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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

The solution of the equations of motion of an aircraft fuselage-landing gear configuration during landings is of interest to the designer who must predict the landing loads which an airplane encounters in service. In general such solutions are difficult because of the highly nonlinear characteristics of the oleo-pneumatic shock strut which couples the lower mass of the landing gear to the fuselage. In the past, attempts to obtain solutions by linearization of these shock strut characteristics have resulted in unrealistic predictions of landing gear motions. Therefore, it has been necessary to carry out most of the theoretical analysis associated with landing gears by means of numerical integration procedures. These numerical methods are tedious, and as a result a large portion of design work has been carried out by means of trial and error drop testing of a system of masses representative of an airplane and landing gear. This in turn has proved to be time consuming and expensive. This paper presents a method for obtaining an analytical solution of the equations of motion for a basically nonlinear system which closely resembles an actual airplane and landing gear configuration. The nonlinear system considered has two degrees of freedom and is composed of a large mass representative of the fuselage-wing combination connected by an oleo-pneumatic shock strut to a wheel. The shock strut is assumed to have velocity-squared hydraulic damping and coulomb friction forces on the strut bearings. The nonlinear spring characteristic of the tire is represented by a sectionally linear spring. In the first part of this paper the equations of motion for this nonlinear system are derived making use of a few simplifications which previous papers have shown to be justified. Also, the degree to which these assumptions limit the results is discussed. Next these equations of motion are solved in analytical form by a method which may be called "equivalent non linearisation." It is shown that this solution is exact only for a specific combination of impact parameters, but that for a wide range of parameters the solution describes the motion of the system adequately for design purposes. Finally, a few analytical solutions are compared with solutions obtained by numerical integration methods; and the results are compared with experimental data for a typical impact. / Master of Science

This thesis reports the investigation into the modelling and simulation of an aircraft tyre and wheel assembly in finite element environment. The finite element simulations basing on aircraft tyre test and operational scenarios could predict the loads transferred from tyre and the stresses distributed to the wheel rim. The virtual analysis could assess the safety criteria of different tyre structures, which would lead to the cost and time circle reduction in tyre R&D process. An H41x16.0R20 radial ply aircraft test tyre and its corresponding test wheel, provided by Dunlop Aircraft Tyres Limited, are adopted as the subject of this research. The material properties, especially the rubber and fabric materials, have been investigated. The finite element hyperelastic models have been utilized to represent rubbers and been correlated to experimental data. The 2D and 3D finite element tyre models, along with the finite element wheel models are created in the commercial finite element code, LS-Dyna. The finite element models have been validated with either industrial standardised simulation results or experimental data. Basing on the validated models, simulations that duplicating static test and dynamic operational scenarios have been developed. The researches have provided knowledge in comparing single and double bead tyre designs with respect to wheel loading mechanisms. The computational model also allowed manufacturers to assess the performance and safety criteria of a particular tyre at its design stage. The development of such models would add to the general drive towards the use of more virtual prototypes in an area traditionally reliant on experimental testing.

Thesis. 1978. E.A.A.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERONAUTICS. / Bibliography: leaves 130-133. / by C.W. Acree, Jr. / E.A.A.

Continuous Descent Arrival (CDA) procedures have been shown to minimize the thrust required during landing, thereby reducing noise, emissions, and fuel usage for commercial aircraft. Thus, implementation of CDA at Atlanta's Hartsfield-Jackson International Airport, the world's busiest airport, would result in significant reductions in environmental impact and airline operating costs. The Air Transportation Laboratory at Georgia Tech, Delta Air Lines, and the local FAA facilities (Atlanta Center and Atlanta TRACON) collaborated to design CDA procedures for early morning arrivals from the west coast. Using the Tool for Analysis of Separation and Throughput (TASAT), we analyzed the performance of various aircraft types over a wide range of weights and wind conditions to determine the optimum descent profile parameters and to find the required spacing between aircraft types at a fixed metering point to implement the procedure. However, to see the full benefits of CDA, these spacing targets must be adhered, lest there will be a loss in capacity or negation of the noise, emissions, and fuel savings benefits. Thus a method was developed to determine adjustments to cruise speeds while aircraft are still en route, to achieve these spacing targets and to optimize fleet wide fuel burn increase. The tool in development, En route Speed Change Optimization Relay Tool (ESCORT), has been shown to solve the speed change problem quickly, incorporating aircraft fuel burn information and dividing the speed changes fairly across multiple airlines. The details of this tool will be explained in this thesis defense. Flight tests were conducted in April-May of 2007, where it was observed that the spacing targets developed by TASAT were accurate but that delivery of these aircraft to the metering point with the desired spacing targets was very challenging without automation. Thus, further flight tests will be conducted in 2008 using the en route spacing tool described above to validate the improvement it provides in terms of accurately delivering aircraft to the metering point.

