U.S. Air Force Life Cycle Management Center

Biodiesel is a renewable substitute, or extender, for petroleum diesel that is composed of a mixture of fatty acid methyl esters (FAME) derived from plant or animal fats. Ultra-low sulfur diesel (ULSD) blended with up to 20% FAME can be used interchangeably with ULSD, is compatible with existing infrastructure, but is also more susceptible to biodegradation. Microbial proliferation and fuel degradation in biodiesel blends has been linked to microbiologically influenced corrosion (MIC), but this has not been studied previously in situ. We, therefore, conducted a yearlong study of B20 storage tanks in operation at two locations, identified the microorganisms associated with visible fuel fouling, and measured in situ corrosion. The bacterial populations were more diverse than the fungal populations, and largely unique to each location. The bacterial populations included members of the Acetobacteraceae, Clostridiaceae, and Proteobacteria. The abundant Eukaryotes at both locations consisted of the same taxa, including a filamentous fungus within the family Trichocomaceae, not yet widely recognized as a contaminant of petroleum fuels, and the Saccharomycetaceae family of yeasts. Increases in the absolute and relative abundances of the Trichocomaceae were correlated with significant, visible fouling and pitting corrosion. This study identified the relationship between fouling of B20 with increased rates of corrosion and the microorganisms responsible, largely at the bottom of the sampled storage tanks.

Over recent decades, the world has experienced a growing demand for and reliance upon unmanned aerial systems (UAS) to perform a broad spectrum of applications to include military operations such as surveillance/reconnaissance and strike/attack. As UAS technology matures and capabilities expand, especially with respect to increased autonomy, acquisition professionals and operational decision makers must determine how best to incorporate advanced capabilities into existing and emerging mission areas. This research seeks to predict which autonomous UAS capabilities are most likely to emerge over the next 20 years as well as the key challenges for implementation for each capability. Employing the Delphi method and relying on subject matter experts from operations, acquisitions and academia, future autonomous UAS mission areas and the corresponding level of autonomy are forecasted. The study finds consensus for a broad range of increased UAS capabilities with ever increasing levels of autonomy, but found the most promising areas for research and development to include intelligence, surveillance, and reconnaissance (ISR) mission areas and sense and avoid and data link technologies.

Next generation textile-based wearable sensing systems will require flexibility and strength to maintain capabilities over a wide range of deformations. However, current material sets used for textile-based skin contacting electrodes lack these key properties, which hinder applications such as electrophysiological sensing. In this work, a facile spray coating approach to integrate liquid metal nanoparticle systems into textile form factors for conformal, flexible, and robust electrodes is presented. The liquid metal system employs functionalized liquid metal nanoparticles that provide a simple "peel-off to activate" means of imparting conductivity. The spray coating approach combined with the functionalized liquid metal system enables the creation of long-term reusable textile-integrated liquid metal electrodes (TILEs). Although the TILEs are dry electrodes by nature, they show equal skin-electrode impedances and sensing capabilities with improved wearability compared to commercial wet electrodes. Biocompatibility of TILEs in an in vivo skin environment is demonstrated, while providing improved sensing performance compared to previously reported textile-based dry electrodes. The "spray on dry-behave like wet" characteristics of TILEs opens opportunities for textile-based wearable health monitoring, haptics, and augmented/virtual reality applications that require the use of flexible and conformable dry electrodes.

In the current environment of military operations requesting short development timelines to counter insurgent tactics, the engineering team often searches for ways to deliver the “80% solution”, typically in 6-12 months. These are labeled rapid development projects. A content analysis of best practices in commercial product development literature, where time to market is often a driving factor, was accomplished showing varying emphasis of systems engineering (SE) technical and technical management processes. This analysis confirms a preconceived notion of “plan upfront and early” by emphasizing Stakeholder Requirements Definition, Architecture Design and Technical Planning. A purposive sampling of Air Force Research Laboratory rapid development project managers and engineers was conducted to identify important SE processes and then compared to the literature content analysis. The results of this sampling did not strongly emphasize one process over another, however Architecture Design and Implementation scored higher among Technical Processes. Decision Analysis, Technical Planning, Technical Assessment and Data Management scored slightly higher among Technical Management Processes. Anecdotal evidence also emphasized iterating prototype designs based on early customer feedback, focusing mostly on managing critical risks and holding frequent early reviews until trust is built in the team.

