Download or read book Investigation of Airfoil Dynamic Stall and Its Influence on Helicopter Control Loads written by Franklin O. Carta and published by . This book was released on 1972 with total page 187 pages. Available in PDF, EPUB and Kindle. Book excerpt: Measurements were made of the unsteady normal force and pitching moment on an NACA 0012 airfoil model oscillated both sinusoidally and nonsinusoidally over a range of incidence angles, including a substantial penetration into stall. The sinusoidal normal force and pitching moment data were reduced and tabulated as functions of the angle of attack, the angular velocity parameter, and the angular acceleration parameter. This generalized form of the data was used to reconstruct the measured sinusoidal aerodynamic response of the model airfoil with excellent results. Additional correlations were made using nonsinusoidal pitch schedules which included periodic ramp changes in angle of attack and a flexured angular blade response to a one-per-rev sinusoidal incidence angle change typical of that for a helicopter blade. The agreement between predicted and measured normal force and moment loops was very good for the ramp motion. (Author).
Download or read book Airfoil Dynamic Stall and Rotorcraft Maneuverability written by and published by . This book was released on 2000 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt: The loading of an airfoil during dynamic stall is examined in terms of the augmented lift and the associated penalties in pitching moment and drag. It is shown that once stall occurs and a leading-edge vortex is shed from the airfoil there is a unique relationship between the augmented lift, the negative pitching moment, and the increase in drag. This relationship, referred to here as the dynamic stall function, shows limited sensitivity to effects such as the airfoil section profile and Mach number, and appears to be independent of such parameters as Reynolds number, reduced frequency, and blade sweep. For single-element airfoils there is little that can be done to improve rotorcraft maneuverability except to provide good static clmax characteristics and the chord or blade number that is required to provide the necessary rotor thrust. However, multi-element airfoils or airfoils with variable geometry features can provide augmented lift in some cases that exceeds that available from a single-element airfoil. The dynamic stall function is shown to be a useful tool for the evaluation of both measured and calculated dynamic stall characteristics of singleelement, multi-element, and variable geometry airfoils.
Download or read book Investigations of Dynamic Stall and Dynamic Stall Control on Helicopter Airfoils written by Anthony D. Gardner and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Review of MIT Research on Airfoil Dynamics Stall 1964 1971 written by Norman D. Ham and published by . This book was released on 1971 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research on the dynamic stall of airfoils and helicopter blades is described, beginning with wind tunnel tests and helicopter flight tests which led to the current research. Flutter criteria, tests of two-dimensional airfoils undergoing large transient motions, and a partial theory of airfoil dynamic stall are presented. The application of the two-dimensional results to the loading and motion of rotor blades due to stall is described. Unsteady boundary layer analyses and tests, and their relationship to the development of a complete flow separation model, to airfoil design, and to blade-vortex interaction effects are summarized.
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 An Experimental Study of Dynamic Stall on Advanced Airfoil Sections Volume 1 Summary of the Experiment written by and published by . This book was released on 1982 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: The static and dynamic characteristics of seven helicopter sections and a fixed-wing supercritical airfoil were investigated over a wide range of nominally two-dimensional flow conditions, at Mach numbers up to 0.30 and Reynolds numbers up to 4x10 to the 6th power. Details of the experiment, estimates of measurement accuracy, and test conditions are described in this volume. The results of the experiment show important differences between airfoils, which would otherwise tend to be masked by differences in wind tunnels, particularly in steady cases. All of the airfoils tested provide significant advantages over the conventional NACA 0012 profile. In general, however, the parameters of the unsteady motion appear to be more important than airfoil shape in determining the dynamic-stall airloads.
Download or read book Investigations of dynamic stall and dynamic stall control on helicopter airfoils written by Anthony D. Gardner and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Phenomenon of Dynamic Stall written by W. J. McCroskey and published by . This book was released on 1981 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stall and its consequences are fundamentally important to the design and operation of flight vehicles. A certain degree of unsteadiness always accompanies the flow over an airfoil or other streamlined body at high angle of attack, but the stall of a lifting surface undergoing unsteady motion is even more complex than static stall. Dynamic stall remains a major unsolved problem with a variety of current applications in aeronautics, hydrodynamics, and wind engineering. This report summarizes the main physical features of the phenomenon and the attempts that have been made to predict it. The information presented is drawn mainly from recent review articles and investigations by the author and his colleagues. Since a large fraction of the existing knowledge has come from experimental research, the details of dynamic stall are discussed principally in physical terms.
