In all-electrical aircrafts, the corresponding electrical ram air fan should be optimised in order to improve its current design in two aspects:

• generate pressure drop at low flows without surge issues;
• cooling of the fan electrical motor at high inlet air temperatures.

The ECS control logics produces two main typical operating points, one with high flow when the ram-air fan creates enough flow to cool both the ECS main heat exchanger and the ECS motor stator, and the second when it only needs to provide a low airflow for the latter necessity. As the pressure drop is similar in both situations but the flow very different, this creates surge problems that should be eliminated for adequate operation.

Meanwhile, the fact that the ram-air fan is located downstream the ECS main heat exchanger implies that the air inlet arrives to the fan at high temperatures, what difficulties its own correct electrical motor cooling, both from a mechanical and electrical points of view.

Considering these objectives, a new fan concept was selected from available bibliographic and consortium expertise, and designed using the consortium skills in deep fundamental fluid mechanics and heat transfer knowledge (Technical University of Catalonia - UPC ), advanced CFD tools and aerodynamic know-how (Thermo Fluids - TF) and engineering capacities of a fan manufacturer (LMB SAS). The proposed design related to surge problem was implemented in a prototype and tested accordingly. In a similar manner, a solution for electrical motor cooling was found. The final solution also considered its impact on the whole ECS pack, in order to maintain its global performance objectives.