Ground resonance

About: Ground resonance is a research topic. Over the lifetime, 336 publications have been published within this topic receiving 3460 citations.

Theory of self-excited mechanical oscillations of helicopter rotors with hinged blades

Abstract: Vibrations of rotary-wing aircraft may derive their energy from the rotation of the rotor rather than from the air forces. A theoretical analysis of these vibrations is described and methods for its application are explained in Chapter one. Chapter two reports the results of an investigation of the mechanical stability of a rotor having two vertically hinged blades mounted upon symmetrical supports, that is, of equal stiffness and mass in all horizontal directions. Chapter three presents the theory of ground vibrations of a two-blade helicopter rotor on anisotropic flexible supports.

Basic Helicopter Aerodynamics

Abstract: Basic Helicopter Aerodynamics is widely appreciated as an easily accessible, rounded introduction to the first principles of the aerodynamics of helicopter flight. Simon Newman has brought this third edition completely up to date with a full new set of illustrations and imagery. An accompanying website www.wiley.com/go/seddon contains all the calculation files used in the book, problems, solutions, PPT slides and supporting MATLAB® code. Simon Newman addresses the unique considerations applicable to rotor UAVs and MAVs, and coverage of blade dynamics is expanded to include both flapping, lagging and ground resonance. New material is included on blade tip design, flow characteristics surrounding the rotor in forward flight, tail rotors, brown-out, blade sailing and shipborne operations. Concentrating on the well-known Sikorsky configuration of single main rotor with tail rotor, early chapters deal with the aerodynamics of the rotor in hover, vertical flight, forward flight and climb. Analysis of these motions is developed to the stage of obtaining the principal results for thrust, power and associated quantities. Later chapters turn to the characteristics of the overall helicopter, its performance, stability and control, and the important field of aerodynamic research is discussed, with some reference also to aerodynamic design practice. This introductory level treatment to the aerodynamics of helicopter flight will appeal to aircraft design engineers and undergraduate and graduate students in aircraft design, as well as practising engineers looking for an introduction to or refresher course on the subject.

Formulation and solution of rotary-wing aeroelastic stability and response problems

Abstract: The state of the art in the formulation and solution of rotary-wing aeroelastic stability and response problems is reviewed in detail. The approximations used in the structural, inertia and aerodynamic operators are discussed. The important role of geometric nonlinearities, due to moderate deflections, and aerodynamic stall in the aeroelastic stability and response problem are identified. It is also shown that geometric nonlinearities are of primary importance in aeroelastic stability calculations, and have a more limited, though important, role in response calculations. Next, formulation of coupled rotor/fuselage problems is described, for both air and ground resonance type problems. Both topics, the isolated blade problem and the coupled rotor/fuselage problem, are treated for both hover and forward flight. Solution of aeroelastic stability and response problems proceeds in two stages. First, the spatial dependence is eliminated by using Galerkin's method, or by using the finite element method. Next the nonlinear, or linear, ordinary differential equation with periodic coefficients have to be solved for stability or response. Efficient numerical methods for accomplishing these objectives are presented in a comprehensive manner. The paper contains a number of illustrative numerical results which are intended to clarify various aspects of the modeling process and serve as representative results for both aeroelastic stability and response calculations for a variety of blade and rotor configurations.

Effect of a Rapid Blade-Pitch Increase on the Thrust and Induced-Velocity Response of a Full-Scale Helicopter Rotor

Abstract: A method has been proposed for predicting the effect of a rapid blade-pitch increase on the thrust and induced-velocity response of a helicopter rotor. General equations have been derived for the ensuing motion of the helicopter. These equations yield time histories of thrust, induced velocity, and helicopter vertical velocity for given rates of blade-pitch-angle changes and given rotor-angular-velocity time histories. The results of the method have been compared with experimental results obtained with a rotor mounted on the Langley helicopter test tower. The calculated and experimental results are in good agreement, although, in general, the calculated thrust-coefficient overshoots are about 10 percent greater than those obtained experimentally.

Helicopter Blade Response and Aeromechanical Stability with a Magnetorheological Fluid Based Lag Damper

Abstract: This paper explores the feasibility of using Magnetorheological (MR) fluid-based dampers for lag damping augmentation in helicopters. An MR damper model is integrated with a rotor aeromechanical model. Two different control schemes are presented-namely the On-Off scheme and the Feedback Linearization scheme. In the On-Off scheme, two criteria are used to obtain equivalent linear damping for the nonlinear MR damper as a function of the size of perturbation and the applied field. The Feedback Linearization scheme uses a feedback controller to linearize the force output of the MR damper. The two control schemes are compared for lag transient response in ground resonance and their ability to reduce periodic damper loads in forward flight. It is shown that an MR damper of a size comparable to an elastomeric damper can provide sufficient damping for ground resonance stabilization and can significantly reduce periodic damper loads with ajudicious choice of operation scheme.