Rotary-wing aircraft equipped with at least one multi-plane pitch stabilizer

Abstract

The present invention relates to a rotary wing (7) aircraft (1) provided with a tail boom (10) carrying a stabilizer (15). The aircraft (1) comprises a pitch stabilization system (25) which is provided with at least one pitch stabilizer comprising a first aerodynamic section (40) and a second aerodynamic section (50). The first aerodynamic section (40) extends from the tail boom (10) from a first root section (41) to a first end section (42) and the second aerodynamic section (50) extends from the stabilizer (15) from a second root section (51) to a second end section (52), the first end section (42) being connected directly to the second end section (52) or via a connecting section (60). Abstract figure: figure 1

Description

Title of the invention: Rotary wing aircraft equipped with at least one multi-plane pitch stabilizer

[0001] The present invention relates to a rotary wing aircraft equipped with at least one multi-plane pitch stabilizer.

[0002] Conventionally, a rotary wing aircraft may comprise a front cell carrying at least one rotary wing. The rotary wing allows the aircraft to operate at both high forward speeds and very low forward speeds, or even allows the aircraft to perform stationary flights.

[0003] A conventional rotary wing aircraft, such as a helicopter, may further comprise a tail boom extending a front cell towards the rear in particular to carry stabilizing surfaces. Such stabilizing surfaces have the function of ensuring stabilization in forward flight of the movements of the rotorcraft.

[0004] In particular, the tail boom conventionally extends from the front cell to a fin which is substantially vertical or slightly inclined relative to the vertical. The concepts of tail boom and fin are well known to those skilled in the art.

[0005] A conventional rotary wing aircraft, and in particular a helicopter, may also comprise a rotor at its rear end. Such a rotor is called a tail rotor, to be distinguished from the rotor forming the rotary wing. The tail rotor is carried by the tail fin. For example, the tail rotor is arranged laterally relative to the tail fin in the case of an unducted tail rotor. Alternatively, the tail fin may form a fairing delimiting an air stream in which the tail rotor is arranged, a ducted tail rotor being known in particular by the brand fenestron®.

[0006] The tail rotor allows the yaw movements of the aircraft to be controlled, by more or less counteracting the torque exerted by the rotating wing on the front cell.

[0007] Similarly, regardless of whether the tail rotor is faired or not, the rudder participates in controlling the yaw movement of the aircraft. Indeed, the rudder generates transverse lift during forward flight. The higher the forward speed of the helicopter, the greater this transverse lift.

[0008] Furthermore, a conventional rotary-wing aircraft, and in particular a helicopter, may include a pitch stabilization system. A pitch stabilization system includes one or two pitch stabilizers. Each pitch stabilizer is a half-wing. For example, a helicopter includes two pitch stabilizers arranged symmetrically on either side of the tail boom or the rudder.

[0009] Such a pitch stabilizer is sometimes called a “horizontal tail.”

[0010] According to one example, an aircraft may comprise two pitch stabilizers on either side of the stabilizer and forming a T-shaped or inverted T-shaped rear assembly with the stabilizer. According to another example, an aircraft may comprise a pitch stabilizer forming an L-shaped or inverted L-shaped rear assembly with the stabilizer. According to another example, the OH 6A helicopter has a Y-shaped rear assembly. According to one example, the CH-1 helicopter has a floating tail carried by the tail boom.

[0011] A pitch stabilizer is generally effective in stabilizing a rotary wing aircraft, its effectiveness increasing in conjunction with the forward speed of the aircraft. In addition, the effectiveness of a pitch stabilizer is maximized by maximizing its wing area.

[0012] However, on a traditional helicopter, the air passing through the rotating main rotor is deflected rearward as the helicopter moves forward. This air can impact the pitch stabilization system, which tends to cause the aircraft to pitch up. However, when flight conditions vary, the deflection of the air passing through the rotary wing is also modified. The same therefore applies to the forces possibly exerted on the pitch stabilization system by this air coming from the rotary wing.

[0013] When a helicopter remains stationary, the airflow passing through the rotating rotary wing may not impact a pitch stabilization system or may generate reduced forces on this pitch stabilization system. During acceleration, the airflow is deflected rearward and the forces exerted by the air passing through the rotary wing on the pitch stabilization system increase, and tend to cause the helicopter to pitch up to a maximum. This phenomenon is known as "pitching bump". To stabilize the helicopter, the pilot must then use his rotary wing blade cyclic control stick to reduce the pitch of this helicopter. This maneuver increases the pilot's workload and the power required to set the rotary wing in motion.As the helicopter's forward speed increases, the airflow from the rotary wing returns to the forward axis and then flows over the pitch stabilization system and therefore no longer induces this pitch bump phenomenon. The pitch bump can also complicate a landing by reducing a pilot's visibility due to the aircraft pitching up.

[0014] Furthermore, it is understood that the optimization of a pitch stabilizer carried out by maximizing its wing surface accentuates the pitch bump.

