A platform including two winged aircraft are tethered during flight by a single tether near their respective centers of gravity. The tether is windable about a reel, so that a distance between the aircraft can be changed during flight. The aircraft contain avionics configured to enable autonomous flight using natural wind gradients. One aircraft imposes aerodynamic forces on the other, through the tether, while flying at an altitude where wind speed is significantly different than wind speed at an altitude of the other aircraft. The two aircraft cruise back and forth within a maximum distance from a station on the ground. Cruise conditions are established using an iterative computer algorithm which utilizes flight measurements. The aircraft communicate information between each other, and the ground, and contain a payload which performs a useful function at high altitudes.