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Air Force Institute of Technology

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Articles 1081 - 1110 of 1674

Full-Text Articles in Aerospace Engineering

Modeling, Stability, And Control Of A Rotatable Tail On A Micro Air Vehicle, Travis J. Higgs Dec 2005

Modeling, Stability, And Control Of A Rotatable Tail On A Micro Air Vehicle, Travis J. Higgs

Theses and Dissertations

This research uses existing experimental wind tunnel data to develop a non-linear model that is used to characterize the stability of a flexible wing Micro Air Vehicle (MAV) with a rotatable tail. The experimental data are curve fit based on either angle of attack or angle of sideslip, and the coupled effect of tail rotation and tail deflection on the force and moment coefficients. Static optimization trims the input and state variables for Steady Level Unaccelerated Flight (SLUF). The resulting initial conditions are fed to an open loop non-linear Simulink/Matlab simulation. The study found that the bare MAV design is …

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Nonlinear Regression Methods For Estimation, Eric B. Nelson Sep 2005

Nonlinear Regression Methods For Estimation, Eric B. Nelson

Theses and Dissertations

Regression techniques are developed for batch estimation and applied to three specific areas, namely, ballistic trajectory launch point estimation, adaptive flight control, and radio-frequency target triangulation. Specifically, linear regression with an intercept is considered in detail. An augmentation formulation is developed. Extensions of theory are applied to nonlinear regression as well. The intercept parameter estimate within the linear regression is used to identify the effects of trim change that are associated with the occurrence of a control surface failure. These estimates are used to adjust the inner loop control gains via a feed-forward command, hence providing an automatic reconfigurable retrim …

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Effects Of Boundary Layer Flow Control Using Plasma Actuator Discharges, Jeffrey M. Newcamp Sep 2005

Effects Of Boundary Layer Flow Control Using Plasma Actuator Discharges, Jeffrey M. Newcamp

Theses and Dissertations

This study addresses the usage and effects of atmospheric plasma discharges on the near wall flow conditions for a Pak-B low-pressure turbine blade. A plasma actuator was built normal to the freestream flow in a low-speed wind tunnel. The test section of the wind tunnel had a contoured upper wall geometry designed to mimic the suction side of a Pak-B turbine blade. A high frequency ac voltage source supplied three voltages in the kilovolt range at four Reynolds numbers in the experiment, between 10,000 and 103,000. The effect of the plasma on the near-wall boundary layer conditions was evaluated at …

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Experimental Investigation Of A Lift Augmented Ground Effect Platform, Roberto T. Igue Sep 2005

Experimental Investigation Of A Lift Augmented Ground Effect Platform, Roberto T. Igue

Theses and Dissertations

This experimental study investigated the feasibility of applying the concept of a skirtless hovercraft into the production of an operational vehicle. A 0.255 m diameter prototype was designed, built and tested. An air bearing table was used as a testing platform, virtually eliminating the influence of friction and providing one degree of freedom for the experiments. Static tests were performed at various heights and craft configurations, providing a wide range of data for comparison. Lift, torque and efficiency were measured and calculated for each setting. Pressure and velocity information was also collected at specific points around the craft when operating …

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Characterization Of The Global Hawk Low Pressure Turbine First Rotor, Timothy L. Garmoe Sep 2005

Characterization Of The Global Hawk Low Pressure Turbine First Rotor, Timothy L. Garmoe

Theses and Dissertations

The Air Force Research Laboratory, Propulsion Directorate at Wright Patterson Air Force Base has studied the performance of turbine blade geometries utilizing a large scale, low speed, drawdown wind tunnel in an effort to better understand gas turbine blade aerodynamics. Currently, the Air Force's Unmanned Aerial Vehicle (UAV) Global Hawk has been operated primarily at flight conditions other than the design point of its Allison AE3007H turbofan engine. This off design condition decreased the Reynolds number at the low pressure turbine causing losses in efficiency and loading. Two different blades were studied to maximize performance of the Global Hawk turbine. …

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Investigation Of The Performance Characteristics Of Re-Entry Vehicles, Charles A. Bilbey Jr. Sep 2005

Investigation Of The Performance Characteristics Of Re-Entry Vehicles, Charles A. Bilbey Jr.

