Rise of the Supersonic Machines

The first supersonic airliner to enter passenger service, the Concorde, carried out its inaugural commercial flights on January 21, 1976, with Air France and British Airways. Despite the fact that the Concorde had a tremendous appeal initially, in all, only 20 were built. Due to the overall pressures on airlines and the rising cost of aviation fuel, its appeal faded rapidly and the last supersonic passenger service was flown on October 24, 2003. Besides the Anglo-French Concorde, the only other supersonic airliner to enter service was the Russian Tu-144 and, at no time did the total number of supersonic airliners in service ever exceed 30. It is a bit perplexing to note that expected progression did not occur all these years on an already validated and reasonably successful concept. This is despite the fact that new technologies such as the use of composites were introduced for the first time on the Concorde.

Astonishingly, there is no supersonic passenger service available today anywhere in the world as no new entrant has made its debut during the last four decades. However, with advances in technology, it was inevitable that supersonic commercial aircraft development transpire. Without much fanfare and without the hype associated with the Concorde, supersonic models have been evolving and the Concorde’s successor may be closer to its first commercial flight.

Development Programmes in the US

The US probably has the lead in developing supersonic airliners. It is worth mentioning here that US airplane maker Convair was nearly successful in converting the B-58 Hustler, the world’s first operational supersonic strategic bomber, into an airliner. After more non-starters such as Boeing’s 2707 supersonic airliner (cancelled in 1971), the US National Aeronautics and Space Administration’s (NASA) High-Speed Research programme (terminated in 1999) and the nearly supersonic Boeing Sonic Cruiser (scrapped in 2001), the NASA announced in February last year, a plan to sponsor the development of a new supersonic passenger carrying jet in collaboration with Lockheed Martin.

The term ‘X-Plane’ has been loosely used in the US for experimental planes and the first supersonic plane, the Bell X-1, was flown in 1947; but this new programme is part of NASA’s New Aviation Horizons initiative aimed at developing Quiet Supersonic Technology (QueSST); an X-series designated plane will probably surface in the near future. For the time being, a single engine QueSST aircraft is being developed at Lockheed Martin’s Skunk Works with the aim to see whether a design with acceptable shockwave signature can be produced. The final QueSST jet is expected to fly at speeds of Mach 1.4, around twice the speed of today’s commercial airliners and carry up to 120 passengers over 5,000 nm. The projected year for fruition of the project is 2019 by way of test-flying an X-Plane although the first commercial flight may take several more years to fructify.

Meanwhile, Virgin Group’s Richard Branson, who once offered to buy British Airway’s Concorde fleet while it was operational, is working with Boom Technology to produce a 40/50-seater capable of a Mach 2.2 cruise over 4,000 nm. However, unlike the NASA QueSST project, the Boom airliner does not aim to reduce sonic boom noise but instead, is focused on over-water operations at very high speeds (one-and-a-half times the QueSST objective). A one-third scale prototype (XB-1) of the three jet engine airliner is under development and initial tests are expected to commence in late 2017 with an entry into service aimed for 2020. If successful, the Boom airliner would complement the much larger QueSST product. Research in the US on hypersonic vehicles by the Defense Advanced Research Projects Agency (DARPA) during the past five decades, was slow in producing attractive results; but in November 2011, the Advanced Hypersonic Weapon was rocket-boosted to hypersonic speed and, in May 2013, the X-51A achieved Mach 5.1. The maturity achieved by these hypersonic programmes has encouraged and inspired the quest for supersonic/hypersonic aircraft for commercial purposes in the US and Europe. The US Air Force Research Lab (AFRL), under a cooperative research and development agreement with UK-based Reaction Engines, is exploring technical details of the Sabre engine developed by it to see whether it offers unique performance and vehicle integration advantages relevant to hypersonic aircraft or two-stage reusable launch vehicles.

European Endeavours

In August 2015, Airbus obtained a US patent for an “ultra-rapid air vehicle” designed to fly at Mach 4.5. The design envisages a take-off like a conventional plane using ordinary turbojet engines. Once it is airborne, an open door in the stern of the plane reveals a rocket motor which starts and sends the aircraft into a near vertical trajectory, accelerating it to supersonic speeds. However, with its unconventional fuselage, a thick delta wing swept back to around 75 degrees and a passenger cabin with only 24 seats, this model is unlikely to ever see commercial use.

