Dissertations / Theses on the topic 'Aerospace engineering – Research'

Given the increasing complexity of systems and the cost associated with test and evaluation of aerospace systems, more efficient methods are sought. Randomized test designs for aviation developmental test activities and other complex systems may not enable safe test conduct and may be prohibitively costly from a financial or time point of view. This research reviews Design of Experiments (DoE) test design approaches applicable to aerospace prototype test and evaluation activities. It proposes the use of Split Plot Optimal Designs to leverage advantages of DoE while satisfying requirements for limited randomization of the test runs. Through the use of case studies, the Split Plot Optimal Design approach is demonstrated to provide a 58% cost and schedule savings versus a One Factor At a Time approach, and 53% savings from the fully randomized Central Composite Design, while maintaining relevant statistical power. Through the use of Monte Carlo data simulation, the designs are evaluated for application to linear and quadratic models, with statistically significant results measured by Chi Squared and Kolmogorov-Smirnov tests.

West Virginia University (WVU) has created the Small Microgravity Research Facility (SMiRF) drop tower through a WVU Research Corporation Program to Stimulate Competitive Research (PSCoR) grant on its campus to increase direct access to inexpensive and repeatable reduced gravity research. In short, a drop tower is a tall structure from which experimental payloads are dropped, in a controlled environment, and experience reduced gravity or microgravity (i.e. "weightlessness") during free fall. Currently, there are several methods for conducting scientific research in microgravity including drop towers, parabolic flights, sounding rockets, suborbital flights, NanoSats, CubeSats, full-sized satellites, manned orbital flight, and the International Space Station (ISS). However, none of the aforementioned techniques is more inexpensive or has the capability of frequent experimentation repeatability as drop tower research. These advantages are conducive to a wide variety of experiments that can be inexpensively validated, and potentially accredited, through repeated, reliable research that permits frequent experiment modification and re-testing.

Development of the WVU SMiRF, or any drop tower, must take a systems engineering approach that may include the detailed design of several main components, namely: the payload release system, the payload deceleration system, the payload lifting and transfer system, the drop tower structure, and the instrumentation and controls system, as well as a standardized drop tower payload frame for use by those researchers who cannot afford to spend money on a data acquisition system or frame. In addition to detailed technical development, a budgetary model by which development took place is also presented throughout, summarized, and detailed in an appendix. After design and construction of the WVU SMiRF was complete, initial calibration provided performance characteristics at various payload weights, and full-scale checkout via experimentation provided repeatability characteristics of the facility. Based on checkout instrumentation, Initial repeatability results indicated a drop time of 1.26 seconds at an average of 0.06g, with a standard deviation of 0.085g over the period of the drop, and a peak impact load of 28.72g, with a standard deviation of 10.73g, for a payload weight of 113.8 lbs.

In order to thoroughly check out the facility, a full-scale, fully operational experiment was developed to create an experience that provides a comprehensive perspective of the end-user experience to the developer, so as to incorporate the details that may have been overlooked to the designer and/or developer, in this case, Kyle Phillips. The experiment that was chosen was to determine the effects of die swell, or extrudate swell, in reduced gravity. Die swell is a viscoelastic phenomenon that occurs when a dilatant, or shear-thickening substance is forced through a sufficient constriction, or "die," such that the substance expands, or "swells," downstream of the constriction, even while forming and maintaining a free jet at ambient sea level conditions. A wide range of dilatants exhibit die swell when subjected to the correct conditions, ranging from simple substances such as ketchup, oobleck, and shampoo to complex specially-formulated substances to be used for next generation body armor and high performance braking systems. To date, very few, if any, have researched the stabilizing effect that gravity may have on the phenomenon of die swell. By studying a fluid phenomenon in a reduced gravity environment, both the effect of gravity can be studied and the predominant forces acting on the fluid can be concluded. Furthermore, a hypothesis describing the behavior of a viscoelastic fluid particle employing the viscous Navier-Stokes Equations was derived to attempt to push the fluid mechanics community toward further integrating more fluid behavior into a unified mathematical model of fluid mechanics. While inconclusive in this experiment, several suggestions for future research were made in order to further the science behind die swell, and a comprehensive checkout of the facility and its operations were characterized. As a result of this checkout experience, several details were modified or added to the facility in order for the drop tower to be properly operated and provide the optimal user experience, such that open operation of the WVU SMiRF may begin in the Fall of 2014.

Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, September 1990.
Thesis Advisor(s): Howard, Richard M. Second Reader: Pagenkopf, Eric L. "September 1990." Description based on title screen as viewed on March 18, 2010. DTIC Identifier(s): Remotely Piloted Vehicles, Flight Maneuvers, Parachute Descents, UAV (Unmanned Air Vehicles), Supermaneuverability, Scale Models, Remote Control, Research Aircraft, Radio Transmission, High Angle of Attack, Aircraft Models, Naval Aircraft, Jet Fighters, Recovery, Theses. Author(s) subject terms:UAV, Supermaneuverability, Emergency Recovery System, Remotely Pioleted Vehicle. Includes bibliographical references (p. 68-70). Also available in print.

The design of NextGen and current-day cockpit displays are critical for efficient pilot performance and situation awareness on the flight deck. Before deployment of a design into the cockpit the costs and benefits that a display design imposes on performance and situation awareness should be considered. In this thesis, a design tool was developed to support the design of NextGen displays for situation awareness and performance. This design tool is a library of pilot performance estimates. Through literature reviews and meta-analyses of empirical data, the library was developed to provide display designers 1) qualitative distinctions of display properties that either support or limit full situation awareness, and 2) quantitative performance time estimates until situation awareness as a function of various display formats. A systematic method was also developed for future augmentation of the library.

This thesis considers vibration drilling in aerospace materials. The tolerances of the drilled holes in aerospace industry are very low since hole quality is an important factor. Conventional methods of drilling create long ribbon formed chips that increases the heat formation and decreases the hole quality. The solution is to introduce low frequency axial vibrations at the drill to break the chips. Smaller chips are easier to evacuate and leads to less heat formation and increased hole quality. Mechanical solutions to create the axial vibrations are commonly used in so called Advanced Drilling Units (ADUs). These drilling machines mounts on the surface to be drilled, actuates the drill with a feeding motion and drills the hole automatically. The ADU PFD1100 from Atlas Copco uses a mechanical chip breaking module called the ChipLet. The ChipLet has fixed amplitude and frequency hence the ChipLet module needs to be replaced to change vibration parameters. This thesis proposes the idea to instead use an electromechanical solution to create the vibration with an electric motor. This would make the possibility to change vibration parameters on the fly. A motor has been coupled to the feeding mechanism of the PFD1100 using a created prototype. The motor modifies the feeding motion of the spindle by doing a superposition of the constant feeding with a sinusoidal motion hence creating vibrations on the spindle. To compare the prototype to the current ChipLet, force and torque data have been gathered and analysed with spectral signal processing using the power spectral density estimate (PSDE). Conventional drilling with both the prototype and the ChipLet have been tested and analysed to use as a baseline and reference. The prototype shows that electronic control of the vibration parameters is possible. The prototype is also capable of breaking the chips although at lower frequency and amplitude than the ChipLet. The PSDE shows that conventional drilling reference frequencies are present in the vibration drilling data sets. The PSDE also shows that both the prototype and the ChipLet have several overtones in addition to the main harmonic.

A large agency of the Federal Government, three public institutions of higher learning, and two agents of State Government in the Commonwealth of Virginia launched a federally funded research and education consortium in 1962. The Virginia Associated Research Center (VARC) promised great success. The University of Virginia, Virginia Polytechnic Institute, and The College of William and Mary joined forces to provide the National Aeronautics and Space Administration's Langley Research Center with a scientific research base and a graduate education program. The Commonwealth initially provided enthusiastic support from the Governor's office and from the State Council for Higher Education.;The three colleges agreed to cooperatively manage and operate the NASA Space Radiation Effects Laboratory on the Virginia Lower Peninsula. NASA funded the costs of operating the laboratory, gave the colleges research time for experiments and provided the colleges with large multidisciplinary grants. In return, the colleges were to set up graduate education programs for NASA employees. These graduate programs were to grant degrees from the respective institutions for course work taken at the VARC site on the Peninsula. The research function of the consortium proved to be more productive than the education function.;Certain criteria for successful and unsuccessful consortia were ascertained from the literature. VARC's characteristics were analyzed according to these specific criteria. The three institutions could not agree on how to operate the facility. Inherently weak governance structures in the consortium led to the failure of the venture; after only five years, the consortium dissolved. The Governor of Virginia placed the Center under the auspices of the college nearest the Peninsula, The College of William and Mary. Though unsuccessful as a consortium, VARC became a means to achievement for the three colleges. Each of the three gained stronger, more reputable physics departments and two of the institutions achieved modern university status. A qualitative analysis emerges as the consortium's operation and characteristics unfold through oral history. The study details circumstances which led to VARC's demise and simultaneously describes a key transitional period for The College of William and Mary in its three hundred year history.

The projected increase in air traffic density has led to the development of NextGen that is expected to revolutionize the way the NAS is currently functioning. For NextGen to be implemented successfully, it is important to understand the humanautomation relationship within a complex system. Controllers will have to rely on automated tools to successfully manage aircraft in their sector. Increasing human trust in automation can lead to an increase in automation acceptance and its proper use. However, we are not aware of any research studies that have attempted to directly train individuals to trust automation. We report on an attempt to train 8 novice air traffic controllers to trust the automated NextGen tools in a radar internship course. Although the results were not statistically significant, the trend in the data suggests that it may be possible to train trust in automation.

In the aviation industry, digitally produced and presented flight, navigation, and aircraft information is commonly referred to as glass flight decks. Glass flight decks are driven by computer-based subsystems and have long been a part of military and commercial aviation sectors. Over the past 15 years, the General Aviation (GA) sector of the aviation industry has become a recent beneficiary of the rapid advancement of computer-based glass flight deck (GFD) systems. While providing the GA pilot considerable enhancements in the quality of information about the status and operations of the aircraft, training pilots on the use of glass flight decks is often delivered with traditional methods (e.g. textbooks, PowerPoint presentations, user manuals, and limited computer-based training modules). These training methods have been reported as less than desirable in learning to use the glass flight deck interface. Difficulties in achieving a complete understanding of functional and operational characteristics of the GFD systems, acquiring a full understanding of the interrelationships of the varied subsystems, and handling the wealth of flight information provided have been reported. Documented pilot concerns of poor user experience and satisfaction, and problems with the learning the complex and sophisticated interface of the GFD are additional issues with current pilot training approaches. A case study was executed to explore ways to improve training using GFD systems at a Midwestern aviation university. The researcher investigated if variations in instructional systems design and training methods for learning glass flight deck technology would affect the perceptions and attitudes of pilots of the learnability (an attribute of usability) of the glass flight deck interface. Specifically, this study investigated the effectiveness of scenario-based training (SBT) methods to potentially improve pilot knowledge and understanding of a GFD system, and overall pilot user experience and satisfaction. Participants overwhelmingly reported positive learning experiences from scenario-based GFD systems flight training, noting that learning and knowledge construction were improved over other training received in the past. In contrast, participants rated the usability and learnability of the GFD training systems low, reporting various problems with the systems’ interface, and the learnability (first-time use) of the complex GFD system. However, issues with usability of the GFD training systems did not reduce or change participant attitudes towards learning and mastering GFD systems; to the contrary, all participants requested additional coursework opportunities to train on GFD systems with the scenario-based flight training format.

In my previous bachelor's thesis I studied an algorithm for the improvement of runway efficiency in normal condition: minimizing the occupation of the runway means serving the greatest number of aircraft with the least possible delay. But other important limitations of airports are the ones in force during low visibility when the number of movements allowed undergoes a relevant reduction. A solution could be the use of technology to support air traffic controllers and pilots to re-establish a good level of situational awareness in order to reduce the limitations in force. In Europe, the technological pillar of the ambitious Single European Sky initiative is the Single European Sky ATM Research project (SESAR). Inside the SESAR project, the RETINA concept is regarding the introduction of augmented reality in aerodrome control tower for the improvement of efficiency and capacity of airports. Within the RETINA concept this thesis aims to study the implementation of new safety nets for aerodrome control tower with the support of augmented reality. This study starts from introduction to air traffic services in order to focus on SESAR project and RETINA concept. Then, concept and graphical solution for Conflicting ATC Clearances Safety Net (CATC) are proposed. Due to Covid-19 pandemic in progress during the thesis work, the implementation and validation activities could not be carried out in RETINA simulator of the University of Bologna labs, so different stand-alone implementation in Unity and validation by questionnaire administered to air traffic controllers are used. This thesis work can be considered as the first iteration in the User-Centered Design process for CATC. After the analysis of the feedback, new iteration in which the design is driven and refined by user-centered evaluation could be setup.

This research developed a process to identify condition deficiencies and sustainment requirements to assist in the development of strategic management plans for aerospace ground test systems that may be unique in design, operation, and/or maintenance.Subject matter experts can use the process to evaluate the condition of a test asset by inputting data into the developed software system. The process was designed around the concept of evaluating the condition of a system against ten parameters that encompass all of the aspects of a system that would be considered in determining its overall condition. A scale of zero (failed) to ten (new condition) is used to score both the current and the future (five years hence) state of the system. A relative aggregate scores approach is used to assign an overall condition value. Questions related to the forecasted workload of the facility and criticality of the asset in meeting the forecasted test programs provide a measure of the asset criticality and thereby assist management with project prioritization. Four different types of condition data output reports are available to management teams.The process was tested and internally validated by evaluating the condition of over three-hundred aerospace ground test assets.

This thesis is concerned with the study of pseudospectral discretizations of optimal control problems governed by ordinary differential equations and with their application to the solution of the International Space Station (ISS) momentum dumping problem. Pseudospectral methods are used to transcribe a given optimal control problem into a nonlinear programming problem. Adjoint estimates are presented and analyzed that provide approximations of the original adjoint variables using Lagrange multi pliers corresponding to the discretized optimal control problem. These adjoint estimations are derived for a broad class of pseudospectral discretizations and generalize the previously known adjoint estimation procedure for the Legendre pseudospectral discretization. The error between the desired solution to the infinite dimensional optimal control problem and the solution computed using pseudospectral collocation and nonlinear programming is estimated for linear-quadratic optimal control problems. Numerical results are given for both linear-quadratic and nonlinear optimal control problems. The Legendre pseudospectral method is applied to formulations of the ISS momentum dumping problem. Computed solutions are verified through simulations using adaptive higher order integration of the system dynamics.

