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Articles 1 - 30 of 82
Full-Text Articles in Engineering
Final Assembly, Testing And Processing Of The Rigidizable Inflatable Get-Away-Special Experiment (Rigex) For Spaceflight Qualification, Jeremy J. Owens
Final Assembly, Testing And Processing Of The Rigidizable Inflatable Get-Away-Special Experiment (Rigex) For Spaceflight Qualification, Jeremy J. Owens
Theses and Dissertations
The purpose of this research is to complete the building, testing, verification, and qualification of the Rigidizable Inflatable Get-Away-Special Experiment (RIGEX) for spaceflight. The process of qualifying a payload for spaceflight is discussed, specifically addressing the issues of operability and survivability verification of a general payload. The spaceflight qualification process is then applied to the RIGEX payload at the Air Force Institute of Technology (AFIT) and at the Johnson Spaceflight Center (JSC) in Houston, TX, capstoning the work of 12 masters students and 3 summer interns that has already gone into the RIGEX project over the last 7 years. The …
Optimal Control Strategies For Constrained Relative Orbits, David J. Irvin Jr.
Optimal Control Strategies For Constrained Relative Orbits, David J. Irvin Jr.
Theses and Dissertations
The US Air Force's ability to protect space assets is enhanced by a proficiency in satellite proximity operations and Space Situational Awareness (SSA). In pursuit of that proficiency, this research develops a key capability of interest to mission planners; the ability of a deputy satellite to "hover" within a defined volume fixed in the vicinity of a chief satellite for an extended period of time. This research finds optimal trajectories, produced with discrete-thrusts, that minimize fuel spent per unit time and stay within the user-defined volume, thus providing a practical hover capability in the vicinity of the chief. The work …
Raman Scattering Study Of Supercritical Bi-Component Mixtures Injected Into A Subcritical Environment, Young Man An
Raman Scattering Study Of Supercritical Bi-Component Mixtures Injected Into A Subcritical Environment, Young Man An
Theses and Dissertations
This research studies the species distribution profiles of methane/ethylene bi-components at downstream locations filled with subcritical nitrogen in a closed chamber. Unique thermodynamic and transport properties of supercritical fluids along with phase transition phenomena during fuel injection process can significantly change combustion characteristics inside a scramjet combustor. Plume properties of supercritical jets are of great interests to the studies of fuel/air mixing and subsequent combustion. The primary goal of this research is to help to clarify whether there is any preferential condensation within the condensed jets. The Raman Scattering technique is used to quantify spatial distribution of injected methane and …
Cyclic Creep And Recovery Behavior Of Nextel™ 720/Alumina Ceramic Matrix Composite At 1200° C In Air And Steam Environments, Bridgett A. Whiting
Cyclic Creep And Recovery Behavior Of Nextel™ 720/Alumina Ceramic Matrix Composite At 1200° C In Air And Steam Environments, Bridgett A. Whiting
Theses and Dissertations
The cyclic creep and recovery behaviors of the N720/Al2O3 composite were investigated in this research. The ceramic matrix composite (CMC) contains a porous alumina matrix with laminated, woven mullite/alumina (NextelTM 720) fibers. The composite does not have an interface between the fiber and matrix. The CMC relies on the porous nature for flaw tolerance. The objective of this study the influences of monotonic creep and cyclic creep loading histories on the creep lifetime, creep strain rate, accumulated creep strain as well as on the recovery of creep strain at near zero stress. The cyclic creep and …
Comparative Study Of Aerodynamic Interference During Aft Dispense Of Munitions, Matthew G. Burkinshaw
Comparative Study Of Aerodynamic Interference During Aft Dispense Of Munitions, Matthew G. Burkinshaw
Theses and Dissertations
Based on forthcoming USAF needs, an investigation was launched to further the understanding of aft dispense of munitions in a high-speed environment. A computational fluid dynamics (CFD) study was performed followed by a wind tunnel experiment. The study consisted of a strut-mounted cone simulating a parent vehicle and a sting mounted cone-cylinder store situated directly behind the cone. The CFD modeled the test objects inside a supersonic wind tunnel in which the experiments took place. The CFD study consisted of evaluating a new strut designed to reduce asymmetry in the airflow aft of the cone. The CFD study also included …