[0015] Document EP 1547919 describes a helicopter having two pitch stabilizing surfaces extending symmetrically on either side of an anteroposterior plane. These stabilizing surfaces can be horizontal, being orthogonal to the anteroposterior plane for example, or can jointly describe a V shape, presenting an angulation between 0° and 90° with said anteroposterior plane. Each pitch stabilizing surface can be equipped with a flap.

[0016] Documents US2369652 and GB 606420 relate to a rotary wing aircraft provided with an upper pitch stabilizing surface and a lower pitch stabilizing surface.

[0017] Document EP 2409917 A1 is also known.

[0018] The present invention therefore aims to propose a rotary wing aircraft equipped with at least one innovative pitch stabilizer making it possible to reduce the pitch bump and / or downforce at low speed.

[0019] The invention thus relates to a rotary wing aircraft provided with a tail boom carrying a fin, the aircraft comprising a rear rotor carried by the fin, the rear rotor being rotatable about a rotor axis and having a rotor diameter, a vertical-longitudinal plane passing through the tail boom transversely separating a first side from a second side of the aircraft, the aircraft comprising a pitch stabilization system which is provided with at least one pitch stabilizer which extends from the first side or the second side, said pitch stabilizer comprising a first aerodynamic section and a second aerodynamic section.

[0020] For example, the first aerodynamic section and the second aerodynamic section comprise a succession of sections which each extend longitudinally from a trailing edge to a leading edge, and in thickness from a lower face to an upper face. Each section is a section of the section concerned along a plane for example parallel to the roll axis and the yaw axis of the aircraft.

[0021] The rotor diameter is in fact equal to twice the distance separating the free end of the rear rotor blades from the axis of rotation of the rear rotor.

[0022] Furthermore, the first aerodynamic section extends spanwise from the tail boom of a first root section to a first end section and the second aerodynamic section extends spanwise from the tail fin of a second root section to a second end section, the first end section being connected directly to the second end section or via a connecting section.

[0023] Since an aircraft can achieve various roll and pitch inclinations in flight, the expression "vertical-longitudinal plane" means that this plane is vertical when the aircraft is placed on a horizontal area.

[0024] Consequently, the pitch stabilizer(s) each comprise at least two aerodynamic planes formed respectively by the first aerodynamic section and the second aerodynamic section, or even a third plane formed by the connecting section. The first aerodynamic section and the second aerodynamic section form offset half-wings. The first aerodynamic section and the second aerodynamic section of the same pitch stabilizer are on the first side or the first aerodynamic section and the second aerodynamic section of the same pitch stabilizer are on the second side of the aircraft. In forward flight, each aerodynamic section produces a lift tending to balance the aircraft in pitch in particular.

[0025] A conventional monoplane pitch stabilizer can be impacted at low speeds by the air passing through the rotary wing and generate a significant pitch angle that the pilot must compensate for. This pitch angle can increase with increasing forward speed of the aircraft up to a maximum angle and then decrease. The curve showing the induced nose-up pitch angle relative to the forward speed forms a hump, which explains why this phenomenon is sometimes called "trim hump".

[0026] Conversely, instead of using such a monoplane pitch stabilizer, the invention proposes a multiplane pitch stabilizer comprising a first aerodynamic section and a second aerodynamic section or even a connecting section. The first aerodynamic section is carried by the tail boom while the second aerodynamic section is carried by the rudder and is therefore offset longitudinally or even vertically from the first aerodynamic section. The first aerodynamic section and the second aerodynamic section may not be directly above each other.The second aerodynamic section may in particular comprise a second root section located at least partially below, above or behind the rear rotor, either longitudinally behind the first aerodynamic section with respect to the forward direction of advance of the aircraft or even vertically in a horizontal plane located above or below the first aerodynamic section. The first aerodynamic section and the second aerodynamic section tend to jointly generate, in forward flight, a lift substantially equivalent to a conventional monoplane stabilizer. On the other hand, the use of two aerodynamic pitch stabilization sections which are in fact offset from each other, in particular longitudinally due to their respective locations on the tail boom and the stabilizer, tends to reduce the pitch bump compared to a conventional aircraft.

[0027] Indeed, the first aerodynamic section and the second aerodynamic section are offset from each other so that the airflow passing through the rotary wing and deflected towards the pitch stabilizer exerts different pressures on the first aerodynamic section and the second aerodynamic section depending on the forward speed. The two aerodynamic sections are sufficiently offset from each other, due to their locations, to be impacted, if necessary, at each moment and at low speeds, differently by the air flow coming from the rotary wing.

