Showing papers on "Aeroelasticity published in 1971"

Theoretical and experimental aerodynamics of the sailwing

Abstract: The sailwing is a unique type of semiflexible foldable wing. A brief description of its construction, basic properties, and some past research, is used to introduce an analytical and experimental study of its aerodynamic characteristics. Emphasis is placed on an approximate structural analysis which treats the nonlinear behavior of the sail deflection. Twodimensional flexible airfoil theory and Prandtl lifting-line theory are used to establish the aerodynamic loading. The results allow prediction of the induced tensions, the nonlinear life curve, induced drag, and aeroelastic divergence of the sail chordwise deflection mode. Selected experimental results are presented for comparison with the theory, along with a brief discussion of the implications of the study regarding flight vehicle applications of the sailwing.

Wake Induced Flutter of Circular Cylinders: Mechanical Aspects

Abstract: In a recent paper, a theory explaining the wake-induced flutter of smooth circular cylinders was developed and vindicated. It was shown that, for moderate spacing of the cylinders (where the aerodynamic coupling between the constituent motions is small), flutter could occur only when the natural frequency, in still air, of vertical oscillations exceeded that of the horizontal motions. The theory, however, took no account of the possibility of mechanical coupling between the constituent motions and, while the results from this theory were corroborated by wind-tunnel tests in which a statically uncoupled mechanical support system was used, no indications were given of the changes in aeroelastic behaviour which might accompany the introduction of simple coupling terms. In this paper, the class of cases wherein the mechanical support system for the leeward cylinder exhibits static coupling is studied using “undamped flutter theory”. It is demonstrated that the appearance of static coupling terms can lead to quite dramatic changes in the flutter characteristics, and that considerable care must be exercised in the design and operation of wind-tunnel dynamic models if meaningful results are to be obtained. An Appendix deals with the general problem of mechanical coupling, using the normal coordinates approach, and aspects of the problem which bear on the subconductor oscillation phenomenon experienced on “bundled” overhead power transmission lines are highlighted.

Wind-tunnel systems and techniques for aircraft/stores compatibilitystudies.

Abstract: A comprehensive presentation of advanced wind-tunnel techniques and facilities used in aircraft store carriage and delivery studies is presented. Extensive static stability, control, and metric store tests aid in predictions of aircraft performance and structural requirements. Investigations with scaled dynamic models are used to determine the flutter boundaries and aeroelastic effects caused by large store aerodynamic and inertia forces. Methods used to obtain mutual aerodynamic interference of wing-pylon-st ore combinations and external store aerodynamic interference on control surface effectiveness are described. State-of-theart scaled dynamic separation and captive trajectory systems, their current and potential capabilities and limitations, are discussed. The quality of wind-tunnel simulation, in the general sense, is discussed and present limitations and potential improvements are pointed out.

A Comparison of Methods for the Analysis of Wing-Tail Interaction Flutter

Abstract: Results of an analytical investigation of the aeroelastic stability of variable sweep aircraft, specifically with respect to wing-tail interaction flutter, are presented. Three aerodynamic representations are employed: 1) modified two-dimensional strip theory containing no wingtail aerodynamic interaction, 2) vortex lattice theory containing aerodynamic interaction of wing on tail only, and 3) subsonic kernel function theory containing a complete evaluation of wing-tail aerodynamic interaction. The capability of the interaction methods is established by an application to an experimental flutter model where wing-tail aerodynamic interaction is known to be of importance. The aerodynamic methods are then applied to a particular high performance variable sweep aircraft. The basic flutter mechanisms for this hypothetical aircraft are generated by wing-fuselage mechanical interaction and are predicted by wing aerodynamics alone. Component aerodynamics on wing and tail without interaction do not predict the mechanism. Aerodynamic interaction causes the reappearance of flutter at a velocity 30% lower than generated by the wing alone.

A Design Study for the Incorporation of Aeroelastic Capability into NASTRAN

Abstract: Module design modification requirements for incorporating aeroelastic capabilities into NASTRAN structural analysis program

Optimization under aeroelastic constraints

Abstract: Optimization of aeroelastic constraints for aircraft design using differential equation idealization and finite element approximation

Manual on Aeroelasticity. Subject and Author Index

Abstract: : In addition to subject and author indexes, the report includes a listing of the contents of the Manual on Aeroelasticity.

Unsteady Flow Around and Aeroelastic Vibration in Turbomachine Cascades

Abstract: : Methods of calculating, and experimental results of research on, unsteady flow in aerodynamic cascades of turbomachines are set forth. The conditions of excitation and damping of blade vibration in compressible and incompressible fluid flow are considered. The theoretical methods are based upon a model of an ideal fluid. The incoming stream may be inhomogeneous and have vortices due to the influence of a preceding cascade. The experimental results pertain to determination of the dynamic stresses brought about by stream inhomogeneity in the turbomachine, as well as to determination of the unsteady aerodynamic forces which excite and damp blade vibrations. Consideration is given to the origination of cascade flutter and the effect of inhomogeneity of an aerodynamic cascade. The experimental research methods are described.

Non-conservative Effects Produced by Thrust of Jet Engine

Abstract: It is well known that an aeroelastic phenomenon may occur if an interaction exists between aerodynamic and elastic forces, and in addition massic forces appear for an aeroelastic dynamic phenomenon.

Shuttle- Dynamics and aeroelasticity - An appraisal

Abstract: Space shuttle vibrational characteristics, investigating dynamic models, aeroelasticity, reentry, wing stall flutter and buffet boundaries

Investigation of Aerodynamic Analysis Problems in Transonis Maneuvering. Volume I.

Abstract: : This report describes the results of a study into the general problems of the aerodynamic analysis of airfoils and wings at transonic flight conditions. The basic guideline of this study was to assess, analyze and interpret the various methods available and to explore their further development where possible. The general aspects of the transonic maneuvering problem were reviewed. Particular emphasis was placed on methods for the analysis of airfoils leading to buffet onset prediction. This program includes a potential flow analysis, supercritical pressure calculations, and boundary layer calculation using either a finite-difference method or an integral method. Methods available for predicting pressures on three-dimensional wings are also compared. (Author)

Composite Wing for Transonic Improvement. Volume II. Advanced Analysis Evaluation.

Abstract: : The program to provide technical support leading to a composite wing for an aircraft transonic improvement program included technology investigations to establish the feasibility of aeroelastic synthesis for composite wing structures. Modifications were made to an existing direct Rayleigh-Ritz anisotropic plate analysis procedure and the resulting procedure was compared with the finite element method for the analysis of wing structures and correlated with experimental data. The results of this investigation and a preliminary formulation of an aeroelastic synthesis procedure are documented in this volume for future systems support reference. (Author)

Horizontal stoppable rotor conversion

Abstract: Stiffened horizontal stoppable hingeless rotor conversion from helicopter to airplane flight speeds

A method for predicting the panel flutter fatigue life of Saturn 5 panels

Abstract: Development of method for predicting fatigue life of panels under flutter conditions with application to Saturn 5 launch vehicle structures