Next generation on-skin electrodes will require soft, flexible, and gentle materials to provide both high-fidelity sensing and wearer comfort. However, many commercially available on-skin electrodes lack these key properties due to their use of rigid hardware, harsh adhesives, uncomfortable support structures, and poor breathability. To address these challenges, this work presents a new device paradigm by joining biocompatible electrospun spider silk with printable liquid metal to yield an incredibly soft and scalable on-skin electrode that is strain-tolerant, conformable, and gentle on-skin. These electrodes, termed silky liquid metal (SLiM) electrodes, are found to be over five times more breathable than commercial wet electrodes, while the silk's intrinsic adhesion mechanism allows SLiM electrodes to avoid the use of harsh artificial adhesives, potentially decreasing skin irritation and inflammation over long-term use. Finally, the SLiM electrodes provide comparable impedances to traditional wet and other liquid metal electrodes, offering a high-fidelity sensing alternative with increased wearer comfort. Human subject testing confirmed the SLiM electrodes ability to sense electrophysiological signals with high fidelity and minimal irritation to the skin. The unique properties of the reported SLiM electrodes offer a comfortable electrophysiological sensing solution especially for patients with pre-existing skin conditions or surface wounds.

Abstract The objective of this work was to develop and demonstrate a probabilistic life prediction method for the prediction of minimum fatigue lives that are typically used in the design of fracture critical rotating turbine engine components. A Monte Carlo analysis was used to predict the variability in fatigue lives based on the distribution of microstructural features that lead to early crack initiation as well as the variability in small fatigue crack growth rates. Two titanium alloys, both with bimodal microstructures, were tested and analysed in this study. The distribution of critical microstructural features was calibrated based on test results and understanding of microstructure neighbourhood effects. Testing was conducted on both alloys and included both smooth and notched specimens. The predictions are presented and compared with the data for smooth and notch geometries for the various loading conditions. A parametric study was performed to identify the importance of several model inputs and to identify areas for future improvement.

Traditional learning curve theory assumes a constant learning rate regardless of the number of units produced. However, a collection of theoretical and empirical evidence indicates that learning rates decrease as more units are produced in some cases. These diminishing learning rates cause traditional learning curves to underestimate required resources, potentially resulting in cost overruns. A diminishing learning rate model, namely Boone’s learning curve, was recently developed to model this phenomenon. This research confirms that Boone’s learning curve systematically reduced error in modeling observed learning curves using production data from 169 Department of Defense end-items. However, high amounts of variability in error reduction precluded concluding the degree to which Boone’s learning curve reduced error on average. This research further justifies the necessity of a diminishing learning rate forecasting model and assesses a potential solution to model diminishing learning rates.

Designing aircraft cockpits to accommodate the wide range of body sizes and shapes existing in the world population has always been a difficult problem for crew station engineers. There is no consensus on the best method for obtaining measurements for body forms that statistically represent the variation within a population. The aim of this research is to compare the two most commonly used anthropometric approaches for dimension specification and flight deck design: the boundary cases multivariate and the percentile univariate. The multivariate approach captured more subjects than the percentile approach (p < .05) for all accommodation assessments using Brazilian Air Force pilots’ anthropometry, but was not as effective as had been suggested in the literature. This study showed that the Boundary Cases Multivariate Method was better at evaluating design criteria for cockpit accommodation than the Percentile Univariate Method for accommodation of the central 90% envelope for the Brazilian Air Force crew application. Practitioner summary: The findings show that the Multivariate Boundary Cases approach can better provide anthropometric limits for the desired accommodation level when multiple body dimensions need to be simultaneously considered in a design. It will help researchers, designers, and engineers to solve complex design situations, make improved judgement and take right decisions. Abbreviations: FAR: federal aviation regulation; CS: certification specification; FAA: federal aviation administration; EASA: European union aviation safety agency; EMB: embraer; FAB: Brazilian Air Force; CAD: computer-aided design; MAM: multivariate anthropometric method; USAF: United States Air Force; PCA: principal component analysis; PC: principal component; JSF: joint strike fighter; NATO: North atlantic treaty organization; ISO: International Organization for Standardization; BPAD: Brazilian pilots anthropometric database; RD: radial distance; Error = A-E: error = achieved – expected; SPSS: statistical package for the social sciences; IBM Corp.: International business machines corporation; Acr. Ht, st: acromion height, sitting; But-kn lgt: buttock-knee length; Eye Ht, sit: eye height, sitting; Knee Ht, sit: knee height, sitting; Sitting Ht: sitting height; Thumbtip rch: thumbtip reach; Accom %: accommodated percentage; Af, Am, …, Zf, Zm: cases A-D and W-Z (“f” for female subjects and “m” for male subjects); T: trainer; A: atack; KC: anker and cargo; F: fighter; NG-BR: new generation - Brasil; PPE: personal protective equipment

