Patent Description:
Unlike conventional aircraft, VTOL aircraft, like helicopters, do not need a runway. They can lift off and land vertically, which means they only need a landing/launch surface large enough to accommodate their airframe. Thus, VTOL aircraft are versatile because they can take off and land from much tighter spaces (and therefore from many more locations) than conventional fixed-wing aircraft. Helicopters, for example, land on, and take off from, building rooftops even in densely populated cities. Some VTOL aircraft use wings because, when cruising, wings are more efficient and lower-maintenance than rotors, thereby extending the range and speed of the aircraft, and enabling longer, faster flights. Helicopters and other wingless VTOL aircraft must utilize flaps or other flight control surfaces to point the rotors in the direction of motion. This is why helicopters initially tilt their noses downward when transitioning from hovering (vertical flight) to cruising (horizontal flight). Winged VTOL aircraft on the other hand, employ various methods for transitioning between hovering and cruising.

Some winged VTOL aircraft use tilting wings to transition between hovering and cruising (and are thus often referred to as "tilt-wing aircraft"). However, tilting an entire wing requires much more force than the smaller flight control surfaces (e.g., aileron, elevator, and rudder) of conventional fixed-wing aircraft. Further, such wings are highly susceptible to wind gusts when they are vertically oriented for hovering.

Thus, other VTOL aircraft attempt to transition between hovering and cruising by tilting just the rotors (not the entire wings), and are thus often referred to as "tilt-rotor aircraft. " In particular, some tilt-rotor aircraft comprise a forward set of rotors (positioned forward of the wings) and a rearward set of rotors (positioned behind the wings) that are all tilted simultaneously. A single tilt mechanism may be configured to tilt both a forward rotor and a rearward rotor. Thus, the forward and rearward rotors cannot be tilted independently of one another. However, tilting all of the rotors still requires substantial force, and such aircraft can become aerodynamically unstable when transitioning between hovering and cruising.

Further, both such designs (both tilt-wing and tilt-rotor designs) create the potential for single-point non-performance events because the aircraft may rely on a single tilting mechanism (either one mechanism that tilts the wings or one mechanism that tilts multiple rotors) to transition between hovering and cruising. Because VTOL must transition from cruising to hovering to land, the wing-tilting may be critical to the aircraft's ability to complete a flight. Thus, non-performance of just one of the tilt mechanisms mid-flight may not be tolerated in many of the above tilt designs.

Other winged VTOL aircraft attempt to overcome this problem by including two separate sets of fixed-position rotors, one dedicated for vertical flight, and another for horizontal flight. However, such aircraft require twice as many rotors (one set for vertical flying and a second set for horizontal flying), making the aircraft heavier (and thus less energy efficient) and more expensive.

Further, all of the winged VTOL aircraft described above (the fixed-rotor aircraft, the tilt-rotor aircraft, and the tilt-wing aircraft) suffer from aerodynamic difficulties when transitioning from hovering to cruising due to the interaction between the flow field generated by the hover mode, the incoming airflow, and the wing geometry. The transition maneuver presents the highest power demand on the aircraft and thus may require a larger, less efficient, and more costly aircraft. Therefore, a winged VTOL that more efficiently transitions between the hover and cruise modes is desired.

<CIT> in an abstract states that "A vertical takeoff and landing aircraft includes a pair of ducted lift/thrust fans that are rotatably movable between a first vertical lift position and a second horizontal thrust position. The lift/thrust fans are disposed within curvilinear fan recesses formed within leading edge portions of the aircraft's wings. A downwardly exhausting, ducted lift fan is disposed within the aircraft's fuselage, aft of the aircraft's pitch axis. A power plant, disposed within the fuselage, is coupled with the lift/thrust fans and the lift fan by a transmission system. The lift/thrust fans and lift fan are positioned with respect to one another to be triangulated about the aircraft's center of gravity and the aircraft's center of lift.

<CIT> in an abstract states that "An aircraft includes an airframe having a fixed-wing section and a plurality of articulated electric rotors, at least some of which are variable-position rotors having different operating configurations based on rotor position. A first operating configuration is a vertical-flight configuration in which the rotors generate primarily vertical thrust for vertical flight, and a second operating configuration is a horizontal-flight configuration in which the rotors generate primarily horizontal thrust for horizontal fixed-wing flight. Control circuitry independently controls rotor thrust and rotor orientation of the variable-position rotors to provide thrust-vectoring maneuvering. The fixed-wing section may employ removable wing panels so the aircraft can be deployed both in fixed-wing and rotorcraft configurations for different missions.

