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Articles 9391 - 9420 of 11199

Full-Text Articles in Aerospace Engineering

Experimental Analysis Of Propeller Interactions With A Flexible Wing Micro-Air-Vehicle, Brian J. Gamble Mar 2006

Experimental Analysis Of Propeller Interactions With A Flexible Wing Micro-Air-Vehicle, Brian J. Gamble

Theses and Dissertations

An investigation into the effects of the propeller slipstream on a flexible wing micro-air-vehicle (MAV) was conducted. The Air Force Research Lab, Munitions Directorate designed a man-portable MAV with a 24 in. wingspan and 6 in. root chord to be used for battle damage assessment and reconnaissance. Two wings have been developed for this MAV. One is a rigid carbon-fiber wing and the other consists of flexible parachute material attached to a carbon-fiber skeleton. Experimental methods were implemented to investigate propeller and wing interactions, characterizing torque and thrust requirements on the motor along with aerodynamic forces on the aircraft as …


Development Of Autonomous Unmanned Aerial Vehicle Platform: Modeling, Simulating, And Flight Testing, Nidal M. Jodeh Mar 2006

Development Of Autonomous Unmanned Aerial Vehicle Platform: Modeling, Simulating, And Flight Testing, Nidal M. Jodeh

Theses and Dissertations

The Advanced Navigation Technology (ANT) Center at the Air Force Institute of Technology (AFIT) conducts extensive research in advanced guidance, navigation, and control to exploit the full potential of autonomous Unmanned Aerial Vehicles (UAV). The research in this thesis describes a UAV research platform developed to support the ANT Center's goals. This platform is now the bedrock for UAV simulation and local flight test at AFIT. The research has three major components. The first component is development of a physical, inertial, and aerodynamic model representing an existing aircraft. A systematic analysis of the airframe leads to a complete geometric, inertial, …


Structural Design Of Wing Twist For Pitch Control Of Joined Wing Sensor Craft, Fred A. Kimler Iii Mar 2006

Structural Design Of Wing Twist For Pitch Control Of Joined Wing Sensor Craft, Fred A. Kimler Iii

Theses and Dissertations

This research investigated two aspects of the aft wing structure of a joined wing SensorCraft. First, the efficacy of a novel approach for incorporating wing twist for pitch control was analyzed. This design involved adding a spanwise sliding joint into the wing structure at the lower aft spar of the vehicle's aft wing. Second, the joint section where the forward and aft wings connect and form the outboard wing was redesigned and analyzed to improve the load transmission between the wing spars. Using MSC.NASTRAN, linear and non-linear static analyses were performed to examine the efficiency of the wing twist sliding …


A Comparison Of Main Rotor Smoothing Adjustments Using Linear And Neural Network Algorithms, Nathan A. Miller Mar 2006

A Comparison Of Main Rotor Smoothing Adjustments Using Linear And Neural Network Algorithms, Nathan A. Miller

Theses and Dissertations

Helicopter main rotor smoothing is a maintenance procedure that is routinely performed to minimize airframe vibrations induced by non-uniform mass and/or aerodynamic distributions in the main rotor system. This important task is both time consuming and expensive, so improvements to the process have long been sought. Traditionally, vibrations have been minimized by calculating adjustments based on an assumed linear relationship between adjustments and vibration response. In recent years, artificial neural networks have been trained to recognize non-linear mappings between adjustments and vibration response. This research was conducted in order observe the character of the adjustment mapping of the Vibration Management …


Alleviation Of Buffet-Induced Vibration Using Piezoelectric Actuators, Shawn D. Morganstern Mar 2006

Alleviation Of Buffet-Induced Vibration Using Piezoelectric Actuators, Shawn D. Morganstern

Theses and Dissertations

Buffet-induced vibration has been problematic for aircraft structures for many years. The F-16 ventral fin, while prone to these effects, lends itself well to the evaluation of modern active structural and flow control technologies. The objective of this research was to determine the most critical natural modes of vibration for the F-16 ventral fin and design piezoelectric actuators capable of reducing buffet-induced ventral fin vibration. A finite element model (FEM) for the fin was developed, tuned and optimized to closely match published modal frequencies. Piezoelectric actuator patches were designed using the strain characteristics of the FEM and integrated into the …


Katysat: Concept Of Operations, Robert J. Twiggs Feb 2006

Katysat: Concept Of Operations, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "KatySat: Concept of Operations" from February 24, 2006.


Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein Feb 2006

Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein

Theses and Dissertations

Recent progress in the generation and sustainment of gas discharges at atmospheric pressure has energized research in the field of plasma-aerodynamics. Plasma actuators are promising devices that achieve flow control with no moving parts, do not alter the airfoil shape and place no parts in the flow. The operation of a plasma actuator is examined using a macroscopic (force and power addition) computational fluid dynamic model of a dielectric barrier discharge, DBD, in Fluent. A parametric approach is adopted to survey the range of requisite magnitudes of momentum and energy delivered to the flow field and to identify the effects …


A Game Theory Approach To Constrained Minimax State Estimation, Daniel J. Simon Feb 2006

A Game Theory Approach To Constrained Minimax State Estimation, Daniel J. Simon

Electrical and Computer Engineering Faculty Publications

This paper presents a game theory approach to the constrained state estimation of linear discrete time dynamic systems. In the application of state estimators, there is often known model or signal information that is either ignored or dealt with heuristically. For example, constraints on the state values (which may be based on physical considerations) are often neglected because they do not easily fit into the structure of the state estimator. This paper develops a method for incorporating state equality constraints into a minimax state estimator. The algorithm is demonstrated on a simple vehicle tracking simulation.


Experimental Evaluation Of A High Fineness Ratio Body With Drag Brakes, Corey J. Florendo, Thomas R. Yechout, Stefan Siegel, Russell M. Cummings, Joseph Kealos Jan 2006

Experimental Evaluation Of A High Fineness Ratio Body With Drag Brakes, Corey J. Florendo, Thomas R. Yechout, Stefan Siegel, Russell M. Cummings, Joseph Kealos

Aerospace Engineering

The Advanced Remote Ground Unattended Sensor uses drag brakes to control its terminal velocity during flight. An experimental evaluation of the geometry was performed at Mach numbers between 0.20 and 0.50 with a 61.5% scale model in the U.S. Air Force Academy Subsonic Wind Tunnel. Configurations tested include baseline drag brakes fully deployed, an array of perforated drag brake designs, as well as various other related drag brake design features. Improvements to the baseline design are discussed and an improved configuration is presented. Limited unsteady computations were performed for selected cases using detached-eddy simulation to understand various experimental results. The …


Experimental Evaluation Of A High Fineness Ratio Body With Drag Brakes, Corey J. Florendo, Thomas R. Yechout, Stefan G. Siegel, Russell M. Cummings, Joseph Kealos Jan 2006

Experimental Evaluation Of A High Fineness Ratio Body With Drag Brakes, Corey J. Florendo, Thomas R. Yechout, Stefan G. Siegel, Russell M. Cummings, Joseph Kealos

Aerospace Engineering

No abstract provided.


The Influence Of Viscosity And Surface Curvature On The Pressure Distribution Of A Stream Thrust Probe, Renee Pasman, Russell M. Cummings Jan 2006

The Influence Of Viscosity And Surface Curvature On The Pressure Distribution Of A Stream Thrust Probe, Renee Pasman, Russell M. Cummings

Aerospace Engineering

Determining the local stream thrust (a vector quantity) from a measured pitot pressure (a scalar quantity) requires either knowledge of the flow direction, or a probe shape that compensates for flow direction. This compensation would ideally make the measured pressure directly proportional to the component of momentum along the probe axis. The flow angle sensitivity required to resolve this component of momentum was determined theoretically previously. A proposed probe nose shape was analyzed using CFD and found to produce flow angle sensitivity close to the required sensitivity. The proposed nose shape was also tested in a wind tunnel at Mach …


Numerical Evaluation Of The Flowfield For A High Fineness Ratio Body With Drag Brakes, Russell M. Cummings, James A. Divine, Thomas R. Yechout, David C. Wetlesen, Joseph J. Kealos Jan 2006

