US Air Force Research Research Articles

Whistler‐Mode Transmission Experiments in the Radiation Belts: DSX TNT Circuit Simulation and Data Analysis

AbstractHigh‐power transmission experiments in the very low frequency (VLF) mode have been conducted by the US Air Force Research Laboratory’s Demonstration and Science Experiments (DSX) satellite in the radiation belts using a novel transmitter that automatically tunes to find the resonance frequency of the transmitter circuit including the antenna. The resulting voltage–frequency curves are used to derive antenna impedance at the resonance. The analysis shows that the antenna reactance is far less than that of a dipole antenna in free space. The derived radiation resistance is up to several tens of kilo Ohms. Most interestingly, it is found that the radiation resistance is inversely proportional to the square of transmission wave frequency. The transmitted power can be up to 80 W for the DSX transmitter with an 82‐m long tip‐to‐tip antenna, showing that the high‐power VLF transmission is feasible. Whistler wave transmission inside the higher‐density plasmasphere is more efficient. Data analysis indicates that the antenna impedance does not vary systematically with the antenna orientation angle relative to the ambient magnetic field. The previous dominant theoretical studies yield not only incorrect values of the impedance but a completely different frequency dependence than that derived from DSX experiments. Instead, the recent theories correctly capture both the antenna impedance magnitude and the frequency dependence.

A Preliminary Technology Readiness Assessment of Morphing Technology Applied to Case Studies

In an innovative system, it is essential to keep under control the crucial development phases, which should consider several aspects involving, for instance, the modeling or the assessment of suitable analytical representations. Aiming to pursue a final demonstration to verify the actual capability of an engineering idea, however, some fundamental elements may have been partially considered. Many projects state the initial and final technology readiness level based on the famous scale introduced by the US National and Aeronautics Space Administration (NASA) many years ago and now widespread in many fields of technology innovation. Its nine-step definition provides a high-level indication of the maturity of the observed innovative system. Trivially, the resolution of that macroscopic meter is not made for catching advancement details, but it rather provides comprehensive information on the examined technology. It is, therefore, necessary to refer to more sophisticated analysis tools that can show a more accurate picture of the development stage and helps designers to highlight points that deserve further attention and deeper analysis. The risk is to perform a very good demonstration test that can miss generality and remain confined only to that specific experimental campaign. Moving on to these assumptions, the authors expose three realizations of theirs concerning aeronautic morphing systems, to the analysis of a well-assessed Technology Readiness Level instrument. The aim is to define the aspects to be further assessed, the aspect to be considered fully mature, and even aspects that could miss some elementary point to attain full maturation. Such studies are not so frequent in the literature, and the authors believe to give a valuable, yet preliminary, contribution to the engineering of breakthrough systems. Without losing generality, the paper refers to the 2.2 version of a tool set up by the US Air Force Research Laboratory (AFRL), and NASA, with the aim to standardize the evaluation process of the mentioned nine-step TRL.

Simulation of a Scramjet Combustor: A Priori Study of Thermochemistry Tabulation Techniques

Large eddy simulations (LES) of a scramjet combustor are reported in this paper. The case under study is a cavity-based combustion chamber that is experimentally studied at the US Air Force Research Laboratory. The chamber is fed by eleven injectors. The computational domains are either simplified including only one or two injectors or complete with the 11 injectors. A good agreement is found between experimental data (velocities measured by PIV) and results from the LES if the kinetic used is chosen with care. A high temperature is found inside the cavity promoting a reactive zone located in the mixing layer where the flow velocity is high. At this location, the combustion occurs first in a diffusion dominated regime followed by the efficient burning of a well mixed mixture (rich then lean). A significant diffusion dominated burning is also found inside the cavity, mostly at the interface between the two recirculation zones. The simulation of the complete geometry revealed a transverse phenomenon on the temperature and mixing fields, but which had nevertheless little effect on the comparison with the available experimental data. A tabulation of the chemistry based on a premixed flamelet library without compressibility effects has been tested a priori on the results of the simulation with one injector. Good results on temperature and $$\hbox {H}_2\hbox {O}$$ fields are found. Significant localized discrepancies appeared on CO and $$\hbox {CO}_2$$ fields due to the complexity of the combustion regimes, while compressibility effects were found to be weak for the configuration studied.

