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  • 1
    Electronic Resource
    Electronic Resource
    Rotor design optimization using a multidisciplinary approach (1992)
    Springer
    Structural and multidisciplinary optimization 5 (1992), S. 70-75 
    Details
    ISSN: 1615-1488
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A multidisciplinary optimization tool for helicopter rotor blade design has been developed. It uses a comprehensive analysis program, CAMRAD/JA, capable of performing analyses in all involved disciplines in a consistent and efficient manner, together with CONMIN's method of feasible directions. Design variables, constraints, and objective functions have been chosen to address actual design requirements in a realistic manner. The optimization procedure setup provides the flexibility to take full advantage of the comprehensive nature of the analysis code, allowing optimization driven by aerodynamic, aeroelastic, and flight mechanics design requirements. The optimization tool is applied to the McDonnell Douglas Helicopter Company AH-64A, a modern, high performance helicopter. Results are presented for combined hover/forward flight performance optimization, fuselage vibration reduction, and combined performance/vibration optimization. Blade aerodynamic and structural properties are used as design variables. The optimized designs show significant improvements and demonstrate that a practical and efficient optimization tool has been developed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01744698
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    Paper (German National Licenses)
    Fulltext
  • 2
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    Development of a piezoelectric actuator for trailing edge flap control of full scale rotor blades (2001)
    Institute of Physics
    Details
    Publication Date: 2001-02-01
    Print ISSN: 0964-1726
    Electronic ISSN: 1361-665X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Institute of Physics
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    PAPER CURRENT
  • 3
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    The use of active controls to augment rotor/fuselage stability (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The use of active blade pitch control to increase helicopter rotor/body damping is studied. Control is introduced through a conventional nonrotating swashplate. State variable feedback of rotor and body states is used. Feedback parameters include cyclic rotor flap and lead-lag states, and body pitch and roll rotations. The use of position, rate, and acceleration feedback is studied for the various state variables. In particular, the influence of the closed loop feedback gain and phase on system stability is investigated. For the rotor/body configuration analyzed, rotor cyclic inplane motion and body roll-rate and roll-acceleration feedback can considerably augment system damping levels and eliminate ground resonance instabilities. Scheduling of the feedback state, phase, and gain with rotor rotation speed can be used to maximize the damping augmentation. This increase in lead-lag damping can be accomplished without altering any of the system modal frequencies. Investigating various rotor design parameters (effective hinge offset, blade precone, blade flap stiffness) indicates that active control for augmenting rotor/body damping will be particularly powerful for hingeless and bearingless rotor hubs.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Rotorcraft Dynamics 1984; p 1-15
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    The use of active controls to augment rotor/fuselage stability (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The use of active blade pitch control to increase helicopter rotor/body damping is studied. Control is introduced through a conventional nonrotating swashplate. State variable feedback of rotor and body states is used. Feedback parameters include cyclic rotor flap and lead-lag states, and body pitch and roll rotations. The use of position, rate, and acceleration feedback is studied for the various state variables. In particular, the influence of the closed loop feedback gain and phase on system stability is investigated. For the rotor/body configuration analyzed, rotor cyclic inplane motion and body roll-rate and roll-acceleration feedback can considerably augment system damping levels and eliminate ground resonance instabilities. Scheduling of the feedback state, phase, and gain with rotor rotation speed can be used to maximize the damping augmentation. This increase in lead-lag damping can be accomplished without altering any of the system modal frequencies. Investigating various rotor design parameters (effective hinge offset, blade precone, blade flap stiffness) indicates that active control for augmenting rotor/body damping will be particularly powerful for hingeless and bearingless rotor hubs.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: American Helicopter Society, Journal (ISSN 0002-8711); 30; 13-22
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Aeroelasticity and mechanical stability report, 0.27 Mach scale model of the YAH-64 advanced attack helicopter (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A 27% dynamically scaled model of the YAH-64 Advanced Attack Helicopter main rotor and hub has been designed and fabricated. The model will be tested in the NASA Langley Research Center V/STOL wind tunnel using the General Rotor Model System (GRMS). This report documents the studies performed to ensure dynamic similarity of the model with its full scale parent. It also contains a preliminary aeroelastic and aeromechanical substantiation for the rotor installation in the wind tunnel. From the limited studies performed no aeroelastic stability or load problems are projected. To alleviate a projected ground resonance problem, a modification of the roll characteristics of the GRMS is recommended.
