An Approach to Helicopter Power Selection

This paper describes a preliminary design method to determine engine ratings for take-off and emergency power to suit two arbitrary flight design requirements for multi-engined helicopters. The method exploits the engine's potential for higher emergency rating and this is profoundly affected by the required test time at that rating. For example, the ratio of emergency to take-off power can be increased from 1.20 to 1.33 if the emergency rating's test time is reduced from the current 2 hours to 1/4 hour for one 150-hour endurance test. The shorter test time can be expected to lead to improved mission fuel efficiency (4%) and reduced engine operating cost (2.5%). Despite superior fuel efficiency, the engine operating cost for a 3-engine installation is higher than for a Twin. The methodology can be used to explore the impact of flight design requirements on engine economics and fuel efficiency.