Interview

interview

Accuracy Analysis of Aerodynamic Calculation of Twodimensional Ballistic correction Projectile based on Missile Datcom

Missile Datcom (hereinafter referred to as Datcom) is an aerodynamic engineering calculation software developed by the US Air Force Research Laboratory. It is commonly used in the preliminary design of the shape scheme of missiles, aircraft and other aircraft. In this paper, Datcom is used to calculate the aerodynamic parameters of a two-dimensional ballistic correction projectile(D2BCP), and the calculated data is compared with the wind tunnel test data. The analysis results show that Datcom calculates the axial force coefficient (CA) of the projectile with large system deviation, however, the deviation can be eliminated by a certain compensation, thereby obtaining a more accurate CA of the projectile. Datcom calculates the normal force coefficient (CN) with high Mach number accuracy, but there is an unacceptable deviation of the projectile CN calculated at small angle of attack ( α ). The calculation of pitching moment coefficient with α (CMa) is higher, but the error is larger under individual Mach numbers.

US Air Force Research Laboratory Perspective on Structural Health Monitoring in Support of Risk Management

The US Air Force (USAF) and US Department of Defense has a long history of research and development in the exploration of on-board sensors being used for detection of damage in aircraft structures. Initial activities can be traced to the early 1980’s which led to an extensive on-aircraft assessment of acoustic emission based (i.e. “passive) sensor system. In the late 1990’s an effort was launched to revitalize the capability which cumulated in the “Hot Spots” program which explored the use of an ultrasonic guided wave (i.e. “active”) sensor system. Each of these programs encountered challenges that have hindered the use of these technologies on fixed-wing military aircraft. This paper briefly reviews these previous efforts, present current USAF Military Standards that define Structural Health Monitoring (SHM) for fixed wing aircraft, and provide a discussion of current and future concepts for research and development to resolve these challenges and enable eventual adaptation of SHM for fixed-wing applications. This will include a summary of current initiatives within the Materials and Manufacturing Directorate of AFRL and notional thoughts on potential projects for future developments required for this capability to be applied to fixed wing military aircraft.

Effects of diluent on laminar burning speed and flame structure of gas to liquid fuel air mixtures at high temperatures and moderate pressures

Gas to liquid (GTL) fuel has gained attention recently because of its clean combustion behavior. Experimental studies have been performed to investigate fundamental combustion characteristics such as laminar burning speed and flame structure of GTL/air/diluent premixed flames. In the present study, the GTL fuel was designated by Syntroleum S-8, supplied by US Air Force Research Laboratory (AFRL), which was synthesized from natural gas using the Fisher–Tropsch (F–T) process. A mixture of 32% iso-octane, 25% n-decane and 43% n-dodecane by volume was used as a surrogate for GTL fuel. In this work, two diluent concentrations of 5% and 10% were used. The diluent is a blend of 86% N2 and 14% CO2 having the same specific heat as the burned gases. Experiments were conducted using a spherical vessel for laminar burning speeds measurement and a cylindrical vessel to investigate the flame structures. The cylindrical vessel was set up in a Z-shape Schlieren system coupled with a high-speed CMOS camera that was used to capture evolutionary behavior of flames at up to 40,000 frames per second. A multi-shell thermodynamic model was used to calculate the laminar burning speed for the smooth and low stretch flames. During the flame expansion, measured pressure rise as a function of time was the input into the thermodynamic model. Power law correlations for laminar burning speeds of GTL/air/diluent premixed flames over a wide range of temperatures (from 490 K to 610 K), pressures (from 0.5 atm to 3.2 atm), equivalence ratios (from 0.7 to 1.2), and two different diluent concentrations of 5% and 10% have been reported. Experimental burning speed results were compared with simulation values calculated by the solution of one dimensional steady premixed flame code from CANTERA using Ranzi’s chemical kinetics mechanisms. Results of simulations are close to the measured values.

