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Articles 1231 - 1260 of 1780

Full-Text Articles in Aerospace Engineering

A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard Mar 2005

A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard

Theses and Dissertations

The Global War on Terror with specific emphasis on the recent military operation in Afghanistan has shown the invaluable contribution that heavy lift helicopters bring to the combatant commander. However, the flight range, altitudes and lift capability required to operate effectively in such an austere environment are pushing the limits of these helicopters. In an attempt to increase the operational capability of the CH-53E, this study will investigate methods for maximizing tail rotor effectiveness at high gross weights and high altitudes. This thesis records an analytical study designed to investigate the intricacies of tail rotor design and, by the computational …

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A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan Mar 2005

A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan

Theses and Dissertations

This thesis further defines the position of greatest fuel savings benefit for the trail aircraft flying in a two-ship formation. The HASC95 vortex lattice code was used for the examination. Investigations of a similar formation of F-16 aircraft and a dissimilar formation of a lead KC-135 aircraft and a trail F-16 aircraft were conducted. The analyses determined the effects of varying airspeed on the optimal position. In addition, flight control surface deflections were taken into account during the analyses. Both investigations trimmed the aircraft in the yaw and roll axes to determine the optimal savings. The similar analysis was conducted …

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Characterization Of Upstream Mixing Cavities And A Downstream Combustion Cavity In Supersonic Flow, Adam P. Quick Mar 2005

Characterization Of Upstream Mixing Cavities And A Downstream Combustion Cavity In Supersonic Flow, Adam P. Quick

Theses and Dissertations

A key area of study in air-breathing hydrocarbon-fueled scramjet combustors is the characterization of cavity-based fuel injection and flame holding. One issue concerns oscillatory disturbances caused by trapped vortices in the main flame holder cavity as a fuel-air mixing enhancement technique. Previous research demonstrates that oscillatory disturbances can be carried downstream via the shear layer and alter the oscillatory characteristics of a downstream cavity. This study investigates the mixing effectiveness of three upstream direct-fueled mixing cavities as well as the effect on the oscillatory behavior of the downstream combustion cavity by the upstream mixing cavity. The three upstream mixing cavities …

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Attitude Model Of A Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data, Jason E. Smith Mar 2005

Attitude Model Of A Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data, Jason E. Smith

Theses and Dissertations

Attitude determination of satellites is normally the job of inertial instruments, such as gyroscopes, or through sensing instruments, such as star trackers or Global Positioning Satellites (GPS). Satellite health monitoring systems watch and determine if the satellite deviates from its normal operating attitude orientation. Knowing the orientation of a satellite is essential in being able to control it in order to complete the satellite's designated mission. While there are a multitude of ways to determine a satellite's orientation, very little research has been done on determining if the attitude of a satellite can be determined directly from telemetry data of …

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Weight Analysis Of Two-Stage-To-Orbit Reusable Launch Vehicles For Military Applications, Richard A. Caldwell Mar 2005

Weight Analysis Of Two-Stage-To-Orbit Reusable Launch Vehicles For Military Applications, Richard A. Caldwell

Theses and Dissertations

In response to Department of Defense (DoD) requirements for responsive and low-cost space access, this design study provides an objective empty weight analysis of potential reusable launch vehicle (RLV) configurations. Each two-stage-to-orbit (TSTO) RLV has a fixed payload requirement of 20,000 lbf to low Earth orbit. The propulsion systems considered in this study include pure rocket, pure turbine, rocket-based-combined-cycle (RBCC), and turbine-based-combined-cycle (TBCC). The hydrocarbon dual-mode scramjet (DMSJ) engines used in the RBCC and TBCC propulsion systems represent possible applications of the current research being performed in the U.S. Air Force HyTech program. Two sensitivity analyses were then performed on …

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A Numerical Analysis For Passive Attitude Stabilization Using A Tethered Balloon On A Gravity Gradient Satellite, Ernest Matias Maramba Mar 2005