<CIT> in an abstract states that "A compound aircraft embodies an array of rotors for vertical flight positioned on support booms and wing elements for cruise flight coupled to a central fuselage housing avionics and a pusher propeller for forward propulsion. The aircraft accommodates a cargo-carrying container with mating of the surfaces between container and fuselage and latching mechanisms for attaching and detaching the container and vehicle. " <CIT> in an abstract states that "An energy efficient VTOL aircraft is capable of flying like helicopter as well as fixed wing airplane based on requirement. The propulsion for the aircraft is either all electric or hybrid/electric. The aircraft comprises vertical and tilting rotors. Each rotor system comprises a compact high power to weight ratio electric motor and an optimized propeller either for cruise or hover depending upon the function. The usage of electric motors for propulsion reduces the noise significantly as compared with traditional aircraft engines and is less complex to design and manufacture. The aircraft also covers a fully autonomous VTOL assist vehicle capable of assisting main aircraft vehicle in vertical take-off and hence reducing energy consumption for main aircraft during vertical take-off, landing and hover. The autonomous vehicle is configured for detaching itself from main vehicle once main vehicle transitions to forward flight to operate like a fixed wing airplane.

Winged VTOL aircraft and related methods are disclosed. Generally, in the figures, elements that are likely to be included in a given example are illustrated in solid lines, while elements that are optional to a given example are illustrated in dashed lines. Further, some elements illustrated in solid lines are illustrated in different positions using dash-dot lines. However, elements that are illustrated in solid lines are not essential to all examples of the present disclosure, and an element shown in solid lines may be omitted from a particular example without departing from the scope of the present disclosure.

<FIG> illustrate various examples of a winged VTOL aircraft in which only the forward rotor(s) (the one or more rotors positioned forward of the wings) tilt. Thus, the rotors positioned behind at least one of the forward set of wings do not tilt (are fixed) and may be oriented in a horizontal position for hovering, in some examples. However, because the forward rotors are configured to tilt, they may be used to help generate vertical thrust during hovering and horizontal thrust during cruising. That is, the rotors may be used to generate thrust during both cruising and hovering, and are not a parasitic loss during hovering like the fixed-position vertical rotors of aircraft having separate horizontal and vertical rotors. And, rather than tilting all of the rotors when transitioning between hovering and cruising (which may make the aircraft aerodynamically unstable and require substantial force), the winged VTOL aircraft illustrated in <FIG> only tilt one or more of the forward rotors, thereby lowering the tilting forces needed to transition between hovering and cruising, and increasing the stability of the aircraft during the transition. Put simply, the winged VTOL aircraft illustrated in <FIG> provide smoother and more effortless transitions between hovering and cruising than other winged VTOL.

And, as will be described in greater detail below, each of the forward rotors of the winged VTOL aircraft illustrated in <FIG> are configured to be independently tilted in some examples. Such a design increases redundancies in the tilt system, thereby reducing the chance that non-performance of one of the tilt mechanisms will negatively impact flight characteristics. Put simply, such a design increases the reliability and performance of the tilt system and the overall propulsion system, making for a safer aircraft.

Beginning with <FIG>, it schematically illustrates aircraft <NUM> comprising an airframe <NUM>, and a propulsion system <NUM> configured to propel the airframe <NUM>. The airframe <NUM> comprises a forward set of wings and an aft set of wings <NUM> and optionally comprises a fuselage <NUM> configured to carry one or more of cargo, crew, and passengers. The fuselage <NUM> optionally comprises a door <NUM> configured to selectively open to permit ingress and egress of one or more of the crew, passengers, and cargo. The propulsion system <NUM> comprises rotors <NUM>, and more specifically, comprises one or more tilt-adjustable rotors <NUM> positioned forward of the forward set of wings <NUM>.

Thus, the fixed-tilt rotors <NUM>, and the single row of the one or more tilt-adjustable rotors <NUM> positioned forward of the forward set of wings 20form a grid of rotors, in some examples. For example, the rotors <NUM> may be arranged in one or more of: a 3x4 configuration (<NUM> rows of four rotors), a 2x4 configuration, a 4x4 configuration, and a 2x6 configuration, although other grid configurations are possible.

As described above, the one or more tilt-adjustable rotors <NUM> are configured to be selectively tilted. In particular, an axis of rotation of the one or more tilt-adjustable rotors <NUM> is configured to be selectively tilted relative to a pitch of the aircraft <NUM>. Thus, in the description herein, "tilting the one or more tilt-adjustable rotors <NUM>" refers to tilting the axis of rotation of the one or more tilt-adjustable rotors <NUM> such that the direction in which the one or more tilt-adjustable rotors <NUM> generate thrust tilts relative to the pitch of the aircraft <NUM>.