Theses and Dissertations

When a non-US spacecraft reenters the Earth's atmosphere, having the ability to accurately determine its performance characteristics is a primary concern. This study investigated the atmospheric re-entry profiles of a maneuverable re-entry vehicle. The re-entry vehicle was modeled as a point mass with aerodynamic properties. Equations of motion were numerically integrated, giving the time histories of position, velocity and flight path angle. The algorithm is able to generate a complete and feasible entry trajectory of a approximately 25-minute flight time in about 5 to 10 seconds on a desktop computer, given the entry conditions and values of constraint parameters. This …

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Operator State Estimation For Adaptive Aiding In Uninhabited Combat Air Vehicles, Christopher A. Russell Sep 2005

Operator State Estimation For Adaptive Aiding In Uninhabited Combat Air Vehicles, Christopher A. Russell

Theses and Dissertations

This research demonstrated the first closed-loop implementation of adaptive automation using operator functional state in an operationally relevant environment. In the Uninhabited Combat Air Vehicle (UCAV) environment, operators can become cognitively overloaded and their performance may decrease during mission critical events. This research demonstrates an unprecedented closed-loop system, one that adaptively aids UCAV operators based on their cognitive functional state A series of experiments were conducted to 1) determine the best classifiers for estimating operator functional state, 2) determine if physiological measures can be used to develop multiple cognitive models based on information processing demands and task type, 3) determine …

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A Prediction Code For The Thrust Performance Of Two-Dimensional, Non-Axisynnetric, Converging Diverging Nozzles, Angela M. Geatz Sep 2005

A Prediction Code For The Thrust Performance Of Two-Dimensional, Non-Axisynnetric, Converging Diverging Nozzles, Angela M. Geatz

Theses and Dissertations

The objective of this research is to develop a prediction code for the Air Force Research Laboratory Propulsion Directorate that can accurately determine the gross thrust coefficient for a user defined nonaxisymmetric two-dimensional converging diverging nozzle. The code includes the effects of friction, angularity, and expansion losses on nozzle efficiency. To demonstrate the prediction method, the generated computational results were compared to experimental data, as well as computational results from other existing nozzle performance codes, for a number of different nozzle geometries. The nozzle internal performance prediction code showed excellent agreement with experimental data in predicting the gross thrust performance …

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The Effect Of Aerodynamic Surfaces Versus Thrust Maneuvers On Reentry Vehicles, Meredith M. Albrecht Sep 2005

The Effect Of Aerodynamic Surfaces Versus Thrust Maneuvers On Reentry Vehicles, Meredith M. Albrecht

Theses and Dissertations

This research effort analyzes the effect of aerodynamic surfaces versus thrust maneuvers on a reentry vehicle. At high altitudes the effect of aerodynamic surfaces on the reentry vehicle is small due to low atmospheric density; however as the vehicle reaches lower altitudes a lift maneuver is very successful in deflecting the vehicle and creating a large impact footprint. When a continuous thrust maneuver is input in the place of a lift maneuver the results are very similar at the highest maneuver altitudes, although the impact footprint shrinks rapidly as the maneuver altitude decreases. Additionally, when the thrust maneuver is along …

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A Flash Vaporization System For Detonation Of Hydrocarbon Fuels In A Pulse Detonation Engine, Kelly C. Tucker Jun 2005

A Flash Vaporization System For Detonation Of Hydrocarbon Fuels In A Pulse Detonation Engine, Kelly C. Tucker

Theses and Dissertations

Current research by the US Air Force and Navy is concentrating on obtaining detonations in a pulse detonation engine (PDE) with low vapor pressure, kerosene based jet fuels. These fuels have a low vapor pressure and the performance of a liquid hydrocarbon fueled PDE is significantly hindered by the presence of fuel droplets. A high pressure, fuel flash vaporization system (FVS) has been designed and built to reduce and eliminate the time required to evaporate the fuel droplets. Four fuels are tested: n-heptane, isooctane, aviation gasoline, and JP-8. The fuels vary in volatility and octane number and present a clear …

