Revolutionary Design Philosophy
The S-12 Twin Voyager emerged from STEMME GmbH's three decades of motorglider expertise, building upon the success of their earlier S10 model. Dr. Reiner Stemme's design team created an aircraft that solves the fundamental compromise inherent in motorgliders: the aerodynamic penalty of carrying an engine and propeller during soaring flight. The S-12's innovative retractable propeller system completely vanishes into a streamlined nose dome within five seconds, transforming the aircraft from a 140-knot touring machine into a pure sailplane with no performance compromise.
Engineering Excellence
At the heart of the S-12 lies a mid-fuselage mounted Rotax 914 F2/S1 turbocharged engine producing 115 horsepower. This Austrian-built powerplant drives a two-bladed variable-pitch propeller through a carbon fiber driveshaft and clutch system, enabling the unique retraction mechanism that sets the S-12 apart from all competitors. The engine's mid-fuselage position optimizes weight distribution and allows the propeller to fold completely flat against the nose when retracted.
The aircraft's 25-meter wingspan incorporates modern winglets and delivers an exceptional 53:1 glide ratio, matching the performance of dedicated competition sailplanes. When the 120-liter fuel system is engaged, the S-12 cruises at 140 knots at 10,000 feet while consuming just 13 liters per hour at 55 percent power, providing an remarkable 950-nautical-mile range.
Certification and Market Entry
Following its prototype debut at AERO Friedrichshafen in April 2015, the S-12 achieved EASA type certification in March 2016, with FAA approval following in 2017. The first U.S. delivery occurred in September 2017, with STEMME commanding a fully-equipped price of $369,000. By 2016, the company had accumulated more than 20 orders, demonstrating strong market acceptance for this premium motorglider.
Advanced Avionics Integration
The S-12 broke new ground by becoming the first certified aircraft to incorporate a non-TSO'd Dynon autopilot system, working alongside specialized soaring equipment including an LX soaring computer with e-Vario and AHRS capabilities. Standard equipment includes Garmin GPS navigation, Mode-S transponder with ADS-B in/out capability, 406 MHz ELT, and comprehensive stall and fire warning systems. This avionics suite transforms long-distance soaring from an endurance test into a precisely managed flight experience.
Operational Capabilities
The side-by-side seating configuration under a bubble canopy accommodates two occupants with 44 pounds of baggage capacity in a dedicated aft compartment, plus additional cockpit storage. The aircraft's 8.42-meter length and 1.75-meter height house retractable landing gear, while the wings fold to just 11.4 meters for hangar storage. Maximum takeoff weight reaches 900 kilograms, with a climb rate of 830 feet per minute enabling rapid altitude acquisition for thermal soaring.
The Manufacturer Legacy
STEMME GmbH traces its roots to 1984 when Dr. Reiner Stemme founded the company in Berlin-Wedding, evolving into a joint-stock company by 1990. The firm's earlier successes include the S10, which first flew in 1986 and achieved certification in 1990, followed by the S6 that debuted in November 2006 with EASA approval in 2008. Operating from Strausberg near Berlin, STEMME continues production today, having established itself as the world's leading manufacturer of high-performance self-launching sailplanes.
Impact on Aviation
The S-12 has redefined the possibilities for cross-country soaring, enabling pilots to launch independently and combine powered flight with thermal soaring to achieve previously impossible range and flexibility. Its influence extends beyond general aviation through the unmanned DZYNE ULTRA derivative, which demonstrates 80-hour endurance capabilities for intelligence and surveillance missions. The S-12 represents not just an evolutionary step in motorglider design, but a fundamental reimagining of what hybrid powered-glider aircraft can achieve when engineering excellence meets innovative thinking.