Rotating proprotor arrangement for a tiltrotor aircraft

TECHNICAL FIELD OF THE INVENTION

0001The present invention relates in general to the field of aircraft and more specifically to a rotating proprotor arrangement for a tiltrotor aircraft having a fuselage mounted engine.

BACKGROUND OF THE INVENTION

0002Without limiting the scope of the invention, its background is described in connection with tiltrotor aircraft.

0003A conventional tiltrotor aircraft configuration can include a fixed engine with a rotating proprotor; however, conventional packaging arrangements of the fixed engine and the rotating proprotor can have significant shortcomings. Further, the location of the fixed engine and the rotating proprotor in relation to each other, as well as to the wing structure, can have significant influence upon the size and weight of the supporting structure, as well as the complexity of servicing procedures. For example, a rotating proprotor that is cantilevered outboard of the tip end of the wing can require significant structure to adequately support and prevent operationally induced deflection. Further, a rotating proprotor embedded in the wing structure can be difficult and time-consuming to perform maintenance thereon. Likewise supporting the engine at the wingtip in a nacelle can add significant structural weight and complexity to the wing/rotor pylon configuration.

0004<patcit id="pcit0001" dnum="EP2778061A"><text>EP2778061</text></patcit> discloses a rotor system, comprising a rotor hub, which comprises a plurality of rotor blades, a rotatable rotor mast coupled to the rotor hub, a swashplate assembly comprising a non-rotating ring engaged with a rotatable ring, a plurality of pitch links mechanically coupling the rotatable ring to the plurality of rotor blades, and a swashplate actuator system. The rotatable ring is configured to rotate with the rotor mast, and the non-rotating ring is configured to engage and guide the rotatable ring. The pitch links are configured to control the pitch angle of each rotor blade. The swashplate actuator system consists of a first actuator and a second actuator, where the first actuator and the second actuator are mechanically coupled to a stationary surface and to the non-rotating ring.

0005<patcit id="pcit0002" dnum="EP2837559A"><text>EP2837559</text></patcit> discloses a tiltrotor aircraft, which includes a fuselage; a wing member having a first rib, a second rib, a first spar, second spar; and an upper wing skin; an engine disposed at a fixed location relative to the wing member; and a proprotor having a spindle gearbox, rotor mast, and a plurality of rotor blades drivable in rotation about the rotor mast, the spindle gearbox being rotatable about a conversion axis. The spindle gearbox is located above the upper wing skin of the wing member.

0006<patcit id="pcit0003" dnum="US2814451A"><text>US2814451</text></patcit> discloses a convertible aircraft having an engine disposed in the fuselage and a gearbox coupled to the engine and two drive shafts.

0007There is a need for mounting an engine of an aircraft within a fuselage in order to simplify rotor pylon and nacelle configuration, reduce space constraints, and/or reduce aircraft moment of inertia for improved maneuverability.

SUMMARY OF THE INVENTION

0008The present invention provides a propulsion system for a tiltrotor aircraft as described in claim 1.

0009In addition, the present invention provides a tiltrotor aircraft as described in claim 12.

BRIEF DESCRIPTION OF THE DRAWINGS

0010For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which: <ul id="ul0001" list-style="none"><li><figref idref="f0001">FIG. 1</figref> is a perspective view of a tiltrotor aircraft in airplane mode in accordance with one embodiment of the present invention;</li><li><figref idref="f0002">FIG. 2</figref> is a perspective view of a tiltrotor aircraft in helicopter mode in accordance with one embodiment of the present invention;</li><li><figref idref="f0003">FIG. 3</figref> is a perspective view of a tiltrotor aircraft in airplane mode in accordance with one embodiment of the present invention;</li><li><figref idref="f0004 f0005 f0006">FIGS. 4A-4C</figref> are partial schematic diagrams of a drive system in accordance with one embodiment of the present invention;</li><li><figref idref="f0006">FIG. 4D</figref> is a partial schematic diagram of a drive system in accordance with an example which is not part of the present invention;</li><li><figref idref="f0006">FIGS. 5A-5B</figref> are partial schematic diagrams of a side view and top view a drive system in accordance with an example which is not part of the present invention;</li><li><figref idref="f0007">FIG. 6</figref> is a partial perspective view of a drive system in accordance with one embodiment of the present invention;</li><li><figref idref="f0008">FIG. 7</figref> is a partial side view of a tiltrotor aircraft in accordance with one embodiment of the present invention;</li><li><figref idref="f0009">FIG. 8</figref> is a partial perspective view of a propulsion system portion of the tiltrotor aircraft in accordance with one embodiment of the present invention;</li><li><figref idref="f0010">FIG. 9</figref> is a front view of a propulsion system portion of the tiltrotor aircraft in accordance with one embodiment of the present invention;</li><li><figref idref="f0010">FIG. 10</figref> is a partial top view of the tiltrotor aircraft in accordance with one embodiment of the present invention;</li><li><figref idref="f0011 f0012">FIGS. 11-13</figref> are various views of a fixed wing extension in accordance with one embodiment of the present invention; and</li><li><figref idref="f0012 f0013">FIGS. 14-16</figref> are various views of a rotatable wing extension in accordance with one embodiment of the present invention.</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

