Essentially a triplane derivative of the S-2 "Wireless" (signifying lack of wing bracing wires) unarmed biplane "scout", the S-3, or "Triplane Speed Scout", possessed a similar fuselage and 100hp Curtiss OXX-3 engine, and initially retained the ducted propeller spinner featured by the biplane. Interplane bracing employed "K"-type struts and, on its second flight during the summer of 1917, the S-3 attained an altitude of 5030m, which was a record at the time. For initial trials, the centre wing was attached to the fuselage at low shoulder position, but the gap between all three wings was subsequently increased and the centre wing was raised above the fuselage. After redesign of the rudder and the discarding of the ducted spinner, the S-3 successfully completed evaluation trials and four were ordered during the course of 1917 for the US Army Signal Corps. It was proposed to arm the S-3 with two unsynchronised Lewis guns which were to fire over the propeller arc, but the S-3s were delivered to the Signal Corps without armament.
Take-off weight: 599 kg / 1321 lb
Empty weight: 440 kg / 970 lb
Wingspan: 7.62 m / 25 ft 0 in
Length: 5.94 m / 19 ft 6 in
Height: 2.62 m / 8 ft 7 in
Wing area: 13.25 sq.m / 142.62 sq ft
Max. speed: 185 km/h / 115 mph