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  • 1
    Publication Date: 2013-08-31
    Description: Two cases were selected for correlation from an experiment that examined the aeromechanical stability of a small-scale model rotor that used tantalum rods instead of blades to simulate vacuum conditions. The first case involved body roll freedom only while the second case included body pitch and roll degrees of freedom together. Analyses from Hughes Helicopters and the U.S. Army Aeromechanics Laboratory were compared with the data and the correlations ranged from poor to good.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA, Ames Research Center, Integrated Technology Rotor Methodology Assessment Workshop; p 27-40
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  • 2
    Publication Date: 2013-08-31
    Description: Three cases were selected for correlation from an experiment that examined the aeromechanical stability of a small-scale model of a hingeless rotor and fuselage in hover. The first case examined the stability of a configuration with 0 degree blade pitch so that coupling between dynamic modes was minimized. The second case was identical to the first except the blade pitch was set to 9 degrees which provides flap-lag coupling of the rotor modes. The third case had 9 degrees of blade pitch and also included negative pitch-lag coupling, and therefore was the most highly coupled configuration. Analytical calculations were made by Bell Helicopter Textron, Boeing Vertol, Hughes Helicopters, Sikorsky Aircraft, the U.S. Army Aeromechanics Laboratory, and NASA Ames Research Center and compared to some or all of the experimental cases. Overall, the correlation ranged from very poor-to-poor to good.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA, Ames Research Center, Integrated Technology Rotor Methodology Assessment Workshop; p 43-65
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  • 3
    Publication Date: 2013-08-31
    Description: The research accomplished in the area of rotor loads over the last 13 to 14 years is reviewed. The start of the period examined is defined by the 1973 AGARD Milan conference and the 1974 hypothetical rotor comparison. The major emphasis of the review is research performed by the U.S. Army and NASA at their laboratories and/or by the industry under government contract. For the purpose of this review, two main topics are addressed: rotor loads prediction and means of rotor loads reduction. A limited discussion of research in gust loads and maneuver loads is included. In the area of rotor loads predictions, the major problem areas are reviewed including dynamic stall, wake induced flows, blade tip effects, fuselage induced effects, blade structural modeling, hub impedance, and solution methods. It is concluded that the capability to predict rotor loads has not significantly improved in this time frame. Future progress will require more extensive correlation of measurements and predictions to better understand the causes of the problems, and a recognition that differences between theory and measurement have multiple sources, yet must be treated as a whole. There is a need for high-quality data to support future research in rotor loads, but the resulting data base must not be seen as an end in itself. It will be useful only if it is integrated into firm long-range plans for the use of the data.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA, Washington, NASA(Army Rotorcraft Technology. Volume 1: Aerodynamics, and Dynamics and Aeroelasticity; p 180-311
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  • 4
    Publication Date: 2019-06-28
    Description: High quality airloads data have been obtained on an instrumented UH-60A in flight and these data provide insight into the aerodynamic limiting behavior of the rotor. At moderate weight coefficients and high advance ratio limiting performance is largely caused by high drag near the blade tip on the advancing side of the rotor as supercritical flow develops on the rotor with moderate to strong, shocks on both surfaces of the blade. Drag divergence data from two-dimensional airfoil tests show good agreement with the development of the supercritical flow regions. Large aerodynamic pitching moments are observed at high advance ratio, as well, and these pitching moments are the source of high torsional moments on the blade and control system loads. These loads occur on the advancing side of the disk and are not related to blade stall which does not occur for these weight coefficients. At high weight coefficients aerodynamic and structural limits are related to dynamic stall cycles that begin on the retreating side of the blade and, for the most severe conditions, carry around to the advancing side of the blade at the presumed first frequency of the blade/control system.
    Keywords: Aerodynamics
    Type: NASA-TM-110396 , A-961611 , NAS 1.15:110396 , USAATCOM-TR-96-A-011
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  • 5
    Publication Date: 2019-06-28
    Description: Four lifting-line methods were compared with flight test data from a research Puma helicopter and the accuracy assessed over a wide range of flight speeds. Hybrid Computational Fluid Dynamics (CFD) methods were also examined for two high-speed conditions. A parallel analytical effort was performed with the lifting-line methods to assess the effects of modeling assumptions and this provided insight into the adequacy of these methods for load predictions.
