Surface roughness can contribute significantly to the drag on an aircraft. Several materials, paints and protective coatings used in Army aircraft have different surface compositions, textures and roughness characteristics. The roughness also changes over time due to weathering and environment. The resulting differences in roughness height can change parasite drag, which affects the performance and operational capability of the aircraft through the engine power required for flight. Current computational fluid dynamics (CFD) methodologies cannot geometrically simulate surface roughness within the time and computational resources typically available for engineering drag estimation of complex shapes. Existing roughness models also assume a single characteristic surface roughness over the entire body, resulting in an over-prediction or under-prediction of the aircraft’s true aerodynamic drag. To address this issue, IAI and its collaborator, University of Maryland, have been awarded a new contract entitled, “Variable Surface Roughness Transition and Turbulence Modeling for Rotor Parasitic Drag.” A numerical model will be developed for variable surface roughness distributions of materials such as glass, metal, paints and protective coatings that can be used in CFD simulations for accurate estimation of the parasite drag of an aircraft. The end product will be a surface roughness numerical model based on efficient engineering algorithms that can be implemented into government and industry production-level CFD codes to estimate parasite drag of an Army aircraft within its design envelope.