Counter-Torque Device for a Helicopter

A ducted fan for a helicopter, comprising:

• a transverse duct;
• and
• a counter-torque device supported within said duct, said counter-torque device including a rotor rotatably mounted within said duct and a stator fixedly mounted within said duct downstream from said rotor,
• said rotor including:
• a rotor hub having a rotor axis, and
• rotor blades extending from said hub, said rotor blades having a modulated angular distribution about said rotor axis, said angular distribution being defined by the equation:
• θi′=θi+Δθi sin(mθi)
• where θi′ is the modulated blade angle for the ith blade;
• θi is the nominal blade angle for the ith blade;
• Δθi is the maximum modulation amplitude for a specific blade of said rotor blades and is equal to Δφ/I where Δφ is phase-modulation amplitude and I is the number of blades, and m is the modulation factor that is not equal to a prime of the number of blades, and
• said stator including:
• a stator hub, and
• a plurality of stator vanes distributed around said stator hub,
• wherein said stator vanes are angularly modulated around said stator hub such that the angular spacing between adjacent vanes of said stator vanes varies around said stator hub for each pair of said adjacent vanes.

A ducted fan for a helicopter, comprising:

• a transverse duct;
• and
• a counter-torque device supported within said duct, said counter-torque device including a rotor rotatably mounted within said duct and a stator fixedly mounted within said duct downstream from said rotor,
• said rotor including:
• a rotor hub having a rotor axis, and
• rotor blades extending from said hub, said rotor blades having an un-modulated angular distribution about said rotor axis such that the angular spacing between adjacent blades is constant around said hub for all pairs of said adjacent blades, and
• said stator including:
• a stator hub, and
• a plurality of stator vanes distributed around said stator hub,
• wherein said stator vanes are angularly modulated around said stator hub such that the angular spacing between adjacent vanes of said stator vanes varies around said stator hub for each pair of said adjacent vanes.

A rotor blade for a ducted tail fan of a helicopter, comprising:

• a leading edge;
• a trailing edge;
• a main portion extending between said leading and trailing edges;
• and
• a series of chord planes extending between said leading and trailing edges along the a respective chord and positioned along the length of said blade as located by stations along the longitudinal axis of said blade,
• wherein a desired chord plane twist (degrees) as a function of each said station location (inches) being defined by the equation:
• Twist(deg)=−0.000447903*ST4+0.0278569*ST3−0.514872*ST2+2.10206*ST+5.41711,
• wherein a chord length (inches) as a function of station location (inches) is defined by the equation:
• Chord(in)=−0.02197*ST2+0.592025*ST−0.8989,
• and wherein a quarter chord off-set (inches) that defines the sweep as a function of station location (inches) is defined by the equation:
• Δc/4=0.02883*ST2−0.7832*ST+4.714−0.41.

A stator for a counter-torque device of a helicopter, said stator comprising:

• a hub;
• and
• a plurality of vanes distributed around said hub,
• wherein said vanes are angularly modulated around said hub such that the angular spacing between adjacent vanes of said vanes varies around said hub for each pair of said adjacent vanes.

A ducted fan for a helicopter, comprising:

• a transverse duct;
• and
• a counter-torque device supported within said duct, said counter-torque device including a rotor rotatably mounted within said duct and a stator fixedly mounted within said duct downstream from said rotor,
• said stator including a hub and a plurality of vanes distributed around said hub, wherein said vanes are angularly modulated around said hub such that the angular spacing between adjacent vanes of said vanes varies around said hub for each pair of said adjacent vanes.

A ducted fan for a helicopter comprising:

• a duct;
• and
• a counter-torque device supported within said duct, said counter-torque device including a rotor rotatably mounted within said duct and a stator fixedly mounted within said duct downstream from said rotor,
• said stator including a hub and a plurality of vanes distributed around said hub, wherein said vanes are angularly modulated around said hub such that the angular spacing between adjacent vanes of said vanes varies around said hub for each pair of said adjacent vanes, and said modulated vanes are configured to be in tension when said rotor is operated.