0011Illustrative embodiments of the system of the present application are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

0012In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as "above," "below," "upper," "lower," or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction.

0013Referring to <figref idref="f0001 f0002">FIGS. 1-2</figref>, an aircraft 100 is illustrated. The aircraft 100 can be a tiltrotor aircraft or unmanned aerial vehicle (UAV). The aircraft 100 includes a fuselage 102, a wing 104, rotatable proprotors 106, wing extensions 108, a tail member 110 and landing gear 112 (<figref idref="f0008">FIG. 7</figref>). Each rotatable proprotor 106 has a plurality of rotor blades 114 associated therewith. The position of rotatable proprotors 106, as well as the pitch of rotor blades 114, can be selectively controlled in order to selectively control direction, thrust, and lift of aircraft 100. The aircraft 100 is generally operable in a cruise mode as shown in <figref idref="f0001">FIG. 1</figref> in which the aircraft 100 orients the rotatable proprotors 106 in a substantially horizontal position to provide a forward thrust in which a lifting force is supplied by wing 104 and wing extensions 108. This cruise mode allows flight in a manner substantially similar to a fixed wing aircraft. The aircraft 100 is also operable in a vertical takeoff and landing (VTOL) mode as shown in <figref idref="f0002">FIG. 2</figref> in which the aircraft 100 orients the rotatable proprotors 106 in a substantially vertical position to provide a lifting thrust. This VTOL mode allows flight in a manner substantially similar to a helicopter. In this embodiment, the aircraft 100 can also operate in a transition mode in which the rotatable proprotors 106 can be in any orientation between horizontal and vertical.

0014In alternative embodiments, the aircraft 100 may not include the wing extensions 108 or the wing extensions 108 could be removable and selectively installed for specific missions, such as long range reconnaissance missions.

0015Referring now to <figref idref="f0003 f0004 f0005 f0006 f0007 f0008">FIGS. 3-7</figref>, the aircraft 100 further comprises an engine 116 and an associated drive system 118A or 118B (<figref idref="f0004 f0005 f0006">FIGS. 4A-4D</figref>) configured to drive the rotatable proprotors 106. The engine 116 is disposed within the fuselage 102 and is disposed substantially symmetrically in the left-right direction about a zero butt line (not shown) of the aircraft 100. The zero butt line (not shown) generally bisects the aircraft 100 into left and right portions. The engine 116 is connected to a centrally located exhaust outlet 120 and two air intakes 122. Similar to the engine 116, the exhaust outlet 120 is disposed substantially symmetrically in the left-right direction about the zero butt line (not shown). As alternative embodiments the exhaust outlet, 120 could exhaust to the left or right sides of the aft fuselage or split into a bifurcated duct exhausting symmetrically on either side of the fuselage. However, while the air intakes 122 are not generally centrally located, the air intakes 122 are disposed in a substantially symmetric manner in the left-right direction about the zero butt line (not shown) on the sides of the fuselage 102. In alternative embodiments, the air intakes 122 may also be located on the upper side of the fuselage with dual inlets or as a single inlet duct that bifurcates around the transmission on its way to the engine 116 or a single duct routed to the engine 116.

