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Air Force Institute of Technology

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Articles 3391 - 3420 of 5700

Full-Text Articles in Engineering

Optimal Coverage Of Theater Targets With Small Satellite Constellations, Axel Rendon Mar 2006

Optimal Coverage Of Theater Targets With Small Satellite Constellations, Axel Rendon

Theses and Dissertations

The daylight passes of a low-Earth orbit satellite over a targeted latitude and longitude are optimized by varying the inclination and eccentricity of an orbit at different altitudes. This investigation extends the work by Emery et al, in which the optimal Right Ascension of the Ascending Node was determined for a circular, matched inclination orbit. The optimal values were determined by a numerical research method based on Emery et al's Matlab program. Results indicate that small increases in inclination raise the number of daylight passes up to 33%. These optimal inclinations depend on the satellite semi-major axis. Eccentricity increases also …

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Experimental Investigation Into The Aerodynamic Ground Effect Of A Tailless Chevron And Lambda-Shaped Ucavs, Won In Mar 2006

Experimental Investigation Into The Aerodynamic Ground Effect Of A Tailless Chevron And Lambda-Shaped Ucavs, Won In

Theses and Dissertations

As future aircraft migrate toward tailless, blended wing body configurations, aircraft designers are faced with a lack of experimental data that represent these types of configurations. A wind tunnel investigation was conducted to identify the ground effect region of two unmanned combat air vehicle (UCAV) models. The AFIT low-speed wind tunnel (LSWT) and ground plane were used to study the forces and moments on the UCAV models in ground effect. The Chevron and Lambda planforms used in this study were originally tested in full-scale for stability and control without ground effects. A static ground plane was used in this study. …

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Structural Design Of Wing Twist For Pitch Control Of Joined Wing Sensor Craft, Fred A. Kimler Iii Mar 2006

Structural Design Of Wing Twist For Pitch Control Of Joined Wing Sensor Craft, Fred A. Kimler Iii

Theses and Dissertations

This research investigated two aspects of the aft wing structure of a joined wing SensorCraft. First, the efficacy of a novel approach for incorporating wing twist for pitch control was analyzed. This design involved adding a spanwise sliding joint into the wing structure at the lower aft spar of the vehicle's aft wing. Second, the joint section where the forward and aft wings connect and form the outboard wing was redesigned and analyzed to improve the load transmission between the wing spars. Using MSC.NASTRAN, linear and non-linear static analyses were performed to examine the efficiency of the wing twist sliding …

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Store Separations From A Supersonic Cone, Richard J. Simko Mar 2006

Store Separations From A Supersonic Cone, Richard J. Simko

Theses and Dissertations

The purpose of this research was to analyze the environment a store would travel through if ejected from a supersonic cone. This was done using the Beggar Computational Fluid Dynamics (CFD) code from the Air Force SEEK Eagle Office at Eglin Air Force Base, FL. CFD simulations were compared to experimental results from a previous AFIT thesis and conclusions were drawn based on whether or not the current wind tunnel setup at AFIT is capable of performing analyses of supersonic store separations. Also included in this research is a study of supersonic base pressure profiles, near-wake velocity profiles, wind tunnel …

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Cfd Investigation Of The Flow Dynamics Inside A Spherical Surface Indentation, Robert C. Vincent Mar 2006

Cfd Investigation Of The Flow Dynamics Inside A Spherical Surface Indentation, Robert C. Vincent

Theses and Dissertations

This study aims to identify the flow structure inside and around a dimple surface indentation that passively reduces flow separation, and to generate characterization parameters for the effectiveness of the aforementioned flow structure in boundary layer separation control. In this study the surface indentation is cut into a flat plate in a diverging channel that creates an adverse pressure gradient. In the baseline flat plate conditions, the shedding vortices formed by the pressure gradient create an oscillating pressure field in the dimple. This geometry has been chosen to simulate the adverse pressure gradient present in the flow regime found on …

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Comparison Of Variance-To-Mean Ratio Methods For Repairables Inventory Management, Lisa J. Mahon Mar 2006

