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  • 1
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    Correlation of airloads on a two-bladed helicopter rotor (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Airloads measured on a two-bladed helicopter rotor in flight, from the Tip Aerodynamic and Acoustic Test, are compared with calculations from a comprehensive helicopter analysis (CAMRAD/JA), and the pressures compared with calculations from a full-potential rotor code (FPR). The flight test results cover an advance ratio range from 0.19 to 0.38. The lowest speed case is characterized by the presence of significant blade-vortex interactions. Good correlation of peak-to-peak vortex-induced loads and the corresponding pressures is obtained. The results of the correlation for this two-bladed rotor are substantially similar to the results for three- and four-bladed rotors, concerning the tip vortex core size for best correlation, calculation of the peak-to-peak loads on the retreating side, and calculation of vortex-induced loads on inboard radial stations.
    Keywords: AERODYNAMICS
    Type: In: AHS and Royal Aeronautical Society, Technical Specialists' Meeting on Rotorcraft Acoustics(Fluid Dynamics, Philadelphia, PA, Oct. 15-17, 1991, Proceedings (A93-29401 10-71); 38 p.
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  • 2
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    Feasibility investigation of general time-domain unsteady aerodynamics of rotors (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The feasibility of a general theory for the time-domain unsteady aerodynamics of helicopter rotors is investigated. The wake theory gives a linearized relation between the downwash and the wing bound circulation, in terms of the impulse response obtained directly in the time domain. This approach makes it possible to treat general wake configurations, including discrete wake vorticity with rolled-up and distorted geometry. The investigation establishes the approach for model order reduction; determines when a constrained identification method is needed; verifies the formulation of the theory for rolled-up, distorted trim wake geometry; and verifies the formulation of the theory for wake geometry perturbations. The basic soundness of the approach is demonstrated by the results presented. A research program to complete the development of the method is outlined. The result of this activity will be an approach for analyzing the aeroelastic stability and response of helicopter rotors, while retaining the important influence of the complicated rotor wake configuration.
    Keywords: AERODYNAMICS
    Type: NASA-CR-177570 , A-90304 , NAS 1.26:177570
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  • 3
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    Correlation of airloads on a two-bladed helicopter rotor (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Airloads measured on a two-bladed helicopter rotor in flight during the Ames' Tip Aerodynamic and Acoustic Test are compared with calculations from a comprehensive helicopter analysis (CAMRAD/JA), and the pressures compared with calculations from a full-potential rotor code (FPR). The flight-test results cover an advance ratio range of 0.19 to 0.38. The lowest-speed case is characterized by the presence of significant blade-vortex interactions. Good correlation of peak-to-peak vortex-induced loads and the corresponding pressures is obtained. Results of the correlation for this two-bladed rotor are substantially similar to those for three- and four-bladed rotors, including the tip-vortex core size for best correlation, calculation of the peak-to-peak loads on the retreating side, and calculation of vortex iduced loads on inboard radial stations. The higher-speed cases are characterized by the presence of transonic flow on the outboard sections of the blade. Comparison of calculated and measured airloads on the advancing side is not considered appropriate because the presence of shocks makes chordwise integration of the measured data difficult. However, good correlation of the corresponding pressures is obtained.
    Keywords: AERODYNAMICS
    Type: NASA-TM-103982 , A-93001 , NAS 1.15:103982
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  • 4
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    Wake model for helicopter rotors in high speed flight (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Two alternative approaches are developed to calculate blade-vortex interaction airloads on helicopter rotors: second order lifting-line theory, and a lifting surface theory correction. The common approach of using a larger vortex core radius to account for lifting-surface effects is quantified. The second order lifting-line theory also improves the modeling of yawed flow and swept tips. Calculated results are compared with wind tunnel measurements of lateral flapping, and with flight test measurements of blade section lift on SA349/2 and H-34 helicopter rotors. The tip vortex core radius required for good correlation with the flight test data is about 20 percent chord, which is within the range of measured viscous core sizes for helicopter rotors.
    Keywords: AERODYNAMICS
    Type: NASA-CR-177507 , USAVSCOM-TR-88-A-008 , NAS 1.26:177507
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  • 5
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    Performance results from a test of an S-76 rotor in the NASA Ames 80- by 120-foot wind tunnel (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A full-scale helicopter rotor wind tunnel test has been conducted which covers a wide range of rotor-shaft angles-of-attack and 0-100 kt thrust conditions. The hover performance data thus obtained were compared with the results of momentum theory calculations; forward flight rotor-performance data were compared with calculations from a comprehensive rotorcraft analysis. These comparisons suggest that hover testing at an outdoor facility in the absence of ground effect is required to make a final determination of the absolute accuracy of the wind tunnel hover data.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 93-3414 , In: AIAA Applied Aerodynamics Conference, 11th, Monterey, CA, Aug. 9-11, 1993, Technical Papers. Pt. 1 (A93-47201 19-02); p. 126-144.
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  • 6
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    Improved Mars Helicopter Aerodynamic Rotor Model for Comprehensive Analyses (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Mars Helicopter is part of the NASA Mars 2020 rover mission scheduled to launch in July of 2020. Its goal is to demonstrate the viability and potential of heavier-than-air vehicles in the Martian atmosphere. Ultimately, it aims to bridge the resolution gap between orbiters and the rover as well as allow access to otherwise inaccessible regions. The low density of the Martian atmosphere and the relatively small-scale rotor result in very low Reynolds number flows. The low density and low Reynolds numbers reduce the lifting force and lifting efficiency, respectively. This paper describes the generation of the improved Mars Helicopter aerodynamic rotor model. The goal is to generate a performance model for the Mars Helicopter rotor using a free wake analysis, since this has a low computational cost for design. The improvements in the analysis are two-fold and are expanded on from two prior publications. First, the fidelity of the simulations is increased by performing higher-order two-dimensional time-accurate OVERFLOW simulations allowing for higher accuracy aerodynamic coefficients and a better understanding of the boundary layer behavior as well as its transient features. Second, a version of the model is generated to duplicate the exact testing conditions in the 25-ft. diameter Space Simulator at the Jet Propulsion Laboratory, which allows for better correlation of rotor performance figures. Previous work correlated performance with that test, but did not consider the higher temperatures in the experiment compared to those of the Martian atmosphere. The higher temperatures in the experiment are expected to give conservative performance estimates, as they give rise to an increase in speed of sound and decrease in observed Reynolds numbers.
    Keywords: Lunar and Planetary Science and Exploration; Aircraft Design, Testing and Performance
    Type: ERF Paper No. 2018-28 , ARC-E-DAA-TN58739 , European Rotorcraft Forum; Sep 18, 2018 - Sep 21, 2018; Delft; Netherlands
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  • 7
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    Calculation of blade-vortex interaction airloads on helicopter rotors (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Two alternative approaches area developed to calculate blade-vortex interaction airloads on helicopter rotors, second-order lifting-line theory and a lifting-surface theory correction. The common approach of using a larger vortex core radius to account for lifting-surface effects is quantified. The second-order lifting-line theory also improves the modeling of low aspect-ratio blades yawed flow, and swept tips. Calculated results are compared with wind-tunnel measurements of lateral flapping, and with flight test measurements of blade section lift on SA349/2 and H-34 helicopter rotors. The tip vortex core radius required for good correlation with the flight test data is about a 20-percent chord, which is within the range of measured viscous core sizes for helicopter rotors.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 26; 470-475
    Format: text
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  • 8
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    Airloads and wake models for a comprehensive helicopter analysis (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Fundamental considerations regarding the theory of modeling of rotary wing airloads, wakes, and aeroelasticity are presented. The topics covered are: airloads and wakes, including lifting-line theory, wake models and nonuniform inflow, free wake geometry, and blade-vortex interaction; aerodynamic and wake models for aeroelasticity, including two-dimensional unsteady aerodynamics and dynamic inflow; and airloads and structural dynamics, including comprehensive airload prediction programs. Results of calculations and correlations are presented.
    Keywords: AERODYNAMICS
    Type: Vertica (ISSN 0360-5450); 14; 3 19; 255-300
    Format: text
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  • 9
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    Airloads, wakes, and aeroelasticity (1990)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Fundamental considerations regarding the theory of modeling of rotary wing airloads, wakes, and aeroelasticity are presented. The topics covered are: airloads and wakes, including lifting-line theory, wake models and nonuniform inflow, free wake geometry, and blade-vortex interaction; aerodynamic and wake models for aeroelasticity, including two-dimensional unsteady aerodynamics and dynamic inflow; and airloads and structural dynamics, including comprehensive airload prediction programs. Results of calculations and correlations are presented.
    Keywords: AERODYNAMICS
    Type: NASA-CR-177551 , A-90165 , NAS 1.26:177551 , USAAVSCOM-TM-90-A-005 , AGARD Special Course on Aerodynamics of Rotorcraft; Apr 02, 1990 - Apr 05, 1990; Brussels; Belgium*Turkey*United States|Apr 09, 1990 - Apr 11, 1990; Ankara; Turkey*United States|May 14, 1990 - May 17, 1990; Moffett, CA; United States
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  • 10
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    Correlation of Puma airloads: Lifting-line and wake calculation (1989)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A cooperative program undertaken by organizations in the United States, England, France, and Australia has assessed the strengths and weaknesses of four lifting-line/wake methods and three CFD methods by comparing their predictions with the data obtained in flight trials of a research Puma. The Puma was tested in two configurations: a mixed bladed rotor with instrumented rectangular tip blades, and a configuration with four identical swept tip blades. The results are examined of the lifting-line predictions. The better lifting-line methods show good agreement with lift at the blade tip for the configuration with four swept tips; the moment is well predicted at 0.92 R, but deteriorates outboard. The predictions for the mixed bladed rotor configuration range from fair to good. The lift prediction is better for the swept tip blade than for the rectangular tip blade, but the reasons for this cannot be determined because of the unmodeled effects of the mixed bladed rotor.
    Keywords: AERODYNAMICS
    Type: NASA-TM-102212 , USAAVSCOM-TR-89-A-006 , A-89209 , NAS 1.15:102212 , AD-A215494 , European Rotorcraft Forum; Sep 12, 1989 - Sep 15, 1989; Amsterdam; Netherlands
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