0016Now referring to <figref idref="f0003">FIGS. 3</figref> and <figref idref="f0004 f0006">4A-4D</figref>, the drive systems 118A and 118B include an engine drive shaft 124 that extends from the engine 116 substantially forward toward the front of the aircraft 100. The engine drive shaft 124 is connected to a direction change gearbox 126 configured to connect the longitudinally extending engine drive shaft 124 to a riser shaft 128 that extends substantially vertically from the direction change gearbox 126. <figref idref="f0006">FIG. 4C</figref> shows an alternate embodiment where drive shaft 124 extends first to an engine reduction gearbox 117 which reduces shaft rotation speed before gearbox 126 and allows accessories such as generators and hydraulic pumps to be driven. The direction change gearbox 126 may include a clutch (not shown). In this embodiment, the direction change gearbox 126 is configured to transfer rotary motion between the engine drive shaft 124 and the riser shaft 128 despite the right angle between the engine drive shaft 124 and the riser shaft 128. In some embodiments, the direction change gearbox 126 comprises components configured to provide a shaft speed reduction so that the speed of the riser shaft 126 is slower than the speed of the engine drive shaft 124. The drive system 118 also includes a power splitting gearbox 130 (also referred to as a midwing gearbox or first gearbox) configured to receive rotation from the riser shaft 124 and transfer rotary motion to each of two interconnect drive shafts (ICDS) 132 that drive the rotor systems 106 via interconnect gearboxes (ICGB or second gearbox) 134 and proprotor gearboxes 136. <figref idref="f0006">FIG. 4D</figref> shows an example of a midwing geartrain 130 where the power splitting gearbox 130 is a single spiral bevel gear, rather than the dual spiral bevel gear of <figref idref="f0004">FIGS. 4A</figref> and <figref idref="f0005">4B</figref> (note that the helical geartrain in the interconnect gearbox 134 must include an additional gear on the right side to insure left and right rotor rotate opposite directions). The interconnect gearbox 134 includes a plurality of gears, such as helical gears, in a gear train. Torque is transferred from the interconnect gearbox 134 to the mast 140 of the rotatable proprotor 106 via the proprotor gearbox 136, which can be spiral bevel gears 142, or quill shaft 150 and spindle gearbox 152 as shown in <figref idref="f0009 f0010 f0011">FIGS. 8-11</figref>. The interconnect gearbox 134, proprotor gearbox 136 or mast 140 can also be used to drive various accessories 144 (e.g. blower, hydraulics, etc.). The interconnect gearbox 134 can be located in an outboard position as shown in <figref idref="f0003">FIGS. 3</figref> and <figref idref="f0004">4A</figref> or an inboard position as shown in <figref idref="f0005">FIG. 4B</figref> with respect to the rotatable proprotors 106.

0017Referring now to <figref idref="f0006">FIGS. 5A and 5B</figref>, examples which are not part of the present invention, which are substantially similar to drive systems 118A and 118B of <figref idref="f0004">FIGS. 4A</figref> and <figref idref="f0005">4B</figref>, except the engine 116 connects directly to midwing gearbox 130 with or without the a reduction gearbox 117 which provides a speed reduction and offset from the interconnect driveshaft line of action. In this embodiment, riser 128 and 90 degree gearbox 126 are deleted to allow a more direct attachment of engine without regard to aircraft fold/wing rotation.

0018Now referring to <figref idref="f0009 f0010">FIGS 8-10</figref>, the rotatable proprotor 106 is disclosed in further detail. The interconnect drive shaft 132 transfers power to the interconnect gearbox 134, which includes a plurality of gears, such as helical gears, in a gear train. In one embodiment, torque is transferred from the interconnect gearbox 134 to a quill shaft 150 that in turn transfers the torque to an input in spindle gearbox 152 of proprotor gearbox 136. In the illustrated embodiment, interconnect drive shaft 132 has a rotational axis 154 that is vertically lower and horizontally aft of the conversion axis 156 of the spindle gearbox 152. Conversion axis 156 is parallel to a lengthwise axis 157 of wing 104.

