Multi-role fighter aircraft are facilitated by operational and platform capabilities that are in turn supported by basic aircraft function. Thermal management (TM) is a basic aircraft function. Effective TM design at the aircraft concept stage can determine if it can support the intended operational and aircraft capabilities early in the aircraft project. In this study, a three-session workshop with a cross-functional team for TM design was conducted at Saab AB. The outcomes from the workshop resulted in a framework for a detailed understanding of the steps to be carried out iteratively for TM design by a cross-functional team. It also provides the dependencies for these steps and the various functional groups that need to be involved in each step. The steps can be used to iterate TM design at the aircraft concept stage and understand the implications on aircraft and operational capabilities. Further, the workshop methodology presented can be used to obtain similar frameworks for design of other basic functions at the aircraft concept stage.

Military aircraft face several contemporary challenges. From a thermal management perspective, they include the more extensive use of electrically driven technologies and more power-hungry tactical systems. These systems demand more cooling power from the aircraft thermal management system. Thermal management systems of modern aircraft face another challenge with shrinking heat sink capability. This is because of platform design aspects. Increasing use of composite materials for airframe skin over traditional metals impedes the dissipation of waste heat through skin. Infrared and radar cross-section signatures are minimised to improve aircraft stealth by minimising the cross-sectional areas of ram air intakes. This reduces the amount of waste heat that can be dumped over-board through ram air. And there are only two options for heat sinks, air (ram or engine fan) and fuel. All these contemporary challenges create a strong need to carry out thermal management design effectively at the aircraft concept stage.

A framework is presented in this thesis that demonstrates how effective thermal management design at the concept stage can be conducted at an aircraft developer like Saab. The framework was created with data collection through workshops, document studies, interviews, and group discussions conducted at Saab. Therefore, the framework is based on industrial reality. It can be tested for application at the aircraft concept stage of Saab projects. Further, the methods created in this thesis can be used in a broader context that transcend their primary application in thermal management design. They can also complement other methods presented in literature on aircraft thermal management. Thus, this thesis makes industrial and scientific contributions to aircraft thermal management design.

Surveillance aircraft perform long-duration missions (>eight hours) that include detection and identification of objects on the ground, the water, or in the air. They have surveillance systems that require large amounts of cooling power (typically 10 s of kW) for long durations. For aircraft application, vapor cycle systems (VCS) are emerging as a more efficient alternative to conventional cooling systems. In this study, a two-part method was applied to a cooling system with a VCS that can be installed on a surveillance aircraft. The first part focused on a parameter tuning study set-up and demonstrated how after identifying the operating conditions, constraints, and requirements, the only cooling system parameter available for tuning was the VCS compressor speed. The second part focused on a modelling and solving strategy for the cooling system and showed how the capacity of an aircraft cooling system was impacted by tuning the VCS compressor speed (Hz) for a surveillance system heat flow rate from 10 kW to 70 kW. The results from this study can be used to design a control strategy for the compressor. In a broader perspective, the two-part method and the results analysis presented can serve as a preliminary method for aircraft VCS control optimization studies.

Aircraft vehicle systems are the systems that enable an aircraft to fly safely. Function, performance, and other emergent properties of a vehicle system are impacted when it is integrated into an aircraft. Emergent properties of vehicle systems are used as criteria to evaluate them. Nowadays, vehicle systems are becoming more functionally-integrated. For an aircraft developer, predicting the emergent properties of a more functionallyintegrated vehicle system might prove more challenging than predicting those of traditional, federated vehicle systems. This paper presents an approach that accounts for various aspects of an aircraft project that might impact an emergent property that the vehicle system is evaluated for. The approach is based on an analysis of data collected through a qualitative study conducted at Saab Aeronautics on the Gripen E/F aircraft project. Theapproach could enable vehicle system designers at the aircraft concept stage make more holistic predictions of the emergent properties of vehicle systems when they are integrated into an aircraft. The holistic approach could enable vehicle system designers anticipate undesirable emergence of a vehicle system at the aircraft concept stage. The undesirable emergence that could otherwise remain unanticipated until later in the life cycle of anaircraft.

Aircraft vehicle systems enable an aircraft to fly safely throughout a mission. Generating feasible vehicle system architectures at the aircraft concept design phase is complex. Aspects from various complex systems theories are used to provide different insights into this complexity. To address this complexity, a framework based on industrial reality that can used recursively is presented. The framework employs various design theories to harness the complexity of vehicle system design at the concept design phase of an aircraft.