Patent Description:
The present disclosure relates generally to aircraft, and more specifically, to aircraft with tiltable proprotors.

Vertical take-off and landing (VTOL) aircraft are aircraft that can take-off and land vertically and hover. To take-off and land vertically and hover, VTOL aircraft can include one or more proprotors that can be tilted between a position for providing vertical thrust for take-off and landing and hover and a position for providing forward thrust for forward flight. VTOL aircraft can include wings like conventional fixed-wing aircraft that provide lift during forward flight.

The pitch of the blades of a proprotor affect the efficiency and thrust of the proprotor. It is often desirable to adjust a pitch of the blades for different operational regimes. For example, when the proprotors are positioned for providing vertical thrust, it may be desirable to have the blades at a pitch that maximizes thrust, but when the proprotors are positioned for providing forward thrust during cruise, it may be desirable to have the blades at a pitch that provides greater efficiency. Blade pitch control actuators may be used to enable adjustment of blade pitch during flight. <CIT> relates to a tilt-prop aircraft capable of switching between a vertical take-off and landing mode and a forward flight mode. <CIT> relates to control system for an aircraft having laterally offset rotors which are tiltable between vertical positions for helicopter mode of operation and horizontal positions for propeller mode of operation and which has roll, pitch and yaw control in both modes of operation with the yaw control in the helicopter mode constituting tilting the rotor pods in opposite directions while applying differential longitudinal cyclic pitch to the rotors and washing out the cyclic pitch in response to increased pod tilting.

In a first aspect, a system for tilting a proprotor of an aircraft according to claim <NUM> is provided. In a second aspect, a method for operating a VTOL aircraft according to claim <NUM> is provided. Preferred embodiments are provided in the dependent claims.

A proprotor tilt and blade pitch adjustment system for a VTOL aircraft mechanically links the pitch of the blades of a proprotor of the aircraft to the tilt angle of the proprotor such that the blade pitch can adjust as the proprotor tilt angle changes. By mechanically linking blade pitch adjustment with proprotor tilting, blade pitch can be coordinated with proprotor tilt position for achieving more efficient proprotor performance without requiring a dedicated blade pitch adjustment actuator, which can save power, weight, and cost.

The proprotor is tiltably mounted to the aircraft and includes one or more actuators that tilt the proprotor. At least one fixed gear is fixed in position relative to the aircraft. A pinion is rotatably connected to a tiltable frame to which the proprotor is mounted and is engaged with the fixed gear such that as the pinion gear moves with the tiltable frame, the pinion revolves around the fixed gear, which causes the pinion to rotate. A cam is connected to the pinion such that the cam rotates along with the pinion. A control rod is operatively coupled to the cam such that as the cam rotates the control rod follows the profile of the cam, which causes the control rod to translate depending on the profile. The control rod is operatively connected to the blades of the proprotor such that as the control rod translates, the pitch of the blades of the proprotor are adjusted. Thus, as the proprotor is tilted about the tilt axis, the pitch of the blades of the proprotor can be adjusted. Accordingly, the system is configured to mechanically link tilting the proprotor and adjusting the pitch of the blades of the proprotor.

It will be appreciated that any of the variations, aspects, features, and options described in view of the systems apply equally to the methods and vice versa. It will also be clear that any one or more of the above variations, aspects, features, and options can be combined.

In the following description of the various examples, reference is made to the accompanying drawings, in which are shown, by way of illustration, specific examples that can be practiced. The description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the described examples will be readily apparent to those persons skilled in the art and the generic principles herein may be applied to other examples. Thus, the present invention is not intended to be limited to the examples shown but is defined by the appended claims.

Described herein are systems and methods for mechanically coupling adjustment of the pitch of the blades of the proprotor with the tilting of a proprotor. Coupling blade pitch to the tilt of the proprotor can enable the operational characteristics of the proprotor to be tuned to the different stages of flight, which can lead to greater efficiency that can result in less energy demand over the course of the flight. The systems and methods described herein enable the blade pitch to be tailored to the different operational regimes of the proprotor while avoiding the need for dedicated blade pitch adjustment actuators. Such dedicated blade pitch adjustment actuators and their associated mounting and wiring systems can add significant weight and cost to the aircraft and create another point of failure. By eliminating the need for such dedicated blade pitch adjustment actuators, the systems and methods described herein can achieve blade pitch adjustment while avoiding the increased weight, cost, and greater points of failure associated with the dedicated blade pitch adjustment actuators.

The system includes a first frame for mounting to a portion of the aircraft, such as the boom or wing of the aircraft, and a second frame to which the proprotor can be mounted. The second frame is tiltably mounted to the first frame at a rotation axis. The second frame is tilted relative to the first frame by at least one actuator, such as a linear actuator that is connected to the second frame eccentrically from the rotation axis. The system includes a first gear located on the rotation axis and fixed in position relative to the first frame and a pinion that moves with the second frame and is engaged with the first gear. As the pinion moves with the second frame, (e.g., along with the second frame as it rotates about the rotation axis) the pinion revolves around at least a portion of the first gear, thereby causing the pinion to rotate. The system includes a cam fixedly connected to the pinion such that the cam rotates with as the pinion rotates. A control rod operatively couples with the cam such that the translational position of the control rod is controlled by the cam. Depending on the cam profile and cam rotational position, the cam can cause the control rod to translate. The control rod is coupled at an opposite end to the blades of the proprotor in such a way that translation of the control rod changes the pitch of the blades. As the proprotor tilts about the tilt axis, the engagement between the first gear and the pinion causes the pinion to rotate, thereby rotating the cam and potentially translating the control rod (depending on the cam profile), which alters the pitch of the blades of the proprotor. Accordingly, the system can adjust the pitch of the blades as the proprotor rotates about the rotation axis.

As used herein, the singular forms "a," "an," and "the" used in the following description are intended to include the plural forms as well unless the context clearly indicates otherwise. It is to be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It is further to be understood that the terms "includes," "including," "comprises," and/or "comprising," when used herein, specify the presence of stated features, integers, steps, operations, elements, components, and/or units but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, units, and/or groups thereof.