Numerical Evaluation Of The Flowfield For A High Fineness Ratio Body With Drag Brakes, Russell M. Cummings, James A. Divine, Thomas R. Yechout, David C. Wetlesen, Joseph J. Kealos

Aerospace Engineering

The Advanced Remote Ground Unattended Sensor (ARGUS) utilizes drag brakes to control its terminal velocity during flight. Computational fluid dynamics predictions were performed at Mach numbers between 0.20 and 0.95 with a full scale model of the ARGUS configuration at conditions to match wind tunnel testing that has been performed at the USAFA Subsonic Wind Tunnel. Configurations consist of brakes fully deployed for a nominal brake fin and a perforated brake fin. Steady-stated computations were performed using the Spalart-Allmaras turbulence model at angles of attack between 0 degrees to 20 degrees at roll angles of 0 degrees and 45 degrees. …


Nonlinear Model Predictive Control Technique For Unmanned Air Vehicles, Nathan Slegers, Jason Kyle, Mark Costello Jan 2006

Nonlinear Model Predictive Control Technique For Unmanned Air Vehicles, Nathan Slegers, Jason Kyle, Mark Costello

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A nonlinear model predictive control strategy is developed and subsequently specialized to autonomous aircraft that can be adequately modeled with a rigid 6-degrees-of-freedom representation. Whereas the general air vehicle dynamic equations are nonlinear and nonaffine in control, a closed-form solution for the optimal control input is enabled by expanding both the output and control in a truncated Taylor series. The closed-form solution for control is relatively simple to calculate and well suited to the real time embedded computing environment. An interesting feature of this control law is that the number of Taylor series expansion terms can be used to indirectly …


Cool Flames At Terrestrial, Partial, And Near-Zero Gravity, Michael R. Foster, Howard Pearlman Jan 2006

Cool Flames At Terrestrial, Partial, And Near-Zero Gravity, Michael R. Foster, Howard Pearlman

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Natural convection plays an important role in all terrestrial, Lunar, and Martian-based, unstirred, static reactor cool flame and low-temperature autoignitions, since the Rayleigh number (Ra) associated with the self-heating of the reaction exceeds the critical Ra (approximately 600) for onset of convection. At near-zero gravity, Ra < 600 can be achieved and the effects of convection suppressed. To systematically vary the Ra without varying the mixture stoichiometry, reactor pressure, or vessel size, cool flames are studied experimentally in a closed, unstirred, static reactor subject to different gravitational accelerations (terrestrial, 1g; Martian, 0.38g; Lunar, 0.16g; a n dr e - duced gravity, ∼10−2g). Representative results show the evolution of the visible light emission using an equimolar n-butane:oxygen premixture at temperatures ranging from 320 to 350 ◦C (593–623 K) at subatmospheric pressures. For representative reduced-gravity, spherically propagating cool flames, the flame radius based on the peak light intensity is plotted as a function of time and the flame radius (and speed) is calculated from a polynomial fit to data. A skeletal chemical kinetic Gray-Yang model developed previously for a one-dimensional, reactive– diffusive system by Fairlie and co-workers is extended to a two-dimensional axisymmetric, spherical geometry. The coupled species, energy, and momentum equations are solved numerically and the spatio-temporal variations in the temperature profiles are presented. A qualitative comparison is made with the experimental results.


Basic Materials Research Programs At The U.S. Air Force Office Of Scientific Research, Herbert C. Carlson, K. C. Goretta Jan 2006

Basic Materials Research Programs At The U.S. Air Force Office Of Scientific Research, Herbert C. Carlson, K. C. Goretta

United States Air Force: Publications

The Air Force Office of Scientific Research (AFOSR) annually sponsors approximately 5000 research scientists at 1000 universities and laboratories, generating about 10,000 Ph.D. graduates per decade, all expected to publish their basic research findings in peer-reviewed journals. After a brief introduction of the nature of AFOSR’s support to basic research in the U.S. and international scientific communities, work it supports at the frontiers of materials science is highlighted. One focused research theme that drives our investment is the MEANS program. It begins with the end in mind; materials are designed with practicable manufacture as an explicit initial goal. AFOSR’s broad …