Aircraft tire wear is a complex phenomenon that depends on a multitude of different interdependent variables. Due to the multitude of variables, there is currently no qualification test or accurate method for predicting tire life. While improving tire life has shown to save as much as 14 million dollars over the lifetime of certain aircraft, the present United States Air Force (USAF) method for realizing that savings is an expensive and time intensive Life Cycle Cost (LCC) evaluation program. In an attempt to perform more predictive laboratory wear testing, the USAF commissioned a 168inch internal drum dynamometer (168i) designed specifically for aircraft tire wear testing. The 96 th Test Group, Aerospace Survivability and Safety Operating Location (96 TG/OL-AC), Landing Gear Test Facility’s (LGTF) 168i has demonstrated the ability to comparatively wear test tires; however, its predictive wear capabilities require further development. Results from these comparative wear tests have highlighted the possibility for generating simple tire wear predictive testing schemes based on tire, brake, and aircraft system level parameters. From these results, an initial predictive tire wear testing program is presented and discussed. To assist predictive laboratory testing, a Finite Element Method (FEM) computational model has also been introduced in an attempt to simulate an aircraft’s Missionized Profile (taxi, takeoff, and landing). These trends demonstrate that predictive tire wear testing on the 168i coupled with FEM computational modeling can be used to predict tire life before fielding the tire.

This paper describes the emerging Issue 2 of the CCSDS-123.0-B standard for low-complexity compression of multispectral and hyperspectral imagery, focusing on its new features and capabilities. Most significantly, this new issue incorporates a closed-loop quantization scheme to provide near-lossless compression capability while still supporting lossless compression, and introduces a new entropy coding option that provides better compression of low-entropy data.

High-strength low-alloy (HSLA) steels are desired for their high strength-to-weight ratio, relatively low cost, good overall mechanical properties, and relative ease of processing. The development of Eglin steel and AF 9628 has facilitated the current wave of research into next-generation HSLA steels. These alloys are characterized by both high levels of strength and increased levels of ductility and impact toughness over traditional HSLA alloys such as AISI 4340/4330. AF 9628 has proven difficult to machine due to strain hardening while turning. Manual and CNC turning experiments were carried out on AF 9628 cylindrical bars based on current machining practices. In an effort to optimize material removal rate and tool life, quantitative measurements of tool flank wear, surface roughness, hardness, microhardness, and chip thickness were taken. Qualitative observations made on microstructural evolution and chip color and morphology are also discussed.

View Video Presentation: https://doi.org/10.2514/6.2022-1680.vid Results from the First AIAA Stability and Control Prediction Workshop are summarized in this paper. The workshop series was developed in support of three primary objectives: (1) to establish best practices for the prediction of stability and control derivatives using industry-standard Computational Fluid Dynamics (CFD) solvers, (2) to provide an impartial forum for evaluating the effectiveness of Reynolds-averaged-Navier-Stokes- and Detached-Eddy-Simulation-based modeling techniques, and (3) to identify areas in need of additional research and development. To address these objectives, the inaugural workshop focused on generating computational aerodynamic predictions for the ONERA version of the NASA/Boeing Common Research Model. The configuration includes the wing, body, horizontal tail, and a vertical tail designed by ONERA. While longitudinal wind tunnel test data for the model had been previously documented, unpublished lateral test data at small sideslip angles provided a unique opportunity for participants to generate blind computational predictions for wind tunnel data comparisons. Additional test cases included assessments of the Mach number effect on static lateral/directional stability and the impact of the wind tunnel sting on longitudinal stability. Participants were invited to generate solutions using two workshop-provided series of structured overset and unstructured grids, in addition to any participant custom grids of interest. Total and component-level breakdowns for the force and moment coefficients for each test case are presented, as well as sectional pressure distribution data on the wing and tail components, to assess the agreement between several different Reynolds-averaged Navier-Stokes CFD solvers.

