Several innovative systems for an aircraft, and aircraft incorporating them, are disclosed. Features include inboard-mounted engine(s) with a belt drive system for turning wing-situated propellers; compound landing gear integrating ski, pontoon and wheel subcomponents; pivotal mounting armatures for landing gear and/or propellers which provide a plurality of possible landing gear and/or propeller configurations; and a compound wing structure featuring extendable wing panels that permit the wing span of the aircraft to be nearly doubled while in flight. Aircraft incorporating such features will enjoy several safety advantages over conventional multi-engine aircraft and will be capable of modifications during flight which permit landings on any of snow, hard surfaces (runways) and water.