A Numerical Analysis For Passive Attitude Stabilization Using A Tethered Balloon On A Gravity Gradient Satellite, Ernest Matias Maramba

Theses and Dissertations

This research effort analyzes the fundamental dynamics governing a satellite with a gravity gradient boom and a tethered balloon. Satellites that use gravity gradient booms for passive attitude control are characterized by undamped pitch oscillations and no roll control. The tethered balloon acts as a high drag device that accounts for the most drag on the satellite system. By attaching a drag device, the system resists rolling movements while also damping oscillations. This could potentially be a cost effective method for increasing satellite stabilization. The goal of this research is to model the dynamics and determine the feasibility of a …

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Performance Study Of Staging Variable On Two-Stage-To-Orbit Reusable Launch Vehicles, James K. Nilsen Mar 2005

Performance Study Of Staging Variable On Two-Stage-To-Orbit Reusable Launch Vehicles, James K. Nilsen

Theses and Dissertations

The purpose of this research is to investigate the effects of staging variables on Two-Stage-To-Orbit reusable launch vehicles, specifically, the question of what measurable factors play important roles in staging performance. Three different configurations (Rocket-Rocket, Turbojet-Rocket and Turbine Based Combined Cycle-Rocket) were considered. The software, Program to Optimize Simulated Trajectories (POST), was used to analyze these configurations. Vehicle coasting time, staging dynamic pressure and staging Mach number were all varied to determine their influence on the final payload.

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Orbit Estimation Algorithms For A Microsatellite Rendezvous With A Non-Cooperative Target, John P. Heslin Mar 2005

Orbit Estimation Algorithms For A Microsatellite Rendezvous With A Non-Cooperative Target, John P. Heslin

Theses and Dissertations

This study investigated the minimum requirements to establish a satellite tracking system architecture for a microsatellite to rendezvous with a non-cooperative target satellite. A prototype optical tracking system was reviewed with emphasis on a proposed tactical employment that could be used by technologically unsophisticated state or non-state adversaries. With the tracking system architecture selected, simulated tracking data was processed with a Non-Linear Least Squares batch orbit estimation algorithm and a Bayes sequential orbit determination filter to update the target satellite's state vector.

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Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey Mar 2005

Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey

Theses and Dissertations

The near-space region of earth's atmosphere above 20 kilometers altitude is greatly underutilized. Lighter-than-air maneuvering vehicles, or airships, using the principle of buoyancy can take advantage of this region to become potential platforms for precision navigation, environmental monitoring, communication relays, missile warning, surveillance, and weapon delivery. These vehicles purportedly provide persistent coverage over large areas of the earth's surface at substantially lower costs than orbiting satellites. This study investigated the technical requirements to loiter an operational payload within this high altitude region using a lighter-than-air maneuvering platform. A parametric analysis was conducted to identify the critical technologies needed to achieve …

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Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz Mar 2005

Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz

Theses and Dissertations

The purpose of this research was to develop a general, statistical model of order-to-delivery times for commercial satellite imagery. The research looked at the current four satellite providers with 3-meter or better imagers in the context of a generalized model of commercial imaging satellite operations. Existing methods use orbit analysis tools to determine the imaging time of a specified target based on defined satellite position and times, but can only develop shortest and longest times to an imaging opportunity. To address the general question of the time it takes to deliver an image for non-specific targets, this research develops a …

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Investigation Of Aerobraking To Return The Space Maneuver Vehicle To Low Earth Orbit From Geotransfer Orbit, Benjamin M. Berlin Mar 2005

Investigation Of Aerobraking To Return The Space Maneuver Vehicle To Low Earth Orbit From Geotransfer Orbit, Benjamin M. Berlin

