The high lift system of large transport aircraft comprises leading edge slats and trailing edge flaps and is deployed during take-off and final approach, providing additional lift to get or stay airborne at low speeds.
Symmetric flap actuation is traditionally assured by coupling all flap surface actuators to a torque shaft system, which extends along the rear spar of both wings and is driven by a centralised hydraulic, electric or hybrid motor. The actuators are located at or near special flap support structures called track beams which transmit the lift produced by the movable flap surfaces to the wing.
Conventional flap drive systems have a low efficiency, require a high installation effort with shafts and gearboxes distributed across most of the wing trailing edges and offer no functional flexibility, e.g. differential surface deflection.
The NEFS consortium is proposing a track integrated single flap drive system for the deployment of wing high lift surfaces. The new system is a fundamental change compared to state-of-the-art high lift systems and will significantly improve the availability, maintainability and flexibility of the system and hence the performance of high lift systems when compared with state of the art systems flown today in commercial transport aircraft. This new technology is an enabler for new functionalities, which are developed in RTD projects like AWIATOR, NACRE or ATEFA.
The main objective of NEFS was to replace the traditional drive systems by a distributed electrical flap drive system that is completely integrated into the flap support structure. The transmission shaft system and centralised motor will be replaced. The track beams were redesigned to enable an optimised system-structure solution for this new flap drive system. This provides the opportunity for an innovative composite design in flap support structures.
The particular targets of NEFS are:
- new functionalities of the high lift system via differential flap setting (DFS), like accelerated vortex decay, roll trim and roll control support;
- reduce the operational interruption caused by high lift systems by at least 15%;
- improve the drive system efficiency by at least 25%;
- 3% in L/D improvement in cruise via differential flap setting (DFS);
- 20% weight reduction of the flap track beam due to highly integrated composite design;
- 5% cost reduction in the manufacturing and assembly of the flap track beam due to minimised part number;
- improved maintainability;
- reduced installation effort (for design and manufacturing).
As a baseline for the boundary conditions and the assessment of improvements, reference data was adopted from a state-of-the-art commercial transport aircraft.
One of the main criteria for the system to be developed is the high requested level of redundancy, primarily concerning the motors and electronics. To address this problem, advanced redundancy concepts will be developed.
Different drive system concepts were conceivable to reach the above-mentioned goals: a high torque/low speed approach with a rather heavy motor, but possibly making an additional gearbox obsolete, will be compared to a geared low torque/high speed drive. The competing solutions were developed by different partners.
A highly integrated composite design was realised to achieve a significant weight reduction of 20% in the flap support structure compared to the metallic reference. In order to integrate a maximum amount of composite expertise into the design, two different concepts were developed by different partners. The concepts were evaluated by all partners and the best solution was realised in the design and manufacturing phase.
During the drive system development it was assured and verified by CATIA installation studies that the drive system fits into the limited space below the track beam fairing, requiring a close link between system and structure development activities.
The analysis of repercussions of system performance and failures on aircraft behaviour requires combined system-aircraft simulation and aircraft performance analysis. Results from this analysis may reveal the necessity of additional monitoring functions or tighter monitoring thresholds.
If successful, the NEFS flap drive and support system will set a benchmark for future aircraft models. The proposed approach will be flexible enough to cover almost all kinds of high lift system requirements including advanced aircraft and wing configurations.
The results of NEFS will be reported and engineering design recommendations will be published in order to assure a seamless exploitation of results. Utilisation of this technology will significantly contribute to the European aerospace industries' capability of supplying products that can maintain 50% of the market for large transport aircraft.
Although the European aircraft systems suppliers' global market share is significant, US system suppliers still have the dominant position in almost all product groups, with the US industry being strongly supported by its government. NEFS RTD work will support the systems industries’ striving for highly competitive products and thus prepare the ground for a balanced market access comparable to the one achieved by Airbus. The same holds true for the partners involved in structure development.