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Aerospace Engineering

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Articles 9061 - 9090 of 11121

Full-Text Articles in Engineering

Optimal Spacecraft Attitude Control Using Aerodynamic Torques, Michael L. Gargasz Mar 2007

Optimal Spacecraft Attitude Control Using Aerodynamic Torques, Michael L. Gargasz

Theses and Dissertations

This thesis introduces a method of three-axis spacecraft attitude control using only aerodynamic torques. Attitude actuation is achieved using four control panels mounted on the rear of a cubical spacecraft bus. The controller consists of an outer loop using linear state feedback to determine desired control torque and an inner loop to choose appropriate control panel angles. The inner loop uses a Jacobian-based approach to invert the nonlinear relationship between panel angles and generated torque. Controller performance is evaluated via simulations, which show that three-axis control is possible over a range of initial angles and angular rates. The analysis used …

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Optimal Sensor Threshold Control And The Weapon Operating Characteristic For Autonomous Search And Attack Munitions, Roland A. Rosario Mar 2007

Optimal Sensor Threshold Control And The Weapon Operating Characteristic For Autonomous Search And Attack Munitions, Roland A. Rosario

Theses and Dissertations

This Thesis considers the optimal employment of a wide area search munition in a battlespace where a target is known to be uniformly distributed among false targets which are Poisson distributed. The Poisson distribution's parameter is obtained from readily available battlespace intelligence. This work formulates and solves the optimal control problem for deriving the optimal sensor threshold schedule in order to maximize the probability of attacking the target during the battlespace sweep while constraining the probability of attacking a false target. The efficiency gained by optimally varying the sensor threshold is compared against the performance achieved with a static, optimum …

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Toward A Flying Mems Robot, Nathan E. Glauvitz Mar 2007

Toward A Flying Mems Robot, Nathan E. Glauvitz

Theses and Dissertations

The work in this thesis includes the design, modeling, and testing of motors and rotor blades to be used on a millimeter-scale helicopter style flying micro air vehicle (MAV). Three different types of motor designs were developed and tested, which included circular scratch drives, electrostatic motors, and comb drive resonators. Six different rotor designs were tested; five used residual stress while one design used photoresist to act as a hinge to achieve rotor blade deflection. Two key parameters of performance were used to evaluate the motor and rotor blade designs: the frequency of motor rotation and the angle of deflection …

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Use Of Two-Way Time Transfer Measurements To Improve Geostationary Satellite Navigation, Benjamin G. Dainty Mar 2007

Use Of Two-Way Time Transfer Measurements To Improve Geostationary Satellite Navigation, Benjamin G. Dainty

Theses and Dissertations

An emerging use of GPS is to provide accurate navigation information for satellites in orbit. The GPS satellites are designed to provide service to terrestrial users, so the antenna array points directly towards the Earth and uses a narrow primary beamwidth. Because GEO altitudes are well above the GPS constellation, the Earth occludes most of the GPS signals to the satellite. Decreased satellite visibility is debilitating, as GPS navigation requires at least four visible satellites to determine position. To assist with the visibility problem, the receiver can look at the GPS satellite transmit antenna side lobes, but this does not …

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Multifrequency Eddy Current Inspection Of Corrosion In Clad Aluminum Riveted Lap Joints And Its Effect On Fatigue Life, Shridhar Natarajan, Anthony Chukwujekwu Okafor Mar 2007

Multifrequency Eddy Current Inspection Of Corrosion In Clad Aluminum Riveted Lap Joints And Its Effect On Fatigue Life, Shridhar Natarajan, Anthony Chukwujekwu Okafor

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Aging aircraft are prone to corrosion damage and fatigue cracks in riveted lap joints of fuselage skin panels. This can cause catastrophic failure if not detected and repaired. Hence detection of corrosion damage and monitoring its effect on structural integrity are essential. This paper presents multifrequency eddy current (EC) inspection of corrosion damage and machined material loss defect in clad A1 2024-T3 riveted lap joints and its effect on fatigue life. Results of eddy current inspection, corrosion product removal and fatigue testing are presented.

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Exploring Effective Methods For Simulating Damaged Structures With Geometric Variation: Toward Intelligent Failure Detection, Daniel A. Mcadams, David Comella, Irem Y. Tumer Mar 2007

Exploring Effective Methods For Simulating Damaged Structures With Geometric Variation: Toward Intelligent Failure Detection, Daniel A. Mcadams, David Comella, Irem Y. Tumer

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Inaccuracies in the modeling assumptions about the distributional characteristics of the monitored signatures have been shown to cause frequent false positives in vehicle monitoring systems for high-risk aerospace applications. to enable the development of robust fault detection methods, this work explores the deterministic as well as variational characteristics of failure signatures. Specifically, we explore the combined impact of crack damage and manufacturing variation on the vibrational characteristics of beams. the transverse vibration and associated eigenfrequencies of the beams are considered. Two different approaches are used to model beam vibrations with and without crack damage. the first approach uses a finite …

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Quantifying Non-Equilibrium In Hypersonic Flows Using Entropy Generation, Ryan W. Carr Mar 2007

Quantifying Non-Equilibrium In Hypersonic Flows Using Entropy Generation, Ryan W. Carr

Theses and Dissertations

The constitutive relations traditionally used for finding shear stress and heat flux in a fluid become invalid in non-equilibrium flow. Their derivation from kinetic theory only demonstrates they are valid only for small deviations from equilibrium. Because it is fundamentally linked to non-equilibrium, entropy generation is used to investigate the limits of the continuum constitutive relations. However, the continuum equations are inherently limited to near equilibrium conditions due to the constitutive relations; thus kinetic theory must be used as a basis for comparison. Direct Simulation Monte Carlo (DSMC), a particle method alternative to continuum methods, is based on kinetic theory …

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Experimental Characterization Of Turbulent Flow Around Cylinder Arrays, Adam D. Harder Mar 2007

Experimental Characterization Of Turbulent Flow Around Cylinder Arrays, Adam D. Harder

Theses and Dissertations

This research was done as part of an effort to develop alternative fire suppressant technologies for aircraft engine nacelles. A circular cylinder array was designed, built, and placed in the AFIT roll-around low speed wind tunnel to model generic clutter inside an engine nacelle. A turbulence grid was fabricated to enable measurements of the effects of turbulence level, independent of airspeed, on the flow over different model configurations. The wind tunnel test section was 12 inches wide x 12 inches high x 24 inches long. Pressure differential measurements were taken on various cylinder configurations. The configurations included one cylinder as …

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Simulation Of The Dynamically Coupled Kc-135 Tanker And Refueling Boom, Jeremy J. Smith Mar 2007

Simulation Of The Dynamically Coupled Kc-135 Tanker And Refueling Boom, Jeremy J. Smith

Theses and Dissertations

Future Air Force requirements for the use of unmanned aircraft will require Automated Aerial Refueling (AAR). Current AAR research requires a precision model to simulate the refueling process of a KC-135 tanker and a UAV. There are existing high fidelity models of the tanker aircraft, refueling boom and proposed receiver aircraft. However, none of the models are coupled. Since boom orientation and motion is known to change the trim of the tanker aircraft, which in turn influences all other aspects of the refueling process, a new model is needed. The new model was created by integrating an existing KC-135 tanker …

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The Aerodynamic Performance Of The 24 Inch Houck Configuration, Michael M. Walker Mar 2007

The Aerodynamic Performance Of The 24 Inch Houck Configuration, Michael M. Walker

Theses and Dissertations

Fuel efficiency of aircraft is of great importance to the military and private sector. A more efficient wing design for UAVs would lead to improvements in mission support while reducing fuel costs for the Air Force. An experimental investigation of one candidate design, the Houck Aircraft Configuration, has been conducted in the AFIT low speed wind tunnel. This aircraft shares similarities to other joined-wing aircraft, but includes curved flow-guides of varying spanwise camber connecting the upper and lower wingtips. Experimental results that the addition of flow guides on the 24" Houck Configuration results in a 2.5% reduction in L/D(sub max) …

