Research on fault analysis and reliability improvement of APU start motor for Korea Utility Helicopter

한국형 기동헬기 APU 시동모터 결함원인 분석 및 신뢰성 개선

  • Kang, Tae-Woo (Aeronautical systems Center, Defence Agency for Technology and Quality) ;
  • Yeom, Hyo-Won (Aeronautical systems Center, Defence Agency for Technology and Quality) ;
  • Lee, Hee-Rang (Aeronautical systems Center, Defence Agency for Technology and Quality) ;
  • Ahn, Jong-Moo (Aeronautical systems Center, Defence Agency for Technology and Quality)
  • 강태우 (국방기술품질원 항공센터) ;
  • 염효원 (국방기술품질원 항공센터) ;
  • 이희랑 (국방기술품질원 항공센터) ;
  • 안종무 (국방기술품질원 항공센터)
  • Received : 2017.03.17
  • Accepted : 2017.06.09
  • Published : 2017.06.30


Korea Utility Helicopter(KUH) is a project to replace the aging helicopter presently being operated by the military with a domestic helicopter. The auxiliary power unit is a device that supplies emergency power to the system by an alternator installed when the main generator fails and the start motor converts the electrical energy of the battery into mechanical rotational energy to rotate the auxiliary power unit engine. With continuing power and operation, defects of the starting motor were found and improvements were carried out to solve it. In the failure mode analysis, the causes of possible defects were classified into 5 categories. Analysis of the 5 factors revealed that the main cause of defects is mechanical wear, which was found to be related to spring pressure. 250 tests were conducted through the theoretically determined pressure and regression analysis was performed with 4 sampling.The results showed that pressure was related to wear rate. In conclusion, early wear and breakage due to wear can be controlled through spring force and test showed the prediction of wear and the validity of the result were confirmed.


Auxiliary power unit;Brush;Failure mode;Mechanical wear;Spring force;Start motor


  1. Korea Defence Standard, "HELICOPTER, UTILITY", KDS1450-4001., Korea, 2012.
  2. Shobert E., "Carbon Brushes", New york chemical publishing Co., 1965.
  3. Myshkin N. K., "Tribological problems in electrical contacts", Tribology International, vol. 24, no. 1, pp. 35-49, 1991. DOI:
  4. Marshall R. A., "The mechanism of current transfer in high current slidingcontacts", Wear, vol. 37, pp. 233-240, 1976. DOI:
  5. Holm R. "Electrical contacts", Springer Verlag, Berlin, 1967. DOI:
  6. Dow T. A. & Stockwell, "Experimental verification of thermoelastic instabilities in sliding contact", J. of Lub. Tech., vol. 99, no. 3, pp. 359-364, 1977. DOI: