Boom Technology has unveiled plans for a 45-seat commercial supersonic aircraft preceded by a technology demonstrator. But will this project succeed where others have failed? BILL READ FRAeS reports.

Ever since the retirement of the Air France and British Airways Concordes in 2003, there have been a succession of initiatives to develop a modern supersonic transport replacement, many of which have failed to get beyond the concept stage. The latest company to propose a ‘Son of Concorde’ design is Denver-based Boom Technology which has unveiled plans for a new 45-seat commercial supersonic jet (SSJ).

The 170ft long, 60ft wingspan Boom SSJ design will feature a delta wing configuration and a swept trailing edge. Powered by three medium-bypass turbofans, the Boom SSJ would be able to fly at a maximum cruising speed of Mach 2.2 (1,451mph) with a maximum range of 9,000nm.

However, a problem which limited the development of Concorde still remains, namely the US Federal Aviation Administration (FAA) restrictions on flying overland due to the noise of the sonic boom. Because of this, Boom’s new design would also be limited to routes over water. According to the company, the SSJ would reduce the transit time between New York and London down to 3.4 hours while flying from San Francisco to Tokyo would take 4.7 hours and 6.75 hours between Los Angeles and Sydney.

Technological advantage

An artist’s impression of Boom Technology’s proposed 45-seat commercial supersonic jet next to the XB-1 ‘Baby Boom’ technology demonstrator that will be used to test the concept. (Boom Technology)

According to Boom Technology CEO and founder Blake Scholl, the new SSJ will take advantage of new technology which has been proven in use. “Technology has moved on since Concorde, particularly with the development of more efficient engines while new construction materials are better able to cope with the rigours of supersonic flight,” says Scholl.

The principal three innovations will be medium-bypass turbofan engines based on a commercial engine core, advanced aerodynamics optimised through simulation tests and carbon fibre reinforced plastic.

Aerodynamic features

Technical illustrations of the Boom XB-1 technical demonstrator showing the chine wing extension and the area-ruled tapering of the rear fuselage. (Boom Technology)

Using data gained from over a thousand simulated wind-tunnel tests, the SSJ has incorporated three additional aerodynamic features: an area-ruled fuselage, a chine, and a refined delta wing. “The Boom aircraft is much more dynamically shaped,” says Scholl. “Supersonic performance is highly sensitive to aircraft cross-sectional area, so the fuselage is ‘area ruled’, where the cross-section area is carefully controlled to reduce disturbances to the surrounding air. Our aircraft features a gentle tapering in the aft cabin where the wings are thickest, reducing cross section and disturbances to the surrounding air. The centre of lift shifts aft as a supersonic aircraft gains speed, creating challenges for balance and control. To mitigate this shift, we incorporate a chine wing extension that stretches toward the nose which generates more lift supersonically than subsonically, contributing to a natural balance across a wide range of speeds. At take-off and landing, the chine generates a stable overwing vortex, increasing lift and reducing take-off and landing speeds.”

The wing of the SSJ also features high-efficiency aerofoils, a gentle camber and a swept trailing edge which reduces supersonic-induced drag and reduces the sonic boom.

New materials

Initial structural components are in fabrication. (Boom Technology)

Boom has also been able to take advantage of newer, lighter materials that were not available when the Concorde was built. Instead of aluminum alloy, the SSJ will use moulded layers of resin-infused carbon fabric to create a strong and lightweight structure in the exact dynamic shape desired. According to Boom, this will enable the SSJ to fly faster than Concorde, as carbon-based materials are better able to handle the stresses of supersonic flight and will not expand as much as aluminium at the high temperatures encountered at speeds of over Mach 2.2.

Boom is sourcing the components for the SSJ from different suppliers. Tencate will provide carbon fibre while the composite structures will be fabricated by Blue Force. The skin components of the aircraft will feature a layer of copper mesh for lightning protection.

Inside the SSJ

Each passenger seat in the SSJ will have a large personal window. (Boom Technology)

The standard production Boom SSJ will be able to carry up to 45 passengers, four flight attendants and two crew. A high-density version is also being considered which could accommodate up to 55 passengers. All the seats on the standard version will have a large personal window, direct aisle access and a dedicated overhead bin. There will also be two lavatories. The cabin would be fitted with an environmental control system which takes compressed air from the engines, cools it through a fuel/air heat exchanger and then expands it to a comfortable cabin pressure. A dual redundant oxygen system is available in case of loss of cabin pressure.

