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.

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.

The document <CIT> describes such a conventional helicopter with a fuselage and a main rotor that creates torque around the helicopter's yaw axis. For counteracting this torque, a tail rotor is provided as anti-torque device. Furthermore, a retractable wing is provided that may be deployed on the retreating side of the fuselage to provide lift. More particularly, respective pitch and retraction angles of the retractable wing are adjustable to prevent roll motion of the helicopter.

The document <CIT> describes another helicopter with a fuselage, which comprises a main rotor that creates torque around the helicopter's yaw axis, and a tail rotor that is provided as anti-torque device for counteracting the torque created by the main rotor. Furthermore, a tractor propeller is provided at a front end of the fuselage. Moreover, a small wing is provided on the retreating side of the fuselage to provide lift in order to help correcting the main rotor's unbalanced lift and counteracting the helicopter's rolling tendency. The small wing extends laterally from the fuselage and is kept relatively small to keep interference with the main rotor's downwash low.

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 uses 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, and wherein the rear section extends between the front section and the aft region. The rotary wing aircraft comprises a pusher propeller that is rotatably mounted at the rear section in the aft region, a main rotor that is rotatably mounted at the front section, and at least one source of asymmetry that is connected in direction of the associated roll axis between the nose region and the main rotor to the front section such that the front section comprises at least in sections an asymmetrical cross-sectional profile in direction of the associated roll axis. The at least one source of asymmetry is located at the port side wall, if the main rotor rotates in clockwise direction, and at the starboard side wall, if the main rotor rotates in counterclockwise direction, wherein the at least one source of asymmetry is configured to generate sideward thrust for main rotor anti-torque from main rotor downwash.

Advantageously, by forming the front section of the fuselage asymmetrically with the at least one source of asymmetry that is configured to generate sideward thrust for main rotor anti-torque from main rotor downwash, a passive anti-torque device may be provided which does not require any actuator, 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.

More specifically, in order to enable use of the at least one source of asymmetry for generation of sideward thrust for main rotor anti-torque from main rotor downwash, the at least one source of asymmetry is preferably located to a side of the rotary wing aircraft that is closest to 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 at least one source of asymmetry is located at the starboard side, i. the right-hand side of the fuselage of the rotary wing aircraft, which is preferably formed as a compound helicopter with the main rotor and the propeller.

By way of example, the at least one source of asymmetry may be formed as a protruding edge of the fuselage that may be arranged close to a lower side of the fuselage. Such a protruding edge may be formed sufficiently large in order to be usable as a step. Furthermore, it may e. be integrated into an aerodynamically shaped skid landing gear. Alternatively, such a protruding edge may be built by a cover of a retractable nose landing gear. In this case, an aerodynamic performance of the compound helicopter in fast forward flight will not be affected by the protruding edge, as it will be retracted into the fuselage together with the retractable nose landing gear such that the overall configuration is aerodynamically clean again. In fact, generation of a respective anti-torque using the protruding edge is mainly necessary in hover condition and slow forward flight.

The at least one source of asymmetry may further include an elongation, i. a convex projection on top of the fuselage of the compound helicopter, i. at an upper side of the fuselage. A suitable elongation may e. be obtained by an appropriate shaping of an upper cowling that covers an upper deck of the compound helicopter. A highest point of the upper cowling may be shifted to an opposite side of the fuselage such that there is a smooth transition, at least with tangent constancy in the upper area of the cross section.

Moreover, in order to further increase generation of sideward thrust for main rotor anti-torque from main rotor downwash, the rear section of the fuselage of the compound helicopter may exhibit 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 aft region of the compound helicopter 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, a transition in the region of the main rotor, preferably in a region between the main rotor and the rear section of the fuselage, from a cross-sectional profile of the compound helicopter's fuselage, 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 may be embodied as a smooth recess. The latter is preferably shaped in order to avoid airflow separation.

In an illustrative realization, the rear section may be provided in the aft region with a shrouded duct or a stabilizer arrangement, to which the propeller is rotatably mounted. An underlying transition of the rear section of the fuselage to the shrouded duct or the stabilizer arrangement is 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 or a respective perimeter of the stabilizer arrangement.

Furthermore, at least one wing-type aerodynamic device, which is also referred to as the "support wing" hereinafter, may be associated with the rear section of the fuselage for additional 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, the associated support wing, as well as the front section, 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 or the stabilizer arrangement, e. from slightly behind of the main rotor to the shrouded duct or the stabilizer arrangement. 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 or the stabilizer arrangement 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 or the stabilizer arrangement, 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 or the stabilizer arrangement 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 or the stabilizer arrangement.