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Characterization Of A Hall Effect Thruster Using Thermal Imaging, James W. Tomaszewski Mar 2007

Characterization Of A Hall Effect Thruster Using Thermal Imaging, James W. Tomaszewski

Theses and Dissertations

A Hall thruster uses ionized xenon as a propellant for space propulsion applications. The heat produced by thruster components and the xenon plasma transfers to space and the spacecraft, impacting thruster and spacecraft design, as well as thruster efficiency and lifetime. Therefore, thermal information was gathered and analyzed in order to better understand the thermal characteristics of an operating thruster and to provide data applicable to improving the thruster efficiency and lifetime. This paper contains analysis of thruster temperatures obtained using a commercially available FLIR A40M thermographic imager in order to characterize a Busek Inc. 200W Hall Effect Thruster operating …

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Investigating Hastily-Formed Collaborative Networks, Joshua S. Campbell, Stanley L. Cooley, Matthew F. Durkin, Brian K. Maddocks Mar 2007

Investigating Hastily-Formed Collaborative Networks, Joshua S. Campbell, Stanley L. Cooley, Matthew F. Durkin, Brian K. Maddocks

Theses and Dissertations

This research explores both the human and technical aspects of the network centric environment in the context of a major disaster or incident of national significance. The National Incident Management System (NIMS) is viewed by the authors as a social network, and an organizational topology is developed to improve its effectiveness. A rapid Network Deployment Kit (RNDK) using commercial off the shelf (COTS) wireless networking technology is also proposed that facilitates immediate NIMS implementation. The integration of logical and technical analyses forms a comprehensive systems engineering proposal to facilitate collaboration in a net-centric environment. It is envisioned that the methodology …

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Experimental Methods To Characterize Nonlinear Vibration Of Flapping Wing Micro Air Vehicles, Adam P. Tobias Mar 2007

Experimental Methods To Characterize Nonlinear Vibration Of Flapping Wing Micro Air Vehicles, Adam P. Tobias

Theses and Dissertations

For urban combat reconnaissance, the flapping wing micro air vehicle concept is ideal because of its low speed and miniature size, which are both conducive to indoor operations. The focus of this research is the development of experimental methods best suited for the vibration testing of the wing structure of a flapping wing micro air vehicle. This study utilizes the similarity of a beam resonating at its first bending mode to actual wing flapping motion. While computational finite element analysis based on linear vibration theory is employed for preliminary beam sizing, an emphasis is placed on experimental measurement of the …

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Experimental Investigation Of Oblique Wing Aerodynamics At Low Speed, Matthew J. Dillsaver Mar 2007

Experimental Investigation Of Oblique Wing Aerodynamics At Low Speed, Matthew J. Dillsaver

Theses and Dissertations

In an effort to increase the range of missiles and guided bombs, the USAF is looking at options for new wing configurations. One such configuration being considered is oblique wings. An oblique wing is a wing that pivots about a point on the aircraft fuselage thereby having one side swept forward and the other swept aft. Additional interest is looking at a wing only configuration that also rotates with one wing tip forward of the other. Studies have shown that this configuration can provide less drag for a given lift at both supersonic cruise and subsonic loiter conditions. This experiment …

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Demonstration Of Clean Particle Seeding For Particle Image Velocimetry In A Closed Circuit Supersonic Wind Tunnel, Charles M. Mcniel Mar 2007

Demonstration Of Clean Particle Seeding For Particle Image Velocimetry In A Closed Circuit Supersonic Wind Tunnel, Charles M. Mcniel

Theses and Dissertations

The purpose of this research was to determine whether solid carbon dioxide (CO2) particles might provide a satisfactory, and cleaner, alternative to traditional seed material for Particle Image Velocimetry (PIV) for use in a closed circuit supersonic wind tunnel. The Air Force Institute of Technology (AFIT) closed circuit pressure-vacuum supersonic wind tunnel was utilized, which achieves a nominal Mach number of Mach 2.9 in a 2.5 inch by 2.5 inch square test section. CO2 was dispensed into the flow as a liquid from a standard compressed gas liquid tank through two different injector styles at two injection …