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Boundary Layer Control Of A Circular Cylinder Using A Synthetic Jet, Christopher K. Smith Jun 2005

Boundary Layer Control Of A Circular Cylinder Using A Synthetic Jet, Christopher K. Smith

Theses and Dissertations

Active control of flow around a circular cylinder at a sub-critical Reynolds number was studied experimentally. The flow was controlled by using a synthetic jet which ran span wise along the cylinder and emanated radially from the cylinder. The experiments were conducted over a two dimensional cylinder in a water tunnel at a Reynolds number of approximately 5800. Seven different jet locations and seven different jet oscillation frequencies were examined. Particle image velocimetry (PIV) was used for flow visualization. The synthetic jet proved to delay flow separation at a wide range of locations and oscillation frequencies. The greatest positive effect …

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An Investigation Of Starting Techniques For Inward Turning Inlets At Flight Speeds Below The On-Design Mach Number, John D. Mack Jun 2005

An Investigation Of Starting Techniques For Inward Turning Inlets At Flight Speeds Below The On-Design Mach Number, John D. Mack

Theses and Dissertations

The purpose of this study was to create and investigate starting techniques aimed at allowing complex, three-dimensional, inward-turning inlets to start by swallowing the shock wave associated with unstarted inlets. The techniques are rooted in supersonic diffuser theory and the Kantrowitz limit; they attempt to alleviate the over contraction that occurs in inward-turning inlets at flight speeds below the on-design Mach number. Five cases, three geometries at two flow conditions and the base non-modified inlet at the two flow conditions, were generated, and all were numerically simulated using a commercially produced numerical solver: CFD++. The simulations were computed using the …

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Parametric Study Of The Towline Shape Of An Aircraft Decoy, Tyler L. Richardson Jun 2005

Parametric Study Of The Towline Shape Of An Aircraft Decoy, Tyler L. Richardson

Theses and Dissertations

Some of today's aircraft use decoys as a defense against enemy weapons. The decoy is towed behind the aircraft with the intention of attracting the weapon propagator by deception, trying to mislead the weapon into detecting it instead of the aircraft. An aircraft deploys a decoy via a towline extending out behind and below the aircraft. However, during some maneuvers, the towline moves up into the jet exhaust plume of the aircraft. The high temperatures of the exhaust can cause damage to the towline cable, ranging from disrupting data flow between the decoy and aircraft to severing the towline altogether. …

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Study Of Magnetogasdynamic Flow Acceleration In A Scramjet Nozzle, Erik K. Ross Jun 2005

Study Of Magnetogasdynamic Flow Acceleration In A Scramjet Nozzle, Erik K. Ross

Theses and Dissertations

The research project studied the benefits of Magnetogasdynamic (MGD) acceleration on a scramjet nozzle. MGD is a technology that relies on electromagnetic fields to extract and/or add energy to flow fields. The scramjet engine in the "AJAX" concept proposed by D.I. Brichkii et al. (2001) of St. Petersburg, Russia would utilize an MGD power generator in the diffuser user which could potentially provide electrical power for the aircraft support systems and an MGD accelerator in the nozzle of the engine. Using an AFRL/VAAC CFD code that was modified for MGD computations, this project investigated the effect conductivity and load factor …

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Design And Ground-Testing Of An Inflatable-Rigidizable Structure Experiment In Preparation For Space Flight, Chad R. Moeller Jun 2005

Design And Ground-Testing Of An Inflatable-Rigidizable Structure Experiment In Preparation For Space Flight, Chad R. Moeller

Theses and Dissertations

As the demand for larger space structures increases, complications arise including physical dimensions, weight, and launch costs. These constraints have forced the space industry to look for smaller, more lightweight, and cost-effective solutions. Future antennas, solar sails, sun shields, and other structures have the potential to be exponentially larger than their launch envelopes. Current research in this area is focused on the use of inflatable, rigidizable structures to reduce payload size and mass, ultimately reducing launch costs. These structures can be used as booms, trusses, wings, or can be configured to almost any simple shape. More complex shapes can be …