Theses and Dissertations

This study investigated the use of ballistic and Double-Dip'' aerobraking reentry to return the Space Maneuver Vehicle (SMV) from geotransfer orbit in no more than two atmosphere passes. Lift and drag accelerations were applied to the two-body problem when either of their magnitudes exceeded 1/1000 g. Lift and drag coefficients, along with the SMV model, were taken from Investigation of Atmospheric Reentry for the Space Maneuver Vehicle by Captain McNabb, AFIT/GA/ENY/04-M03. Target perigees were formulated using the two-body problem. The orbit from each target perigee was numerically integrated around a planar earth model using a fourth order Runge-Kutta method. Ballistic …

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Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson Mar 2005

Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson

Theses and Dissertations

Under certain conditions, high energy electron fluxes can increase over short periods of time in the outer radiation belt and diffuse to low altitudes. Sudden increases of high energy electron densities at low altitudes can drastically damage unsuspecting low-earth-orbit satellites. The progression of electron flux increases from a geosynchronous orbit to low-earth orbit during an electron event is somewhat unknown. If the beginning of electron flux increases at low-earth-orbits could be anticipated, warnings could be issued to space system operators allowing time to take proper measures to protect and minimize satellite damage extending satellite lifetimes and space mission operations. The …

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Fuel-Air Injection Effects On Combustion In Cavity-Based Flameholders In A Supersonic Flow, William H. Allen Jr. Mar 2005

Fuel-Air Injection Effects On Combustion In Cavity-Based Flameholders In A Supersonic Flow, William H. Allen Jr.

Theses and Dissertations

The Air Force Research Lab, Propulsion Directorate, Wright-Patterson Air Force Base, Ohio has studied several designs regarding cavity flameholding for supersonic RAMJET (SCRAMJET) applications. The most recent of these studies have concluded that direct injection of ethylene fuel into the aft cavity ramp produced an efficient, robust flameholder given specific freestream condition and fuel flow rate. The main goals of this experiment are: 1) study the effect on combustion of direct fuel and air injection in the main flameholding cavity and 2) characterization of the operational limits (i.e., sustained combustion limits) over a variety of fuel and air flow rates. …

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Development Of A Higher-Order Upwind Algorithm For Compressible Fluid Flow, Barry A. Croker Mar 2005

Development Of A Higher-Order Upwind Algorithm For Compressible Fluid Flow, Barry A. Croker

Theses and Dissertations

A global fourth-order solution method that incorporates compact differencing with Roe's approximate Riemann solver was investigated. This method was incorporated into a one-dimensional numerical simulation of the compressible Euler equations, and applied to a one-dimensional shock tube problem. The method was also extended to two dimensions, and applied to a two-dimensional shock tube problem and an advecting vortical structure problem on both rectilinear and curvilinear meshes. The results were compared to a third-order Roe scheme and a fourth-order compact difference scheme. An order of accuracy determination showed that it has an order of accuracy somewhere near fourth order, with absolute …

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Numerical Analysis And Optimization Of The Ultra Compact Combustors, Roger T. Greenwood Mar 2005

Numerical Analysis And Optimization Of The Ultra Compact Combustors, Roger T. Greenwood

Theses and Dissertations

In an effort to increase thrust per weight ratio and decrease pollutant emissions of aero-turbine jet engines, a circumferentially burning Ultra Compact Combustor (UCC) with a Cavity-in-a-Cavity design has been developed. A numerical analysis of this design has been conducted and compared with experimental results. The CFD model has been validated through a wide range of conditions and four alternative physical configurations of the UCC have been modeled. Emissions, combustor efficiencies, temperature and velocity profiles, and pressure drop values were used as comparison parameters. Numerical results indicate that increasing the outflow area will increase the pressure drop over the combustor …

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Maneuver Estimation Model For Relative Orbit Determination, Tara R. Storch Mar 2005

