Interview 4

 
 



Emmanuel Detaille, Chief Technology Officer, Coexpair


Q1: You are involved in the activities aiming to check the feasibility and to manufacture new structural concepts of the landing gear doors to reduce vibration levels. Could you please explain us the work performed to develop the new design of the Nose Landing Gear Door (NLGD)?

A1: Coexpair & SLCA are currently working on the design of the NLGD (i.e. frontward door as shown on figure 18). The objective is to replace the current sandwich NLGD by a monolithic structure for flight test.

Some major development steps have been identified to meet the objectives defined at the beginning of AFLoNext project :

  • Door concept selection
  • Detailed design of the door
  • Design of the mold
  • Manufacturing of the door

The current design proposals are based on both the load cases and Interface Control Drawings (ICD) provided by Airbus Spain and the background from previous IMS&CPS project (see figure 19):

Step 1 – Concept generation

  • review of preliminary requirements between SLCA & Coexpair (compliance matrix)
  • analysis on how to meet main requirements (e.g. same shape envelope, same connections as current ones etc.)
  • ranking of all generated concepts in three main families on the basis of a trade-off conducted with several criteria : technical (inspectability, withstand load cases…), production (suitability for potential serial production), Aflonext requirements (time schedule with respect to flight test)
  • current auxiliary parts kept identical to ease door installation on the aircraft

Step 2 – Final design based on selected NLGD concept (see figure 20).

  • FEM analysis to freeze the lay-up in each section
  • Definition of ply groups for preforming in each area
  • Definition of the final geometry (3-D CAD model)
  • Definition of adaptations of some existing connections if needed


Q2: What were the criteria for selection of the final NLGD concept?

A2: As described previously, the ranking of all generated concepts has been operated in three main families on the basis of a trade-off conducted with several criteria : technical (inspectability, withstand load cases…), production (suitability for potential serial production), Aflonext requirements (time schedule with respect to flight test).


Q3: What are the stakes of the Finite Element Model (FEM) analysis?

A3: There are several stakes:

1. Functionality – Check similar global stiffness of the new NLGD to be able to close both the doors during the test.

2. Safety – Check no delamination propagation under ultimate loads (1.5 times the maximum load ever seen during all the life of the aircraft) & check no failure of the door (in case of door actuation failure). This method is similar to certification for parts for serial production, the difference is that in this case, as the door will fly only a few dozens of minutes (and not for several years), the qualification process near the authorities for the flight test will not require, for example, fatigue tests (tests used to show that a part can withstand a load several dozens of thousands of time over several years).


Q4: What can you tell us about the manufacturing process that will be used i.e. the Same Qualified Resin Transfer Moulding (SQRTM)?

A4: SQRTM is a robust alternative to Autoclave combining advantages of RTM (closed mold process) with advantages of autoclave (high toughness resins)

  • SQRTM is an Out-of-Autoclave (OOA) process
  • material allowables generated by SQRTM are equal or slightly better than ones obtained by autoclave
  • closed model process (see figure 5) as RTM (in comparison to autoclave : very good control of thickness so of the volume of fiber, and so of the mechanical properties + possibility of high level of integration of functionalities)
  • SQRTM allows use of program-specific prepreg (“same qualified”), including toughened systems such as Hexply 8552, Hexply M21, Cycom 977, Cycom 5250-4 BMI, and Toray 3900-2 (BMS 8-276)[1]
  • tape-laid, drape-formed or hand-laid then debulked under vacuum
  • tooling is Al, steel or Invar
  • possibility of net edge
  • as tool is heated, small quantity of prepreg resin is injected into tool to fill tool cavity around edges of part, resin hydrostatic pressure maintained at 8-9 Bar during cure

[1] Cycom 977-2 and Cycom 5250-4 are registered trademarks of Cytec. Hexply 8552 and Hexply M21E are registered trademarks of Hexcel. Toray 3900-2 is a registered trademark of Toray.