Limited Production Excellence
The TST-14 Bonus entered a highly specialized market with extremely limited production numbers, with sources indicating only 10 to 20 aircraft were ever manufactured. This scarcity reflected both the niche nature of the motor glider market and the specialized composite construction techniques required for production. By comparison, only two TST-14M motor glider variants existed in the United States as of recent records, highlighting the aircraft's exclusivity in the American soaring community.
The Manufacturer
TeST sro, operating as a division of Comp-Let sro, established manufacturing operations in Velké Meziříčí, Czech Republic. The company focused on advanced composite sailplane construction, though detailed company founding dates and current operational status remain unclear from available records. The Czech Republic's aerospace industry had been developing specialized glider manufacturing capabilities following the country's political transition in the 1990s, with TeST representing part of this emerging aviation sector.
Advanced Composite Design
The TST-14's construction emphasized cutting-edge composite techniques, featuring ribless composite sandwich wing structures that set it apart from conventional sailplane designs. Each wing weighed exactly 40 kilograms and incorporated a single spar constructed with carbon fiber composite flange plates and polyurethane foam/fiberglass composite web plates. This forward-swept wing configuration provided the aircraft with distinctive handling characteristics and structural efficiency.
The aircraft's T-tail design complemented its high-wing configuration, creating a clean aerodynamic profile essential for soaring performance. At 27 feet in length with a cabin height of just 3 feet 7 inches, the TST-14 prioritized aerodynamic efficiency over spacious accommodations.
Dual Power Options
The motor glider variant TST-14M featured a retractable 50-horsepower Rotax 503UL two-stroke piston engine, a powerplant with more than 30,000 units produced worldwide, ensuring parts availability and maintenance support. The engine's extension and retraction system operated through fully automatic electric servo motors controlled by two cockpit-mounted buttons, allowing pilots to transition seamlessly between powered and unpowered flight.
Fuel capacity of 22.6 liters provided approximately 2.5 hours of continuous powered flight, with fuel consumption rated at 0.074 kilograms per kilometer. This efficiency enabled a range of 275 kilometers when operating under continuous power, though typical motor glider operations involved brief power periods for launch and altitude gain.
The Revolutionary BonusJet
Desert Aerospace LLC of Albuquerque transformed the conventional TST-14 into the groundbreaking TST-14J BonusJet through installation of a retractable PBS TJ-100 turbine engine. This Czech-manufactured jet engine produced 220 pounds of thrust while weighing just 45 pounds, creating the world's most accessible jet-powered sailplane.
Bob Carlton, an experienced jet aircraft pilot, owned and operated one of the few BonusJet examples, using it for demonstration flights and pilot training for other jet-powered aircraft including the SubSonex and BD-5J. Carlton's aircraft made its public debut at the 2010 Soaring Society of America Convention in Little Rock, Arkansas, with first flight occurring in May 2010.
The jet engine required a two-minute cooldown period before retracting into the fuselage, adding operational complexity but enabling unprecedented performance for a sailplane. Certification test flights concluded successfully in 2010, though the variant remained extremely limited in production.
Performance Characteristics
The TST-14M achieved a maximum speed of 93 mph and cruise speed of 71 mph under power, with a never-exceed speed of 127 mph. Its stall speed of 40 mph provided excellent slow-speed handling characteristics essential for soaring operations. The aircraft could reach 13,000 feet using engine power alone, with higher altitudes achievable through thermal soaring.
Rate of sink measured 0.65 meters per second at 85 kilometers per hour, indicating respectable but not exceptional soaring performance compared to pure competition sailplanes. Wing loading of 8.00 pounds per square foot contributed to the aircraft's gentle handling characteristics.
Certification Challenges
The TST-14 was never certified in the United States due to prohibitive expense, limiting American operations to Special Light Sport Aircraft registration or Experimental category operation. This certification gap restricted the aircraft's market penetration in the world's largest general aviation market.
The aircraft's gross weight of 992 pounds, or 1,041 pounds with optional ballistic parachute system, placed it within light sport aircraft parameters, though the lack of formal certification prevented commercial sales in the United States.
Legacy and Current Status
The TST-14 Bonus represents a fascinating footnote in sailplane development, demonstrating advanced composite construction techniques and pioneering jet propulsion integration. Its extremely limited production numbers ensure its status as one of aviation's rarest aircraft types, with the BonusJet variant representing perhaps the most exclusive jet aircraft ever built.
The aircraft's innovative design elements, particularly its composite construction methods and retractable propulsion systems, influenced subsequent sailplane development even as the type itself remained a commercial curiosity rather than a market success.