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  • 1
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    Aeroelastic considerations for torsionally soft rotors (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A research study was initiated to systematically determine the impact of selected blade tip geometric parameters on conformable rotor performance and loads characteristics. The model articulated rotors included baseline and torsionally soft blades with interchangeable tips. Seven blade tip designs were evaluated on the baseline rotor and six tip designs were tested on the torsionally soft blades. The designs incorporated a systemmatic variation in geometric parameters including sweep, taper, and anhedral. The rotors were evaluated in the NASA Langley Transonic Dynamics Tunnel at several advance ratios, lift and propulsive force values, and tip Mach numbers. A track sensitivity study was also conducted at several advance ratios for both rotors. Based on the test results, tip parameter variations generated significant rotor performance and loads differences for both baseline and torsionally soft blades.
    Keywords: AERODYNAMICS
    Type: NASA. Ames Research Center Rotorcraft Dynamics 1984; p 117-136
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Aeroelastic considerations for torsionally soft rotors (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A research study was initiated to systematically determine the impact of selected blade tip geometric parameters on conformable rotor performance and loads characteristics. The model articulated rotors included baseline and torsionally soft blades with interchangeable tips. Seven blade tip designs were evaluated on the baseline rotor and six tip designs were tested on the torsionally soft blades. The designs incorporated a systemmatic variation in geometric parameters including sweep, taper, and anhedral. The rotors were evaluated in the NASA Langley Transonic Dynamics Tunnel at several advance ratios, lift and propulsive force values, and tip Mach numbers. A track sensitivity study was also conducted at several advance ratios for both rotors. Based on the test results, tip parameter variations generated significant rotor performance and loads differences for both baseline and torsionally soft blades. Azimuthal variation of elastic twist generated by variations in the tip parameters strongly correlated with rotor performance and loads, but the magnitude of advancing blade elastic twist did not. In addition, fixed system vibratory loads and rotor track for potential conformable rotor candidates appears very sensitive to parametric rotor changes.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Aeroelastic model helicopter rotor testing in the Langley TDT (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Wind-tunel testing of a properly scaled aeroelastic model helicopter rotor is considered a necessary phase in the design development of new or existing rotor systems. For this reason, extensive testing of aeroelastically scaled model rotors is done in the Transonic Dynamics Tunnel (TDT) located at the NASA Langley Research Center. A unique capability of this facility, which enables proper dynamic scaling, is the use of Freon as a test medium. A description of the TDT and a discussion of the benefits of using Freon as a test medium are presented. A description of the model test bed used, the Aeroelastic Rotor Experimental System (ARES), is also provided and examples of recent rotor tests are cited to illustrate the advantages and capabilities of aeroelastic model rotor testing in the TDT. The importance of proper dynamic scaling in identifying and solving rotorcraft aeroelastic problems, and the importance of aeroelastic testing of model rotor systems in the design of advanced rotor systems are demonstrated.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Full-scale testing of an Ogee tip rotor (1978)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Full scale tests were utilized to investigate the effect of the ogee tip on helicopter rotor acoustics, performance, and loads. Two facilities were used: the Langley whirl tower and a UH-1H helicopter. The text matrix for hover on the whirl tower involved thrust values from 0 to 44 480 N (10,000 lb) at several tip Mach numbers for both standard and Ogee rotors. The full scale testing on the UH-1H encompassed the major portion of the flight envelope for that aircraft. Both near field acoustic measurements and far field flyover data were obtained for both the ogee and standard rotors. Data analysis of the whirl tower test shows that the ogee tip does significantly diffuse the tip vortex while providing some improvement in hover performance at low and moderate thrust coefficients. Flight testing of both rotors indicates that the strong impulsive noise signature of the standard rotor can be reduced with the ogee rotor. Analysis of the spectra indicates a reduction in energy in the 250 Hz and 1000 Hz range for the ogee rotor. Forward flight performance was significantly improved with the ogee configuration for a large number of flight conditions. Further, rotor control loads were reduced through use of this advanced tip rotor.
