Unknown

The Tupolev Unknown was a secret experimental aircraft developed during the late 1970s as part of the Soviet Union’s effort to create a high‑speed, high‑altitude reconnaissance platform. Initiated in 1975 under the codename “Project Sapphire,” the design team, led by senior engineers from the Tupolev Design Bureau, combined a blended‑wing layout with a low‑observable radar cross‑section, making it one of the first Soviet attempts at stealth. The aircraft featured a twin‑engine turbofan arrangement, variable‑sweep wings, and an advanced fly‑by‑wire control system that allowed stable flight at both subsonic cruise and sustained Mach 2.2 dash speeds. Extensive use of carbon‑fiber composites reduced weight and contributed to its reduced infrared signature, while onboard sensor suites included side‑looking airborne radar and high‑resolution optical cameras capable of gathering intelligence from deep within hostile airspace.

Flight testing began in 1979 at the Ramenskoye test centre, but the program was cancelled in 1982 after the prototype suffered a structural failure during a supersonic dive. Although it never entered production, the Unknown’s conceptual innovations influenced later Russian designs such as the Sukhoi Su‑57 and helped pave the way for modern low‑observable aircraft, cementing its place as a pivotal, though largely hidden, milestone in aviation history.