PURPOSE: To improve an antitorque characteristic in adding a thrust by turbine exhaust to that of a fan as one body with an output turbine as well as to reduce the extent of vibrations by driving this output turbine of an antitorque tail rotor directly through high temperature and pressure bleed air out of a main engine.

CONSTITUTION: High temperature, pressure bleed air out of a main engine 1 gets into a scroll 6 by way of a modulating valve 3 and a bleeding duct 2, driving an output turbine 7 of an antitorque tail rotor 10 via a stator 14. Exhaust out of the output turbine 7 is exhaust to the outside by way of an exhaust thruster 8. Driving force of the output turbine 7 is transmitted to a fan 9 as one body with this turbine, and this fan 9 rotates so that a thrust is generate, a thrust by exhaust out of the exhaust thruster 8 is added to that by the fan 9, so that torque made by a main thruster 15 thruster 8 is added to that by the fan 9, so that torque made by a main thruster 15 is neutralized. In addition, since mechanical vibration is not used for drive of the antitorque tail rotor 10, vibrations are thus reduced.