[0028] Under the effect of the pressure of the air passing through the rotary wing, the first aerodynamic section and the second aerodynamic section individually tend to generate a maximum nose-up pitch angle that is in fact smaller than the maximum pitch angle reached with a conventional monoplane stabilizer. Indeed, the wing surface area of ​​each aerodynamic section is smaller than the wing surface area of ​​a conventional monoplane stabilizer, the sum of the wing surfaces of the two aerodynamic sections being able to be substantially equivalent to the wing surface area of ​​a conventional monoplane stabilizer. Furthermore, the maximum forces exerted on each aerodynamic section of a pitch stabilizer according to the invention are reached at actually different forward speeds due to the longitudinal offset of the first and second aerodynamic sections.

[0029] At each instant, the first aerodynamic section and the second aerodynamic section then jointly generate a reduced trim bump compared to a usual system. Illustratively, instead of having a large trim bump, the invention makes it possible to obtain two small trim bumps reached at different forward speeds, these two trim bumps jointly generating an overall trim bump reduced compared to a monoplane system.

[0030] For a given wing surface, the invention makes it possible to significantly reduce the pitch bump phenomenon compared to a conventional helicopter. As a result, the invention makes it possible to improve, on the one hand, the performance of the aircraft since the rotary wing requires less power in order to compensate for the pitch bump, and on the other hand, flight safety during critical phases of approach or landing.

[0031] The aircraft may further comprise one or more of the following characteristics, taken alone or in combination, which in particular make it possible to optimize the operation of the aircraft.

[0032] Depending on the stabilization to be provided, the aircraft may comprise two so-called pitch stabilizers according to the invention arranged on either side of the vertical-longitudinal plane.

[0033] Unlike a usual system comprising two horizontal planes arranged transversely on either side of a tail boom for example, this variant proposes two multi-plane stabilizers.

[0034] For example, the two pitch stabilizers are symmetrical with respect to the vertical-longitudinal plane.

[0035] According to another possibility, the aircraft may comprise a single pitch stabilizer according to the invention arranged at the first side, and a single stabilization surface arranged at the second side.

[0036] A pitch stabilizer according to the invention may optionally be associated with a conventional fixed plane or one having reduced dimensions.

[0037] According to a possibility compatible with the previous ones, the first aerodynamic section can be arranged longitudinally in the first third of the tail boom starting from the drift.

[0038] The first aerodynamic section may be carried by the tail boom near the stabilizer. For example, the first aerodynamic section may be arranged substantially in the same location as a conventional empennage. On the other hand, the second aerodynamic section is carried by the stabilizer to be distant from the first aerodynamic section and to be impacted differently by the flow passing through the rotary wing for the same forward speed.

[0039] According to a possibility compatible with the previous ones, the rear rotor can be arranged laterally with respect to the drift or in an air stream delimited by the drift.

[0040] According to a possibility compatible with the previous ones, a first quarter-chord line of the first aerodynamic section at the tail boom can be separated longitudinally from a vertical-transverse rotor plane containing the rotor axis by a first longitudinal distance between 0.7 times the rotor diameter included and twice the rotor diameter included.

[0041] Since an aircraft can achieve various roll and pitch inclinations in flight, the expression "vertical-transverse rotor plane" means that this plane is vertical when the aircraft is placed on a horizontal area. In other words, the first longitudinal distance corresponds to the distance separating in a horizontal plane the quarter-chord point of the first root section and the vertical-transverse rotor plane.

[0042] For the record, the concept of quarter chord line is known to those skilled in the art. Each aerodynamic section is an aerodynamic member which usually comprises a succession of sections according to its span. The chord of a section represents the length of the straight line segment linking the leading edge to the trailing edge of this section, the quarter chord line passing through a quarter of this segment starting from the leading edge.

[0043] This feature may allow adjustment of the nose-up pitch angle generated by the pitch stabilization system, while minimizing aerodynamic interactions with the tail rotor.

[0044] According to a possibility compatible with the previous ones, a second quarter-chord line of the second aerodynamic section at the level of the drift can be separated longitudinally of a vertical-transverse rotor plane containing the rotor axis by a second longitudinal distance between 0.6 times the rotor diameter included and the rotor diameter included, or even less than the first longitudinal distance.

[0045] In other words, the second longitudinal distance corresponds to the distance separating in a horizontal plane the quarter chord point of the second root section and the vertical-transverse rotor plane.

[0046] This feature may allow adjustment of the nose-up pitch angle generated by the pitch stabilization system, while minimizing interactions with the tail rotor.

[0047] According to a possibility compatible with the previous ones, a second quarter-chord line of the second aerodynamic section at the level of the second root section can be positioned in azimuth relative to the rotor axis in an angular range from -30° inclusive to +180° inclusive, with a position at 0° reached horizontally facing the point of the rear rotor furthest longitudinally from the tail boom and a position at +90° located vertically above a position at -90°.

[0048] This feature may allow adjustment of the nose-up pitch angle generated by the pitch stabilization system, while minimizing interactions with the tail rotor.

