A High Fidelity Brownout Model for Real-Time Flight Simulations and Trainers

A critical operational problem for Army rotorcraft is "brownout" caused by excessive dust and debris kicked up by helicopter rotorwash during take-off and landing. Dust and debris can eliminate visibility creating a safety hazard and severely damaging engine parts and rotor blades. Brownout has accounted for a significant number of military helicopter accidents in Iraq and Afghanistan. Recently it has been recognized that brownout related mishaps can be greatly reduced through prior training. However, brownout rendering in training simulators is typically simplistic, lacking the level of physical fidelity required to properly characterize the formation and structure of the brownout cloud. This paper describes the development and implementation of a physics-based brownout model that can capture the complex flow field generated by rotorcraft maneuvering in the vicinity of the ground as well as the physical process of debris entrainment, transport, and visual obscuration. The model can be operated at high fidelity for off-line brownout analysis or at lower fidelity in real-time piloted simulations. A central element of the model is an advanced rotorwash solution based on real-time, free vortex wake methods that can represent the complex flow field of maneuvering rotorcraft in proximity to the ground. This rotorwash model is coupled to a debris entrainment and transport model and a visual obscuration model to create a complete physics-based model of brownout. This paper will describe these models, their validation, and the integration of the real-time brownout module into one of the U.S. Army's Advanced Prototyping Engineering and Experimentation (APEX) laboratory rotorcraft flight simulations at Redstone Arsenal in Huntsville, AL.