The Digital Thread for Structural Sizing Applied to a Large Drone

Aircraft design is a highly complex process that involves a multitude of analyses and challenges. The aircraft must be able to withstand the various forces it will encounter during flight, including aerodynamic and aero-elastic loads, inertia loads and vibrations. Usually, the flight physics team is responsible for evaluating the loads that the aircraft will experience during its lifetime and selecting those that are seen as most critical for structural integrity. After screening, a “balanced” loads set, combining external and inertia loads in a physical meaningful way, will be supplied to the internal loads team. While the flight physics team would evaluate 100 000 mission points, the internal loads team would receive just a few 10 000 loadcases. To further focus and accelerate the sizing process airframe subsection teams will receive a subset of these and referred to as the critical loadcases. All primary structural components are then sized against this critical set; the design is updated, and a new set of loads is generated, leading to the next loop. This process will repeat itself a few times until the program creates the loads and stress certification dossier. Both loads management and sizing are critical to the success of the program. The ability to get the right loads on the right component faster allows the stress team to kick off the sizing process earlier and with more confidence. The stress analyst then relies not only on quick access to loads, but also on geometric details and material data to feed the stress methods that evaluate various failure modes and reduce the weight of the structural members while maintaining an acceptable margin of safety. Unfortunately for the industry, both loads management and sizing remain tediously manual, resulting in errors, missed weight targets and program delays. The objective of this paper therefore is to describe a novel approach for structural sizing of a large drone bringing loads management, design, FEA and stress analysis together in a digital thread. The upcoming sections will describe the type of drone and how its structural layout and GFEM were constructed. It will continue with a loads review and describe the loads down-selection process, and which methods were used for sizing and how they have been integrated. It will conclude by showing the results of the sizing process and cover how everything can be linked in a digital thread.