Acoustic signature variation of aircraft utilizing a clutch

Abstract

An aircraft is provided including an airframe, an extending tail, and a counter rotating coaxial main rotor assembly including an upper rotor assembly and a lower rotor assembly. A translational thrust system including a propeller is positioned at the extending tail. The translational thrust system provides translational thrust to the airframe. A drive system is configured to operate both the main rotor system and the translational thrust system. The drive system includes a clutch configured to selectively couple or decouple the propeller from the drive system.

What is claimed: 
     
         1 . An aircraft comprising:
 an airframe;   an extending tail;   a counter rotating, coaxial main rotor assembly including an upper rotor assembly and a lower rotor assembly;   a translational thrust system including a propeller positioned at the extending tail, the translational thrust system providing translational thrust to the airframe; and   a drive system configured to operate both the main rotor assembly and the translational thrust system, the drive system including a clutch configured to selectively couple or decouple the propeller from the drive system.   
     
     
         2 . The aircraft according to  claim 1 , wherein the clutch includes an input and an output generally defined along an axis parallel to an axis of rotation of the propeller. 
     
     
         3 . The aircraft according to  claim 1 , wherein the drive system includes a main gearbox coupled to the main rotor assembly, the clutch being positioned between the main gearbox and the translational thrust system. 
     
     
         4 . The aircraft according to  claim 3 , wherein the clutch is positioned adjacent the translational thrust system such that a transmission shaft extending between the main gearbox and the clutch is longer than an output shaft extending between the clutch and the propeller. 
     
     
         5 . The aircraft according to  claim 1 , wherein the clutch is configured to selectively couple of decouple the propeller in response to an input generated by a pilot of the aircraft. 
     
     
         6 . The aircraft according to  claim 1 , wherein the clutch is a multi-plate wet clutch. 
     
     
         7 . The aircraft according to  claim 1 , wherein a rotational speed of the main rotor assembly and a rotational speed of the propeller are independently controlled through the clutch. 
     
     
         8 . A method of operating an aircraft, comprising:
 selecting an operational mode of the aircraft; and   decoupling a translational thrust system from a main rotor system of the aircraft according to the operational mode of the aircraft.   
     
     
         9 . The method according to  claim 8 , wherein the operational mode of the aircraft is engine start-up. 
     
     
         10 . The method according to  claim 8 , wherein the operational mode of the aircraft includes approaching a target. 
     
     
         11 . The method according to  claim 8 , wherein the operational mode of the aircraft is high speed flight. 
     
     
         12 . The method according to  claim 8 , wherein the translational thrust system is decoupled from the main rotor system via a clutch. 
     
     
         13 . The method according to  claim 8 , wherein the translational thrust system is decoupled from the main rotor system in response to an input generated by a pilot of the aircraft. 
     
     
         14 . An aircraft, comprising:
 an airframe;   an extending tail;   a main rotor assembly configured to rotate about a first rotational axis;   a translational thrust system positioned at the extending tail, wherein the translational thrust system may be selectively coupled and decoupled from the main rotor assembly.