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Design & Manufacture of a ground based structural/systems demonstrator (Phase 2)

Final Report Summary - GBSSD(2) (Design and manufacture of a ground based structural/systems demonstrator (phase 2))

Executive Summary:

Phase two of the ground based demonstrator (GBD) project was launched at the end of 2010 with the objective of developing a detailed design for the leading edge (LE) of a laminar flow wing. In the first half of the GBSSD(2) project the design was fluid. Although initially targeted at Kruegers two and six, after two months the investigation was refocused on the areas of Krueger four and Krueger five. This was a challenge for the design team because of the immaturity of Krueger mechanism design in this area. Many changes had to be made to datums, component locations and bolt positions to resolve clashes. As a result the project was delayed by six months and ran over budget.

However, by the end of 2011 the mechanism design was finally established and work on detailed design could proceed. Concept down-select was achieved in April 2012 allowing the design to develop towards C-maturity and the detailed interfaces to be negotiated. The project was completed in July 2012 with a successful C-Mat review of the design.

The achievement of this design was an important milestone in the Clean Sky programme because it forms the 'baseline design' taken into GBD phase three. During GBSSD(2) work continued on establishing the feasibility of the wing ice protection system (WIPS) culminating in thermal fatigue testing of a representative section of the LE with integral WIPS.

Project Context and Objectives:

Phase two of the GBD was launched with the objective of developing a detailed design for the LE of a laminar flow wing for the next generation of medium and long range aircraft. A number of key challenges were addressed:

1. the maintenance of joint tolerances, panel waviness and aero profile within the tight tolerances required for natural laminar flow (NLF). The assembly and joint tolerances required were specified by Airbus United Kingdom (UK) and these are set out in the next section.
2. the incorporation of an integrated WIPS within the LE skin and the demonstration of the performance of the assembly under thermal cycling conditions.
3. the provision of a LE erosion shield that will maintain a high standard of surface finish under operational conditions at the same time as providing full lightning protection.
4. a structural design which, although compromised by the large under-nose aperture for the Krueger flap was capable of carrying the high aerodynamic loads fed into the structure by the Krueger deployment mechanism.
5. the integration of a novel concept Krueger mechanism with linkages and actuators that occupies a substantial portion of the LE volume.
6. optimisation of the structure for the Krueger was constrained by the need to use drive gearboxes and drive links from existing aircraft.
7. the requirement to maintain system segregation in a very narrow LE cross-section.

Aerodynamic 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 across line of flight (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:

Six substantial engineering reports have been issued with the results of GBSSD phase two (see project deliverables):

1. Down-select presentation 04 April 2012
2. QRHF50002 GBSSD design and interfaces
3. DEVR8493_301 WIPS reliability and maintainability
4. DEV8477 issue two thermal cycling report
5. DEVR8542_301 wing ice protection integration
6. 12CTC0021PDR issue two lightning protection

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

List of Websites:

No website has been created for the GBD project