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Characterization Of A Rotary Flat Tail As A Spoiler And Parametric Analysis Of Improving Directional Stability In A Portable Uav, Troy A. Leveron Jun 2005

Characterization Of A Rotary Flat Tail As A Spoiler And Parametric Analysis Of Improving Directional Stability In A Portable Uav, Troy A. Leveron

Theses and Dissertations

The United States Air Force Research Lab, Munitions Directorate, Flight Vehicles, Integration Branch (AFRL/MNAV), has developed a flexible wing micro air vehicle (MAV) to be used with special tactics groups. In keeping with the requirement that this MAV be compact, previous research developed a rotatable tail mechanism which resulted in tail movement similar to that of a bird's tail. In this study the design of this tail was modified to produce a more storable vehicle. The redesign also allowed the tail to deflect upward to large angles, enabling the tail to be used as a spoiler. The aerodynamic effects of …

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Experimental Investigation Into The Aerodynamic Ground Effect Of A Tailless Chevron-Shaped Ucav, Brett L. Jones Jun 2005

Experimental Investigation Into The Aerodynamic Ground Effect Of A Tailless Chevron-Shaped Ucav, Brett L. Jones

Theses and Dissertations

This experimental study adequately identified the ground effect region of an unmanned combat air vehicle (UCAV). The AFIT 3' x 3' low-speed wind tunnel and a ground plane were used to simulate the forces and moments on a UCAV model in ground effect. The chevron planform used in this study was originally tested for stability and control and the following extends the already existing database to include ground effects. The ground plane was a flat plate mounted with cylindrical legs. To expand the capabilities of the AFIT 3' x 3' low-speed wind tunnel, hot-wire measurements and flow visualization revealed an …

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Drag Estimates For The Joined-Wing Sensor Craft, Ryan L. Craft Jun 2005

Drag Estimates For The Joined-Wing Sensor Craft, Ryan L. Craft

Theses and Dissertations

This research studied the drag effects of the joined-wing sensor craft technology demonstrator being developed at the Air Force Research Laboratory (AFRL). Although many performance parameters have been studied and evaluated for this vehicle, to date no detailed drag estimates have been conducted for the AFRL configuration. Previous performance parameters of the aircraft have been estimated based solely on a constant lift-to-drag ratio assumption. Using the Air Vehicles Technology Integration Environment created by Dr. Maxwell Blair, and supplemented by MATLAB code, this study explored three different drag prediction methods to determine accurate estimates of both parasite and induced drag. The …

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An Approach For Optimizing The On-Orbit Servicing Architecture For The Space-Based Radar Constellation, Michael L. Mcconnell Mar 2005

An Approach For Optimizing The On-Orbit Servicing Architecture For The Space-Based Radar Constellation, Michael L. Mcconnell

Theses and Dissertations

Satellite systems, once operational, are essentially a consumable item with no capacity to maintain, repair, or upgrade them while on-orbit. In order to avoid having to replace costly space assets, the Defense Advanced Research Projects Agency (DARPA) and Air Force Space Command (AFSPC) are looking to developing programs to provide an on-orbit servicing capability for future satellite systems under development, such as the Space-Based Radar (SBR) system. DARPA and AFSPC are studying on-orbit servicing using the Orbital Express platform as part of an Analysis of Alternatives for the SBR program. Like their satellite clients, on-orbit servicing assets are expected to …

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Analysis Of Online-Delaunay Navigation For Time Sensitive Targeting, David Chow Mar 2005

Analysis Of Online-Delaunay Navigation For Time Sensitive Targeting, David Chow

Theses and Dissertations

Given the drawbacks of leaving time-sensitive targeting (TST) strictly to humans, there is value to the investigation of alternative approaches to TST operations that employ autonomous systems. This paper accomplishes five things. First, it proposes a short-hop abbreviated routing paradigm (SHARP) - based on Delaunay triangulations (DT), ad-hoc communication, and autonomous control - for recognizing and engaging TSTs that, in theory, will improve upon persistence, the volume of influence, autonomy, range, and situational awareness. Second, it analyzes the minimum timeframe need by a strike (weapons enabled) aircraft to navigate to the location of a TST under SHARP. Third, it shows …