[0049] For example, the tail rotor may be arranged in an air stream delimited by the fin, the second root section of the second aerodynamic section being arranged at least partially above the air stream, the second aerodynamic section having a negative dihedral and a forward sweep, the first aerodynamic section having a positive dihedral as well as a rear sweep and being connected to the second aerodynamic section by the connecting section, the second quarter chord line of the second aerodynamic section at the second root section being positioned in azimuth relative to the rotor axis in an angular range from +90° inclusive to +180° inclusive.

[0050] Such a feature tends to minimize interactions with the tail rotor.

[0051] According to a possibility compatible with the previous ones, when the first end section is connected to the second end section via the connecting section, the connecting section can be curved and have an average curvature varying between 0.02 times the rotor diameter included and 0.4 times the rotor diameter included.

[0052] Alternatively, the first end section may be connected to the second end section via the connecting section, the connecting section may extend in an inclined plane, this inclined plane extending from the first end section to the second end section, this inclined plane having a lower inclination or equal to 30° relative to a vertical axis when the aircraft is resting on a horizontal area.

[0053] Thus, the connection section can be vertical or almost vertical.

[0054] According to a possibility compatible with the previous ones, the first aerodynamic section and the second aerodynamic section can have a taper ratio between 0.6 inclusive and 1.2 inclusive, the first aerodynamic section and the second aerodynamic section having a chord which varies away from the tail boom / rudder assembly linearly or non-linearly or linearly per segment.

[0055] Each aerodynamic section extending from a root section present at the tail boom or the stabilizer to an end section, possibly connected to the connecting section, the taper rate may be equal to the quotient of the chord at the root section and the chord at the end section.

[0056] According to one possibility, the leading edges and the trailing edges of the first aerodynamic section and second aerodynamic section can each describe a straight line segment.

[0057] According to a possibility compatible with the previous ones, the first aerodynamic section can have a rear arrow with a arrow angle between 10° inclusive and 60° inclusive, the second aerodynamic section having a front arrow with a arrow angle between -10° inclusive and -60° inclusive.

[0058] This feature tends to give a triangular shape to the pitch stabilizer when viewed from above. This feature tends to minimize the pitch bump by judiciously positioning the first aerodynamic section relative to the second aerodynamic section.

[0059] According to a possibility compatible with the previous ones, the first aerodynamic section can have a positive dihedral between 0° inclusive and 60° inclusive, the second aerodynamic section having a negative dihedral between 0° inclusive and -60° inclusive.

[0060] This feature tends to give a triangular shape to the pitch stabilizer when viewed from behind. This feature tends to minimize the pitch bump by judiciously positioning the first aerodynamic section relative to the second aerodynamic section.

[0061] According to a possibility compatible with the previous ones, the trailing edge at the first root section can be separated: i) longitudinally and seen from above from the leading edge at the second root section by a longitudinal distance of between 0.5m inclusive and 2.5m inclusive, and ii) vertically and seen from a position behind the aircraft by a height of between -1m (less one meter) inclusive and 2m inclusive starting from the first aerodynamic section and considering that the height is positive when the second aerodynamic section is present in a horizontal plane located above the first aerodynamic section when the aircraft is resting on a horizontal area.

[0062] The expression "longitudinally separated and seen from above" means that a first vertical-transverse plane passing through the trailing edge at the level of the first root section is longitudinally separated from a second vertical-transverse plane, passing through the leading edge at the level of the second root section and parallel to the first vertical-transverse plane, by a longitudinal distance of between 0.5m inclusive and 2.5m inclusive.

[0063] Similarly, a horizontal plane passing through the trailing edge at the level of the first root section is separated from a horizontal plane passing through the leading edge at the level of the second root section by a height between -1m inclusive and 2m inclusive in a direction moving away from the ground.

[0064] This characteristic tends to minimize the trim bump by judiciously positioning the first aerodynamic section relative to the second aerodynamic section, or may even tend to limit interactions with the rear rotor if necessary.

[0065] The invention and its advantages will appear in more detail in the context of the description which follows with examples given for illustrative purposes with reference to the appended figures which represent:

[0066] [Fig.l], a side view of an aircraft according to the invention having a ducted tail rotor,

[0067] [Fig.2], a side view of a rear assembly of an aircraft according to the invention having an unducted rear rotor,

[0068] [Fig.3], a top view of a pitch stabilization system according to the invention,

[0069] [Fig.4], a rear view of the pitch stabilization system of [Fig.3],

[0070] [Fig.5], a side view of the pitch stabilization system of [Fig.3],

[0071] [Fig.6], a rear view of a pitch stabilization system according to the invention,

[0072] [Fig.7], a rear view of a pitch stabilization system according to the invention, And

[0073] [Fig.8], a diagram explaining the invention.

[0074] Elements present in several distinct figures are assigned a single reference.

[0075] Three directions X, Y and Z orthogonal to each other are shown in some figures.

[0076] The first direction X is said to be longitudinal. The term “longitudinal” relates to any direction parallel to the first direction X.