Additionally, the one or more fixed-tilt rotors <NUM> are not configured to tilt relative to the pitch of the aircraft <NUM>. Thus, the one or more fixed-tilt rotors <NUM> may have a fixed tilt angle. In particular, the tilt angle may be defined as the angle between the axis of rotation (thrust vector) of the one or more fixed-tilt rotors <NUM> and a pitch of the aircraft <NUM>. In some examples, the one or more fixed-tilt rotors <NUM> are fixed in a horizontal position, such that their axis of rotation is substantially orthogonal to a pitch of the aircraft <NUM> (thus they may have a tilt angle of approximately <NUM> degrees), and are thus configured to provide vertical thrust (antiparallel to gravity) when the pitch of the aircraft is substantially parallel to level ground (orthogonal to gravity). Herein, the term "substantially" when used in connection with an orientation means within five angular degrees of the stated orientation. Thus, the pitch of the aircraft is substantially parallel to level ground when it is within five angular degrees of being parallel to level ground, or horizontal. In some such examples, the one or more tilt-adjustable rotors <NUM> are configured to be adjusted to the horizontal position to operate the aircraft <NUM> in a hover mode.

Providing such thrust in the vertical direction (e.g., operating in the hover mode) enables the aircraft <NUM> to take off and land vertically. As such, the aircraft <NUM> may be a VTOL aircraft, and thus may be referred to herein as "VTOL aircraft <NUM>. " Further, because the aircraft <NUM> comprises a forward and an aft set of wings <NUM>, the aircraft <NUM> may be referred to herein as "winged VTOL <NUM>. " Finally, because the one or more tilt-adjustable rotors <NUM> are configured to be tilted, the aircraft <NUM> may be referred to herein as "winged tilt-rotor VTOL aircraft <NUM>.

The one or more tilt-adjustable rotors <NUM> are configured to tilt relative to a pitch of the aircraft <NUM> (i.e., the tilt angle of the tilt-adjustable rotors <NUM> is adjustable). In particular, the one or more tilt-adjustable rotors <NUM> are configured to be selectively tilted between a first position <NUM> (illustrated in dash-dot lines in <FIG>) and a second position <NUM> (illustrated in solid lines in <FIG>). Pitch refers to the angle the nose (e.g., front <NUM>) of the aircraft <NUM> points relative to the horizon. <FIG> and <FIG>, which will be described in greater detail below, help visualize this pitch by showing a transverse axis <NUM> or pitch axis <NUM>, motion about which changes the pitch.

In one example, the first position <NUM> is a hover position in which the one or more tilt-adjustable rotors <NUM> are configured to provide a substantially (within five degrees antiparallel to gravity) vertical thrust (relative to gravity) and the second position <NUM> is a cruise position in which the one or more tilt-adjustable rotors <NUM> are configured to provide a substantially horizontal thrust (relative to gravity). Thus, the first position may be referred to as a forward-thrusting position, and/or a horizontal-thrusting position, and the second position may be referred to as a vertical-thrusting position.

As one such example, the first position <NUM> is a horizontal position in which the one or more tilt-adjustable rotors <NUM> are parallel to a pitch of the aircraft <NUM>, and an axis of rotation of the one or more tilt-adjustable rotors <NUM> is orthogonal to the pitch of the aircraft <NUM>. Additionally or alternatively, the second position <NUM> is a vertical position in which the one or more tilt-adjustable rotors <NUM> are orthogonal to the pitch of the aircraft <NUM>, and the axis of rotation of the one or more tilt-adjustable rotors is parallel to the pitch of the aircraft <NUM>. Thus, in such examples where the first position <NUM> is the horizontal position and the second position <NUM> is the vertical position, the one or more tilt-adjustable rotors <NUM> are configured to tilt approximately <NUM> degrees.

However, in other such examples, the first position <NUM> is different than the horizontal position and/or the second position <NUM> is different than the vertical position. For example, the first position <NUM> may be a position past the horizontal position, where the axis of rotation (and thus the direction of thrust) of the one or more tilt-adjustable rotors <NUM> points towards a rear <NUM> of the aircraft <NUM>. In another example, the first position <NUM> may be a position closer to the vertical position than the horizontal position, where the axis of rotation (and thus the direction of thrust) of the one or more tilt-adjustable rotors <NUM> points towards the front <NUM> of the aircraft <NUM>. In yet further examples, the one or more tilt-adjustable rotors <NUM> are configured to tilt more than or less than <NUM> degrees.

In some examples, the one or more tilt-adjustable rotors <NUM> are configured to be independently tilted - and thus in some such examples, differentially tilted. For example, and as described below in greater detail, the one or more tilt-adjustable rotors <NUM> are differentially tilted (e.g., tilted to different positions) to accomplish yaw control. In some examples, the independent selective tilting is accomplished via separate tilt mechanisms. As one such example, each of the one or more tilt-adjustable rotors <NUM> is coupled to its own tilt mechanism (e.g., tilt mechanism <NUM> described below with reference to <FIG>), and each tilt mechanism is independently electrically controlled by a controller <NUM>.

An increase in safety, reliability, and performance of the propulsion system <NUM> is achieved by providing such independent selective tilting of the one or more tilt-adjustable rotors <NUM>. In particular, because each of the one or more tilt-adjustable rotors <NUM> may comprise its own tilt mechanism, non-performance of one of the tilt mechanisms does not affect the ability of the other rotors (the rotors not coupled to the non-performing tilt mechanism) to tilt. In this way, the propulsion system <NUM> comprises added redundancy to ensure that non-performance of one of the tilt mechanisms does not compromise the ability to control and land the aircraft <NUM>.