The cockpit will be fitted with Honeywell avionics, as well as centre sticks and rudder pedals for both seats, allowing a pilot in either seat to fly the aircraft. A manually-controlled hydraulically-powered system will enable the pilots to fly with a lightweight touch while giving precise, responsive control of roll, pitch, and yaw. It will also include an electronic yaw damper that will provide control across a wide range of speeds.

Baby Boom demonstrator

Artist's concept of the Boom XB-1 demonstrator. (Boom Technology)

To trial the technologies to be used in the full-size Boom SSJ, Boom Technology is constructing a 1/3 scale version XB-1 Supersonic Demonstrator. Nicknamed the ‘Baby Boom’, the 68ft long, 17ft wingspan prototype is to be assembled at Boom’s headquarters at Centennial Airport in Denver. The aircraft’s systems have been ground tested, initial structural components are in fabrication and final assembly and vehicle integration is to commence shortly.

The XB-1 will have an airworthiness certificate in the experimental R&D category and will be used to demonstrate the key technologies for efficient supersonic flight, namely an advanced aerodynamic design, lightweight materials capable of withstanding the pressures and temperatures of supersonic flight and an efficient super-cruise propulsion system. As with the full-size aircraft, the demonstrator will also feature an area-ruled fuselage, a refined delta wing and a chine wing extension.

The XB-1 will be powered by three 3,500lb thrust General Electric J85-21 turbojets (as used in the F-5), two located under the wing and one in the tail. Each engine will be fed by two variable geometry supersonic intakes which will compress oncoming Mach 2.2 air, efficiently slowing to the ideal subsonic speed for the engine. Digitally-controlled movable surfaces precisely position shock waves to achieve ideal compression at a wide range of speeds and flight conditions, while blow-in doors provide extra airflow for take-off. Each engine will also be fitted with a variable geometry nozzle system.

The full size Boom SSJ will also be powered by three engines but a manufacturer has not yet been selected. Boom believes that using medium bypass engines will provide the SSJ with sufficient thrust for supersonic flight while also reducing noise around airports. The company also decided on Mach 2.2 as being the optimal speed to fly, as this will enable the aircraft to comply both with airport noise regulations and to operate efficiently at cruise speeds. “We decided to use three engines to help lower take-off noise,” explains Scholl. “Three-engine aircraft are also treated as more reliable by FAA regulations and the ETOPS (extended range twin engine operational performance standards) rules permit new three-engine aircraft to fly more directly over water routes than twins, leading to faster flight times.”

The demonstrator will store 7,000lb of jet fuel in 11 separate fuel tanks. An aft trim tank would hold fuel during supersonic flight, shifting the aircraft’s centre-of-gravity as the centre of lift moves backwards.

Boom Technology plans to begin the first test flights of the Baby Boom at the end of 2017. The demonstrator will be capable of the same Mach 2.2 speed as the larger SSJ. Subsonic tests will be flown from Centennial airport and supersonic test flights in a supersonic test corridor near Edwards Air Force Base in California. The supersonic tests of the prototype will be conducted with the assistance of The Spaceship Company, the manufacturing arm of Virgin Galactic. In addition to flight test support and operations, The Spaceship Company will also supply Boom Technology with engineering and manufacturing services.

Following the flight tests of the Baby Boom, work will begin on the full-size version of the aircraft which Boom hopes to begin flying in the early 2020s.

Commercial rationale

Engineering development of the XB-1 Baby Boom is in progress. (Boom Technology)

However, while the engineering challenges of supersonic flight are being tackled, what are the economic prospects for a new commercial supersonic passenger aircraft when Concorde (and its only rival the Russian Tupolev Tu-144) failed to be an economic success?