[0077] The second direction Y is called transverse. The term “transverse” relates to any direction parallel to the second direction Y.

[0078] Finally, the third direction Z is said to be in elevation. The expression “in elevation” relates to any direction parallel to the third direction Z.

[0079] The expression "longitudinal distance" associated with two points designates a distance between two vertical planes when the aircraft is resting on a horizontal area, these two planes containing two transverse axes passing through these two points.

[0080] [Fig.l] shows an aircraft 1 with a rotary wing 7 according to the invention. This aircraft 1 extends along a roll axis parallel to the first direction X from a nose 2 to a rear end 3, in elevation along a yaw axis parallel to the third direction Z from a landing gear to a top, and transversely from a first side 101 to a second side 102 along a pitch axis parallel to the second direction Y.

[0081] In particular, this aircraft 1 comprises a tail boom 10 carrying a fin 15. A vertical-longitudinal plane PVL passing through the tail boom 10 transversely separates the first side 101 from the second side 102 of the aircraft 1. This vertical-longitudinal plane PVL is vertical when the aircraft 1 is resting on a horizontal area 100 and extends from the nose 2 to the rear end 3. This vertical-longitudinal plane PVL contains for example the yaw axis and the roll axis of the aircraft 1.

[0082] The tail boom 10 can extend towards the rear a front cell 5 carrying the rotary wing 7. The front cell 5 rests on the ground via a landing gear 6. Therefore, the tail boom 10 can extend from a front section 11 connected to the front cell 5 to a rear section 12 connected to the stabilizer 15.

[0083] The aircraft 1 further comprises a rear rotor 20 carried by the fin 15. The rear rotor 20 is provided with a plurality of blades 21 jointly movable in rotation around a rotor axis AX. The free ends of the blades describe a circle having a rotor diameter D.

[0084] According to the example of [Fig.l], the rear rotor 20 may be a shrouded rotor arranged in an air stream 16 delimited by the drift 15.

[0085] According to the example of [Fig.2], the rear rotor 20 may be an unducted rotor carried by the fin 15 while being offset transversely relative to this fin 15.

[0086] Whatever the embodiment and with reference again to [Fig.l], the aircraft 1 comprises a pitch stabilization system 25.

[0087] The pitch stabilization system 25 is provided with one or more pitch stabilizers 30 according to the invention. For the sake of clarity, the expression “each pitch stabilizer 30” is used hereinafter in the presence of one or more pitch stabilizers. Reference 30 may designate any pitch stabilizer according to the invention, while references 31, 32 designate particular stabilizers if necessary.

[0088] Each pitch stabilizer 30 extends either from the first side 101 or from the second side 102.

[0089] Each pitch stabilizer 30 comprises a first aerodynamic section 40 and a second aerodynamic section 50.

[0090] The first aerodynamic section 40 comprises a plurality of first aerodynamically profiled sections along its span. Each first profiled section extends longitudinally from a first trailing edge BF1 to a first leading edge BAI, namely substantially parallel to the vertical-longitudinal plane PVL. In addition, each first section of the first aerodynamic section 40 extends in thickness from a first lower face EXT1 to a first upper face INT1. Similarly, the second aerodynamic section 50 comprises in span a plurality of second aerodynamically profiled sections which extend longitudinally from a second trailing edge BF2 to a second leading edge BA2 and in thickness from a second lower face EXT2 to a second upper face INT2.

[0091] In particular, the first aerodynamic section 40 extends in span from the tail boom 10 from a first root section 41 to a first end section 42. For example, the first aerodynamic section 40 is arranged longitudinally in the first third 13 of the tail boom 10 starting from the fin 15.

[0092] Conversely, the second aerodynamic section 50 extends in span from the drift 15 of a second root section 51 to a second end section 52.

[0093] The first end section 42 is connected directly to the second end section 52 or via a connecting section 60 according to the example of [Fig.l].

[0094] Consequently, the first aerodynamic section 40 and the second aerodynamic section 50 are offset from each other and impacted by the air flow passing through the rotary wing 4 during its rotation differently for the same forward speed.

[0095] Furthermore, the first aerodynamic section 40 and / or the second aerodynamic section 50 may comprise profiled sections having usual aerodynamic profiles, for example but not necessarily of the NACA or OA type.

[0096] Optionally, the first aerodynamic section 40 and / or the second aerodynamic section 50 may comprise standard cruise trim adjustment members, such as stationary flaps known in English as “tabs”. » allowing the rope of a section of a stabilizer to be locally increased, or called in English “Gurney tabs”.

[0097] Optionally, the first aerodynamic section 40 and / or the second aerodynamic section 50 may comprise a wavy trailing edge of the type called in English “wavy trailing edge” or a member called in English “splitter” for reducing drag.

[0098] Optionally, the first aerodynamic section 40 and / or the second aerodynamic section 50 may comprise a leading edge slat, called a “slat” in English, for improving the aerodynamic performance in flight during a rapid climb.

