference; Jun 20, 1994 - Jun 23, 1994; Colorado Springs, CO; United States|Journal of Aircraft; 32; 5; 1072-1078
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  • 4
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    Lift-Enhancing Tabs on Multielement Airfoils (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The use of flat-plate tabs (similar to Gurney flaps) to enhance the lift of multielement airfoils is extended here by placing them on the pressure side and near the trailing edge of the main element rather than just on the furthest downstream wing element. The tabs studied range in height from 0.125 to 1.25% of the airfoil reference chord. In practice, such tabs would be retracted when the high-lift system is stowed. The effectiveness of the concept was demonstrated experimentally and computationally on a two-dimensional NACA 63(sub 2)-215 Mod B airfoil with a single-slotted, 30%-chord flap. Both the experiments and computations showed that the tabs significantly increase the lift at a given angle of attack and the maximum lift coefficient of the airfoil. The computational results showed that the increased lift was a result of additional turning of the flow by the tab that reduced or eliminated now separation on the flap. The best configuration tested, a 0.5%-chord tab placed 0.5% chord upstream of the trailing edge of the main element, increased the maximum lift coefficient of the airfoil by 12% and the maximum lift-to-drag ratio by 40%.
    Keywords: Aerodynamics
    Type: NASA-TM-112914 , NAS 1.15:112914 , AIAA Paper 93-3504 , Journal of Aircraft; 32; 3; 649-655|Applied Aerodynamics; Aug 09, 1993 - Aug 11, 1993; Monterey, CA; United States
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  • 5
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    Aerodynamics of a Simple Three-Dimensional High-Lift System (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Experimental results are presented for a three-element high-lift system with a half-span flap and both a full- and three-quarter span slat. The simplified wing spanned the wind-tunnel test section with no wing sweep or wing tip. Full- and part-span slat configurations were tested to investigate the three-dimensional effects of a finite-span slat in a landing configuration. With a part-span slat, flow visualization and surface pressures revealed two vortices at the flap tip and one at the slat tip. Compared to the full-span slat case, the part-span slat configuration stalled at a lower angle of attack and yielded reduced lift at all angles of attack. At a representative approach attitude (10 deg), wake surveys indicated comparable induced drag for the full- and part-span slat configurations while the profile drag was more than doubled with a part-span slat. The vorticity contribution of the slat-tip vortex was minimal, suggesting that the vortex dissipates through viscous interaction with the main-element boundary layer. The addition of a lower-surface fence at the slat tip yielded two co-rotating vortices and partially alleviated the profile drag increase of the part-span slat.
    Keywords: Aerodynamics
    Format: text
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  • 6
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    Computational Investigation of a Semi-Span Flap (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The current study computationally examines one of the principle three-dimensional features of the flow over a high-lift system, the flow associated with a flap edge. Structured, overset grids were used in conjunction with an incompressible Navier-Stokes solver to compute the flow over a two-element high-lift configuration. The computations were run in a fully turbulent mode using the one-equation Baldwin-Barth model. Specific interest was given to the details of the flow in the vicinity of the flap edge, so the geometry was simplified to isolate this region. The geometry consisted of an unswept wing, which spanned a wind tunnel test section, equipped with a single element flap. Two flap configurations were computed; a full-span and a half-span Fowler flap. The chord based Reynolds number was 3.7 million for all cases. The results for the full-span flap agreed with two-dimensional experimental results and verified the method. Grid topologies and related issues for the half-span flap geometry are discussed. Results of the half-span flap case are presented with emphasis on the flow features associated with the flap edge.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: AIAA Paper 95-0185 , 6th International Symposium on Computational Fluid Dynamics; Sep 04, 1995 - Sep 08, 1995; Lake Tahoe, NV; United States
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  • 7
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    Experiments in High-Lift for High-Speed Civil Transports (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: The lecture will present experimental work pertaining to HSCT high-lift aerodynamic testing. The effects of Reynolds number and test techniques will be discussed. The performance of attached-flow and leading-edge vortex-control high-lift devices will also be presented. All of the aerodynamic data presented will be from experiments performed prior to the HSR program. The subject of airframe noise testing and its relevance to highlift testing will be discussed but no quantitative data will be presented.
    Keywords: Aircraft Design, Testing and Performance
    Type: An Overview of High-Lift Aerodynamics; Jun 23, 1995 - Jun 24, 1995; San Diego, CA; United States
    Format: text
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  • 8
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    Tip Fence for Reduction of Lift-Generated Airframe Noise (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The present invention is directed toward a unique lift-generated noise reduction apparatus. This apparatus includes a plurality of tip fences that are secured to the trailing and leading assemblies of the high-lift system, as close as possible to the discontinuities where the vortices are most likely to form. In one embodiment, these tip fences are secured to some or all of the outboard and inboard tips of the wing slats and flaps. The tip fence includes a generally flat, or an aerodynamically shaped plate or device that could be formed of almost any rigid material, such as metal, wood, plastic, fiber glass, aluminum, etc. In a preferred embodiment, the tip fences extend below and perpendicularly to flaps and the slats to which they are attached, such that these tip fences are aligned with the nominal free stream velocity of the aircraft. In addition to reducing airframe noise, the tip fence tends to decrease drag and to increase lift, thus improving the overall aerodynamic performance of the aircraft. Another advantage presented by the tip fence lies in the simplicity of its design, its elegance, and its ready ability to fit on the wing components, such as the flaps and the slats. Furthermore, it does not require non-standard materials or fabrication techniques, and it can be readily, easily and inexpensively retrofited on most of the existing aircraft, with minimal design changes.
    Keywords: Aircraft Design, Testing and Performance
    Format: application/pdf
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