In one aspect, there is provided an aircraft, including a fuselage having a longitudinal axis extending from a front portion through an aft portion; first and second tail members extending from the aft portion; a first cross-flow fan system rotatably mounted to the first tail member; and a second cross-flow fan system rotatably mounted to the second tail member. The first and second cross-flow fan systems are configured to provide a forward thrust vector and an anti-torque vector on the aircraft. The first and second cross-flow fan systems can have a rotational axis oriented generally vertically. In another aspect, there is an aircraft including a fuselage having a front portion and a tail portion; and a cross-flow fan system supported by the tail portion. Embodiments include a cross-flow fan system retrofittable onto an aircraft and methods for retrofitting an aircraft with a cross-flow fan system.