The opinions of design, test and analysis engineers from industry and government laboratories on the status and future of stability and control prediction are presented in this paper. Air transport, fighter and flying wing configurations, considered to be representative of the platforms of concern to a vast majority of the commercial and military industries, are discussed. Static and dynamic stability as well as control effectiveness are used to describe the stability and control characteristics. Achievements necessary to advance the current status are decomposed into relatively straightforward and technologically challenging obstacles to overcome. Finally, a roadmap to address these obstacles is presented.

This paper presents the results of a computational investigation of the 1st AIAA Workshop for Integrated Propeller Prediction (WIPP) using the HPCMP CREATETM-AV Kestrel simulation tools. There is a renewed interest in the propeller-driven aircraft for unmanned aerial vehicles, electric aircraft, and flying taxies. Computational resources can significantly accelerate the generation of aerodynamic models for these vehicles and reduce the development cost if the prediction tools can accurately predict the aircraft/propeller aerodynamic interactions. Unfortunately, limited propeller experimental data are available to validate computational methods. The first AIAA workshop for the integrated propeller prediction was therefore established to address this problem. The objective of this workshop was to generate an open-access powered wind tunnel test database for computational validation of propeller effects on the wing aerodynamics, specifically for the wing-tip-mounted propellers. The propeller selected for the workshop has four blades with a diameter of 16.2 in. The wing has a root and tip chord of 11.6 and 8.6 in, respectively. The wing/propeller configuration was mounted vertically in the Lockheed Martin low-speed wind tunnel and was tested with and without propeller, power-off and power-on with nominal thrust coefficients of 0.04, 0.2, and 0.4. In addition, the wing was mounted on a turnable plate and was tested at different angles of attack by rotating the plate. Two Mach numbers were tested: 0.08 and 0.11. Measurements include wing balance data to measure the wing integrated forces and moments and wing pressure taps at different spanwise locations including behind the propeller. Finally, a wake survey data was used to measure flow parameters behind the propeller at different downstream locations. Two different simulation approaches are used: one using a grid including wind tunnel walls and the second using a subset grid overset to an adaptive Cartesian grid that fills the space between the overset grid and wind tunnel walls. The predictions of both approaches have been compared with available experimental data. The results show a good agreement for all tested conditions. The measured and predicted data show that wing aerodynamic performance is improved by the spinning tip-mounted propeller.

Future systems development includes Command and Control (C2) technology to support Air Battle Managers (ABMs) and fighter pilots as they support complex missions employing autonomous Unmanned Aircraft Systems (UAS) within a larger System of Systems. In complex, evolving, and dynamic environments, the human operator’s ability to efficiently observe, orient, decide, and act is imperative. However, the operator’s performance can be degraded during changes in UAS custody between ABMs and pilots, which significantly increases operator cognitive workload beyond that typically seen in previous missions. Unfortunately, C2 technology development often places a heavy focus on automation and hardware, leaving the human operator underrepresented to the detriment human-automation interactions. Currently, Digital Engineering and Model-based Systems Engineering (MBSE) tools are rapidly being adopted in system development, integration, and management to support the complex development effort necessary to integrate these systems. The current research integrated human considerations in MBSE tools to analyze human-automation teaming during the development process. The method supports representation of the automation assistance and human operators during a modeled mission simulation in a pair of specialized activity diagrams referred to as the Mission Actor Diagram and the OODA <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> Activity Diagram, permitting analysis of errors and bottlenecks during operation. This method illustrates the potential to reduce operator cognitive workload, improve operator decision making, and increased system performance, while reducing time spent in system redesign.

The Automatic Air Collision Avoidance System (Auto ACAS) is a technology under development by the Air Force Research Laboratory in partnership with Lockheed Martin. Auto ACAS provides last resort air-to-air collision protection during air combat training operations by automatically maneuvering aircraft away from each other while minimizing interference with pilot operations. The Auto ACAS software was integrated onto an existing, commonly used Air Combat Maneuvering Instrumentation (ACMI) pod that is currently carried by many US and foreign fighter aircraft. With current fiscal constraints, this type of high-risk/high-cost testing is nearly impossible to execute. However, through use of the United States Air Force Test Pilot School (TPS) Test Management Projects (TMP) along with novel usage of the NF-16D VISTA aircraft this program was initialized as a lowrisk/low-cost test program. With the initial ground work laid at TPS, the test program integrated the Auto ACAS into F-16 test aircraft. Further testing was focused on nuisance potential during dynamic maneuvering; ensuring the system only took-over control of the aircraft at the last possible moment and did not interfere with typical pilot flying. Furthermore, Auto ACAS has propelled automation in the cockpit to new levels since this technology takes over control of the aircraft before the pilot recognizes the need. This level of automation required unique test and safety planning tools. With increased aircraft automation the flight test efforts had to respond to aircrew needs while understanding how automation could and could not counter aircrew limitations. This Auto ACAS test program was unique in its technology, but the method of test could be easily transferrable to other flight test programs. Other programs could emulate cost and risk reduction through similar efforts including using schools for initial data gathering and simulation where available. This paper will cover the entire Auto ACAS flight test program as well as the unique flight test methods required for testing this type of technology. Additionally, lessons learned from test planning, safety planning and test execution will be presented with an emphasis on test point buildup, utilization of low-cost TPS support, and end-game benefits of the specific workarounds implemented to deal with a fiscally constrained environment.

