Patent Description:
An example for a rotary wing aircraft with a main rotor and a propeller is a so-called compound helicopter. In such a compound helicopter, the main rotor accomplishes essentially lifting duties, but usually also accomplishes propulsive duties at least at low or medium forward speeds in forward flight of the compound helicopter. The propeller, in turn, is mainly provided to off-load the main rotor from its propulsive duties at higher forward speeds in forward flight and may enable the compound helicopter to travel with comparatively high forward speeds which would not be reachable by use of the main rotor alone.

However, in operation the main rotor creates a torque around the yaw axis of the compound helicopter. This torque must be counteracted by a suitable anti-torque device to guarantee a required yaw stability of the compound helicopter in flight operation.

The document <CIT> describes a compound helicopter with a main rotor and a tail propeller. The tail propeller is mounted to a circular shroud which is attached to the compound helicopter's fuselage. The circular shroud is further provided with a rudder that is pivotally mounted to the circular shroud downstream of the tail propeller. In operation, the tail propeller creates an air stream which is directed through the circular shroud toward the rudder and which may be deflected by the rudder to counteract the torque created by the main rotor.

The document <CIT> describes a compound helicopter with a main rotor, a tail boom, and a tail propeller mounted to an aft region of the tail boom, wherein the tail propeller is used only for forward thrust during an airplane mode of flight and during transition from vertical helicopter flight to forward airplane mode of flight, when the main rotor may be feathered in a no-lift attitude. Required anti-torque balancing forces during hovering mode are developed by differentially controlled aileron forces when respective wings are aligned vertically with main rotor downwash. Furthermore, a vertically moveable horizontal airfoil is provided on the tail boom, with controllable means which can provide anti-torque reaction forces from the main rotor downwash during the hovering mode.

The document <CIT> describes a compound helicopter with a main rotor, a tail propeller, and a tail boom extending through an area of downwash from the main rotor. The tail boom forms a plenum chamber to which associated linear nozzles are connected. The associated linear nozzles are fixedly coupled to the tail boom and adapted to discharge a sheet of fluid created from pressurized air in the plenum chamber in a direction substantially tangential to an outer surface of the tail boom to divert main rotor downwash and thereby produce a force that counteracts biasing torque created by the main rotor. The pressurized air is provided by a fan or by directing exhaust air from a power plant of the compound helicopter into the plenum chamber. The compound helicopter further comprises a yaw control member which is movably coupled to the tail boom and selectively positionable based on pilot input.

The document <CIT> describes a compound helicopter with a main rotor, a tail propeller and a tail boom that is surrounded by a cycloidal rotor. The cycloidal rotor has individual blades which are essentially parallel to the longitudinal axis of the tail boom. In operation, the cycloidal rotor is driven to provide anti-torque that counteracts biasing torque created by the main rotor.

The document <CIT> describes a compound helicopter with a fuselage, at least one engine, a roll axis, at least one main rotor, and at least one housing mounted to said fuselage. An air inlet and an air outlet are provided along at least a part of a circumference of the at least one housing, said air inlet and said air outlet being formed by angularly offset and separate gaps between an inside segment and an outside segment essentially extending respectively longitudinally in direction of said roll axis. At least one rotatable compressor with a plurality of airfoil blades is provided radial inside said at least one housing between said air inlet and said air outlet, said at least one rotatable compressor being drivable by said at least one engine about a fan axis and each chord of said airfoil blades is essentially radial oriented with regard to said fan axis. The rotatable compressor drives an impeller/ducted fan for the generation of forward propelling force.

The document <CIT> describes a rotorcraft that is designed for vertical take-off and landing while being as quiet and safe as technically possible. The rotorcraft comprises a pair of concentric shaft electric motors configured to differentially control at least one overhead rotor in a counter-rotating configuration, a plurality of electric fans vertically pointed, and a pusher propeller that is rotatably mounted to a shrouded duct.

However, the above-described anti-torque devices for compound helicopters with a main rotor and a propeller are generally complex and require actuatable components, such as rudders, differentially controlled ailerons or moveable airfoils, additional fans, pilot-moveable yaw control members, or cycloidal rotors. These actuatable components increase an overall system complexity and an overall weight of these anti-torque devices.

Various other anti-torque devices are known from conventional helicopters which, in contrast to the above-described compound helicopters, are not provided with a propeller. In such conventional helicopters, wherein a respective main rotor creates torque around the helicopter's yaw axis, usually a tail rotor is provided as anti-torque device to provide anti-torque that counteracts the torque created by the respective main rotor. Moreover, as main rotor downwash of such a conventional helicopter generally flows around its tail boom, the tail boom may be provided with additional anti-torque devices in the form of strakes or vortex generators to alter the flow of downwash in order to generate a compensation force that counteracts at least partially the torque created by the respective main rotor such that a respective down-sizing of the tail rotor is enabled. Furthermore, a fairing may be added as additional anti-torque device to the tail boom of such a conventional helicopter to create the compensation force, or the profile of the tail boom as such may be modified. Other additional anti-torque devices may likewise be added to the tail boom, such as e. a rotating cylinder that use the so-called Magnus effect to generate the compensation force. Illustrative conventional helicopters with main rotors, tail rotors and such additional anti-torque devices are described in the documents <CIT>, <CIT>, and <CIT>.

If a respectively created compensation force suffices to counteract biasing torque created by the main rotor, it is also possible to omit provision of the tail rotor. Illustrative helicopters with a main rotor and an anti-torque device that enables omission of a respective tail rotor are described in the documents <CIT>, <CIT>, and <CIT>.

