Installation Penalty of Aero-Engines on Narrow Body Aircraft

Abstract

Decades of improvements of engine efficiency on internal engine components through better materials, design methods and novel fabrication techniques have resulted in fuel consumption reductions. Another major factor for improving engine fuel consumption has been the increase of bypass ratio. However, this has a significant impact on engine dimensions and weight, and, consequently, the installation of the engine on the airframe.
Evaluation of engine installation penalties is not a new topic; literature provides various studies on aerodynamic effects. These primarily studied the effects of drag increase and the impact on drag of engine location and nacelle shape. This article investigates the performance impact of installation penalties from an increase in bypass ratio on narrow body aircraft, specifically the fuel consumption, weight and stability. Additionally,
an analysis is made comparing aircraft retrofit and redesign for increased bypass ratio engines. It can be concluded from retrofit analyses that engine size is more significant than its location. Changes in aerodynamic center, CLα , and CMAC cause stability/controllability criteria to shift to the left. Heavier engines at the same spanwise location cause a more forward CG location, which may become limiting. With the engine increasing in size (thus increasing the drag and increasing the weight), the overall increase in fuel burn is 5.9%. However,
the decrease in fuel burn due when the SFC and engine effects are considered together, the fuel burn drops by 50%. The reduction in fuel burn thereby negating the increase in engine weight, drag, and integration issues.
From BPR 10 onwards, the decreasing trend in tail size stagnates and actually reverses, indicating that larger tail sizes might be required for even larger BPR engines.