21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-5.6.2

ENGINE SUB-IDLE MODEL

Cafarelli R., Gandolfo A., Sbuttoni A., Polidoro R.
Alenia Aerospazio, Italy

Keywords: engine, sub-idle, model

Modern unstable aircraft require to consider any flight operation leading to a possible catastrophic event. Therefore semi-empirical mathematical models have been implemented either to assess the risk in advance of critical flight trials (e.g. engine relight) or to reduce the number of high demanding trials. Engine Sub-Idle model has been designed to suit the above purpose. It provides performance characteristics when the engine thermodynamic cycle is not totally activated. The model has been focused on forces and moments balance applied on the engine to enable to withstand aircraft systems loads and its assistance/resistance characteristics. The Engine Sub-Idle model results have been compared to the zero aircraft system loads flight results. Engine rundown behaviour is well represented by the model in all flight conditions tested. The engine starting performance proves that at the design point and higher altitudes/Mach the model provides good results. At lower altitudes/Mach the model data are pessimistic in term of time to idle. An improvement of the model data is planned and a further verification will be performed in association with the engine

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