US Air Force Research Lab using fuel cells to power lift platforms

US Air Force Research Lab using fuel cells to power lift platforms

The 5th International Conference on Science & Engineering in Mathematics, Chemistry and Physics 2017 (ScieTech 2017), The Ramada Bintang Hotel, Kuta, Bali, Indonesia 21 - 22 January 2017

The 5th International Conference on Science & Engineering in Mathematics, Chemistry and Physics 2017 (ScieTech 2017), The Ramada Bintang Hotel, Kuta, Bali, Indonesia 21 - 22 January 2017

A Quantitative Metric to Enable Unmanned Aircraft Systems to Remain Well Clear

A critical challenge for integrating Unmanned Aircraft Systems (UAS) is developing a means to sense and avoid (SAA) other aircraft. One of the main functions of SAA is to ensure the UAS remains well clear from other air traffic. Human pilots determine well clear subjectively, but SAA systems need a quantified alternative means of compliance. The UAS Science and Research Panel (SARP) brought together key researchers to define guiding principles for UAS Well Clear (UWC). The SARP aligned research efforts from NASA, MIT Lincoln Laboratory, and the US Air Force Research Laboratory to evaluate three UWC candidates in four simulation environments. These UWC candidates were evaluated against eight agreed operational suitability metrics, resulting in a recommended quantitative definition for UWC. This paper will describe the technical rationale for this recommendation, subsequent operational considerations, and potential to extend the work to small UAS.

Challenges in Measuring External Currents Driven by the Solar Wind-Magnetosphere Interaction

In studying the Earth's geomagnetism, it has always been a challenge to separate magnetic fields from external currents originating from the ionosphere and magnetosphere. While the internal magnetic field changes very slowly in time scales of years and more, the ionospheric and magnetospheric current systems driven by the solar wind -magnetosphere interaction are very dynamic. They are intimately controlled by the ionospheric electrodynamics and ionospheremagnetosphere coupling. Single spacecraft observations are not able to separate their spatial and temporal variations, and thus to accurately describe their configurations. To characterize and understand the external currents, satellite observations require both good spatial and temporal resolutions. This paper reviews our observations of the external currents from two recent LEO satellite missions: Space Technology 5 (ST-5), NASA's first three-satellite constellation mission in LEO polar orbit, and Communications/Navigation Outage Forecasting System (C/NOFS), an equatorial satellite developed by US Air Force Research Laboratory. We present recommendations for future geomagnetism missions based on these observations.

Composites come together

In the future, composites will incorporate electronic and optoelectronic functionality and tailorability into structural components. This will require the efforts and collaboration of a diverse range of sectors, says Richard A. Vaia of the US Air Force Research Laboratory in conversation with Cordelia Sealy.Download : Download full-size image Richard A. Vaia.

Vestibulo‐ocular Reflex (VOR) Impact on USAF Undergraduate Pilot Training Proficiency

Objectives: The US Air Force (USAF) enrolls 1400 Specialized Undergraduate Pilot Trainees (SUPT) at 3 locations within the United States each year. SUPT training has an estimated accumulated cost of $1M to $1.5M per trainee. Attrition rates from training have ranged from 7.8% to 36.9%. The cost associated with trainee disqualification is estimated at $1M per percentage point of annual attrition. One percent of UPT disqualifications are due to medical factors and another 1.5% are due to failure to adapt to flying. Methods: In 1994 the USAF conducted rotary chair vestibulo-ocular (VOR) test on 150 SUPT candidates at the USAF Research Laboratory, Brooks Air Force Base as part of the second phase of the Enhanced Flight Screening- Medical Study (EFS-M). Retrospective review of SUPT scores was correlated with pre-training VOR test results of the original 150 pilots who participated in the EFS-M VOR data collection. Twenty-year prospective survey data collected from EFS-M study pilots was correlated to initial EFS-M VOR test results to identify trends in their subsequent pilot career progression and incidence of in-flight physiologic events deemed linked to vestibular illusions. Results: VOR performance trends exist between USAF pilot trainee cohorts. VOR performance can predict initial flight training proficiency in SUPT candidates. Long term follow-up survey responses indicate that VOR performance can predict flight career proficiency in SUPT training candidates. Conclusions: A validated correlation between VOR results and flight performance can help establish VOR test parameters associated with successful flight training ability.