[0099] Optionally, the first aerodynamic section 40 and / or the second aerodynamic section 50 may comprise at least one active movable flap for adjusting the balance during cruising.

[0100] Figures 3 to 7 show at least one pitch stabilizer 30.

[0101] Whatever the number of pitch stabilizers 30, the first aerodynamic section 40 of a pitch stabilizer 30 according to the invention may be located at a first longitudinal distance L1 from the rotor axis AX, i.e. in top view, between 0.7 times the rotor diameter D inclusive and twice the rotor diameter D inclusive.

[0102] More precisely, a first quarter-chord line YAC1 of the first aerodynamic section 40 in the first root section 41 is separated longitudinally from a vertical-transverse rotor plane PVT containing the rotor axis AX by the first longitudinal distance L1 possibly between 0.7 times the rotor diameter D inclusive and twice the rotor diameter D inclusive. The vertical-transverse rotor plane PVT is a plane containing the rotor axis AX which is vertical when the aircraft rests on a horizontal area 100.

[0103] The second aerodynamic section 50 may be located at a second longitudinal distance L2 from the rotor axis AX, i.e., in top view, between 0.6 times the rotor diameter D inclusive and the rotor diameter D inclusive.

[0104] More precisely, a second quarter-chord line YAC2 of the second aerodynamic section 50 in the second root section 51 is separated longitudinally from the vertical-transverse rotor plane PVT by a second longitudinal distance L2 between 0.6 times the rotor diameter D inclusive and the rotor diameter D inclusive.

[0105] Furthermore, the trailing edge BF1 at the first root section 41 may be separated from the leading edge BA2 at the second root section 51 by a longitudinal distance DIS of between 0.5m inclusive and 2.5m inclusive. In other words, a vertical / transverse trailing edge plane PVTBF1 containing the first edge trailing edge BF1 at the level of the first root section 41 and vertical when the aircraft rests on a horizontal area 100 is separated by the longitudinal distance DIS from a vertical / transverse leading edge plane P PVTBA2 containing the second leading edge BA2 at the level of the second root section 51 and vertical.

[0106] According to another aspect, the first aerodynamic section 40 and the second aerodynamic section 50 optionally have a taper ratio of 0.6 inclusive and 1.2 inclusive, the first aerodynamic section 40 and the second aerodynamic section 50 each having respective chords which vary away from the tail boom / stabilizer assembly linearly or non-linearly or linearly per segment.

[0107] According to the example illustrated in [Fig.3], the chords of the first aerodynamic section 40 and of the second aerodynamic section 50 decrease linearly as they move away from the tail boom / rudder assembly.

[0108] According to another aspect, the first aerodynamic section 40 has a rear sweep. The first aerodynamic section 40 is therefore inclined towards the rear of the aircraft 1. For convenience, a sweep angle is considered positive in the presence of a rear sweep and negative in the presence of a forward sweep.

[0109] This first aerodynamic section 40 thus has a first sweep angle Fl between 10° inclusive and 60° inclusive. For example, the first sweep angle is measured between a first vertical-transverse plane PVTYAC1 orthogonal to the vertical-longitudinal plane PVL and passing through the quarter chord of the first root section 41 and a median quarter chord line YAC1 with respect to the quarter chord of each section.

[0110] Conversely, the second aerodynamic section 50 has a forward sweep. The second aerodynamic section 50 then has a sweep angle F2 between -10° inclusive and -60° inclusive. For example, the second sweep angle is measured between a second vertical-transverse plane PVTYAC2 orthogonal to the vertical-longitudinal plane PVL and passing through the quarter chord of the second root section 51 and a median quarter chord line YAC2 with respect to the quarter chord of each section.

[0111] According to another aspect and with reference to [Fig. 4], the first trailing edge BF1 at the level of the first root section 41 is separated vertically from the second leading edge BA2 at the level of the second root section 51 by a height H of between -1 m inclusive and 2 m inclusive starting from the first aerodynamic section 40. In other words, the height H separates a first horizontal plane PHI, which is horizontal when the aircraft 1 rests on a horizontal area 100 and passes through the first trailing edge BF1 at the level of the first root section 41, and a second horizontal plane PH2, which is horizontal and passes through the second trailing edge BF1 at the level of the first root section 41, BA2 attack of the second root section 51. The height is considered positive when the second horizontal plane is above the first horizontal plane.

[0112] According to another aspect, the first aerodynamic section 40 has a positive dihedral of between 0° and 60°, the second aerodynamic section 50 having a negative dihedral of between 0° and -60°. A dihedral angle is usually noted as positive when the section concerned tends to rise away from its root. The angles of the dihedrals can be measured, for example, relative to the quarter-chord lines mentioned above.