As used herein, the term "proprotor" refers to a variable tilt propeller in which the direction of thrust of the propeller can be changed by changing the tilt angle of the propeller. For example, the tilt angle can be changed from an angle that provides at least some degree of vertical thrust, such as for vertical take-off and landing, to an angle that provides at least some degree of horizontal thrust, such as for forward flight. As used herein, a proprotor lift configuration refers to any proprotor orientation in which the proprotor thrust is providing primarily lift to the aircraft and proprotor forward flight configuration refers to any proprotor orientation in which the proprotor thrust is providing primarily forward thrust to the aircraft.

As used herein, "vertical take-off and landing" ("VTOL") refers to the capability of an aircraft to move substantially vertically without lift being provided solely by wings of the aircraft. While this term encompasses directly vertical take-off and landing (i.e., vertical movement without any horizontal movement), it also encompasses vertical movement in combination with horizontal movement. It will be understood by a person having ordinary skill in the art that a VTOL aircraft may be capable of non-vertical take-off and landing. For example, a winged VTOL, such as various examples described herein, can take-off and land in a traditional airplane manner utilizing the lift provided by its wings at suitable airspeeds.

<FIG> shows an aircraft <NUM> in a forward flight configuration. The aircraft <NUM> includes a fuselage <NUM>, wings <NUM> mounted to the fuselage <NUM>, and one or more rear stabilizers <NUM> mounted to the rear of the fuselage <NUM>. The aircraft <NUM> can be a vertical take-off and landing (VTOL) aircraft, and may be a passenger aircraft. A plurality of rotors <NUM> are mounted to the wings <NUM> and are configured to provide lift, such as for take-off and landing. A plurality of proprotors <NUM> are mounted to the wings <NUM> and are tiltable between lift configurations in which they provide a portion of the lift required for vertical take-off and landing and hovering, and forward flight configurations (as shown in <FIG>) in which they provide forward thrust to the aircraft <NUM> for horizontal flight.

During take-off and landing, the proprotors <NUM> are tilted to lift configurations in which their thrust is directed upward for providing lift. For forward flight, the proprotors <NUM> tilt from their lift configurations to their forward flight configurations in which their thrust is directed forward for providing forward propulsion. In other words, the pitch of the proprotors <NUM> is varied from a tilt angle in which the proprotor provides lift for take-off and landing (and, optionally, hover) to a tilt angle in which the proprotor provides forward thrust to the aircraft <NUM> for forward flight. The proprotors <NUM> can each be tilted by one or more actuators. The actuator(s) can be electrically powered. Optionally, each proprotor has a single actuator for adjusting its tilt. According to various embodiments, the aircraft <NUM> can include one or more damper mechanisms connected to each tiltable proprotor configured to limit a rate of change of the tilt angle of the tiltable proprotor, such as in the event that the actuator becomes disconnected or otherwise fails.

When the aircraft <NUM> is in full forward flight, lift may be provided entirely by the wings <NUM>, and the rotors <NUM> may be shut-off. The blades <NUM> of the rotors <NUM> may be locked in low drags positions for aircraft cruising. In some embodiments, the rotors <NUM> each have two blades <NUM> that are locked in minimum drag positions for cruising in which one blade is directly in front of the other blade as illustrated in <FIG>. In some embodiments, the rotors <NUM> have more than two blades. In some embodiments, the proprotors <NUM> include more blades <NUM> than the rotors <NUM>. For example, as illustrated in <FIG>, the rotors <NUM> may each include two blades and the proprotors <NUM> may each include five blades. According to various embodiments, the proprotors <NUM> can have from <NUM> to <NUM> blades.

According to various embodiments, the aircraft includes only one wing <NUM> on each side of the fuselage <NUM> (or a single wing that extends across the entire aircraft) and at least a portion of the rotors <NUM> are located rearward of the wings <NUM> and at least a portion of the proprotors <NUM> are located forward of the wings <NUM>. In some embodiments, all of the rotors <NUM> are located rearward of the wings <NUM> and all of the proprotors are located forward of the wings <NUM>. According to some embodiments, all rotors <NUM> and proprotors <NUM> are mounted to the wings-i.e., no rotors or proprotors are mounted to the fuselage. According to various embodiments, the rotors <NUM> are all located rearwardly of the wings <NUM> and the proprotors <NUM> are all located forward of the wings <NUM>. According to some embodiments, all rotors <NUM> and proprotors <NUM> are positioned inwardly of the wing tips <NUM>.

According to various embodiments, the rotors <NUM> and proprotors <NUM> are mounted to the wings <NUM> by booms <NUM>. The booms <NUM> may be mounted beneath the wings <NUM>, on top of the wings, and/or may be integrated into the wing profile. According to various embodiments, one rotor <NUM> and one proprotor <NUM> are mounted to each boom <NUM>. The rotor <NUM> may be mounted at a rear end of the boom <NUM> and a proprotor <NUM> may be mounted at a front end of the boom <NUM>. In some embodiments, the rotor <NUM> is mounted in a fixed position on the boom <NUM>. In some embodiments, the proprotor <NUM> is mounted to a front end of the boom <NUM> via a hinge or other system. The proprotor <NUM> may be mounted to the boom <NUM> such that the proprotor <NUM> is aligned with the body of the boom <NUM> when in its forward flight configuration, forming a continuous extension of the front end of the boom <NUM> that minimizes drag for forward flight.

The aircraft is operated during take-off and landing by positioning the proprotors in lift configurations and providing the required lift to the aircraft via the combined lift provided by the rotors and proprotors. According to various embodiments, during take-off and landing and/or hover, the proprotors can be maintained in predetermined lift configurations that can be the same across all proprotors or different for different proprotors. According to various embodiments, the tilt of at least some of the proprotors can be actively adjusted during take-off and landing and/or hover to provide the required stability and/or maneuvering. As discussed further below, the pitches of the blades of the proprotors (also referred to herein as the pitch angle and angle of attack) are mechanically linked to the tilt of the proprotors such that the blade pitch is coordinated with the proprotor tilt, such as to achieve maximum thrust when the proprotor is in the lift configuration and to achieve increased efficiency when the proprotor is in the forward flight configuration.

