Development and manufacturing of cost efficient highly integrated composite structures Christina Altkvist, Jonas Wahlbäck, Per Hallander, Tonny Nyman Stockholm 2010-10-19 Flygteknik 2010

Development and manufacturing of cost efficient highly integrated composite structures Saab research activities has been carried out within the FP6 European project ALCAS ALCAS – Advanced Low Cost Aircraft Structures The objective is to reduce the operating costs of relevant European aerospace products by 15%, through the cost effective application of carbon fibre composites to aircraft primary structure, taking into account systems integration Flygteknik 2010 2010-10-19

Agenda Background Material down selection Airliner Wing Platform Hot Drape Forming Manufacturing Center Wing Box Rear Spar Summary and Conclusions Business Jet Wing Platform Target and assumptions Manufacturing of Sub Scale Wing Box Testing Cost & Weight Flygteknik 2010 2010-10-19

ALCAS Overview 60 partners from 18 European countries A total budget of 101.64 million euro Duration: 2005-02-01 - - 2011-01-31 Coordinated by Airbus Organized into four technical platforms Airliner Wing Airliner Fuselage Business Jet Wing BJ Fuselage Flygteknik 2010 2010-10-19

The Airliner Wing Platform WP1.2 Lateral Wing Box Global Spar deformation Saab: Analytical prediction of deformation after curing for Lateral Wing Box Rear Spar WP1.3 Centre Wing Box Saab: Design and cost efficient manufacturing of Centre Wing Box Rear Spar Flygteknik 2010 2010-10-19

The Business Jet Wing Platform A BJ Wing reference model was defined Four teams - four different technologies Partner 1 Partner 2 Saab (Sweden) Partner 4 Saab: Design and cost efficient manufacturing of BJ Sub Scale Wing Box with high level of structural integration Test set-up One shot curing Flygteknik 2010 2010-10-19

Material down selection For CWB Rear spar and BJ Wing SSWB cost savings can be achieved by Less expensive raw materials → Investigate ”non aircraft grade” carbon fiber Innovative prepreg processing methods → Investigate ”out-of-autoclave” cure Less expensive prepreg handling & layup → Investigate ”thick plies” and use ATL Initial concept Prepreg system, MTM44-1 from ACG with an out-of-autoclave process. FAW=268 g/m2 Processing trials to determine a suitable cure cycle and investigate laminate quality when moving from thin flat laminate to thick complex structures Back-up solution Autoclave process with Airbus qualified prepreg system M21 Porosity problems in C-shaped spar Flygteknik 2010 2010-10-19

The Airliner Wing Platform Design, manufacturing and testing of an inner wing and centre wing box Overall objective: 20% weight saving in the wing structure, with zero increase in recurring cost against the reference state-of-the-art metallic wing.  Various composite materials and processes used in different components Structural test will be carried out to validate the design Saab: CWB rear spar Length: 2.5 m Web height: 0.9 m Flange width: 300 mm Thickness: 16-22 mm Flygteknik 2010 2010-10-19

Hot Drape Forming Trials Manufacturing concept: Flat layup of a stack of prepreg Hot Drape Forming on male tool Curing in autoclave Manufacturing trials to: develop the HDF process and to investigate influene of lay-up sequence u x = 0 along line corresponding to 1% global strain y = 0 along line Hot drape forming of flat laminates with fully interleaved layup was very challenging A patch layup design preferable from a manufacturing point of view Flygteknik 2010 2010-10-19

Manufacturing – Full Scale CWB Rear Spar Design: Monolithic inward facing ‘C’ section spar with fully interleaved lay up Integration: Bolting selected for spar to skin attachment and for stiffener to spar attachment Material: Prepreg T800/M21 Tooling: Invar/Steel female mould tools Process: Hand lay up on male tool. Autoclave curing in female tool. 1) Manual Lay-up 2) Set up in female tool 3) After Curing 4) Loaded into assembly jig Flygteknik 2010 2010-10-19

