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Alternative Unleaded Fuels for General Aviation Piston Airplanes: A Pathway to Sustainability
No full textThis study examines the transition from leaded 100 low lead (100LL) aviation gasoline to unleaded alternatives in general aviation (GA) piston-engine aircraft, driven by environmental and health concerns highlighted by the U.S. Environmental Protection Agency\u27s (EPA) endangerment finding. Through a systematic literature review and synthesis, it identifies key unleaded fuel candidates, including 91UL, 94UL (Swift UL94), Auto Gas (Mogas), General Aviation Modification Inc. (GAMI) G100UL, Swift 100R, and LyondellBasell/VP Racing UL100E, evaluating their status, compatibility, advantages, and challenges. The analysis addresses regulatory efforts such as the FAA\u27s Eliminate Aviation Gasoline Lead Emissions (EAGLE) initiative aiming for a lead-free system by 2030, alongside technical, economic, liability, and distribution hurdles. Findings emphasize GAMI G100UL and Swift 100R as promising drop-in replacements for both low- and high-compression engines, underscoring the need for industry collaboration to ensure safety, sustainability, and operational viability in GA for decades to come
Trajectory
No full textTrajectory follows Clara, a young girl whose fascination with the stars begins under a quiet sky beside her brother. Drawing inspiration from a tattered book, a devoted science teacher, and the strong women in her life, Clara\u27s childhood curiosity grew into a fierce determination. Through obstacles of responsibility and doubt, she remained resilient allowing dreams to push her. Her journey mirrors the very concept of Trajectory, being shaped by gravity, directed by force, and always ascending. This story is a gentle reminder to reach beyond limitations and toward endless possibility
Charles Forbes \u27Beano\u27 Russell. CWGC Certificate
Full text linkCommonwealth War Graves Commission (CWGC) Certificate for RAF cadet Charles Forbes ‘Beano’ Russell who died on July 22, 1941, while training to be a pilot at 5BFTS. He is buried in the CWGC British Plot. at Oak Ridge Cemetery, Arcadia
Clewiston Civic Park - Remembering Riddle Field
No full textClewiston Civic Park spans 4.14 acres of beautifully landscaped grounds in the heart of town, offering a peaceful setting with walking paths, a playground, picnic tables, and inviting swings that line the walkways. At the center of the park, stands a memorial honoring the WWII British Cadets who were at 5BFTS (Riddle Field) between 1941 and 1945, adding historical significance to this charming community space.https://commons.erau.edu/bfts-images-riddle-field/1006/thumbnail.jp
Editor\u27s Note: Celebrating 35 Years of Scholarly Excellence
Full text linkA letter from the editor, Dr. Dahai Liu, on the JAAER\u27s 35th anniversary
Aeroacoustics Applications to Jets and Rotors
Full text linkAeroacoustics plays a critical role in the advancement of propulsion technologies for both conventional and emerging aerial systems. This dissertation investigates two key topics: noise suppression in supersonic rectangular jets and rotor noise characterization in hover and ground effect. Using high-fidelity numerical simulations and theoretical analyses, this research aims to develop effective noise mitigation strategies and improve predictive methodologies.
The first part of this study focuses on the reduction of noise in supersonic rectangular jets through active control techniques. A novel approach utilizing unsteady microjet actuation at the nozzle lip is explored to disrupt the formation of large-scale turbulent structures responsible for noise generation. High-fidelity simulations capture the unsteady flow dynamics and acoustic propagation, revealing how microjets alter the dominant frequency modes of coherent structures. Through Spectral Proper Orthogonal Decomposition (SPOD), the study identifies the impact of actuation on the energy distribution across the frequency spectrum. Results demonstrate a measurable reduction in Overall Sound Pressure Level (OASPL), particularly at peak radiation angles, confirming the potential of microjet-based strategies for adaptive noise suppression in jet propulsion systems.
The second focus of this dissertation is on rotor noise characterization, particularly in the context of eVTOL applications. Although the study is limited to a single rotor configuration, it serves as a foundational step toward understanding the aeroacoustic behavior of multirotor systems in Urban Air Mobility (UAM). This research, conducted as part of a NASA University Leadership Initiative (ULI), combines computational and experimental efforts to validate numerical approaches for rotor noise prediction. High-fidelity computational fluid dynamics (CFD) and aeroacoustic solvers are employed to analyze a scaled eVTOL propeller in hover and edgewise flight, out and in ground-effect (IGE) conditions. Results show that ground reflections amplify lateral noise levels due to constructive interference, and modifications in directivity patterns are identified based on observer locations. The study also examines how wake interactions influence acoustic signatures when the rotor is at close proximity to the ground and how the Method-of-Images (MOI) can be utilized to simplify acoustic predictions of ground-effect scenarios.
