Open Access. Powered by Scholars. Published by Universities.®

Engineering Commons™

Open Access. Powered by Scholars. Published by Universities.®

Aerospace Engineering

Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 10321 - 10350 of 11115

Full-Text Articles in Engineering

Experimental Investigation Of A Supersonic Boundary Layer Including Favorable Pressure Gradient Effects, Joel J. Luker Dec 1995

Experimental Investigation Of A Supersonic Boundary Layer Including Favorable Pressure Gradient Effects, Joel J. Luker

Theses and Dissertations

This study used advanced laser Doppler velocimetry techniques to measure the turbulence intensities and Reynolds shear stresses in Mach 2.8 turbulent flat plate and Mach 2.9 favorable pressure gradient (FPG) boundary layers. The FPG was generated using a convex curved wall and had a strength of ß = 0.1, where ß is Clauser's equilibrium parameter. The maximum magnitude of the 'extra' strain rates normalized by the main strain rates was 0.1, which meant the FPG was considered to be a strong pressure gradient. The fiat plate results indicated that the LDV procedures used in this experiment prevented angular biasing of …

Go to article

Influence Of A Moving Endwall On The Tip Clearance Vortex In An Axial Compressor Cascade, Lawrence J. Peter Dec 1995

Influence Of A Moving Endwall On The Tip Clearance Vortex In An Axial Compressor Cascade, Lawrence J. Peter

Theses and Dissertations

This experiment involved the design, construction, validation and testing of a new facility for the investigation of vortices generated by compressor rotor blade tip clearance with a moving endwall. A five-tube pressure rake placed downstream of the trailing edge of a cascade of blades measured the pressure field for flow coefficients ranging from 20 to 1.66 and tip clearances of 0.33, 1.0, 1.7 and 2.4 percent chord. Contour plots of mass averaged pressure loss coefficient appear to show the no-flow tip vortex becomes entrained and diffused by the moving wall boundary layer. The high loss region near the moving wall …

Go to article

Prediction Of An Axial Compressor Stage Characteristic From A One-Point Measurement, Shahnaz M. Punjani Dec 1995

Prediction Of An Axial Compressor Stage Characteristic From A One-Point Measurement, Shahnaz M. Punjani

Theses and Dissertations

This study focuses on predicting axial compressor stage characteristics using a single performance point comprised of mass flow, temperature and pressure rise coefficients obtained in experimental testing and a generic stage temperature characteristic. A new temperature characteristic is generated using a mapping technique where changes in stage blade angles are iterated from assumptions of free vortex flow and constant increment of flow turning angle with increased flow incidence. If additional data corresponding to the new curve are available, the characteristic is adjusted using non-linear least squares estimation, Essentially, the modified mapped curve results from a re-estimated change in the stator …

Go to article

Frequency Effects On Fatigue Behavior Of A Unidirectional Metal Matrix Composite At Elevated Temperature, Robert N. Pittman Dec 1995

Frequency Effects On Fatigue Behavior Of A Unidirectional Metal Matrix Composite At Elevated Temperature, Robert N. Pittman

Theses and Dissertations

The fatigue response and life of a unidirectional SCS-6/Ti-6-4 metal-matrix composite were examined under tension-tension, load-controlled conditions at elevated temperatures and different frequencies. Composite specimens were fatigued at frequencies of 0.01, 0.1, 1 and 10 Hz, and at three stress levels. Plots of cycles to failure versus maximum stress and test frequency showed that fatigue life was more cycle-dependent at higher frequencies and more time-dependent at lower frequencies. Comparisons of tests at 427°C with their counterparts at 370°C and 538°C showed that these frequency effects were magnified as temperature increased: lower frequency tests at 538°C exhibited greater time-dependence than tests …

Go to article

Vehicle Thermal Control With A Variable Area Inlet, Thomas R. Layne Dec 1995

Vehicle Thermal Control With A Variable Area Inlet, Thomas R. Layne

Theses and Dissertations

This study developed a variable area inlet and controller that regulated the temperature of an electrical component with ram air. The intent of the variable area inlet was to reduce vehicle drag by eliminating inefficiencies associated with component cooling and fixed area inlets. These inefficiencies arise from vehicles moving at varying speeds through varying air temperatures. The hardware model consisted of an electrical component mounted inside a right-circular cylindrical duct. The variable area inlet, mounted in the front of the duct, consisted of a butterfly valve that was actuated by a stepper controller acted on the feedback signal of a …

Go to article

Investigation Of Aerodynamic Alterations For Improving The Kc-135 Boom Performance During Aerial Refueling, Debra A. Nawrocki Dec 1995

Investigation Of Aerodynamic Alterations For Improving The Kc-135 Boom Performance During Aerial Refueling, Debra A. Nawrocki

Theses and Dissertations

This study investigated the eligibility of the KC-135 air refueling boom for improved capabilities in the areas of control and performance. By using a thick airfoil cross-section for the boom tube, rather than the current circular cross-section, the ability to increase the lift characteristics was verified Prior compiled test data was used for comparison against analytical computer solutions. The possibility and effects of control frequency oscillations were also examined due to the unstable nature of the flow at test conditions. Additionally, the effect of other cross-section shapes, such as the blunt fairing, on the size of the flyable envelope for …

Go to article

Effects Of Base Cavity Depth On A Free Spinning Wrap-Around Fin Missile Configuration, Jon A. Struck Dec 1995

Effects Of Base Cavity Depth On A Free Spinning Wrap-Around Fin Missile Configuration, Jon A. Struck

Theses and Dissertations

This study investigated the role base cavity depth plays in altering the overall subsonic aerodynamic forces on a free spinning axisymmetric body with wrap around fins. Wind tunnel usage allowed the forces to be monitored for varying base cavity depths and angles of attack. A base cavity depth analysis was also performed on a non-spinning axisymmetric body for comparison. Oil visualizations were conducted on the non-spinning configuration to further describe airflow patterns around the body and within the cavity. Results revealed that the aerodynamic forces, mostly drag, changed with increasing cavity depth but not to the extent previously believed. The …

Go to article

Numerical Study Of A Transpiration Cooled Rocket Nozzle, Jay A. Landis Dec 1995

Numerical Study Of A Transpiration Cooled Rocket Nozzle, Jay A. Landis

Theses and Dissertations

This study proved that transpiration cooling provides a better cooling scheme than regenerative cooling for long operating duration, liquid-fueled rocket engine nozzles. This proof was made on the basis of maximum wall temperature. This study compared transpiration cooling to regenerative cooling in the throat region of the Space Shuttle Main Engine Main Combustion Chamber. The study also analyzed the effects of porosity, solid thermal conductivity, and porous sphere size on a porous wall made of packed spheres. The transpiration cooled nozzle operated 35% cooler than a regeneratively cooled nozzle, but the temperature gradient at the hot gas surface was 72 …

Go to article

Full Lyapunov Exponent Placement In Reentry Trajectories, Michael H. Platt Dec 1995

Full Lyapunov Exponent Placement In Reentry Trajectories, Michael H. Platt

Theses and Dissertations

This study investigated the ability to control the chaotic reentry of a Delta-Clipper like vehicle by setting the values of initial arid final principal dynamical directions as well as the Lyapunov exponents. A model of the original controlled reentry vehicle was created through the use of the equations of motion in conjunction with an atmospheric model. A modified linear quadratic regulator allowed the set up of a boundary value problem which specified the Lyapunov exponents and determined the gain matrix as a function of time. The gain matrix can eventually be used in the control system of the vehicle.

Go to article

Experimental Investigation Of Non-Adiabatic Supersonic Slot Injection Into A Supersonic Cross-Flow, Kelly C. Tucker Dec 1995

Experimental Investigation Of Non-Adiabatic Supersonic Slot Injection Into A Supersonic Cross-Flow, Kelly C. Tucker

Theses and Dissertations

Turbulence and mean flow measurements were acquired downstream of a normal, supersonic (M=1.6), two-dimensional, slot injection into Mach 3.0 flow (Re/m = 15x106). Two non-adiabatic cases Ti/T∞ = 1.11 and Ti/T∞ = 0.93) were studied. Multiple overheat anemometry and conventional mean flow analysis, as well as shadowgraph and schlieren photography, were utilized to study the turbulent mixing layer. The mean flow data included the Pitot, cone-static, and Mach number profiles. The measured turbulence data included shear stresses, mass flux, total temperature turbulence intensities, and turbulent heat fluxes. The temperature and density variation …