According to various embodiments, each rotor and/or each proprotor can be individually controlled by the flight controller according to the various operational degrees of freedom. According to various embodiments, the only degree of freedom of the rotor is the rotational speed of the rotor. According to various embodiments, the degrees of freedom of at least a portion of the proprotors includes the rotational speed of the proprotors, and the degree of tilt of the proprotors (combined with the blade pitch of the proprotors). According to various embodiments, any of these degrees of freedom can be actively controlled by the flight controller (either autonomously or in response to pilot commands) during take-off and landing in order to provide the appropriate stability and maneuvering.

Once the aircraft has achieved sufficient altitude to commence forward flight, the proprotors begin tilting forward toward their forward flight configurations such that their thrust provides a combination of lift and thrust, with a decreasing proportion of lift as the proprotors are tilted further toward their forward flight configurations. The pitch angle of the blades can be adjusted as the proprotors tilt forward toward their forward flight configurations. For instance, in the forward flight configuration, the blades of the proprotor can be at a pitch angle that results in less drag relative to a pitch angle of the blades when in the lift configuration. The rotors can remain active during at least a portion of the period in which the proprotors are tilted forward to continue to provide rotor-based lift. At any point after the forward airspeed is high enough that the wings provide sufficient lift to maintain the aircraft's altitude, the rotors can be deactivated.

The tilt of at least some of the proprotors can be actively controlled to provide additional stability and/or maneuverability control during cruising. In some embodiments, the tilt of at least some of the proprotors is actively controlled during take-off and landing and/or hover. In some embodiments, the tilt of the proprotors is fixed (i.e., non-varying) during cruise. According to some embodiments, the tilt of the outermost proprotors can be actively and independently controlled during vertical take-off and landing and/or hover to provide yawing moments as needed. The range of tilt angle of the tiltable proprotor(s) is at least <NUM> degrees, such that the proprotors can tilt between the forward flight configuration and the lift configuration.

<FIG> is a perspective view of the aircraft <NUM> of <FIG> illustrating the proprotor positions in the lift and forward flight configurations, according to one or more examples of the disclosure. The proprotors <NUM> can tilt about the tilt axis <NUM> that is perpendicular to the forward direction of the aircraft. For forward flight, the proprotors tilt from the lift configuration, which provides vertical thrust, to a forward flight configuration, which provides forward thrust.

As described further below, the aircraft <NUM> can include a system to tilt the proprotors <NUM> between the lift configuration and the forward flight configuration. The system can mechanically link adjustment of the pitch angle of the blades of the proprotor <NUM> to the adjustment of the tilt of the proprotors <NUM>.

<FIG> illustrates an exemplary system <NUM> for coupling tilting a proprotor with adjusting the pitch angle of blades of the proprotor. The system <NUM> is configured such that the pitch angle of the blades of the proprotor can correspond with the tilt position of the proprotor without requiring independent systems for tilting the proprotor and adjusting the pitch angle of the blades. Accordingly, the system <NUM> reduces the complexity and cost of the aircraft.

The system <NUM> rotatably couples a proprotor <NUM> to a boom <NUM> of an aircraft, proprotor <NUM> to boom <NUM> of aircraft <NUM>. The system <NUM> includes a fixed frame <NUM> for mounting to the aircraft (e.g., the proprotor <NUM> can be connected to a boom <NUM> via a bracket <NUM> of the fixed frame <NUM>) and a proprotor frame <NUM> to which the proprotor <NUM> mounts. The proprotor frame <NUM> can be tiltably connected to the fixed frame <NUM> at a joint <NUM>.

The system <NUM> can include one or more arm(s) <NUM> connected to the proprotor frame <NUM>. A linear actuator <NUM> can be connected to the arm(s) <NUM> tilt the proprotor <NUM> about the joint <NUM>. The actuator <NUM> can be, for example, a ball screw actuator or a pneumatic actuator. Alternatively, rotary actuator, such as a stepper motor or a servomotor, can be mounted at the joint or can drive a gear train that has an output gear located at the joint or engaged with a gear located at the joint.

The system <NUM> includes a cam <NUM> that can rotate in correspondence with tilting of the proprotor <NUM>. A control rod (discussed further below) is operatively coupled with the cam <NUM> such that the control rod can translate when the cam <NUM> rotates. The control rod is coupled at its opposite end to the blades <NUM> of the proprotor <NUM> such that translation of the control rod adjusts the pitch angle of the blades <NUM> of the proprotor <NUM>. Accordingly, the system <NUM> couples the pitch angle of the blades <NUM> of the proprotor <NUM> to the tilt of the proprotor <NUM>. During operation, a control system of the aircraft can send a proprotor tilt adjustment command to the actuator <NUM>. The actuator <NUM> may extend or retracted, causing the proprotor to increase or decrease its degree of tilt. As the proprotor tilt changes, the cam <NUM> rotates. This, in turn, can cause the control rod to translate, which adjusts the pitch of the blades <NUM>.

<FIG> shows a detail view of an exemplary system <NUM> for mechanically linking tilting a proprotor of an aircraft between a vertical thrust position and a forward thrust position with adjusting the pitch angle of blades of the proprotor. The system <NUM> can be used for system <NUM> of <FIG>. The system <NUM> includes a fixed frame <NUM> for mounting to a portion of a VTOL aircraft (such as to the fuselage, wing, or a boom structure), and a proprotor frame <NUM> for mounting the proprotor <NUM> that is rotatably mounted to the fixed frame <NUM> at a rotation axis <NUM>. The system <NUM> includes a gear <NUM>, a pinion (not shown in figure), a cam <NUM>, a control rod <NUM>, and a pair of arms <NUM>.