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 at least one source of asymmetry comprises a plate-shaped protrusion of the fuselage.

According to one aspect, the plate-shaped protrusion forms an accessible step.

According to one aspect, the plate-shaped protrusion is integrally formed with the fuselage.

According to one aspect, the at least one source of asymmetry comprises an asymmetrically shaped upper deck of the rotary wing aircraft, wherein the asymmetrically shaped upper deck comprises an asymmetrically shaped upper starboard side wall extension.

According to one aspect, the at least one source of asymmetry comprises an asymmetrically shaped upper deck cowling of the rotary wing aircraft.

According to one aspect, the rotary wing aircraft further comprises a retractable nose landing gear with a pivotable cover, wherein the at least one source of asymmetry comprises the pivotable cover in opened state.

According to one aspect, the at least one source of asymmetry is arranged in the nose region.

According to one aspect, the at least one source of asymmetry is pivotable and/or retractable.

According to one aspect, the at least one source of asymmetry comprises a deflectable flap.

According to one aspect, the rear section comprises an asymmetrical cross-sectional profile in direction of the associated roll axis.

According to one aspect, the rear section comprises at least one airfoil-shaped aerodynamic device that extends from the front section to the aft region, wherein 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 rotary wing aircraft further comprises an uncovered propeller drive shaft, in particular a cylinder shaft or a conical 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. Preferably, the uncovered tail propeller shaft is inclined and may have an offset to the roll axis of the compound helicopter seen from above.

In an alternative realization, the propeller and the main rotor are powered by separate engines. These separate engines may be of different types. Thus, provision of the uncovered propeller drive shaft may be omitted and engine hybridization is enabled with high redundancy, as the rotary wing aircraft may be operated in forward flight with each one of the separate engines independent of the other one.

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

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-type 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 extends in direction of the yaw axis Y from a lower side <NUM> to 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 at the rear section <NUM> in the aft region <NUM>. By way of example, 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 is a pusher propeller.

However, it should be noted that the shrouded duct <NUM> may also be omitted such that the propeller <NUM> would be unducted. In this case, a suitable mounting arrangement may be provided in the aft region <NUM> of the compound helicopter <NUM> for rotatably mounting the unducted propeller to the rear section <NUM>. Alternatively, the shrouded duct <NUM> may e. be replaced by a stabilizer arrangement (<NUM> in <FIG>), and so on.

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. By way of example, the asymmetrical cross-sectional profile <NUM> is at least approximately C-shaped, as illustrated with a series of 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 aft region <NUM> and, more particularly, 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>.

Illustratively, the compound helicopter <NUM> further comprises an uncovered propeller drive shaft <NUM>, in particular a cylinder shaft as described below at <FIG> or a conical shaft as described below at <FIG>, that is configured to create a Magnus effect upon rotation in main rotor downwash. The uncovered propeller drive shaft <NUM>, and likewise the shrouded duct <NUM>, may be inclined and may have an offset to the roll axis R of the compound helicopter <NUM> seen from above. Preferably, the uncovered propeller drive shaft <NUM> is configured to drive the propeller <NUM> in operation and, illustratively, extends coupling- and bearing-free between the front section <NUM> of the fuselage <NUM> and the propeller <NUM>.

According to one aspect, the front section <NUM> comprises at least one source of asymmetry, as described below at <FIG>. This source of asymmetry is preferably also configured to generate sideward thrust for main rotor anti-torque from main rotor downwash of the compound helicopter <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.

<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 propeller <NUM> is rotatably mounted to the shrouded duct <NUM> and driven by the uncovered propeller drive shaft <NUM>. However, illustration of the wing-type aerodynamic device <NUM> is omitted for simplicity and clarity of the drawing.

More particularly, <FIG> clarifies the connection of the airfoil-shaped aerodynamic device <NUM> to the shrouded duct <NUM>. Furthermore, 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> is also further clarified.

According to one aspect, at least one source of asymmetry <NUM> is connected to the front section <NUM>, preferably close to the lower side <NUM> of the fuselage <NUM>, such that the front section <NUM> comprises at least in sections an asymmetrical cross-sectional profile in direction of the associated roll axis R of <FIG>. The at least one source of asymmetry <NUM> is preferably configured to generate sideward thrust for main rotor anti-torque from main rotor downwash, as described in more detail at <FIG>.

