Small Supersonic Airliner
|Aerion||AS2 Supersonic Business Jet||12||1.5|
|Lockheed Martin||Quiet SST (QueSST)||N/A||1.4|
|Supersonic Aerospace||Quiet SST (QSST)||12||1.7|
|Supersonic Aerospace||Quiet SST (QSST-X)||30||1.7|
|DARPA||Quiet Supersonic Platform||??||2.0|
|NASA||Shaped Sonic Boom Demonstration||N/A||1.1|
|Sukhoi OKB||S-21 Super Sonic Business Jet||5-8||1.8-2.2|
|Sukhoi OKB||S-51 Supersonic Passenger Jet||30-50||1.8-2.2|
The supersonic passenger jet appears to be one of the very few areas of technology where aviation has taken a step backward. Inevitably, questions arise concerning the need for and feasibility of passenger travel faster than the speed of sound. Bringing supersonic travel to commercial aviation has been a goal for many decades. The current target is to have the Small Supersonic Airliner in the air soon after 2020, with cruise speed of Mach 1.6-1.8, range of 4000 nm, payload of 35-70 passengers, sonic boom no higher than 65-70 PLdB, reduced airport noise, and improved fuel efficiency. Accomplishing this goal involves solving a number of technological and regulatory challenges.
The shape of an environmentally friendly airframe is quite distinct from that of an economical airframe. The end of the airframe should be preferably be round to reduce the sonic boom, yet also sharp to obtain a low-drag, fuel efficient airframe. Because the airframe shapes suitable for each type of performance are contrary to each other, the technologies to develop the two shapes are incompatible. Software can help design and analyze optimum shapes which meet both requirements. Researchers can verify its CFD-based design technology by developing a demonstrator aircraft and conducting flight experiments.
With NASA’s High-Speed Research program having once again revealed how difficult it would be to design and produce a full-size airliner with a sonic boom quiet enough to fly over land, the alternative of small- or medium-size supersonic aircraft for civilian passengers began attracting more attention. Although no company had yet to begin actual development of an SSBJ, the idea itself was not new. Fairchild Swearingen, McDonnell Douglass, Lockheed- California, and British Aerospace had all seriously looked at the possibility in the mid-1980s, and the fractional-ownership company NetJets had come to believe that an SSBJ would fit well with its business model.4 Because smaller supersonic aircraft would inherently have a weaker sonic boom, Seebass was among those who became most interested in pursuing this concept.
Of the business jet players, Dassault had the most skills and technologies to lead an SSBJ project, but in March 1999 the company shelved its SSBJ project (though in 2004 it confirmed that it was still studying the idea). A SSBJ would have been great way to crush the G500/Global Express market segment, from which Dassault found itself largely excluded. In June 1998, Boeing announced that it was considering an SSBJ, and was talking with former Gulfstream associate Sukhoi. This sounded like a good opportunity for a trans-Atlantic joint venture with Dassault, but the French company showed few signs of interest.
NASA's N+2 program issued contracts to Boeing and Lockheed Martin for low-boom demonstrator concepts. Outline targets called for a manned aircraft capable of day-and-night flight and designed to cruise at or above Mach 1.4 and 50,000 ft. It also called for an optimal sonic boom level of around 75 PLdB (perceived decibel level) under the aircraft’s track and 70-75 PLdB off-track. Both levels are considerably lower than the Concorde’s noise level of 105 PLdB.
A vision of the Small Supersonic Aircraft pays particular attention to the critical issues of improving supersonic cruise efficiency, reducing sonic boom and airport noise, integrating the systems, minimizing high altitude emissions, assimilating into the air transportation system of the future, and possibly a new regulatory framework to permit overland supersonic passenger flight.
The Concorde, the only supersonic passenger airliner ever in actual practical use, made its final flight in 2003 never to return to the skies. Even though it was a remarkable technological achievement, from the economic point of view the Concorde was an utter failure. This experience turned aircraft manufacturers toward simpler subsonic jets and away from the more challenging supersonic projects.
The introduction of supersonic commercial aircraft has the potential to bring revolutionary changes to U.S. competitiveness as well as provide broad economic benefits to the global economy. As the world is becoming “flatter” and air travel more and more common, the availability of faster means of transportation could become a catalyst of growth. The benefits of supersonic passenger travel include reduced travel time for business leading to increased productivity, shortened travel time for leisure, the ability to provide rapid response in disaster situations, and faster delivery of time-critical goods.
The value of time has been growing, resulting in a premium being placed on the ability to get to the destination faster. Quicker delivery of time-critical cargo could save lives, as in the case of organ transplants. Cutting the time of travel in half could expedite diplomatic negotiations, which also saves lives. The benefits are numerous.
If supersonic travel becomes available at a reasonable cost, the effect could be as great as that experienced by society when subsonic passenger jets were first introduced. The United States has the chance to boost its technological leadership and in the process provide enormous economic benefits both domestically and globally. Economic benefits to the country and companies “first to market” with supersonic passenger jets fully justify the development cost.
