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  • AIRCRAFT DESIGN, TESTING AND PERFORMANCE  (5)
  • 1
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    Aeroelastic Stability of Rotor Blades Using Finite Element Analysis (1982)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The flutter stability of flap bending, lead-lag bending, and torsion of helicopter rotor blades in hover is investigated using a finite element formulation based on Hamilton's principle. The blade is divided into a number of finite elements. Quasi-steady strip theory is used to evaluate the aerodynamic loads. The nonlinear equations of motion are solved for steady-state blade deflections through an iterative procedure. The equations of motion are linearized assuming blade motion to be a small perturbation about the steady deflected shape. The normal mode method based on the coupled rotating natural modes is used to reduce the number of equations in the flutter analysis. First the formulation is applied to single-load-path blades (articulated and hingeless blades). Numerical results show very good agreement with existing results obtained using the modal approach. The second part of the application concerns multiple-load-path blades, i.e. bearingless blades. Numerical results are presented for several analytical models of the bearingless blade. Results are also obtained using an equivalent beam approach wherein a bearingless blade is modelled as a single beam with equivalent properties. Results show the equivalent beam model.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-166389 , NAS 1.26:166389
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Flap-lag-torsion flutter analysis of a constant life rotor (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The constant lift rotor (CLR) employs a control input of pitch moment to several airfoil sections which are free to pivot on a continuous spar, allowing them to change their pitch to obtain the desired lift. A flap-lag-torsion flutter analysis of a constant lift rotor blade in hover was developed. The blade model assumes rigid body flap and lead-lag motions at the root hinge and each strip undergoes an independent torsional motion. The results are presented in terms of root locus plots of complex eigenvalues as a function of thrust. The effects of several parameters (including structural damping, center of gravity and elastic axis offset from aerodynamic center, compressibility pitch-lag and pitch-flap coupling) on the blade dynamics are examined. With a suitable combination of lag damper and pitch-flap coupling, it is possible to design a constant lift rotor blade free from flutter instability.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-152244 , SU-JIAA-TR-17
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Gust response of hingeless rotors (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The gust response of a coupled hingeless rotor-fuselage system is studied in both hover and forward flight. Each rotor blade undergoes flap bending, lag bending, and torsional deflections. The blades are discretized into beam elements, each with fifteen nodal degrees of freedom. The fuselage is permitted three translational (vertical, longitudinal, and lateral) and two rotational (pitch and roll) degrees of freedom. The formulation considers a three-dimensional gust field wherein each gust velocity component can have an arbitrary variation in space and time. Aerodynamic loads are obtained using quasisteady strip theory. Wake-induced effects are introduced through dynamic inflow modeling. Dynamic stall and reverse flow effects are also included. Equations governing the rotor-fuselage gust response are linearized about the vehicle propulsive trim state and the blade steady-state defected positions, and solved by time integration. The effects of several parameters on the helicopter gust response are illustrated, including dynamic inflow, lag stiffness, forward speed, gust profile, gust penetration rate, and gust velocity direction.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: American Helicopter Society, Journal (ISSN 0002-8711); 31; 33-46
    Format: text
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  • 4
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    Finite element analysis for bearingless rotor blade aeroelasticity (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A conventional articulated rotor blade has mechanical flap and lag hinges, a lag damper, and a pitch bearing. In connection with an interest in designs of greater mechanical simplicity and increased maintainability, hingeless and bearingless rotors have been developed. A hingeless blade lacks the hinges and is cantilevered at the hub. It does have a pitch bearing for pitch control. A bearingless design eliminates the hinges and the pitch bearing as well. In the present investigation of bearingless rotor blade characteristics, finite element analysis has been successfully applied to determine the solutions of the nonlinear trim equations and the linearized flutter equations of multiple-load-path blades. The employed formulation is based on Hamilton's principle. The spatial dependence of the equations of motion is discretized by dividing the flexbeams, the torque tube, and the outboard into a number of elements.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Annual Forum; May 04, 1982 - May 07, 1982; Anaheim, CA
    Format: text
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  • 5
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    Flap-lag-torsion aeroelastic stability of circulation-controlled rotors in hover (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The results of a theoretical investigation of the flap-lag-torsion stability of circulation controlled rotors in hover are presented. Stability boundaries are presented as a function of thrust and lag frequency, at several levels of blowing coefficient, for flap frequencies of 1.1/rev and 1.8/ rev. The effects of several parameters on the blade flap-lag stability are examined, including structural damping, structural coupling, pitch-lag and pitch-flap coupling, and the blade feathering motion. The trailing edge blowing can have a major impact on the blade aeroelastic stability, which should be considered in the rotor design. The implications of these results for the current CCR and X-Wing rotorcraft designs are considered.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AHS 78-64 , In: American Helicopter Society, Annual National Forum; May 15, 1978 - May 17, 1978; Washington, DC
    Format: text
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