Search

The primary purpose of this study is to develop a nonlinear feedback control law for the F / A-I8 fighter aircraft that performs a fast half-loop maneuver. This feedback law is developed using a singular perturbation approach. A secondary purpose of this study is to establish a baseline for time optimal half-loop maneuvers. The singular perturbation approach makes it possible to develop a state feedback control law which rotates the velocity vector through one hundred and eighty degrees at a maximum equilibrium pitch rate with a nearly constant angle of attack. The response of the aircraft to the control law is compared to simulations of half-loop maneuvers generated at NASA Langley Research Center. Master of Science

A wing with a Wortmann FX-63-137-ESM airfoil section has been used to study some unique problems encountered in wing aerodynamics in the range of Reynolds numbers between 50,000 and 500,000. The wind-tunnel testing conducted in the 6'x 6' Stability tunnel included strain-gauge data, pressure data, and flow-visualization studies. The laminar separation bubble which frequently occurs on the upper surface of the wing is found to dominate its performance and gives rise to a hysteresis loop for lift and drag. Changes in airfoil performance due to positive flap or control surface deflections resemble changes witnessed at higher Reynolds numbers. Negative deflections are seen to considerably change the stall behavior and the flow over the airfoil. This is due to the considerably greater effect on the separation bubble for negative flap deflections. The structure and mechanism of the laminar separation bubble can also be altered by the introduction of selected acoustic disturbance and increased free-stream turbulence. The wind-tunnel test-section environment is, therefore, capable of considerably altering wing performance in this regime. Ph. D. incomplete_metadata

A reduced order model describing the energy and heading angle dynamics of a scramjet missile is developed using a singular perturbation technique. The cruise analysis is briefly reviewed to determine the conditions at which the missile will cruise most efficiently. The turn and climb performance of the missile over the conditions of interest is then examined and a family of extremal trajectories is constructed which asymptotically approach the cruise at an intermediate altitude. Master of Science

In recent years the problem of designing a feedback control law to stabilize a linear, time-varying uncertain system has received considerable attention. However, the problem is usually limited to the case of systems which satisfy the "matching" assumptions. Moreover, the question of the existence of a linear stabilizing control, if a nonlinear stabilizing control exists, is still unanswered. In the present work an attempt is made to design a stabilizing, linear, feedback control law for a specific second order, linear system which contains time-varying uncertainties into both the state and input matrices and does not satisfy the matching conditions. For specific values of the uncertainty bounds this system is quadratically stabilizable but not quadratically stabilizable via linear control. Master of Science

A polygonal body of revolution consisting of discrete meridional members joined by regular polygons is optimized for maximum drag and drag coefficient. The meridional, or primary members, carryall of the radial loads and the membrane structure transfers applied pressure loads to the primary members. The shape of the secondary membrane is found such that the performance index is optimized. Several methods are utilized to solve for the optimum conditions, and an application of these solutions to a parachute design is shown. The results are presented in parametric form with pressure distributions, structural flexibility, and skirt closure angle being the parameters investigated. In general, the results verified experimental data in several areas and that the current shapes used in design cover the optimum region, although refinements could be made in some areas. Of particular significance is the difference in shape for optimum drag and drag coefficient. For maximum drag force, the fullness or the lobing between meridional members should be a maximum throughout the span of the gore, whereas, for the maximum drag coefficient design, the lobing is a minimum in the region near the vent and gradually increases as the meridional distance increases. It was found that the pressure distribution influences the optimum design. For a typical distribution that increases as the meridional distance increases, the gore width should be increased near the skirt for an optimum drag coefficient. Parameter studies show that by increasing the secondary structure flexibility the drag increases, although it is a secondary effect for present designs. A well-known parameter in optimum parachute design is the suspension line length, and this study verifies that increasing the length improves the drag. Optimum conditions are found by use of the maximum principle, steepest descent, and the Rayleigh-Ritz method. Ph. D.

Modern, high performance aircraft are required to be able to fly and be controlled over a wide variety of flight conditions. In order to predict the aircraft behavior and control requirements over the entire flight regime it is necessary to have a proper aerodynamic model. Flight conditions at high angles of attack lead to separated flows making the aerodynamic model more difficult to obtain. In this research wind tunnel experiments are performed on an F-5 air-craft model at high angles of attack, with small oscillations about the body oriented roll axis. In addition the free stream environment can be configured in one of three ways: l) straight uniform flow, 2) curved flow to simulated a horizontal turn, and 3) rolling flow to simulated a roll motion about the relative Velocity vector. Ph. D.

Singular subarcs arise in quite a few problems of flight dynamics. The present study is devoted to the specific problem of ascent and acceleration of a vehicle in atmospheric flight in which a variable-thrust arc forms a part of the optimal trajectory. A two-parameter family of singular arcs was generated for time-range-fuel problems of an ascending rocket, using the modelling of Zlatskiy and Kiforenko. The short-term optimality of the singular subarcs has been checked in terms of certain necessary conditions: the classical Clebsch condition, the Kelley condition or the Generalized Legendre-Clebsch condition and the Goh condition. All these are found to be satisfied computationally for all the candidates. The calculations were repeated for simplified thrust-along-the-path modelling and similar results on optimality obtained. Master of Science

Wind tunnel experiments have been conducted on six different wingtip configurations to determine their wake vortex characteristics. The trailing wingtip vortex was probed by a 1/8 inch diameter five hole yawhead pressure probe in the VPI & SU Stability Wind Tunnel. The vortex tangential and axial velocity profiles are compared at five and twenty chord lengths downstream. Primary focus is placed on the Whitcomb winglet and its individual components, the upper winglet alone and the lower winglet alone. It is shown that the Whitcomb winglet and the upper winglet configuration both produce two distinct vortices of the same rotation. The maximum tangential velocity in each vortex is about 64 percent less than that produced by a conventional wingtip configuration. The axial velocity profiles exhibit strong velocity deficits throughout the vortex core. Aerodynamic force tests were conducted to compare the lift and drag characteristics of the wingtip configurations. Both the Whitcomb winglet and the upper winglet configuration have a remarkable ability to increase the lift-drag ratio and reduce the drag coefficient. Ph. D.