In some examples, the one or more tilt-adjustable rotors <NUM> are variably adjustable and are configured to tilt to more positions that just the first position <NUM> and the second position <NUM>. In particular, the one or more tilt-adjustable rotors <NUM> are configured to tilt to one or more positions between the first position <NUM> and the second position <NUM> in some examples. As just one example, one or more of the one or more tilt-adjustable rotors <NUM> are configured to be selectively tilted between the first position <NUM> and the second position <NUM> to adjust a yaw of the aircraft <NUM>. In particular, tilting one of the one or more tilt-adjustable rotors <NUM> towards the first position <NUM> may cause the aircraft <NUM> to turn towards the side of the aircraft <NUM> on which that rotor (the one that was tilted towards the first position <NUM>) is located. For example, if one of the one or more tilt-adjustable rotors <NUM> that is positioned on the right side of the aircraft <NUM> is selectively tilted towards the first position <NUM> while the other rotors of the one or more tilt-adjustable rotors <NUM> remain in the second position <NUM>, the aircraft <NUM> may turn to the right (referred to as "positive yawing motion"), and vice versa for a rotor positioned on the left side of the aircraft <NUM>.

In this way, the one or more tilt-adjustable rotors <NUM> may be configured to serve the yaw adjustment functions traditionally performed by a rudder. More simply, the one or more tilt-adjustable rotors <NUM> may be configured to serve the role of a conventional rudder, and thus may replace the rudder. As such, the aircraft <NUM> does not include a rudder, in some examples. Thus, a reduction in the cost and complexity of the aircraft <NUM> is achieved in examples where the rudder is omitted. And, even in examples where a rudder is still included in the aircraft <NUM>, the ability of the tilt-adjustable rotors <NUM> to provide yaw control adds redundancy to the flight control system. Put simply, the tilt-adjustable rotors <NUM> may serve as a back-up to the rudder in the event of rudder non-performance. Thus, even in examples where a rudder is included in the aircraft <NUM>, an increase in the reliability, performance, and safety of the yaw control system is achieved by configuring the one or more tilt-adjustable rotors <NUM> to be variably adjusted to more positions than just the first position <NUM> and the second position <NUM>.

The one or more tilt-adjustable rotors <NUM> are positioned forward of the forward set of wings <NUM> relative to the front <NUM> and the rear <NUM> of the aircraft <NUM>. In the description herein, "forward" and "rearward" are used to refer to the relative positioning of components in relation to a horizontal direction of motion of the aircraft <NUM> when the one or more tilt-adjustable rotors <NUM> are tilted towards the second position <NUM>, such that they are generating at least some non-zero horizontal thrust with respect to gravity (e.g., at least a component of the thrust vector of the one or more tilt-adjustable rotors <NUM> is orthogonal to gravity). For example, when the one or more tilt-adjustable rotors <NUM> are tilted to the second position <NUM>, the tilt-adjustable rotors <NUM> generate thrust in a direction that is not antiparallel with respect to gravity, and thus cause the aircraft <NUM> to move to the left in the example of <FIG>.

Example axis system <NUM> shown in <FIG> and <FIG> further illustrates what is meant by "forward" and "rearward. " On axis system <NUM>, "forward" refers to a more positive position on longitudinal axis <NUM> (also referred to herein as "roll axis <NUM>"), and vice versa for "rearward. " Thus, the "front <NUM>" and the "rear <NUM>" of the aircraft <NUM> are used to refer to ends of the aircraft <NUM> in relation to the direction of horizontal motion of the aircraft <NUM>.

Similarly, "above" and "below" are used herein to describe the relative positioning of components in relation to a vertical direction of thrust generated by the one or more fixed-tilt rotors <NUM>. Example axis system <NUM> shown in <FIG> and <FIG> further illustrates what is meant by "above" and "below. " On axis system <NUM>, "above" refers to a more positive position on vertical axis <NUM> (also referred to herein as "yaw axis <NUM>"), and vice versa for "below. " Thus, the "top" and the "bottom" of components of the aircraft <NUM> are used to refer to ends of the components in relation to the direction of thrust generated by the one or more fixed-position rotors <NUM>.

In some examples, the entire rotor of each of the one or more tilt-adjustable rotors <NUM> is positioned forward of the forward set of wings <NUM>. In some such examples, the one or more tilt-adjustable rotors <NUM> are positioned forward of the forward set of wings <NUM> even in the first position <NUM>, such that no portion of the one or more tilt-adjustable rotors <NUM> overlaps (e.g., is positioned on top of) the forward set of wings <NUM>. That is, the one or more tilt-adjustable rotors <NUM> fully clear a front/leading edge of the forward set of wings <NUM>. However, in other examples, at least a portion of at least one of the one or more tilt-adjustable rotors <NUM> overlaps with (e.g., extends over the top of) at least one of the forward set of <NUM> when the at least one of the one or more tilt-adjustable rotors <NUM> is in the first position <NUM> and is spinning.