A ducted fan for a helicopter comprising:

• a duct having a longitudinal axis;
• a counter-torque device supported within said duct, said counter-torque device including a rotor rotatably mounted within said duct and rotatable in a rotor plane that is transverse to the longitudinal axis of said duct and operable to create a flow of air through said duct;
• and
• noise reducing resonators integrated into said duct and structured to reduce noise generated by said counter-torque device during operation of said rotor,
• wherein noise reducing resonators are positioned in said rotor plane.

A ducted fan for a helicopter, comprising:

• a duct defining an annular inwardly facing duct surface;
• a counter-torque device supported within said duct, said counter-torque device including a rotor rotatably mounted within said duct and operable to create a flow of air through said duct;
• and
• a noise reducing layer of material attached to said duct surface and structured to reduce said noise generated by said counter-torque device during operation of said rotor.

A ducted fan for a helicopter comprising:

• a duct;
• a counter-torque device supported within said duct, said counter-torque device including a rotor rotatably mounted within said duct and operable to create a flow of air through said duct, said counter-torque device generating a noise during operation of said rotor;
• and
• means for reducing said noise generated by said counter-torque device during operation of said rotor,
• wherein said duct includes a rotor region that extends within a plane of said rotor, and said means is positioned in at least said rotor region of said duct and on said plane of said rotor.

A ducted fan for a helicopter comprising:

• a duct;
• a counter-torque device supported within said duct, said counter-torque device including a rotor rotatably mounted within said duct and operable to create a flow of air through said duct, said counter-torque device generating a noise during operation of said rotor;
• and
• means for reducing said noise generated by said counter-torque device during operation of said rotor,
• wherein said duct includes a rotor region that extends within a plane of said rotor, and said means is positioned at least in areas of said duct other than on said plane of said rotor.

A rotor for a counter-torque device for a helicopter, comprising:

• a hub having a rotor axis;
• and
• blades extending from said hub, said blades having a modulated angular distribution about said rotor axis, said angular distribution being defined by the equation:
• θi′=θi+Δθi sin(mθi)
• where θi′ is the modulated blade angle for the ith blade;
• θi is the nominal blade angle for the ith blade;
• Δθi is the maximum modulation amplitude for a specific blade of said blades, m is the modulation factor, and Δθi is not a constant for said rotor as a whole, and wherein the resulting rotor is substantially balanced.

A counter-torque device for a helicopter, comprising:

• a duct with a longitudinal axis;
• and
• a rotor secured within said duct for rotation within said duct about said longitudinal axis of said duct, said rotor having:
• a hub having a rotor axis;
• and
• blades extending from said hub, said blades having a modulated angular distribution about said rotor axis, said angular distribution being defined by the equation:
• θi′=θi+Δθi sin(mθi)
• where θi′ is the modulated blade angle for the ith blade;
• θi is the nominal blade angle for the ith blade;
• Δθi′ is the maximum modulation amplitude for a specific blade of said blades, m is the modulation factor, and Δθi is not a constant for said rotor as a whole, and wherein the resulting rotor is substantially balanced.

A rotor for a counter-torque device for a helicopter, comprising:

• a hub having a rotor axis;
• and
• blades extending from said hub, said blades having an modulated angular distribution about said rotor axis, said angular distribution being defined by the equation:
• θi′=θi+Δθi sin(mθi),
• where θi′ is the modulated blade angle for the ith blade;
• θi is the nominal blade angle for the ith blade;
• Δθi is the maximum modulation amplitude and is equal to Δφ/I where Δφ is phase-modulation amplitude for a given blade of said blades, and I is the number of blades, and m is the modulation factor that is not equal to a prime of the number of blades.

A method for determining a substantially balanced, modulated angular spacing between blades of a tail rotor for a helicopter, comprising:

• selecting a modulation factor m;
• selecting a number of blades for attachment to a rotor;
• determining the modulated angular spacing between each of the rotors using a modified sinusoidal law wherein
• θi′=θi+Δθi sin(mθi),
• where θi′ is the modulated blade angle for the ith blade;
• θi is the nominal blade angle for the ith blade;
• Δθi is the maximum modulation amplitude for a given blade of the blades, m is the modulation factor, and Δθi is not a constant for the rotor as a whole.