Manufacturing Result Layup started in April 2007 Assembly completed in June 2007 Final inspection and delivery in September Good geometrical tolerances with female tool Waviness and porosity in some areas of the spar corners due to insufficient debulking of the lay-up To verify the manufacturing process testing of travellers cut out from the spar was carried out. This testing together with supporting stress analysis resulted in an approval of the rear spar. Flygteknik 2010 2010-10-19

Summary and Conclusions One piece C-spar with metal stiffener most optimal from weight- and cost point of view Initial manufacturing with out-of-autoclave material gave raise to a high degree of porosity. Further development needed but tight time schedule made it impossible Hot drape forming of prepreg material without wrinkles difficult in tapered areas when fully interleaved design rules applies The female tool gives a good outer surface and the tolerance is more or less given by the spring back of the flanges. Machining of the outer surface is not needed. The height of the spar is controlled by using Invar in the web of the tool. Flygteknik 2010 2010-10-19

Preamble The Business Jet Wing Platform F7X Preamble The Business Jet Wing Platform Sub Scale Wing Box - SSWB Design a composite wing box with 10 % reduced weight and 20% reduced RC compared to a metallic reference. 4 teams – 4 different approaches. Common approach: High level of integration – less assembly. Demonstrate each technology through manufacturing and verification. LRI RTM Prepreg ”Mix” Flygteknik 2010 2010-10-19

Target and assumptions Manufacture a wing box with Skin, stringers and spars integrated and cured in one operation. Further cost reductions: Thick prepreg ATL Automated Tape Laying HDF Hot Drape Forming Design philosophy: No use of fasteners between upper skin and adjacent spars. To have rigid surrounding tools and ”adjustable” internal tools. Have Recurring Cost as top priority during the design phase. Flygteknik 2010 2010-10-19

Manufacturing Lay up started In mid January. Demolding end of January. Inspection and trimming in February. Assembly with metallic structure from end February to end of April. Strain Gauge installation beginning of May. Delivery to Prague for verification mid May. Notably: 4 month from manufacturing start to delivery. Flygteknik 2010 2010-10-19

Manufacturing Result Composite Box Prepreg solution in combination with this tool concept seems to be robust. First attempt successful. Geometrical tolerances acceptable. Scale up should be possible. (Tools are low weighted) Both tool surface and ”bag” surface of smooth condition. Laminate quality very good. No delaminations. No “porosity” detected. (Edge areas) Rear Spar difficult to manufacture due to shape. Flygteknik 2010 2010-10-19

Two very satisfied engineers. (Without helmets) Test and Test result. Test started end of July 2009 and final testing was performed at lunch time 11 September 2009. 200% LL was reached without failure. Static and fatigue. To test the critical spar/skin splice area, artificial defects and Impact damages was introduced. Impact damages were introduced after the limit load test. No damage propagation was detected during the fatigue load session. The innovative design concept without fasteners between forward and rear spar and upper skin was verified by this test. Overall good agreement between the measured and predicted strain values from FEM. Test set up in Prague Two very satisfied engineers. (Without helmets) Flygteknik 2010 2010-10-19

Cost & Weight Cost and Weight Assessment is on going together with Dassault and involved partners. Initial results indicated a rather high weight but on the other hand, a very low cost which was in line with the design approach. The initial results were “considered” to include too much company specific skills and advantages. Due to this, efforts have been taken to harmonize the manufacturing values. (Common standardized values to be used for all 4 concepts) With harmonized values it can be concluded: The prepreg box has the lowest manufacturing cost. The prepreg box has (together with Dassault’s LRI) the lowest weight. Number and type of fasteners have a huge impact on the total cost. Flygteknik 2010 2010-10-19

Summary & Conclusions The Business Jet Wing Platform Composite Box We do see a potential of this design concept specially from a cost point of view. With a redefined design principles we believe the weight could be reduced significantly. Assembly The assembly cost could be reduced with use of more robotic drilling and relaxing of (harmonizing) sealing requirements. Questions! Thank you for your attention! Flygteknik 2010 2010-10-19