Performance losses and washing recovery of a helicopter engine compressor operating in ground-idle conditions

Helicopters operate often in dusty environments. During landings and takeoffs the engine ingests huge amounts of contaminants that might deposit inside the compressor. In this paper, the ground-idle operation of a helicopter engine compressor has been reproduced on a compressor test unit. The Allison 250 C18 compressor has been subjected to multiple runs under severe conditions of dust ingestion. At the end of each run, the performance curve was recorded while the performance loss has been measured during the operations. Finally, the compressor washing has been carried out and the performance curve has been recorded again. The characteristic curve are representative of the level of contamination of the machine, while the exposure time directly affects the performance loss. The results show the modification and the downward shift of the characteristic curves that lead to a gradual loss of the compressor performance. A detailed photographic report of the first compressor stages has been included in this work. The pictures show the deposition patterns on the blades and the compressor surfaces. The comparison of the pictures of the internal surfaces, before and after the removal of the deposits by the droplet action, highlights the parts that are more critical to clean.