As shown in <FIG>, the gear <NUM> is located along the rotation axis <NUM>. The gear <NUM> can be fixed in position relative to the fixed frame <NUM>. For instance, as shown in <FIG>, the gear <NUM> is connected to an internal pin <NUM> that attaches to the fixed frame <NUM>. One or more of the shafts <NUM> can surround an internal pin <NUM>, which is shown clearly by the cutaway view of the left shaft <NUM> of <FIG>. A set of bearings <NUM> is located between each shaft <NUM> and the fixed frame <NUM> such that the shafts <NUM> are rotatably mounted to the fixed frame <NUM>.

The proximal end of the arms <NUM> can engage with the proprotor frame <NUM>. The engagement between the arms <NUM> and the proprotor frame <NUM> can be a fixed connection, such as by bolting or welding the arms <NUM> to the proprotor frame <NUM>. Optionally, both the arms <NUM> and the proprotor frame <NUM> can be fixedly connected to the shafts <NUM>. The distal end of the arms <NUM> can connect to one or more actuators <NUM> (see <FIG>) that drive the arms <NUM> to rotate about the rotation axis <NUM>. As the actuator <NUM> drives the arms <NUM>, the proprotor <NUM> is rotated about the rotation axis <NUM>.

The engagement between the gear <NUM>, pinion, cam <NUM> and control rod <NUM> is shown more clearly in <FIG>, which shows a detail view of a portion of the exemplary system <NUM> of <FIG>. The pinion <NUM> is mounted within pinion housing <NUM>, which is coupled in a fixed position to the arm <NUM> and/or the proprotor frame <NUM>. Accordingly, the pinion <NUM> is rotationally coupled to the proprotor frame <NUM> such that the pinion <NUM> moves with the proprotor frame <NUM> (e.g., as the proprotor frame <NUM> and proprotor <NUM> rotate about the rotation axis <NUM>). The pinion <NUM> is also engaged with the gear <NUM>. Rotation of the pinion housing <NUM> drives the pinion <NUM> around at least a portion of the gear <NUM>, which causes the pinion <NUM> to rotate via the toothed engagement with the gear <NUM>.

The cam <NUM> is fixedly connected to the pinion <NUM>, such as via the internal pin <NUM>, such that the cam <NUM> rotates with the pinion <NUM>. The cam <NUM> is also operatively coupled to a first end of the control rod <NUM>, such that the control rod <NUM> translates relative to the internal pin <NUM> during at least a portion of the rotation of the cam <NUM>. The control rod <NUM> is coupled at a second end to the blades of the proprotor (as will be described below) such that translation of the control rod <NUM> adjusts the pitch angle of the blades.

As the proprotor frame <NUM> rotates about the rotation axis <NUM> (e.g., to tilt the proprotor <NUM>), the pinion <NUM> revolves around the gear <NUM>, which rotates the cam <NUM> and translates the control rod <NUM>, thereby adjusting the pitch angle of the blades of the proprotor <NUM>. Accordingly, the system <NUM> mechanically links tilting the proprotor <NUM> with adjusting the pitch angle of the blades of the proprotor <NUM>.

The control rod <NUM> can be engaged with the cam <NUM> via a follower that follows the cam <NUM> as the cam <NUM> rotates. The follower can be, for example, a roller or a pin. As shown in <FIG>, the control rod <NUM> engages the cam <NUM> via a roller <NUM>. The roller <NUM> travels along the outer surface of the cam <NUM> as the cam <NUM> rotates. To remain engaged with the outer surface of the cam <NUM>, the control rod <NUM> can be biased in compression against the cam <NUM>, such as via a spring (not shown in figure).

The cam profile (e.g., shape of its outer surface that the control rod follows) controls the position of the control rod. The profile of the cam <NUM> can include one or more portions that cause translation of the control rod <NUM> and can include one or more portions do not cause the control rod <NUM> to translate. For example, the cam <NUM> can have one or more spiral portions that cause translation of the control rod <NUM> and/or one or more circular portions that do not cause the control rod <NUM> to translate. In the example shown in <FIG>, the cam <NUM> includes a spiral profile that will cause the control rod <NUM> to continuously translate throughout the range of tilt of the proprotor.

<FIG> shows another detail view of a portion of the exemplary system <NUM> of <FIG> and <FIG>. Whereas <FIG> depicts the control rod <NUM> engaged with two sides of the outer surface of the cam <NUM> (e.g., in the corner area of the snail-shaped cam), <FIG> depicts the control rod <NUM> engaged with only one side of the outer surface of the cam <NUM>. The position of the control rod <NUM> depicted in <FIG> compared to that of the control rod of <FIG> can be obtained by rotating the cam <NUM> in a clockwise direction such that the roller <NUM> moves in a counterclockwise direction as it follows the surface of the cam <NUM>.

As the roller <NUM> follows the spiral portion of the cam <NUM>, the control rod <NUM> may translate toward or away from the internal pin <NUM> at the center of the cam <NUM>. For instance, if the cam <NUM> rotates in a clockwise direction, as the roller <NUM> follows the spiral portion of the cam <NUM>, the control rod <NUM> translates away from the internal pin <NUM>. Opposite, if the cam <NUM> rotates in a counter-clockwise direction, the control rod <NUM> can translate towards the internal pin <NUM> as the roller <NUM> follows the spiral portion of the cam <NUM>. As the roller <NUM> follows the circular portion of the cam <NUM>, the control rod <NUM> may remain at a constant distance and not translate relative to the internal pin <NUM>. For example, the cam <NUM> can include a spiral profile for the first <NUM> degrees of rotation, with a circular profile for the remaining <NUM> degrees of rotation, such that the control rod <NUM> only translates away from the internal pin <NUM> during the first <NUM> degrees of rotation of the cam <NUM>. As noted above, the control rod <NUM> can be biased in compression against the cam <NUM> via a spring <NUM>.

