Dubbed the S-4T, the new design is based on Joby’s all-electric S-4 passenger aircraft, modified with a hybrid-electric propulsion system and an autonomous flight control system.
Electric aircraft developer Joby Aviation and defence contractor L3Harris plan to demonstrate a modified version of Joby’s S-4 rotorcraft for the US Army in the coming days.
Speaking to FlightGlobal at the Army Aviation Association of America conference in Nashville on 16 April, executives from the two companies say a demo flight of the new aircraft, dubbed the S-4T, will take place for army officials next week at Joby’s production facility in Marina, California.
The project is taking aim at an emerging requirement from the US Army for an uncrewed, vertical take-off and landing (VTOL) aircraft in the Group 4 category; defined by the Pentagon as having a maximum gross take-off weight greater than 598kg (1,320lb) and operating below 18,000ft.
The army is looking to equip such an aircraft with precision strike armaments and sensors to offer a low-altitude reconnaissance platform for its frontline combat aviation units.
L3Harris began working with Joby in August of 2025 to develop a variant of the all-electric S-4 passenger rotorcraft that would be suitable for military service. That collaboration spawned the S-4T – a hybrid-electric design that maintains the S-4’s multiple tiltrotor configuration but replaces the cockpit with an autonomous flight control system.
“We’ve been looking at different platform providers over time, and that brought us to Joby, because their platform and their technology in this space is actually furthest along across the competitive landscape,” says Jason Lambert, president of intelligence, surveillance and reconnaissance at L3Harris.
That endorsement is a major win for Joby, which has been pursuing defence business as the company pursues civil type certification for the S-4, which was designed as a passenger air taxi and urban air mobility vehicle. Lengthy development and certification timelines on the civil side are pushing electric VTOL developers like Joby to seek near-term revenue in the defence world.
“We see this really huge vote of confidence in Joby and what we can do in the dual-use space,” says John Barranco, a former Bell AH-1 pilot in the US Marine Corps who is now Joby’s head of defence policy.
Joby and other eVTOL manufacturers, including Archer and Beta Technologies, have delivered test aircraft to the US Air Force, but have thus far failed to secure any firm orders from military operators.
“Pure electric is not really ideal for a military application,” notes Lambert. “But a hybrid engine very much is applicable for military applications.”
Known for modifying a wide range of commercial aircraft for defence applications, the partnership with Joby marks the first instance of L3Harris converting a hybrid aircraft, Lambert confirms.
The hybrid-electric propulsion system installed in the S-4T offers several notable military advantages, a