Maneuver Estimation Model For Relative Orbit Determination, Tara R. Storch

Theses and Dissertations

While the use of relative orbit determination has reduced the difficulties inherent in tracking geosynchronous satellites that are in close proximity, the problem is often compounded by stationkeeping operations or unexpected maneuvers. If a maneuver occurs, observations will no longer fit predicted data, increasing the risk of misidentification and cross-tagging. The goal of this research was to develop a model that will estimate the magnitude, direction, and time of a suspected maneuver performed by a collocated satellite in geosynchronous orbit. Relative motion was modelled using Hill's equations, and least squares estimation was employed to create both a linear non-maneuver model …

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Engineering Tools For Variable Stiffness Vibration Suppression And Isolation, Michael F. Winthrop Jan 2005

Engineering Tools For Variable Stiffness Vibration Suppression And Isolation, Michael F. Winthrop

Theses and Dissertations

With the advent of smart materials, the concept of semi-active control or dynamic control of stiffness and/or damping for vibration control of structures has become practical and has seen limited use. Semi-active control has advantages over active and passive control methods, since it provides almost as much capability as active control while requiring much less power. Its main disadvantage is its inherent nonlinearity, greatly complicating engineering design. The purpose of this research is to extend semi-active control vibration isolation tools and methods considering space launch and on-orbit systems.

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Wind Tunnel Investigation Of The Static Stability And Control Effectiveness Of A Rotary Tail In A Portable Uav, Jose R. Rivera Parga Dec 2004

Wind Tunnel Investigation Of The Static Stability And Control Effectiveness Of A Rotary Tail In A Portable Uav, Jose R. Rivera Parga

Theses and Dissertations

The Air Force Research Lab, Munitions Directorate, Flight Vehicles Integration Branch (AFRL/MNAV) developed a man-portable, carbon-fiber matrix UAV with a flexible rectangular wing of 24" span and 6" chord, 18.2" length. There is a need for the development of smaller and lighter UAV's to perform certain missions. The objective of this experimental study was to determine the behavior and the aerodynamic characteristics of rotary tails. The bird-inspired rotary tail mechanism studied enabled control of two degrees of freedom and was configured to provide elevator deflection and rotation. Its effects on the static stability and control effectiveness were measured using the …

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Analytical Solution For Low-Thrust Minimum Time Control Of A Satellite Formation, John Sang-Pil Seo Sep 2004

Analytical Solution For Low-Thrust Minimum Time Control Of A Satellite Formation, John Sang-Pil Seo

Theses and Dissertations

Satellite formations or distributed satellite systems provide advantages not feasible with single satellites. Efficient operation of this platform requires the use of optimal control of the entire satellite formation. While the optimal control theory is well established, only a very simple dynamical system affords an analytical solution. Any practical optimal control problem solves the resulting two-point boundary value (TPBV) problem numerically. The relative satellite dynamics using Hill's coordinate system and approximations made by Clohessy and Wiltshire, combined with body-fixed thruster control, result in a linearized dynamic system. This dissertation provides the analysis for the minimum time satellite formation control by …

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Quantifying Initial Condition And Parametric Uncertainties In A Nonlinear Aeroelastic System With An Efficient Stochastic Algorithm, Daniel R. Millman Sep 2004

Quantifying Initial Condition And Parametric Uncertainties In A Nonlinear Aeroelastic System With An Efficient Stochastic Algorithm, Daniel R. Millman

Theses and Dissertations

There is a growing interest in understanding how uncertainties in flight conditions and structural parameters affect the character of a limit cycle oscillation (LCO) response, leading to failure of an aeroelastic system. Uncertainty quantification of a stochastic system (parametric uncertainty) with stochastic inputs (initial condition uncertainty) has traditionally been analyzed with Monte Carlo simulations (MCS). Probability density functions (PDF) of the LCO response are obtained from the MCS to estimate the probability of failure. A candidate approach to efficiently estimate the PDF of an LCO response is the stochastic projection method. The objective of this research is to extend the …