Nevertheless, most of the above-described anti-torque devices of conventional helicopters are not suitable for use in a compound helicopter with a main rotor and a tail propeller as they require presence of a conventional tail rotor. However, a conventional tail rotor has usually a comparatively high power consumption, especially in hover condition, and is quite noisy. In contrast, the above-described anti-torque devices which do not need presence of a conventional tail rotor are bulky and/or require actuatable components, such as additional fans, rotatable truncated cones or rotatable cylinders. These actuatable components, however, increase an overall system complexity and an overall weight of the anti-torque devices.

It is, therefore, an object of the present invention to provide a new compound helicopter and, more generally, a new rotary wing aircraft with a main rotor and a tail propeller, which is equipped with an improved anti-torque device that exhibits a comparatively low overall system complexity and a reduced overall weight.

This object is solved by a rotary wing aircraft with a main rotor and a tail propeller, said rotary wing aircraft comprising the features of claim <NUM>. More specifically, according to the present invention a rotary wing aircraft is provided that extends along an associated roll axis between a nose region and an aft region and that comprises a fuselage with a front section and a rear section, wherein the front section comprises a port side wall and a starboard side wall. The rotary wing aircraft comprises a main rotor that is rotatably mounted at the front section, a shrouded duct that is arranged in the aft region, and a pusher propeller that is rotatably mounted to the shrouded duct. The rear section extends in prolongation to one of the port side wall or the starboard side wall between the front section and the shrouded duct and comprises an asymmetrical cross-sectional profile in direction of the associated roll axis. Furthermore, the rear section is configured to generate sideward thrust for main rotor anti-torque from main rotor downwash.

Advantageously, by forming the rear section of the fuselage such that the rear section is configured to generate sideward thrust for main rotor anti-torque from main rotor downwash, a passive anti-torque device may be provided, which is at least approximately self-balancing. This passive anti-torque device does not require any complex actuation mechanism, thereby avoiding the weight and the need for redundancy of an active system. Accordingly, a reduced overall system complexity of the inventive passive anti-torque device may be obtained and, consequently, a required maintenance effort for the anti-torque device will be comparatively low.

Furthermore, as no conventional tail rotor is required for generating anti-torque, less power is needed in hover condition, in which a conventional tail rotor usually consumes up to <NUM>% of the overall consumed power. Thus, less fuel is needed and a gain of lifting capacity may be obtained.

In an illustrative realization, in order to enable generation of high sideward thrust for main rotor anti-torque from main rotor downwash, the rear section of the fuselage of the compound helicopter preferably exhibits a shape that is similar to a profile of a so-called high lift airfoil, such that comparatively high sideward thrust may already be generated at comparatively low downwash air speed. Preferably, at least the main part of the rear section of the fuselage is asymmetrically located to a side of the compound helicopter that is farther away from an approaching rotor blade of the main rotor in the sense of rotation of the main rotor. In other words, if the main rotor rotates in counterclockwise direction, the main part of the rear section of the fuselage is located at the starboard side of the compound helicopter.

Preferably, a vertical cut through the rear section of the fuselage at a position that is close to the shrouded duct resembles to a high lift airfoil. This high lift airfoil is orientated at that position preferably at least approximately in vertical direction providing "lift", i. sideward thrust in the same direction in which the main rotor is rotating. In other words, if the main rotor rotates in counterclockwise direction, the sideward thrust likewise points into this direction.

Thus, less power is needed in hover condition as generation of downward drag in response to main rotor downwash is reduced due to a transformation of the main rotor downwash into sideward thrust, compared to the downward drag that is created by a conventional tail boom in response to main rotor downwash. Consequently, a gain of lifting capacity and fuel savings may be realized.

Advantageously, an underlying transition from a cross-sectional profile of the compound helicopter's fuselage in the region of the main rotor, which may be symmetrical similar to a cross-sectional profile of a conventional helicopter, to the high lift airfoil-shaped cross-sectional profile of the rear section of the fuselage is preferably performed by a smooth recess which is shaped in order to avoid airflow separation. Similarly, an underlying transition of the rear section of the fuselage to the shrouded duct is also preferably smooth, such that the rear section of the fuselage has at least approximately a shaping that corresponds to one quarter of the shrouded duct.

In addition to the rear section of the fuselage, at least one wing-type aerodynamic device, which is also referred to as the "support wing" hereinafter, may be provided for generation of sideward thrust for main rotor anti-torque from main rotor downwash. In operation of the compound helicopter, a certain amount of main rotor downwash is present mainly in hover condition. Therefore, "lift" in horizontal direction, i. sideward thrust, may advantageously be generated simultaneously by the rear section of the fuselage and the support wing from the main rotor downwash in order to counteract the torque created by the main rotor in the hover condition.

Preferably, the support wing is mainly oriented vertically. More specifically, the support wing may connect the compound helicopter's upper deck to the shrouded duct, e. from slightly behind of the main rotor to the shrouded duct. Advantageously, the support wing also exhibits a shape that is similar to a profile of a high lift airfoil. Preferably, the support wing has its greatest width at an area located between <NUM>% of the length of the main rotor's rotor blades and an outer end of the rotor blades.

Advantageously, the support wing and the rear section of the fuselage support the shrouded duct on both sides of the compound helicopter, as there is no center part of the rear section of the fuselage, compared to a conventional tail boom. Preferably, a tail propeller drive shaft is arranged between the support wing and the rear section of the fuselage. This tail propeller drive shaft may also generate sideward thrust via the so-called Magnus effect, which occurs if a cylinder or cone is rotated in an airflow that is oriented perpendicular to its rotation axis.

The tail propeller drive shaft is preferably rotatably mounted to the shrouded duct, preferentially via a bearing that is supported by a predetermined number of provided stator profiles, such as e. three stator profiles. Preferably the stator profiles are mounted to the shrouded duct close to a respective location of the support wing and upper and lower edges of the rear section of the fuselage, where it is connected to the shrouded duct.

Alternatively, instead of providing a tail propeller drive shaft, the tail propeller may be powered independent of the main rotor, e. by means of a separate engine. This separate engine may be of a different type than a respective main engine that powers the main rotor such that engine hybridization is enabled with high redundancy, as the compound helicopter may be operated in forward flight with each one of the engines independent of the other one.

According to one aspect, the rear section comprises at least one airfoil-shaped aerodynamic device that extends from the front section to the shrouded duct. The at least one airfoil-shaped aerodynamic device is configured to generate sideward thrust for main rotor anti-torque from main rotor downwash.

According to one aspect, the at least one airfoil-shaped aerodynamic device comprises a deflectable flap.

According to one aspect, the rear section comprises at least one rotatable airfoil-shaped aerodynamic device that is configured to generate sideward thrust for main rotor anti-torque from main rotor downwash. The at least one rotatable airfoil-shaped aerodynamic device is rotatable to enable adjustment of the generated sideward thrust.

According to one aspect, the asymmetrical cross-sectional profile is at least approximately C-shaped.

According to one aspect, the rotary wing aircraft further comprises at least one wing-type aerodynamic device that extends between the front section and the shrouded duct. The at least one wing-type aerodynamic device and the rear section are connected to opposite sides of the shrouded duct.

According to one aspect, the at least one wing-type aerodynamic device is mounted to the shrouded duct and to an aircraft upper deck and has a width that increases from the aircraft upper deck over a predetermined length of the at least one wing-type aerodynamic device, preferably over at least <NUM>% of the length of the at least one wing-type aerodynamic device.

According to one aspect, the at least one wing-type aerodynamic device is configured to generate sideward thrust for main rotor anti-torque from main rotor downwash.

According to one aspect, the at least one wing-type aerodynamic device is rotatable to enable adjustment of the generated sideward thrust.

According to one aspect, the at least one wing-type aerodynamic device comprises a deflectable flap.

According to one aspect, the rotary wing aircraft further comprises an uncovered propeller drive shaft that is configured to create a Magnus effect upon rotation in main rotor downwash.

By using an uncovered propeller drive shaft, provision of a respective drive shaft cowling may be omitted. Thus, an overall weight and respective costs of the compound helicopter may advantageously be reduced.

According to one aspect, the uncovered propeller drive shaft extends coupling- and bearing-free between the front section and the shrouded duct.

According to one aspect, the uncovered propeller drive shaft comprises a big diameter cylinder shaft or a big diameter conical shaft.

According to one aspect, the rotary wing aircraft is embodied as a compound helicopter, wherein the front section of the fuselage forms a cabin for passengers and/or cargo, and wherein the main rotor forms a single rotor plane.

Thus, an improved compound helicopter with a reduced total number of constituting components and a reduced overall system complexity may be provided. This improved compound helicopter is embodied for an efficient cruise flight and enables higher flight speeds than usually achievable with conventional compound helicopters.

<FIG> shows an illustrative rotary wing aircraft <NUM> with a fuselage <NUM> and a main rotor <NUM>. By way of example, the rotary wing aircraft <NUM> is shown with three mutually orthogonal axes P, R, and Y. The axis P represents a transversal axis that corresponds to the pitch axis inherent to the rotary wing aircraft <NUM>, the axis R represents a longitudinal axis that corresponds to the roll axis inherent to the rotary wing aircraft <NUM>, and the axis Y represents a vertical axis that corresponds to the yaw axis inherent to the rotary wing aircraft <NUM>.

By way of example, the rotary wing aircraft <NUM> is illustrated in forward flight. Thus, only components that are required for forward flight and that are related to the present invention are illustrated in more detail, while illustration of other components is omitted, for simplicity and clarity of the drawing. For instance, neither the fuselage <NUM> is illustrated in greater detail for showing e. respective doors and windows, nor a possible landing gear, which may be a wheel-tape landing gear or a skid-type landing gear mounted to the fuselage <NUM>, is shown, and so on.

Illustratively, the fuselage <NUM> extends along the roll axis R from a nose region <NUM> to an aft region <NUM> of the rotary wing aircraft <NUM>. The fuselage <NUM> comprises a front section <NUM> and a rear section <NUM>. Illustratively, the front section <NUM> comprises a port side wall <NUM> and a starboard side wall <NUM>. Preferably, the rear section <NUM> extends in prolongation to one of the port side wall <NUM> or the starboard side wall <NUM>.

More specifically, the rear section <NUM> preferably extends in prolongation to a side of the fuselage <NUM> that is farther away from an approaching rotor blade of the main rotor <NUM> in the sense of rotation of the main rotor <NUM>. Assuming that the main rotor <NUM> rotates in counterclockwise direction, the rear section <NUM> of the fuselage <NUM> would be located at the starboard side of the compound helicopter <NUM> and, thus, be arranged in prolongation to the starboard side wall <NUM> as illustrated.

By way of example, the front section <NUM> merges into the rear section <NUM> at an associated transition or recess area <NUM>. In other words, starting at the nose region <NUM> of the fuselage <NUM> and travelling along the roll axis R, the fuselage <NUM> has the front section <NUM> that merges at the transition or recess area <NUM> into the rear section <NUM> that, in turn, terminates in the aft region <NUM>.

The front section <NUM> preferably forms a cabin <NUM> for passengers and/or cargo. The cabin <NUM> and, more generally, the fuselage <NUM> illustratively comprises an upper limit <NUM> that separates the cabin <NUM> from an upper deck <NUM>. The upper deck <NUM> is preferably covered by a cowling <NUM>. By way of example, the cowling <NUM> may cover one or more suitable engines and a main gear box that rotates the main rotor <NUM> in operation. Accordingly, the main rotor <NUM> is rotatably mounted at the front section <NUM> of the fuselage <NUM>.

Preferably, the main rotor <NUM> forms a single rotor plane <NUM> and is adapted to provide lift and forward or backward thrust during operation. Illustratively, the main rotor <NUM> is embodied as a multiblade main rotor with a plurality of rotor blades <NUM>, <NUM>, <NUM>, <NUM>, <NUM> which are coupled at an associated rotor head <NUM> to a rotor mast <NUM>, which rotates in operation of the rotary wing aircraft <NUM> around an associated rotor axis.

According to one aspect, the rotary wing aircraft <NUM> is embodied as a compound helicopter with a propeller <NUM> that is at least adapted for generating forward thrust in operation. Accordingly, the rotary wing aircraft <NUM> is referred to hereinafter as the "compound helicopter <NUM>", for simplicity and clarity.

The propeller <NUM> and the main rotor <NUM> may be driven completely independent from each other. In particular, different types of engines may be used to drive the propeller <NUM> and the main rotor <NUM>, such as e. an air breathing propulsion engine for the main rotor <NUM> and an electric motor for the propeller <NUM>.

Preferably, the propeller <NUM> is rotatably mounted to a shrouded duct <NUM>. Illustratively, the shrouded duct <NUM> is mounted to the rear section <NUM> of the fuselage <NUM> and, more specifically, arranged in the aft region <NUM> of the compound helicopter <NUM>. Accordingly, the propeller <NUM> forms a tail propeller and, more particularly, preferably a pusher propeller.

The rear section <NUM> of the fuselage <NUM> illustratively extends between the front section <NUM> of the fuselage <NUM> and the shrouded duct <NUM>. Preferably, the rear section <NUM> comprises an asymmetrical cross-sectional profile <NUM> in direction of the roll axis R of the compound helicopter <NUM> and is configured to generate sideward thrust for main rotor anti-torque from main rotor downwash. According to one aspect, the asymmetrical cross-sectional profile <NUM> is at least approximately C-shaped, as illustrated by way of example with a series of cross-sectional profiles <NUM>, <NUM>, <NUM>, <NUM>. In contrast to the rear section <NUM>, the front section <NUM> of the fuselage <NUM> may at least partly exhibit a symmetrical cross-sectional profile, as e. illustrated in the region of the rotor mast <NUM> by means of a symmetrical cross-sectional profile <NUM>.

It should be noted that the cross-sectional profiles <NUM>, <NUM>, <NUM>, <NUM>, <NUM> clarify the function of the recess area <NUM>. In fact, the cross-sectional profile <NUM> has an almost oval shape, which is by way of example approximately egg-shaped. This oval shape merges at the recess area <NUM> into an airfoil shape, which is at least approximately C-shaped, as illustrated by the cross-sectional profiles <NUM>, <NUM>, <NUM>, <NUM>.

Preferably, the rear section <NUM> comprises at least one airfoil-shaped aerodynamic device <NUM> that extends from the front section <NUM> to the shrouded duct <NUM>. By way of example, only one airfoil-shaped aerodynamic device <NUM> is shown. This airfoil-shaped aerodynamic device <NUM> is illustratively arranged in prolongation to the starboard side wall <NUM>.

In an illustrative realization, the airfoil-shaped aerodynamic device <NUM> is formed as or by a wing. This wing is, however, not arranged transversally to the roll axis R, but instead at least approximately in parallel to the roll axis R.

The airfoil-shaped aerodynamic device <NUM> may form the rear section <NUM>, at least partly. According to one aspect, the airfoil-shaped aerodynamic device <NUM> is configured to generate sideward thrust for main rotor anti-torque from main rotor downwash.

In addition, the rear section <NUM> preferably further comprises at least one wing-type aerodynamic device <NUM> that extends between the front section <NUM> and the shrouded duct <NUM>. By way of example, only one wing-type aerodynamic device <NUM> is shown. Illustratively, the wing-type aerodynamic device <NUM> is at least approximately arranged in prolongation to the port side wall <NUM>.

Preferably, the wing-type aerodynamic device <NUM> is mounted to the shrouded duct <NUM> and to the upper deck <NUM> of the compound helicopter <NUM>. Illustratively, the wing-type aerodynamic device <NUM> and the airfoil-shaped aerodynamic device <NUM> are connected to opposite sides of the shrouded duct <NUM>. According to one aspect, the wing-type aerodynamic device <NUM> is also configured to generate sideward thrust for main rotor anti-torque from main rotor downwash of the compound helicopter <NUM>.

According to one aspect, the compound helicopter <NUM> further comprises an uncovered propeller drive shaft <NUM> that is configured to create a Magnus effect upon rotation in main rotor downwash. The uncovered propeller drive shaft <NUM> is configured to drive the propeller <NUM> in operation and preferably extends coupling- and bearing-free between the front section <NUM> of the fuselage <NUM> and the shrouded duct <NUM>.