<FIG> shows an example where the control rod <NUM> has a roller <NUM> engaged with an outer surface of the cam <NUM>. Alternate configurations may have a different engagement between the control rod and cam. For instance, <FIG> shows a top perspective view of an exemplary system <NUM> that includes a control rod <NUM> with a pin <NUM> engaged with a track <NUM> of a cam <NUM>. The pin <NUM> engages the track <NUM> of the cam <NUM> such that the cam <NUM> can both push and pull the pin <NUM> and the control rod as the cam <NUM> rotates.

The system <NUM> can be used for system <NUM> of <FIG>. Similar to the systems discussed above, the system <NUM> connects a proprotor <NUM> to a portion of an aircraft (to a boom <NUM> as shown in <FIG>). Distinct from the systems above, however, the system <NUM> includes a control rod <NUM> with a pin <NUM> that rides in a track. This configuration is more clearly visible the detailed pop-out of the cam <NUM>, which shows the pin <NUM> of the control rod <NUM> engage with the track <NUM> in the cam <NUM>. As the cam <NUM> rotates, such as by engagement with the pinion <NUM> rotating as it revolves around the gear <NUM>, the pin <NUM> can follow the track <NUM>, thereby translating the control rod <NUM>.

The gear <NUM> can be fixed in position relative to the fixed frame <NUM>, which is fixedly mounted to the aircraft. For instance, as shown in <FIG>, the gear <NUM> is connected to the fixed frame <NUM>. The pinion <NUM> can be rotatably mounted to the fixed frame <NUM>, such that the pinion <NUM> is rotationally coupled to the proprotor frame <NUM> and moves with the proprotor frame <NUM>.

The track <NUM> can include a spiral portion and a circular portion. As the pin <NUM> follows spiral portion of the track <NUM>, the control rod <NUM> can translate toward or away from a center of the cam <NUM>. As the pin <NUM> follows a circular section of the track <NUM>, however, the control rod <NUM> can remain at a constant distance and not translate relative to the center of the cam <NUM>. Optionally, the track <NUM> of the cam <NUM> can be a variety of geometries, based on the type of translation desired. To remain engaged with the track <NUM>, the control rod <NUM> can be biased in compression or tension against the cam <NUM>, such as via a spring (not shown in figure).

Another exemplary cam-control rod configuration is shown in <FIG>. Unlike system <NUM>, in system <NUM> the control rod <NUM> is held in tension. Similar to the systems described above, the system <NUM> can include a proprotor frame <NUM> rotatably mounted to a fixed frame <NUM> that is mounted to a portion of the aircraft (such as to the fuselage, wing, or a boom structure). The system <NUM> can be configured such that one or more actuators (not shown in figure) drive the proprotor frame <NUM> to rotate about the rotation axis <NUM> to tilt a proprotor mounted to the proprotor frame <NUM> between a vertical thrust position and a forward thrust position.

Similar to the systems described above, the system <NUM> includes a control rod <NUM> that engages a cam <NUM>, which rotates based on an engagement with a pinion <NUM> engaged with a gear <NUM>. The gear <NUM> can be fixed in position relative to the fixed frame <NUM>. For instance, as shown in <FIG>, the gear <NUM> is connected to the fixed frame <NUM>. The cam <NUM> is fixedly connected to the pinion <NUM>, such as via the shaft <NUM>, so that the cam <NUM> rotates with the pinion <NUM>. The pinion <NUM> can be rotatably mounted to the fixed frame <NUM>, such as via a bearing mounting to rib <NUM>, such that the pinion <NUM> is rotationally coupled to the proprotor frame <NUM> and moves with the proprotor frame <NUM>. The pinion <NUM> revolves around the gear <NUM> as the proprotor frame <NUM> moves, which rotates the cam <NUM>.

The control rod <NUM> includes a clevis <NUM> and a follower <NUM>, which is a roller in this example. As shown, the cam <NUM> is engaged with the follower <NUM> such that the follower <NUM> rolls along the cam <NUM> as it rotates. The follower <NUM> is rotatably attached to the clevis <NUM> of the control rod <NUM>. The control rod <NUM> is in tension (a force is applied-such as via one or more springs-along axis <NUM> to the left in the view of <FIG>) such that the follower <NUM> is forced against the cam <NUM>. Thus, as the follower <NUM> rolls along the cam <NUM>, the control rod <NUM> may translate along axis <NUM> (depending on the profile of the cam <NUM>). As above, the cam <NUM> can have any suitable profile that for achieving the desired relationship between blade pitch and proprotor tilt.

The clevis <NUM> includes a slot <NUM> that through which the shaft <NUM> may extend. The clevis <NUM> is separated from the shaft <NUM> by a bushing, which is shown more clearly in <FIG>, which shows a detail cutaway view of the bushing <NUM> and clevis <NUM> interface of the system <NUM> of <FIG>. The bushing <NUM> can include engagement surfaces <NUM> on the areas of the bushing <NUM> that engage with the clevis <NUM>, with the engagement surfaces <NUM> shaped such that the clevis <NUM> is prevented from rotating, which in turn prevents the control rod attached to the clevis <NUM> (e.g., the control rod <NUM> shown in <FIG>) from rotating. As shown in <FIG>, the engagement surfaces <NUM> of the bushings <NUM> are flat, which corresponds to flat surfaces of the clevis <NUM>. Optionally, these surfaces may be another shape, based on the shape of corresponding surfaces of the clevis <NUM>. For example, the engagement between the clevis <NUM> and the bushings <NUM> may involve circular, elliptical, or angled surfaces.