In some examples, the one or more tilt-adjustable rotors <NUM> comprise one or more inner rotors <NUM> and one or more outer rotors <NUM>. For example, as shown in <FIG>, the one or more tilt-adjustable rotors <NUM> optionally comprise four rotors, two inner rotors and two outer rotors. However, in other examples, the one or more tilt-adjustable rotors <NUM> comprise more or less than four rotors. As one such example, the one or more tilt-adjustable rotors <NUM> comprise two rotors, one on each side of the fuselage <NUM>. In yet another such example, the one or more tilt-adjustable rotors <NUM> comprise six rotors, three on each side of the fuselage <NUM>. In yet further such examples, the one or more tilt-adjustable rotors <NUM> comprise eight rotors, four on each side of the fuselage <NUM>.

When included, the one or more outer rotors <NUM> are positioned farther from a central longitudinal axis of the aircraft <NUM> than the one or more inner rotors <NUM>. Thus, when the fuselage <NUM> is included, the one or more outer rotors <NUM> are positioned farther from the fuselage <NUM> than the one or more inner rotors <NUM>. In some examples, the one or more inner rotors <NUM> and the one or more outer rotors <NUM> are staggered in front of, and behind, one another. As one such example, the one or more outer rotors <NUM> are positioned rearward of the one or more inner rotors <NUM>, closer to the rear <NUM> of the aircraft <NUM> than the one or more inner rotors <NUM>.

Staggering the rotors <NUM> may reduce a length of one or more support elements <NUM> configured to support the rotors <NUM>, while also keeping the rotors <NUM> clear of the one or more wings <NUM>. The one or more wings <NUM> may be tapered for structural efficiency.

The one or more fixed-tilt rotors <NUM> are positioned behind the one or more tilt-adjustable rotors <NUM>. In particular, the one or more fixed-tilt rotors <NUM> are positioned behind the forward set of wings <NUM> (closer to the rear <NUM> of the aircraft <NUM> than at least one of forward set of wings <NUM>). As described above, the one or more fixed-tilt rotors <NUM> do not tilt (their tilt angle is fixed). More specifically, they do not tilt relative to the pitch of the aircraft <NUM>. That is, the axis of rotation of the one or more fixed-tilt rotors <NUM> is not configured to be tilted relative to the pitch of the aircraft <NUM>.

As one example, the one or more fixed-tilt rotors <NUM> are fixed in the horizontal position where an axis of rotation of the one or more fixed-tilt rotors is orthogonal to the pitch of the aircraft <NUM>. In the horizontal position, the rotors <NUM> face up, in a direction antiparallel to gravity. Thus, when the aircraft is flying vertically upwards (against gravity) the one or more fixed-tilt rotors <NUM> face up, in the direction that they generate thrust (antiparallel to gravity). In some examples, the one or more fixed-tilt rotors <NUM> are fixed in the first position <NUM>, such that the one or more fixed-tilt rotors <NUM> are parallel to the one or more tilt-adjustable rotors <NUM> when the one or more tilt-adjustable rotors <NUM> are in the first position <NUM>.

In some examples, the one or more fixed-tilt rotors <NUM> comprise one or more forward fixed-tilt rotors <NUM> and one or more aft fixed-tilt rotors <NUM>. When included, the one or more forward fixed-tilt rotors <NUM> are positioned forward of the one or more aft fixed-tilt rotors <NUM>.

In some examples, and as shown in <FIG>, the one or more fixed-tilt rotors <NUM> are arranged in rows. In particular, the one or more fixed-tilt rotors <NUM> may be arranged in one or more rows behind the forward set of wings <NUM>. Although only two rows (the one or more forward fixed-tilt rotors <NUM> and the one or more aft fixed-tilt rotors <NUM>) are shown in <FIG>, the aircraft <NUM> comprises additional rows of the one or more fixed-tilt rotors <NUM> in other examples.

In some examples, such as the examples shown in <FIG> and <FIG>, the one or more fixed-tilt rotors <NUM> comprise eight rotors, four of the one or more forward fixed-tilt rotors <NUM>, and four of the one or more aft fixed-tilt rotors <NUM>. However, in other examples, the one or more fixed-tilt rotors <NUM> comprise more or less than eight rotors and/or more than two rows of rotors. In an example not falling under the scope of the claims, the one or more fixed-tilt rotors <NUM> comprise only four of the one or more forward fixed-tilt rotors <NUM> and none of the one or more aft fixed-tilt rotors <NUM> (only one row of rotors). In another example, the one or more fixed-tilt rotors <NUM> comprise twelve rotors, four of the one or more forward fixed-tilt rotors <NUM>, four of the one or more aft fixed-tilt rotors <NUM>, and an additional four rotors positioned behind the one or more aft fixed-tilt rotors <NUM>, forming another row of rotors (for a total of three rows of fixed-tilt rotors). In an example not falling under the scope of the claims, the one or more fixed-tilt rotors <NUM> comprise six of the one or more forward fixed-tilt rotors <NUM> and none of the one or more aft fixed-tilt rotors <NUM>.