Comparison Of Variance-To-Mean Ratio Methods For Repairables Inventory Management, Lisa J. Mahon

Theses and Dissertations

In an effort to improve aircraft availability, this research compared the efficiency of ten methods of determining variance-to-mean ratios (VTMRs, VMRs, V/Ms) for repairable, spare aircraft parts known as repairables. These methods are base pipeline quantity, Hill-Stevens (220 LRUs), a variation of Hill-Stevens (10 1s), Hill-Stevens (230 LRUs), the Sherbrooke, a variation of Sherbrooke (10 1s), historical data, a new regression function, variance-to-mean ratio equals 1.00 or variance-to-mean ratio equals 1.01. Using VTMRs derived from quarterly organizational intermediate maintenance (OIM) demands for line-replaceable units (LRUs) from the D200A Secondary Item Requirement System (SIRS) databases in aircraft sustainability model scenarios and …

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Simulation Of Weapons Release From Cargo Aircraft, Paul M. Wilson Mar 2006

Simulation Of Weapons Release From Cargo Aircraft, Paul M. Wilson

Theses and Dissertations

The purpose of this study is to develop a computer simulation capable of providing an accurate flight history of an air-dropped munitions dispenser system in order to conduct proof of concept testing. The simulation is intended to serve as an adaptable tool for the development and testing of any cargo aircraft based weapons dispenser system. The simulation allows the user to conduct low-cost, time efficient, and effective tests of various design concepts in determining their operational feasibility and performance envelope. The munitions dispenser system is intended to provide a retrofit combat capability to the USAF C-17 aircraft, delivering massive amounts …

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Fretting Fatigue Behavior Of Shot-Peened In 100, Jonathan L. Ng Mar 2006

Fretting Fatigue Behavior Of Shot-Peened In 100, Jonathan L. Ng

Theses and Dissertations

The fretting fatigue behavior of shot-peened of IN 100 was investigated in this study. S-N curves were obtained for two different shot-peened intensities (7A and 12A) and were compared to those of unpeened specimens. Stress relaxation behavior under fretting fatigue was also investigated after their measurements were obtained using the X-ray diffraction method. The crack initiation location and the crack angle orientation along the surface were determined using optical and scanning electron microscopy (SEM). Cracks initiated near the trailing edge and on the contact surface for both 7A and 12A shot-peened specimens. Finite element analysis was performed using commercially available …

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Creep-Rupture Behavior Of A Woven Ceramic Matrix Composite At Elevated Temperatures In A Humid Environment, Jennifer L. Ryba Mar 2006

Creep-Rupture Behavior Of A Woven Ceramic Matrix Composite At Elevated Temperatures In A Humid Environment, Jennifer L. Ryba

Theses and Dissertations

This study focused on moisture and temperature effects on the embrittlement and stress-rupture life of the SiC/SiC CMC Syl-iBN/BN/SiC. The Syl-iBN/BN/SiC is composed of Sylramic fibers with an in-situ layer of boron nitride (Syl-iBN), boron nitride interphase (BN), and SiC matrix. Stress rupture tests and monotonic tests were performed on the specimens. Tests were conducted under 100% humidity and laboratory air environments at three temperatures, 450°C, 750°C, and 950°C. These temperatures were chosen because they fall below the intermediate range, within the range, and above the range, respectively. This study found that while this CMC does experience embrittlement at intermediate …

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Covariance Estimation And Autocorrelation Of Norad Two-Line Element Sets, Victor P. Osweiler Mar 2006

Covariance Estimation And Autocorrelation Of Norad Two-Line Element Sets, Victor P. Osweiler

Theses and Dissertations

This thesis investigates NORAD two-line element sets (TLE) containing satellite mean orbital elements for the purpose of estimating a covariance matrix and formulating an autocorrelation relationship. Orbit propagation is performed using Simplified General Perturbations Number 4 (SGP4) analytical model as implemented within Satellite Took Kit. For a given satellite, TLEs from a span of two weeks are used to calculate position and velocity differences of estimated state vectors in order to characterize their variance behavior and compute a covariance matrix for the most recent TLE. Six satellites and eight time spans are investigated, with all state vector differences evaluated in …

