Paul Lewis/OBERPFAFFENHOFEN
Fairchild Dornier has chosen a novel hybrid winglet/rake configuration for its planned Envoy 7 executive aircraft version of the 728JET. The winglet is also being considered for a proposed new extended range (ER) development of the manufacturer's 70-seat regional jet and the already launched stretch 928JET derivative.
The manufacturer has been conducting wind tunnel testing on five winglet designs, including four from Fairchild Dornier and one from Aviation Partners of Seattle. The recently selected internal configuration is shaped like a shark's fin and combines the characteristics of an upward blended winglet with the aft sweep of a raked wingtip.
The new winglet is intended to reduce cruise drag by at least 3.6% in order to extend the aircraft's performance and, at the same time, improve vortex management. "Aero-dynamically we think this wingtip treatment is the best solution. It weighs less and induces much smaller bending moments in the wing because it is not as big as competing designs, but gets us the same drag reduction," says Duncan Koerbel, Fairchild Dornier vice president 728/928/Envoy 7.
Fairchild Dornier plans to initially fit the winglet to the Envoy 7, which is due to fly at the end of next year with deliveries to follow in mid 2004.
Designers have been looking to enhance the aircraft's performance at altitude through better wing efficiency in order to raise the internal weight allowance for the executive interior from 6,000lb to 8,500lb (2720kg to 3860kg) without eroding the aircraft's targeted 4,000nm (7400km) range.
The company is also looking at using the winglet on the 90-110-seat 928JET (Flight International, 8-14 May), as well as a proposed ER version of the baseline 70-seater which would be available from early 2005. The aircraft would represent a further growth on the 728JET's optional maximum take-off weight of 35,990kg (81,548lb). It draws on changes incorporated into the Envoy 7, which will have a MTOW of 39,500kg, but reduced number of cycles.
Raising the aircraft's MTOW is one option for recovering an overrun in the aircraft's empty weight and meeting payload range performance. The 728JET is currently around 500kg over the empty weight agreed with launch customer Lufthansa. The 728JET's baseline MTOW is set at 35,200kg.
Source: Flight International
