A theory and method have been developed and design change drawn, for the estimation of certain stability derivatives for wings of arbitrary platform in subsonic flow. / Ph. D.

Wing structures often contain nonlinearities which affect their aeroelastic behavior and performance characteristics. Aerodynamic flows at transonic Mach numbers generate nonlinear aerodynamic forces on the wing affecting the aeroelastic response of the wing. Analysis techniques accounting for these structural and aerodynamic nonlinearities, and an understanding of their potential influence on the flutter mechanism of two-dimensional and three-dimensional wing-structures model are the main objective of this study. Two different categories of structural nonlinearities, i.e. (i) distributed nonlinearity and (ii) concentrated nonlinearity , are considered. The concentrated nonlinearities are mathematically modeled using Asymptotic Expansion method which based on on the Krylov-Bogoliubov-Mitropolski technique. The effective stiffness coefficient of a nonlinear element is defined as the ratio of the amplitude of the Fourier series expansion of the load and the amplitude of the displacement of that element. The effects of distributed nonlinearities on the aeroelastic characteristic of three-dimensional wing model are also investigated. The influences of this type of nonlinearity is treated in a quasi-nonlinear approach, which allows the variation of the the natural frequencies and damping factor of the structure model with respect to the amplitude of the motion. The transonic aerodynamic pressure distributions have been obtained by solving the unsteady Transonic Small Disturbance ( TSD ) flow equation using finite-difference techniques. An Alternating Direction Implicit ( ADI ) algorithm was used for two-dimensional flow model, and an Approximate Factorization ( AF ) algorithm was used for three-dimensional flow model. The finite-state generalized aerodynamic forces used in the aeroelastic analysis have been calculated by employing the Method of Harmonic Oscillation and the Pulse Transfer Function analysis. The solution of the aeroelastic equation in frequency domain is obtained by representing the equation in a finite-state form through the modal approach using Lagrange’s equation. The flutter boundary is obtained by solving this equation using the classical U-g method and root locus analysis. Flutter analysis of a two degree-of-freedom , two-dimensional typical wing sections with nonlinear torsional springs are studied. The aeroelastic responses of the system are obtained by integrating the nonlinear structural terms and aerodynamic terms simultaneously using Newmark-β and Wilson-θ methods. Flutter results obtained from both time integration and eigenvalue solutions are compared. These two results, in general, are in agreement. Flutter behavior of a simple three-dimensional swept wing model is also investigated. Comparison of the flutter boundary obtained by using the eigenvalue solution with flutter data from wind-tunnel experiments are made. / Ph. D.

no abstract provided by author / Master of Science

This thesis considers the problem of the directional instability, as exhibited by aircraft with tricycle landing gear, during the landing roll after touchdown. The approximate equations of motion are solved on an analog computer to describe the motion of an aircraft as it moves along the runway after it has landed. It is shown that during the landing roll the tricycle landing gear arrangement with a locked nosewheel is basically an unstable configuration. The principle cause of this instability is the nosewheel itself, since it contributes a large destabilizing component to the aircraft’s overall directional stability. This undesirable influence can be reduced by using the elevator, or the horizontal tail, to keep the nosewheel lightly loaded during the landing roll. Because of the inherent instability of a tricycle landing gear, some type of control is needed to keep the aircraft on the runway during the landing roll. Both the rudder and the nosewheel were examined to determine their effectiveness as steering controls. It was found that the airplane is more easily controlled if either the elevator or the horizontal tail is used to reduce the load on the nosewheel. / Master of Science

Several mathematical models are developed for a hose-drogue refueling system in an attempt to represent the physical system accurately and to subsequently observe the dynamic response of the system under different initial conditions. The mathematical models examined include a flexible hose model and a model which includes elastic bending effects. The equations of motion include aerodynamic, gravitational, and tensile forces, and solutions of the refueling system are found using fewer assumptions than in previous work. Once the equations of motion are developed, they are separated into equilibrium and perturbation portions. Solutions of the nonlinear equilibrium tension distribution are obtained by solving the equations in closed form using a two point boundary value problem solver program. The solution to the linear equilibrium tension distribution is found and compared to the nonlinear solutions. Results indicate that the behavior of the solutions is similar, but the linear solution gives larger values of tension near the hose attachment point. The perturbation equation is discretized using a finite difference scheme and the resulting first order differential matrix equation is integrated to calculate the dynamic response for given parameters and initial conditions with the various equilibrium tension distribution solutions. Results show negligible differences between the different tension values upon substitution and it is therefore recommended that the linear approximation to the equilibrium tension distribution be used in analysis of this hose-drogue refueling system because of the ease in obtaining solutions with this method. / M.S.