As discussed above, translation of the control rod of any of the above exemplary systems can adjust the pitch angle of the blades of the proprotor. The control rod can be operatively engaged with a plurality of blades such that translation of the control rod causes rotation of the blades. <FIG> shows a cutaway detail view of an exemplary hub <NUM> of a proprotor, showing an example of the coupling of a control rod <NUM> with the blades <NUM> of the proprotor, according to one or more examples of the disclosure. The hub <NUM> can include an engine shaft <NUM>, a spring <NUM>, a bearing <NUM>, a plate <NUM>, a pitch plate <NUM> and a number of links <NUM>. The blades <NUM> are mounted to the hub <NUM>. For instance, each blade <NUM> can include blade roots <NUM> that connect to the links <NUM>. The control rod <NUM> connects to the pitch plate <NUM> and/or the plate <NUM> of the hub <NUM>. The other end of the control rod <NUM> can connect to a system configured to translate the control rod <NUM> while tilting a proprotor, as discussed above.

The engine shaft <NUM> surrounds the spring <NUM> and the bearing <NUM> and connects to the plate <NUM> that connects to the pitch plate <NUM> engaged with the links <NUM>. The engine shaft <NUM> connects to the engine (not shown in figure) of the hub <NUM>. The plate <NUM> is constrained in rotation by a spline interface to the engine shaft <NUM> such that the plate <NUM> rotates with the engine shaft <NUM>. The control rod <NUM> is prevented from rotating along with the plate <NUM> via the bearing <NUM>. The pitch plate <NUM> connects to the blade roots <NUM> via links <NUM>. As shown in <FIG>, the links <NUM> are dog-bone links, however other linkage types are contemplated, such as pitch links, etc. The spring <NUM> can maintain the control rod <NUM> in tension or compression. In the example of <FIG>, the spring <NUM> maintains the control rod <NUM> in tension by pressing the control rod <NUM> against the pitch plate <NUM>.

As the control rod <NUM> translates (e.g. advances or retracts axially), the plate <NUM> and/or pitch plate <NUM> translates, which causes the links <NUM> to adjust the pitch angle of the blades <NUM> by rotating each blade <NUM> about a central axis <NUM> of the blade <NUM>. Rotating each blade <NUM> about the central axis <NUM> adjusts the pitch angle of the blades <NUM>. Accordingly, translation of the control rod <NUM> can adjust the pitch angle of the blades <NUM> of the proprotor.

As discussed above, adjusting the pitch of the blades of a proprotor based on the tilt of the proprotor can enable the propeller operational characteristics to be tuned to the different stages of flight, which can lead to greater efficiency that can result in less energy demand over the course of the flight. The relationship between blade pitch and proprotor tilt can be selected by selecting the desired cam profile (e.g., the profile of cam <NUM>). A wide variety of relationships between blade pitch and proprotor tilt are achievable based on the selection of the cam profile. <FIG> is a graph that shows examples of some of these relationships.

The graph of <FIG> shows blade pitch as a function of proprotor tilt angle. The proprotor tilt angle, which is provided on the X-axis of the graph of <FIG>, is the angle of the rotational axis of the proprotor relative to a line that extends parallel to a longitudinal axis of the aircraft and intersects the rotational axis of the proprotor. The rotational axis of the proprotor is shown in the example of <FIG>, as rotational axis <NUM>-A when the proprotor is in a forward flight position (rotational axis <NUM>-A is coincident with the line that extends parallel to the longitudinal axis <NUM> of the aircraft and intersects the rotational axis of the proprotor) and rotational axis <NUM>-B when the proprotor is in a lift position. Zero degrees of tilt angle on the graph of <FIG> corresponds to the proprotor having a rotational axe that is parallel to the longitudinal axis <NUM> of the aircraft-e.g., for providing forward thrust for forward flight, and ninety degrees of tilt angle corresponds to the proprotors providing vertical thrust, such as for vertical take-off and landing.

The pitch of the blades, which is provided on the Y-axis of the graph of <FIG>, can be defined as the angle between the chord of the blade and the plane of rotation and may be measured at a specific point along the length of the blade. <FIG> is a diagram showing an example of the definition of blade pitch. The blade <NUM> (only one is shown for simplicity but it will be understood that each proprotor will include multiple blades) revolves about proprotor rotational shaft <NUM> and is mounted such that it can rotate about a pitch axis <NUM>, enabling the pitch <NUM> of the blade <NUM> to be adjusted. The plane that contains the pitch axis <NUM> and is traversed by the blade <NUM> when the blade <NUM> rotates can be referred to as the disc plane <NUM>. The pitch <NUM> of the blade <NUM> can be defined as the angle between the chord <NUM> of the blade <NUM> (a line joining the leading edge and trailing edge of the blade <NUM>) and a line <NUM> lying within disc plane <NUM> that is perpendicular to the pitch axis <NUM>. The pitch values shown in <FIG> are merely exemplary and it will be understood by a person of ordinary skill in the art that the pitch values will depend on the specific design of the blades and the location along the blades where the pitch is measured. Similarly, the proprotor tilt values shown in <FIG> are merely exemplary and it will be understood by a person of ordinary skill in the art that a different range of proprotor tilt could be used, including a negative tilt angle associated with the proprotor being tilted somewhat downwardly.

<FIG> includes four different lines <NUM>-<NUM> indicating four different relationships between blade pitch and proprotor tilt. Each line is associated with a different cam profile. Lines <NUM>, <NUM>, and <NUM> have maximum blade pitches (maximums for the given line) at a zero proprotor tilt angle. This can be the blade pitch for forward flight in which the higher blade pitch can provide better efficiency at the relatively high airspeeds of forward flight.

Line <NUM> has a very low blade pitch at zero proprotor tilt. This could result in the blades creating a relatively high drag at high airspeeds, which can be useful to slow down the aircraft, such as for landing. This low blade pitch may also be useful for increasing the efficiency of the proprotor at low airspeeds, such as during a conventional (airplane style) take-off. The blade pitch quickly increases to a maximum so that the proprotor need only be tilted a relatively small amount to achieve the maximum blade pitch, which may be a desirable blade pitch for forward flight. With this relationship, the proprotor need only be tilted a small amount relative to the minimum tilt (e.g., zero tilt as shown, a small positive tilt, a small negative tilt, etc.) to achieve a more optimal blade pitch for the high speeds of forward flight.