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Aerodynamic Analysis Of Lattice Grid Fins In Transonic Flow, Karl S. Orthner Jun 2004

Aerodynamic Analysis Of Lattice Grid Fins In Transonic Flow, Karl S. Orthner

Theses and Dissertations

Lattice grid fins have been studied for missile tail control for several years. A lattice grid fin can be described as an unconventional missile control surface comprised of an outer frame supported by an inner lattice grid of lifting surfaces. This unconventional fin design offers favorable lift characteristics at high angle of attack as well as almost zero hinge moments allowing the use of small and light actuators. In addition, they promise good storability for potential tube-launched and internal carriage dispenser-launched applications. The drawback for the lattice grid fins is the high drag and potentially poor radar cross section performance …

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Detached Eddy Simulation Analysis Of Pak-B Low Pressure Turbine Blade, Kyle Malone Jun 2004

Detached Eddy Simulation Analysis Of Pak-B Low Pressure Turbine Blade, Kyle Malone

Theses and Dissertations

Two cases were computationally investigated using the detached eddy simulation (DES) turbulence model: an unmodified Pak-B blade and a Pak-B blade with a dimple located at 65% of axial chord. Both cases were created so that they simulated an infinite span with an infinite number of dimples. The cases were run for an inlet Reynolds number of 25,000. The computed results were used to resolve the location of separation and reattachment, visualize the streamlines for the dimpled case, build velocity magnitude contour and vector plots, and map the thickness of the boundary layer. The results were then compared to previous …

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Magnetogasdynamic Flow Acceleration In A Scramjet Nozzle, Brian H. Harrington Jun 2004

Magnetogasdynamic Flow Acceleration In A Scramjet Nozzle, Brian H. Harrington

Theses and Dissertations

The effect of magnetogasdynamic (MGD) interactions on flow acceleration and thrust in a scramjet accelerator/nozzle are examined numerically at a free-stream flight condition of Mach 8. The parameters of conductivity pattern and load factor are varied in both inviscid and viscous flow regimes with the intent of increasing axial force exerted on the flow through a scramjet accelerator. The numerical code solves the Navier-Stokes equations with additional source terms for the MGD forces and energy interactions. An accelerating Lorentz force is applied to the flow resulting from a constant magnetic field and an electric field produced by two continuous side …

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Isomer Heat Exchanger Combustor Replacement For A Supersonic Ramjet Powered Vehicle, Jonathan C. Cox Jun 2004

Isomer Heat Exchanger Combustor Replacement For A Supersonic Ramjet Powered Vehicle, Jonathan C. Cox

Theses and Dissertations

This study investigated the possibility of utilizing a Triggered Isomer Heat Exchanger (TIHE) within a ramjet engine to power a supersonic Conventional Air Launched Cruise Missile (CALCM). A computational ramjet engine was created using engine analysis software. This model was then run through a simulated cruise missile mission using AEDsys, a mission analysis and engine performance software suite. The replacement of the combustor with a TIHE led to an impressive range increase for the supersonic cruise missile.

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Fretting Fatigue Behavior Of Shot-Peened Titanium Alloy Tl-6al-4v Under Seawater Conditions, William Y. Allen Jun 2004

Fretting Fatigue Behavior Of Shot-Peened Titanium Alloy Tl-6al-4v Under Seawater Conditions, William Y. Allen

Theses and Dissertations

The fretting fatigue behavior of the shot-peened titanium alloy, Ti-6Al-4V, was investigated under a corrosive environment of synthetic seawater. Fretting fatigue tests were performed over a wide stress range to determine the effect of seawater at high and low cycle fatigue regimes. The results from this study showed: (1) seawater significantly reduces the fretting fatigue life of shot-peened Ti-6Al-4V at both high and low cycle fatigue relative to its counterpart in ambient laboratory conditions, (2) shot peening increases the fretting fatigue life of Ti-6Al-4V when tested under dry and seawater conditions relative to its counterpart of unpeened Ti-6Al-4V, (3) surface …

