Exploring Aerodynamic Methods for Mitigating Brownout

Rotorcraft brownout, which is caused by the entrainment of dust and ground debris by the rotorwash during take-off and landing, is a critical operational problem, and has caused a significant number of military helicopter accidents in theater. Brownout affects safe operations due to the reduction of visibility, in addition to damaging engine components and rotor blades. Recent experience gained from multi-national operations in brownout with a variety of rotorcraft configurations, as well as ongoing work with validated analyses at Continuum Dynamics, Inc. (CDI), suggests that aerodynamic modifications to the aircraft may offer a true solution to the brownout problem, at least in terms of pilot visibility. This paper describes an ongoing combined numerical and experimental research effort investigating the feasibility of aerodynamic solutions to brownout that can be retrofitted to current rotorcraft and/or incorporated into future designs without degrading performance or posing a risk to operations or personnel. Performance degradation is a key consideration for aircraft in combat operations in high/hot/dusty environments, and this effort focuses on solutions to brownout that do not require addition of significant onboard equipment or consumables. This paper reviews the numerical simulation methodology, presents new validation and describes preliminary work assessing the effect of changing fundamental rotor properties (e.g. solidity, twist, blade number etc) on rotorcraft brownout properties. The development and preliminary testing of a dynamic scale rotor test facility, loosely modeled around the Princeton University Dynamic Model Track, for testing aerodynamic concepts for mitigating brownout is also presented.