This dissertation advances the development of quieter and more efficient propulsion technologies while also developing reliable numerical tools. The insights from the jet noise suppression study lay the groundwork for future active control strategies, while the rotor noise investigation strengthens predictive methodologies for eVTOL applications, providing accurate tools and frameworks for the research group and the academic community
Modeling the Dynamics of Flexible Aerospace Vehicles Using the Theory of Functional Connections
Full text linkModeling and control of flexible vehicles is a topic of high interest in the aerospace field and a key challenge lies in finding accurate mathematical representations of the flexible dynamics of continuous elastic structures that allow simple integration into estimation and control algorithms. The answer was found in approximating the dynamics of these systems with sets of coupled Ordinary Differential Equations (ODE) for which a well-established estimation and control theory is available. Each of the techniques employed to achieve this goal is characterized by its own strengths and limitations. Hence, the main objective of this research is to develop the essential tools to enable a modeling methodology capable to represent the coupled structural and attitude dynamics of flexible spacecrafts in a simple and compact form while addressing the limitations in existing techniques. The aim of the research is pursued by employing the Theory of Functional Connections (TFC), that is a recently developed mathematical framework to perform functional interpolation in combination with the Lagrangian mechanics. Specifically, after providing an overview of this two fundamental tools, the key principles of the developed theory are outlined, and the resulting modeling strategy is presented in its general logic. Selected applications of the theory to cases of practical interest will be shown. In each case, a full explanation of the theoretical derivation of the solution is provided to show how the theory can be applied in the practice. Finally, numerical simulations were run to validate the resulting models and show the potential of the proposed theory in developing accurate and efficient representations of the dynamics of flexible structures and vehicles. The results show effectiveness of the methodology and open the possibility of extending it to more complex objects and investigating the interaction between the resulting models and some control and estimation algorithms
High-Latitude Ionospheric Irregularities Characterized Through Machine Learning Methods
Full text linkThis study uses Machine Learning and data-driven techniques to understand plasma irregularities in high-latitude regions better. By combining observations and recent findings from modeling, the goal is to identify and classify scintillation signatures caused by different types of irregularities in the ionosphere. The focus is on irregularities from electron precipitation in the auroral oval and ExB drifts in the polar cap. Using Machine Learning tools, the study aims to distinguish between different scintillation signatures and link them to their sources, improving our ability to detect and characterize these events. Using multiple instruments and advanced filtering, the aim is to enhance the accuracy of the scintillation event database and classify irregularities more effectively in high-latitude areas, ultimately advancing our understanding of plasma dynamics in these regions.
A novel approach to distinguish the most similar ionospheric time series scintillation signatures from a random group of signatures without any prior information is introduced. This classification is based on the correlation between the input signatures in phase and power in Timeseries Clustering. The observed similarity of the signatures was likely due to steepening spectra during an auroral front.
Based on the successful distinction, a hypothesis was formulated: Predominant irregularity mechanisms in the auroral oval are expected to vary from those in the polar cap due to high-latitude ionospheric dynamics. If different mechanisms generate different plasma structures as predicted by theoretical models, then it could be presumed that the scintillation signatures in these two regions have different characteristics. This was tested with a classification algorithm during five geomagnetic storm days. Using time-series hierarchical clustering to compare groups of signatures for pairs of stations, one from the auroral oval vs. one from the polar cap, a decision tree model was trained to classify the signatures. For hours in which both stations were located in their characteristic regions as confirmed by electron energy flux observations, the model achieved a good performance, whereas in hours with similar structures over both stations, the signatures could not be distinguished well. The model performance also depended on the structure of the decision tree classifier, the resolution of the available datasets also for the station labels, and the data quality.
The scintillation signature database generated in the previous step was extended by additional observations and estimates that also play a major role in theoretical models: plasma drift, irregularity thickness and layer height, and spectral characteristics. The importance of each parameter for the classification was analyzed using a factor analysis, and the estimation process was optimized for those major factors. The major steps to use this enhanced database and theoretical predictions to train a Support Vector Machine to attempt to link irregularity types with their corresponding scintillation signatures were discussed.