[0113] According to another aspect, in the presence of a connecting section 60, the connecting section 60 may be vertical or quasi-vertical. This connecting section 60 then extends in an inclined plane PINC going from the first end section 42 to the second end section 52. For example, this inclined plane PINC has an inclination PREF less than or equal to 30° with a vertical axis PREF when the aircraft 1 rests on a horizontal area 100.

[0114] According to the example illustrated with dotted lines in [Fig.4], the connection section 60 is curved and has an average curvature varying between 0.02 times the rotor diameter D included and 0.4 times the rotor diameter D included.

[0115] According to another aspect and with reference to [Fig. 5], the second quarter-chord line of the second aerodynamic section 50 at the second root section 51 is positioned in azimuth relative to the rotor axis AX in an angular range DTHETA from -30° inclusive to +180° inclusive, with a position POS0 at 0° reached horizontally facing the point of the rear rotor 20 furthest longitudinally from the tail boom 10 and a position POS90 at +90° located vertically above a position at -90°. The position POS0 is thus closer to the rear end 3 of the aircraft than the position POS180 reached at +180°.

[0116] Furthermore, according to the embodiment of figures 3 to 5 the rear rotor 20 is arranged in an air stream 16 delimited by the fin 15. The second root section 51 of the second aerodynamic section 50 of a stabilizer 30 according to the invention is further arranged above the air stream 16. In addition, the second aerodynamic section 50 has a negative dihedral and a forward sweep whereas on the contrary the first aerodynamic section 40 has a positive dihedral as well as a rear sweep. The first aerodynamic section 40 can further be connected to the second aerodynamic section 50 by the connecting section 60. Finally, the second quarter-chord line of the second aerodynamic section 50 at the second root section 51 can be positioned in azimuth relative to the rotor axis AX in an angular range DTHETA ranging from +90° inclusive to +180° inclusive.

[0117] According to Figures 3 to 5, the aircraft 1 comprises two pitch stabilizers 31, 32 arranged on either side of the vertical-longitudinal plane PVL. For example, the two pitch stabilizers 31, 32 are symmetrical with respect to the vertical-longitudinal plane PVL.

[0118] According to [Fig.6], the pitch stabilization system 25 comprises only one pitch stabilizer 31.

[0119] According to [Fig.7], the pitch stabilization system 25 comprises a single pitch stabilizer 31 arranged at the first side 101, and a single stabilization surface 33 arranged at the second side 102.

[0120] Whatever the embodiment, [Fig.8] illustrates the operation of a pitch stabilizer according to the invention.

[0121] This [Fig.8] presents a diagram comprising on the ordinate a pitch-up angle of the aircraft 1, and on the abscissa a forward speed of the aircraft 1.

[0122] Curve C1 illustrates the pitch-up angle obtained with a monoplane stabilizer having a given wing surface. Curve C2 shows the pitch-up angle obtained with a stabilizer C2 having this same wing surface distributed between the first aerodynamic section 40 and the second aerodynamic section 50. Curve C3 illustrates the pitch-up angle that would be obtained with the first aerodynamic section 40 alone and curve C4 illustrates the pitch-up angle that would be obtained with the second aerodynamic section 50 alone.

[0123] Curve C1 has a significant pitch bump reaching a maximum for a speed of 20 knots. On the other hand, the first aerodynamic section 40 and the second aerodynamic section 50 generate bumps having on the one hand smaller amplitudes than those of curve C1 but also offset in forward speeds. Thus, a multi-plane pitch stabilizer according to the invention tends to generate at low speeds a maximum pitch angle that is significantly smaller than with a conventional mono-plane stabilizer.

[0124] Naturally, the present invention is subject to numerous variations as to its implementation. Although several embodiments have been described, it is understood that it is not conceivable to exhaustively identify all possible modes. It is of course conceivable to replace a means described by an equivalent means without departing from the scope of the present invention defined by the claims.

[0125] For example, the embodiments of figures 3 to 6 could comprise a first aerodynamic section 40 connected directly to the second aerodynamic section 50. Conversely, the embodiment of [Fig.7] could comprise a first aerodynamic section 40 connected to the second aerodynamic section 50 by a connecting section 60.

Claims

Claims

1. Aircraft (1) with a rotary wing (7) provided with a tail boom (10) carrying a fin (15), the aircraft (1) comprising a tail rotor (20) carried by the fin (15), the tail rotor being rotatable about a rotor axis (AX) and having a rotor diameter (D), a vertical-longitudinal plane (PVL) passing through the tail boom (10) transversely separating a first side (101) from a second side (102) of the aircraft (1), the aircraft (1) comprising a pitch stabilization system (25) which is provided with at least one pitch stabilizer (30) which extends from the first side (101) or the second side (102), said pitch stabilizer (30) comprising a first aerodynamic section (40) and a second aerodynamic section (50),characterized in that the first aerodynamic section (40) extends in span from the tail boom (10) of a first root section (41) to a first end section (42) and the second aerodynamic section (50) extends in span from the tail fin (15) of a second root section (51) to a second end section (52), the first end section (42) being connected directly to the second end section (52) or via a connecting section (60), a trailing edge (BF1) at the first root section (41) being separated: i) longitudinally and seen from above from a leading edge (BA2) at the second root section (51) by a longitudinal distance (DIS) of between 0.5m inclusive and 2.5m inclusive,and ii) vertically and seen from a position behind the aircraft at a height (H) between -1m inclusive and 2m inclusive starting from the first aerodynamic section (40) and considering that the height is positive when the second aerodynamic section is present in a horizontal plane located above the first aerodynamic section (40) when the aircraft (1) is resting on a horizontal area (100).,