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A Systems Engineering Approach To Integrated Structural Health Monitoring For Aging Aircraft, Alan P. Albert, Efstathios Antoniou, Stephen D. Leggiero, Kimberly A. Tooman, Ramon L. Veglio Mar 2006

A Systems Engineering Approach To Integrated Structural Health Monitoring For Aging Aircraft, Alan P. Albert, Efstathios Antoniou, Stephen D. Leggiero, Kimberly A. Tooman, Ramon L. Veglio

Theses and Dissertations

The United States Air Force and many of its Coalition partners have extended the original service life of some of their aging aircraft due to fiscal constraints. This life extension often requires increased periodic and in-depth inspections; increasing maintenance costs and resulting in longer periods of aircraft downtime. A structural health monitoring system for aging aircraft could reduce the current inspection burden, and thus decrease costs and system downtime. This presentation describes a baseline systems engineering methodology for system definition of an aging aircraft structural health monitoring system. Analysis was performed to quantify the potential benefit a structural health monitoring …

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Control Demonstration Of A Thin Deformable In-Plane Actuated Mirror, Gina A. Peterson Mar 2006

Control Demonstration Of A Thin Deformable In-Plane Actuated Mirror, Gina A. Peterson

Theses and Dissertations

Current imaging satellites are limited in resolution and coverage area by the aperture size of their primary optical mirror. To get a large optical mirror into space, current launch weight and size restrictions must be overcome. Membrane-like optical mirrors can overcome these restrictions with their very lightweight and flexible properties. However, thin, deformable membrane mirrors are very susceptible to the space environment and require active control for surface stabilization and shaping. The primary goal of this research is to demonstrate that an in-plane actuated membrane-like deformable optical mirror can be controlled to optical wavelength tolerances in a closed-loop system. Fabrication …

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Design, Build And Validation Of A Small-Scale Combustion Chamber Testing Facility, Eric R. Dittman Mar 2006

Design, Build And Validation Of A Small-Scale Combustion Chamber Testing Facility, Eric R. Dittman

Theses and Dissertations

This study investigated the design parameters necessary for the construction and use of a testing facility built to test the combustor section of engines. User inputs were acquired by interview and used in the decisions made in arrangement of pieces of machinery and how different systems were to interact. The design was then carried out as the various parts of the facility were built and installed. Software was designed which controlled the different parts of the combustion process and monitored the different products of combustion as well as the properties of the air and fuel used in the combustion. These …

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Aerodynamic Loss And Mixing Over A Cavity Flame Holder Located Downstream Of Pylon-Aided Fuel Injection, Lane C. Haubelt Mar 2006

Aerodynamic Loss And Mixing Over A Cavity Flame Holder Located Downstream Of Pylon-Aided Fuel Injection, Lane C. Haubelt

Theses and Dissertations

Cavity-based fuel injection and flame holding found in hydrocarbon-fueled scramjet applications are of interest. The Air Force Research Lab (AFRL) and the Air Force Institute of Technology (AFIT) at Wright-Patterson Air Force Base in Ohio are investigating the enhancement of fuel-air mixing with small pylons that project into the supersonic flow upstream of a flame holder cavity. This follows previous qualitative (Mie scattering and NO-PLIF visualizations) results which suggested that injection behind pylons, may improve fuel-air mixing. Three pylons geometries (medium, tall, and wide) shaped as thin triangular wedges with a 30o inclination angle were tested and compared to baseline …

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Experimental Analysis Of Propeller Interactions With A Flexible Wing Micro-Air-Vehicle, Brian J. Gamble Mar 2006

Experimental Analysis Of Propeller Interactions With A Flexible Wing Micro-Air-Vehicle, Brian J. Gamble

Theses and Dissertations

An investigation into the effects of the propeller slipstream on a flexible wing micro-air-vehicle (MAV) was conducted. The Air Force Research Lab, Munitions Directorate designed a man-portable MAV with a 24 in. wingspan and 6 in. root chord to be used for battle damage assessment and reconnaissance. Two wings have been developed for this MAV. One is a rigid carbon-fiber wing and the other consists of flexible parachute material attached to a carbon-fiber skeleton. Experimental methods were implemented to investigate propeller and wing interactions, characterizing torque and thrust requirements on the motor along with aerodynamic forces on the aircraft as …

