Download or read book Analysis of Helicopter Rotor Blade Torsional Oscillations Due to Stall written by Peter Crimi and published by . This book was released on 1975 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Analysis of Helicopter Rotor Blade Torsional Oscillations Due to Stall written by Peter Crimi and published by . This book was released on 1975 with total page 68 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Analysis of Stall Flutter of a Helicopter Rotor Blade written by Peter Crimi and published by . This book was released on 1973 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: A study of rotor blade aeroelastic stability was carried out, using an analytic model of a two-dimensional airfoil undergoing dynamic stall and an elastomechanical representation including flapping, flapwise bending and torsional degrees of freedom. Results for a hovering rotor demonstrated that the models used are capable of reproducing both classical and stall flutter. The minimum rotor speed for the occurrence of stall flutter in hover, was found to be determined from coupling between torsion and flapping. Instabilities analogous to both classical and stall flutter were found to occur in forward flight. However, the large stall-related torsional oscillations which commonly limit aircraft forward speed appear to be the response to rapid changes in aerodynamic moment which accompany stall and unstall, rather than the result of an aeroelastic instability. The severity of stall-related instabilities and response was found to depend to some extent on linear stability. Increasing linear stability lessens the susceptibility to stall flutter and reduced the magnitude of the torsional response to stall and unstall.

Download or read book Investigation of Helicopter Control Loads Induced by Stall Flutter written by P. J. Arcidiacono and published by . This book was released on 1970 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: An analytical study was conducted to determine if available unsteady normal force and moment aerodynamic test data could be used in conjunction with existing helicopter rotor aeroelastic and variable inflow analyses to provide a method for predicting the stall flutter response of a helicopter rotor blade. For this purpose, incompressible unsteady aerodynamic data for an NACA 0012 airfoil executing pure sinusoidal pitching motions were employed. To apply such data under rotor blade operating conditions where multiharmonic motions and velocity variations exist, the data were expressed as functions of instantaneous section angle of attack, angular velocity, and angular acceleration. In addition, scaling procedures were developed in an attempt to account for the effects of compressibility. Limited application of the resulting analysis to define the aeroelastic characteristics of several blade designs showed that significant self-excited torsional oscillations of the stall flutter type could, in fact, be predicted for certain combinations of flight conditions and blade designs. Correlation studies, to evaluate the ability of the analysis to predict control loads, were performed with CH-53A maneuvering flight test data and with level flight test data from the NH-3A (S-61F). (Author).

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effects of Blade Stall on Helicopter Rotor Blade Bending and Torsional Loads written by S. V. LaForge and published by . This book was released on 1965 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt: The highest blade dynamic loads tend to occur under conditions of retreating blade stall. An investigation is made to compare measured and calculated blade bending loads under such conditions. The analysis is based on the use of normal modes and the numerical solution of the differential equations of motion (which eliminates the limitations caused by using harmonics of airloads). It also permits more accurate allowance for aerodynamic nonlinearities in the stalled region. The analysis also includes negative aerodynamic torsional damping when blade stall occurs, as well as the effects of blade bending and torsional deformations on airloads. Finally, the analysis includes an investigation of the effect of hysteresis of the lift coefficient/angle of at8tack relationship in stall. It is concluded that, in order to accurately calculate blade loads under conditions of retreating blade stall, the effects of lift hysteresis and negative aerodynamic torsional damping must be included, in addition to the usual nonlinearities in lift and moment coefficients. It is further concluded that a numerical integration of the differential equation (as opposed to a solution utilizing harmonics of airload) and inclusion of the effects of blade deformation are essential to achieve accurate definition of the airloads. (Author).

Download or read book The Shock and Vibration Digest written by and published by . This book was released on 1976 with total page 602 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Response and Airloading of Helicopter Rotor Blades Due to Dynamic Stall written by Wayne Robert Johnson and published by . This book was released on 1970 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt: An aerodynamic model is constructed for the application of the properties of dynamic stall of airfoils to the calculation of the airloads and blade motion of helicopter rotor blades. Dynamic stall occurs on an airfoil undergoing pitching motion at high angle of attack, and is characterized by peak section lift and moment much larger than the corresponding static stall loads. A method is developed for the solution of the equations of motion of a rotor blade by means of harmonic analysis. The effect of dynamic stall on the blade torsional motion at high advance ratio is examined, and comparison is made with the limited experimental data available. An increase in the dynamic stall angle is shown to significantly decrease the amplitude of the pitch motions. (Author).

Download or read book Dynamic Stall of Small Wind Systems written by Richard B. Noll and published by . This book was released on 1983 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Bramwell s Helicopter Dynamics written by A. R. S. Bramwell and published by Elsevier. This book was released on 2001-04-06 with total page 403 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the original publication of 'Bramwell's Helicopter Dynamics' in 1976, this book has become the definitive text on helicopter dynamics and a fundamental part of the study of the behaviour of helicopters. This new edition builds on the strengths of the original and hence the approach of the first edition is retained. The authors provide a comprehensive overview of helicopter aerodynamics, stability, control, structural dynamics, vibration, aeroelastic and aeromechanical stability. As such, Bramwell's Helicopter Dynamics is essential for all those in aeronautical engineering.THE single volume comprehensive guide for anyone working with helicopters Written by leading worldwide experts in the field