An investigation to determine the low-speed lateral-directional characteristics of a generic 74-degree delta wing-body configuration employing the latest generation, gothic planform vortex flaps has been conducted. In addition, the theoretical estimates from VORSTAB were compared against experimental data to aid in documenting this new method. VORSTAB is an extension of the Quasi-Vortex-Lattice Method of Lan which empirically accounts for vortex breakdown effects in the calculation of longitudinal and lateral-directional aerodynamic characteristics. The experimental results indicated that leading-edge deflections of 30 and 40 degrees significantly reduce the magnitude of the wing effective dihedral relative to the baseline for a specified angle of attack or lift coefficient. For angles of attack greater than 15 degrees, these flap deflections reduce the configuration directional stability despite improved vertical tail effectiveness. Asymmetric leading edge deflections are shown to be inferior to conventional ailerons in generating rolling moments. Asymmetric leading-edge deflections are effective in producing side force at moderate to high angles of attack. VORSTAB lateral-directional calculations provide ballpark estimates at low to moderate angles of attack. The theory does not account for vortex flow induced, vertical tail effects at high angles of attack and should not be used for this angle of attack region. The empirical formulae for predicting vortex burst effects are not reliable in their present form. Although the basic trends are correct, the magnitude of the predicted vortex burst effect is typically over-estimated. / Master of Science

Aircraft Cruise Performance is examined by using energy-state modelling to investigate fuel-range optimal trajectories. Chattering controls are considered appropriate when the hodograph is non-convex. Classical steady-state cruise, simple chattering-cruise and the extended chattering-cruise models are studied as constrained parameter-optimization problems. The term "extended chattering" refers to vehicle system modelling extended to maintain vertical equilibrium only on the average. Numerical solution is obtained using a variable-metric gradient-protection algorithm and computational results are presented for three different aircraft. This study shows that simple chattering cruise for certain specific energies can result in substantial fuel savings over classical steady-state cruise. However extended chattering cruise results in only marginal fuel savings when compared to simple chattering cruise. / Master of Science

During the design of an aircraft it becomes necessary to predict the aircraft handling qualities. Previously, this has been done through the use of pilot opinion ratings of similar vehicles. However, it is desirable to develop more objective means of predicting handling qualities which also do not require the expensive flight testing or simulation necessary to obtain pilot ratings directly. An analysis of the closed-loop pilot-airframe system is performed, utilizing the linear human-pilot transfer function in conjunction with conventional servoanalysis techniques. Boundaries are developed on aircraft frequency and damping ratio for "good" longitudinal short-period control. The lateral phugoid mode is also investigated and the conclusion reached is that this mode cannot be controlled in a manner resulting in "good" pilot ratings. Comparison of the results obtained for the longitudinal short-period mode with experimental data indicates that the analysis is valid. Experimental data is lacking for comparison in the case of the lateral phugoid mode. / M.S.

To provide quality benchmark data (that can be used in numerical simulation comparisons) and to examine the effects of combustion on a typical ramjet engine flowfield, a water-cooled, stainless steel dump combustor model was developed. A two-component Laser Doppler Anemometer (LOA) was used to measure the mean and turbulent velocities in the axial and tangential directions and provide a comparison between combusting and isothermal flows. However, before any LOA measurements could be taken, the combustor had to be configured to run in a suitably stable mode. Stability was identified by the pressure spectra obtained under various running conditions using piezoelectric pressure transducers wired to a spectrum analyzer. Operational parameters such as fuel composition, fuel injection location, acoustic configuration, and equivalence ratio were varied until instabilities were minimized. The optimal configuration ran with upstream fuel injection (premixed mode) at the duct center line and an orifice plate installed immediately upstream of the fuel injectors, with propane as the fuel. Once stability was achieved, LOA data was taken. The results showed some significant differences between the reacting and nonreacting flows. The most significant effect was the difference between the inherent recirculation regions for each case. Combustion decreased the length of the region by approximately 50 percent, while increasing the maximum negative velocities. This made for a more compact, but stronger, recirculation region. Since the recirculation region acts as the main flame holder and is a major source of turbulence, the changes in this region significantly altered the dump combustor flowfield. / Master of Science

A methodology is developed to address the analyses of combat aircraft attrition. The operations of an aircraft carrier task force are modeled using the systems dynamics simulation language DYNAMO. The three mission-roles include: surface attack, lighter escort, and carrier defense. The level of analysis is performed over the entire campaign, going beyond the traditional single·sortie analysis level. These analyses are performed by determining several measures of effectiveness (MOEs) for whatever constraints are applied to the model. The derived MOEs include: Campaign Survivability (CS), Fractlon of Force Lost (FFL), Exchange Ratio (ER), Relative Exchange Ratio (RER), Possible Crew Loss (PCL), and Replacement Cost (RC). RER is felt to be the most useful MOE since it considers the initial inventory levels of both friendly and enemy forces, and its magnitude is easy for the analyst to relate to (an RER greater than one is a prediction of a friendly force’s victory). The simulation model developed in this research is run for several experiments. The effects of force size on the MOEs ls studied, as well as a hypothetical multimission aircraft deployed to perform any of the three missions (albeit at lower effectiveness than the speciallzed aircraft for their given roles but nonetheless with a higher availability). Evaluation of specific technological improvements such as smaller radar cross section, higher thrust/weight, improved weapons ranges, is made using the MOEs. Also, a cost-effectiveness tradeoff methodology is developed by determining the acquisition cost ratio (ACR) for certain modified alternatives the baseline by determining the required initial inventory of modified aircraft to produce the same total effectiveness of the baseline aircraft. / Ph. D.