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Small remotely piloted aircraft (10-25 kg) powered by internal combustion engines typically operate on motor gasoline, which has an anti-knock index (AKI) of >80. To comply with the single-battlefield-fuel initiative in DoD Directive 4140.25, interest has been increasing in converting the 1-10 kW power plants in the aforementioned size class to run on lower AKI fuels such as diesel and JP-8, which have AKIs of ~20. It has been speculated that the higher losses (short-circuiting, incomplete combustion, heat transfer) that cause these engines to have lower efficiencies than their conventional-scale counterparts may also relax the fuel-AKI requirements of the engines. To investigate that idea, the fuel-AKI requirement of a 3W-55i engine was mapped and compared to that of the engine on the manufacturer-recommended 98 octane number (ON) fuel.

As the cost and complexity of modern aircraft systems increases, emphasis has been placed on model-based design as a means for reducing development cost and optimizing performance. To facilitate this, an appropriate modeling environment is required that allows developers to rapidly explore a wider design space than can cost effectively be considered through hardware construction and testing. This wide design space can then yield solutions that are far more energy efficient than previous generation designs. In addition, non-intuitive cross-coupled subsystem behavior can also be explored to ensure integrated system stability prior to hardware fabrication and testing. In recent years, optimization of control strategies between coupled subsystems has necessitated the understanding of the integrated system dynamics.

Future aircraft systems are projected to have order of magnitude greater power and thermal demands, along with tighter constraints on the performance of the power and thermal management subsystems. This trend has led to the need for a fully integrated design process where power and thermal systems, and their interactions, are considered simultaneously. To support this new design paradigm, a general framework for codifying and checking specifications and requirements is presented. This framework is domain independent and can be used to translate requirement language into a structured definition that can be quickly queried and applied to simulation and measurement data. It is constructed by generalizing a previously developed power quality analysis framework. The application of this framework is demonstrated through the translation of thermal specifications for airborne electrical equipment, into the SPecification And Requirement Evaluation (SPARE) Tool.

The rapid expansion of the market for remotely piloted aircraft (RPA) includes a particular interest in 10-25 kg vehicles for monitoring, surveillance, and reconnaissance. Power-plant options for these aircraft are often 10-100 cm3 internal combustion engines. Both power and fuel conversion efficiency decrease with increasing rapidity in the aforementioned size range. Fuel conversion efficiency decreases from ∼30% for conventional-scale engines (>100 cm3 displacement) to <5% for micro glow-fuel engines (<10 cm3 displacement), while brake mean effective pressure decreases from >10 bar (>100 cm3) to <4 bar (<10 cm3). Based on research documented in the literature, the losses responsible for the increase in the rate of decreasing performance cannot be clearly defined. Energy balances consisting of five pathways were experimentally determined on two engines that are representative of Group-2 RPA propulsion systems and compared to those in the literature for larger and smaller engines.

The performance of a more-electric aircraft (MEA) power system electrical accumulator unit (EAU) architecture consisting of a 57000 rpm induction machine (IM) coupled to a controllable shaft load and controlled using direct torque control (DTC) is examined through transient modeling and simulation. The simplicity and extremely fast dynamic torque response of DTC make it an attractive choice for this application. Additionally, the key components required for this EAU system may already exist on certain MEA, therefore allowing the benefits of EAU technology in the power system without incurring a significant weight penalty. Simulation results indicate that this architecture is capable of quickly tracking system bus power steps from full regenerative events to peak load events while maintaining the IM's speed within 5% of its nominal value.

This paper presents the concept of a dual latent heat sink for thermal management of pulse heat generating electronic systems. The focus of this work is to verify the effectiveness of the concept during charging through experimentation. Accordingly, custom components were built and a prototype version of the heat sink was fabricated. Experiments were performed to investigate the implementation feasibility and heat transfer performance. It is shown that this heat sink is practicable and helps in arresting the system temperature rise during charging (period of pulse heat load).