Download or read book Investigation of Helicopter Control Loads Induced by Stall Flutter written by Peter J. Arcidiacono and published by . This book was released on 1970 with total page 179 pages. Available in PDF, EPUB and Kindle. Book excerpt: An analytical study was conducted to determine if available unsteady normal force and moment aerodynamic test data could be used in conjunction with existing helicopter rotor aeroelastic and variable inflow analyses to provide a method for predicting the stall flutter response of a helicopter rotor blade. For this purpose, incompressible unsteady aerodynamic data for an NACA 0012 airfoil executing pure sinusoidal pitching motions were employed. To apply such data under rotor blade operating conditions where multiharmonic motions and velocity variations exist, the data were expressed as functions of instantaneous section angle of attack, angular velocity, and angular acceleration. In addition, scaling procedures were developed in an attempt to account for the effects of compressibility. Limited application of the resulting analysis to define the aeroelastic characteristics of several blade designs showed that significant self-excited torsional oscillations of the stall flutter type could, in fact, be predicted for certain combinations of flight conditions and blade designs. Correlation studies, to evaluate the ability of the analysis to predict control loads, were performed with CH-53A maneuvering flight test data and with level flight test data from the NH-3A (S-61F). (Author).

Download or read book Dynamic Stall written by Peter Crimi and published by . This book was released on 1973 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt: Problems associated with unsteady stall are summarized and past experimental and theoretical studies, relating primarily to dynamic stall of helicopter rotor blades, are reviewed. The problems attendant to analytic treatment of dynamic stall, including identification of relevant flow elements and definition of unsteady separation, are then discussed, and the basis for a theory which accounts for viscous effects and viscous-inviscid interactions analytically is presented. Results of computations are compared with measured loading on an airfoil undergoing sinusoidal pitching motion. The amounts of lift overshoot and their variation with frequency are in good agreement. Analyses of wake-induced stall and stall flutter of a helicopter rotor blade are then presented. The results indicate that the large stall-related torsional oscillations which commonly limit helicopter forward speed are the response to rapid changes in aerodynamic moment which accompany stall and unstall, rather than the consequence of an aeroelastic instability. (Author).

Download or read book Smart Helicopter Rotors written by Ranjan Ganguli and published by Springer. This book was released on 2015-12-16 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Exploiting the properties of piezoelectric materials to minimize vibration in rotor-blade actuators, this book demonstrates the potential of smart helicopter rotors to achieve the smoothness of ride associated with jet-engined, fixed-wing aircraft. Vibration control is effected using the concepts of trailing-edge flaps and active-twist. The authors’ optimization-based approach shows the advantage of multiple trailing-edge flaps and algorithms for full-authority control of dual trailing-edge-flap actuators are presented. Hysteresis nonlinearity in piezoelectric stack actuators is highlighted and compensated by use of another algorithm. The idea of response surfaces provides for optimal placement of trailing-edge flaps. The concept of active twist involves the employment of piezoelectrically induced shear actuation in rotating beams. Shear is then demonstrated for a thin-walled aerofoil-section rotor blade under feedback-control vibration minimization. Active twist is shown to be significant in reducing vibration caused by dynamic stall. The exposition of ideas, materials and algorithms in this monograph is supported by extensive reporting of results from numerical simulations of smart helicopter rotors. This monograph will be a valuable source of reference for researchers and engineers with backgrounds in aerospace, mechanical and electrical engineering interested in smart materials and vibration control. Advances in Industrial Control aims to report and encourage the transfer of technology in control engineering. The rapid development of control technology has an impact on all areas of the control discipline. The series offers an opportunity for researchers to present an extended exposition of new work in all aspects of industrial control.

Download or read book Helicopter Theory written by Wayne Johnson and published by Courier Corporation. This book was released on 2012-03-07 with total page 1122 pages. Available in PDF, EPUB and Kindle. Book excerpt: Monumental engineering text covers vertical flight, forward flight, performance, mathematics of rotating systems, rotary wing dynamics and aerodynamics, aeroelasticity, stability and control, stall, noise, and more. 189 illustrations. 1980 edition.

Download or read book Stalling of Helicopter Blades written by F. B. Gustafson and published by . This book was released on 1946 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Theoretical studies have predicted that operation of a helicopter rotor beyond certain combinations of thrust, forward speed, and rotational speed might be prevented by rapidly increasing stalling of the retreating blade. The same studies also indicate that the efficiency of the rotor will increase unitl these limits are reached or closely approached, so that it is desirable to design helicopter rotors for operation close to the limits imposed by blade stalling. Inasmuch as the theoretical predictions of blade stalling involve numerous approximations and assuptions of blade stalling, an experimental investigation was needed to determine whether, in actual practice, the stall did occur and spread as predicted and to establish the amount of stalling that could be present without severe vibration or control difficulties being introduced.

Download or read book Sensitivity Analysis of Torsional Vibration Characteristics of Helicopter Rotor Blades Part 2 Aerodynamics and Sensitivity Analysis written by and published by . This book was released on 1974 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt: A theoretical investigation of dynamic response characteristics of rotor blades was carried out with special emphasis on torsional degrees-of-freedom. Coupled equations of motion for flapwise bending and torsion were formulated at varying azimuth positions for rotor blades with noncollinear aerodynamic, elastic and mass axes. Both structural and aerodynamic mass, damping and stiffness coefficients were included. The variations of a sample blade at different flight conditions were investigated from these equations. The obtained numerical results were illustrated. The sensitivity of overall blade vibration characteristics to torsional oscillations was also investigated from the equations of motion for the sample blade. The illustrated results show the importance of torsional degrees-of-freedom in rotor blade analysis. Various possibilities of improving the overall response by tuning blade geometric, structural and aerodynamic characteristics are discussed.

Download or read book Monthly Catalog of United States Government Publications written by and published by . This book was released on 1975 with total page 2834 pages. Available in PDF, EPUB and Kindle. Book excerpt: