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Air Force Institute of Technology

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Articles 1261 - 1290 of 1674

Full-Text Articles in Aerospace Engineering

Three Dimensional Formation Flight Control, James K. Hall Mar 2000

Three Dimensional Formation Flight Control, James K. Hall

Theses and Dissertations

Automating the control of an aircraft flying in formation necessitates the extension of the theory of formation flight control to allow for three dimensional maneuvers. The formation was modeled as a two-aircraft, leader and wingspan, formation. Both aircraft has its own three dimensional, rotating and translating, Cartesian axes system, with special attention being given to the motion of the leader in relation to the wingspan. The controller operated using the equations of motion expressed in the rotating reference frame of the wing aircraft. The control system has seven states, three inputs and three disturbance signals to model the dynamics of …

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Measurements Of The Effects Of Tunnel Wall Proximity On The Velocity Field Upstream Of A Rod With Vortex Shedding In Low-Speed Flow, David R. Hopper Mar 2000

Measurements Of The Effects Of Tunnel Wall Proximity On The Velocity Field Upstream Of A Rod With Vortex Shedding In Low-Speed Flow, David R. Hopper

Theses and Dissertations

High cycle fatigue is an important consideration in blade design for turbomachinery. Blades in an engine undergo countless loading cycles in a lifetime, the result of pressure waves that propagate upstream and downstream from disturbances in the flow. Better understanding of these effects would allow blade designers to reduce the effects of high cycle fatigue, such as costly recurring maintenance or catastrophic engine failure. An experimental study was undertaken to determine the unsteady flow field upstream of a single cylinder in a subsonic flow. Von Karman vortex shedding from the cylinder produced a forcing function much like periodic blade passage …

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Finite Element Model Updating Using Antiresonant Frequencies, Keith W. Jones Mar 2000

Finite Element Model Updating Using Antiresonant Frequencies, Keith W. Jones

Theses and Dissertations

The applications of antiresonant frequencies to finite element (FE) model updating are few and usually limited to numerical examples. This work uses antiresonant frequencies in the model updating of an experimental structure and analyzes the physical correctness of the updated model by using it to detect damage. Antiresonant frequencies were used in the FE model updating of a six-meter aluminum truss. The model used rigid links to model welded and bolted joints. Rigid link dimensions were used as parameters in an iterative update based on eigenvalue and antiresonance sensitivities. The first update used 11 natural frequencies and 21 antiresonant frequencies …

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Space Range Scheduling And The Lean Aerospace Initiative (Lai), Alan M. Matuszak Mar 2000

Space Range Scheduling And The Lean Aerospace Initiative (Lai), Alan M. Matuszak

Theses and Dissertations

This study describes how lean principles and thinking can be applied to space range operations. The "lean" concepts of the right thing, right place, and the right time are applicable and relevant to this study. The basis for the lean concepts and principles considered is the Lean Aerospace Initiative (LAI). The LAI originated from the International Motor Vehicle Program (IMVP) that was conducted by a team from the Massachusetts Institute of Technology (MIT). The LAI is a collaborative research program involving government, industry, labor, and academia (primarily MIT). The partnership began in 1993 through support of the U.S. Air Force …

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Investigation Into The Adaptation Of A Steam Injector For Use On A Liquid Rocket Engine, Charles B. Mcfarland Mar 2000

Investigation Into The Adaptation Of A Steam Injector For Use On A Liquid Rocket Engine, Charles B. Mcfarland

Theses and Dissertations

This thesis investigated the properties of a steam injector to see if the concept might be suitable for use on a liquid rocket engine. A steam injector is a device developed in the 1850's to inject feedwater into the boiler on a steam locomotive without any moving parts. The injectors uses a small portion of the steam generated in the boiler to increase the pressure of the feedwater to a level high than the pressure in the boiler. Previous experiments claim that condensation of steam to water was necessary for an injector to work. This experiment tested injection without condensation …

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Dynamic Route Replanning And Retasking Of Unmanned Aerial Reconnaissance Vehicles, David E. Pritchard Mar 2000

Dynamic Route Replanning And Retasking Of Unmanned Aerial Reconnaissance Vehicles, David E. Pritchard

Theses and Dissertations

Many common operational situations in High Altitude Endurance (HAE) UAV reconnaissance necessitate more direct human involvement in the aircraft control process than is currently acknowledged or allowed. The In-Flight Replanning System (IFRS) is developed as a notional solution, with the Global Hawk HAE UAV as the reconnaissance system model. Problematic scenarios for current in-flight mission replanning systems are presented and revisited with the IFRS, demonstrating improved replanning results.

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Computational Fluid Dynamics Testing For Drag Reduction Of An Aircraft Laser Turret, Gregory J. Schwabacher Mar 2000

Computational Fluid Dynamics Testing For Drag Reduction Of An Aircraft Laser Turret, Gregory J. Schwabacher

Theses and Dissertations

A computational study was conducted on the use of aft-mounted fairings for passive drag reduction on a sphere at Re=866,000. The sphere dimensions and operating Reynolds number were selected to approximate the flow around a proposed aircraft laser turret for which experimental data was available. To establish the validity of the computational model, flow predictions were compared to sphere data available in the open literature. The model, exercised in both the laminar and turbulent modes, showed good agreement with the published data. Two proposed laser turret fairings were then evaluated computationally: a large fairing (beginning at 49.5 degrees past the …

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Mission Route Planning With Multiple Aircraft & Targets Using Parallel A* Algorithm, Ergin Sezer Mar 2000

Mission Route Planning With Multiple Aircraft & Targets Using Parallel A* Algorithm, Ergin Sezer

Theses and Dissertations

The general Mission Route Planning (MRP) Problem is the process of selecting an aircraft flight path in order to fly from a starting point through defended terrain to target(s), and return to a safe destination. MRP is a three-dimensional, multi-criteria path search. Planning of aircraft routes involves an elaborate search through numerous possibilities, which can severely task the resources of the system being used to compute the routes. Operational systems can take up to a day to arrive at a solution due to the combinatorial nature of the problem, which is not acceptable, because time is critical in aviation. Also, …

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Monotonic And Fatigue Loading Behavior Of An Oxide/Oxide Ceramic Matrix Composite, Steven G. Steel Mar 2000

Monotonic And Fatigue Loading Behavior Of An Oxide/Oxide Ceramic Matrix Composite, Steven G. Steel

Theses and Dissertations

This thesis evaluates an oxide/oxide ceramic matrix composite, N720/A, for high temperature aerospace applications. The composite consists of a porous alumina matrix reinforced by ten plies of Nextel 720 fibers in a balanced 8 harness satin weave. Monotonic tensile and fatigue tests were performed at room temperature and 1200 °C. The effect of moisture on 1200 °C fatigue life was also examined. Modulus, maximum and minimum strain, and stress-strain hysteresis were monitored to characterized fatigue damage. Retained strength of all specimens that survived 100000 fatigue cycles was tested. Microscopy and fractography were used to examine damage and fracture surfaces. N720/A …

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Simulations Of Flowing Supercritical N-Decane, Jeffery T. Thornburg Mar 2000

Simulations Of Flowing Supercritical N-Decane, Jeffery T. Thornburg

Theses and Dissertations

The Air Force is interested in the research of supercritical jet and rocket fuels, as well as the effects of thermally induced fuel degradation. As future flight vehicles travel at ever increasing Mach numbers, greater heat loads will be imposed upon the fuel. The primary purpose of this study is to develop a computational model for predicting fuel decomposition and bulk fuel temperatures in a stimulated heated flow reactor. The System for Thermal Diagnostic Studies (STDS), located in the Air Force Research Laboratory's Fuels Branch, is used to analyze fuels under supercritical temperatures and pressures. Computational simulations of the STDS …

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Improving Uav Handling Qualities Using Time Delay Compensation, Andrew J. Thurling Mar 2000

Improving Uav Handling Qualities Using Time Delay Compensation, Andrew J. Thurling

Theses and Dissertations

This research investigated control loop time delay and its effect on UAV handling qualities. Compensation techniques to improve handling qualities in the presence of varying amounts of time delay were developed and analyzed. One technique was selected and successfully flight-tested on a UAV. Flight-testing occurred at a constant flight condition with varying levels of additional time delay introduced into the control loop. Research pilots performed a pitch tracking task and gave Cooper-Harper ratings and comments. Tracking errors were used as a quantitative measure of Pilot/Display/UAV system performance. Predictive pitch compensation was found to significantly reduce pilot workload and improve Cooper-Harper …

