By Guy Norris in Seattle
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 between 340 and 450kg (750-1,000lb) in weight.
The fully automatic system, which is thought to be the first practical application of the long-studied variable camber concepts evaluated by both Airbus and Boeing since the 1980s, will be “completely transparent to the flight crew” 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 0.5º 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 35kg of weight, Sinnett says the predicted "0.4 count in drag reduction" will convert into approximately 450kg of saved weight. The system will be capable of moving the trailing edge through a 3º arc, with the edge being set up and down by as much as 1.5º 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 the simpler flaps and the extension of the integrated FCS to include both vertical and lateral gust alleviation. The system also includes drooped spoilers which, for the first time, can be used to tailor the flow between the wing structure and the trailing edge flap. “We will control the slot very closely, which is what you use to re-energize the flow,” he adds.
Boeing also reveals it is also developing a new, integrated form of cockpit voice (CVR) and flight data recorder (FDR) into a single system dubbed the enhanced airborne flight recorder (EAFR).
Smiths Aerospace is to build the system under subcontract from 787 avionics prime Rockwell Collins as part of the communications and surveillance system. Building on the most recent developments of the digitally-based, solid-state CVR/FDR, the EAFR will “combine data acquisition functions and the FDR, and incorporate crash protected memory,” says Sinnett.
Although meeting the data collection and crash-protection requirements of the latest US Federal Aviation Administration mandates, Boeing’s original EAFR concept “didn’t meet the letter of the law” in some specific areas including power supply. “We had to work with the FAA to get an acceptable means of compliance with multiple sources of power by putting two on the aircraft,” says Sinnett who adds the EAFRs will be located “in the nose and one in back.”