<FIG> shows the compound helicopter <NUM> of <FIG> with the fuselage <NUM>, the main rotor <NUM>, the propeller <NUM>, the shrouded duct <NUM>, and the uncovered propeller drive shaft <NUM>. According to <FIG>, the fuselage <NUM> comprises the front section <NUM> that merges at the recess area <NUM> into the rear section <NUM>, the rear section <NUM> comprises the airfoil-shaped aerodynamic device <NUM> and the wing-type aerodynamic device <NUM>, the propeller <NUM> is rotatably mounted to the shrouded duct <NUM> and driven by the uncovered propeller drive shaft <NUM>, and the wing-type aerodynamic device <NUM> connects the upper deck <NUM> to the shrouded duct <NUM>.

More particularly, <FIG> clarifies the coupling- and bearing-free extension of the uncovered propeller drive shaft <NUM> between the front section <NUM> of the fuselage <NUM> and the shrouded duct <NUM>. In addition, merging of the front section <NUM> along the recess area <NUM> into the rear section <NUM> of the fuselage <NUM> is also further clarified and it can be recognized that the merging is essentially achieved by redirecting, i. deflecting the port side wall <NUM> of the compound helicopter <NUM> in the recess area <NUM> toward the starboard side wall <NUM> such that both walls <NUM>, <NUM> are commonly connected to the shrouded duct's starboard side, i. the right-hand side of the shrouded duct <NUM>. Moreover, the connection of the wing-type aerodynamic device <NUM> at the shrouded duct's port side, i. the left-hand side of the shrouded duct <NUM>, which is preferably almost diametrically opposed to the connection of a respective upper edge of the airfoil-shaped aerodynamic device <NUM>, is likewise further clarified.

According to one aspect, the shrouded duct <NUM> forms a swept back structure <NUM>. This swept back structure <NUM> is preferably provided to adapt main rotor downwash at the shrouded duct <NUM> to a preferred behavior of the compound helicopter <NUM> during transition from hover condition to forward flight.

Illustratively, a bottom line <NUM> of the rear section <NUM> of the fuselage <NUM> is shown. This bottom line <NUM> is preferably angled by a predetermined inclination angle <NUM> relative to a horizontal reference plane <NUM>. By way of example, the predetermined inclination angle <NUM> is a positive (dihedral) angle that may be selected dependent on a required sideward thrust that is to be generated by the rear section <NUM> of the fuselage <NUM> in operation.

It should, nevertheless, be noted that the dihedral angle is only shown and described by way of example and not for restricting the present invention accordingly. Moreover, it should be noted that instead of selecting the illustrative dihedral angle e. a negative (anhedral) angle may likewise be selected for the predetermined inclination angle <NUM>. In this case, an increase of up to <NUM>% of generated sideward thrust may be obtained, resulting in a possibly achievable increase of more than <NUM>% of a respectively generated counteracting moment.

Furthermore, according to one aspect a rear door <NUM> and/or additional equipment, such as e. a winch, may be arranged in the recess area <NUM>. The rear door <NUM> may e. be a sliding or dual cantilever door. By way of example, the rear door <NUM> may be slidable into the fuselage <NUM>, i. toward the cabin <NUM>. Thus, in forward flight with opened door, there is no additional drag generated by the rear door <NUM>.

Preferably, this rear door <NUM> is accessible from a rear side of the compound helicopter <NUM>, i. coming from the rear section <NUM>. Thus, the compound helicopter's cabin <NUM> may be loaded from the rear side. Advantageously, by positioning the rear door <NUM> in the recess area <NUM>, penalties to the overall aerodynamic performance of the compound helicopter <NUM> due to the rear door <NUM> may be avoided.

More particularly, <FIG> clarifies the merging of the front section <NUM> along the recess area <NUM> into the rear section <NUM> of the fuselage <NUM> by redirecting, i. deflecting the port side wall <NUM> of the compound helicopter <NUM> in the recess area <NUM> toward the starboard side wall <NUM>. Furthermore, the connection of the airfoil-shaped aerodynamic device <NUM> and the wing-type aerodynamic device <NUM> to preferably almost diametrically opposed sides <NUM>, <NUM> of the shrouded duct <NUM> is also further clarified.

<FIG> shows the compound helicopter <NUM> of <FIG> with the fuselage <NUM>, the main rotor <NUM>, the propeller <NUM>, the shrouded duct <NUM>, and the uncovered propeller drive shaft <NUM>. According to <FIG>, the fuselage <NUM> comprises the front section <NUM> that merges at the recess area <NUM> into the rear section <NUM>, the rear section <NUM> comprises the airfoil-shaped aerodynamic device <NUM> and the wing-type aerodynamic device <NUM>, the main rotor <NUM> comprises the rotor blades <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and the rotor head <NUM> which is arranged in the front section <NUM> of the fuselage <NUM>, the propeller <NUM> is rotatably mounted to the shrouded duct <NUM> and driven by the uncovered propeller drive shaft <NUM>, and the wing-type aerodynamic device <NUM> connects the upper deck <NUM> to the shrouded duct <NUM>.

More particularly, <FIG> clarifies the arrangement of the main rotor <NUM> and its rotor head <NUM> in the front section <NUM> of the fuselage <NUM>, as well as the merging of the front section <NUM> along the recess area <NUM> into the rear section <NUM> of the fuselage <NUM> by redirecting, i. deflecting the port side wall <NUM> of the compound helicopter <NUM> in the recess area <NUM> toward the starboard side wall <NUM>. Furthermore, the connection of the airfoil-shaped aerodynamic device <NUM> and the wing-type aerodynamic device <NUM> to the almost diametrically opposed sides <NUM>, <NUM> of <FIG> of the shrouded duct <NUM> is also further clarified. Preferably, at least the connection of the airfoil-shaped aerodynamic device <NUM> to the shrouded duct <NUM> is formed as a smooth transition <NUM>, preferentially over at least <NUM>% of an overall perimeter of the shrouded duct <NUM>.