Continuing Evolution Of Aerodynamic Concept Development Using Collaborative Numerical And Experimental Evaluations, Russell M. Cummings, Scott A. Morton Jan 2006

Continuing Evolution Of Aerodynamic Concept Development Using Collaborative Numerical And Experimental Evaluations, Russell M. Cummings, Scott A. Morton

Aerospace Engineering

Traditionally, computational predictions and experimental evaluations of aerodynamic concepts have been conducted separately, with little collaboration other than post priori comparisons of results. This has led to distrust and even antagonism between the computational and the experimental communities. These difficulties probably began when early computational fluid dynamic practitioners boasted that wind tunnels would become secondary in aerodynamic concept development within a few short years, a prediction that has not come true. On the contrary, it is believed that a great deal of synergy can be cultivated when computational and experimental evaluations are conducted in an integrative fashion. A variety of …


Critical Hypersonic Aerothermodynamic Phenomena, John J. Bertin, Russell M. Cummings Jan 2006

Critical Hypersonic Aerothermodynamic Phenomena, John J. Bertin, Russell M. Cummings

Aerospace Engineering

The challenges in understanding hypersonic flight are discussed and critical hypersonic aerothermodynamics issues are reviewed. The ability of current analytical methods, numerical methods, ground testing capabilities, and flight testing approaches to predict hypersonic flow are evaluated. The areas where aerothermodynamic shortcomings restrict our ability to design and analyze hypersonic vehicles are discussed, and prospects for future capabilities are reviewed. Considerable work still needs to be done before our understanding of hypersonic flow will allow for the accurate prediction of vehicle flight characteristics throughout the flight envelope from launch to orbital insertion.


Field-Scale Demonstration Of Induced Biogeochemical Reductive Dechlorination At Dover Air Force Base, Dover, Delaware, Lonnie G. Kennedy, Jess W. Everett, Erica Becvar, Donald Defeo Jan 2006

Field-Scale Demonstration Of Induced Biogeochemical Reductive Dechlorination At Dover Air Force Base, Dover, Delaware, Lonnie G. Kennedy, Jess W. Everett, Erica Becvar, Donald Defeo

United States Air Force: Publications

Biogeochemical reductive dechlorination (BiRD) is a new remediation approach for chlorinated aliphatic hydrocarbons (CAHs). The approach stimulates common sulfate-reducing soil bacteria, facilitating the geochemical conversion of native iron minerals into iron sulfides. Iron sulfides have the ability to chemically reduce many common CAH compounds including PCE, TCE, DCE, similar to zero valent iron (Fe0). Results of a field test at Dover Air Force Base, Dover, Delaware, are given in this paper. BiRD was stimulated by direct injection of Epson salt (MgSO4·7H2O) and sodium (L) lactate (NaC3H5O3) in five …


Design And Fabrication Of A Full-Featured Labscale Hybrid Rocket Engine, Kyle Platt Jan 2006

Design And Fabrication Of A Full-Featured Labscale Hybrid Rocket Engine, Kyle Platt

Electronic Theses and Dissertations

The design, development, integration and testing of a full-featured, Lab-Scale Hybrid Rocket Engine was not only envisioned to be the chosen method of putting student payloads into space, but to be an invaluable teaching resource. The subject of the present thesis is the analysis, design, development, integration and demonstration of a lab-scale hybrid rocket motor. The overarching goal of this project was to establish a working developmental lab model from which further research can be accomplished. The lab model was specifically designed to use a fuel source that could be studied in normal laboratory conditions. As such, the rocket engine …


Autonomous Controls Algorithmfor Formation Flying Of Satellites, Luis Santiago Jan 2006

Autonomous Controls Algorithmfor Formation Flying Of Satellites, Luis Santiago

Electronic Theses and Dissertations

This document describes the design and analysis of the Navigation, Guidance and Control System for the KnightSat project. The purpose for the project is to test and demonstrate new technologies the Air Force would be interested in for research and development. The primary mission of KnightSat is to show how a constellation of satellites can maintain relative position with each other autonomously using the Microwave Electro Thermal (MET) thruster. The secondary mission is to use multiple satellite imagery to obtain 3 dimensional stereo photographs of observable terrain. Formation flying itself has many possible uses for future applications. Selected missions that …