A unique perspective of system integration is presented in terms of statistical design and analysis. Advanced statistical concepts are employed to quantify the variance of the statistical models as well as to specify model truncation error. Three models are developed for this study: 1) a supersonic wing section; 2) a supersonic turbojet system and; 3) an integrated supersonic wing section and supersonic turbojet. The three models are analyzed and separately and surrogate models are developed for each model independently using Design of Experiments and advanced statistical analyses. The individual surrogate models are statistically validated compared to their respective models. The individual wing and turbojet surrogate models are then used to estimate the performance of the combined wing and turbojet system surrogate model performance.

An IPTMS hardware facility has been established in the laboratories of the Aerospace Systems Directorate of the Air Force Research Laboratory (AFRL) at Wright-Paterson Air Force Base (WPAFB). This hardware capability was established to analyze the transient behavior of a high power Electrical Power System (EPS) coupled virtually to a Thermal Management System (TMS) under fast dynamic loading conditions. The system incorporates the use of dynamic electrical load, engine emulation, energy storage, and emulated thermal loads operated to investigate dynamics under step load conditions. Hardware architecture and control options for the IPTMS are discussed. This paper summarizes the IPTMS laboratory demonstration system, its capabilities, and preliminary test results.

The two-phase flow modeling is done using the level set method to identify the interface of vapor and liquid. The modifications to the incompressible Navier-Stokes equations to consider surface tension, viscosity, gravity and phase change are discussed in detail. The governing equations are solved using finite difference method. In the present work, investigations on the effect of thermal conductivity and latent heat of vaporization of liquid on heat transfer in a 44 µm thick liquid film containing vapor bubble with droplet impact is investigated. The importance of thermal conductivity and latent heat of vaporization of liquid on heat transfer is identified. The variation of heat flux with thermal conductivity and latent heat is plotted. The computed liquid and vapor interface, velocity vector and temperature distributions at different time instants are also visualized for better understanding of the heat removal.

Advances in the past decade of the energy and power densities of lithium-ion based batteries for hybrid electric vehicles and various consumer applications have been substantial. Rechargeable high rate lithium-ion batteries are now exceeding 6 kW/kg for short discharge times (<15 seconds). Rechargeable lithium-ion polymer batteries, for applications such as remote-control aircraft, are achieving simultaneously high energy density and high power density (>160 Whr/kg at >1.0 kW/kg). Some preliminary test data on a rechargeable lithium-ion polymer battery is presented. The use of high rate rechargeable lithium-ion batteries as a function of onboard power, electric laser power level, laser duty cycle, and total mission time is presented. A number of thermal management system configurations were examined to determine system level weight impacts. Lightweight configurations would need a regenerative thermal energy storage subsystem.

Aircraft power demands continue to increase with the increase in electrical subsystems. These subsystems directly affect the behavior of the power and propulsion systems and can no longer be neglected or assumed linear in system analyses. The complex models designed to integrate new capabilities have a high computational cost. This paper investigates the possibility of using a hardware-in-the-loop (HIL) analysis with real time integration. A representative electrical power system is removed from a turbine engine model simulation and replaced with the appropriate hardware attached to a 350 horsepower drive stand. In order to update the model to proper operating conditions, variables are passed between the hardware and the computer model. Using this method, a significant reduction in runtime is seen, and the turbine engine model is usable in a real time environment. Scaling is also investigated for simulations to be performed that exceed the operating parameters of the drive stand.

The interdependency between propulsion, power, and thermal subsystems on military aircraft such as the F-35 Joint Strike Fighter (JSF) and F-22 Raptor continues to increase as advanced war-fighting capabilities including solid-state radars, electronic attack, electric actuation, and Directed Energy Weaponry (DEW) expand to meet Air Force needs. Novel analysis and testing methodologies are required to predict these interdependencies and address adverse interactions prior to costly hardware prototyping. As a result, the Air Force Research Laboratory (AFRL) has established a dynamic hardware-in-the-loop (HIL) test-bed wherein transient simulations can be integrated through advanced real-time simulation with prototype hardware for integrated system studies and analysis. This paper details a test-bed configuration where a dynamic simulation of an aircraft turbine engine is utilized to control a dual-head electric drive stand.

