The aircraft includes a fuselage and at least one wing extending from the fuselage. The wing includes first and second original portions and a plug portion positioned between the first and second original portions. A propulsion system is positioned on the at least one wing. The propulsion system includes at least one electric powerplant and at least one combustion powerplant. Each powerplant delivers power to a respective air mover for propelling the aircraft. The electric powerplant and/or the combustion powerplant is positioned outboard from the plug portion. A method for retrofitting an aircraft includes segmenting a wing of an aircraft into two original portions, positioning a plug portion between the two original portions, and connecting the plug portion to one of the two original portions, the first nacelle and/or the second nacelle.