    Keywords: Aeronautics (General)
    Type: NASA-TM-110421 , NAS 1.15: 110421 , A-962753 , USAATCOM TR-96-A-008
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  • 6
    Publication Date: 2019-06-28
    Description: Selected research and technology activities at Ames Research Center are summarized. These activities exemplify the Center's varied and productive research efforts for 1994.
    Keywords: General
    Type: NASA-TM-108858 , NAS 1.15:108858 , A-950019
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  • 7
    Publication Date: 2018-12-01
    Description: This paper presents a method for the estimation of blade airloads, based on the measurements of flap bending moments. In this procedure, the blade rotation in vacuum modes is calculated, and the airloads are expressed as an algebraic sum of the mode shapes, modal amplitudes, mass distribution, and frequency properties. The method was validated by comparing the calculated airload distribution with the original wind tunnel measurements which were made using ten modes and twenty measurement stations. Good agreement between the predicted and the measured airloads was found up to 0.90 R, but the agreement degraded towards the blade tip. The method is shown to be quite robust to the type of experimental problems that could be expected to occur in the testing of full-scale and model-scale rotors.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
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  • 8
    Publication Date: 2019-06-28
    Description: The analysis CAMRAD/JA is used to model two aircraft, a Puma with a swept-tip blade and a UH-60A Black Hawk. The accuracy of the analysis in predicting the torsion loads is assessed by comparing the predicted loads with measurements from flight tests. The influence of assumptions in the analytical model is examined by varying model parameters and comparing the predicted results to baseline values for the torsion loads. Flight test data from a research Puma are used to identify the source of torsion loads. These data indicate that the aerodynamic section moment in the region of the blade tip dominates torsion loading in high-speed flight. Both the aerodynamic section moment at the blade tip and the pitch-link loads are characterized by large positive (nose-up) moments in the first quadrant with rapid reversal of load so that the moment is negative in the second quadrant. Both the character and magnitude of this loading are missed by the CAMRAD/JA analysis.
    Keywords: AERODYNAMICS
    Type: NASA-TM-104006 , A-93047 , NAS 1.15:104006 , USAATCOM-TR-92-A-014
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  • 9
    Publication Date: 2019-06-28
    Description: The conference proceedings contains 14 formal papers and the results of two panel discussions. In addition, a transcript of discussion that followed the paper presentations and panels is included. The papers are of two kinds. The first seven papers were directed specifically to the correlation of industry and government mathematical models with data for rotorcraft stability from six experiments. The remaining 7 papers dealt with related topics in the prediction of rotor aeroelastic or aeromechanical stability. The first of the panels provided an evaluation of the correlation that was shown between the mathematical models and the experimental data. The second panel addressed the general problems of the validation of mathematical models.
    Keywords: AERONAUTICS (GENERAL)
    Type: NASA-CP-10007 , A-86381 , NAS 1.55:10007 , USAAVSCOM-CP-88-A-001 , AD-A200007
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  • 10
    Publication Date: 2019-06-28
    Description: A method is developed to estimate the blade normal airloads by using measured flap bending moments; that is, the rotor blade is used as a force balance. The blade's rotation is calculated in vacuum modes and the airloads are then expressed as an algebraic sum of the mode shapes, modal amplitudes, mass distribution, and frequency properties. The modal amplitudes are identified from the blade bending moments using the Strain Pattern Analysis Method. The application of the method is examined using simulated flap bending moment data that have been calculated for measured airloads for a full-scale rotor in a wind tunnel. The estimated airloads are compared with the wind tunnel measurements. The effects of the number of measurements, the number of modes, and errors in the measurements and the blade properties are examined, and the method is shown to be robust.
    Keywords: AERODYNAMICS
    Type: NASA-TM-100020 , A-87311 , NAS 1.15:100020 , USAAVSCOM-TR-87-A-8 , AD-A185858
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