Congestion and delay problems at airports have received much attention in recent years because of the unbalanced condition between demand and supply. Recent demand forecasts indicate that the problems are expected to increase in the next decade. Relieving congestion of the air transportation networks requires several strategies to enhance the runway capacity. Among these strategies is reducing the runway occupancy time a critical factor in affecting runway capacity. And one approach to reducing the runway occupancy time (ROT) is locating the high speed exits optimally. In addressing the reduction of the runway occupancy time, a full information on the distribution of aircraft landing distance is required. The landing performance at a specific airport may be found by observing the actual landings. However, this is costly and may not be transferable to other airports. An alternative approach is to use a simulation model. A simulation model was built at Center for Transportation Research at Virginia Tech based on point mass kinematics in the flying phase over runway and the ground roll phase on runway to predict the landing roll distance and time to a specified exit speed. Many influencing parameters were incorporated into the model, and then were calibrated using the field data obtained from real operations. The prediction of a nominal landing roll distance and time to decelerate to a specified exit speed is not sufficient for estimating ROT because the additional time to reach a designated exit should be taken into account. To compute the additional time, a braking adjustment scheme is selected from several alternative schemes. The combination of the selected braking adjustment scheme and the simulation model approximates very closely the observed ROT. An optimization model is formulated to determine the exit locations so as to minimize the weighted average ROT of the defined aircraft mix. A polynomial-time solution algorithm is developed for this model using Dynamic Programming technique. The major input parameters for the model are the distribution of the landing roll distance to the specified exit speed and the information on the aircraft mix. The model structured to address the problem of designing a new runway as well as the problem of improving an existing runway. A runway capacity model is used to convert the optimized ROT into capacity gains. Four scenarios are analyzed. Among the scenarios, one is based on the present Air Traffic Control procedures, and three are based on the future developments. The capacity analysis reveals that the ROT does not affect the runway capacity for landing operations. However, the ROT is found as a critical factor for the runway capacity for mixed operations. Hence, the ROT should be optimized for the current system and more crucially for the future developments. The capacity gains by optimizing the ROT under the current Air Traffic Control systems and standards are estimated 2 to 7 more operations per hour. These gains will increase to 20 more operations per hour in the future environment. / Ph. D.

This study outlines the development and use of several techniques providing an automated landing, roll out and turnoff of an aircraft, in an airport environment. A maximum runway occupancy time and a certain level of reliability are achieved by the use of a computer software called the Probabilistic Computer Model of Optimal Runway Turnoffs. A bunching of eight optimal high speed exits, representing four TERPS categories, is performed on a single runway. Feasibility of the system is determined by the use of Inertial Navigation and other aids such as the Microwave Landing System, Filtering Devices, Electronic Cockpit Airfield Display Formats, Real Time Flight Simulation and Field Testing, and a Braking Guidance Policy. It is suggested that future testing and a review of the Model be done. / M.S.

The object of this thesis is to determine the directional stability of a tricycle-geared aircraft during the landing roll. The motion of the aircraft is simulated by a computer program based on the appropriate equations of motion. Empirical aircraft and tire data are utilized in order to improve the simulation process. The stability of the aircraft is obtained by analyzing the motion of the vehicle after an initial disturbance about the vertical axis of the aircraft. The influence of the aircraft's velocity and other parameters on the stability is then determined. For the single-engine Cessna, the results show that a steady-state yaw angle is obtained after an initial disturbance. The results are presented graphically to show the effect of various parameters on the aircraft's stability. / Master of Science

A general numerical simulation of closely coupled lifting surfaces in steady and unsteady ground effects was developed. This model was coupled with the equations of motion to simulate aerodynamic-dynamic interaction. The resulting model was then coupled with a feedback-control law to form a general nonlinear unsteady numerical simulation of control of an aircraft in and out of ground effect. The aerodynamic model is based on the general unsteady vortex-lattice method and the method of images. It is not restricted by planform, angle of attack, sink rate, dihedral angle, twist, camber, etc. as long as stall or vortex bursting does not occur. In addition, it has the versatility to model steady and unsteady aerodynamic interference. The present model can be used to simulate any prescribed flare and to model the effects of cross and/or head winds near the ground. The present results show the influences of various parameters on the aerodynamic coefficients for both steady and unsteady flows. Generally, the ground increases the aerodynamic coefficients; the greater the sink rates, the stronger the effects. Increasing the aspect ratio increases both the steady and unsteady ground effects. An exception is a large aspect-ratio wing with large camber. The present results are generally in close agreement with limited exact solutions and experimental data. In the aerodynamic-dynamic simulation, the equations of motion were solved by Hammlng's predictor-corrector method. The aircraft, air stream, and control surfaces were treated as a single dynamic system. The entire set of governing equations was solved simultaneously and interactively. The aerodynamic-dynamic model was used to study a configuration that resembles a Cessna 182 airplane. The ground lowers the effectiveness of the tail in controlling pitch, increases the lift and drag, and makes the hinge-moment less negative. Proportional and rate control laws were used in a feedback system to control pitch. One set of gains was used in and out of ground effect. For the same control input, the pitch angle responds faster and overshoots more near the ground than it does far from the ground. The present results demonstrate the feasibility of using the current simulation to model more complicated motions and the Importance of including the unsteady ground effects when analyzing the performance of an airplane during a landing maneuver. / Ph. D.