Tiltrotor Aircraft Flotation Stability Simulation

For rotorcraft emergency water landings, Title 14 of the Code of Federal Regulations (CFR) paragraph 29.801 specifies ditching certification requirements to minimize the probability of immediate injury to or escape provisions for the occupants. Currently, rotorcraft flotation behavior is determined for symmetrical regular waves and at specified sea states by scalemodel tests. The cost and development time associated with scale-model testing is relatively expensive and encumbered with scaling error. This paper presents the state-of-the-art tiltrotor aircraft flotation stability simulation methodology developed at Bell Helicopter based on the multi-material Arbitrary Lagrangian-Eulerian (ALE) technique in LS-Dyna®. The methodology is validated by correlating with the existing BA609 tiltrotor scale-model test data. It is demonstrated that the developed analytical tool is capable of simulating (or "virtual-testing") the tiltrotor flotation (i.e., buoyancy and stability) phenomena correctly subjected to a Sea State 4 hydrodynamics wave condition.