Go to article

Applications Of Nonlinear Control Using The State-Dependent Riccati Equation, David K. Parrish Dec 1995

Applications Of Nonlinear Control Using The State-Dependent Riccati Equation, David K. Parrish

Theses and Dissertations

This thesis examines the relatively new theory of nonlinear control using state dependent coefficient factorizations to mimic linear state space systems. The control theory is a nonlinear quadratic approach, analogous to linear quadratic regulation. All implementations examined in this thesis are done strictly numerically. This thesis is meant to provide a proof of concept for both satellite control and for an artificial pancreas to regulate blood glucose levels in diabetics by automatic insulin injection. These simulations represent only a first step towards practical use of the NQR method, and do not address noise rejection or robustness issues.

Go to article

Design Of Flight Control Laws For Aircraft With Flexible Wings Using Quantitative Feedback Theory, Christina L. Osmon Dec 1995

Design Of Flight Control Laws For Aircraft With Flexible Wings Using Quantitative Feedback Theory, Christina L. Osmon

Theses and Dissertations

Aircraft composed of lightweight composite materials are extremely enticing since their structural weight is greatly reduced. However, the control of these aircraft is complicated by the resultant flexibility of the wings. Two avenues of approach are possible; stiffen the wings thus losing some of the weight reduction benefits, or design the lateral/directional flight control system cognizant of the wing's flexibility. In this thesis the second approach is taken. The design of three lateral/directional flight control systems for the sub-sonic flight envelope of the F-18 is presented. The Quantitative Feedback Theory (QFT) robust control design technique is used. These designs incorporate …

Go to article

Multiple Model Adaptive Control Of The Vista F-16, Michael J. Stepaniak Dec 1995

Multiple Model Adaptive Control Of The Vista F-16, Michael J. Stepaniak

Theses and Dissertations

Multiple model adaptive control (MMAC) is investigated using the high-fidelity, nonlinear, six-degree-of-freedom Simulation Rapid-Prototyping Facility VISTA F-16. Detection of single actuator and sensor failures is considered, with an MMAC algorithm initially pursued which allows a controller specifically designed for each particular failure condition to replace the standard F-16 Block 40 flight control system (FCS) once the failure is detected. The synthesis of certain discrete-time LQG/PI controllers (those using control variables linearly dependent on state derivatives) is shown to be unattainable due to numerical difficulties. A novel control technique, termed control redistribution, is introduced which redistributes control commands (that would normally …

Go to article

Design And Analysis Of A Navigation System Using The Federated Filter, Stephen J. Delory Dec 1995

Design And Analysis Of A Navigation System Using The Federated Filter, Stephen J. Delory

Theses and Dissertations

The purpose of this paper was to design and analyse a federated filter design, to be used for retrofit of an Embedded GPS/INS (EGI) navigation unit into an existing Kalman filter-based air navigation system. A design was selected and simulations were conducted in the Distributed Kalman Filter Simulation software (DKFSIM). As well, a centralized Kalman filter design was simulated under identical conditions for comparison purposes. The federated filter was shown to be a feasible design, with accuracy in position and velocity very close to centralized Kalman filter values. The federated filter design also showed some attractive fault detection and isolation …

Go to article

Dynamic Pulse Buckling Of Columns With Viscous Damping, Murli Kadandale Dec 1995

Dynamic Pulse Buckling Of Columns With Viscous Damping, Murli Kadandale

Masters Theses

This is a study of dynamic pulse buckling of columns with viscous damping. The differential equations of motion were obtained using the Bemoulli-Navier hypothesis. The effects of axial and rotary inertia were included in the analysis. The Voigt-Kelvin model for a viscoelastic material is used. The Finite Difference Method was employed to solve the differential equations of motion. First columns without geometrical imperfections were studied, and a correlation between the damping modulus and the more familiar damping ratio was obtained. Then beams with initial geometrical imperfection were studied. A suitable dynamic buckling criterion was defined. It was observed that viscous …

Go to article

A Systems Engineering Approach To Aircraft Kinetic Kill Countermeasures Technology: Development Of An Active Aircraft Defense System For The C/Kc-135 Aircraft, Mark C. Cherry, Bruce R. Dewitt, Christopher G. Dusseault, Joel J. Hagan, Brian S. Peterson Dec 1995