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Comparative Analysis Of Two-Stage-To-Orbit Rocket And Airbreathing Reusable Launch Vehicles For Military Applications, Joseph M. Hank Mar 2006

Comparative Analysis Of Two-Stage-To-Orbit Rocket And Airbreathing Reusable Launch Vehicles For Military Applications, Joseph M. Hank

Theses and Dissertations

The Department of Defense (DoD) has identified operationally responsive, low-cost access to space as vital to maintaining U.S. military supremacy. Reusable Launch Vehicles (RLVs) will allow the U.S. to keep a technological advantage over our adversaries, and advances in airbreathing propulsion technology have made it feasible for use in space launch vehicles. This study considers two-stage-to-orbit (TSTO) RLV configurations, each using combinations of propulsion including pure rocket, pure turbine, rocket-based-combined-cycle (RBCC), and turbine-based-combined-cycle (TBCC) for the both stages. This study explores the advantages of airbreathing propulsion in those key areas when compared to a baseline configuration, using vehicle empty mass …

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Optimization Of A Low Heat Load Turbine Nozzle Guide Vane, Jamie J. Johnson Mar 2006

Optimization Of A Low Heat Load Turbine Nozzle Guide Vane, Jamie J. Johnson

Theses and Dissertations

Often turbomachinery airfoils are designed with aerodynamic performance foremost in mind rather than component durability. However, future aircraft systems require ever increasing levels of gas-turbine inlet temperature causing the durability and reliability of turbine components to be an ever more important design concern. As a result, the need to provide improved heat transfer prediction and optimization methods presents itself. Here, an effort to design an airfoil with minimized heat load is reported. First, a Reynolds-Averaged Navier-Stokes (RANS) flow solver was validated over different flow regimes as well as varying boundary conditions against extensive data available in literature published by the …

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Fretting Fatigue Behavior Of Nickel Alloy In-100, Elhoucine Madhi Mar 2006

Fretting Fatigue Behavior Of Nickel Alloy In-100, Elhoucine Madhi

Theses and Dissertations

In this study, a systematic investigation of the fretting fatigue behavior of nickel alloy, IN-100 was carried out. The study includes both experimental work and the corresponding analysis of the contact conditions, and the latter is accomplished using the finite element method. Fretting fatigue tests were performed over a wide range of axial stresses to examine both low and high cycle fretting fatigue under constant contact load and the influence of different pad geometries was also explored. It was observed that fretting reduced the fatigue strength of IN- 100, and that increasing cylindrical pad radii does not have the same …

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Development Of Autonomous Unmanned Aerial Vehicle Platform: Modeling, Simulating, And Flight Testing, Nidal M. Jodeh Mar 2006

Development Of Autonomous Unmanned Aerial Vehicle Platform: Modeling, Simulating, And Flight Testing, Nidal M. Jodeh

Theses and Dissertations

The Advanced Navigation Technology (ANT) Center at the Air Force Institute of Technology (AFIT) conducts extensive research in advanced guidance, navigation, and control to exploit the full potential of autonomous Unmanned Aerial Vehicles (UAV). The research in this thesis describes a UAV research platform developed to support the ANT Center's goals. This platform is now the bedrock for UAV simulation and local flight test at AFIT. The research has three major components. The first component is development of a physical, inertial, and aerodynamic model representing an existing aircraft. A systematic analysis of the airframe leads to a complete geometric, inertial, …

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Simulation Of A Moving Elastic Beam Using Hamilton's Weak Principle, Elliott J. Leigh Mar 2006

Simulation Of A Moving Elastic Beam Using Hamilton's Weak Principle, Elliott J. Leigh

Theses and Dissertations

Hamilton's Law is derived in weak form for slender beams with closed cross sections. The result is discretized with mixed space-time finite elements to yield a system of nonlinear, algebraic equations. An algorithm is proposed for solving these equations using unconstrained optimization techniques, obtaining steady-state and time accurate solutions for problems of structural dynamics. This technique provides accurate solutions for nonlinear static and steady-state problems including the cantilevered elastica and flatwise rotation of beams. Modal analysis of beams and rods is investigated to accurately determine fundamental frequencies of vibration, and the simulation of simple maneuvers is demonstrated.