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Stochastic Capability Models For Degrading Satellite Constellations, Cole W. Gulyas Mar 2005

Stochastic Capability Models For Degrading Satellite Constellations, Cole W. Gulyas

Theses and Dissertations

This thesis proposes and analyzes a new measure of functional capability for satellite constellations that incorporates the instantaneous availability and mission effectiveness of individual satellites. The capability measure yields a continuous score between zero and one accounting for the degree to which the constellation meets operational requirements. The measure is computed from an average of satellite capabilities, composed of the product of the satellite's instantaneous availability and value score. Instantaneous availability is acquired by modeling the satellite degradation status as either a time-homogenous, continuous-time Markov chain (CTMC) if it possesses functions with exponential lifetime distributions, or as a time-homogenous, semi-Markov …

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Pulse Detonation Engine Thrust Tube Heat Exchanger For Flash Vaporization And Supercritical Heating Of Jp-8, Christen L. Miser Mar 2005

Pulse Detonation Engine Thrust Tube Heat Exchanger For Flash Vaporization And Supercritical Heating Of Jp-8, Christen L. Miser

Theses and Dissertations

Research has shown that performance of liquid hydrocarbon fueled pulse detonation engines is limited by the time required to evaporate liquid fuel droplets within the mixture. Vaporization of liquid fuels prior to injection has been shown to decrease ignition times and also increases fuel efficiency; however, the size and efficiency of the vaporization system used are not feasible for use in future pulse detonation aircraft concepts. The purpose of this research is to harness the waste heat of pulse detonation engine thrust tubes to generate a steady-state, self-sustained flash vaporization and supercritical heating system using JP-8 as the working fluid …

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Structures Of Angled Aerated-Liquid Jets In March 1.94 Supersonic Cross Flow, Dion R. Dixon Mar 2005

Structures Of Angled Aerated-Liquid Jets In March 1.94 Supersonic Cross Flow, Dion R. Dixon

Theses and Dissertations

The structures of aerated-liquid jets injected into a supersonic crossflow have been studied experimentally. Aerated-liquid injectors with diameters of 0.020", 0.040" and 0.060" were flush mounted on the bottom plate of a supersonic wind tunnel to provide normal and angled injection. Free stream Mach number and temperature were held constant at 1.94 and 500°F, respectively. Water at room temperature was used as the liquid injectant and nitrogen gas used as the aerating gas. Wide ranges of test conditions for injection angle (θ), injector orifice diameter (d0), jet-to-air momentum flux ratios (q0), and gas-to-liquid ratios (GLR), were …

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Evaluation Techniques For Determining Damping Mechanisms On Titanium Plates, Kyle S. Allen Mar 2005

Evaluation Techniques For Determining Damping Mechanisms On Titanium Plates, Kyle S. Allen

Theses and Dissertations

High cycle fatigue (HCF) is the single largest cause of component failure for all modern military gas turbine engines. Hard coatings, such as magnesium aluminate spinel, have been found to provide significant damping properties. Past studies have had difficulties isolating the contributions of these hard coating damping layers from other damping mechanisms. This study explored techniques for assessing the contribution of different damping mechanisms on titanium plates during vibration testing. The study investigated 2nd bend and 2-stripe modes. Two different specimen sizes were tested in both a clamped-free-free-free and free-free-free-free condition. Specimens were tested at varying pressures. Increases in pressure …

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Boundary Layer Flow Control Using Plasma Induced Velocity, Brian E. Balcer Mar 2005

Boundary Layer Flow Control Using Plasma Induced Velocity, Brian E. Balcer

Theses and Dissertations

An examination of the effects of plasma induced velocity on boundary layer flow was conducted. A pair of thin copper film electrodes spanned the test section, oriented at thirty degrees from normal to the free stream flow. An adverse pressure gradient was imposed over the electrode configuration using a pressure coefficient profile similar to that associated with suction side of a Pac-B low pressure turbine blade. In addition, suction was applied to keep flow attached on the upper wall, inducing separation over the electrode. The electrode is supplied by an AC source at three different power levels with the free …