In some examples, the aircraft <NUM> includes the same number of rotors in each row, including the front row comprising the one or more tilt-adjustable rotors <NUM>. Said another way, the one or more tilt-adjustable rotors <NUM> comprise the same number of rotors as the number of fixed-tilt rotors in a single row of the one or more fixed-tilt rotors <NUM>. Thus, in such examples, when only one row of the one or more fixed-tilt rotors <NUM> is included in the aircraft <NUM> (either the one or more forward fixed-tilt rotors <NUM> or the one or more aft fixed-tilt rotors <NUM>), the aircraft <NUM> includes the same number of the one or more tilt-adjustable rotors <NUM> as the one or more fixed-tilt rotors <NUM>. However, in other examples, the aircraft includes different numbers of rotors in each row of the rotors <NUM>.

The forward and aft set of wings <NUM> are fixed wings that do not tilt. Thus, when the fuselage <NUM> is included, the forward and aft set of wings <NUM> are fixedly coupled to the fuselage <NUM>, and as such, do not tilt relative to the fuselage <NUM>. In some examples, the forward and aft set of wings <NUM> are coupled to the fuselage <NUM> proximate a top of the fuselage <NUM> (relative to a direction of thrust generated by the one or more fixed-tilt rotors <NUM>). In particular, the forward and aft set of wings <NUM> are coupled to the fuselage <NUM> near the top of the fuselage <NUM> in such examples, to accommodate the door <NUM>, and to permit unobstructed access to the fuselage <NUM> via the door <NUM> for passengers, cargo, and crew. Thus, in some such examples, the door <NUM> is positioned below the forward and aft set of wings <NUM>. However, in other examples, the door <NUM> and the forward and aft set of wings <NUM> are coupled to the fuselage <NUM> at other relative locations. As one such example, the forward and aft set of wings <NUM> are coupled to the fuselage <NUM> in-between the top and the bottom of the fuselage <NUM> (e.g., near a middle of the fuselage <NUM>), and the door <NUM> is included next to (behind and/or in front of) the forward and aft set of wings <NUM>.

In some examples, the forward and aft set of wings <NUM> comprise a single pair of wings, one wing on the right side of the aircraft <NUM>, and one wing on the left side of the aircraft <NUM>. The wings <NUM> comprise a forward set of wings <NUM> and an aft set of wings <NUM>. In yet further examples, the wings <NUM> comprise additional sets of wings (i.e. more than two sets of wings). The aft set of wings <NUM> are positioned behind the forward set of wings <NUM>, more proximate the rear <NUM> of the aircraft <NUM>.

At least one of the fixed-tilt rotors <NUM> is positioned between the forward set of wings <NUM> and the aft set of wings <NUM>. For example, as shown in <FIG> and <FIG>, four of the one or more forward fixed-tilt rotors <NUM> are positioned between the forward set of wings <NUM> and the aft set of wings <NUM>. Additionally at least one of the fixed-tilt rotors <NUM> is positioned behind the aft set of wings <NUM>. For example, as shown in <FIG> and <FIG>, four of the one or more aft fixed-tilt rotors <NUM> are positioned behind the aft set of wings <NUM>.

In some examples, the door <NUM> is included between the forward set of wings <NUM> and the aft set of wings <NUM>. In other examples, at least a portion of the door <NUM> is included below the forward set of wings <NUM>, as schematically and optionally illustrated in the example of <FIG>.

In some examples, the aircraft <NUM> comprises a tail <NUM>. In some such examples, such as the examples shown in <FIG> and <FIG>, the tail <NUM> is not directly coupled to the fuselage <NUM>, and instead is spaced away from (e.g., behind) the fuselage <NUM>. In some such examples, the tail <NUM> is coupled to the fuselage <NUM> via one or more mechanical connections, such as via one or more support elements <NUM>.

However, in other examples, the aircraft <NUM> does not include the tail <NUM>. As explained above, because the one or more tilt-adjustable rotors <NUM> may be adjusted (e.g., tilted) to accomplish yaw control, the tail and concomitant rudder may be omitted from the aircraft <NUM>, in some examples. As such, a reduction in the cost, complexity, weight (and therefore fuel consumption) is achieved in examples where the tail <NUM> is omitted.