0019Referring in particular to <figref idref="f0010">FIGS. 9 and 10</figref>, interconnect drive shaft 132 includes a plurality of segments that share a common rotational axis 154. Location of interconnect drive shaft 132 aft of the aft wing spar 178 provides for optimal integration with interconnect gearbox 134 without interfering with the primary torque transfer in the quill shaft 150 between interconnect gearbox 134 and spindle gearbox 152; as such, the conversion axis 156 of spindle gearbox 152 is parallel to the rotational axis 154 and interconnect drive shaft 132, but located forward and above rotational axis 154.

0020The rotatable proprotor 106 can include a plurality of rotor blades 114 coupled to a yoke 158. The yoke 158 can be coupled to a mast 140. Mast 140 is coupled to a proprotor gearbox 136. It should be appreciated that rotatable proprotor 106 can include other components, such as a swashplate 160 that is selectively actuated by a plurality of actuators 162 to selectively control the pitch of rotor blades 114 via pitch links 164 (<figref idref="f0009">FIG. 8</figref>). Proprotor gearbox 136 is configured to transfer power and reduce speed to mast 140. Further, proprotor gearbox 136 provides operational support of rotatable proprotor 106.

0021During operation, a conversion actuator 166 (shown at least in <figref idref="f0009">FIG. 8</figref>) can be actuated so as to selectively rotate proprotor gearbox 136 about a conversion axis 156, which in turn selectively positions rotatable proprotor 106 between airplane mode (shown in <figref idref="f0001">FIG. 1</figref>) and helicopter mode (shown in <figref idref="f0002">FIG. 2</figref>). The operational loads, such as thrust loads, are transmitted through rotor mast 140 and into the spindle gearbox 152 of proprotor gearbox 136 and thus the structural support of spindle gearbox 152 is critical.

0022In the illustrated embodiment, the spindle gearbox 152 of proprotor gearbox 136 is mounted to an inboard pillow block 168 with an inboard bearing assembly (not shown). Similarly, spindle gearbox 152 of proprotor gearbox 136 is mounted to an outboard pillow block 170 with an outboard bearing assembly (not shown). Thus, spindle gearbox 152 is structurally supported but rotatable about conversion axis 156 by conversion actuator 166. Inboard pillow block 168 is structurally coupled to an inboard rib 172 (first rib). Similarly, outboard pillow block 170 is structurally coupled to an outboard rib 174 (second rib). In one embodiment, an inboard intermediate support (not shown) is utilized as a structural element between inboard pillow block 168 and inboard rib 172, and an outboard intermediate support (not shown) is similarly utilized as a structural element between outboard pillow block 170 and outboard rib 174. It should be appreciated that the exact structural configuration is implementation specific, and that structural components can be combined and/or separated to meet implementation specific requirements.

0023Spindle gearbox 152 of proprotor gearbox 136 is located above a surface of an upper wing skin, while also being approximately centered between inboard rib 172 and outboard rib 174. One advantage of locating the proprotor gearbox 136 above the surface of upper wing skin is that the fore/aft location of proprotor gearbox 136 can be easily tailored to align the aircraft center of gravity (CG) with the conversion axis 156 while the rotatable proprotor 106 is in helicopter mode, while also aligning the aircraft center of gravity (CG) with the wing aerodynamic center of lift while the rotatable proprotor 106 is in airplane mode. Because the aircraft center of gravity (CG) shifts as the rotatable proprotor 106 rotates between helicopter mode and airplane mode, the distance from the location of rotatable proprotor 106 in helicopter mode and airplane mode center of lift must correspond. As such, locating proprotor gearbox 136 above the wing (e.g., above an airfoil surface profile of the upper wing skin) allows the exact fore/aft location to be optimized accordingly, while also structurally attaching the proprotor gearbox 136 with in a zone of the torque box formed by coupling the forward wing spar 176 (first spar), aft wing spar 178 (second spar), inboard rib 172, and outboard rib 174 together. The proprotor gearbox 136 is rotatable about a conversion axis 156, the conversion axis 156 and the rotor mast axis of rotation 180 intersecting at an intersection point, the intersection point being located in a central region within the torque box.