A Systems Engineering Approach To Aircraft Kinetic Kill Countermeasures Technology: Development Of An Active Aircraft Defense System For The C/Kc-135 Aircraft, Mark C. Cherry, Bruce R. Dewitt, Christopher G. Dusseault, Joel J. Hagan, Brian S. Peterson

Theses and Dissertations

Modern Surface to Air Missiles (SAMs) present a significant threat to today's military and civilian aircraft. Current countermeasure systems such as flares and chaff rely on decoying the missile threat and do not provide adequate protection against advanced computerized missiles (Schaffer, 1993:1). An aircraft defense system that actively seeks out and defeats an incoming missile by placing a physical barrier in the missile's path offers a promising alternative to current countermeasures technology. This thesis reports the preliminary design of an active aircraft defense system for the protection of the C/KC-135 aircraft from SAMs. The developed system utilizes a kinetic kill …

Go to article

Systems Analysis Of Gps Electrical Power System Redesign, Kevin J. Walker Dec 1995

Systems Analysis Of Gps Electrical Power System Redesign, Kevin J. Walker

Theses and Dissertations

A systematic analysis is applied to the electrical power subsystem of the Global Positioning Satellite (GPS) system. Results determined the most appropriate power source and conversion system Options. Photovoltaic solar arrays, the current power system, were not included in the analysis. The best electrical power subsystem options found in the analysis include a solar power source with either a dynamic or direct conversion technique, and a direct conversion nuclear source. The two solar options are designed, at a low level of detail, to provide the same level of power the current GPS photovoltaic solar array system provides. These two designs …

Go to article

Numerical Simulation Of Supersonic Turbulent Boundary Layer Flow Under The Influence Of Mild Pressure Gradients, Eric T. Fick Dec 1995

Numerical Simulation Of Supersonic Turbulent Boundary Layer Flow Under The Influence Of Mild Pressure Gradients, Eric T. Fick

Theses and Dissertations

Mach 2.9 boundary layer flow (Re/m ≈ 1.75x107) under the influence of mild pressure gradients is studied numerically. Baldwin-Lomax and k - ω turbulence models are incorporated into a cell centered finite volume flow solver and the results are compared with hot wire anemometry and Laser Doppler Velocimetry (LDV) measurements obtained for the same geometries in the AFIT Mach 2.9 wind tunnel. Agreement between the present simulations obtained with the k - ω turbulence model and experimental velocity profiles is excellent in all test sections. Nondimensional turbulent shear stress predictions closely match experimental data in the …

Go to article

Validation Of The Articulated Total Body Model Data Set Describing The Large Advanced Dynamic Anthropomorphic Manikin, Joel J. Hagan Dec 1995

Validation Of The Articulated Total Body Model Data Set Describing The Large Advanced Dynamic Anthropomorphic Manikin, Joel J. Hagan

Theses and Dissertations

Recent cut-backs in Department of Defense spending have presented a need to augment full-scale ejection seat testing with computer simulation. To this end, the U.S. Air Force's Armstrong Laboratory has developed a data set describing the Advanced Dynamic Anthropomorphic Manikin (ADAM) for use in conjunction with the Articulated Total Body (ATB) model for the purpose of simulating the dynamics of the ADAM during sled track ejections. The purpose of this thesis is to validate the ADAM data set by graphically comparing ADAM joint angular displacements calculated by the ATB model with those measured during ejection seat sled track tests. The …

Go to article

Experimental Investigation Of A Supersonic Turbulent Boundary Layer With Adverse Pressure Gradient, Chad S. Hale Dec 1995

Experimental Investigation Of A Supersonic Turbulent Boundary Layer With Adverse Pressure Gradient, Chad S. Hale

Theses and Dissertations

Laser Doppler Velocimetry (LDV) measurements were made to quantify the effect of adverse pressure gradient on the compressible turbulent flow structure in a Mach 2.9 boundary layer (Re/m= 1.75 x 107). Measurements included profiles of 2-D mean velocities, turbulence intensities, Reynolds shear stresses, intermittency, flatness and skewness. In addition, mean strain rates were also measured. The boundary layer measurements were acquired for both flat plate and compression ramp models. LDV measurements were made at two locations on the compression ramp model at 68 cm and 71 cm downstream of the nozzle throat. At these locations, Β …

Go to article

Mach 2.9 Investigation Into The Flow Structure In The Vicinity Of A Wrap-Around Fin, Richard E. Huffman Jr. Dec 1995

Mach 2.9 Investigation Into The Flow Structure In The Vicinity Of A Wrap-Around Fin, Richard E. Huffman Jr.