The Wireless Integrated Cockpit Information Display (WICID) program developed a method for pilots to remotely control and display carry-on laptop based applications from the aircraft cockpit. Because flight safety concerns do not allow the pilot/copilot to use the standard keyboard and mouse devices during flight, the WICID program developed a multifunction display (MFD) that uses customized input devices such as bezel keys and a touch screen. The subsequent design of the WICID system became especially valuable in enhancing certain technologies critical to the military cockpit. This paper will address how the WICID system topology is uniquely suited to improve cockpit access to four main technology categories: Enhanced Situation Awareness (SA), Mission Planning/On-board Replanning, Enhanced Communication, and Navigation Aids.

The Wireless Integrated Cockpit Information Display (WICID) program originated as a request to remotely control and display laptop based applications from a cockpit without use of the standard keyboard and mouse devices. The resulting system utilized multifunction displays to allow control and display from a single device. The foundations of this system are divided into three technologies: 1) remote display, 2) customized input interface, and 3) application control. This modular approach provides a highly flexible and extendible system capable of remotely controlling several Microsoft Windows based applications, hosted across several processors, without requiring any modifications to those applications.

The Engine Supplier Base Initiative (ESBI) is a joint Air Force/Industry cooperative agreement aimed at achieving affordable precision investment cast airfoil and large structural components for man-rated gas turbine engines. The ESBI program will obtain these goals through the implementation of business and technology improvements with specific focus on increased product quality and reduced cycle time. This program has brought together competitors in the business to solve sector wide problems. This paper presents the framework of the teaming approach as well as results achieved in quality and cycle time improvements through technical and business process improvements.

The concept of geomagnetic cutoff rigidities is presented in relation to the determination of radiation dosage from galactic cosmic rays and solar proton events. Examples for both aircraft routes and spacecraft orbits are presented.

Aircraft power demands continue to increase with the increase in electrical subsystems. These subsystems directly affect the behavior of the power and propulsion systems and can no longer be neglected or assumed linear in system analyses. The complex models designed to integrate new capabilities have a high computational cost. Hardware-in-the-loop (HIL) is being used to investigate aircraft power systems by using a combination of hardware and simulations. This paper considers three different real-time simulators in the same HIL configuration. A representative electrical power system is removed from a turbine engine simulation and is replaced with the appropriate hardware attached to a 350 horsepower drive stand. Variables are passed between the hardware and the simulation in real-time to update model parameters and to synchronize the hardware with the model.

A primary challenge in performing integrated system simulations is balancing system simulation speeds against the model fidelity of the individual components composing the system model. Traditionally, such integrated system models of the electrical systems on more electric aircraft (MEA) have required drastic simplifications, linearizations, and/or averaging of individual component models. Such reductions in fidelity can take significant effort from component engineers and often cause the integrated system simulation to neglect critical dynamic behaviors, making it difficult for system integrators to identify problems early in the design process. This paper utilizes recent advancements in co-simulation technology (DHS Links) to demonstrate how integrated system models can be created wherein individual component models do not require significant simplification to achieve reasonable integrated model simulation speeds.

As aircraft continue to increase their power and thermal demands, transient operation of the power and propulsion subsystems can no longer be neglected at the aircraft system level. The performance of the whole aircraft must be considered by examining the dynamic interactions between the power, propulsion, and airframe subsystems. Larger loading demands placed on the power and propulsion subsystems result in thrust, speed, and altitude transients that affect the aircraft performance and capability. This results in different operating and control parameters for the engine that can be properly captured only in an integrated system-level test. While it is possible to capture the dynamic interactions between these aircraft subsystems by using simulations alone, the complexity of the resulting system model has a high computational cost.

Modern military engines desire both the fuel efficiency of high-bypass turbofans and the high specific thrust of a low-bypass turbofan. Using traditional engine architectures, performance and efficiency are in conflict, so an engine is usually designed to best meet requirements for its primary mission. While the concept of a variable cycle engine is not new, recent advances in engine architecture technology suggest that adding a second bypass stream to a traditional turbofan can provide significant benefits. This “third stream” (the core flow being the primary stream and the inner bypass being the second stream) airflow can be independently modulated so that engine airflow demand can be matched with the available inlet flow at a variety of operating points, thereby reducing spillage drag. Additionally, the third stream air provides a valuable heat sink for cooling turbine cooling air or dissipating other aircraft heat loads.