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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.

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.

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.

In this paper, a parametric average-value modeling approach is applied to a high-frequency six-phase aircraft generation subsystem. This approach utilizes a detailed switch-level model of the system to numerically establish the averaged dynamic relationships between the ac inputs of the rectifier and the dc-link outputs. A comparison between the average-value and detailed models is presented, wherein, the average-value model is shown to accurately portray both the large-signal time-domain transients and the small-signal frequency-domain characteristics. Since the discontinuous switching events are not present in the average-value model, significant gains can be realized in the computational performance. For the study system, the developed average-value simulation executed more than two orders of magnitude faster than the detailed simulation.

Future Air Force intelligence, surveillance, and reconnaissance (ISR) platforms, such as high-altitude Uninhabited Aerial Vehicles (UAV), may drastically change the requirements of aircraft power systems. For example, there are potential interactions between large pulsed-power payloads and the turbine engine that could compromise the operation of the power system within certain flight envelopes. Until now, the development of large-scale, multi-disciplinary (propulsion, electrical, mechanical, hydraulic, thermal, etc.) simulations to investigate such interactions has been prohibitive due to the size of the system and the computational power required. Moreover, the subsystem simulations that are developed separately often are written in different commercial-off-the-shelf simulation programs.

Flow rate monitoring plays a crucial role for precise motion control in many hydraulic systems and for detection of faults and fluid loss in hydraulic system components and circuits. In some situations, however, direct measurement of fluid flow is not possible. Besides, flowmeters are generally non-robust, expensive, and slow in response. In this paper, we have proposed an alternative approach to direct flow measurement for circuits that contain a combination of proportional valves and actuators. A nonlinear state-space representation is used to model the valve orifice area variation with respect to the valve spool position. Kalman Filtering is then utilized to estimate the valve's orifice area in real-time by fusing data from robust low-cost pressure transducers and position sensors. A close agreement is achieved between the estimated and the measured orifice areas for a valve with a complex wedge-shape orifice profile.

This paper examines the combustion and emissions produced using a prototype fuel injector nozzle for pilot-ignited direct-injection natural gas engines. In the new geometry, 7 individual equally-spaced gas injection holes were replaced by 7 pairs of closely-aligned holes (“paired-hole nozzle”). The paired-hole nozzle was intended to reduce particulate formation by increasing air entrainment due to jet interaction. Tests were performed on a single-cylinder research engine at different speeds and loads, and over a range of fuel injection and air handling conditions. Emissions were compared to those resulting from a reference injector with equally spaced holes (“single-hole nozzle”). Contrary to expectations, the CO and PM emissions were 3 to 10 times higher when using the paired-hole nozzles. Despite the large differences in emissions, the relative change in emissions in response to parametric changes was remarkably similar for single-hole and paired-hole nozzles.

Ice and snow accretion on aircraft surfaces imposes operational and safety challenges, severely impacting aerodynamic performance of critical aircraft structures and equipment. For optimized location-based ice sensing and integrated ‘smart’ de-icing systems of the future, microwave resonant-based planar sensors are presented for their high sensitivity and versatility in implementation and integration. Here, a conformal, planar complementary split ring resonator (CSRR) based microwave sensor is presented for robust detection of localized ice and snow accretion. The sensor has a modified thick aluminum-plate design and is coated with epoxy for greater durability. The fabricated sensor operates at a resonant frequency of 1.18 GHz and a resonant amplitude of -33 dB. Monitoring the resonant frequency response of the sensor, the freezing and thawing process of a 0.1 ml droplet of water is monitored, and a 60 MHz downshift is observed for the frozen droplet.

Traction tests were run during February, 1993 and 1994. The snow tests were conducted at a fairly constant temperature of -2°C and the ice tests at an air temperatures ranging from -4 to -35°C. The test vehicles were a standard midsize automobile and highway maintenance gravel trucks. The automobiles on packed snow at -6°C has an average braking force coefficient of 0.35, a lateral force coefficient of 0.38 and a traction force coefficient of 0.20. The corresponding values for a straight truck are: 0.23, 0.35 and 0.15. An automobile on bare ice at -6°C has an average braking force coefficient and lateral force coefficient of 0.09, and a traction force coefficient of about 0.08. The valves for the truck on bare ice in the same order are 0.06, 0.07 and about 0.04. A relationship was developed between the average braking force coefficient, ambient temperature and the amount of standard highway winter aggregate used on the road.

The movement to more-electric architectures during the past decade in military and commercial airborne systems continues to increase the complexity of designing and specifying the electric power system. In particular, the electrical power system (EPS) faces challenges in meeting the highly dynamic power demands of advanced power electronics based loads. This paper explores one approach to addressing these demands by proposing an electrical equivalent of the widely utilized hydraulic accumulator which has successfully been employed in hydraulic power system on aircraft for more than 50 years.