According to one aspect, the wing-type aerodynamic device <NUM> has a width <NUM> that increases from the upper deck <NUM> over a predetermined length of the wing-type aerodynamic device <NUM>. More specifically, the width <NUM> illustratively starts to increase at the upper deck <NUM> and increases in direction of the shrouded duct <NUM>.

The width <NUM> may increase such that a maximum width value is reached at an area located between <NUM>% of the length of the rotor blades <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and their outer ends. Preferably, the width <NUM> increases over at least <NUM>% of the length of the wing-type aerodynamic device <NUM>. Illustratively, <NUM>% of the length of the wing-type aerodynamic device <NUM> is reached at a location <NUM>.

<FIG> shows the compound helicopter <NUM> of <FIG> with the fuselage <NUM>, the main rotor <NUM>, the propeller <NUM>, the shrouded duct <NUM>, and the uncovered propeller drive shaft <NUM>. According to <FIG>, the fuselage <NUM> comprises the front section <NUM> that merges at the recess area <NUM> into the rear section <NUM>, the rear section <NUM> comprises the airfoil-shaped aerodynamic device <NUM> and the wing-type aerodynamic device <NUM>, the propeller <NUM> is rotatably mounted to the shrouded duct <NUM> and driven by the uncovered propeller drive shaft <NUM>, and the wing-type aerodynamic device <NUM> connects the upper deck <NUM> to the shrouded duct <NUM>. More specifically, <FIG> further illustrates the smooth transition <NUM> from the rear section <NUM> to the shrouded duct <NUM> according to <FIG>.

<FIG> shows the uncovered propeller drive shaft <NUM> of <FIG> which, according to one aspect, comprises a big diameter cylinder shaft <NUM>. This big diameter cylinder shaft <NUM> has preferably a diameter comprised in a range from <NUM> to <NUM> times the diameter of a conventional tail rotor drive shaft. Preferably, the big diameter cylinder shaft <NUM> enables creation of the so-called Magnus effect for generating additional sideward thrust in operation from main rotor downwash of the main rotor <NUM> of the compound helicopter <NUM> of <FIG>.

As described above at <FIG>, the uncovered propeller drive shaft <NUM> and, thus, the big diameter cylinder shaft <NUM> preferably extends coupling- and bearing-free between the front section <NUM> of the fuselage <NUM> and the shrouded duct <NUM>. For purposes of illustration, the big diameter cylinder shaft <NUM> is, therefore, shown with two suitable bearings <NUM>, <NUM> at its axial ends, which are provided to rotatably support the big diameter cylinder shaft <NUM>.

In order to enable the coupling- and bearing-free extension of the big diameter cylinder shaft <NUM> between the front section <NUM> of the fuselage <NUM> and the shrouded duct <NUM>, the big diameter cylinder shaft <NUM> must be sufficiently stiff for a reliable and secure functioning. This may be achieved by forming the big diameter cylinder shaft <NUM> using carbon composites, especially high modulus fiber.

<FIG> shows the uncovered propeller drive shaft <NUM> of <FIG> which, according to another aspect, comprises a big diameter conical shaft <NUM>. This big diameter conical shaft <NUM> has preferably a largest diameter comprised in a range from <NUM> to <NUM> times the diameter of a conventional tail rotor drive shaft. Preferably, the big diameter conical shaft <NUM> also enables creation of the so-called Magnus effect for generating additional sideward thrust in operation from main rotor downwash of the main rotor <NUM> of the compound helicopter <NUM> of <FIG>.

As described above at <FIG>, the uncovered propeller drive shaft <NUM> and, thus, the big diameter conical shaft <NUM> preferably extends coupling- and bearing-free between the front section <NUM> of the fuselage <NUM> and the shrouded duct <NUM>. For purposes of illustration, the big diameter conical shaft <NUM> is, therefore, shown with two suitable bearings <NUM>, <NUM> at its axial ends, which are provided to rotatably support the big diameter conical shaft <NUM>. Preferably, the bearing <NUM> supports the big diameter conical shaft <NUM> at the shrouded duct <NUM> of <FIG>.

In order to enable the coupling- and bearing-free extension of the big diameter conical shaft <NUM> between the front section <NUM> of the fuselage <NUM> and the shrouded duct <NUM>, the big diameter conical shaft <NUM> must be sufficiently stiff for a reliable and secure functioning. This may be achieved by forming the big diameter conical shaft <NUM> using carbon composites, especially high modulus fiber.

<FIG> shows the uncovered propeller drive shaft <NUM> of <FIG>, which either comprises the big diameter cylinder shaft <NUM> of <FIG> or the big diameter conical shaft <NUM> of <FIG>. In an illustrative operation of the main rotor <NUM> of the compound helicopter <NUM> of <FIG>, the uncovered propeller drive shaft <NUM> is rotated in main rotor downwash <NUM> in a rotation direction <NUM>. Thus, as a result of the Magnus effect, the uncovered propeller drive shaft <NUM> generates a sideward force <NUM>. This sideward force <NUM>, in turn, results in sideward thrust applied to the rear section <NUM> of the fuselage <NUM> of the compound helicopter <NUM> of <FIG>.

It should be noted that the Magnus effect is well-known to the person skilled in the art. Therefore, for brevity and conciseness the Magnus effect and its application for generation of sideward thrust by means of the uncovered propeller drive shaft <NUM> is not described in more detail.

