Flying Test Bed Performance Testing of High-Bypass-Ratio Turbofans 2009-01-3133

The commercial turbofan trend of increasing bypass ratio and decreasing fan pressure ratio has seen its latest market entry in Pratt & Whitney's PurePower™ product line, which will power regional aircraft for the Bombardier and Mitsubishi corporations, starting in 2013. The high-bypass-ratio, low-fan-pressure-ratio trend, which is aimed at diminishing noise while increasing propulsive efficiency, combines with contemporary business factors including the escalating cost of testing and limited availability of simulated altitude test sites to pose formidable challenges for engine certification and performance validation. Most fundamentally, high bypass ratio and low fan pressure ratio drive increased gross-to-net thrust ratio and decreased fan temperature rise, magnifying by a factor of two or more the sensitivity of in-flight thrust and low spool efficiency to errors of measurement and assumption, i.e., physical modeling. These configuration-driven challenges come at a time of significantly increased test costs and limited availability of Altitude Test Facilities (ATF).

This paper details the process developed and applied on the PurePower™ Geared Turbofan™ demonstrator engine to address the challenges posed by this combination of engine cycle trends and business conditions. The potential is explored for combining ground-based scale model and rig testing, sea level full-scale testing, and flight testing in the Flying Test Bed (FTB) to achieve in-flight thrust and component performance assessments of the same or better uncertainty as legacy high BPR turbofans achieved in an ATF-based process. In-flight thrust is addressed directly in this paper, and component performance is addressed by considering fan efficiency, which is typically the most sensitive component parameter in high BPR applications.