A Sustainable, Systematic Process For Continuous Program Improvement, Nikos J. Mourtos Jan 2006

A Sustainable, Systematic Process For Continuous Program Improvement, Nikos J. Mourtos

Faculty Publications

The USA Accreditation Board for Engineering and Technology (ABET) adopted recently a new set of criteria for evaluating engineering programmes. One of these (criterion 3) refers to programme outcomes and assessment. In this article, the author describes the design and implementation of a sustainable, systematic process for defining and assessing programme outcomes. This process involves analysing each outcome into elements, defining a set of attributes for each element, selecting outcome indicators and performance targets, and developing special rubrics for an accurate assessment of student skills. The author also describes a systematic way of addressing specific programme outcomes through course and …


Response To "Comment On Variational Approach To The Volume Viscosity Of Fluids" [Phys. Fluids 18, 109101 (2006)], Allen J. Zuckerwar, Robert L. Ash Jan 2006

Response To "Comment On Variational Approach To The Volume Viscosity Of Fluids" [Phys. Fluids 18, 109101 (2006)], Allen J. Zuckerwar, Robert L. Ash

Mechanical & Aerospace Engineering Faculty Publications

We respond to the Comment of Markus Scholle and therewith revise our material entropy constraint to account for the production of entropy. (c) 2006 American Institute of Physics.


Galileo Probe, Monish Ranjan Chatterjee Jan 2006

Galileo Probe, Monish Ranjan Chatterjee

Electrical and Computer Engineering Faculty Publications

The Galileo mission to Jupiter was formally approved by the United States Congress in 1977, several years before the space shuttle Columbia made its maiden flight into Earth orbit. The mission was a cooperative project involving scientists and engineers from the United States, Germany, Canada, Great Britain, France, Sweden, Spain, and Australia. Even though the Voyager 1 and Voyager 2 spacecraft had performed flybys of planet Jupiter and its sixteen moons in 1979, the Galileo mission was envisioned to initiate several novel observations of Jupiter, the most massive gas planet of the solar system, and its principal moons, and conduct …


Perchlorate Toxicity And Risk Assessment, David R. Mattie, Joan Strawson, Jay Zhao Jan 2006

Perchlorate Toxicity And Risk Assessment, David R. Mattie, Joan Strawson, Jay Zhao

United States Air Force: Publications

Ammonium perchlorate is the oxidizer ingredient in solid propellant mixtures for rockets, missiles and munitions such as Titan, Minuteman, Peacekeeper, Hawk, Polaris and the Space Shuttle. Perchlorate salts may also be used in medicine, matches, munitions and pyrotechnics (illuminating and signaling flares, colored and white smoke generators, tracers, incendiary delays, fuses, photo-flash compounds and fireworks). Perchlorate is also found in lubricating oils, finished leather, fabric fixer, dyes, electroplating, aluminum refining, manufacture of rubber, paint and enamel production, as an additive in cattle feed, in magnesium batteries and as a component of automobile air bag inflators.'


United States Air Force Posture Statement 2006, U.S. Air Force Jan 2006

United States Air Force Posture Statement 2006, U.S. Air Force

United States Air Force: Publications

Over a century ago, America crossed the threshold of powered flight and gave wings to the world. Soon military leaders realized the implications of this development, and warfare was changed forever. America was fortunate to have "Great Captains" with the vision to imagine the possibilities of air and space power - Airmen like Billy Mitchell, Frank Andrews, Hap Arnold, Ira Eaker, Jimmy Doolittle, Bennie Schriever. They have given us a proud heritage of courage, excellence and innovation. In so doing, they also give us a sense of perspective and a way to understand the Air Force's future.


