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Articles 1 - 25 of 25
Full-Text Articles in Engineering
Effects Of Foreign Object Damage From Small Hard Particles On The High-Cycle Fatigue Life Of Ti-6a1-4v, Joseph L. Hamrick Ii
Effects Of Foreign Object Damage From Small Hard Particles On The High-Cycle Fatigue Life Of Ti-6a1-4v, Joseph L. Hamrick Ii
Theses and Dissertations
Thin rectangular samples of Ti-6Al-4V were damaged by four methods to represent foreign object damage found in turbine engine blades: 1) impact with 2 mm and 5 mm diameter glass spheres at 305 m/s, 2) impact with 2 mm and 4 mm diameter steel spheres at 305 m/s, 3) quasi-static displacement controlled indentation using steel chisels with 1 mm, 2 mm and 5 mm diameter tips and 4) shearing notches with a 2 mm diameter chisel point under a quasi-static loading condition. Finite element analysis was used to study the relationship between the stress state created by the plastic damage …
Reverse Engineering Of Foreign Missiles Via Genetic Algorithm, Jon D. Wollam
Reverse Engineering Of Foreign Missiles Via Genetic Algorithm, Jon D. Wollam
Theses and Dissertations
One mission of the National Air Intelligence Center (NAIC) is the reverse engineering of foreign missile weapon systems from incomplete observational data. In the past, intuition and repeated runs of a missile performance model were required to converge to a solution compatible with observed flight characteristics. This approach can be cumbersome and time consuming, as well as being subject to undesirable influences from the analyst's preconceptions and biases. An alternative approach has been created to apply genetic algorithm (GA) techniques to allow automation of the process, wider exploration of the design space, and more optimal solutions matching the observational data. …
Space-Available Transportation: An Analysis Of The Cost Of Providing 'Free' Travel, Frank J. Long
Space-Available Transportation: An Analysis Of The Cost Of Providing 'Free' Travel, Frank J. Long
Theses and Dissertations
The purpose of this study is to estimate the costs borne by the government for providing space-available travel to eligible uniformed services personnel and their dependents. As the primary provider of the space-available privilege, it is important that the Air Force have an estimate of the burden that the administration of that privilege places on the budget. In January 1993, the Air Force discontinued its 15-year-old practice of charging a fee for space-available travel aboard AMC-owned or controlled aircraft. The fee had been set at $10 in 1978 and was collected to recover a portion of the costs associated with …
Flow Separation Prevention On A Turbine Blade In Cascade At Low Reynolds Number, James P. Lake
Flow Separation Prevention On A Turbine Blade In Cascade At Low Reynolds Number, James P. Lake
Theses and Dissertations
The problem of flow separation from a low pressure turbine blade was investigated. The operating conditions under which the separation occurred were documented through measurement of surface pressure coefficients, boundary layer velocity and turbulence profiles, total pressure loss coefficient and wake velocity momentum deficit. Three different means for reducing the losses associated with the flow separation were also investigated. A boundary layer trip, dimples, and V-grooves were studied as passive means requiring no additional energy to reduce the separation losses. The boundary layer trip was only successful for an inlet and axial chord Reynolds number of 50k with a reduction …
Closely Supervised Reactive Control Of An Uninhabited Aerial Vehicle, Roy G. Glassco
Closely Supervised Reactive Control Of An Uninhabited Aerial Vehicle, Roy G. Glassco
Theses and Dissertations
Closely Supervised Reactive Control is an alternative control method for uninhabited aerial vehicles that incorporates some of the benefits of both manual and autonomous operations. Utilizing an onboard camera, an operator can control a UAV by manually choosing desired targets. The flight path of the uninhabited vehicle is determined autonomously from the camera gimbal angles. The operator of the payload (i.e. camera), has close supervision of the aircraft. The aircraft, using an onboard computer, is given autonomous control to alter flight path to fly towards a target and at a specified range, loiter over the target. In the basic mode …
Wind Tunnel Investigation Of Joined Wing Configurations, Jennifer Corneille
Wind Tunnel Investigation Of Joined Wing Configurations, Jennifer Corneille
Theses and Dissertations
The Air Force Research Laboratory's Munitions Directorate is looking to extend the range of its small smart bomb. One proposed idea is to retrofit the bombs with a wing kit, particularly a joined wing configuration. A typical joined wing configuration is one where the wings are positioned in such a way that they form a diamond in both plan and front views. The purpose of this study is to conduct low speed wind tunnel testing of the joined wing configuration to help determine if the joined wing is more beneficial than a single wing configuration. Configurations with differing sweep angles …
Solving An Inverse Control Problem Using Predictive Methods, Chad J. Davis
Solving An Inverse Control Problem Using Predictive Methods, Chad J. Davis
Theses and Dissertations
Model Predictive Control is the class of control methods that optimizes a specified performance index in order to minimize the weighted future output deviations from a setpoint trajectory. This thesis applies MPC in the inverse sense -- known aircraft outputs are applied in the performance index as setpoints in an attempt to determine what control histories caused those outputs. Using this method, aircraft mishap investigators could then have a means of determining what the control surface deflections were throughout an incident since Flight Data Recorder data does not include control surface deflections. The actual Flight Data Recorder data from aircraft …
Close Formation Flight Control, Andrew W. Proud
Close Formation Flight Control, Andrew W. Proud
Theses and Dissertations
In this research the close formation flight control problem is addressed. The formation consists of a lead and wing aircraft, where the wing flies in close formation with the lead, such that the lead's vortices produce aerodynamic coupling effects, and a reduction in the formation's drag is achieved. A controller, i.e., a formation-hold autopilot for the wing aircraft, is designed such that the formation's geometry is maintained in the face of lead aircraft maneuvers. In the formation flight control system, the wing and lead aircraft dynamics are coupled due to kinematic effects, and, in the case of close formations, additional …
Tip Vortex And Crenulation Effects In A Compressor Cascade With Moving Endwall, Barry W. St Germain
Tip Vortex And Crenulation Effects In A Compressor Cascade With Moving Endwall, Barry W. St Germain
Theses and Dissertations
The effects of changing Reynolds number and flow coefficients on the velocity and pressure flow fields within a linear cascade with moving endwall were investigated in this experimental thesis. All flow field measurements were taken at a constant compressor blade tip gap clearance of 1.0 % chord and endwall speed of 318.6 ft/s (97.1 m/s), with flow coefficients of 0.40, 0.52, 0.62 and 0.72. All data acquisition occurred in a plane 23 % chord downstream of the trailing edge plane of the linear cascade. Hotwire probes determined the complete passage, three-dimensional fowled behind both crenulated and regular blade geometries. Vector …
Whole Spacecraft Vibration Isolation, Gregory G. Karahalis
Whole Spacecraft Vibration Isolation, Gregory G. Karahalis
Theses and Dissertations
The Department of Defense identified launch vibration isolation as a major research interest. Reducing the loads a satellite experiences during launch will greatly enhance the reliability, lifetime, and payload to structure ratio. DoD satellite programs stand to benefit significantly from advances in vibration isolation technology.
Effects Of Pressure Gradients On Turbulent Boundary Layer Flow Over A Flat Plate With Riblets, Franklin L. Dement Jr.
Effects Of Pressure Gradients On Turbulent Boundary Layer Flow Over A Flat Plate With Riblets, Franklin L. Dement Jr.
Theses and Dissertations
The Air Force Institute of Technology Boundary Layer Research Facility test section was modified to create controlled non-zero streamwise pressure gradients. The capability of the modified facility to reproduce theoretical laminar boundary layer velocity profiles and to create a self-preserving flow with an adverse streamwise pressure gradient was verified with three-dimensional laser Doppler anemometry. The effects of streamwise adverse and favorable pressure gradients on turbulent boundary layer flow characteristics (velocity profiles, turbulence and skin friction) and vortex formation over a flat plate with riblets at low speed (U = 5 mIs) were studied. Normal and spanwise velocity profiles for both …
Robust Eigenstructure Assignment Using Positive Definite Output Feedback Control, Adam G. Harris
Robust Eigenstructure Assignment Using Positive Definite Output Feedback Control, Adam G. Harris
Theses and Dissertations
This research investigates a method of eigenstructure assignment for the classes of controllers known as positive definite output feedback control. The research began with a closed loop system with output feedback control that utilizes a collocated actuator-sensor pair. It is shown that this system is robust because it is globally stable for positive definite feedback. Analytical analysis is then completed to determine gains that minimize a cost function that is the error between the desired and achievable (assuming positive definite output feedback) eigenstructure. Examples are given at the end of the thesis to validate the computer code and theory results.
