Joby Aviation S4-T (technology demonstrator)
(Photo credit: Joby Aviation)
S4-T (technology demonstrator)
Joby Aviation
Santa Cruz, California, USA
www.jobyaviation.com
Founded in 2009 by JoeBen Bevirt, CEO, Joby Aviation is a venture-backed startup aerospace company is located in Santa Cruz and San Carlos, California (USA), that is developing and will manufacture piloted all-electric vertical takeoff and landing (eVTOL) passenger aircraft for fast, quiet, and affordable on-demand air taxi services for the advanced air mobility (AAM) industry. Joby plans to start commercial operations as soon as 2025. Bevirt had previously founded the photography accessory company, JOBY (now owned by the British company, Vivendum).
S4-T uncrewed autonomous turbine hybrid-electric eVTOL full-scale technology demonstrator aircraft
The S4-T is an uncrewed autonomous turbine hybrid-electric eVTOL full-scale technology demonstrator aircraft. The technology demonstrator eVTOL uses an S4 airframe, carries no passengers and has Joby's Superpilot autonomous flight control to fly the aircraft. Joby Aviation, Inc. announced the first flight of its turbine electric, autonomous vertical take-off and landing (VTOL) aircraft took place on November 7, 2025 at their facility in Marina, California, USA.
While few specifications for the aircraft have been made available at this time, the aircraft has six tilt-propellers, six electric motors and is powered by a hybrid-electric power source using a turbine engine. As this is a uncrewed prototype, the aircraft carries no passengers. The aircraft has one high main gull-wing and one V tail. The aircraft has fixed tricycle wheeled landing gear. From Joby Aviation's pictures, the FAA tail number is N5421A. According to the FAA website, the aircraft certificate for the eVTOL was issued in 2022, the model of the aircraft is called the JAS4-1 and is an experimental aircraft.
According to the company, the turbine hybrid-electric eVTOL aircraft builds on their proven all-electric technology eVTOL aircraft that has completed more than 50,000 miles of flight testing and has entered the final stage of the FAA’s type certification process for commercial aircraft.
As of 2025, Joby's Superpilot autonomous technology stack has been in development for more than five years. The Superpilot consists of multiple autonomous functions such as autonomous mission management used for an optimal flight path. Radar and perception processing high-rate data for environmental awareness for safe navigation during flight. Its sensor fusion uses data from LiDAR, radar and cameras to have an accurate state and position of the aircraft. The technology stack also includes a digital data link used for communication and command control between the aircraft and ground stations. A safety and reliability feature is also built into the system to handle failures and supply contingency actions automatically.
Of note, in July and August of 2025, Joby Aviation successfully participated in Resolute Force Pacific (REFORPAC), a U.S. Air Force contingency exercise designed to test the ability of the military to rapidly mobilize and sustain operations in the large region of the Indo-Pacific oceans. REFORPAC took place from July 10-August 8, 2025. The Indo-Pacific is a vast maritime region that includes the Indian Ocean and includes the entire Pacific Ocean. (That is, the oceans from East Africa to the oceans that meet the western coasts of the Americas.) The large scale deployment of aircraft and personnel includes practicing rapid refueling skills, munitions loading, combat search and rescue and working with friendly nations.
Joby used a Cessna Caravan 208 that contained their Superpilot autonomous flight control for the 2025 REFORPAC military exercise. The aircraft was managed from ground control stations at multiple locations. The primary control station used for most of the exercise was in the range of 3,000 miles (4,828 km) away from the aircraft. The Cessna Caravan logged 43.7 hours of autonomous flight, flying a total of 7,342 miles (11,816 km). Six sorties were flown and one roundtrip ferry flight were successfully completed. A safety pilot was also onboard the aircraft to monitor the system’s performance.
“AFWERX has partnered with Joby’s team for several years with increasingly complex development and demonstration efforts of autonomy to support contested logistics missions,” said LCol Jonathan Gilbert, AFWERX Prime division chief.
According to the company, the hybrid-electric VTOL aircraft will provide air taxi service, air cargo and other long range air missions for civilian, commercial and defense customers. Joby Aviation has stated they will continue ground and flight testing of the S4-T prototype until they have demonstration flights for government customers which is planned for 2026.
Specifications:
- Aircraft type: Uncrewed autonomous turbine hybrid-electric VTOL technology demonstrator aircraft
- Piloting: Joby's Superpilot autonomous technology stack
- Capacity: Air cargo or other equipment
- Cruise speed: Unknown
- Propellers: 6 propellers
- Electric motors: 6 electric motors
- Power source: Turbine hybrid-electric power source
- Fuselage: Carbon fiber composite
- Windows: No windows
- Wings: 1 high main gull wing
- Tail: 1 V tail
- Landing gear: Fixed tricycle wheeled landing gear
- Safety features: Distributed Electric Propulsion (DEP) uses multiple propellers or electric ducted fans, each powered by electric motors, to increase safety through redundancy. If one or more components fail, the remaining ones can still ensure a safe landing. There are also redundancies of critical components in the sub-systems of the aircraft providing safety through redundancy. Having multiple redundant systems on any aircraft decreases having any single point of failure.
Related Aircraft:
- Joby Aviation Lotus (defunct)
- Joby Aviation Monarch (defunct)
- Joby Aviation S2 (defunct)
- Joby Aviation S4 1.0 (technology demonstrator)
- Joby Aviation S4 2.0 (pre-production prototype)
- Joby Aviation S4 (production prototype)
- Joby Aviation SHy4 (technology demonstrator)
Company Insights:
Resources:
- Joby Aviation website
- Joby Aviation Facebook
- Joby Aviation Twitter
- Joby Aviation YouTube
- Joby Aviation Instagram
- Joby Aviation LinkedIn
- Article: Joby collaborates with L3Harris to pursue defense applications for autonomous hybrid VTOL aircraft, Vertical Magazine, Aug. 1, 2025
- Article: Joby completes landmark U.S. defense exercise with autonomous flight technology, Vertical Magazine, Sept. 3, 2025
- Article: Joby celebrates first flight of turbine electric demonstrator aircraft, Vertical Magazine, Nov. 13, 2025
- Article: Autonomous electric VTOL aircraft for US military makes successful first flight, Interesting Engineering, Nov. 14, 2025
- Article: First flight for Joby's ultra-long-range eVTOL, New Atlas, Nov. 22, 2025
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