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To obtain a system level, integrated perspective on vehicle energy management, the traditional methods for conducting preliminary design, gauging independent requirements, must be abandoned. This method does not capture critical interactions between the various aircraft subsystems. Instead, a more global appreciation for interactions across boundaries needs to be realized with a mosaic scheme, where models are integrated and co-simulated. The advantage of this approach is to enhance the preliminary design stage by predicting integration issues early in the development process. Legacy design practice involved gathering data from multiple vendors in order to produce design iterations. The ability to link models directly is extremely beneficial, as requirements no longer have to be executed independently. This approach reduces cumbersome iterations between model owners and accelerates trade studies.

The optimal integration of vehicle subsystems is of critical importance in the design of future energy efficient fighter aircraft. The INVENT (INtegrated Vehicle ENergy Technology) program has been dedicated to this endeavor through modeling/simulation of thermal management, power generation & distribution, & actuation subsystems. Achieving dual cooling & power generation capability from a single subsystem would be consistent with current efforts in system integration optimization. In this paper, we present a reconfiguration of an archetypal closed-loop air cycle system for a modern fighter as an open-loop gas generator cycle operating interchangeably between refrigeration and auxiliary power modes. A numerical model was developed within NPSS to assess maximum power extraction capabilities of a system originally designed for cooling purposes under different operating conditions.

Current industry trends demonstrate aircraft electrification will be part of future platforms in order to achieve higher levels of efficiency in various vehicle level sub-systems. However, electrification requires a substantial change in aircraft design that is not suitable for re-winged or re-engined applications as some aircraft manufacturers are opting for today. Thermal limits arise as engine cores progressively get smaller and hotter to improve overall engine efficiency, while legacy systems still demand a substantial amount of pneumatic, hydraulic and electric power extraction. The environmental control system (ECS) provides pressurization, ventilation and air conditioning in commercial aircraft, making it the main heat sink for all aircraft loads with exception of the engine fuel thermal management system.