Atomic Force Microscope Tip Spontaneous Retraction From Dielectric Surfaces Under Applied Electrostatic Potential, S. F. Lyuksyutov, P. B. Paramonov, O. V. Mayevska, M. A. Reagan, E. Sancaktar, R. A. Vaia, S. Juhl Jan 2006

Atomic Force Microscope Tip Spontaneous Retraction From Dielectric Surfaces Under Applied Electrostatic Potential, S. F. Lyuksyutov, P. B. Paramonov, O. V. Mayevska, M. A. Reagan, E. Sancaktar, R. A. Vaia, S. Juhl

United States Air Force: Publications

A time-resolved method for tip’ retraction at µs-scale away from dielectric surfaces has been developed. Analysis of the forces in the system comprising AFM tip, water meniscus, and polymer film suggests that an electrostatic repulsion of the tip from the surface in the double-layered (water and polymer) system, and water condensation in the tip–surface junction are the dominant factors enabling the mechanical work for tip retraction. Nanostructures of 5–80nm height are formed in polymeric surfaces as a result. This interesting physical phenomenon could be used for nanostructures patterning in polymeric materials at enhanced aspect ratio.


Force Protection Using Composite Sandwich Structures, R. L. Sierakowski, M. L. Hughes Jan 2006

Force Protection Using Composite Sandwich Structures, R. L. Sierakowski, M. L. Hughes

United States Air Force: Publications

In the recent past, advances have been made in the attempt to utilize composite materials as components in protective structures such as those employed by the Air Force to secure critical military assets. In such applications, where lightweight materials that exhibit large levels of energy absorption and high strength/stiffness characteristics are desirable, composite sandwich constructions offer an attractive solution.

In an attempt to evaluate the suitability of certain sandwich structures for use in force protection applications, several sandwich constructions with somewhat novel core materials were identified. A group of thermoplastic core materials have been developed that possess features of both …


Atomic Force Microscopy Of Bacillus Spore Surface Morphology, Ruth A. Zolock, Guangming Li, Charles Bleckmann, Larry Burggraf, Douglas C. Fuller Jan 2006

Atomic Force Microscopy Of Bacillus Spore Surface Morphology, Ruth A. Zolock, Guangming Li, Charles Bleckmann, Larry Burggraf, Douglas C. Fuller

United States Air Force: Publications

Bacillus spore surface morphology was imaged with atomic force microscopy (AFM) to determine if characteristic surface features could be used to distinguish between four closely related species; Bacillus anthracis Sterne strain, Bacillus thuringiensis var. kurstaki, Bacillus cereus strain 569, and Bacillus globigii var. niger. AFM surface height images showed an irregular topography across the curved upper surface of the spores. Phase images showed a superficial grain structure with different levels of phase contrast and significant differences in average surface morphologies among the four species. Although spores of the same species showed similarities, there was significant variability within each …


Effect Of Operator Control Configuration On Unmanned Aerial System Trainability, John Neumann Jan 2006

Effect Of Operator Control Configuration On Unmanned Aerial System Trainability, John Neumann

Electronic Theses and Dissertations

Unmanned aerial systems (UAS) carry no pilot on board, yet they still require live operators to handle critical functions such as mission planning and execution. Humans also interpret the sensor information provided by these platforms. This applies to all classes of unmanned aerial vehicles (UAV's), including the smaller portable systems used for gathering real-time reconnaissance during military operations in urban terrain. The need to quickly and reliably train soldiers to control small UAS operations demands that the human-system interface be intuitive and easy to master. In this study, participants completed a series of tests of spatial ability and were then …


Reduction Of Vortex-Driven Oscillations In A Solid Rocket Motor Cold Flow Simulation Through Active Control, Jami Ward Jan 2006

Reduction Of Vortex-Driven Oscillations In A Solid Rocket Motor Cold Flow Simulation Through Active Control, Jami Ward

Electronic Theses and Dissertations

Control of vortex-driven instabilities was demonstrated via a scaled-down, cold-flow simulation that modeled closed-end acoustics. When vortex shedding frequencies couple with the natural acoustic modes of a choked chamber, potentially damaging low-frequency instabilities may arise. Although passive solutions can be effective, an active control solution is preferable. An experiment was performed to demonstrate an active control scheme for the reduction of vortex-driven oscillations. A non-reacting experiment using a primary flow of air, where both the duct exit and inlet are choked, simulated the closed-end acoustics. Two plates, separated by 1.27 cm, produced the vortex shedding phenomenon at the chamber's first …