Blake Scholl is confident that the aircraft will be a success. “Every passenger wants faster flights; every airline would like to offer a faster and more differentiated service to their passengers,” he remarks. “The question is costs and fares. Concorde was troubled by high operating costs, driven by fuel consumption, and low utilisation and load factors, due to the necessarily high fares. The viability of supersonic flight depends on the ability to reduce operating costs sufficiently to allow a viable business model, i.e. it must be possible to achieve good load factors and strong margins, at fares passengers will pay. Surprisingly, this requires just a 30% efficiency improvement over Concorde’s 50 year-old airframe and engines. The fundamental technologies required for this exist today and have recently been accepted by regulators (such as composite structures).”
Scholl also views the smaller size of the SSJ as an advantage. “A major problem with Concorde is that it had more seats than could be filled at the required prices,” he comments. “The Boom aircraft has 45 seats, similar to the premium cabin in a typical widebody aircraft. If you can fly a widebody aircraft with good load factor, you can also fly a Boom aircraft with the same schedule with good load factors.”

Boom has announced that it intends to market the SSJ for $200m, excluding options and interior. The aircraft could also be configured as an ultra VIP personal or business aircraft. The company has already secured its first tentative order. In exchange for its help in developing the design, Virgin has the option to purchase the first ten aircraft.

Tickets for the initial commercial flights of the Boom SSJ are expected to cost about $5,000, compared to an average of $12,000 for Concorde. Scholl believes that passengers will pay more for speed. “Today, passengers pay a 4-5X premium for business class, even though those seats don’t arrive any sooner than economy,” he says. “Passengers will pay a premium for non-stop service, so it is reasonable to expect higher fares for still faster service.”

Supersonic challenges

Mock-up of the XB-1 Baby Boom demonstrator. (Boom Technology)

Prof Jeff Jupp FRAeS, former Chairman of the RAeS Greener by Design Group, considers some of the technical and economic challenges facing a return to commercial supersonic flight:

"A successor to Concorde was being investigated long before its retirement in 2003. To make an adequate business case a large aircraft with transpacific range was considered by a European consortium including British Aerospace in the 1990s. However, apart from the formidable technical challenges, the business case just did not make sense. It was found that all classes of passengers were prepared to pay a premium of an extra one third of their normal fare to halve the flight time. This was not enough to support the purchase price and direct operating costs of such an aircraft even if sold in hundreds – which also would have raised a major environmental concern with that number of aircraft flying at 50,000 to 60,000ft altitude. However, with today’s advances and, if the size of the aircraft is reduced, the technical problems should certainly be more manageable.

Starting with the sonic boom, to a first order for a correctly designed aircraft, there are only two things that matter, the boom being proportional to the weight and inversely proportional to the length of the aircraft. So a small, lightweight, long ‘needle nose’ aircraft may well generate a low boom which is tolerable for overland routing. Hence the current interest in supersonic business jets. The business case may also hold up, as although the aircraft will be expensive the clientele will not be too concerned at the cost of travel and with the relatively small numbers the environmental impact may well be tolerated.

However, an aircraft carrying 45 passengers plus crew is potentially a much more demanding project! Certainly, one can see a major reduction in the weight of the aircraft relative to Concorde but significant concerns must still be there on whether the boom will restrict the aircraft to overwater operation and whether the take-off noise would be tolerated. Today’s engines are certainly more efficient and quieter than Concorde but unfortunately high bypass fans are not usable at supersonic speeds as the jet exhaust velocity must be higher than the flight speed to generate any thrust. This will demand a bypass ratio of order 1 rather than the ten of modern subsonic transports, maintaining the emphasis very much on take-off noise. While Concorde had a derogation from the noise regulations, that was only because of very infrequent exposure. It would be virtually inconceivable for such a derogation to be given from today’s much tighter noise requirements if the aircraft was to be sold in sufficient numbers to make commercial sense. Maintenance costs are another issue, with more complex systems such as the variable intakes and fuel centre of gravity management.With a high purchase price per seat and inevitably high fuel and maintenance charges, for the fare to remain at levels that will attract enough passengers, the business case is only likely to make sense if considerable numbers are sold, exacerbating the sonic boom, noise and environmental concerns.

So, while being much more amenable to technical solutions today, the challenges facing the Boom Supersonic project remain formidable, particularly the economic one! Nonetheless, Boom have assembled a very experienced team, and they may well deliver a successful project!"

Bill Read
13 January 2017

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