Design And Analysis Of On-Orbit Servicing Architectures For The Global Positioning System Constellation, Gregg A. Leisman, Adam D. Wallen
Design And Analysis Of On-Orbit Servicing Architectures For The Global Positioning System Constellation, Gregg A. Leisman, Adam D. Wallen
Theses and Dissertations
Satellites are the only major Air Force systems with no maintenance, routine repair, or upgrade capability. The result is expensive satellites and a heavy reliance on access to space. At the same time, satellite design is maturing and reducing the cost to produce satellites with longer design lives. This works against the ability to keep the technology on satellites current without frequent replacement of those satellites. The Global Positioning System Joint Program Office realizes that it must change its mode of operations to quickly meet new requirements while minimizing cost. The possibility of using robotic servicing architectures to solve these …
A Statistical Analysis Of Space Structure Mode Localization, Amy M. Cox
A Statistical Analysis Of Space Structure Mode Localization, Amy M. Cox
Theses and Dissertations
Cyclic structures, such as antenna arrays, multi-bay trusses, and compressor blades, are significantly impacted by slight changes to system periodicity. Manufacturing errors of 5% or less can result in drastic changes to a structure's modal behavior. This change in modal behavior is significant, since it may result in the focusing of modal energy to individual substructures of the system. Poor modal identification can result in poorly designed control systems, resulting in shape control and pointing issues for space antennae. Additionally, modal energy localization may damage individual system components due to unanticipated levels of cyclic loading, leading to high cycle fatigue.
Progressive Failure Analysis Of Composite Panels, Stephen M. Spottswood
Progressive Failure Analysis Of Composite Panels, Stephen M. Spottswood
Theses and Dissertations
The objective of this research was to determine the physical response, including material failure, of a curved composite panel designed to resist transverse loading. The cause of the material failure, in the form of delamination, fiber and/or matrix failure, was determined through various criterion based on non-linear movement using a finite element analysis technique. Data generated both with and without the addition of progressive failure criteria, was compared with previously published experimental data, noting where the theory diverges from the experimental results. The inclusion of various failure criterion, to include maximum stress, Lee, and Hashin, provided a more realistic representation …
Space Maneuver Vehicle Orbital Mission Planner: Development Of Application And Analysis Of On-Demand Maneuvering Ability, Shon P. Williams
Space Maneuver Vehicle Orbital Mission Planner: Development Of Application And Analysis Of On-Demand Maneuvering Ability, Shon P. Williams
Theses and Dissertations
The USAF has developed the Space Maneuver Vehicle (SMV) to fulfill the requirement for flexibility, rapid response, and on-demand maneuverability of space assets. This reusable satellite merges the efficiency and readiness of aircraft-like operations with the capability of global coverage from space. Designed to provide over 10,500 fps of velocity change (or delta-v) while in orbit, the SMV out-maneuvers existing satellites by up to 100 times. This thesis helps transition the SMV to the operational area by demonstrating their responsiveness to varied mission taskings. The SMV Orbital Mission Planner allows the operator to place any number of SMVs in orbit …
Fatigue Response Of Repaired Thick Aluminum Panels With Bondline Flaws, David S. Conley
Fatigue Response Of Repaired Thick Aluminum Panels With Bondline Flaws, David S. Conley
Theses and Dissertations
his research investigated the fatigue response of precracked 558 x 177.8 x 6.35 mm (22.0 x 7.0 x 0.25 in) 2024-T351 aluminum panels repaired with single-sided partially bonded, unidirectional, eighteen ply boron/epoxy reinforcements. Disbonds were introduced into the bondline of each repair during the adhesion process using teflon inserts. Five different disbond configurations, with varying disbond locations and sizes, were tested. Each repaired panel was subjected to constant amplitude cyclic fatigue loading with a maximum stress of 120MPa. Results from the different configurations were compared against one another and against repaired panels with no debonds to assess the effect of …
Toward Development Of An Integrated Aerospace Power Doctrine, Toby G. Doran
Toward Development Of An Integrated Aerospace Power Doctrine, Toby G. Doran
Theses and Dissertations
This thesis discusses the state of the Air Force, decision making factors in the making of military doctrine, the definition of doctrine, Air Force doctrines today, new ways to develop doctrine, including models and hypothesis-research-analysis loops, space doctrine, control of space, space superiority and a call for aerospace power doctrine.
A Nonlinear Pre-Filter To Prevent Departure And/Or Pilot-Induced Oscillations (Pio) Due To Actuator Rate Limiting, Michael J. Chapa
A Nonlinear Pre-Filter To Prevent Departure And/Or Pilot-Induced Oscillations (Pio) Due To Actuator Rate Limiting, Michael J. Chapa
Theses and Dissertations
Closed loop instability caused by excess phase lag induced by actuator rate limiting has been suspected in many aircraft departures from controlled flight and pilot-induced oscillations (PIO). As part of the joint Air Force Institute of Technology Test Pilot School (AFITITPS) program, a nonlinear rate limiter pre-filter (RLPF) was developed to minimize the phase lag induced by rate limiting. RLFF performance was evaluated inside the feedback path, but primary emphasis was on the pilot command path. Closed loop computer and motion-based flight simulation were conducted to prepare for the flight test. The HAVE FILTER flight test project was flown using …
Simsat: A Satellite System Simulator And Experimental Test Bed For Air Force Research, James E. Colebank, R. Dan Jones, Randall D. Pollak, Donald M. Mannebach, George R. Nagy
Simsat: A Satellite System Simulator And Experimental Test Bed For Air Force Research, James E. Colebank, R. Dan Jones, Randall D. Pollak, Donald M. Mannebach, George R. Nagy
Theses and Dissertations
SIMSAT (the SIMulation SATellite) is an AFIT-sponsored program to develop a laboratory-based physical satellite simulator. SIMSAT supports experimentation in areas of attitude control, precision pointing, and vibration suppression. SIMSAT development began with the purchase of a three-axis gas bearing which simulates a torque-free space environment. SIMSAT subsystems provide power, attitude control, telemetry, and structural support to experimental payloads. Project challenges included integration of attitude control software/hardware, high-output power storage devices, remote communications, high-frequency data collection, structural design, and computer display outputs.