<FIG> shows the compound helicopter <NUM> of <FIG> with the fuselage <NUM>, the main rotor <NUM>, the propeller <NUM>, the shrouded duct <NUM>, and the uncovered propeller drive shaft <NUM>. However, illustration of the wing-type aerodynamic device <NUM> is omitted for simplicity and clarity of the drawing.

According to <FIG>, the fuselage <NUM> comprises the front section <NUM> that merges at the recess area <NUM> into the rear section <NUM>, the rear section <NUM> comprises the airfoil-shaped aerodynamic device <NUM>, the main rotor <NUM> comprises the rotor blades <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and the rotor head <NUM> which is arranged in the front section <NUM> of the fuselage <NUM>, and the propeller <NUM> is rotatably mounted to the shrouded duct <NUM> and driven by the uncovered propeller drive shaft <NUM>. However, in contrast to <FIG>, where the rear section <NUM> of the fuselage <NUM> comprises only one airfoil-shaped aerodynamic device <NUM> by way of example, the rear section <NUM> now illustratively comprises first and second airfoil-shaped aerodynamic devices <NUM>, <NUM>.

The airfoil-shaped aerodynamic devices <NUM>, <NUM> preferably form the rear section <NUM> at least partly. Illustratively, the airfoil-shaped aerodynamic devices <NUM>, <NUM> are separated from each other by an air gap <NUM>.

<FIG> shows the compound helicopter <NUM> of <FIG> with the fuselage <NUM>, the main rotor <NUM>, the propeller <NUM>, the shrouded duct <NUM>, and the airfoil-shaped aerodynamic devices <NUM>, <NUM>. However, illustration of the uncovered propeller drive shaft <NUM> is omitted for simplicity and clarity of the drawing.

According to <FIG>, the fuselage <NUM> comprises the front section <NUM> that merges at the recess area <NUM> into the rear section <NUM>, the rear section <NUM> comprises the airfoil-shaped aerodynamic devices <NUM>, <NUM>, the main rotor <NUM> comprises the rotor blades <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and the rotor head <NUM> which is arranged in the front section <NUM> of the fuselage <NUM>, and the propeller <NUM> is rotatably mounted to the shrouded duct <NUM>. The airfoil-shaped aerodynamic devices <NUM>, <NUM> are separated from each other by the air gap <NUM>.

By way of example, the airfoil-like shaping of the airfoil-shaped aerodynamic devices <NUM>, <NUM> is illustrated by means of the asymmetrical cross-sectional profile <NUM> with the series of cross-sectional profiles <NUM>, <NUM>, <NUM> according to <FIG>. Each one of the cross-sectional profiles <NUM>, <NUM>, <NUM> is now illustratively split into two separate cross-sectional profiles such that a first series of cross-sectional profiles <NUM>, <NUM>, <NUM> is associated with the airfoil-shaped aerodynamic device <NUM>, and a second series of cross-sectional profiles <NUM>, <NUM>, <NUM> is associated with the airfoil-shaped aerodynamic device <NUM>. Illustratively, the cross-sectional profiles <NUM>, <NUM> correspond to the cross-sectional profile <NUM>, the cross-sectional profiles <NUM>, <NUM> correspond to the cross-sectional profile <NUM>, and the cross-sectional profiles <NUM>, <NUM> correspond to the cross-sectional profile <NUM>. Preferably, the cross-sectional profiles <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are at least approximately C-shaped.

<FIG> shows an alternative airfoil-shaped aerodynamic device <NUM> which may be used with the compound helicopter <NUM> instead of the airfoil-shaped aerodynamic device <NUM> described above. According to one aspect, the airfoil-shaped aerodynamic device <NUM> comprises at least one deflectable flap <NUM>. Preferably, the deflectable flap <NUM> is actuatable, e. in response to pilot input.

By way of example, the airfoil-shaped aerodynamic device <NUM> has first and second airfoil-shaped aerodynamic devices <NUM>, <NUM>, similar to the airfoil-shaped aerodynamic devices <NUM>, <NUM> described above at <FIG> and <FIG>. The airfoil-shaped aerodynamic device <NUM> is provided to generate sideward thrust <NUM> for main rotor anti-torque from main rotor downwash, which is labeled with the reference sign <NUM> similar to <FIG>. Similarly, the airfoil-shaped aerodynamic device <NUM> is provided to generate sideward thrust <NUM> for main rotor anti-torque from the main rotor downwash <NUM>. Illustratively, the airfoil-shaped aerodynamic device <NUM> is provided with the deflectable flap <NUM> to enable adjustment of the generated sideward thrust <NUM> to a respectively required magnitude.

<FIG> shows the wing-type aerodynamic device <NUM> and the uncovered propeller drive shaft <NUM> of the compound helicopter <NUM> described above, together with another alternative airfoil-shaped aerodynamic device <NUM> that may be used with the compound helicopter <NUM> instead of the airfoil-shaped aerodynamic device <NUM> described above. According to <FIG>, the uncovered propeller drive shaft <NUM> is rotatable in the rotation direction <NUM> to create by means of the Magnus effect the sideward thrust <NUM>. However, instead of being fixedly mounted, the wing-type aerodynamic device <NUM> is now preferably rotatable to enable adjustment of the generated sideward thrust.

More specifically, the wing-type aerodynamic device <NUM> is preferably rotatable around its longitudinal axis such that the magnitude of respectively generated sideward thrust may either be adjusted, as symbolized with two different sideward thrust vectors <NUM>, <NUM>, or inverted, as illustrated with an inverted sideward thrust vector <NUM>. Preferably, the wing-type aerodynamic device <NUM> is rotatable in response to pilot input.