Radar Orbit Analsis Tool Using Least Squares Estimator, Sandra M. Rashash
Radar Orbit Analsis Tool Using Least Squares Estimator, Sandra M. Rashash
Theses and Dissertations
Most objects tracked in space follow a regular Keplerian orbit; unfortunately, non-Keplerian objects such as maneuvering satellites, tethered systems, and thrusting ballistic missiles are becoming more common. It is important to be able to distinguish between Keplerian and non-Keplerian objects due to the potential risk of a tethered satellite being mistaken for an object on re-entry. This research focused on creating a computer model that can detect the non-gravitational acceleration present in non-Keplerian orbits. A 3rd order Taylor series expansion was used to model the dynamics and to produce simulated radar data. Linear least squares estimation was used to estimate …
Finite Element Analysis Of Lamb Waves Acting Within A Thin Aluminum Plate, Sejin Han
Finite Element Analysis Of Lamb Waves Acting Within A Thin Aluminum Plate, Sejin Han
Theses and Dissertations
Structural health monitoring (SHM) is an emerging technology that can be used to identify, locate and quantify structural damages before failure. Among SHM techniques, Lamb waves have become widely used since they can cover large areas from one single location. Due to the development of various structural simulation programs, there is increasing interest in whether SHM data obtained from the simulation can be verified by experimentation. The objective of this thesis is to determine Lamb wave responses using SHM models in ABAQUS CAE(a Finite Element Analysis(FEA) program). These results are then compared to experimental results and theoretical predictions under isothermal …
Navigation Using Orthogonal Frequency Division Multiplexed Signals Of Opportunity, Jamie S. Velotta
Navigation Using Orthogonal Frequency Division Multiplexed Signals Of Opportunity, Jamie S. Velotta
Theses and Dissertations
The global positioning system (GPS) provides high-accuracy position measurements anywhere in the world. However, a limitation of this system is that a line of sight to multiple satellites is required; therefore, it is unsuitable to use indoors or in urban canyons. Also, in the presence of radio-frequency interference or jamming, GPS may be unavailable. Alternative methods of navigation and positioning are need to either compliment GPS as a backup or for use in areas unreachable by satellites. This research analyzes a feature-based correlation approach for determining reception differences between two Orthogonal Frequency Division receivers for the purpose of TDOA calculations. …
Common Aero Vehicle Autonomous Reentry Trajectory Optimization Satisfying Waypoint And No-Fly Zone Constraints, Timothy R. Jorris
Common Aero Vehicle Autonomous Reentry Trajectory Optimization Satisfying Waypoint And No-Fly Zone Constraints, Timothy R. Jorris
Theses and Dissertations
To support the Global Strike mission, an autonomous trajectory optimization technique is presented to minimize the flight time, satisfy terminal and intermediate constraints, and remain within the specified vehicle heating and control limitations. "Waypoints" are specified for reconnaissance or multiple payload deployments and "no-fly zones" are specified for geopolitical restrictions or threat avoidance. The Hypersonic Cruise Vehicle (HCV) is used as a simplified two-dimensional platform to compare multiple solution techniques. The solution techniques include a unique geometric approach, an analytical dynamic optimization technique, and a numerical approach. This numerical technique is a direct solution method involving pseudospectral methods and nonlinear …
Validation Of The Afit Small Scale Combustion Facility And Oh Laser-Induced Fluorescence Of An Atmospheric Laminar Premiext Ed Flame, Stephen J. Koether
Validation Of The Afit Small Scale Combustion Facility And Oh Laser-Induced Fluorescence Of An Atmospheric Laminar Premiext Ed Flame, Stephen J. Koether
Theses and Dissertations
