Counter-torque device with rotor and flow-straightening stator, both of which are ducted, and phase modulation of the blades of the rotor, for helicopter

• US 5,588,618 A
• Filed: 08/30/1994
• Issued: 12/31/1996
• Est. Priority Date: 05/04/1994
• Status: Expired due to Term

• Current Assignee: Eurocopter France
• Original Assignee: Eurocopter France
• Inventors: Routhieau, Vincent Jean-Luc, Arnaud, Remy E., Marze, Henri-James R., Arnaud, Gilles L.
• Primary Examiner(s): Barefoot, Galen L.
• Application Number:
  US08/298,080
• Time in Patent Office: 854 Days
• Field of Search: 244/17.11, 244/17.19, 244/17.21, 415/119, 415/209.1, 416/203
• US Class Current: 244/17.19
• CPC Class Codes: B64C 2027/8254 Shrouded tail rotors, e.g. "Fenestron" fans
• CPC Class Codes: B64C 27/82 characterised by the provision of an auxiliary rotor or fluid-jet device for counter-balancing lifting rotor torque or changing direction of rotorcraft

Abstract

A flow-straightener with stationary vanes and aerodynamic profile is mounted downstream of the rotor with blades in the transverse duct passing through the fairing at the tail of the helicopter. The blades of the rotor are distributed angularly about the axis of the rotor with uneven azimuth modulation, such that any angle between two arbitrary blades of the rotor is different from any angle between two arbitrary vanes of the flow-straightener.

Claims

1. Counter-torque device for a helicopter, comprising a variable-pitch multi-blade rotor mounted so that it can rotate substantially coaxially in a duct for a flow of air of axis substantially transversal to the helicopter and passing through a fairing incorporated into the tail part of the helicopter, so that the pitch change axes of the blades move in a plane of rotation substantially perpendicular to the axis of the fairing duct, as well as a flow-straightening stator fixed into the duct downstream of the rotor and including stationary vanes located substantially in a star configuration about the axis of the duct and each exhibiting an asymmetric aerodynamic profile, of which the camber and the angular setting with respect to the axis of the duct are such that the vanes straighten out the airflow downstream of the rotor substantially parallel to the axis of the duct, wherein the blades of the rotor are distributed angularly about the axis of the rotor with uneven azimuth modulation, such that any angle between any two arbitrary blades of the rotor is different from any angle between any two arbitrary vanes of the flow-straightener.

2. Counter-torque device according to claim 1, wherein the vanes of the flow-straightener are each inclined to the radial direction, from the axis of the duct towards its periphery, and in the opposite direction from the direction of rotation of the rotor.

3. Counter-torque device according to claim 1, wherein the vanes of the flow-straightener are inclined at a slant, from the centre of the duct to its periphery and from upstream to downstream of the duct.

4. Counter-torque device according to claim 1, wherein the spacing, along the axis of the duct, between the plane of rotation of the rotor and the leading edge of the vanes of the flow-straightener, at the periphery of the duct, is a distance (dr) lying between 1.5 c and 2.5 c, where c is the chord of the blades of the rotor.

5. Counter-torque device according to claim 1, wherein the vanes of the flow-straightener support inside the duct a body which is substantially coaxial with the duct, and containing members for driving the rotor and members for collectively controlling the pitch of the blades of the rotor, which is mounted so that it can rotate on the body.

6. Counter-torque device according to claim 1, wherein the vanes of the flow-straightener have an aerodynamic profile of the NACA 65 type, with a relative thickness lying between approximately 8% and approximately 12%, an angle of attack setting to the axis of the duct which is negative and lies between approximately 2°

and approximately 2.5°

, and a camber lying between approximately 20° and

approximately 28°

.

7. Counter-torque device according to claim 1, wherein a transmission arm, transmitting a driving power to the rotor, is located inside the duct substantially at the location of one of the vanes of the flow-straightener, the profiled vanes of which are a number at least equal to the number of the blades of the rotor, decreased by one.

8. Counter-torque device according to claim 1, wherein the blades of the rotor have an aerodynamic profile of OAF type, with a relative thickness and camber which are progressive depending upon the span, the relative thickness decreasing from approximately 13.9% to approximately 9.5%, and the twist decreasing from approximately 17°

to approximately 6.9°

or from approximately 7.25°

to approximately -1.2°

, between 0.4 R and R, where R is the radius of the rotor.

9. Counter-torque device according to claim 1, wherein the duct comprises two parts, one of which is a collector, corresponding to that part of the duct which is situated upstream of the plane of rotation of the rotor, and the other of which is a diffuser corresponding to that part of the duct which is situated downstream of the plane of rotation of the rotor, the collector comprising a convergent inlet nozzle, delimited by an annular wall which is convex towards the upstream end and rounded with a constant radius (Rc), and which is extended towards the plane of rotation of the rotor by a cylindrical zone of a first length (L1), and the diffuser comprising, from the plane of rotation of the rotor towards the downstream end, a cylindrical zone of a second length (L2), extending the cylindrical zone of the collector, then a frustoconical divergent nozzle of vertex half-angle (α

), and a divergent outlet delimited by an annular wall which is convex towards the downstream end and rounded with radius (r).

10. Counter-torque device according to claim 9, wherein the position of the plane of rotation of the rotor in the cylindrical part of the duct, which part is formed by the cylindrical zones of the collector and of the diffuser is defined as a function of the chord (c) of the blades of the rotor, of their positive pitch range, of the distance (a) between their leading edge and the pitch change axis, and the maximum deformation (f) of the blade, characterizing its rigidity in flap, so that the lengths L1 and L2 of the cylindrical zones are such that:

L1>

a sin (β

max)+f and L2<

(c-a) sin (β

max), where β

max is the maximum positive pitch angle of the blades of the rotor.

11. Counter-torque device according to claim 9, wherein the length (L1) of the cylindrical zone of the collector lies between approximately 2% and approximately 8% of the diameter (φ

) of the duct measured in its cylindrical part, the constant radius (Rc) of the convergent inlet nozzle of the collector is approximately 8% of the diameter (φ

) of the duct and the length (L2) of the cylindrical zone of the diffuser progresses between approximately 1% and approximately 3.5% of the diameter (φ

) of the duct.

12. Counter-torque device according to claim 9, wherein the vertex half-angle (α

) of the frustoconical divergent nozzle is chosen between approximately 5° and

approximately 20°

.

13. Counter-torque device according to claim 9, wherein the annular wall of the divergent outlet nozzle of the diffuser has a first constant radius (r1) less than approximately 1.6% of the diameter (φ

) of the duct, over a circular arc (AA) extending towards the front of the helicopter, a second constant radius (r2), lying between approximately 4.3% of the diameter (φ

) of the duct and the radius (Rc) chosen for the convergent nozzle of the collector, over a circular arc (BB) extending towards the rear of the helicopter, and two zones (AB) with progressive radius progressing between r1 and r2 joining together the zones of constant radius (r1 and r2) symmetrically on either side of a longitudinal axis (YY) of the helicopter.

14. Counter-torque device according to claim 13, wherein the front zone of constant radius (r1) extends over a circular arc (AA) corresponding to a subtended angle of at least 210°

, and the rear zone of constant radius (r2) extends over a circular arc (BB) corresponding to a subtended angle of 90°

, symmetrically above and below the said longitudinal axis (YY) of the helicopter.

15. Counter-torque device according to claim 1 wherein each said blade of the rotor is mounted radially about the axis of the rotor diametrically opposite to another one of said blades.