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Ground Based Structural/Systems Demonstrators

Final Report Summary - GKN GBSSD (Ground based structural/systems demonstrators)

Executive Summary:

This report details the outputs from the Clean Sky GBSSD phase one programme of work, work package one (WP1): 'Line of flight (LOF) and across line of flight (ALOF) joint concepts for leading edge (LE) panels' and of WP2: 'Wing ice protection systems (WIPS) for metal and carbon fibre reinforced plastic (CRFP) LE components'. The latter WP deals with design considerations for the application of an electrothermal ice protection system onto the surface of the ground based demonstrator laminar flow wing. The programme of work was undertaken by GKN Aerospace Services Limited.

The following conclusions were reached:

1. Top cover attachment: A joggled joint configuration is a viable configuration for the top cover to LE assembly. Joggle spring has been found to occur, but it is considered that this can be compensated in the mould tooling design.
2. Metallic LE: The control of the machining or rolling of aluminium LE thickness has been shown to adequately achieve natural laminar flow (NLF) tolerances. If a metallic LE is adopted for GBSSD phase two it is recommended that this joggled mechanical solution is used. A method for post assembly machining or filling of the fasteners heads will need to be fully investigated.
3. Composite LE: Two concepts applicable to a composite LE have been shown to completely eliminate any concern regarding step tolerances and fastener head disruption. It is recommended that both concepts are further developed during GBSSD phase two if a composite LE solution is adopted. The post assembly machining concept may be suitable for integration with the erosion shield / protection integration, eliminating the necessary fasteners and ensuring a NLF LE.
4. WIPS: Four electrothermal heater mat integration options were examined, namely: bonded to the internal surface of a metallic LE; bonded to the outside surface of a metallic skin; bonded to the outside surface of a composite skin; fastened to the external surface. The relative merits of these systems, in terms of thermal integration, aerodynamic compliance, manufacturability, and maintenance and repair have been summarised.

Project Context and Objectives:

The purpose of WP1 was to conduct a trade study and subsequent evaluation of a range of joint concepts applicable to the LE to wing box upper cover on the Clean Sky NLF wing.

The focus of the programme was the development of concepts that help to mitigate or eliminate the current steps and gaps problem seen as critical to the development of an NLF wing.

From the initial trade study a number of concepts were selected to be taken forward into the evaluation stage. The concepts chosen were divided into four categories:

1. advanced mechanical solution
2. a bonded solution
3. post assembly finishing solution
4. coating solution.

Within each of these categories a number of small scale demonstrator components were manufactured and assembled to assess and evaluate each concept, in line with the assembly and tolerance document supplied by Airbus United Kingdom (UK) and set out in the next section.

Requirements

All tolerance requirements were set using the allowable surface tolerances for A340FTB document supplied by Airbus UK (101105_SFWA_Pres_WP21, 'Allowable surface tolerances for A340FTB', Paul Phillips, Airbus UK). This document defines all the aerodynamic surface tolerances for an NLF wing. All demonstrator components manufactured for phase one have been evaluated against these criteria.

The overall profile deviation is required to be less than +/-0.8mm in critical areas such as the D nose. The primary joint considered by the study is between the LE skin and wing box cover. This is an ALOF joint. The allowable step deviation for this joint is h = +0.26 / -0.07mm where the positive value is for a forward facing step. The gap generated by the joint will be filled post assembly using next generation filler material supplied by Airbus UK. This gap will be controlled to a maximum width of 3mm and a height tolerance of +/-0.07mm. A similar tolerance applies to bolt heads and all other sharp changes in profile.

The acceptance of surface waviness is strongly dependent on its characteristics and location and whether a single or a multiple wave form but typically the b/a (deviation by half wavelength) value must be less than 2:1 000 in order to satisfy laminar flow requirement.

The requirement for surface roughness is defined by two measurable values: the peak value - Rt shall be less than 2.0 µm and the Ra value better than 0.2 µm.

Project Results:

Main Scientific and Technical Results

Two engineering reports have been issued with the results of GBSSD phase one:

For WP1: 11CTC0018PFR

'GBSSD phase one - LOF and ALOF joint concepts for LE'

GKN Aerospace Composites Technology Centre, Filton

For WP2: DEV/R/8220/301

'Ground based demonstrator phase one report' GKN Aerospace Luton

Potential Impact:

The manufacture, flight test, and certification of a composite NLF wing would mark two important milestones. Firstly it would indicate that the advantages posed by composite materials are being fully exploited and allow for the next generation of wing design to fly. Secondly it would significantly contribute to the reduction in fuel consumption and carbon dioxide (CO2) emissions.

The work carried out in GBD phase one lays the ground work for the follow-on phases two and three which will provide the validation of the design and manufacturing concepts formulated in phase one.

List of Websites:

No website has been created for the GBD project