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 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 Analysis of Oscillatory Pressure Data Including Dynamic Stall Effects written by Franklin O. Carta and published by . This book was released on 1974 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: The dynamic stall phenomenon was examined in detail by analyzing an existing set of unsteady pressure data obtained on an airfoil oscillating in pitch. Most of the data were for sinusoidal oscillations which penetrated the stall region in varying degrees, and here the effort was concentrated on the chordwise propagation of pressure waves associated with the dynamic stall. It was found that this phenomenon could be quantified in terms of a pressure wave velocity which is consistently much less than free-stream velocity, and which varies directly with frequency. It was also found that even when the stall region has been deeply penetrated and a substantial dynamic stall occurs during the downstroke, stall recovery near minimum incidence will occur, followed by a potential flow behavior up to stall inception.
Download or read book The Aerothermodynamics of Aircraft Gas Turbine Engines written by and published by . This book was released on 1978 with total page 770 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Evaluation of Airfoil Dynamic Stall Characteristics for Maneuverability written by and published by . This book was released on 2000 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: The loading of an airfoil during dynamic stall is examined in terms of the augmented lift and the associated penalties in pitching moment and drag. It is shown that once stall occurs and a leading-edge vortex is shed from the airfoil there is a unique relationship between the augmented lift, the negative pitching moment, and the increase in drag. This relationship, referred to here as the dynamic stall function, shows limited sensitivity to many parameters that influence rotors in flight. For single-element airfoils it appears that there is little that can be done to improve rotorcraft maneuverability except to provide good static clmax characteristics and the chord or blade number that is required to provide the necessary rotor thrust. The loading on a helicopter blade during a severe maneuver is examined and it is shown that the blade's dynamic stall function is similar to that obtained in two-dimensional wind tunnel testing. An evaluation of three-dimensional effects for flight and an oscillating wing in a wind tunnel suggests that the two problems are not proper analogues. The utility of the dynamic stall function is demonstrated by evaluating sample theoretical predictions based on semi-empirical stall models and CFD computations. The approach is also shown to be useful in evaluating multi-element airfoil data obtained from dynamic stall tests.
Download or read book The Influence of Sweep on the Aerodynamic Loading of an Oscillating NACA 0012 Airfoil written by and published by . This book was released on 1979 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigation of the Effect of Torsional Natural Frequency on Stall Induced Dynamic Loading written by F. J. Tarzanin and published by . This book was released on 1974 with total page 163 pages. Available in PDF, EPUB and Kindle. Book excerpt: For helicopter flight conditions at high blade loadings or airspeeds, the rotor control system experiences a rapid load growth resulting from stall-induced blade torsional moments. These loads frequently grow so large that the aircraft flight envelope is restricted. This report describes an analytical study that determined the effect of changing blade torsional properties on control loads for a wide range of flight conditions. (Modified author abstract).
Download or read book Compressibility Effects on Dynamic Stall of Oscillating Airfoils written by and published by . This book was released on 1990 with total page 43 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study's aim was to obtain a basic understanding of the effect of compressibility on the phenomenon of dynamic stall under typical flight conditions encountered by a helicopter in forward flight, so that eventually a means for its control can be devised and thus, its flight envelope can be expanded. The first phase of the study was devoted to building a drive system to produce the necessary unsteady airfoil motion. A novel design was arrived at and built. It uses a four-bar chain mechanism of which the airfoil is one of the links. The drive can produce a sinusoidal variation of the angle of attack as : alpha = alpha sub 0 + alpha sub m(sin omega+), with the mean angle of attack alpha0, continuously variable from 0 to 15 deg, the amplitude of oscillation alpha sub m, from 2 to 10 degs and the frequency from 0-100 Hz, in an oncoming flow Mach number M, from 0-0.5. The drive was installed in the indraft wind tunnel at NASA Ames Research Center. Stroboscopic schlieren studies and interferograms as well as holographic interferometry studies were conducted for a wide range of flow conditions, amplitudes and frequencies. Results show that compressibility effects appear at M = 0.3, that a dynamic stall vortex forms for all Mach numbers, and that for M> or = 0.3, the dynamic stall angle decreases as M increases. On the other hand, increasing the degree of unsteadiness, delays deep stall monotonically at all Mach numbers. Amplitude has a dominant effect, and dynamic stall occurs at lower angles of attack at lower amplitudes, yet this angle of attack is always higher than the static stall angle. (edc).
Download or read book An Experimental Study of Dynamic Stall on Advanced Airfoil Sections written by and published by . This book was released on 1982 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The static and dynamic characteristics of seven helicopter sections and a fixed wing supercritical airfoil were investigated over a wide range of nominally two-dimensional flow conditions. The results of the experiment show important differences between airfoils, which would otherwise tend to be masked by differences in wind tunnels, particularly in steady cases. All of the airfoils tested provide significant advantages over the conventional NASA 0012 profile. However, the parameters of the unsteady motion appear to be more important than airfoil shape in determining the dynamic-stall airloads.