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Experimental Study Of The Subsonic Aerodynamics Of A Blended Wing Body Air Vehicle With A Focus On Rapid Technology Assessment, David A. Gebbie Mar 2005

Experimental Study Of The Subsonic Aerodynamics Of A Blended Wing Body Air Vehicle With A Focus On Rapid Technology Assessment, David A. Gebbie

Theses and Dissertations

The subsonic aerodynamic performance of a blended wing body aircraft constructed using selective laser sintering was assessed in the AFIT low-speed wind tunnel. The scaled-down model of a strike tanker aircraft consisted of a shaped fuselage and sweptback wings. The Reynolds number, based on mean wing chord, during testing was on the order of 105 while the Mach number ranged from 0.10 to 0.20. The model evaluation and analysis process included force and moment measurements acquired from a wind tunnel balance, pressure data measured with 8 taps located on the model’s upper surface, a comparison to computational fluid dynamics (CFD) …

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Mixing Effects Of Pylon-Aided Fuel Injection Located Upstream Of A Flameholding Cavity In Supersonic Flow, Daniel R. Montes Mar 2005

Mixing Effects Of Pylon-Aided Fuel Injection Located Upstream Of A Flameholding Cavity In Supersonic Flow, Daniel R. Montes

Theses and Dissertations

The Air Force Research Lab (AFRL), Propulsion Directorate, Wright-Patterson Air Force Base, Ohio is conducting ongoing research into propulsive efficiency in supersonic ramjet (scramjet) technology. One current focus of this research is the usefulness of flameholding cavities implemented in the supersonic hydrocarbon-fueled combustion chamber. Because good mixing and proper cavity-core interaction lead to more efficient combustion, methods of optimizing fuel/air mixing both within and upstream the cavity are investigated. In a cooperative effort with the Air Force Institute of Technology (AFIT), AFRL provided a supersonic wind tunnel outfitted with an existing cavity design. A circular injection port was placed upstream …

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Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt Mar 2005

Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt

Theses and Dissertations

This thesis encompasses a feasibility analysis of a parachute extracted generic precision guided munition from the cargo bay of a C-130 aircraft in flight. This analysis utilizes the USAF Beggar code and incorporates full physics effects as well as aerodynamic loading assuming an inviscid aircraft and viscous store for a time-accurate solution. Both an immediate and time varying application of the parachute force are utilized as well as two different ordnance body styles at zero and 5 degrees AOA with the store placed on centerline and offset in the cargo bay. The time accurate parachute model is based on empirical …

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Full Capability Formation Flight Control, Ryan K. Osteroos Mar 2005

Full Capability Formation Flight Control, Ryan K. Osteroos

Theses and Dissertations

The subject of automatic formation flight control is of current interest to the development of Unmanned Aerial Vehicles (UAV). Previous control approaches have been refined in this work to allow more robust maneuvering and to include a fourth control parameter. The equations of motion for each aircraft as a point mass, expressed in a wind-axis coordinate system, are coupled into differential equations that model the two aircraft system dynamics. Control laws are developed that include proportional and integral action. Gains are determined based on formation performance. Lead maneuvers are simulated and the controller is gauged on its ability to maintain …

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Computational Aeroelastic Analysis Of Micro Air Vehicle With Experimentally Determined Modes, Joshua A. Stults Mar 2005

Computational Aeroelastic Analysis Of Micro Air Vehicle With Experimentally Determined Modes, Joshua A. Stults

Theses and Dissertations

A computational aeroelastic analysis of a micro air vehicle (MAV) is conducted. This MAV has a 24 inch wing span, and is designed for local area reconnaissance. Wind tunnel data for the MAV with a rigid carbon fiber wing and a flexible carbon fiber ribbed nylon wing are compared to CFD results incorporating static and dynamic deformations. We use laser vibrometry to determine the mode shapes of the flexible wing. From these shapes, CFD grid deformations are calculated as part of a closely-coupled aeroelastic solution method. The accuracy of MAV performance predictions using CFD with and without aeroelastic modeling is …

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