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Advanced Laminar Flow tAilplane

Periodic Reporting for period 3 - ALFA (Advanced Laminar Flow tAilplane)

Reporting period: 2019-09-01 to 2020-10-31

A growth of aviation travel is foreseen for the next decades placing an increased emphasis on the environmental challenges. Natural laminar flow technology is considered as one of the promising techniques to reduce fuel consumption within the aerospace industry since it reduces aerodynamic drag. The ALFA project aspires to bring the Natural Laminar Flow (NLF) technology to a next level by offering new profitable design solutions. The scope of the ALFA project is to develop, design and manufacture a full-scale Natural Laminar Flow Horizontal Tail-Plane Demonstrator that complies with the NLF requirements as defined by the aircraft integrator to ensure natural laminar flow will be achieved. The driving NLF requirements are related to very stringent superior surface quality in terms of steps, gaps, waviness, profile, roughness, disturbances etc. whilst still being competitive in weight, production cost/time, maintainability & reparability.

The reduction of the aerodynamic drag of the aircraft by application of NLF on the Horizontal Tail-Plane of a typical business jet will offer a potential of 1% decrease of fuel burn thereby reducing the environmental impact of the expected growth of aviation travel.

The main project objectives of the ALFA project are:
1) To develop, design and manufacture a full-scale NLF HTP (Natural Laminar Flow Horizontal Tail-Plane) Demonstrator
2) To push forward the maturity-level of NLF technology towards market introduction on business jets
The main emphasis at the start of the ALFA project has been on converging and interpreting the stringent Natural Laminar Flow (NLF) requirements in relation to typical HTP structures. The driving NLF requirements are related to superior surface quality in terms of steps, gaps, waviness, profile, roughness etc. whilst still being competitive in weight, production cost/time, maintainability & reparability. During a close collaboration with the aircraft integrator, several conceptual design solutions were generated with high potential to comply with the NLF requirements whilst remaining competitive to all other HTP characteristics.

This has accumulated in a trade-off phase were the design solutions were evaluated in terms of NLF feasibility and cost, weight and maintainability aspects. The outcome of the trade-off phase was a selection of the technologies to be included on the Demonstrator.
The main features of the technologies focussed on were:
1) Optimized assembly processes to minimize the tolerances.
2) Two innovative manufacturing technologies for the leading edge, based on RTM technology (single sided tool) and autoclave technology, with different, promising multi-criteria evaluations, while both technologies have the potential to achieve the laminar criteria.
3) Automated masking operation for fastener heads.

A detailed Demonstrator lay-out has been generated and a detailed design phase has been initiated to further converge towards part-release. In parallel, mono-tool and assembly tool conceptual design has been started.
Certain specific technologies that have been selected for the HTP Demonstrator can be considered beyond the state of the art. These technologies include:

1) Application of an approximate 50 [um] thick anti-abrasion Ni-coating on a curved composite Leading Edge by means of a chemical/electrical deposition process complying to NLF requirements in terms of stringent surface quality.

2) Control of Leading Edge interface to Torsion-Box in order to be compliant to the stringent NLF step and gap requirements.

3) Production of an Hi-Tape UD composite Leading Edge using an automated fiber placement process applying dry fibers to a male mould.

4) Introducing integrally stiffened thermoplastic material on primary aircraft structure (Horizontal Stabilizer Torsion-Box Skins).

The successfulness of the above pursued technologies can only be sufficiently evaluated at the end of the project. In case of full success, and competiveness against non-NLF HTP designs, a NLF-zone on the upper and lower skins up to 50% of the cord can be expected.
The expected level of NLF would reduce the fuel burn of a typical business-jet with 1% and could be considered as a noticeable contribution in reducing the environmental impact of the foreseen growth of global aviation.

The expected results until the end of the project will be a manufactured HTP Demonstrator allowing an assessment of the capacity to manufacture such structure at an affordable price. This will open the door to an exploitation of ALFA results in a future aircraft program, thereby increasing the competitiveness of Europe’s business jet manufacturers and suppliers.
Overview of ALFA Demonstrator