Construction in the AFIT combustion facility is complete and the objective of this report is to explain the steps taken to make the laboratory operational. The infinite radius Ultra-Compact Combustor (UCC) sectional model has been delivered and is fully installed with all fuel, air and instrument lines. Every major system in the lab has been tested and is functioning properly. Laboratory operating procedure has been established to ensure both safety and continuity in experimental results. Finally, the lab has been certified through official safety channels and combustion experiments are underway. The unique capability of the AFIT combustion laboratory is the …
Flight Dynamic Response Of Hale Aircraft To Kc-135 Flowfield, Amanda J. Devuono
Flight Dynamic Response Of Hale Aircraft To Kc-135 Flowfield, Amanda J. Devuono
Theses and Dissertations
This research effort examines the static effects of a KC-135 flowfield on a flexible winged Sensorcraft model. The KC-135 flowfield data is generated by a vortex lattice code and integrated into Sensorcraft model for analysis. Building on previous research, a refueling situation was modeled to note the effects of the Sensorcraft at varying locations within the flowfield. The Sensorcraft model was analyzed for both rigid and flexible wings as a means of comparision. Flowfield locations of interest were determined and trimmed conditions were computed for each flowfield location. Utilizing the trimmed condition and flowfield locations, the nonlinear set of EOM's …
Rotorcraft Smoothing Via Linear Time Periodic Methods, Christopher S. Schulz
Rotorcraft Smoothing Via Linear Time Periodic Methods, Christopher S. Schulz
Theses and Dissertations
This research presents the development of an on line linear time periodic rotor vibration controller. The Cramer-Rao bound is developed for a linear time periodic system in order to identify the quality of identified system parameters, which are used in system models for controller development. The methods developed in this work allow model parameters can be verified for accuracy and likewise adjusted to improve controller accuracy.
Performing Particle Image Velocimetry In A Supersonic Wind Tunnel Using Carbon Dioxide As The Seed Material, Donald W. Peltier Iii
Performing Particle Image Velocimetry In A Supersonic Wind Tunnel Using Carbon Dioxide As The Seed Material, Donald W. Peltier Iii
Theses and Dissertations
Particle image velocimetry (PIV) was performed utilizing clean seed particles generated by injecting liquid carbon dioxide (CO2) directly into an open-circuit blowdown Mach 2.9 supersonic wind tunnel. Rapid atomization and cooling of the liquid CO2 created a preponderance of nearly uniform and well dispersed microscopic dry ice particles which were illuminated using a frequency double Nd:YAG laser. Ample light was scattered from the flow tracers, which provided a strong signal to noise ratio. The particles completely sublimed into an innocuous gas downstream of the test section causing no side effects or problems with wind tunnel operation. A …
Structural Optimization Of A Distributed Actuation System In A Flexible In-Plane Morphing Wing, James T. Westfall
Structural Optimization Of A Distributed Actuation System In A Flexible In-Plane Morphing Wing, James T. Westfall
Theses and Dissertations
Structural weight and efficiency are hurdles for morphing aircraft being realizable on the full-scale level. The optimal distribution and orientation of actuators throughout an in-plane flexible morphing wing structure is investigated. The drive to minimize structural weight causes a wing to be more flexible and the location and orientation of the actuators become more critical as the structure becomes more flexible. NextGen's N-MAS morphing wing is used as a case study. The wing is modeled as a number of unit cells assembled in a scissor-like structure, each comprised of four linkages pinned together and an actuator. The flexible skin of …
Cfd Analysis Of A T-38 Wing Fence, Daniel A. Solfelt
Cfd Analysis Of A T-38 Wing Fence, Daniel A. Solfelt
Theses and Dissertations
A computational study of the effects of a wing fence on the T-38 Talon was performed. RANS simulations were conducted using the CFD solver AVUS to examine the flow around the T-38 and the fence at a Reynolds number of 10 million. The T-38 was modeled as a half aircraft with a symmetry plane down the center line and did not include the empennage. The engine inlet and exhaust were modeled as sink and source boundary conditions using mass flow and pressure specifications. Two fence geometries placed 26" from the wing tip were tested. The first fence, called a simple …
