Supersonic Trail Blazers: Trying To Break The Acceptance Barrier

Sukhoi began work on a 6-10-passenger supersonic business aircraft in 1987; Gulfstream likewise on its SSBJ in the following year. A loose association of the two projects was formed on June 13, 1989, and the Russian company submitted the first draft of a detailed specification in October 1991. The U.S. partner withdrew in 1992 from what it called the Gulfstream VI-SU, but Sukhoi continued for a time, having postponed the maiden flight date from 1994 to the late 1990s in the later-unrealized hope of developing new technology and securing alternative partners. A new model of the Sukhoi SBJ was being promoted in the early 2010, but to no avail.

Oct. 14, 1947: the Bell X-1 exceeded Mach 1, heralding the supersonic age foreseen over a decade before by some in the National Advisory Committee for Aeronautics, notably its research scientist, John Stack. The previous January, NACA had published Technical Note 1179 on the characteristics of supersonic airfoils and thereby gave a lift to an aviation industry still feeling its way with the science. And also in 1947, a contemporary artist gave this impression of how a supersonic, 10-passenger aircraft might look when employing sweptback surfaces and what appear to be seven turbojet engines.

Conceived between 1998 and 2000 in a joint feasibility study with Lockheed Martin, the Supersonic Business Jet had, by the NBAA Convention of October 2000, become the Quiet Supersonic Jet (QSJ). Two designs were pursued over the following three years, and by 2003 the QSJ was seen to have variable-geometry wings, a T-tail and two engines mounted on the rear fuselage. Later (perhaps current) studies are known as Whisper and include fixed sweepback and Gulfstream’s Quiet Spike boom-mitigation system. NASA assigned the experimental designation X-54 to Gulfstream in 2008, but no such aircraft emerged.

Between August 2006 and February 2007, a NASA F-15B Eagle flew a series of test sorties from the then-Dryden Flight Research Center to evaluate a Pinocchio-like extending, 24-ft. spike ahead of the aircraft as a means of diminishing the sonic boom. It proved effective at speeds up to Mach 1.8, but not to a degree that would permit civil aircraft to fly supersonically over populated areas. Quiet Spike is patented by Gulfstream and was part of the development program for that company’s SBJ.

A 6-12-month study of a three-nonafterburning-engine Falcon SST was announced by Dassault in September 1997 with a possible view to collaboration with risk-sharing partners. A model was unveiled in May 1998 and by that October, $5 million had been invested out of the $1 billion estimated costs of the full program. An aircraft “could be flying by 2004.” However, the Mach 1.8, cranked-delta-wing Falcon program was terminated in March 1999 when it was deduced that there was no engine available that conformed to Stage 3 noise limitations. World sales were estimated to be 150-200.

By 2001, Boeing, Northrop Grumman and Lockheed Martin were working on conceptual designs for DARPA of a highly efficient Quiet Supersonic Platform (QSP) to enhance U.S. long-range precision-strike forces. Employing a “joined-wing” configuration, the Northrop QSP contender was intended to produce such a small sonic boom that it could operate over land without restrictions. The work held promise of civil spinoffs: Northrop was partnered with Raytheon’s business-jet unit on the project and studied a bizjet employing the technology.

During the early 2000s, Dassault was coordinating a consortium of three dozen companies to establish the technical feasibility of an environmentally compliant, small supersonic transport aircraft (S4TA) under an EU contract. Appreciating the compromises to be made, HISAC was divided into three families for investigation: low-noise, long-range and low-boom. Then there were the “red lines” of transatlantic range, operation from small airports, Mach 1.4-1.8 cruising and noise 8 PLdB below ICAO Chapter 4. None of the designs progressed to detail and, as recently as 2019, Dassault declared it had no interest in building supersonic business aircraft.

Although conceived as part of a military contract (the Northrop Grumman Quiet Supersonic Platform), the Shaped Sonic Boom Demonstrator contributed to civil programs seeking shockwave mitigation. It also was funded by NASA’s Office of Aeronautics. Under a $3.4 million study, a Northrop F-5E light fighter received a new forward fuselage shaped to modify and lessen the sonic boom. First flown on July 24, 2003, the aircraft proved capable of reducing sound levels by about one-third, compared with a standard F-5, as measured by airborne and ground sensors.

Far-sighted plans for a supersonic airliner begun in 1997 by the Japan Aerospace Exploration Agency (JAXA) have included work on boom mitigation through use of unpowered models dropped from high-altitude balloons. Most recently, beginning in 2010, JAXA staged the drop test for Simplified Evaluation of Non-symmetrically Distributed sonic boom (D-SEND) with an air vehicle called the Silent SuperSonic Concept Model. The latter completed its trials satisfactorily in July 2015, launched from a test site in Sweden.

During 2003, Tupolev’s design bureau completed its concept for a supersonic business jet, hoping for funding to launch development early the following year. Powered by two NPO Saturn AL-32M turbofans, and selling for $50 million, this 6-10-seat aircraft was foreseen as the technology demonstrator for a supersonic airliner to be produced by a partnership of European countries. Ambitiously, it was intended to cruise at Mach 2.2. However, no funds were committed, and the venture was abandoned before it could be launched.