Theses and Dissertations

A ceiling-mounted semi-cylindrical model containing a single wrap-around fin (WAF) was tested in the AFIT Mach 2.9 test facility. Flow visualization using oil- low streaklines, schlieren images and shadowgraph photography revealed a A-shock at the fin-body juncture and the development of an asymmetric bow-shock about the fin. Quantitative measurements were taken with a 100 cone-static pressure probe, a Pitot pressure probe and two cross-wire hot-film probes (u-v and u-w components, respectively). Measurements were made at cutting-planes from the inlet of the test section to aft of the model, with emphasis placed in the vicinity of the WAF. Results include cutting-plane …

Go to article

Methodology For Implementing Fracture Mechanics In Global Structural Design Of Aircraft, Clifton D. Nees Dec 1995

Methodology For Implementing Fracture Mechanics In Global Structural Design Of Aircraft, Clifton D. Nees

Theses and Dissertations

The analysis and design criteria of fracture mechanics are investigated for implementation with the Automated Structural Optimization System (ASTROS) global optimization design tool. The main focus is the optimal design of aircraft wing panels by applying fracture mechanics design criteria within the global finite element model. This effort consists of four main phases: investigation of fracture mechanics analysis methods and design criteria, formulation of a computational technique for damage tolerance design consistent with global optimization requirements, integration of the technique into the ASTROS design tool, and demonstration of the results.

Go to article

Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb Dec 1995

Compressible Turbulence Measurement In The Mixing Layer Of An Adiabatic Normal Slot Injection Into Supersonic Flow, Christopher D. Whitcomb

Theses and Dissertations

In this study mean flow and compressible turbulence measurements were taken at a station x = 72W downstream of the injection, where W is the injector throat width, of an adiabatic 2-D Mach 1.6 normal slot injection into a Mach 2.9 flow. Data were collected using a conventional Pitot probe, a cone-static probe, and multiple overheat cross-wire anemometry. In addition, schlieren and shadowgraph flow visualization was used to investigate the flow structure at both the injection point and at the downstream data collection point. From these measurements, mass flux component turbulence intensities of 8% to 10% were seen. The total …

Go to article

Fatigue Response Of Cracked Aluminum Panel With Partially Bonded Composite Patch, Jason J. Denney Dec 1995

Fatigue Response Of Cracked Aluminum Panel With Partially Bonded Composite Patch, Jason J. Denney

Theses and Dissertations

More and more aircraft, both commercial and military, are being called upon to fly well beyond their economic and structural service lives. Budget cuts and dwindling new aircraft development has forced the United States Air Force (USAF) to look toward more reliable structural repairs. One of these repair techniques, which was the subject of this study, is the repair of metallic aircraft structures using high strength composite materials. This study investigated the fatigue response of a precracked, 508x1 52x1 mm, 2024-T3 aluminum panel repaired with a partially bonded, unidirectional, three-ply boron/epoxy composite reinforcement with ply lengths of 68, 56 and …

Go to article

Sub-Optimal Control Of Rigid Spacecraft Reorientation Using Three Momentum Wheels, Gregory W. Schultz Dec 1995

Sub-Optimal Control Of Rigid Spacecraft Reorientation Using Three Momentum Wheels, Gregory W. Schultz

Theses and Dissertations

This thesis addresses sub-optimal employment of 3 momentum wheels for large angle reorientation of rigid spacecraft with minimal induced spacecraft motion during maneuvers. In addition to development of general theory for 3 wheel vehicles, simulation results for a vehicle using momentum wheels for secondary attitude control (GPS Block IIR) are compared to results for a vehicle using them for primary attitude control (the Hubble Space Telescope), to demonstrate practical applications and limitations. While the control laws were developed assuming no external perturbing torques on the vehicle, reorientation scenarios were run both in a torque free environment as well as an …