With any technology, the first products are relatively expensive and target an upper tier of the market. Supersonic travel is no exception; the logical first customers are business people who would require supersonic business jets.
Improved propulsion efficiency is critical to the vision of the Small Supersonic Airliner primarily because otherwise supersonic travel will be prohibitively expensive. Efficiency goals need to be addressed in conjunction with the environmental issues. The lift/drag ratio of a supersonic jet is much lower than that of a subsonic aircraft. Reducing the drag could in part be accomplished by reducing the weight of the aircraft. The use of new light weight materials could be part of the solutions.
As shown by repeated studies, generating sufficient passenger loads to justify the expense of a supersonic airliner would most likely require overland supersonic routes from a large number of airports. This meant solving the acoustic issues of jet noise, especially when taking off, and the sonic boom when accelerating and cruising. The sonic boom due to lift cannot be avoided. The aircraft’s weight must be transmitted to the ground.
The problem of overcoming “noise pollution” created by the sonic boom is arguably the most challenging in creating the Small Supersonic Airliner. At supersonic speeds, pressure waves from the nose and the tail of the aircraft coalesce into two shock waves that propagate in a cone behind the aircraft, and at the ground level are perceived as a loud sound (or two loud sounds heard in rapid succession) usually called sonic boom. At long distances from the aircraft (far field) such as at the ground level, the pressure waves are more pronounces as two shocks from the nose and the tail of the aircraft because all the other pressure waves end up being combined into them. The resulting acoustic disturbance is an environmental concern and a violation of FAA regulations.
In a technical paper entitled "Sonic-Boom Minimization" published in the Journal of the Acoustical Society of America, Vol. 51, No. 2, Pt. 3, February 1972, pp. 686-694, the authors A. R. George and Richard Seebass developed the theory for tailoring the area and lift distribution versus aircraft length to minimize the shock strength at the ground given parameters of aircraft weight, flight altitude and Mach number. To minimize the shock strength, the sum of the area and lift must exactly follow the George and Seebass distribution. In a publication entitled "Sonic-Boom Minimization with Nose Bluntness Relaxation," published as NASA TP-1348, 1979, Darden added a shape for a relaxed bluntness nose that reduced bluntness drag greatly with a slight increase in boom. In contrast with intuition, the near-field pressure distribution requires a strong leading edge compression that quickly reduces in magnitude, followed by a gradually increasing weak compression that rapidly inverts into a weak expansion, followed by a stronger trailing edge expansion that gradually recompresses to ambient.
Aircraft configured according to George-Seebass-Darden's theory for shock minimized distributions are impractical designs because the distributions require: 1. either blunt noses or relaxed bluntness noses whose shapes result in higher drag than minimum drag shapes, which lead to reduced performance; 2. smooth distributions through the engine nacelle region, which is not possible with existing engine designs; 3. a one-dimensional simplifying assumption so the distributions are only calculated directly under the vehicle, which means that non-planar and azimuthally varying effects are not considered; and 4. an expansion behind the aft end of the vehicle to keep the aft shock from coalescing, contrary to a minimum wave drag shape which compresses the flow field for about the last quarter of the vehicle's length. Additional techniques are therefore desired to reduce sonic boom disturbances generated by a realistic vehicle.
The shaping of the sonic boom involves constructing the frame of the aircraft to create shock and expansion zones in such a way that they partly cancel each other. For example, the fuselage could be intentionally shaped to create shock and expansion zones that will compensate for the shock and expansion zones produced by the wings of the aircraft and its engine nacelles.13,15 A number of other approaches have also been proposed and could be utilized for shaping the sonic boom. A blunt-nosed spike extended from the front of the aircraft, or extendable on a boom, could deflect air pressure and to some degree disrupt the air flow patterns that contribute to the sonic boom.
These aircraft can have a business class product with higher density because they can pack more seats into an aircraft, compared to lie-flat seats. They they need the lie-flat business class seat because the flight time is more like a trip from DC to Chicago.
Results shown exclusively in October 2016 to Aviation Week of an independent study into market prospects for the supersonic transport by forecaster Boyd Group International suggests as many as 1,300 aircraft worth $260 billion will be needed over a 10-year period. The biggest potential market sector is predicted to be North America, with an estimated requirement for 377 aircraft, while European carriers would be the second-biggest user group with a requirement for more than 360. The Middle East and Africa region could be the third-biggest customer group with about 250 aircraft, while the Asia-Pacific and China sectors could potentially take up to 128 and about 100, respectively.
Boyd Group International, an aviation consulting firm in Evergreen, was hired by Boom to look at the viability of supersonic flights for a wider audience. The report says the “ability of the aircraft to slash flight times for the important premium passenger could result in it becoming a necessary part of global airline fleets in order to remain competitive.” It also states that “while the projected costs of the Boom airliner indicate full ability to accommodate fares charged on current-generation airliners, the enormous advantage of reduced travel time could allow carriers to charge a premium over service on conventional airliners.”
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