Performance trade-off studies for a retrofit Hybrid Laminar Flow Control System

Recent work in the UK, studying the possible retrofit of a hybrid laminar flow control (HLFC) system to a medium-sized aircraft, is reviewed. The key feature of the work was the use of robust boundary layer tools to design HLFC systems based on direct control of N-factors using a discrete suction chamber technique. The improved HLFC designs were applied to a representative aircraft configuration, leading to a significant reduction in predicted suction mass flow rates, and therefore in pump power requirements and suction system weight. The use of PSE methods to assess suction requirements was further found to reduce predicted suction rates by nearly 25%, increasing the net drag benefit by 10%. Modifications to the wing geometry that were advantageous for laminar flow usually introduced unacceptably large wave drag penalties: the most promising direction for future research therefore appears to be increasing the chord-wise extent of the suction control system. Nevertheless, extrapolating the predicted retrofit HLFC system performance to the entire wing upper surface, tailplane and fin would suggest a potential 61/2 - 7% reduction of total aircraft drag for the representative aircraft at cruise.