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Decade:
1970-1979
Collection:
National Advisory Committee for Aeronautics Collection
General Theory of Aerodynamic Instability and the Mechanism of Flutter
Date: December 1, 1979
Creator: Theodorsen, Theodore
Description: The aerodynamic forces on an oscillating airfoil or airfoil-aileron combination of three independent degrees of freedom were determined. The problem resolves itself into the solution of certain definite integrals, which were identified as Bessel functions of the first and second kind, and of zero and first order. The theory, based on potential flow and the Kutta condition, is fundamentally equivalent to the conventional wing section theory relating to the steady case. The air forces being known, the mechanism of aerodynamic instability was analyzed. An exact solution, involving potential flow and the adoption of the Kutta condition, was derived. The solution is of a simple form and is expressed by means of an auxiliary parameter k. The flutter velocity, treated as the unknown quantity, was determined as a function of a certain ratio of the frequencies in the separate degrees of freedom for any magnitudes and combinations of the airfoil-aileron parameters.
Contributing Partner: UNT Libraries Government Documents Department
Permallink:digital.library.unt.edu/ark:/67531/metadc53413/
General Potential Theory of Arbitrary Wing Sections
Date: December 1, 1979
Creator: Theodorsen, T.
Description: The problem of determining the two dimensional potential flow around wing sections of any shape is examined. The problem is condensed into the compact form of an integral equation capable of yielding numerical solutions by a direct process. An attempt is made to analyze and coordinate the results of earlier studies relating to properties of wing sections. The existing approximate theory of thin wing sections and the Joukowski theory with its numerous generalizations are reduced to special cases of the general theory of arbitrary sections, permitting a clearer perspective of the entire field. The method which permits the determination of the velocity at any point of an arbitrary section and the associated lift and moments is described. The method is also discussed in terms for developing new shapes of preassigned aerodynamical properties.
Contributing Partner: UNT Libraries Government Documents Department
Permallink:digital.library.unt.edu/ark:/67531/metadc53411/
An approximate spin design criterion for monoplanes, 1 May 1939
Date: January 1, 1976
Creator: Seidman, O.
Description: An approximate empirical criterion, based on the projected side area and the mass distribution of the airplane, was formulated. The British results were analyzed and applied to American designs. A simpler design criterion, based solely on the type and the dimensions of the tail, was developed; it is useful in a rapid estimation of whether a new design is likely to comply with the minimum requirements for safety in spinning.
Contributing Partner: UNT Libraries Government Documents Department
Permallink:digital.library.unt.edu/ark:/67531/metadc53319/
Methods of analyzing wind-tunnel data for dynamic flight conditions
Date: January 1, 1976
Creator: Donlan, C. J.
Description: The effects of power on the stability and the control characteristics of an airplane are discussed and methods of analysis are given for evaluating certain dynamic characteristics of the airplane that are not directly discernible from wind tunnel tests alone. Data are presented to show how the characteristics of a model tested in a wind tunnel are affected by power. The response of an airplane to a rolling and a yawing disturbance is discussed, particularly in regard to changes in wing dihedral and fin area. Solutions of the lateral equations of motion are given in a form suitable for direct computations. An approximate formula is developed that permits the rapid estimation of the accelerations produced during pull-up maneuvers involving abrupt elevator deflections.
Contributing Partner: UNT Libraries Government Documents Department
Permallink:digital.library.unt.edu/ark:/67531/metadc53322/
Spin tests of a low-wing monoplane to investigate scale effect in the model test range, May 1941
Date: January 1, 1976
Creator: Donlan, C. J.
Description: Concurrent tests were performed on a 1/16 and a 1/20 scale model (wing spans of 2.64 and 2.11 ft. respectively) of a modern low wing monoplane in the NACA 15 foot free-spinning wind tunnel. Results are presented in the form of charts that afford a direct comparison between the spins of the two models for a number of different conditions. Qualitatively, the same characteristic effects of control disposition, mass distribution, and dimensional modifications were indicated by both models. Quantitatively, the number of turns for recover and the steady spin parameters, with the exception of the inclination of the wing to the horizontal, were usually in good agreement.
Contributing Partner: UNT Libraries Government Documents Department
Permallink:digital.library.unt.edu/ark:/67531/metadc53320/