The at least one source of asymmetry <NUM> may be formed as an integral part of the fuselage <NUM>. According to one aspect, the at least one source of asymmetry <NUM> is embodied as an integrally formed protruding edge of the fuselage <NUM>. Alternatively, the at least one source of asymmetry <NUM> may be pivotable and/or retractable, e. retractable into the fuselage <NUM>.

By way of example, the protruding edge is formed as a plate-shaped protrusion <NUM> of the fuselage <NUM>. The plate-shaped protrusion <NUM> is illustratively integrally formed with the fuselage <NUM>. According to one aspect, the plate-shaped protrusion <NUM> forms an accessible step, e. a step that is suitable to support passenger access into the cabin <NUM> of the compound helicopter <NUM>.

<FIG> shows a simplified cross-sectional profile <NUM> of the compound helicopter <NUM> of <FIG> and, more particularly, of the front section <NUM> of the fuselage <NUM> of the compound helicopter <NUM>, which comprises the at least one source of asymmetry <NUM>. According to <FIG>, the fuselage <NUM> comprises the port side wall <NUM> and the starboard side wall <NUM>, as well as the lower side <NUM>. On top of the fuselage <NUM> is the upper deck <NUM> that is illustratively covered by the cowling <NUM>. The at least one source of asymmetry <NUM> comprises the plate-shaped protrusion <NUM> that is arranged close to the lower side <NUM> of the fuselage <NUM>.

According to one aspect, the at least one source of asymmetry <NUM> may further, or alternatively, be formed by an asymmetric shaping of the upper deck <NUM>. More specifically, the upper deck <NUM> may comprise an asymmetrically shaped upper starboard side wall extension <NUM>. By way of example, the asymmetrically shaped upper starboard side wall extension <NUM> is formed by an asymmetric shaping of the cowling <NUM> and, more particularly, by an asymmetric arrangement of the cowling <NUM> on the upper deck <NUM>.

It should be noted that the upper starboard side wall extension <NUM> is provided assuming that the main rotor <NUM> of the compound helicopter <NUM> of <FIG> rotates in counterclockwise direction. If, however, the main rotor <NUM> rotates in clockwise direction, then an upper port side wall extension should be provided instead.

In operation, the front section <NUM> of the fuselage <NUM> is subject to main rotor downwash <NUM> of the main rotor <NUM> of <FIG>. The main rotor downwash <NUM> is illustratively deviated by the asymmetrically shaped upper starboard side wall extension <NUM>, as illustrated with arrows <NUM>, such that sideward thrust <NUM> is generated by means of suction. Similarly, the plate-shaped protrusion <NUM> deviates the main rotor downwash <NUM>, as illustrated with arrows <NUM>, such that sideward thrust <NUM> is generated by means of compression. The generated sideward thrust <NUM> and the generated sideward thrust <NUM> form together a total sideward thrust <NUM> generated by the at least one source of asymmetry <NUM> for main rotor anti-torque.

It should be noted that, in order to enable adjustment of the magnitude of the sideward thrust <NUM>, the plate-shaped protrusion <NUM> may be equipped with a deflectable flap <NUM>. The deflectable flap <NUM> may be actuatable, e. in response to pilot input.

<FIG> shows the simplified cross-sectional profile <NUM> of <FIG> of the compound helicopter <NUM> of <FIG> and, more particularly, of the nose region <NUM> of the front section <NUM> of the fuselage <NUM> of the compound helicopter <NUM>, which comprises the at least one source of asymmetry <NUM>. According to <FIG>, the fuselage <NUM> comprises the port side wall <NUM> and the starboard side wall <NUM>, as well as the lower side <NUM>. On top of the fuselage <NUM> is the upper deck <NUM>. However, in contrast to <FIG> illustration of the cowling <NUM> is omitted for simplicity of the drawing.

According to one aspect, the at least one source of asymmetry <NUM> is arranged in the nose region <NUM> and comprises now by way of example a pivotable cover <NUM> in opened state. The pivotable cover <NUM> is illustratively arranged on the lower side <NUM> of the fuselage <NUM>.

As illustrated in part (A) of <FIG>, the pivotable cover <NUM> is preferably associated with a retractable nose landing gear <NUM>. By way of example, the retractable nose landing gear <NUM> is of the wheel type and, thus, comprises one or more wheels <NUM>.

