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The two primary wire construction types being used in military aircraft today are cross-linked Ethylene Tetrafluoroethylene (XL-ETFE) and composite fluoropolymer / polyimide tape wrap with an outer Polytetrafluoroethylene (PTFE) tape wrap. These insulations offer significant improvements over earlier polyimide (MIL-DTL-81381) and polyvinyl chloride (PVC) constructions but are not without drawbacks. XL-ETFE provides a low smoke, high fluid resistant, non-arc tracking insulation that is durable during installation and ground repair operations. However, durability and abrasion resistance are reduced at elevated temperatures, and maximum operating temperature peaks at 200 degrees Celsius. Composite insulation provides a more abrasion resistant solution with the inclusion of polyimide tape for hard surface chafe conditions and a PTFE outer layer that improves wear life during wire to wire contact.

This paper describes GEM Power's Total Battery Management System (TBMS), a new approach to the management of all battery types including aviation batteries, by means of treatment and analysis of a matrix of battery parameters (MoP). In addition to current and voltage, the MoP includes battery ohmic resistance (Rohm), chemical resistance (Rch), electrical double layer capacity (EDLC) and battery instantaneous open circuit voltage (Ei). The MoP is created by collecting the battery's stationary and transient voltage responses to specifically designed charging/depol pulses.

The AFRL, Electrochemistry and Thermal Sciences Branch has evaluated numerous aircraft battery designs and chemistries since the 1960s. Recent experiments on advanced battery chemistries have shown poor performance at ultra low temperatures below −20° C. Aircraft battery designs stress low weight and volume and maximum capacity. One design concept uses lower capacity cells in a series parallel configuration to reduce overall battery resistance and should also improve ultra low temperature performance. Our organization has begun experiments with series-parallel cell designs to evaluate the concept and to solve low temperature performance issues. Progress, observations on the effect of different chemistries, and the impact on aircraft battery characteristics are discussed.

In this paper, a new control strategy is proposed which is simple in structure and has the straightforward goal of minimizing the stator current amplitude for a given load torque. It is shown that the resulting induction motor efficiency is reasonably close to optimal and that the approach is insensitive to variations in rotor resistance. Although the torque response is not as fast as in field-oriented control strategies, the response is reasonably fast. In fact, if the mechanical time constant is large relative to the rotor time constant, which is frequently the case, the sacrifice in dynamic performance is insignificant relative to FO strategies.

Aviation battery maintenance is trending toward maintenance on-condition. NiCd, VRLA, or prospective Li-ion batteries are used to start engines, provide emergency back-up power, and assure ground power capability for maintenance and pre-flight checkout. As these functions are mission essential, State of Health (SoH) recognition is critical. GEM Power has developed a technological approach for SoH recognition, based on a battery equivalent schematic. The schematic is derived from a Matrix of Parameters (MoP), which includes ohm resistance, chemical resistance, electrical double layer capacity (EDLC), and open circuit voltage (OCV) [1].

Poly Alpha Olefins (PAO) are extensively used as cooling fluid for thermal management in avionics cooling applications owing to their superior physical and chemical properties, such as greater fluidity at low temperature, lower volatility, a higher viscosity index, lower pour point, better oxidative and thermal stability as well as low toxicity. Solvents doped with minute concentration of nanoparticles are termed as “Nanofluid”. Anomalous enhancements in thermo-physical property values as well as in heat transfer performance of nanofluids have been reported using nanofluids (compared to that for the neat solvent). The thermal interfacial resistance between the nanoparticle and the solvent molecules (Kapitza Resistance) is the dominant factor controlling the efficacy of the nanofluids for cooling applications.

There is a need to develop improved film capacitors for high temperature, high energy density and high reliability applications. The work reported here has resulted in self-healing capacitor technology applicable to a wide variety of polymer film substrates that prevents catastrophic failures and provides safe, reliable operation in power electronic circuits. This paper describes the performance of 500-2000 Volt metalized film capacitors operating at up to 160°C under a variety of duty conditions. Data on equivalent series resistance (ESR) and power dissipation (DF), peak and Root Means Square (RMS) current ratings, and other critical performance parameters are presented. The features and benefits of both dry wrap-and-fill and liquid-impregnated hermetically sealed constructions are discussed. This work was sponsored by the US Army Research Laboratory.

