Of the hundreds of structural parts and hundreds of moving parts on a commercial airplane, there are very few that are both structural and moving that also face the aerodynamic and mechanical-performance demands placed on landing gear doors. Among the largest moving structures on an aircraft, they must perform flawlessly under all flight conditions and meet a host of contingency requirements in the event of aircraft power loss or landing-gear failure.
Daher-Socata (Tarbes facility) is the Tier1 in charge of the development, design and build the main landing gear door (MLGD) for the A350 XWB (4mx2,2m).
The MLGD solid laminate skin is layed up on this Coriolis automated fiber placement system mounted on the end of a KUKA robot.
The doors are hinged back-to-back in the center of the fuselage and open only when the landing gear are retracted or deployed. Located under each wing, adjacent to the fuselage, each landing gear levers inward for storage under the fuselage. The MLGDs are flat and rectangular except for a 0.9m wide curved tab that extends from the end opposite the hinges to conform with the fuselage curvature.
Daher-Socata made the decision to design the A350 XWB’s MLGD with warp built in to keep the door snug and rattle-free.
Engineers discovered that constantly changing air pressures as the aircraft changes altitude and airspeed cause the MLGD to change shape. Designers determined where and how these changes occurred and then used that data to optimize the design.
After several iterations, Daher-Socata designers settled on a final “warped” design that included an apparent gap of unspecified dimension at the door closure between the MLGD edge and the landing gear opening in the plane’s underside. To match both objectives: to properly stress the door and to meet aerodynamic requirements.
Based on the article “Main landing gear doors designed for all contingencies” published in High-Performance Composites