A Systems Engineering Approach To Analyzing Weather Input Sensitivities Of The Joint Precision Air Drop System, David L. Gemas
A Systems Engineering Approach To Analyzing Weather Input Sensitivities Of The Joint Precision Air Drop System, David L. Gemas
Theses and Dissertations
The United States Air Force is partnering with the United States Army as well as allied nations to develop a revolutionary advance in logistical support known as the Joint Precision Air Drop System (JPADS). The focus of this study is to develop a process to quantitatively analyze system sensitivities to various types of weather inputs and the corresponding effect on system accuracy. Weather balloons were used to provide representative "truth" to which forecast weather could be compared. Each data type was fed into the JPADS Mission Planner to produce navigation points which could then be compared statistically. The process was …
Real-Time Gps-Alternative Navigation Using Commodity Hardware, Jordon L. Fletcher
Real-Time Gps-Alternative Navigation Using Commodity Hardware, Jordon L. Fletcher
Theses and Dissertations
Modern navigation systems can use the Global Positioning System (GPS) to accurately determine position with precision in some cases bordering on millimeters. Unfortunately, GPS technology is susceptible to jamming, interception, and unavailability indoors or underground. There are several navigation techniques that can be used to navigate during times of GPS unavailability, but there are very few that result in GPS-level precision. One method of achieving high precision navigation without GPS is to fuse data obtained from multiple sensors. This thesis explores the fusion of imaging and inertial sensors and implements them in a real-time system that mimics human navigation. In …
Catalytic Partial Oxidation Reforming Of Jp8 And S8, Thomas G. Howell
Catalytic Partial Oxidation Reforming Of Jp8 And S8, Thomas G. Howell
Theses and Dissertations
Catalytic partial oxidation (CPOX) reforming experiments were performed using a 10 kW Aspen Products Group, Inc. fuel processing prototype utilizing military logistic fuels JP8 and S8. S8 is a sulfur-free Fisher-Tropsch fuel, while JP8 is a multi-fuel blend, which could impact reforming efficiency, product distribution and byproduct production. Sulfur contained within the JP8 will adversely affect the product distribution; therefore, desulfurization beds, capable of removing up to 1000 ppm sulfur, were incorporated into the system. The catalyst used in the prototype is noble metal dispersed on cordierite monolith. The goal of this experiment was to evaluate the efficiency and product …
A Comparison Of Film Cooling Techniques In A High Speed, True Scale, Fully Cooled Turbine Vane Ring, Michael J. Umholtz
A Comparison Of Film Cooling Techniques In A High Speed, True Scale, Fully Cooled Turbine Vane Ring, Michael J. Umholtz
Theses and Dissertations
An effort was undertaken to understand the impact of different film cooling configurations in a true scale turbine vane for three proprietary airfoil designs. The measurements for this study were taken at the United States Air Force Turbine Research Facility (TRF). The TRF enabled heat transfer data to be obtained on full scale turbine hardware under realistic engine conditions. The surface heat flux of the turbine blades was analyzed using the impulse response method. The overall effectiveness was compared between airfoil types at 60% span over varying streamwise locations on both suction and pressure surfaces. Using an approximated massflow, a …
Automated Carrier Landing Of An Unmanned Combat Aerial Vehicle Using Dynamic Inversion, Nicholas A. Denison
Automated Carrier Landing Of An Unmanned Combat Aerial Vehicle Using Dynamic Inversion, Nicholas A. Denison
Theses and Dissertations
Dynamic Inversion (DI) is a powerful nonlinear control technique which has been applied to several modern flight control systems. This research utilized concepts of DI in order to develop a controller to land an Unmanned Combat Aerial Vehicle (UCAV) on an aircraft carrier. The Joint Unmanned Combat Air System (J-UCAS) Equivalent Model was used as the test aircraft. An inner-loop DI controller was developed to control the pitch, roll, and yaw rate dynamics of the aircraft, while an outer-loop DI controller was developed to provide flight path commands to the inner-loop. The controller design and simulation were conducted in the …
Damage Considerations Of A Flexible Micro Air Vehicle Wing Using 3-D Laser Vibrometry, Leo L. Mendoza Jr.