    Keywords: ACOUSTICS
    Type: Helicopter Acoustics; p 277-308
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Aeromechanical stability of a hingeless rotor in hover and forward flight: Analysis and wind tunnel tests (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A research effort of analysis and testing was conducted to investigate the ground resonance phenomenon of a soft in-plane hingeless rotor. Experimental data were obtained using a 9 ft. (2.74 m) diameter model rotor in hover and forward flight. Eight model rotor configurations were investigated. Configuration parameters included pitch flap coupling, blade sweep and droop, and precone of the blade feathering axis. An analysis based on a comprehensive analytical model of rotorcraft aerodynamics and dynamics was used. The moving block was used to experimentally determine the regressing lead lag mode damping. Good agreement was obtained between the analysis and test. Both analysis and experiment indicated ground resonance instability in hover. An outline of the analysis, a description of the experimental model and procedures, and comparison of the analytical and experimental data are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85683 , NAS 1.15:85683 , AVRADCOM-TR-83-B-5 , AD-A134612
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Parametric tip effects for conformable rotor applications (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A research study was initiated to systematically determine the impact of selected blade tip geometric parameters on aeroelasticity conformable rotor performance and loads characteristics. The model articulated rotors included baseline and torsionally soft blades with interchangeable tips. Seven blade tip designs were evaluated on the baseline rotor and three tip designs were tested on the torsionally soft blades. The designs incorporated a systematic variation in three geometric parameters: sweep, taper, and anhedral. The rotors were evaluated in the NASA Langley Transonic Dynamics Tunnel at several advance ratios, lift and propulsive force values, and tip Mach numbers. Based on the test results, tip parameter variations generated significant rotor performance and loads difference for both baseline and torsionally soft blades. Azimuthal variation of elastic twist generated by the tip parameters strongly correlated with rotor performance and loads, but the magnitude of advancing blade elastic twist did not correlate.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-85682 , NAS 1.15:85682 , AVRADCOM-TR-83-B-4 , AD-A134633
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Method for predicting rotor free-wake positions and the resulting rotor blade airloads (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Computer program has been designed and written to predict rotor free-wake positions and resulting rotor blade airloads without requiring time-consuming and tedious calculations. This program was written in FORTRAN IV for use on an IBM-360 computer.
    Keywords: MECHANICS
    Type: LAR-10674
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Loads and performance data from a wind-tunnel test of model articulated helicopter rotors with 2 different blade torsional stiffnesses (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A passive means of tailoring helicopter rotor blades to improve performance and reduce loads was evaluated. The parameters investigated were blade torsional stiffness, blade section camber, and distance between blade structural elastic axis and blade tip aerodynamic center. This offset was accomplished by sweeping the tip. The investigation was conducted at advance ratios of 0.20, 0.30, and 0.40. Data are presented without analysis; however, cross referencing of performance data and harmonic loads data may be useful to the analyst for validating aeroelastic theories and design methodologies as well as for evaluating passive aeroelastic tailoring or rotor blade parameters.
    Keywords: AERODYNAMICS
    Type: NASA-TM-84573 , L-15507 , NAS 1.15:84573 , AVRADCOM-TR-82-B-9
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Flight investigation of the response of a helicopter to the trailing vortex of a fixed-wing aircraft (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A flight investigation was conducted to quantitatively determine the response of a medium-weight helicopter to the trailing-vortex system of a fixed-wing aircraft. Flight tests and analytical tools were both utilized in the investigation. The flight tests involved an extensively instrumented UH-1H helicopter and a C-54 aircraft. Penetrations of the vortex system by the UH-1H were made at the following nominal conditions: the C-54 flew at 5500 feet altitude at a nominal gross weight of 58,000 pounds and an indicated airspeed of 115 knots in a cruise configuration. The UH-1H, nominally 7200 pounds gross weight, flew at 60 knots indicated airspeed during the penetrations at separation distances of 6.64 nautical miles to 0.42 nautical mile between aircraft. In general, the data analyzed for the above tests indicated that no unsafe penetration occurred. Further, penetrating vehicle attitude changes and structural loads were nominal. In addition, the response of the helicopter did not change appreciably with decreased separation distance.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Atmospheric Flight Mechanics Conference; Jun 07, 1976 - Jun 09, 1976; Arlington, TX
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Wind-tunnel investigation of the effects of blade tip geometry on the interaction of torsional loads and performance for an articulated helicopter rotor (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Langley transonic dynamics tunnel was used to determine the degree of correlation between rotor performance and the dynamic twist generated by changes in blade tip geometry using an articulated rotor with four different tip geometries at advance ratios of 0.20, 0.30 and 0.35. Based on the data obtained, it is concluded that: (1) there appears to be no strong correlation between blade torsion loads and rotor performance prediction; (2) for a given rotor task at each advance ratio investigated, both the azimuthal variation of torsional moment and the mean torsional moment at 81% radius are configuration dependent; (3) reducing the nose down twist on the advancing blade appears to be more important to forward flight performance than increasing the nose down twist on the retreating blade; (4) the rotor inflow model used was important in predicting the performance of the adaptive rotor; and (5) neither rigid blade solidity effects, inflow environment, nor blade torsion loads can be used alone to accurately predict active rotor performance.
    Keywords: AERODYNAMICS
    Type: NASA-TP-1926 , AVRADCOM-TR-81-B-5 , L-14674
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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