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Finite Element Solution: Nonlinear Flapping Beams For Use With Micro Air Vehicle Design, Robert L. Walker Mar 2007

Finite Element Solution: Nonlinear Flapping Beams For Use With Micro Air Vehicle Design, Robert L. Walker

Theses and Dissertations

The development and use of Micro Air Vehicles is becoming more and more important to the military. Size, weight, maneuverability, stealth, and fuel consumption are just some of the constraints on a future Micro Air Vehicle. Perfect blueprints for a small scale flying machine are both insects and humming birds. Medium sized hummingbirds are found to have wings-beats at a frequency of 18-28 Hz. There is a vast amount of complexity to just how these creatures can create lift; however, this study looks at different beams made of common materials with 1st natural bending frequencies in this range. This study …

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Three Dimensional Analysis Of A Composite Repair And The Effect Of Overply Shape Variation On Structural Efficiency, David A. Sutter Mar 2007

Three Dimensional Analysis Of A Composite Repair And The Effect Of Overply Shape Variation On Structural Efficiency, David A. Sutter

Theses and Dissertations

This research characterizes, in the elastic range, a scarf joint with overply using digital image correlation photogrammetry and finite element modeling. Additionally, the effect of varying the overply's geometric profile is examined. Specimens are constructed from AS4/3501-6 prepreg with a [0±45/90]2S layup. A fixture is used to achieve a consistent scarfed hole in each panel. The patch and adhesive (FM 300) are co-cured to the panels using positive pressure, which minimizes repair porosity. Three variations in the overply geometry are used: circular, rooftop-end, and tooth-end. The full strain field in each uni-axially loaded specimen is captured using digital image …

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Optimal Control Of A Circulare Satellite Formation Subject To Gravitational Perturbations, Jason L. Baldwin Mar 2007

Optimal Control Of A Circulare Satellite Formation Subject To Gravitational Perturbations, Jason L. Baldwin

Theses and Dissertations

Satellite formations, otherwise known in the space community as satellite clusters or distributed satellite systems, have been studied extensively over the last 10 to 15 years. For use in remote sensing applications, formations consisting of smaller, simpler satellites provide numerous advantages over individual satellites. The image resolution capabilities of small-satellite formations constitute a significant technological leap in the ability to synthesize critical information. This research utilizes the nonlinear satellite dynamics, including gravitational perturbations, to search for the optimal fuel cost for maintaining a circular formation. The system dynamics were developed in an earth-centered inertial coordinate frame using the methods of …

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Lamb Wave Propagation In Varying Thermal Environments, Jennifer P. Andrews Mar 2007

Lamb Wave Propagation In Varying Thermal Environments, Jennifer P. Andrews

Theses and Dissertations

During flight, launch, and reentry, external surfaces on aerospace vehicles undergo extreme thermo-acoustic loads resulting in structural degradation. Structural health monitoring techniques are being devised to evaluate the health of these structures by locating and quantifying structural damage during and after flight. One such technique uses Lamb wave propagation to assess damage on the surface and through the thickness of thin materials. The objective of this study was to assess the sensitivity of piezo-generated Lamb wave propagation to isothermal and thermal gradient environments using both theoretical and experimental methods. Experimental isothermal tests were conducted over a temperature range of 0-225 …

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Determining Logistics Ground Support Manpower Requirements For A Reusable Military Launch Vehicle, Sydney C. Michalski Mar 2007

Determining Logistics Ground Support Manpower Requirements For A Reusable Military Launch Vehicle, Sydney C. Michalski

Theses and Dissertations

Successful space-based technologies like satellite imagery and GPS have increased military demand for a rapid-response launch capability. AF Space Command's Operationally Responsive Spacelift program was developed to ensure that the AF has the capability to launch a payload into orbit within hours of a tasking notification, and requires development of a new space launch vehicle. The Reusable Military Launch Vehicle (RMLV) is currently in the design phase. The AF Research Laboratory sponsored development of the MILEPOST simulation model in order to assess the turnaround time, and thus responsiveness, of various design alternatives. The focus of this thesis is to improve …