Go to article

A Differential Gps Aided Ins For Aircraft Landings, Ryan L. Britton Dec 1995

A Differential Gps Aided Ins For Aircraft Landings, Ryan L. Britton

Theses and Dissertations

The Department of Defense (DOD) and the commercial airline industry are in the process of replacing the instrument landing system (ILS) for aircraft precision approach landings. The use of differential Global Positioning System (DGPS) is thought to be a viable replacement for ILS precision approaches. This thesis explores the integration of an INS, DGPS, Barometric Altimeter, Pseudolite, and Radar Altimeter for a tanker type and a single engine aircraft precision approach. These devices are integrated using an extended Kalman filter (EKF). For the tanker type aircraft federal Aviation Administration (FAA) requirements for a Category I and a Category II precision …

Go to article

Velocity Determination For An Inverted Pseudolite Navigation Reference System, Jeffrey M. Hebert Dec 1995

Velocity Determination For An Inverted Pseudolite Navigation Reference System, Jeffrey M. Hebert

Theses and Dissertations

As navigation systems continue to improve in performance and features, the Air Force must develop better Navigation Reference Systems (NRS) to keep pace with technology. Specifically, with the advent of enhanced, integrated Global Positioning System (GPS) and Inertial Navigation System (INS) navigators, emphasis is placed on the measuring performance in the presence of GPS jamming. To meet these needs, a new NRS, dubbed the Sub-Meter Accuracy Reference System (SARS), is being developed by the 746th Test Squadron, Holloman AFB, New Mexico. SARS uses a unique, inverted GPS pseudolite positioning system to determine a reference trajectory. This research investigates two post …

Go to article

A Quantitative Feedback Theory Fcs Design For The Subsonic Envelope Of The Vista F-16 Including Configuration Variation And Aerodynamic Control Effector Failures, Vicent J. Cacciatore Dec 1995

A Quantitative Feedback Theory Fcs Design For The Subsonic Envelope Of The Vista F-16 Including Configuration Variation And Aerodynamic Control Effector Failures, Vicent J. Cacciatore

Theses and Dissertations

Fault tolerant flight control systems for combat aircraft are an alternative to excessively redundant aircraft designs or reconfigurable control laws. However, due to the range of flight conditions within a combat aircraft's operational flight envelope, the variety of its configurations, and the unavailability of an aerodynamic data base for damaged aircraft, designing fault tolerant systems is a complicated endeavor. Quantitative Feedback Theory is a robust control design technique especially well-suited to manage the structured parametric uncertainty inherent in this problem, and consequently is applied as the primary design tool for this research. Furthermore, realistic failure models are developed for the …

Go to article

Wing Flexure Compensation For Aircraft Attitude And Position Determination In An Inverted Carrier-Phase Positioning System, Bradley W. Mahlum Dec 1995

Wing Flexure Compensation For Aircraft Attitude And Position Determination In An Inverted Carrier-Phase Positioning System, Bradley W. Mahlum

Theses and Dissertations

In response to the ever increasing accuracies in inertial navigation systems, the U. S. Air Force must develop higher accuracy reference systems. These reference systems must also be small enough to be utilized in the testing of navigation systems onboard fighter aircraft. One such proposed system utilizes carrier-phase Global Positioning System (CPGPS) transmitters mounted on MM-9 pods with receivers on the ground. This research examines one possible method of utilizing this system to determine the attitude and position of the aircraft, given position estimates for the transmitter's locations. The transmitter positioning algorithm showed that the geometry will be problematic for …

Go to article

Optimal Formation Flight Control, Shawn B. Mccamish Dec 1995

Optimal Formation Flight Control, Shawn B. Mccamish

Theses and Dissertations

Automatic formation flight involves controlling multiple wing aircraft equipped with standard Mach-hold, altitude-hold, and heading-hold autopilots in order to maintain a desired position relative to a lead aircraft throughout formation maneuvers. Changes in the lead aircraft's states, including formation heading, velocity, altitude, and geometry changes, are treated as disturbance and are rejected by the formation flight control system. The work in this thesis is a continuation of five previous theses, dealing with the design of formation flight control systems. The goal of the optimal formation flight control design is to achieve robust formation maintenance in the face of formation maneuvers …

Go to article

First Prev Next Last