Development and Designer Vision
Peter Phillips embarked on the ambitious Speedtwin project in 1981 with a clear objective: creating the world's first twin-engine aircraft capable of performing intentional aerobatic maneuvers including spins. This represented a significant departure from conventional twin-engine design philosophy, which typically prioritized stability and safety margins that would prevent such extreme flight attitudes.
The initial ST1 prototype incorporated an eclectic mix of components that demonstrated Phillips' resourceful engineering approach. Modified Victa Airtourer wings provided the aerodynamic foundation, while a welded steel tube fuselage offered the structural integrity necessary for aerobatic loads. The wooden vertical tail and fixed landing gear sourced from a DHC-1 Chipmunk completed this hybrid design, which took its maiden flight on September 30, 1991.
Limited Production History
Only two examples of the Speedtwin ever reached completion, making it one of the rarest twin-engine aircraft designs. The original ST1 prototype served as the proof-of-concept vehicle, powered by twin Continental O-200-A flat-four engines producing 100 horsepower each. This aircraft demonstrated the feasibility of Phillips' vision by successfully completing aerobatic sequences that would be impossible or prohibited in conventional twin-engine aircraft.
Tragically, Peter Phillips died on March 18, 1996, just as development of the second prototype was beginning. The ST2, representing a more refined iteration of the design, did not achieve first flight until March 27, 2007 – over a decade after the designer's death. This production aircraft featured significant improvements over the prototype, including more powerful Avia M 332 inverted four-cylinder engines initially producing 139 horsepower each.
Technical Evolution and Performance
The ST2 underwent continuous refinement throughout its development, eventually receiving 205-horsepower Titan/Lycoming IO-390 flat-four engines that significantly enhanced its performance envelope. This powerplant upgrade provided a power-to-weight ratio of 0.275 kilowatts per kilogram at maximum aerobatic weight, enabling impressive climb rates and sustained aerobatic sequences.
The aircraft's design incorporated a flat-sided aluminum monocoque fuselage construction with rounded decking, representing a departure from the prototype's steel tube framework. Tandem seating positioned the pilot in the front seat for solo operations, with dual controls allowing instructional flights. The cockpit configuration included a baggage compartment behind the rear seat, making the Speedtwin practical for cross-country flights between aerobatic demonstrations.
With a takeoff run of just 202 meters and wing loading of 79.7 kilograms per square meter at maximum aerobatic weight, the Speedtwin demonstrated impressive short-field performance. The NACA 23012 airfoil, transitioning to NACA 2412 toward the wingtips, provided excellent handling characteristics throughout the aircraft's expanded envelope.
Public Recognition and Airshow Presence
The Speedtwin earned recognition within the aviation community through appearances at three Farnborough Airshows in 1994, 1996, and 2012. These high-profile demonstrations showcased the aircraft's unique capabilities to international audiences, including aviation professionals and potential customers who had never witnessed intentional spinning in a twin-engine aircraft.
The 1994 and 1996 appearances occurred during Peter Phillips' lifetime, allowing the designer to personally demonstrate his creation's revolutionary capabilities. The 2012 appearance, sixteen years after Phillips' death, demonstrated the continued interest in this unique design concept.
Corporate Changes and Future Vision
Speedtwin Developments assumed control of the aircraft program in 2000, four years after the original designer's death. In 2012, the company announced a rebranding initiative, renaming the aircraft the Comet 1 with "E2E" representing "Engineered to excel." This marketing shift accompanied ambitious expansion plans including retractable landing gear, armament options, and turboprop engine variants.
The company initially considered offering kit versions for homebuilders, recognizing the potential market for amateur-built aerobatic twins. However, this concept was ultimately withdrawn, likely due to the complexity of certifying such an unconventional aircraft for amateur construction and the specialized nature of its intended mission.
Legacy and Rarity
The Phillips ST-1 Speedtwin remains virtually unique in aviation history as a certified spinning twin-engine aircraft. The early 2000s taxiing accident that seriously damaged the original ST1 prototype reduced the world's population of flying examples to potentially just one aircraft – the ST2. This extreme rarity, combined with the aircraft's specialized capabilities, ensures its place in aviation history as a bold experiment that successfully challenged conventional twin-engine design limitations.
The Speedtwin's 400-liter fuel capacity and comfortable tandem seating arrangement demonstrated that aerobatic capability need not compromise practical cross-country performance, though the limited production run prevented widespread adoption of Phillips' innovative concept.