Damage Considerations Of A Flexible Micro Air Vehicle Wing Using 3-D Laser Vibrometry, Leo L. Mendoza Jr.
Theses and Dissertations
In recent years there has been a major push towards a new class of unmanned aerial vehicles: micro air vehicles. A great amount of research has been done towards the aerodynamics, aeroelasticity, construction, and flight characteristics of flexible wing micro air vehicles. However, there has not been much research done regarding possible structural deficiencies of a flexible micro air vehicle wing. The focus of this research is to evaluate the effects of damage on a flexible micro air vehicle wing, particularly its natural frequencies and mode shapes, using three dimensional laser vibrometry. The flexible micro air vehicle wing studied was …
Efficiency And Pressure Loss Characteristics Of An Ultra-Compact Combustor With Bulk Swirl, James T. Radtke
Efficiency And Pressure Loss Characteristics Of An Ultra-Compact Combustor With Bulk Swirl, James T. Radtke
Theses and Dissertations
Research was conducted on a novel combustor design using a highly centrifugal loaded circumferential cavity to enhance flame speeds and lower mixing time to lower overall combustion time achieving improved efficiency and stability. This Ultra-Compact Combustor (UCC) is fed air with a bulk swirl, resembling gas leaving a compressor without the final set of compressor guide vanes to straighten the flow, at higher than normal Mach numbers for a combustor. The larger Mach numbers in the combustor do not cause a total pressure loss in excess of what Rayleigh theory would dictate for the given heat addition taking place within …
Compressive Creep Behavior Of Nextel™ 720/Alumina Ceramic Matrix Composite At 1200°C In Air And In Steam Environment, Neil R. Szymczak
Compressive Creep Behavior Of Nextel™ 720/Alumina Ceramic Matrix Composite At 1200°C In Air And In Steam Environment, Neil R. Szymczak
Theses and Dissertations
The aerospace community continues to push the envelope in engineering aircraft that fly higher, faster, and safer while operating with a greater degree of efficiency. To meet these operational requirements innovative aerospace components must be designed to operate in aggressive environments. This research will investigate the ultimate compressive strength and the compressive creep behavior of NextelTM 720/Alumina ceramic matrix composite at 1200 °C in air and 100% steam environments. The effects of creep loading history on the tensile and compressive material behavior will also be examined. The primary strengths of the N720/A composite are its oxide/oxide composition which inherently …
Critical Life Prediction Research On Boron-Enhanced Ti-6al-4v, Kevin A. Schwendiman
Critical Life Prediction Research On Boron-Enhanced Ti-6al-4v, Kevin A. Schwendiman
Theses and Dissertations
Research on boron-enhanced Ti-6-4 has demonstrated the following improvements to the Ti-6-4 alloy: up to 40% increase in ultimate tensile strength, up to 30% increase in modulus/stiffness, while maintaining greater than 10% ductility at RT conditions. The increased properties are attributed to small additions of boron (-or= wt%), which refine the microstructure and result in a small volume fraction (~6 vol%) of fine TiB whiskers. Previous research indicates potential for substantial improvements in fatigue, fatigue crack growth, and fracture toughness. However, uncertainty regarding these second-tier mechanical properties is currently limiting implementation of this class of titanium alloys. This study of …
Development Of Cursor-On-Target Control For Semi-Autonomous Unmanned Aircraft Systems, Joshua D. Crouse
Development Of Cursor-On-Target Control For Semi-Autonomous Unmanned Aircraft Systems, Joshua D. Crouse
Theses and Dissertations
The research presented in this thesis focuses on developing, demonstrating, and evaluating the concept of a Cursor-on-Target control system for semi-autonomous unmanned aircraft systems. The Department of Defense has mapped out a strategy in which unmanned aircraft systems will increasingly replace piloted aircraft. During most phases of flight autonomous unmanned aircraft control reduces operator workload, however, real-time information exchange often requires an operator to relay decision changes to the unmanned aircraft. The goal of this research is to develop a preliminary Cursor-on-Target control system to enable the operator to guide the unmanned aircraft with minimal workload during high task phases …
