This paper presents design arrangements and performances of high bypass ratio compound fan-shaft engines. Helicopter rotor drive power can be obtained from the propulsion fan engine by unloading the fan. This is accomplished by using variable fan guide vanes that can be closed to reduce fan air flow or by reducing fan speed. These methods of unloading the fan are substantiated by the results of tests. The basic designs considered are for engines in the 5 to 30 lb/sec gas producer airflow size class and which have a two-spool coaxial front fan with a bypass ratio of approximately 8.0 and pressure ratio of approximately 1.4. The front fan configuration is used to superchange the gas producer. The flow of energy that results during power sharing between propulsive fan thrust and helicopter rotor drive power is discussed; in addition, fan shaft engine performance data are presented as applied to representative stowed-rotor convertiplanes of 15,000 and 60,000-lb design gross weights.

This content is only available via PDF.