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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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    Hub loads analysis of the SA349/2 helicopter (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The forces and moments at the rotor hub of an Aerospatiale SA349/2 helicopter were investigated. The study included three main topics. First, measured hub forces and moments for a range of level flight conditions (mu = 0.14 to 0.37) were compared with predictions from a comprehensive rotorcraft analysis to examine the influence of the wake model on the correlations. Second, the effect of changing the blade mass distribution and blade chordwise center of gravity location on the 3/rev nonrotating frame hub loads was studied for a high-speed flight condition (mu = 0.37). Third, the use of higher harmonic control to reduce nonrotating frame 3/rev hub shear forces was investigated. The last two topics were theoretical studies only.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: American Helicopter Society, Journal (ISSN 0002-8711); 35; 51-63
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  • 3
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    Vibration analysis of the SA349/2 helicopter (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Helicopter airframe vibration is examined using calculations and measurements for the SA349/2 research helicopter. The hub loads, which transmit excitations to the fuselage, are predicted using a comprehensive rotorcraft analysis and correlated with measuring hub loads. The predicted and measured hub loads are then coupled with finite element models representing the SA349/2 fuselage. The resulting vertical acceleration at the pilot seat is examined. Adjustments are made to the airframe structural models to examine the sensitivity of predicted vertical acceleration to the model. Changes of a few percent to the damping and frequency of specific models lead to large reductions in predicted vibration, and to major improvements in the correlations with measured pilot-seat vertical acceleration.
    Keywords: AERONAUTICS (GENERAL)
    Type: NASA-TM-102794 , A-90083 , NAS 1.15:102794
    Format: application/pdf
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  • 4
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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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  • 5
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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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  • 6
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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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  • 7
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    Navier-Stokes Calculations for a Highly-Twisted Rotor Near Stall (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The viscous flow field near the surface of a hovering rotor blade was studied for blade twist distributions typical of a till rotor blade and a conventional helicopter rotor blade. Three blade geometries were studied, including a tilt rotor blade twist distribution (baseline), conventional helicopter rotor blade twist distribution, and the baseline twist distribution with 2 deg of precone. The results give insight into the delayed stall phenomenon often observed for highly twisted rotors. Calculations were performed for a high thrust condition near stall using the thin-layer Navier-Stokes CFD code TURNS. Effects of built-in twist on section force coefficients, skin friction, velocities, surface pressures, and boundary layer shape factor are discussed. Although the rotor thrust coefficient was nominally the same for the cases using the two twist distributions, large differences were found in the section in-plane and normal force coefficients. These preliminary results imply that the blade outboard region, rather than the inboard region, provides the majority of the performance advantage of the baseline case over the low twist case. Skin friction, velocities near the blade, and surface pressures for the two twist distributions reveal significant differences in the blade outboard region.
    Keywords: Aerodynamics
    Type: NASA-TM-111741 , NAS 1.15:111741 , Aeromechanics Specialists; Jan 19, 1994 - Jan 21, 1994; San Fransisco, CA; United States
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  • 8
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    Analysis and correlation of SA349/2 helicopter vibration (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Helicopter airframe vibration is examined using calculation and measurements for the SA349/2 research helicopter. The hub loads, which transmit excitation to the fuselage, are predicted using a comprehensive rotorcraft analysis and correlated with measured hub loads. The predicted and measured hub loads are then coupled with finite element models representing the SA349/2 fuselage. The resulting vertical acceleration at the pilot seat is examined. Adjustments are made to the airframe structural models to examine the sensitivity of predicted vertical acceleration to the model. Changes of a few percent to the damping and frequency of specific modes lead to large reductions in predicted vibration and to major improvements in the correlations with measured pilot seat vertical acceleration.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AIAA PAPER 91-1222 , AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; Apr 08, 1991 - Apr 10, 1991; Baltimore, MD; United States
    Format: text
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  • 9
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    Aeroelastic loads and stability investigation of a full-scale hingeless rotor (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An analytical investigation was conducted to study the influence of various parameters on predicting the aeroelastic loads and stability of a full-scale hingeless rotor in hover and forward flight. The CAMRAD/JA (Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics, Johnson Aeronautics) analysis code is used to obtain the analytical predictions. Data are presented for rotor blade bending and torsional moments as well as inplane damping data obtained for rotor operation in hover at a constant rotor rotational speed of 425 rpm and thrust coefficients between 0.0 and 0.12. Experimental data are presented from a test in the wind tunnel. Validation of the rotor system structural model with experimental rotor blade loads data shows excellent correlation with analytical results. Using this analysis, the influence of different aerodynamic inflow models, the number of generalized blade and body degrees of freedom, and the control-system stiffness at predicted stability levels are shown. Forward flight predictions of the BO-105 rotor system for 1-G thrust conditions at advance ratios of 0.0 to 0.35 are presented. The influence of different aerodynamic inflow models, dynamic inflow models and shaft angle variations on predicted stability levels are shown as a function of advance ratio.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-103867 , A-91157 , NAS 1.15:103867 , DGLR/AAAF/AIAA/RAeS International Forum on Aeroelasticity and Structural Dynamics; Jun 03, 1991 - Jun 06, 1991; Aachen; Germany
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  • 10
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    Computing The Dynamics Of Helicopters (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Comprehensive Analytical Model of Rotorcraft Aerodynamics (CAMRAD) computer program designed to calculate performance of, loads on, and noise generated by, helicopter rotor; vibration of helicopter and its response to gusts; dynamics and handling qualities of helicopter in flight; and aeroelastic stability of helicopter as system. Analysis consistent combination of structural, inertial, and aerodynamical mathematical models applicable to wide range of problems and wide class of vehicles. Written in FORTRAN 77.
    Keywords: MACHINERY
    Type: ARC-12337 , NASA Tech Briefs (ISSN 0145-319X); 15; 2; P. 46
    Format: text
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