0024The location of the spindle gearbox 152 portion of proprotor gearbox 136 provides an efficient structural support for enduring operational loads by being mounted to inboard rib 172 and outboard rib 174, which together with a forward wing spar 176 and an aft wing spar 178, form a structural torque box. For example, when aircraft 100 is in helicopter mode, torque about mast axis 180 is reacted by the torque box collectively formed by inboard rib 172, outboard rib 174, forward wing spar 176, and aft wing spar 178. It should be noted that location of spindle gearbox 152 of proprotor gearbox 136 also positions the mast axis 180, while in helicopter mode, inboard of outboard rib 174, outboard of inboard rib 172, forward of aft spar 178, and aft of forward spar 176, which allows the axis of the torque to be inside of the torque box structure, rather than cantilevered outside of the torque box structure. In contrast, a spindle gearbox location outside (such as outboard, forward, or aft) would cause a moment that would increase operational loading, thus requiring heavier and less efficient structural support.

0025Referring now to <figref idref="f0011 f0012">FIGS. 11-13</figref>, the wing extension 108 having a fixed position is shown in greater detail. More specifically, <figref idref="f0011">FIG. 11</figref> shows a front view of the rotatable proprotor 106 in airplane mode with the wing extension 108 in a fixed position. As shown, the wing extension 108 includes a first portion 200 having an orientation that is similar to that of the wing 104 and a second portion 202 that is canted slightly upwards. Alternatively, the wing extension 108 does not have to be canted and can be substantially straight with respect to the orientation of the wing 108. Moreover, the wing extension 108 can be dihedral shaped. <figref idref="f0011">FIG. 12</figref> shows a perspective view of the rotatable proprotor 106 in airplane mode with the wing extension 108 in a fixed position. <figref idref="f0012">FIG. 13</figref> shows a perspective view of the rotatable proprotor 106 in helicopter mode with the wing extension 108 in a fixed position. In another embodiment, the wing extension 108 is upwardly foldable to reduce to footprint of the aircraft 100 for storage. In some embodiments, manual pinning and folding/unfolding of the wing extensions 108 can be utilized. However, in alternative embodiments, automated and/or automatic locking/unlocking and folding/unfolding may be utilized.

0026Referring now to <figref idref="f0012 f0013">FIGS. 14-16</figref>, the wing extension 108 having a rotatable position corresponding to the rotatable proprotor 106 is shown in greater detail. More specifically, <figref idref="f0012">FIG. 14</figref> shows a front view of the rotatable proprotor 106 in airplane mode with the wing extension 108 in a corresponding airplane mode position. As shown, the wing extension 108 includes a first portion 200 having an orientation that is similar to that of the wing 104 and a second portion 202 that is canted slightly upwards. Alternatively, the wing extension 108 does not have to be canted and can be substantially straight with respect to the orientation of the wing 108. Moreover, the wing extension 108 can be dihedral shaped. <figref idref="f0013">FIG. 15</figref> shows a perspective view of the rotatable proprotor 106 in airplane mode with the wing extension 108 in a corresponding airplane mode position. <figref idref="f0013">FIG. 16</figref> shows a perspective view of the rotatable proprotor 106 in helicopter mode with the wing extension 108 in a corresponding helicopter mode position.

0027The wing extension 108 includes at least one mount connected to the interconnect gearbox 134 or proprotor gearbox 136 associated with drive system 118 or 138 such that winglet 108 rotates about the conversion axis 156. Rotatable wing extensions 108 increase cruise efficiency without increasing rotor download excessively in hover, while still allowing the aircraft 100 the ability to fold and fit into confined spaces. The wing extensions 108 are generally horizontal when the aircraft 100 is in a cruise configuration. Because the wing extensions 108 are generally vertical in hover or VTOL configurations, the wing extensions 108 are generally streamline with the rotor system 106 thrust direction. The wing extension 108 does not attach directly to structural components of the wing 104, but rather, attach to components carried in the rotatable proprotor 106.

0028In another embodiment, the wing extension 108 is upwardly foldable from the airplane mode position or aft foldable from the helicopter mode to reduce to footprint of the aircraft 100 for storage. In some embodiments, manual pinning and folding/unfolding of the wing extensions 108 can be utilized. However, in alternative embodiments, automated and/or automatic locking/unlocking and folding/unfolding may be utilized.

0029The invention is limited by the scope of the appended claims.