More likely to succeed is the Long Term Advanced Propulsion Concepts and Technologies (LAPCAT) programme launched by European Commission. The first part concluded in April 2008 and the second one LAPCAT II started in October that year. While the first part aimed at reducing the duration of antipodal flights ( flights between two diametrically opposite points on the globe) to less than four hours, the second part retained only two concepts from the first part — one for Mach 5 and the other for Mach 8 cruise flight. The project lasted for four years and involved 16 partners representing six European member states. British company Reaction Engines Limited (REL) produced the 139-metrelong hypersonic plane with four liquid hydrogen-powered Synergistic Air-Breathing Rocket Engines (SABRE). It is designed to carry 300 passengers and cruise at hypersonic speed. As it uses liquid hydrogen as fuel instead of fossil fuel, it is also greener and would only produce water vapour and nitrous oxide instead of carbon emissions. The model is not yet launched commercially and awaits an opportune moment.

REL has also envisaged the Scimitar pre-cooled engine, a derivative of SABRE, which exploits the unique thermodynamic properties of liquid hydrogen by using REL’s lightweight heat exchangers. The A2 vehicle, which is designed to be propelled by the Scimitar engine, has exceptional range (10,800 nm both subsonic and supersonic) and is therefore able to service a large number of routes whilst simultaneously avoiding flight at supersonic speeds over populated areas as also the related sonic booms that can be heard on the ground. Its good subsonic performance enables it to service conventional subsonic overland routes.

The LAPCAT concepts are being shared with other countries, notably Japan’s Aerospace Exploration Agency (JAXA) which is working on a hypersonic airliner called Hytex. The Hytex’s turbojet engine has been successfully tested in a flight experiment which simulates speeds up to Mach 1.8. Hytex uses liquid hydrogen both as a fuel and coolant for travel flying at hypersonic speeds. Both LAPCAT-II and JAXA are part of a hypersonic knowledge transfer project between Europe and Japan called Hikari which involves 16 partners, 12 of them in Europe and four in Japan. The project aims at furthering Japan’s tenuous efforts to develop supersonic and hypersonic airliners by providing it with Europe’s high-speed technology research programmes, including LAPCAT (propulsion and aircraft concepts), Atllas (materials and structures), and Zehst (zero emissions high speed technologies and aircraft concepts).

Russian Plans

The prototype of the Russian Tu-144 actually flew two months before the Concorde prototype, but, as the design had most certainly been stolen in parts from the Concorde development programme, some glitches remained unresolved. Although it was the first supersonic commercial transport aircraft to exceed Mach 2, its fate was sealed by two crashes, one in 1973 and the other in 1978. The programme died an early death although the aircraft was later used for training space-bound pilots.

SMALLER SUPERSONIC BUSINESS JETS MAY MAKE AN ENTRY BEFORE AIRLINERS DO AS THEY ARE MORE LIKELY TO FIND WILLING AND AFFLUENT USERS

More recently, Russian media had reported Russian ambitions to produce a huge supersonic cargo plane called the Perspective Airborne Complex of Transport Aviation (PAKTA) capable of flying at Mach 1.6 and carrying up to 180 tonnes over a range of 3,800 nm. Unconfirmed reports mention 2030 as the date of implementation and, while the programme is essentially projected as being a heavy cargo one possibly for transportation of tanks and armoured vehicles, the possibility of its fruition is ruled out by analysts as being too expensive for the current Russian economy to afford. On the other hand, the research into supersonic design may produce an airliner which would be far less expensive to produce. Russia may then produce its competitor to US and European supersonic airliners.

Conclusion

There is little doubt that a supersonic airliner will emerge in the future; the exact time frame is predicated to finding an acceptable noise level emanating from the shock wave inherent to supersonic flight. What cost technology extracts in return for providing that acceptable noise level, will determine whether or not and when, the new designs become financially viable for commercial use. The Boom XB-1, slated to debut late this year, is expected to consume three times the fuel per seat-mile than current options over long haul sectors. This figure raises an interrogation mark over the feasibility of commercial supersonic operations carrying a large number of passengers. However, the much smaller supersonic business jets may make an entry before airliners do as they are more likely to find willing and affluent users.

An independent survey by Boyd Group International Strategic Aviation Solutions for Aviation Week suggests the market is ready to implement supersonic passenger airliners, with an estimated demand for as many as 1,300 aircraft worth $260 billion across multiple airlines. It is only a matter of time before the right noise level is available and at the right cost.