Preferably, the pivotable cover <NUM> is pivotable toward a side of the compound helicopter <NUM> of <FIG> that is closest to an approaching rotor blade of the main rotor <NUM> of <FIG> in the sense of rotation of the main rotor <NUM>. In other words, if the main rotor <NUM> rotates in counterclockwise direction, the pivotable cover <NUM> is pivotable toward the starboard side wall <NUM>, i. the right-hand side of the fuselage <NUM>. Accordingly, the pivotable cover <NUM> in its opened state protrudes from the lower side <NUM> of the fuselage <NUM> illustratively away from the starboard side wall <NUM> and may, thus, act similar to the plate-shaped protrusion <NUM> of <FIG> and deviate main rotor downwash as illustrated with the arrows <NUM> of <FIG>, such that sideward thrust <NUM> is generated.

In part (B) of <FIG>, the retractable nose landing gear <NUM> of part (A) is omitted, for simplicity. In contrast to part (A), part (B) shows an illustrative realization in which the pivotable cover <NUM> in its opened state is essentially arranged in parallel to the port side wall <NUM> and may, thus, deviate main rotor downwash as illustrated with arrows <NUM> to generate the sideward thrust <NUM>. Again, the described arrangement of the pivotable cover <NUM> assumes counterclockwise rotation of the main rotor <NUM> of the compound helicopter <NUM> of <FIG>. In the case of clockwise rotation, the pivotable cover <NUM> in its opened state would essentially be arranged in parallel to the starboard side wall <NUM> instead.

At this point, it should be noted that the pivotable cover <NUM> may not generate the sideward thrust <NUM> in closed state. However, the sideward thrust <NUM> is usually mainly required for main rotor anti-torque in hover condition and slow forward flight of the compound helicopter <NUM> of <FIG>. The pivotable cover <NUM> will, nevertheless, mainly be in opened state in the hover condition and may be in opened state in slow forward flight, but will essentially be in the closed state during normal or fast forward flight of the compound helicopter <NUM>. In other words, the pivotable cover <NUM> will be in opened state when generation of the sideward thrust <NUM> is required, and in closed state otherwise.

<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 propeller <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 propeller <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 propeller <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 propeller <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 propeller <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 the main rotor downwash (<NUM> in <FIG>) 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.

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 device <NUM> described above may be realized with one, two or more separate airfoil-shaped aerodynamic devices. 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. In addition, or alternatively, respective leading and trailing edges of the shrouded duct described above may be moveable forward and aft in direction of the roll axis. Moreover, the wing-type aerodynamic device <NUM> described above may have a width that increases from the upper deck over a predetermined length of the wing-type aerodynamic device <NUM>. More specifically, the width may start to increase at the upper deck and then increase in direction of the aft region of the compound helicopter. By way of example, the width may increase such that a maximum width value is reached at an area located between <NUM>% of the length of the rotor blades and their outer ends. For instance, the width may increase over at least <NUM>% of the length of the wing-type aerodynamic device <NUM>.

Further illustrative modifications are described below with reference to <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. However, in contrast to the configurations described above, which respectively comprise only one airfoil-shaped aerodynamic device <NUM>, now illustratively first and second airfoil-shaped aerodynamic devices <NUM>, <NUM> are provided instead. Similarly, instead of being provided with only one wing-type aerodynamic device <NUM>, now first and second wing-type aerodynamic devices <NUM>, <NUM> are provided.

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>), and wherein the rear section (<NUM>) extends between the front section (<NUM>) and the aft region (<NUM>),
a pusher propeller (<NUM>) that is rotatably mounted at the rear section (<NUM>) in the aft region (<NUM>),
a main rotor (<NUM>) that is rotatably mounted at the front section (<NUM>), and
at least one source of asymmetry (<NUM>) that is connected in direction of the associated roll axis (R) between the nose region (<NUM>) and the main rotor (<NUM>) to the front section (<NUM>) such that the front section (<NUM>) comprises at least in sections an asymmetrical cross-sectional profile (<NUM>) in direction of the associated roll axis (R), wherein the at least one source of asymmetry (<NUM>) is located at the port side wall (<NUM>), if the main rotor (<NUM>) rotates in clockwise direction, and at the starboard side wall (<NUM>), if the main rotor (<NUM>) rotates in counterclockwise direction, and wherein the at least one source of asymmetry (<NUM>) is configured to generate sideward thrust (<NUM>) for main rotor anti-torque from main rotor downwash (<NUM>).