Symposium: Neuroergonomics, technology, and cognition

This symposium describes collaborative research on neuroergonomics, technology, and cognition being conducted at George Mason University and the US Air Force Research Laboratory (AFRL) as part of the Center of Excellence in Neuroergonomics, Technology, and Cognition (CENTEC). Six presentations describe the latest developments in neuroergonomics research conducted by CENTEC scientists. The individual papers cover studies of: (1) adaptive learning systems; (2) neurobehavioral synchronicity during team performance; (3) genetics and individual differences in decision making; (4) vigilance and mindlessness; (5) interruptions and multi-tasking; and (6) development of a simulation capability that integrates measures across these domains and levels of analysis.

Aeroelastic and Aerothermoelastic Analysis in Hypersonic Flow: Past, Present, and Future

H YPERSONIC flight began in February 1949 when a WAC Corporal rocket was ignited from a U.S.-captured V-2 rocket [1]. In the six decades since this milestone, there have been significant investments in the development of hypersonic vehicle technologies. The NASA X-15 rocket plane in the early 1960s represents early research toward this goal [2,3]. After a lull in activity, the modern era of hypersonic research started in the mid-1980s with the National Aerospace Plane (NASP) program [4], aimed at developing a single-stage-to-orbit reusable launch vehicle (RLV) that used conventional runways. However, it was canceled due mainly to design requirements that exceeded the state of the art [1,5]. A more recent RLV project, the VentureStar program, failed during structural tests, again for lack of the required technology [5]. Despite these unsuccessful programs, the continued need for a low-cost RLV, as well as the desire of the U.S. Air Force (USAF) for unmanned hypersonic vehicles, has reinvigorated hypersonic flight research. An emergence of recent and current research programs [6] demonstrate this renewed interest. Consider, for example, the NASA Hyper-X experimental vehicle program [7], the University of Queensland HyShot program [8], the NASA Fundamental Aeronautics Hypersonics Project [9], the joint U.S. Defense Advanced Research Projects Administration (DARPA)/USAF Force Application andLaunch fromContinentalUnited States (FALCON) program [10], the X-51 Single Engine Demonstrator [11,12], the joint USAF Research Laboratory (AFRL)/Australian Defence Science and Technology Organisation Hypersonic International Flight Research Experimentation project [13], and ongoing basic hypersonic research at the AFRL (e.g., [14–20]). The conditions encountered in hypersonic flows, combined with the need to design hypersonic vehicles, have motivated research in the areas of hypersonic aeroelasticity and aerothermoelasticity. It is evident from Fig. 1 that hypersonic vehicle configurations will consist of long, slender lifting body designs. In general, the body, surface panels, and aerodynamic control surfaces are flexible due to minimum-weight restrictions. Furthermore, as shown in Fig. 2, these

SPRAY CHARACTERISTICS OF A PRESSURE-SWIRL FUEL INJECTOR SUBJECTED TO A CROSSFLOW AND A COFLOW

An analysis of fuel spray was conducted using flow visualization and phase Doppler particle anemometry (PDPA) in an experimental facility housed at the Propulsion Directorate of the US Air Force Research Laboratory (AFRL). In order to model typical real-world aircraft engine conditions, this test facility was equipped with a pressure-swirl injector in combination with heated crossflow air normal to the fuel (JP-8) injection and, optionally, with coflow air parallel to the primary direction of fuel injection. Results are presented for fixed fuel rate (Reynolds number for the liquid flow of 9200 and a liquid jet Weber number of 7100) and varied crossflow velocity for four momentum flux ratios. Flow visualization and coherent structure velocimetry clearly demonstrated how the crossflow reoriented the conical spray pattern and led to large spatial variation in the measured Sauter mean diameter. At locations downstream of the injector, the PDPA data demonstrated that the vertical component of velocity was relatively low for small droplets and high for large drop sizes. This bimodal behavior may be rationalized by considering the initial propagation direction of the spray, the residence time of the fuel droplets, and the shear of the surrounding flow field. The addition of a coflow stream of air to the system led to significant reductions in Sauter mean diameter of the droplets in the region of the spray cone downstream of the fuel injector. The coflow also tended to disrupt the bimodality of the drop size distribution.