In some examples, at least one of the forward and aft set of wings <NUM> and/or the optional tail <NUM> includes one or more flight control surfaces <NUM>. When included, the one or more flight control surfaces <NUM> are configured to adjust the orientation (e.g., yaw, pitch, and/or roll) of the aircraft <NUM>. As one example, the one or more flight control surfaces <NUM> comprise ailerons configured to adjust the roll of the aircraft <NUM>. As another example, the one or more flight control surfaces <NUM> additionally or alternatively comprise a rudder configured to adjust the yaw of the aircraft <NUM>. In yet another example, the one or more flight control surfaces <NUM> additionally or alternatively comprise elevators configured to adjust the pitch of the aircraft <NUM>. In yet further examples, the forward and aft set of wings <NUM> additionally or alternatively comprise flaps configured to increase the lift of the forward and aft set of wings and/or spoilers configured to decrease the lift of the forward and aft set of wings <NUM>.

In some examples, the aircraft <NUM> comprises one or more support elements <NUM> configured to support at least one of the rotors <NUM>. In particular, the one or more support elements <NUM> are configured to secure the rotors <NUM> to the forward and aft set of wings <NUM>. Thus, when included, the one or more support elements are coupled to at least one of the forward and aft set of wings <NUM> and at least one of the rotors <NUM> to secure the at least one of the rotors <NUM> to the at least one of the forward and aft set of wings <NUM>.

The one or more support elements <NUM> comprise one or more of booms, spars, beams, or other mechanical support structures that are strong enough to support the weight of the rotors <NUM> and their associated actuators (e.g., motors, tilt mechanisms, etc.). Thus, in such examples, rather than coupling directly to the forward and aft set of wings <NUM>, the rotors <NUM> instead couple to the one or more support elements <NUM>, which in turn couple to the forward and aft set of wings <NUM>. In examples where the rotors <NUM> couple to the one or more support elements <NUM>, the one or more tilt-adjustable rotors <NUM> are configured to selectively tilt relative to the one or more support elements <NUM>. Further, the one or more fixed-tilt rotors <NUM> are fixed relative to the one or more support elements <NUM> and are not configured to tilt relative to the one or more support elements <NUM>.

In some examples, the one or more support elements <NUM> extend in a lengthwise direction along the aircraft <NUM>, substantially parallel to the longitudinal axis <NUM> and substantially orthogonal to the forward and aft set of wings <NUM>. That is, the one or more support elements <NUM> extend front-to-back relative to the aircraft <NUM>. Because of this lengthwise orientation, the one or more support elements <NUM> are only configured to support one of the rotors <NUM> in each row of the rotors <NUM>, in some such examples. Thus, in some such examples, the number of the one or more support elements <NUM> is equal to the number of rotors in each row of the rotors <NUM>. One such example is shown in <FIG> and <FIG>, in which the aircraft <NUM> comprises four of the rotors <NUM> in each row, and thus four of the one or more support elements <NUM>. Further, because the examples shown in <FIG> and <FIG> comprise three rows of rotors <NUM>, each of the one or more support elements <NUM> supports three of the rotors <NUM>: one of the one or more tilt-adjustable rotors <NUM>, one of the one or more forward fixed-tilt rotors <NUM>, and one of the one or more aft fixed-tilt rotors <NUM>.

In some examples, the one or more support elements <NUM> are cross-linked and/or otherwise interconnected to provide increased mechanical stability. In yet further examples, the one or more support elements <NUM> are forked to support more than one rotor in a given row of the rotors <NUM>. For example, one or more of the one or more support elements <NUM> comprises a two-prong forked front end that is configured to support two of the one or more tilt-adjustable rotors <NUM>.

In some examples, such as the examples shown in <FIG> and <FIG>, the one or more support elements <NUM> span the distance between the forward set of wings <NUM> and the aft set of wings <NUM>, and extend beyond the forward set of wings <NUM> and the aft set of wings <NUM> along the longitudinal axis <NUM> (i.e. along a length of the aircraft <NUM>). In particular, in some such examples, the one or more support elements <NUM> extend forward of the forward set of wings <NUM> and are coupled to the one or more tilt-adjustable rotors <NUM> in this most forward section, and extend aft of the aft set of wings <NUM> are coupled to the one or more aft fixed-tilt rotors <NUM> in this most aft section.

In some examples, the one or more support elements <NUM> are coupled to both the forward set of wings <NUM> and the aft set of wings <NUM>. However, in other examples, the one or more support elements <NUM> are only coupled to one of the forward set of wings <NUM> or the aft set of wings <NUM>. In some such examples, the one or more tilt-adjustable rotors <NUM> are coupled to a front end of the one or more support elements <NUM>, and the one or more fixed-tilt rotors <NUM> are coupled to the one or more support elements <NUM> behind at least one of the one or more wings <NUM>. In particular, when the one or more fixed-tilt rotors <NUM> comprise more than one row of rotors (as in the examples of <FIG> and <FIG>), the one or more forward fixed-tilt rotors <NUM> are coupled to the one or more support elements <NUM> between the forward set of wings <NUM> and the aft set of wings <NUM>, and the one or more aft fixed-tilt rotors <NUM> are coupled to the one or more support elements <NUM> behind the aft set of wings <NUM>.