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Validation Of A Scaled Plane Strain Hypervelocity Gouging Model, Ronald J. Pendleton Mar 2006

Validation Of A Scaled Plane Strain Hypervelocity Gouging Model, Ronald J. Pendleton

Theses and Dissertations

The phenomenon of high speed impact is of great interest to the Air Force of Scientific Research and the Air Force Research Laboratory's Holloman High Speed test track. Rocket sled tests at the facility frequently are limited to velocities lower than actually attainable due to damage to the rail in the form of gouges. Direct observation of the gouging phenomenon is not currently possible. This leaves computational modeling as the only means to study the phenomenon. A computer model has previously been used to model the development of gouging at the Holloman High Speed Test Track. However, this model has …

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Effect Of Hold Times On Fatigue Behavior Of Nextel 720™/Alumina Ceramic Matrix Composite At 1200°C In Air And In Steam Environment, John M. Mehrman Mar 2006

Effect Of Hold Times On Fatigue Behavior Of Nextel 720™/Alumina Ceramic Matrix Composite At 1200°C In Air And In Steam Environment, John M. Mehrman

Theses and Dissertations

The aerospace field requires structural materials that can maintain superior mechanical properties while subjected to high temperatures and oxidizing environments. This research investigated the effect of hold times at maximum load on fatigue performance of a Nextel 720/Alumina ceramic matrix composite at 1200 C, explored the influence of environment on material response to cyclic loading with hold times at maximum load, and assessed the effects of loading history on material behavior and environmental durability. The N720/A composite relies on an oxide/oxide composition for inherent oxidation resistance and a porous matrix with no interphase between the fiber and matrix for damage …

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Alleviation Of Buffet-Induced Vibration Using Piezoelectric Actuators, Shawn D. Morganstern Mar 2006

Alleviation Of Buffet-Induced Vibration Using Piezoelectric Actuators, Shawn D. Morganstern

Theses and Dissertations

Buffet-induced vibration has been problematic for aircraft structures for many years. The F-16 ventral fin, while prone to these effects, lends itself well to the evaluation of modern active structural and flow control technologies. The objective of this research was to determine the most critical natural modes of vibration for the F-16 ventral fin and design piezoelectric actuators capable of reducing buffet-induced ventral fin vibration. A finite element model (FEM) for the fin was developed, tuned and optimized to closely match published modal frequencies. Piezoelectric actuator patches were designed using the strain characteristics of the FEM and integrated into the …

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Predicting The Effects Of Contingency Contracting On Local Economies, Donald J. Wagoner Mar 2006

Predicting The Effects Of Contingency Contracting On Local Economies, Donald J. Wagoner

Theses and Dissertations

In recent years, Air Force personnel have been deployed in support of contingency operations to various points on the globe. The Department of Defense spends millions of dollars to support and sustain forces during contingency operations. The Air Force deploys Contingency Contracting Officers (CCO) to support personnel during these operations. During a contingency operation contracting officers will normally establish short-term contracts as quickly as possible to meet mission requirements with little concern for the local economy. This research concluded that the actions of Air Force CCOs can affect the local economy in a deployed location. By providing contingency contracting officers …

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Hazardous Materials Transportation: A Meta-Analysis Of State Level Policy And Regulations, David J. Pastika Mar 2006

Hazardous Materials Transportation: A Meta-Analysis Of State Level Policy And Regulations, David J. Pastika

Theses and Dissertations

Every day, over 800,000 hazmat transactions take place across the United States. This segment of transportation is expected to grow at a modest two percent a year for the foreseeable future but differences of regulations between the state and Federal level have been a growing concern for both the government and members of the hazmat industry. A patchwork of often inconsistent permits, registration requirements, and hazmat organizational structures at the state level often create barriers to the efficient means of commerce for hazmat carriers and shippers. This thesis explores the history of hazardous regulations since de-regulation of the trucking industry …