Space Launch Operations And The Lean Aerospace Initiative, Troy L. Endicott
Space Launch Operations And The Lean Aerospace Initiative, Troy L. Endicott
Theses and Dissertations
This study analyzes current expendable launch procedures and identifies truly lean, value-added steps in launch operation enterprises as they relate to the Lean Aerospace Initiative (LAI). LAI and the concepts of lean thinning are discussed and followed by a review of current and future launch system requirements and their opportunities for lean practices. The study also discusses in detail current Delta II expendable launch processing operations and presents results in a case study that show how lean principles have helped the Delta II launch team drastically reduce on-pad time, restructure its testing philosophy, and streamline its operations flow. Many of …
East Coast Abort Modeling With Rtls Elimination For The Space Shuttle-Liquid Fly Back Booster Launch System, Thomas L. Miller Jr.
East Coast Abort Modeling With Rtls Elimination For The Space Shuttle-Liquid Fly Back Booster Launch System, Thomas L. Miller Jr.
Theses and Dissertations
This study investigates the ability of the proposed Liquid Fly Back Booster, a replacement for the Space Shuttle's Solid Rocket Boosters (SRBs), to eliminate the need for the Return to Launch Site (RTLS) abort mode. A Fortran model of a nominal launch trajectory was perturbed to simulate a single Space Shuttle Main Engine-out (SSME-out) abort scenario at different times in the launch with the goal being to abort to the southern most landing site possible. The model accounts for vehicle lift, drag, dynamic pressure, throttling times and includes atmospheric effects to enhance fidelity. Results show the RTLS abort mode can …
Anti-Ballistic Missile Laser Predictive Avoidance Of Satellites: Theory And Software For Real-Time Processing And Deconfliction Of Satellite Ephemerides With A Moving Platform Laser, David J. Vloedman
Theses and Dissertations
The Anti-Ballistic missile Laser (ABL) Project is committed to defense against attack from enemy-launched Theater Ballistic Missiles using an airborne laser platform to disable an enemy missile in the boost phase of launch. Wielding a laser of this power and scope requires that no collateral damage be caused by laser energy which may escape from the theater of engagement. The most likely track of such a laser would pose a significant threat to space-based assets. The Predictive Avoidance algorithm is designed to predict the path of a given laser firing sequence, and perform real-time forecasting of, and deconfliction with, the …
A Comparative Analysis Of The Iridium® And Globalstar® Satellite Transmission Paths, Kenneth E. Crowe
A Comparative Analysis Of The Iridium® And Globalstar® Satellite Transmission Paths, Kenneth E. Crowe
Theses and Dissertations
Globalstar and Iridium will provide valuable global communications assets for business, humanitarian aid and military operations. However, the level of coverage and the quality of the transmission path of these systems are strongly dependent on the latitude of the user and, due to their orbital characteristics, both systems provide reduced levels of coverage at low latitudes. Additionally, the L- and S-Band frequencies utilized by these systems are prone to ionospheric interference at low latitudes. The results of extensive simulation analysis indicate that the Globalstar constellation architecture provides a considerably better transmission path than Iridium's in several important areas, including path …
Heat Transfer To The Inclined Trailing Wall Of An Open Cavity, Orval A. Powell
Heat Transfer To The Inclined Trailing Wall Of An Open Cavity, Orval A. Powell
Theses and Dissertations
Experimental and computational heat transfer investigations were performed on a cavity with an inclined trailing wall (20-degrees to the horizontal), simulating one under investigation for use in a scramjet engine. Heat transfer data are reported in the form of Stanton number obtained using a curve fit to the recorded transient surface temperature history under cold flow conditions. Ascending from the reattachment point, the Stanton number increased by nearly 50% due to flow compression. This effect of flow compression was also evident at the junction of the cavity floor and inclined trailing wall, where the Stanton number also increased by 50%. …