2. Aircraft according to claim 1, characterized in that said aircraft (1) comprises two said pitch stabilizers (31, 32) arranged on either side of said vertical-longitudinal plane (PVL).

3. Aircraft according to claim 2, characterized in that the two pitch stabilizers (31, 32) are symmetrical with respect to the vertical-longitudinal plane (VLP).

4. Aircraft according to claim 1, characterized in that said aircraft (1) comprises a single pitch stabilizer (31) arranged at the first side (101), and a single stabilization surface (33) arranged at the second side (102).

5. Aircraft according to any one of claims 1 to 4, characterized in that the first aerodynamic section (40) is arranged longitudinally in the first third (13) of the tail boom (10) starting from the fin (15).

6. Aircraft according to any one of claims 1 to 5, characterized in that a first quarter chord line (YAC1) of the first aerodynamic section (40) in the first root section (41) is separated longitudinally from a vertical-transverse rotor plane (PVT) containing the rotor axis (AX) by a first longitudinal distance (Ll) between 0.7 times the rotor diameter (D) and twice the rotor diameter (D).

7. An aircraft according to any one of claims 1 to 6, wherein the first aerodynamic section (40) has a first quarter chord line (YAC1) in the first root section (41); characterized in that a second quarter chord line (YAC2) of the second aerodynamic section (50) in the second root section (51) is longitudinally separated from a vertical-transverse rotor plane (PVT) containing the rotor axis (AX) by a second longitudinal distance (L2) between 0.6 times the rotor diameter (D) inclusive and the rotor diameter (D) inclusive.

8. Aircraft according to any one of claims 1 to 7, characterized in that a second quarter-chord line of the second aerodynamic section (50) at the second root section (51) is positioned in azimuth relative to the rotor axis (AX) in an angular range (DTHETA) from -30° inclusive to +180° inclusive, with a position (POS0) at 0° reached horizontally opposite the point of the rear rotor (20) furthest longitudinally from the tail boom (10) and a position (POS90) at +90° situated vertically above a position at -90°.

9. Aircraft according to claim 8, characterized in that the tail rotor (20) is arranged in an air stream (16) delimited by the fin (15), the second root section of the second aerodynamic section (50) being arranged at least partially above the air stream (16), the second aerodynamic section (50) having a negative dihedral and a forward sweep, the first aerodynamic section (40) having a positive dihedral and a rear sweep and being connected to the second aerodynamic section by the connecting section (60), the second quarter chord line of the second aerodynamic section (50) at the second root section (51) being positioned in azimuth relative to the rotor axis (AX) in an angular range (DTHETA) from +90° inclusive to +180° inclusive.

10. Aircraft according to any one of claims 1 to 9, characterized in that the first end section (42) being connected to the second end section (52) via the connecting section (60), the connecting section (60) is curved and has an average curvature varying between 0.02 times the rotor diameter (D) inclusive and 0.4 times the rotor diameter (D) inclusive.

11. Aircraft according to any one of claims 1 to 10, characterized in that the first end section (42) being connected to the second end section (52) via the connecting section (60), the connecting section (60) extends in an inclined plane (PINC), this inclined plane (PINC) going from the first end section (42) to the second end section (52), this inclined plane (PINC) having an inclination (PREF) less than or equal to 30° relative to a vertical axis when the aircraft (1) rests on a horizontal area (100).

12. An aircraft according to any one of claims 1 to 11, characterized in that the first aerodynamic section (40) and the second aerodynamic section (50) have a taper ratio of between 0.6 inclusive and 1.2 inclusive, the first aerodynamic section (40) and the second aerodynamic section (50) having a chord which varies away from the tail boom / rudder assembly linearly or non-linearly or linearly per segment.

13. Aircraft according to any one of claims 1 to 12, characterized in that the first aerodynamic section (40) has a rear sweep with a sweep angle (Fl) of between 10°

14. inclusive and 60° inclusive, the second aerodynamic section (50) having a forward arrow with a arrow angle (F2) between -10° inclusive and -60° inclusive. Aircraft according to any one of claims 1 to 13, characterized in that the first aerodynamic section (40) has a positive dihedral between 0° inclusive and 60° inclusive, the second aerodynamic section (50) has a negative dihedral between 0° inclusive and -60° inclusive.

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