enabled. One of the best known examples of an aircraft capable of supercruise was Concorde. Due to its long service as a commercial airliner, Concorde holds the record for the most time spent in supercruise; more than all other aircraft combined. Supersonic transports A supersonic transport (SST) is a civil aircraft designed to transport passengers at speeds greater than the speed of sound. The only supersonic civilian aircraft to see service were the Soviet produced Tupolev Tu-144 which first flew in 1968 and last transported passengers in 1978, with NASA retiring it from any use in 1997; and the Franco-British produced Concorde, which first flew in 1969 and remained in service until 2003. Since 2003, there have been no supersonic civilian aircraft in service. A key feature of these designs is the ability to maintain supersonic cruise for long periods, so low drag is essential to limit fuel consumption to a practical and economic level. As a consequence, these airframes are highly streamlined and the wings have a very short span. The requirement for low speeds when taking off and landing is met by using vortex lift: as the aircraft slows, lift must be restored by raising the nose to increase the angle of attack of the wing. The sharply swept leading edge causes the air to twist as it flows over the wing, speeding up the airflow locally and maintaining lift. Other SST projects have included: France – Sud Aviation Super-Caravelle Russia-United States – Sukhoi-Gulfstream S-21 Soviet Union – Tupolev Tu-244, Tupolev Tu-444 United Kingdom – Bristol Type 223 United States – Convair Model 58-9, Boeing 2707, Lockheed L-2000, Douglas 2229, SAI Quiet Supersonic Transport, High Speed Civil Transport Supersonic business jet Supersonic business jets (SSBJ) are a proposed class of small supersonic aircraft. None have yet flown. Typically intended to transport about ten passengers, SSBJs are about the same size as traditional subsonic business jets. Projects for both large-scale and business jet (see lower) passenger supersonic and hypersonic airliners (Aerion SBJ, Spike S-512, HyperMach SonicStar, Next Generation Supersonic Transport, Tupolev Tu-444, Gulfstream X-54, LAPCAT, Reaction Engines LAPCAT A2, Zero Emission Hyper Sonic Transport, SpaceLiner, etc.) were proposed and now are under development. Supersonic strategic bombers A strategic bomber must carry a large bomb load over long distances. Consequently, it is a large aircraft typically with an empty weight exceeding 25,000 kg. Some have also been designed for related