Cfd Investigation Of Effect Of Depth To Diameter Ratio On Dimple Flow // Computational Fluid Dynamics Investigation Of Effect Of Depth To Diameter Ratio On Dimple Flow Dynamics, Robert B. Etter
Theses and Dissertations
This study aimed to further the understanding of laminar flow through a dimple with the goal of mitigating flow separation. Dimples of various depth to diameter ratios (0.05, 0.15) were examined for three different dimple diameters and chordwise locations, corresponding to diameter based (ReD) and chordwise location based (Rex) Reynolds number combinations of ReD 20500\Rex 5000, ReD 20500 Rex 77000, and ReD 9000 Rex 21000. For the last combination, a dimple of depth to diameter ratio of 0.25 was also examined. The dimples were placed in a flat plate located in a diverging channel causing an adverse pressure gradient encouraging …
Structural Stability Of A Joined-Wing Sensorcraft, Brandon J. Adams
Structural Stability Of A Joined-Wing Sensorcraft, Brandon J. Adams
Theses and Dissertations
This thesis employed a multi-disciplinary design approach to determine the structural stability of the Boeing Joined-Wing SensorCraft. Specifically, this thesis sought to characterize the free vibration modes, ensure a buckling safe design and determine the influence of the geometric and aeroelastic nonlinearities associated with this joined-wing design. The clamped free vibration modes were developed for a wind tunnel model and were compared to the free-free vibration modes, several differences were found. Linear static analyses were performed on numerous maneuver loads and gust conditions to determine the critical loading condition. The SensorCraft was then redesigned for the critical load case to …
The Aerodynamic Performance Of The Houck Configuration Flow Guides, Dermot N. Killian Ii
The Aerodynamic Performance Of The Houck Configuration Flow Guides, Dermot N. Killian Ii
Theses and Dissertations
In an effort to explore efficient wing designs for UAV's, the Air Force is investigating the patented Houck Aircraft Configuration, which is a joined-wing aircraft with curved flow guides of varying camber connecting the upper and lower wingtips. Models were drawn in three-dimensions using Solidworks® with upper and lower wings drawn as identical NACA 2412 airfoil sections for all models. A variety of airfoil sections between the upper and lower wingtips were drawn and rotated to achieve a combination of cant and angle of attack variation. Subsequently, a solid part was lofted through these sections and merged with the upper …
High Temperature Degradation Of 5250-4 Polymer Resin, Patrick E. Link
High Temperature Degradation Of 5250-4 Polymer Resin, Patrick E. Link
Theses and Dissertations
5250-4 bismaleimide resin is used in high performance polymer matrix composites with high temperature aeronautical applications. This thesis investigated the thermal and oxidative degradation of 5250-4 neat resin powder in argon, air, and oxygen environments. The powder was aged at 163 deg. C, 177 deg. C, and 190 deg. C in all environments for at least 250 hours. Isothermal thermo-gravimetric analysis demonstrated that weight loss was negligible for aging in the argon environment, indicating weight loss is the result of an oxidative process at these temperatures. The 5250-4 powder exhibited an initial period of weight gain before eventually losing weight …
A Small-Scale 3d Imaging Platform For Algorithm Performance Evaluation, Steven A. James
A Small-Scale 3d Imaging Platform For Algorithm Performance Evaluation, Steven A. James
Theses and Dissertations
In recent years, world events have expedited the need for the design and application of rapidly deployable airborne surveillance systems in urban environments. Fast and effective use of the surveillance images requires accurate modeling of the terrain being surveyed. The process of accurately modeling buildings, landmarks, or other items of interest on the surface of the earth, within a short lead time, has proven to be a challenging task. One approach of high importance for countering this challenge and accurately reconstructing 3D objects is through the employment of airborne 3D image acquisition platforms. While developments in this arena have significantly …