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We derive approximate, closed-form expressions for the cycle-averaged forces produced by flapping wings operating in a regime similar to birds and small unmanned aerial vehicles. The model is 2-D and intended mainly as an aid to performance and stability analysis, and control design. The model accounts for the nonlinear behavior of lift at high angles of attack, corrections for unsteadiness, as well as an elementary expression for drag. As an elementary application of the model, we determine the conditions under which the power consumption is minimized and those under which the range is maximized. We demonstrate how the model can be employed gainfully for stability analysis and control design.

This paper presents first-principle and numerical studies of flapping flight with the objective of optimizing the force production and propulsive effciency. Strouhal number is identified as a critical parameter affecting all of these variables, and the optimum ranges of Strouhal number are calculated. The results of the calculations, in particular, explain why a value in the range of 0.2-0.4 is usually preferred by nature's flyers. Next, an attempt is made to quantify the effects of wing flexibility on force generation and propulsive efficiency, and it is shown that there exists a critical value of wing elasticity at which propulsive efficiency is maximized, and moreover, this value is driven primarily by the dynamics of the bending motion of the wing rather than twisting.

This paper considers the problems of (a) modelling the ight mechanics of a tail-less MAV equipped with exible articulated wings, and (b) the analysis of its turning performance. The wings are assumed to have two degrees of freedom - heave and twist. They are assumed to be actuated from the root, which is the abstraction of an experimental control mechanism being developed by the authors. The dihedral and twist angles at the wing root are controlled. A novel actuator concept of axial tension to control wing stiffness has been explored in this paper. It is shown that axial tension in the wing has a significant effect on the turning performance of the aircraft, although the effect is not uniformly beneficial in nature. The effect of exibility on the steady state turning performance of the aircraft has been demonstrated by comparing it with that of a rigid aircraft, and with that of a similar aircraft possessing a wing with different elastic properties.

Contents: Analytical determination of generalized, linear viscoelastic stress-stain reations from uniaxial, biaxial, and triaxial experimental creep and relaxation data. Survey and development of methods for the de termination of strains in solid propellants. Parameter calculations of simple propellant grains for temperature cycling, pressuriza tion, and acceleration. Stress analysis of propellant grains using dis placement equations. Finite difference solution of ordinary and partial differential equations. Studies relating to structural analysis of solid propellants. Investigation of the failure of solid fuels under combined stresses.