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Discrete Event Simulation Model Of The Ground Maintenance Operations Cycle Of A Reusable Launch Vehicle, John T. Pope Iii Mar 2006

Discrete Event Simulation Model Of The Ground Maintenance Operations Cycle Of A Reusable Launch Vehicle, John T. Pope Iii

Theses and Dissertations

The Air Force uses a family of expendable launch vehicles to meet its spacelift needs. Unfortunately, this method is not responsive: months of preparation are typically required and launch costs are high. Consequently, the Air Force seeks a reusable military launch vehicle that can be launched inexpensively and quickly regenerated between flights. Air Force Research Laboratory personnel desire a tool to help evaluate candidate designs and perform tradeoff studies necessary to acquire a launch vehicle that will achieve Air Force goals. The objective of this research was first to develop a conceptual model of maintenance operations needed to regenerate a …

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A Discrete Event Simulation Model For Evaluating Air Force Reusable Military Launch Vehicle Prelaunch Operations, Adam T. Stiegelmeier Mar 2006

A Discrete Event Simulation Model For Evaluating Air Force Reusable Military Launch Vehicle Prelaunch Operations, Adam T. Stiegelmeier

Theses and Dissertations

As the control and exploitation of space becomes more important to the United States military, a responsive spacelift capability will become essential. Responsive spacelift could be defined as the ability to launch a vehicle within hours or days from the time a launch order is given, instead of the weeks or months it takes currently. As the Air Force contemplates moving toward a reusable military launch vehicle (RMLV) capability, it faces key design and ground processing decisions that will affect the vehicle regeneration timeline. This thesis develops a computer simulation model that mimics RMLV prelaunch operations-those activities that take place …

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Classification Characteristics Of Carbon Nanotube Polymer Composite Chemical Vapor Detectors, Huynh A. Hinshaw Mar 2006

Classification Characteristics Of Carbon Nanotube Polymer Composite Chemical Vapor Detectors, Huynh A. Hinshaw

Theses and Dissertations

The first step in combating a chemical weapons threat is contamination avoidance. This is accomplished by the detection and identification of chemical agents. The Air Force has several instruments to detect chemical vapors, but is always looking for lighter, faster, and more accurate technology for a better capability. This research is focused on using carbon nanotube polymer composite sensors for chemical detection. More specifically, models are developed to classify three sets of sensor data according to vapor using various multivariate techniques. Also, prediction models of a mixed sensor output are developed using neural networks and regression analysis. The classifiers developed …

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Assessing Resource Value And Relationships Between Objectives In Effects-Based Operations, Robert D. Jones Mar 2006

Assessing Resource Value And Relationships Between Objectives In Effects-Based Operations, Robert D. Jones

Theses and Dissertations

The purpose of this research was developing techniques to calculate the value of a resource within the context of campaign objectives, to identify competing objectives, and to identify conflicting objectives to improve a commander’s ability to allocate limited resources. A methodology was developed to express a campaign’s objective hierarchy in terms of a set of desired end states for the campaign’s system of systems. Value theory was used to identify the resource's value in terms of the direct and indirect effects that are produced to achieve the campaign’s objectives. Binding resource constraints within an integer program were used to identify …

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Analysis Of Patient Information: An Empirical Modeling Approach, Tony A. Murphy Mar 2006

Analysis Of Patient Information: An Empirical Modeling Approach, Tony A. Murphy

Theses and Dissertations

With rising costs and increasing complexities, many hospitals seek to better understand the intricate details of their operations. Increasingly, these organizations have a strong desire to accurately predict the resources required to effectively treat their patient load. This research investigates patient length-of-stay in a hospital neurological unit using an empirical modeling approach. Factors significantly affecting patient length of stay were identified and used to construct a regression model. The predictive model provides hospital decision makers with a compact tool to input what-if scenarios and predict future patient treatment lengths, thus, allowing the hospital to properly allocate resources.

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