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Optical Metrology Of Adaptive Membrane Mirrors, John W. Wagner Mar 2000

Optical Metrology Of Adaptive Membrane Mirrors, John W. Wagner

Theses and Dissertations

Current space-based imaging platforms are significantly constrained in both size and weight by the launch vehicle. Increased payload size and weight results in increased cost and a decrease in launch responsiveness. The USAF Scientific Advisory Board (SAB) identified "Large lightweight structures for optics and antennas" as a revolutionary primary technology to be developed for the Air Force of the 21st Century. A membrane primary mirror in a space-based imaging system has the ability to overcome current payload constraints and meet evolutionary needs of the future. The challenge of membrane optics in space is the process of implementing adaptive optics technology …

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Active And Adaptive Control For Payload Launch Vibration Isolation, Julian R. Jarosh Mar 2000

Active And Adaptive Control For Payload Launch Vibration Isolation, Julian R. Jarosh

Theses and Dissertations

The Department of Defense has identified launch vibration isolation as a major research interest. Reducing the loads a satellite experiences during launch will greatly enhance its reliability and lifetime, and reduce payload structural mass. DoD space programs stand to benefit significantly from advances in vibration isolation technology. This study explores potential hybrid vibration isolation using active and adaptive control with a passive vibration isolator. The active control methods are Proportional-Integral-Derivative (PID) control and a skyhook damper. Lyapunov analysis is used to develop the structural adaptive control scheme. Simulink and Matlab simulations investigate these control methodologies on a lumped mass dynamic …

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Effects Of Foreign Object Damage From Small Hard Particles On The High-Cycle Fatigue Life Of Ti-6a1-4v, Joseph L. Hamrick Ii Dec 1999

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 …

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Reverse Engineering Of Foreign Missiles Via Genetic Algorithm, Jon D. Wollam Dec 1999

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. …

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Space-Available Transportation: An Analysis Of The Cost Of Providing 'Free' Travel, Frank J. Long Sep 1999

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 …

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Closely Supervised Reactive Control Of An Uninhabited Aerial Vehicle, Roy G. Glassco Jun 1999

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 …

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Wind Tunnel Investigation Of Joined Wing Configurations, Jennifer Corneille Jun 1999

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 …

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Flow Separation Prevention On A Turbine Blade In Cascade At Low Reynolds Number, James P. Lake Jun 1999

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 …

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Solving An Inverse Control Problem Using Predictive Methods, Chad J. Davis May 1999

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 …

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Close Formation Flight Control, Andrew W. Proud May 1999

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 …

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Variable Area Inlet For Vehicle Thermal Control, Thomas R. Layne, Milton E. Franke, Darrell B. Ridgedly Apr 1999

Variable Area Inlet For Vehicle Thermal Control, Thomas R. Layne, Milton E. Franke, Darrell B. Ridgedly

AFIT Patents

A variable area inlet structure for a vehicle utilizing ram air for coolant is described which comprises a variable area inlet device in the ram air inlet in the form of a butterfly valve, damper, shutter, or similar structure, a temperature sensor in thermal contact with a component within the vehicle to be cooled by ram air flow, a controller and actuator, responsive to the temperature sensor and operatively connected to the variable area device, for controlling the inlet area in response to the component temperature.

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Progressive Failure Analysis Of Composite Panels, Stephen M. Spottswood Mar 1999

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 …

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Design And Analysis Of On-Orbit Servicing Architectures For The Global Positioning System Constellation, Gregg A. Leisman, Adam D. Wallen Mar 1999

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 …

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East Coast Abort Modeling With Rtls Elimination For The Space Shuttle-Liquid Fly Back Booster Launch System, Thomas L. Miller Jr. Mar 1999

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 …

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Tip Vortex And Crenulation Effects In A Compressor Cascade With Moving Endwall, Barry W. St Germain Mar 1999

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 …

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Robust Eigenstructure Assignment Using Positive Definite Output Feedback Control, Adam G. Harris Mar 1999

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.

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Fatigue Response Of Repaired Thick Aluminum Panels With Bondline Flaws, David S. Conley Mar 1999

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 …

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A Statistical Analysis Of Space Structure Mode Localization, Amy M. Cox Mar 1999

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.

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Toward Development Of An Integrated Aerospace Power Doctrine, Toby G. Doran Mar 1999

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.

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