This thesis investigates failure in sandwich panels due to bending, specifically localised buckling or wrinkling, a predominant failure mechanism for thin gauge honeycomb sandwich panels loaded in bending or compression. Over the past 60 years, considerable work has been devoted to understanding wrinkling and trying to predict failure loads in damaged and undamaged panels accurately. Existing wrinkling expressions were shown to over-estimate failure loads by over 100%. Discrepancies between wrinkling expressions and experimental failure loads were previously attributed to imperfections and irregularities in the structure. The aim of this thesis is to investigate this problem and try to accurately predict failure loads and understand the underlying failure mechanisms in damaged and undamaged panels, using a combination of numerical and analytical techniques. Classical wrinkling models use a continuum core to model complex cellular honeycomb cores. This type of model reduces complex cellular geometry to a series of effective properties that provide constant support to the face sheet. In reality, honeycomb cores provide support around the periphery of the cell walls and not across the entire surface of the face sheet. Due to the nature of wrinkling and the size of the wavelength, incorrect representation of the core could affect the failure loads and model. This study made direct comparisons between linear buckling loads of a discrete-cored sandwich panel and a continuum-cored sandwich panel. Discrete properties were converted to continuum properties within a Finite Element package. The result conclusively showed that both models predict the same linear failure loads, disproving the theory that the core representations contribute to the difference between experimental and analytical models. It was also shown that existing wrinkling models can accurately predict linear wrinkling loads. These linear model loads do not necessarily match the collapse strength of the physical panel and in most cases predict a significantly higher value. The research then moves on to developing expressions to convert cellular geometry into continuum properties accurately. Expressions are developed for honeycomb structures with fillets in their junctions. Both out-of-plane and in-plane modulus properties are reviewed and the models are verified against Finite Elements models and experimental results. Studies showed that the restrained in-plane modulus can be up to ten times stiffer than the commonly used free modulus value. This has a significant effect on the wrinkling stress. By using the correct value, the discrete model and continuum models predict the same loads. The classical wrinkling expressions also predict the same wrinkling stress as the Finite Element models. After establishing that the core representation is not the cause of the prediction error, the thesis turns to non-linear Finite Element models to predict failure loads and failure mechanism of thin-gauge sandwich honeycomb structures loaded in bending. A continuum three-dimensional non-linear Finite Element model, with bilinear plasticity, is compared with a set of experiments that use different types of Nomex cores and face sheets. The models show that the panels fail prematurely due to core crushing because of wrinkles forming in the face sheets. Experimental results indicate similar trends. The final section examines the affect of impact damage in honeycomb sandwich structures. Due to the thin face sheets and thick cores used on many aircraft and marine components, sandwich panels offer little resistance to impact events. Resulting damage usually consists of a layer of crushed core and a shallow dent in the face sheet. This type of damage often leads to a significant reduction in the load-carrying capacity of the panel through a full range of damage sizes. Finite element and analytical models were developed to accurately predict and capture the localised wrinkling failure mechanism which occurs in the impacted area. Models were directly compared to experimental results, with a high degree of correlation. The numerical and analytical models showed that impact damaged panels were failing due to wrinkling instability and not due to premature core crushing, which is the case with undamaged panels. They showed that two factors influence the wrinkling failure load: damage depth and damage diameter.

abstract: Over the years, aviation safety has been influenced by continuous implementations of both proactive and reactive policies by both regulatory boards and also, aviation service providers. This achievement has been possible mainly because of the safety management tools like the Aviation Safety Action Program (ASAP) which derives its roots from the much earlier Aviation Safety Reporting System (ASRS). Federal Aviation Administration (FAA) provides guidelines and procedures for installation and development of an ASAP, for every airline in the United States. In this study, how different United States air carriers apply ASAP in their organizations is investigated.
Dissertation/Thesis
Masters Thesis Technology 2016

No Fault Founds (NFFs) are an expensive problem faced by the airline industry. The underlying cause of NFFs are a major focus of research work in the field, but the dearth of consistent data is a roadblock faced by many decision makers. An important risk factor identified is the occurrence rate of NFFs.

This research work aims to help decision makers in the Airline Maintenance, Repair and Overhaul teams, when faced with recurring NFFs, to make a choice based on value derived from the system and risk preference of the decision maker under uncertainty. The value of the aircraft fleet is laid out using Net Present Value at every decision point along the system life cycle while accounting for the uncertainty in the failure rate information. Two extreme decisions are considered for the decision maker to choose between: rebooting the system every time a failure occurs and results in an NFF which allows for it to recur while reducing uncertainty of the failure rate; or eliminating the failure mode which assumes that the failure does not recur and therefore completely removes the uncertainty. Both decisions have their associated uncertain costs that affect the NPV calculated. We use a Monte Carlo approach to estimate the expected profit from deciding to eliminate the failure mode. We make use of Expected Utility Theory to account for the risk preference of a decision maker under uncertainty and build an Expected Utility Maximizing decision framework.

To conclude we give some guidance to interpret the results and understand what factors influence the optimal decision. We conclude that not accounting for uncertainty in estimating a failure rate for the future along with uncertainty in NFF costs can lead to an undesirable decision. If the decision maker waits too long to gather more information and reduce uncertainty, then rebooting the system for the remaining life could be more worthwhile than spending the large amount of money to Eliminate a failure mode. Finally, we conclude that, despite uncertainties in information of occurrence rates and costs of NFFs, an Expected Utility maximizing decision between the two options considered – Reboot and Eliminate – is possible given the available information.