Each line <NUM>-<NUM> shows the blade pitch decreasing to a minimum blade pitch (minimum for the given relationship) that is associated with a maximum proprotor tilt-tilt that may be used for vertical flight and hover. The minimum blade pitch can be optimal for the low air speed and high thrust requirements of vertical flight and hover. Lines <NUM> and <NUM> demonstrate that the minimum blade pitch need not be zero. The particular proprotor tilt angle at which the blade pitch minimum is reached can be selected based on the cam profile, as demonstrated by the different locations of this point for the various relationships (e.g., point <NUM>).

Each relationship <NUM>-<NUM> is achieved by a different cam profile. Cam profiles can include multiple regions having different shaped to achieve the changes in relationship between the blade pitch and proprotor tilt of the various lines <NUM>-<NUM>. For example, line <NUM> can be achieved by a cam profile that includes a spiral section that corresponds to the range of zero degrees proprotor tilt to the proprotor tilt angle of point <NUM>. The spiral section (continuously changing radius) transitions to a circular section (constant radius) that provides for the unchanging blade pitch associated with proprotor tilt angles past point <NUM>. Line <NUM> can be achieved by a first spiral section, followed by a second spiral section that has a different rate of change of the radius than the first spiral section, followed by a circular section. Line <NUM> can be achieved by a cam profile that has continuously varying rates of change of radius.

The relationships shown in <FIG> are merely examples illustrating that many different relationships can be achieved by the appropriate selection of the cam profile. A person of ordinary skill in the art will understand that the desired relationship between blade pitch and proprotor tilt can be achieved by the appropriate cam profile design.

In one or more examples, any of the systems described above, such as system <NUM>, system <NUM>, system <NUM>, system <NUM>, and aircraft <NUM> can include a damper, as shown in the exemplary system <NUM> of <FIG>, for limiting a rate of tilt of the proprotor, such as in the event of actuator failure. The damper <NUM> of system <NUM> is connected between the boom <NUM> of an aircraft, such as aircraft <NUM> of <FIG> and <FIG>, and the proprotor frame <NUM>, to which a proprotor (not shown) mounts. The damper <NUM> can be housed within an outer shell of the boom <NUM>. In one or more examples, the boom <NUM> can include a rib <NUM>, and the actuator <NUM> and the damper <NUM> can be positioned on opposite sides of the rib <NUM>. The proprotor frame <NUM> is titltably connected to the fixed frame <NUM> such that the proprotor frame <NUM> (and the proprotor) can tilt about rotation axis <NUM>. The actuator <NUM> is connected to the proprotor frame <NUM> and drives the tilting of the proprotor about the rotation axis <NUM>.

In one or more examples, the actuator <NUM> can be a linear actuator. Alternatively, the actuator can be a rotary actuator, as shown in the exemplary system <NUM> of <FIG>. The system <NUM> is otherwise similar to system <NUM> of <FIG> in that it includes a damper <NUM> connected between a boom <NUM> of an aircraft and a proprotor frame <NUM>, which is tiltably connected to the fixed frame <NUM> such that the proprotor frame <NUM> (and the proprotor) can tilt about the rotation axis <NUM>. System <NUM> includes a rotary actuator <NUM> connected to the proprotor frame <NUM> that drives the tilting of the proprotor about the rotation axis <NUM>. In the illustrated embodiment, the rotary actuator <NUM> includes an electric motor connected to a gear train that drives a worm gear. The worm gear drives a gear to rotate about the rotation axis <NUM>, which tilts the proprotor.

If the actuator <NUM> (or actuator <NUM> of <FIG>) were to become disconnected from the proprotor frame <NUM>, catastrophic failure may occur, as the proprotor could begin rapidly tilting without control. In one or more examples, the system <NUM> could include a second (redundant) actuator that is also connected to the proprotor frame <NUM> such that if the first actuator <NUM> becomes disconnected, the second actuator can nonetheless control the tilting of the proprotor about the rotation axis <NUM>. However, adding a second actuator may complicate the system <NUM>, increase cost, and add more weight to the aircraft. Rather than implementing a second actuator, the system <NUM> instead includes a damper mechanism such as damper <NUM>. In the event that the actuator <NUM> becomes disconnected from the proprotor frame <NUM>, the damper <NUM> dissipates energy and, thereby, limits the rate of change of tilt of the proprotor, which eliminates the catastrophic result of the actuator <NUM> disconnecting from the proprotor frame <NUM>. The damper <NUM> can include a balanced hydraulic or pneumatic cylinder, which as is known in the art includes a piston that slides within a cylinder, the piston including a plurality of apertures through which fluid flows as the piston moves within the cylinder. The damper <NUM> is a passive damper configured to apply a force (a hydraulic or pneumatic force) to the proprotor frame <NUM> (and proprotor) only when the tilt angle of the proprotor is being adjusted (i.e., no bias is applied when the proprotor is at rest). In one or more examples, the system <NUM> may include one or more redundant actuators as well as a damper mechanism such as damper <NUM>.

The damper <NUM> can be configured to limit the rate of change of the tilt angle of the proprotor frame <NUM> in both tilt directions. The damper <NUM> can be positioned such that a force vector of the damper <NUM> can extend beneath the tilt axis, such as tilt axis <NUM> of <FIG>. In one or more examples, the damper <NUM> can be configured to limit the rate of change of the tilt angle of the proprotor to a predetermined threshold value in the event that the actuator <NUM> becomes disconnected from the proprotor frame <NUM>.

In one or more examples, controlling an aircraft that includes one or more dampers, as discussed above can include receiving a command at a controller to adjust a tilt angle of a tiltable proprotor that is tiltable between a lift position for providing lift for the aircraft and a forward flight position for providing forward propulsion for the aircraft, and controlling at least one actuator to adjusting the tilt angle of the tiltable proprotor according to the command, wherein at least one passive damper is connected to the tiltable proprotor to limit a rate of change of the tilt angle of the tiltable proprotor.