    Keywords: AERODYNAMICS
    Type: NASA-CR-178284 , NAS 1.26:178284 , MDHC-150-V-1003
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Application of higher harmonic blade feathering on the OH-6A helicopter for vibration reduction (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The design, implementation, and flight test results of higher harmonic blade feathering for vibration reduction on the OH-6A helicopter are described. The higher harmonic control (HHC) system superimposes fourth harmonic inputs upon the stationary swashplate. These inputs are transformed into 3P, 4P and 5P blade feathering angles. This results in modified blade loads and reduced fuselage vibrations. The primary elements of this adaptive vibration suppression system are: (1) acceleration transducers sensing the vibratory response of the fuselage; (2) a higher harmonic blade pitch actuator system; (3) a flightworthy microcomputer, incorporating the algorithm for reducing vibrations, and (4) a signal conditioning system, interfacing between the sensors, the microcomputer and the HHC actuators. The program consisted of three distinct phases. First, the HHC system was designed and implemented on the MDHC OH-6A helicopter. Then, the open loop, or manual controlled, flight tests were performed, and finally, the closed loop adaptive control system was tested. In 1983, one portion of the closed loop testing was performed, and in 1984, additional closed loop tests were conducted with improved software. With the HHC system engaged, the 4P pilot seat vibration levels were significantly lower than the baseline ON-6A levels. Moreover, the system did not adversely affect blade loads or helicopter performance. In conclusion, this successful proof of concept project demonstrated HHC to be a viable vibration suppression mechanism.
    Keywords: AERODYNAMICS
    Type: NASA-CR-4031 , NAS 1.26:4031
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    A Galerkin type finite element method for rotary-wing aeroelasticity in hover and forward flight (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A Galerkin finite element method for the spatial discretization of the nonlinear, nonselfadjoint, partial differential equations governing rotary-wing aeroelasticity is presented. This method reduces algebraic manipulative labor significantly when compared to the global Galerkin method based on assumed modes. Furthermore, the Galerkin finite element method is ideally suited to treat rotor blades with discontinuous mass and stiffness distribution and structurally redundant configurations as they appear in bearingless rotors. Implementation of the method is illustrated for the coupled flap-lag aeroelastic problem of hingeless rotor blades in hover and forward flight. Numerical results for stability and response illustrate the numerical properties and convergence behavior of the method. It is concluded that the Galerkin finite element method is a practical tool for solving rotary-wing aeroelastic stability and response problems.
    Keywords: STRUCTURAL MECHANICS
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Application of the Finite Element Method to Rotary Wing Aeroelasticity (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A finite element method for the spatial discretization of the dynamic equations of equilibrium governing rotary-wing aeroelastic problems is presented. Formulation of the finite element equations is based on weighted Galerkin residuals. This Galerkin finite element method reduces algebraic manipulative labor significantly, when compared to the application of the global Galerkin method in similar problems. The coupled flap-lag aeroelastic stability boundaries of hingeless helicopter rotor blades in hover are calculated. The linearized dynamic equations are reduced to the standard eigenvalue problem from which the aeroelastic stability boundaries are obtained. The convergence properties of the Galerkin finite element method are studied numerically by refining the discretization process. Results indicate that four or five elements suffice to capture the dynamics of the blade with the same accuracy as the global Galerkin method.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165854 , NAS 1.26:165854 , UCLA-ENG-80-81
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Study to eliminate ground resonance using active controls (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effectiveness of active control blade feathering in increasing rotor body damping and the possibility to eliminate ground resonance instabilities were investigated. An analytical model representing rotor flapping and lead-lag degrees of freedom and body pitch, roll, longitudinal and lateral motion is developed. Active control blade feathering is implemented as state variable feedback through a conventional swashplate. The influence of various feedback states, feedback gain, and weighting between the cyclic controls is studied through stability and response analyses. It is shown that blade cyclic inplane motion, roll rate and roll acceleration feedback can add considerable damping to the system and eliminate ground resonance instabilities, which the feedback phase is also a powerful parameter, if chosen properly, it maximizes augmentation of the inherent regressing lag mode damping. It is shown that rotor configuration parameters, like blade root hinge offset, flapping stiffness, and precone considerably influence the control effectiveness. It is found that active control is particularly powerful for hingeless and bearingless rotor systems.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-166609 , NAS 1.26:166609
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 10
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    Advance finite element modeling of rotor blade aeroelasticity (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An advanced beam finite element has been developed for modeling rotor blade dynamics and aeroelasticity. This element is part of the Element Library of the Second Generation Comprehensive Helicopter Analysis System (2GCHAS). The element allows modeling of arbitrary rotor systems, including bearingless rotors. It accounts for moderately large elastic deflections, anisotropic properties, large frame motion for maneuver simulation, and allows for variable order shape functions. The effects of gravity, mechanically applied and aerodynamic loads are included. All kinematic quantities required to compute airloads are provided. In this paper, the fundamental assumptions and derivation of the element matrices are presented. Numerical results are shown to verify the formulation and illustrate several features of the element.
    Keywords: AERODYNAMICS
    Type: American Helicopter Society, Journal (ISSN 0002-8711); 39; 2; p. 56-68
    Format: text
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    NASA TECHNICAL REPORTS
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