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ImpNLFFD Report Summary

Project ID: 641530
Funded under: FP7-JTI
Country: United Kingdom

Final Report Summary - IMPNLFFD (Design, Manufacturing, Qualification and Assembly of an Improved NLF Wing Leading Edge and Upper Cover Flight Test Article)

Executive Summary:
The ImpNLFFD program is an on going area of research and technology aimed at developing the capability and understanding of Natural Laminar Flow (NLF) for the next generation of civil aircraft. It is undertaken in support of the Smart Fixed Wing Aircraft (SFWA) program to mature a NLF technology stream for a future short range transport aircraft and is intended to support the TRL process by the design, manufacture, test and demonstration of an integrated NLF wing leading edge and Upper Cover assembly, as a flight test demonstrator

The NLF aerofoil coupled with improved aero-smoothness, offers higher efficiencies in aerodynamic performance and a reduction in drag, contributing to an overall increase in an aircraft’s efficiency. This in turn allows for potential reductions in aircraft emissions by reducingfuel burn. Achieving these reductions would be a significant step towards reaching the ACARE goals for 2020, including a 50% reduction in CO2 emissions and an 80% reduction in NOx emissions.

The requirements of a NLF wing differ significantly from a conventional turbulent wing, requiring changes to the architecture of the wing, the aerofoil definition, the detailed design concepts and manufacturing processes. The aerodynamic performance of a natural laminar flow wing is highly dependent on meeting very high aero-smoothness tolerances including steps and gaps, surface roughness and surface waviness tolerances, in the regions where laminar flow is to be maintained.

Project Context and Objectives:
The demonstrator aims to validate that a jointed wing concept (Leading Edge + Upper Cover) can be manufactured in realistic and repeatable conditions appropriate to a civil short range aircraft to the required level of aerodynamic surface quality to achieve Natural Laminar Flow. The particular challenges this presents are summarised below.
• Open section leading to reduced stiffness;
• Krueger Mechanism space requirement leading to shallower rib & reduced stiffness;
• Reduced wing section leading to reduced stiffness;
• Accommodation of Krueger mechanism leading to a wider rib spacing;
• Demanding surface finish requirements leading to reduced 3D disturbances (mechanical fastening);
• Reduced access for drilling / fitting assembly to wing box.

From experience on existing Clean Sky Smart Fixed Wing Aircraft (SFWA) calls, current Leading Edge and Upper Cover design and manufacture capability, and thorough investigation into the Call, GKN recognise the very demanding tolerance and hence manufacturing requirements to achieve a successful demonstrator outcome. The Leading Edge and Upper Cover design has been progressed by GKN up to an intermediate standard in the previous project call and therefore recognise the
challenges imposed on satisfying high tolerance requirements. Importantly, GKN are aware that ‘traditional’ wing manufacture and assembly techniques will be unable to achieve the required tolerances and have established, during the previous call, techniques and process to optimise the design and manufacturing techniques specifically for NLF. For this call, the flight demonstrator, GKN have employed existing LE and Upper Cover design and manufacture capability employed with Airbus, along with composite materials and advanced manufacturing techniques to provide the step change in technology required to meet the challenging aerodynamic performance, weight and cost criteria for the next generation of large civil aircraft fitted with advanced NLF wings. The Baseline Work Package consists of the following components; (Starboard Wing Only):

Mid-Scale Demonstrator
• Representative section of the composite Upper Cover to validate manufacturing concepts and provide engineering feedback to design and stress activities;
• Provide critical spring compensation data for full scale tooling suite manufacture.

Composite Upper Cover:
The Upper Cover is 8.6m in length and 1.7m in chord at maximum point. It has six stringers at 200mm pitch. It covers eleven wingbox ribs, nominally at 800mm pitch. The basic skin thickness varies from 13.5mm to 5.4mm.

• Composite Upper Cover similar in size to A340 Panel No.4 top;
• Composite Co-Cured stringers and spar-cap to enable required stiffness of Upper Cover;
• During assembly phase, metallic rib feet will be mechanically fastened to the Upper Cover and the aerodynamic surface recovered using the GKN process developed within the specific work package.

Metallic Leading Edge
The Leading Edge consists of four skin sections split roughly equally along the span of the BLADE wing. The skins consist of a thin aluminium skin portion with integrally machined stiffeners. For all four sections there are two spanwise stiffeners. For one local portion there are a number of chordwise stiffeners. LE Rib attachment flanges are integrally machined at all locations.

• Metallic D-Nose (Leading Edge Skins)
• LE metallic ribs
• Attachment brackets and butt straps
• Corner rad crown tension fittings for attachments to the transition structure

Project Results:
GKN Aerospace has delivered the critical leading edge assemblies and upper covers that form part of the NLF wing section on the starboard wing of the Airbus A340 flight test aircraft. These structures offer NLF levels of performance through the adoption, by GKN Aerospace, of a totally new design approach and the application of novel manufacturing technologies that deliver the ultra-high tolerances and exceptional surface finish required. The ImpNLFFD programme is allowing GKN to progress innovative technologies, concepts and capabilities with the potential to bring about a step change in aircraft fuel consumption.
The key challenge with designing and manufacturing an NLF wing, with the many aerodynamic benefits that it promises, stems from the need to tightly control the wing surface. It is vital to eliminate features such as steps, gaps, surface roughness and waviness or fastener heads as these all lead to more traditional ‘turbulent flow’ performance levels. The GKN Aerospace team has created these integrated, co-cured composite upper covers and very high tolerance leading edge surfaces using the same structured design and development process applied in commercial aircraft programs. As a result, GKN’s first part was of very high quality and has been delivered for the flight test program.

Potential Impact:
The achievement of a flying technology demonstrator is a key step towards the introduction of the laminar flow wing concept for the next generation of civil passenger aircraft. The adoption of Natural Laminar Flow technology will bring fuel efficiency savings of around 10-15% with a corresponding benefit in CO2 emission reduction. The aerospace sector currently contributes in excess of €30Bn to Europe's balance of trade. The timing of the Clean Sky project provides a critical impetus to NLF
development targeted on first introduction on the A30X. Winning the aircraft production competition with this aircraft will secure and expand Europe's valuable aerospace sector for the next 30-40 years.

Furthermore, the establishment of Natural Laminar Flow Wing design is a "break-through technology" which will have a major impact on the level of aircraft CO2 and NOx emissions. As aircraft designs using this technology are introduced into the civil aircraft fleet, significant progress will be made towards the achievement of the ACARE goals on airborne emission reduction. As a result of the Clean Sky work this can be achieved first by European aircraft suppliers before 2020.
Ultimately our competitors will be forced by commercial considerations to follow this technical lead with perhaps a 10 year delay, with the world-wide civil aircraft fleet having adopted NLF technology by 2030.

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GKN Aerospace Services Limited
United Kingdom
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