According to one aspect, the airfoil-shaped aerodynamic device <NUM> now comprises three separate airfoil-shaped aerodynamic devices <NUM>, <NUM>, <NUM>, which are respectively provided to generate sideward thrust for main rotor anti-torque from main rotor downwash. By way of example, the airfoil-shaped aerodynamic device <NUM> generates sideward thrust <NUM>, and the airfoil-shaped aerodynamic device <NUM> generates sideward thrust <NUM>.

Preferably, at least one of the three separate airfoil-shaped aerodynamic devices <NUM>, <NUM>, <NUM> is rotatable around its longitudinal axis, such that the magnitude of respectively generated sideward thrust may either be adjusted, or inverted. By way of example, the airfoil-shaped aerodynamic device <NUM> is rotatable around its longitudinal axis such that the magnitude of respectively generated sideward thrust may either be adjusted, as symbolized with two different sideward thrust vectors <NUM>, <NUM>, or inverted, as illustrated with an inverted sideward thrust vector <NUM>. Preferably, the airfoil-shaped aerodynamic device <NUM> is rotatable in response to pilot input.

According to one aspect, the rotatable airfoil-shaped aerodynamic device <NUM> and/or the wing-type aerodynamic device <NUM> have forward and rearward connections to the front section <NUM> and the shrouded duct <NUM> of the compound helicopter <NUM> described above with a reduced diameter such that a more circular cross section is provided at these forward and rearward connections. Thus, drag that is generated in rotated position of the rotatable airfoil-shaped aerodynamic device <NUM> and/or the wing-type aerodynamic device <NUM> at the forward and rearward connections is reduced. Alternatively, the forward and rearward connections may have an inclined end profile.

<FIG> shows the arrangement of <FIG> with the wing-type aerodynamic device <NUM>, the uncovered propeller drive shaft <NUM>, and the airfoil-shaped aerodynamic devices <NUM>, <NUM>. However, in contrast to <FIG> the rotatable airfoil-shaped aerodynamic device <NUM> is now replaced by a fixedly mounted airfoil-shaped aerodynamic device <NUM> that is merely intended to generate a fixed amount of sideward thrust, e. the sideward thrust <NUM> of <FIG>. Furthermore, instead of being entirely rotatable as described at <FIG>, the wing-type aerodynamic device <NUM> now merely comprises a deflectable flap <NUM> that enables adjustment of the magnitude of respectively generated sideward thrust, as symbolized with the two different sideward thrust vectors <NUM>, <NUM>, or its inversion, as illustrated with an inverted sideward thrust vector <NUM>.

At this point, it should be noted that modifications to the above-described realizations are within the common knowledge of the person skilled in the art and, thus, also considered as being part of the present invention. For instance, the airfoil-shaped aerodynamic devices described above may be realized with one, two or three separate airfoil-shaped aerodynamic devices. However, more than three separate airfoil-shaped aerodynamic devices may likewise be implemented. Furthermore, the shrouded duct described above may at least partly be reduced in its length, i. have a reduced or recessed area such as a cut-out which may e. be arranged in a bottom part of the shrouded duct between the airfoil-shaped aerodynamic device and the wing-type aerodynamic device. Moreover, respective leading and trailing edges of the shrouded duct described above may be moveable forward and aft in direction of the roll axis. Further exemplary modifications are described below with reference to <FIG> and <FIG>.

<FIG> shows the propeller <NUM> and the airfoil-shaped aerodynamic device <NUM> as well as the wing-type aerodynamic device <NUM> of the compound helicopter <NUM> described above. By way of example, the airfoil-shaped aerodynamic device <NUM> is shown with the two airfoil-shaped aerodynamic devices <NUM>, <NUM>, as e. described above at <FIG>.

However, the wing-type aerodynamic device <NUM> is now shown with two separate wing-type aerodynamic devices <NUM>, <NUM>. Furthermore, instead of being rotatably mounted to the shrouded duct <NUM> as described above, the propeller <NUM> is now rotatably mounted to a stabilizer arrangement <NUM> with vertical stabilizers <NUM>, <NUM> and a horizontal stabilizer <NUM>, by means of horizontal struts <NUM>, <NUM> and a vertical strut <NUM>. In this configuration, the vertical stabilizers <NUM>, <NUM> are preferably mounted to the airfoil-shaped aerodynamic device <NUM> and the wing-type aerodynamic device <NUM>, respectively.

Claim 1:
A rotary wing aircraft (<NUM>) that extends along an associated roll axis (R) between a nose region (<NUM>) and an aft region (<NUM>), comprising:
a fuselage (<NUM>) with a front section (<NUM>) and a rear section (<NUM>), wherein the front section (<NUM>) comprises a port side wall (<NUM>) and a starboard side wall (<NUM>)
a main rotor (<NUM>) that is rotatably mounted at the front section (<NUM>),
a shrouded duct (<NUM>) that is arranged in the aft region (<NUM>), and
a pusher propeller (<NUM>) that is rotatably mounted to the shrouded duct (<NUM>), wherein the rear section (<NUM>) extends in prolongation to one of the port side wall (<NUM>) or the starboard side wall (<NUM>) between the front section (<NUM>) and the shrouded duct (<NUM>);
characterized in that the rear section (<NUM>)
comprises an asymmetrical cross-sectional profile (<NUM>) in direction of the associated roll axis (R), and
wherein the rear section (<NUM>) is configured to generate sideward thrust (<NUM>,<NUM>) for main rotor anti-torque from main rotor downwash (<NUM>).