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Cold Flow Testing Of A Modified Subscale Model Exhaust System For A Space Based Laser, David B. Jarrett Jun 2004

Cold Flow Testing Of A Modified Subscale Model Exhaust System For A Space Based Laser, David B. Jarrett

Theses and Dissertations

The aim of this research was a continued study of gas-dynamic phenomena that occurred in a set of stacked nozzles as reported by Captains Ian Bautista in 2003 and Scott Bergren in 2002. The arrangement of the stacked nozzles was a modified version of a 1/5th scale-model of one quadrant of the conceptual Space Based Laser Integrated Flight Experiment (SBL IFX) gas dynamic laser. Rather than cylindrical rings of nozzles, the stacked nozzles were flat and able to be rotated about a vector normal to the nozzle exits. This set of stacked flat nozzles was installed on a blow-down/vacuum wind …

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Shock Tube Investigation Of Pressure And Ion Sensors Used In Pulse Detonation Engine Research, Robert J. Mcmillan Jun 2004

Shock Tube Investigation Of Pressure And Ion Sensors Used In Pulse Detonation Engine Research, Robert J. Mcmillan

Theses and Dissertations

Shock tubes utilize a difference in pressures between gases separated by a diaphragm to create a shock wave when the diaphragm ruptures. By using sensors of known spacing, the speed of the wave can be determined. The AFIT 2-inch shock tube was reassembled and tested to ensure proper and safe operation. A high-speed data acquisition system was configured to take data at 2 MS/s. This research showed that the Mach number of the shock waves produced in this shock tube fall within 7% of theoretical values at speeds under Mach 3 and within 9% at higher speeds. The peak velocity …

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An Assessment Of Modern Methods For Rotor Track And Balance, Michael J. Renzi Jun 2004

An Assessment Of Modern Methods For Rotor Track And Balance, Michael J. Renzi

Theses and Dissertations

One routine maintenance item facing the helicopter industry today is the issue of rotor track and balance (RT&B). While the task of reducing vibrations is often overlooked as simply an unimportant maintenance concern, what should not be overlooked is the extensive amount of time and money committed by maintenance to smoothing an aircraft. If there were a way to make the process of rotor track and balance more efficient it would be a huge boost to the helicopter industry in both time and money. The first steps towards research into new and improved methods is to evaluate what is currently …

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Aeroelastic Analysis Of A Joined-Wing Sensorcraft, Jennifer J. Sitz Jun 2004

Aeroelastic Analysis Of A Joined-Wing Sensorcraft, Jennifer J. Sitz

Theses and Dissertations

This study performed an aeroelastic analysis of a joined-wing SensorCraft. The analysis was completed using an aluminum structural model that was splined to an aerodynamic panel model. The force and pressure distributions were examined for the four aerodynamic panels: aft wing, fore wing, joint, and outboard tip. Both distributions provide the expected results (elliptical distribution), with the exception of the fore wing. The fore wing appears to be affected by interference with the joint. The use of control surfaces for lift and roll was analyzed. Control surfaces were effective throughout most of the flight profile, but may not be usable …

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A Study Of A Skirtless Hovercraft Design, Edward A. Kelleher May 2004

A Study Of A Skirtless Hovercraft Design, Edward A. Kelleher

Theses and Dissertations

Initial study into three possible skirtless hovercraft designs. The designs utilize Coanda nozzles and a Coanda wing surface to generate lift and create a pressure cushion below the craft. The pressure cushion is to be maintained by an air curtain created by flow spill from the Coanda wing surface. Three proposed skirtless hovercraft designs were analyzed via computational fluid dynamics to ascertain their lift generation capabilities. The three designs were adaptations from William Walter's hybricraft primer and his patent for a fan driven lift generation device. Each design featured Coanda nozzles, or nozzles that utilize the Coanda effect, to redirect …

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