In one or more examples, any of the systems described above, such as system <NUM>, system <NUM>, system <NUM>, system <NUM>, system <NUM>, system <NUM>, and aircraft <NUM> can include a tilt rotor lock mechanism, as shown in the exemplary system <NUM> of <FIG>, which shows a side view of the system <NUM> in a first configuration, according to one or more examples of the disclosure. The system <NUM> can be implemented in an aircraft with a tiltable proprotor instead of, or in addition to, redundant actuators and/or a damper mechanism, and can lock the tilt of the proprotor in place.

The system <NUM> is positioned between a boom <NUM> and proprotor <NUM> of an aircraft, and can include a tension spring <NUM> connected to a pulley <NUM> via connector <NUM>, with the pulley <NUM> also connected via connector <NUM> to a pawl <NUM>. The pawl <NUM> can be selectively engaged with a sector gear <NUM> based on movement of the pulley <NUM>, with the pawl <NUM> configured to move towards the sector gear <NUM> as the pulley <NUM> moves away from the actuator <NUM>. The pulley <NUM> is coupled to the actuator <NUM> in normal operation.

In the event that the actuator <NUM> and the pulley <NUM> become disconnected (e.g., the actuator <NUM> becomes disconnected from the proprotor <NUM>), the pulley <NUM> moves away from the actuator <NUM> because of the bias from the spring <NUM>, as shown in the configuration of system <NUM> shown in <FIG>. Whereas the <FIG> shows the pawl <NUM> not engaged with the sector gear <NUM> and the pulley <NUM> located adjacent to the actuator <NUM>, <FIG> shows the pawl <NUM> engaged with the sector gear <NUM> and the pulley <NUM> no longer located adjacent to the actuator <NUM>. The tension spring <NUM> can automatically draw the pulley <NUM> away from the actuator <NUM> in the event that the actuator <NUM> and pulley <NUM> become disconnected, thereby forcing the pawl <NUM> to engage the sector gear <NUM>. When the pawl <NUM> engages the sector gear <NUM>, the proprotor can be prevented from tilting further in one or both directions. By preventing further tilting in one or both directions, the system <NUM> can prevent catastrophic failure from occurring should the actuator become disconnected from the proprotor without requiring redundant actuators or damping mechanisms. <FIG> shows a front view of the exemplary system of <FIG>, according to one or more examples of the disclosure.

In one or more examples, the sector gear <NUM> can be a ratchet with ridges that contact the pawl <NUM>. Such exemplary configurations are shown in <FIG>, which shows an exemplary ratchet configuration <NUM>, according to one or more examples of the disclosure. The ratchet configuration <NUM> includes a sector gear <NUM> that has a number of ridges <NUM> that have a sloped side and a straighter side. The pawl <NUM> rides over the sloped sides but catches on the straighter sides. As such, the proprotor will be ablet to tilt in a first direction (e.g., permitted to tilt counterclockwise in the illustrated configuration) but not a second direction (e.g., not permitted to tilt clockwise in the illustrated configuration). This may be useful in permitted the proprotor to move to a desired failure state tilt angle, such as a lift configuration, in which the proprotor can still be used during at least a portion of the flight. Such a ratchet mechanism could also be used with any of the damper configurations described above to provide a slower rate of tilt in the ratcheting direction.

Alternatively, the sector gear and pawl can be configured to lock the proprotor in both directions. 8B illustrates an exemplary lock configuration <NUM> that has a sector gear <NUM> that has a number of ridges <NUM> that have two straight sides and a locking mechanism <NUM> that engages the ridges <NUM>. When the locking mechanism <NUM> is forced against the gear sector <NUM>, the locking mechanism will engage with the ridges <NUM>. The locking mechanism <NUM> will be unable to ride past the ridges <NUM> in either direction because of their straight sides, locking the sector gear <NUM> (and, thereby, the proprotor) in position.

Accordingly, described herein are systems and methods for mechanically linking the tilt of a proprotor of an aircraft with the pitch of blades of the proprotor. The systems enable blade pitch to be tailored to the different operational regimes of the proprotor while avoiding the need for dedicated blade pitch adjustment actuators and the cost, weight, and failure points associated with such dedicated blade adjustment actuators.

<FIG> illustrates an alternative spring configuration and a feature for providing a "midlife" check capability to ensure that the pawl mechanism is not jammed. In the illustrated embodiment, the mechanism <NUM> can be bolted to the rod end fitting <NUM> using one or more bolts <NUM> or other removable attachment features. The bolts <NUM> can be removed during routine maintenance to verify that the pawl engages the sector gear. The tilt actuator can then be driven to change the tilt of the rotor for some duration to confirm that the pawl engaged. The illustrated embodiment includes a torsion spring <NUM> in place of a tension spring and cable, which can provide a weight savings, decrease required volume, and increase ruggedness.

The foregoing description, for the purpose of explanation, has been described with reference to specific examples. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The examples were chosen and described in order to best explain the principles of the techniques and their practical applications. Others skilled in the art are thereby enabled to best utilize the techniques and various examples with various modifications as are suited to the particular use contemplated.

Claim 1:
A system for tilting a proprotor (<NUM>) of an aircraft (<NUM>) and simultaneously adjusting a pitch of blades of the proprotor, the system comprising:
a first frame (<NUM>) for mounting to the aircraft;
a second frame (<NUM>) for mounting the proprotor, wherein the second frame is rotatably mounted to the first frame at a rotation axis (<NUM>);
a first gear (<NUM>) located along the rotation axis and fixed in position relative to the first frame;
a pinion (<NUM>) that moves with the second frame and is engaged with the first gear such that the pinion can revolve around at least a portion of the first gear, wherein revolution of the pinion causes the pinion to rotate;
a cam (<NUM>) that is fixedly connected to the pinion such that the cam rotates with the pinion; and
a control rod (<NUM>) operatively coupled at a first end with the cam such that rotation of the cam can cause translation of the control rod, wherein the control rod can be coupled at a second end to the blades of the proprotor such that translation of the control rod alters the pitch of the blades.