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Prioritizing Satellite Payload Selection Via Optimization, Benjamin S. Kallemyn Mar 2007

Prioritizing Satellite Payload Selection Via Optimization, Benjamin S. Kallemyn

Theses and Dissertations

This thesis develops optimization models for prioritizing payloads for inclusion on satellite buses with volume, power, weight and budget constraints. The first model considers a single satellite launch for which the budget is uncertain and constellation requirements are not considered. Subsequently, we include constellation requirements and provide a more enhanced model. Both single-launch models provide a prioritized list of payloads to include on the launch before the budget is realized. The single-launch models are subsequently extended to a sequence of multiple launches in two cases, both of which incorporate an explicit dependence on the constellation composition at each launch epoch. …

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Effects Of Prior Aging At Elevated Temperature In Air And In Argon Environments On Creep Response Of Pmr-15 Neat Resin, Joseph L. Broeckert Mar 2007

Effects Of Prior Aging At Elevated Temperature In Air And In Argon Environments On Creep Response Of Pmr-15 Neat Resin, Joseph L. Broeckert

Theses and Dissertations

Creep behavior of PMR-15 neat resin, a polyimide thermoset polymer, aged in air or argon gaseous environments at 288 °C for up to 1000 h was evaluated. Creep tests were performed at 288 C at creep stress levels of 20 and 10 MPa. Creep periods of at least 25 h in duration were followed by recovery at zero stress. Weight loss and growth of the oxidation layer were also monitored and correlated with aging time. The aging time in both air and argon environments had a strong influence on the creep and recovery response of PMR-15 neat resin. Samples aged …

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Black Rock Planet: The Next Two Challenges, Robert J. Twiggs Feb 2007

Black Rock Planet: The Next Two Challenges, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs titled "Black Rock Planet: The Next Two Challenges" from February 22, 2007.

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Soldier/Hardware-In-The-Loop Simulation-Based Combat Vehicle Duty Cycle Measurement: Duty Cycle Experiment 2, Mark Brudnak, Mike Pozolo, Victor Paul, Syed Mohammad, Marc Compere, Et Al. Jan 2007

Soldier/Hardware-In-The-Loop Simulation-Based Combat Vehicle Duty Cycle Measurement: Duty Cycle Experiment 2, Mark Brudnak, Mike Pozolo, Victor Paul, Syed Mohammad, Marc Compere, Et Al.

Publications

This paper describes a human-in-the-loop motion-based simulator interfaced to hybrid-electric power system hardware both of which were used to measure the duty cycle of a combat vehicle in a virtual simulation environment. The project discussed is a greatly expanded follow-on to the experiment published in [1]. This paper is written in the context of [1] and therefore highlights the enhancements. The most prominent of these enhancements is the integration (in real-time) of the Power & Electric System Integration Lab (P&E SIL) with a motion base simulator by means of a “long haul” connection over the Internet (a geographical distance of …

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F- 16xl Unsteady Simulations For The Cawapi Facet Of Rto Task Group Avt- 113, Scott A. Morton, David R. Mcdaniel, Russell M. Cummings Jan 2007

F- 16xl Unsteady Simulations For The Cawapi Facet Of Rto Task Group Avt- 113, Scott A. Morton, David R. Mcdaniel, Russell M. Cummings

Aerospace Engineering

This work represents the USAF Academy portion of a culmination of three years of cooperative research in the Cranked Arrow Wing Aerodynamics International (CAWAPI) RTO Task Group, AVT-113. The objective of the group was to compute high resolution CFD simulations of a subset of the conditions created in the CAWAP flight test program managed by NASA Langley researchers and others. Seven flight conditions were chosen with four of them at symmetric conditions of medium to high angle of attack and subsonic Mach numbers, one symmetric condition at a transonic low angle of attack condition, and two conditions at medium angle …

