Turbofan Ice Crystal Rollback Investigation and Preparations Leading to Inaugural Ice Crystal Engine Test at NASA PSL-3 test Facility

Abstract

This paper documents some of the events leading up to the inaugural ice crystal icing, turbofan engine test conducted in the Propulsion Systems Laboratory (PSL) at NASA Glenn Research Center in Cleveland, OH. For the past 25 years there has been increasing concern in the aviation industry over icing phenomena encountered during flight, including a little understood phenomenon called “Ice Crystal Icing”. Several groups of experts drawn from Industry and Government research agencies were assembled to address this and related problems. Those groups include the Engine Harmonization Working Group (from 1988 – 2007), the Engine Icing Working Group (2009 ), and then the Ice Crystal Consortium was formed in 2009. As flowdown from the EHWG and EIWG, the Technology Plan has two tasks which are pertinent to this paper: Task 3: Fundamental physics of ice accretion and shedding, and Task 4: Test methods and facilities. Somewhat in parallel with the above efforts, from 1988 through 1997, the Lycoming (later AlliedSignal, then Honeywell ) turbofan engine model ALF502R-5 installed on the British Aerospace (Bae146) aircraft experienced uncommanded thrust reductions (rollbacks) when cruising in the vicinity of major thunderstorms at normal cruise altitudes and speeds. As a result, Honeywell began a series of studies to better understand and resolve the issues. Those studies included creating computer models for an engine design that pre-dated computers, rig testing in an altitude chamber, and, eventually, flight tests. During flight testing, the rollback phenomenon was observed and characterized, via an instrumented engine, S/N LF01. This paper discusses those tests and findings. Changes in production engine hardware eventually alleviated the condition, and all fielded engines were retrofitted, eliminating the issue. Honeywell, as a member of the above-mentioned working groups and the ICC, was aware of an industrywide need for more data on the Ice Crystal phenomenon, and began discussions with the EIWG and ICC, along with test facilities planning to modify engine test cells to reproduce Ice Crystals. The NASA facility became available first, and LF01, in its un-modified flight test configuration, was brought out of storage and prepared for testing. Honeywell also designed and fabricated all of the cabling, a test frame, and prepared a large amount of ancillary equipment, and installed its engine into the Propulsion Systems Laboratory (PSL) at NASA Glenn Research Center in Cleveland, OH. Ice Crystal testing was successfully conducted from February 7 through March 2, 2013. Honeywell is currently preparing an identical ALF502R-5 engine, (S/N LF11) with a greatly expanded suite of instrumentation, to be tested at PSL sometime in 2015. Data from both engines will be used by the ICC to address their Tasks 3 and 4, and will be used by NASA to better understand Ice Crystals, while enabling them to improve their computer models, such as NPSS, and further validate and enhance their testing capabilities.