Lockheed Martin (LM) has teamed with the Air Force Research Laboratory (AFRL) to evaluate over wing nacelle (OWN) configurations to better understand and exploit their potential performance characteristics for improving aircraft energy efficiency, threat avoidance, community noise abatement, and speed agility. This study represented a first-of-its kind detailed parametric study of OWN concepts using modern, high fidelity analysis and design processes to assess their feasibility for future mobility configurations. This effort assessed the impact of configuration type (i.e. low wing, high wing, and low wing/slipper mount), engine size, and engine placement and orientation on aerodynamic performance, acoustic characteristics (including the effects of wing shielding), structural weight, and aircraft stability and control characteristics. In addition, aircraft shape optimization was performed to ensure a true assessment of the performance potential of the OWN concept by minimizing adverse nacelle / wing interference effects. Results from this study indicate that OWN engine installations have the potential to improve aerodynamic efficiency as much as 5% compared to conventional under wing nacelle (UWN) engine installations at transonic cruise conditions (M > 0.80).
Lockheed Martin (LM) has teamed with the Air Force Research Laboratory (AFRL) to study the integration challenges and potential benefits of distributed propulsion (DP) systems on a conventional next generation commercial / military transport. While significant research has been conducted by industry on the power system benefits of DP systems, little has been done to look at the potential integration benefits of this class of propulsion system. The research presented in this paper is directed at answering one question: Do DP systems offer integration benefits? Findings herein indicate that the answer to this question is yes. Specifically, it was shown that DP systems can offer as much as an 8% improvement in transonic efficiency compared to conventional under wing engine installations with equivalent propulsive areas. Arriving at this conclusion required extensive analysis and design work on numerous DP configurations, models with high geometric fidelity to adequately simulate the internal flow paths, and a consistent thrust-to-drag bookkeeping approach to account for propulsive efficiency and integration effects. This effort represents a first-of-its kind detailed parametric study of the integrated characteristics of DP systems using modern, high fidelity CFD based analysis and design processes, the results of which can be applied to any fan driven DP system.
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