NBAA Convention News

Five-year Euro SSBJ study inconclusive as to engine type

 - October 14, 2009, 12:46 PM

High-Speed AirCraft (Hisac), a European research program studying the feasibility of a supersonic business jet (SSBJ), is coming to a close at the end of this year. The research has shown better understanding of the performance such a vehicle could achieve, but it came to no conclusion about the types of engines that would be needed.

Business jet manufacturer Dassault (Booth No. 1541) led the Hisac project. Other major stakeholders were Italy’s Alenia Aeronautica and Russia’s Sukhoi. A total of 37 organizations, including engine makers Rolls-Royce (Booth No. 2266) and Snecma (Booth No. 5152), participated in the five-year effort.

The European Commission approved the ?27 million ($38 million) Hisac program as part of its sixth R&D Framework Program in September 2004. Speed specifications ranged from Mach 0.95 to Mach 1.8, while range was seen between 4,000 and 5,000 nm. Various concepts were studied, including some optimized for overwater supersonic flights, with laminar-flow, variable-geometry or delta wings.

Other concepts targeted overland supersonic flights, endeavoring to reduce the sonic boom effects. To achieve this, the study determined that desired features should include light weight, suitable shapes and an optimized speed/altitude combination. The defunct Concorde created a boom (measured in air pressure difference) of 100 pascal, whereas the SSBJ, because of its smaller size, naturally has a pascal boom of 50.

“With an optimized shape the boom can be cut to 20 [pascal],” Bruno Stoufflet, Dassault’s v-p for scientific strategy, R&D and advanced business, told NBAA Convention News. For example, one way to cut the nacelles’ contribution to the boom would be to mount the engines on top of the aft fuselage section. Flying transonic also could be a solution because the shockwave cannot reach the ground below a speed of about Mach 1.15.

Another major problem with a supersonic aircraft is the noise it creates other than the sonic boom. Conventional jets have reduced their nuisance factors through the use of high-bypass (and thus high-diameter) turbofans. However, because of their drag those types of engines are not suitable for an SSBJ. As a tradeoff, Hisac research engineers have determined a bypass ratio of 3:1 is most desirable.

Variable-cycle engines also could be a solution to adapt the engine to speed and altitude during the flight. However, because of their cost such concepts not yet made it to civil aircraft.

The group also has thoroughly studied pollutant emissions, as well as emissions having a greenhouse effect, such as CO2 and water vapor. It performed simulations with various configurations and various engine combustors at different speed/altitude combinations. Yet, for a given distance, an SSBJ would burn 50 to 100 percent more fuel than a conventional business jet, it concluded.

Hisac was also responsible for development of digital models for noise, pollution, sonic boom, engines and aerodynamics. It conducted acoustic tests on “innovative propulsion configurations,” where engines are located above the aft fuselage. The program also involved wind tunnel tests of scale models.

While Dassault acknowledged the research is still behind that being carried out in the U.S., the Hisac partners are eager for a demonstration program that would be a follow-on to the recent work. As the market for an $80- to $100 million SSBJ would be limited, Dassault is hoping such a project would be the fruit of transatlantic cooperation.