Since the time series signatures are crucial to the validity of the machine learning database, the data processing was optimized to remove non-irregularity-related effects. Also, the irregularity scale sizes and dynamics considered in the filtering approach and the effect of an adaptive cutoff frequency on the ML model were investigated. Similarly to the findings from the Timeseries Clustering approach, large-scale contributions to the signature occur to be an important parameter to distinguish different high-latitude source regions.
Due to the sparse plasma drift velocity observations available at GNSS-relevant intermediate scale sizes, a technique using spaced GNSS receivers was implemented at a new location in Svalbard, Norway. In collocation with the Incoherent Scatter Radar in Svalbard, this one-dimensional array can probe polar cap scintillation events. However, during the selected case studies, no significant events were detected
Acoustic-Gravity Wave Propagation Based on Solutions to the Generalized Multi-component Transport Equations
Full text linkNonlinear atmospheric models have provided important insight into acoustic waves generated by natural and man-made hazards, which may steepen into shocks or N-waves while also dissipating when propagating in the thermosphere. Although models have yielded results that agree with observations of ionospheric perturbations, dynamical models for the diffusive and stratified lower thermosphere often use single gas approximations with height-dependent physical properties that omit the dynamics of the major and minor constituents. Thus, the inter-species diffusion associated with these flows (e.g. variations of mean molecular weight, and specific heat) are not accounted for. This approximation is simpler and less computationally expensive than a true multi-fluid model, yet captures the important physical transitions between molecular and atomic gases in the lower thermosphere. However, models with time-dependent composition have been shown to outperform commonly used models with fixed composition; these time-dependent effects have been included in a one-gas model by adding an advection equation for the molecular weight, finding closer agreement to a true binary-gas model (e.g. Walterscheid [2012]). Here, we solve the hydrodynamic conservation equations for a multi-component flow, based on the method described by [Ern and Giovangigli 1994], with an emphasis on the effects of mass-diffusion on a vertically propagating atmospheric waves that reach the lower thermosphere. The application of the transport equations to the neutral, non-reactive atmosphere resembles an extension of the Navier-Stokes equations applied to a multi-component fluid (also known as the Multi-component Navier-Stokes equations), allowing for the modeling of species interactions [Arnault, 2022]. This description includes classical dissipative terms, such as viscosity and thermal conduction, as done in Pineyro [2018], and molecular diffusion. To investigate the impact of mass diffusion, the equations were analyzed under conditions where linear acoustic and gravity wave solutions are permitted. From this analysis, a dispersion relation was obtained that measured the impact of mass-diffusion on any atmosphere, given certain neutral atmospheric parameters. Nonlinear solutions were also analyzed to investigate the interplay between nonlinear effects and dissipative processes. The model developed, a modified version of Pineyro [2018], is applied to various studies in 1D and 2D to analyze the nonlinear behavior of gravity waves under conditions where species diffusion can impact the wave. Mass diffusion will additionally affect the fluctuations of the composition of the upper atmosphere as it is modulated by waves. For the well-mixed lower atmosphere, the impact is insufficient to necessitate the full multi-component flow equations. However, when the wave reaches thermospheric altitudes, where the diffusive separation is more apparent, the impact of mass-diffusion may become relevant. The relative contributions of diffusion processes to determining the dynamics of short-period waves in the lower thermosphere are investigated and quantified in this thesis. The results indicate that barodiffusion is the dominant diffusion mechanism driving wave dissipation, with acoustic attenuation most pronounced when atmospheric constituents have markedly different molecular masses, a condition typically found in the upper layers of planetary atmospheres. On Earth, species diffusion plays an increasingly significant role in acoustic attenuation at altitudes above approximately 150km, contributing up to 16% of the total absorption. This effect is primarily due to the high concentrations of atomic oxygen and helium. On Venus, species diffusion can account for as much as 45% of the total dissipation above about 200km, where the atmosphere is characterized by a ternary mixture of helium, hydrogen, and atomic oxygen. Mars exhibits a pattern similar to Earth, with species diffusion contributing around 17% of the total absorption due to its quaternary atmospheric composition of carbon dioxide, nitrogen, atomic oxygen, and carbon monoxide. In contrast, on Titan, Uranus, and Neptune, species diffusion plays a comparatively minor role, with bulk and shear viscosity effects dominating wave attenuation in these atmospheres