Hydrodynamic ram occurs when a projectile with sufficient kinetic energy impacts a fluid-filled tank and generates large pressure fluctuations within the tank, potentially contributing to the tank's failure. A common product of a hydrodynamic ram event is the transient spray, or liquid spurt, generated through the projectile's penetration orifice. Previous work described the resulting transient spray in distinct, sequential phases. Additional research noted cavities, for missiles entering water, as having distinct phases or features. Hence, experiments were constructed using two synchronized high-speed cameras to capture the interior cavity features through the tank's polycarbonate wall and the corresponding exterior transient spray phases. Research was conducted to relate the interior and exterior observations with 0.95 cm steel spheres ranging from 1,800, 1,495, to 1,200 m/s. Synchronized high-speed image pairs were collected within 0.2 μs of each other and proved crucial for confidently relating the interior cavity features to the exterior transient spray. Analyzing the synchronized image pairs yielded correlation of the pre-spurt, main spurt, and low-frequency pulsation transient spray phases to the respective cavity contraction, cavity separation, and cavity collapse features. Further delineation of the cavity phase into separate transitional phases provided insight for further hydrodynamic ram research to determine the physical relationship to the transient spray.

The design and performance of a room temperature electrical substitution radiometer for use as an absolute standard for measuring continuous-wave laser power over a wide range of wavelengths, beam diameters, and powers are described. The standard achieves an accuracy of 0.46% (k = 2) for powers from 10 mW to 100 mW and 0.83% (k = 2) for powers from 1 mW to 10 mW and can accommodate laser beam diameters (1/e2) up to 11 mm and wavelengths from 300 nm to 2 μm. At low power levels, the uncertainty is dominated by sensitivity to fluctuations in the thermal environment. The core of the instrument is a planar, silicon microfabricated bolometer with vertically aligned carbon nanotube absorbers, commercial surface mount thermistors, and an integrated heater. Where possible, commercial electronics and components were used. The performance was validated by comparing it to a National Institute of Standards and Technology primary standard through a transfer standard silicon trap detector and by comparing it to the legacy “C-series” standards in operation at the U.S. Air Force Metrology and Calibration Division (AFMETCAL).

View Video Presentation: https://doi.org/10.2514/6.2023-0421.vid The following study is a cooperation of AFWERX Agility Prime, MOOG Aircraft Group, and the United States Air Force Lifecycle Management Center with respect to the prototype electric vertical takeoff and landing (eVTOL) aircraft, the SureFly S250. The objective of the investigation is to analyze the performance characteristics of the single rotor, as well as the contra rotating rotor system. High fidelity computational fluid dynamics (CFD) was leveraged to analyze induced velocities in hover, integrated loads, vortex ring state (VRS), and the rotors in ground effect (IGE). The CFD results were compared to test stand data when available, as well as empirical data.

Early research on time phasing primarily focuses on the theoretical foundation for applying the cumulative distribution function, or S-curve, to model the distribution of development expenditures. Minimal methodology prior to 2002 provides for estimating the S-curve’s parameter values. Brown et al. (2002) resolved this shortcoming through regression analysis, but their methodology is not specific to aircraft and does not consider aircraft-specific variables, such as first flight. Using a sample of 26 Department of Defense aircraft programs, we build upon Brown et al.’s work by examining whether a model driven by aircraft-specific variables can more accurately predict budget requirements. As a baseline, we compare our model to the commonly cited 60/40 “rule of thumb,” which assumes 60% expenditures at 50% schedule. We discover that our developed Weibull model explains 74.6% of total variation in annual budget, improving the estimation of budgets by 6.5%, on average, over the baseline 60/40 model.