GRAHAM WARWICK / WASHINGTON DC
Gulfstream's proposed supersonic business jet has evolved into a variable-geometry design as the company tries to satisfy requirements for take-off distance, airport noise, subsonic range, supersonic performance and low sonic boom.
The company has completed windtunnel tests at NASA Langley that validated configuration details designed to suppress sonic boom. The design concepts, involving airframe shaping, show promising signature characteristics, says Pres Henne, senior vice-president, programmes, engineering and test.
Initial sonic boom overpressures of less than 0.096 millibar (0.2lb/ft2) and peak overpressures of 0.24-0.29 millibar appear achievable, he says. This compares with initial shock strengths of over 0.96 millibar for Concorde, and could make supersonic flights over land acceptable.
Supersonic overland capability is key to Gulfstream's forecasts of potential sales of 180-350 aircraft.
Goals for the Quiet Supersonic Jet (QSJ) include a cruise speed of around Mach 1.8, range of 8,900km (4,800nm), take-off field length of 2,000m (6,500ft) and an airport noise level 10dB quieter than Stage 4, which Henne says is achievable.
Variable wing sweep is a factor in meeting the field length requirement and "fundamental" to achieving the noise estimates, says Henne.
Variable geometry increases complexity and will make certification more difficult, but the positives outweigh the negatives, he says. There is also a weight penalty, and Gulfstream faces a challenge in achieving its 45,400kg (100,000lb) take-off gross weight target for the QSJ, the limit for meeting the sonic boom and field length requirements.
An aircraft with a cabin cross-section similar to the Gulfstream G550 long-range business jet results in a gross weight of over 68,000kg, while a configuration meeting the 45,400kg gross-weight limit has a smaller cabin cross-section that does not meet the comfort requirements for 5h flights.
The QSJ is still in the early design stage. A "fundamental requirement" before launching a small civil supersonic aircraft production programme, Henne says, is a flight demonstrator to substantiate boom suppression technology and provide regulators with a means to specify a rational sonic boom rule.
Source: Flight International
