Boeing plans to test and develop a trailing-edge variable camber (TEVC) system for the 787, which it says will reduce cruise drag and save the equivalent of 340-450kg (750-1,000lb) in weight. The fully automatic system, thought to be the first practical application of the variable camber concepts evaluated by both Airbus and Boeing since the 1980s, will be “completely transparent to the flightcrew”, says 787 systems director Mike Sinnett.
Linked directly into the flight-management system and digital flight control system, the TEVC will operate by deflecting the trailing edge flaps in 0.5° increments while in cruise. The motion will be driven by an electric power drive unit integrated with the torque-tube-driven flap actuation mechanism. Although the TEVC control unit will add around 36kg of weight, Sinnett says the predicted “0.4-point count in drag reduction” will convert into roughly 450kg of saved weight. The system will be capable of moving the trailing edge through a 3° arc, with the trailing edge being set up and down by as much as 1.5° either side of a neutral setting position.
Boeing says the TEVC initiative is possible because of the clean sheet design of the 787 flight-control system (FCS), added to the adoption of simpler flaps and extension of the integrated FCS to include both vertical and lateral gust alleviation. The system also includes drooped spoilers that, for the first time, can be used to tailor the flow between the wing structure and the trailing-edge flap.