The cross-flow fan has unique advantages for aircraft applications because of its effectively rectangular arrangement with length adjustable to distribute along the wing span and diameter scalable to integrate with the wing thickness. Fig. 6 shows an example of how a cross-flow fan can be integrated into a wing for propulsion and flow control (e.g. boundary-layer ingestion and wake filling), as proposed by Dornier [23] in 1962. In this case, the cross-flow fan is placed inside a thick wing and distributed over the span creating a distributed propulsion system (e.g. [24] and [25]). Boundary-layer air from the suction and/or pressure surfaces is ingested into the fan, energized by it, and expelled downstream to produce thrust. As the fan spans over most of the wing, the exhaust flow also reduces the wake deficit producing a wake-filling effect [26] and [27].