Protonex to extend soldier-worn portable power management

Massachusetts-based Protonex Technology has received a $3 million contract from the US Air Force Research Laboratory (AFRL), to develop its next-generation soldier-worn portable power managers (SPMs). These units dramatically reduce a soldier's logistics burden, by minimizing the number and type of batteries a soldier needs to carry.

Nonlinear Flight Control Systems Design for Hypersonic Vehicles: Results and Open Problems

Air-breathing hypersonic vehicles (HSVs) are regarded as one of the most promising technology for achieving reliable and cost-effective access to space. Notwithstanding the recent successes of NASA's X-43A and AFRL's X-51 experimental vehicles, the design of flight control systems for HSVs is still an open problem, due to the complexity of the dynamics and the unprecedented level of coupling between the airframe and the propulsion system. The slender geometries and light structures required for these aircraft cause significant flexible effects, whereas a strong coupling between propulsive and aerodynamic forces results from the integration of the scramjet engine into the fuselage. Because of the variability of the vehicle characteristics with flight conditions, significant uncertainties affect the vehicle models, which in turn are known to be unstable and non-minimum phase with respect to the regulated output. Finally, the presence of unavoidable constraints on the control inputs and the stringent requirements imposed by hypersonic regimes on the flight envelope render the control design an even harder endeavor, especially concerning controlling the propulsion system. In this paper, we present an account of nonlinear adaptive control techniques that have been developed, in collaboration with the US Air Force Research Laboratories, towards the design of flight control systems for HSVs. In particular, we present several steps leading to the design of a flight control system architecture comprised of a robust adaptive inner-loop controller and a self-optimizing guidance system. Finally, we briefly discuss open problems and current research directions.

Computer modelling of magnetotherapy in orthopedic treatments

PurposeThe paper aims to clarify the method/methodology of establishing a computer model of the electromagnetic therapy connected with some knee joint problems. Two cases are considered: the arthritis of the knee and the fracture of bone. In both cases the analysis of eddy current distribution in the knee is made. It gives results which can be helpful in the planning of treatment. The paper presents the exemplary results of eddy current distribution inside a bone. A short discussion on the safety aspect of magnetotherapy has been carried out.Design/methodology/approachIn order to calculate the eddy current distribution in human knee joint the low frequency finite‐difference time‐domain algorithm has been applied. The numerical model of the leg was based on US Air Force Research Laboratory data and the electrical properties of tissues were modeled using 4‐Cole‐Cole approximation with parameters taken from Gabriels.FindingsThe paper presents the general methodology which can be used in magnetotherapy to estimate a magnetic flux density of stimulators and value of current density inside the knee joint. Both factors mentioned above can be helpful in therapeutical processes, i.e. in magnetoteraphy.Research limitations/implicationsThe eddy current distribution is limited to the presented model and it is obvious it can be different for another one as it is shown in the paper but it is also shown that the biggest value of eddy current density is just in the vicinity of the joint, so it can help in a therapeutical process.Practical implicationsThe methodology of estimating the values of current density and magnetic flux density can be used by physiologists and doctors to determine the value of current density which gives therapeutical effect.Originality/valueThe efficient application of low frequency finite‐difference time‐domain algorithm to the electromagnetic therapy connected with some knee joint problems has been shown and the general methodology has been conducted.

Commentary: Natural nanophotonics

The US Air Force Research Laboratory, Materials and Manufacturing Directorate (AFRL/RX) is heading up an international team of government, industrial and university researchers investigating biologically based (natural) materials and devices for electronic and photonic applications. This opens up an exciting new field for bioengineering demonstrating that biotechnology can benefit many areas, in addition to genomic sequencing and clinical diagnosis and treatment alone.