This paper presents a summary of a Honeywell collaborative IR&D project for development of a high-performance sensorless method for a Permanent Magnet Synchronous Motor (PMSM) based on Extended Kalman Filter (EKF). The parameters of a high speed 90kW industrial PMSM is employed for validating the proposed sensorless method through simulation. The simulation results demonstrate that the sensorless PMSM drive can work satisfactorily over the whole speed range with full torque and speed control accuracy. With the proposed flux linkage estimator, the new sensorless PMSM drive exhibits robustness against machine parameter variations. Good performance is obtained even when the stator resistance is changed by 200%, or the flux linkage is weakened by 20%. Detailed design and modeling of the sensorless PMSM drive are described in this paper.

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.

New generation, high purity, Thin Plate Pure Lead/Tin (TPPL) Valve Regulated Lead-Acid batteries (VRLA) from EnerSys offer major benefits over competing lead-acid and nickel-cadmium systems. The advantages of the TPPL technology include higher engine start capability over a wide range of temperature extremes, extended storage life, reduced maintenance and operating costs, weight reduction, rapid recharge capability, deep discharge recovery and enhanced vibration resistance. As a consequence of the benefits highlighted above, TPPL products are gaining wide acceptance in both military and civil aircraft applications, previously dominated by nickel-cadmium and/or the conventional lead-acid systems.

Paralleling synchronous generators requires a priori voltage matching and frequency synchronization. Exceeding normal limits can lead to severe electrical transients. The classical three-phase short circuit analysis is extended to include the case of two initially unloaded synchronous generators. An analytical solution is developed neglecting winding resistances and saturation. Of particular interest is the tendency to induce negative field currents that cause inverse voltages across the rotating rectifier in a brushless design. Typical aircraft generator parameters are used to predict the paralleling transient vs. initial rotor electrical angle mismatch. Results are compared to simulation and limited test results.

Heat transfer by phase change is an attractive method of cooling since large amounts of heat can be removed with relatively small temperature differences. Droplet cooling is one method whereby very high heat transfer rates coupled with good temperature uniformity across surfaces can be provided, which is important in microelectronics where even small temperature gradients across the chip can cause component failure. When a droplet strikes a heated surface, it flattens into a splat whose thickness is much smaller than the diameter of the droplet, and high heat fluxes can be obtained due to the formation and evaporation of a thin liquid film on the heated surface. In this study, time and space resolved heat transfer characteristics for a single droplet striking a heated surface were experimentally measured, and the results are compared to a model of droplet evaporation.

Molten salts are ionic, nonflammable, nonvolatile liquids with high ionic conductivity, oxidation voltage greater than 5 V vs. Li and high thermal stability (>300°C). So far the application of molten salts in batteries has been limited to those operating at relatively high temperature (>150°C). Rechargeable lithium-ion and lithium batteries have attained wide acceptance in both commercial and military applications. However, most of the solvents used in these cells are volatile and flammable; hence, they represent a significant safety hazard, especially, when operated at higher temperatures. Therefore the application of molten salts as electrolytes in lithium and lithium-ion cells containing LiMn2O4 (cathode) was investigated. The preliminary results show that rechargeable lithium and lithium-ion cells can be constructed and operated using molten salts as electrolytes. Test cells were cycled at ambient temperature and at higher temperature (55°C).

Two recent studies highlight the unique cooling requirements of Directed Energy Weapons (DEW) and identify methods to address these requirements. Both systems generate substantial heat loads, one requiring more than 1 MW of cooling. Furthermore, much of the heat is generated within a small volume, resulting in a high heat flux. Both spray cooling with ammonia and microchannel heat exchangers with de-ionized water or ammonia were considered. In each case it was determined that the ultimate heat sink would be the ambient air. In one study the heat transfer process was more challenging due to a relatively narrow allowable temperature range and a maximum allowable temperature near the ambient air temperature. Heat transfer options considered the use of a liquid loop with either direct ram air cooling, an air cycle cooling system, and a vapor cycle cooling system.