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Circulation Control And Its Application To Extreme Short Take-Off And Landing Vehicles, Julianna B. De La Montanya, David D. Marshall Jan 2007

Circulation Control And Its Application To Extreme Short Take-Off And Landing Vehicles, Julianna B. De La Montanya, David D. Marshall

Aerospace Engineering

Circulation Control is a high-lift method discovered in 1935 when Henry Coanda accidentally stumbled upon the technology. Research was conducted in the 1970‘s and 1980‘s to develop this technique, but the idea fell out of vogue until recently. Energy is introduced into the flow field by means of a jet ejected tangentially from a slot located near the trailing edge of the airfoil; thus changing the effective chamber of the airfoil and increasing lift. Extreme Short Take-Off and Landing (ESTOL) vehicles can use this technology to alleviate today‘s congested airports by reutilizing the small runways that are currently unexploited due …

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The Role Of Error In The Conceptual Design Of A Transport Aircraft, Robert A. Mcdonald Jan 2007

The Role Of Error In The Conceptual Design Of A Transport Aircraft, Robert A. Mcdonald

Aerospace Engineering

A fidelity trade environment was demonstrated by using it to simulate a decision making process for a transport aircraft. This scenario was not possible without the fidelity trade environment. The role of system feedback and coupling in error stability was also investigated.
A sensitivity approach which relies on the system sensitivity matrix was used to rapidly approximate the propagation of error through the complex system. In verification tests, the sensitivity approach provided approximate results substantially similar to a Monte Carlo approach that was many orders of magnitude more expensive. The rapid sensitivity approach to modeling error propagation enabled the responsive …

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The Happy Accidents Of Teaching Aircraft Design, David W. Hall, Russell M. Cummings Jan 2007

The Happy Accidents Of Teaching Aircraft Design, David W. Hall, Russell M. Cummings

Aerospace Engineering

The aircraft design curriculum at Cal Poly has grown and evolved over the past decades to include a full year of senior aircraft design and an introductory aircraft design course in the sophomore year. The combination of sophomore and senior aircraft design courses has created the circumstance where a “cult” of aircraft design has developed. The curriculum is producing students who are enthusiastic and motivated education, as well as being competent designers after they graduate. A number of “happy accidents” has led to this fortunate situation, including: allowing the sophomores to perform a full aircraft design, having the sophomores work …

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Wing-Nacelle Assembly Multidisciplinary Performance Optimization, Yevgeniy M. Gisin, David D. Marshall Jan 2007

Wing-Nacelle Assembly Multidisciplinary Performance Optimization, Yevgeniy M. Gisin, David D. Marshall

Aerospace Engineering

The paper analyzes the aerodynamics benefits of above-wing mounting of turbofan engines and performs a trade-off study of the structural limitations with this mounting method. This research is based on the US Patent #6,308,913, aiming to quantify the actual benefit derived from the drag reduction measure described in the patent. The paper focuses on the analysis of a turbofan engine, which when installed above an aircraft’s wing creates a flow field optimized to reduce the overall drag experienced by the wing nacelle assembly. This installation is designed to reduce wave drag during transonic cruise and therefore the wing-nacelle geometry was …

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Comparison Of Des And Urans For Unsteady Vortical Flows Over Delta Wings, L. A. Shiavetta, K. J. Badcock, Russell M. Cummings Jan 2007

Comparison Of Des And Urans For Unsteady Vortical Flows Over Delta Wings, L. A. Shiavetta, K. J. Badcock, Russell M. Cummings

Aerospace Engineering

The unsteady behaviour of delta wing vortical flows is still a subject which is a challenge for numerical methods, such as computational fluid dynamics. New approaches to turbulence modelling, such as detached eddy simulation (DES) have been proposed which allow for greater accuracy of the numerical predictions. However, this increase in accuracy comes with a considerable increase in computational expense compared to traditional turbulence modelling. This investigation considers the use of both DES and unsteady Reynolds averaged Navier-Stokes (URANS) turbulence methods in the prediction of unsteady vortical flows. Calculations using DES are initially considered for two test cases and the …

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