In some examples, the one or more support elements <NUM> are spaced away from the fuselage <NUM>. That is, the one or more support elements <NUM> are separated from the fuselage <NUM> by a gap and do not directly physically contact the fuselage <NUM> in such examples.

In some examples, the one or more support elements <NUM> comprise one or more inner support elements <NUM> and one or more outer support elements <NUM>. When included, the one or more inner support elements <NUM> are positioned more proximate the fuselage <NUM> than the one or more outer support elements <NUM>. As just one such example, such as the examples shown in <FIG> and <FIG>, the one or more support elements <NUM> comprise two of the one or more inner support elements <NUM> (one on each side of fuselage <NUM>) and two of the one or more outer supports elements <NUM> (one on each side of the fuselage <NUM>). However, in other examples, the aircraft <NUM> includes different numbers of the one or more inner support elements <NUM> and the one or more outer support elements <NUM>.

In some examples, at least one of the one or more support elements <NUM> couples to the tail <NUM> to provide mechanical support to the tail <NUM>. In one such example, such as the examples shown in <FIG> and <FIG>, the one or more inner support elements <NUM> couple to the tail <NUM> to at least partially hold and support the tail <NUM> (e.g., to couple the tail <NUM> to the fuselage <NUM>). Thus, the tail <NUM> is at least partially coupled to the fuselage <NUM> via the one or more support elements <NUM>.

The support elements <NUM> provide increased rigidness to the airframe <NUM> because they are tied to both the wings <NUM> and the rotors <NUM>. That is, the support elements <NUM> provide mechanical support to both the wings <NUM> and the rotors <NUM>. In examples where both the forward set of wings <NUM> and the aft set of wings <NUM> are included, the support elements <NUM> provide increased rigidness to the airframe <NUM> by coupling to both the forward set of wings <NUM> and the aft set of wings <NUM>.

In some examples, the aircraft <NUM> additionally comprises one or more power sources <NUM> that are configured to supply electrical power to various actuators of the aircraft <NUM>, such as the electric motors that spin the rotors <NUM> to generate thrust. Thus, the one or more power sources <NUM> may be referred to herein as "rotor power sources <NUM>. " Additionally or alternatively, the one or more power sources <NUM> are configured to supply electrical power to the tilt mechanisms that tilt the one or more tilt-adjustable rotors <NUM> and/or the flight control actuators that adjust the one or more flight control surfaces <NUM>. In some examples, the power sources <NUM> comprise batteries, such as rechargeable (e.g., lithium ion) batteries. In some such examples where the power sources <NUM> only comprise batteries, the aircraft <NUM> is a fully electric aircraft. However, in other examples, the power sources <NUM> additionally comprise liquid fuel (e.g., petroleum-based jet fuel). In such examples, the aircraft <NUM> is a hybrid electric aircraft <NUM> that is powered by both electric batteries and fuel.

In some examples, the one or more power sources <NUM> are positioned exterior to the forward and aft set of wings <NUM> and/or the fuselage <NUM>, and are coupled to the one or more wings <NUM>, in some examples. Specifically, in some such examples, the one or more power sources <NUM> are coupled to the one or more support elements <NUM>, which as described above, are in turn coupled to the forward and aft set of wings <NUM>. In some such examples, the one or more power sources <NUM> are coupled to a bottom of the one or more support elements <NUM>, beneath (with respect to the direction of thrust of the one or more fixed-tilt rotors <NUM>) the one or more support elements <NUM> and the forward and aft set of wings <NUM>, and/or within the support elements <NUM>. In some such examples, the one or more power sources <NUM> are additionally or alternatively only coupled to the one or more inner support elements <NUM>, and not to the one or more outer support elements <NUM>, as shown in the examples of <FIG> and <FIG>. However, in other examples, the one or more power sources <NUM> are coupled to all of the one or more support elements <NUM>.

In some examples, the one or more power sources <NUM> are only coupled to the forward and aft set of wings <NUM> and are not directly coupled to, or included within, the fuselage <NUM>. Thus, in such examples, the one or more power sources <NUM> are positioned away from the fuselage <NUM> and are only coupled to the fuselage <NUM> indirectly via the coupling to the one or more wings <NUM>. However, in other examples, the one or more power sources <NUM> are included exterior to the fuselage <NUM> (e.g., coupled to the forward and aft set of wings <NUM> away from the fuselage <NUM>) and interior to the fuselage <NUM>.

By including at least one of the one or more power sources <NUM> exterior to the fuselage <NUM> (and in particular beneath the forward and aft set of wings <NUM> and/or the one or more support elements <NUM>) an increase in cooling efficiency and accessibility of the one or more power sources <NUM> is achieved. In particular, by positioning the one or more power sources <NUM> exterior to the fuselage <NUM> and below the forward and aft set of wings <NUM>, the one or more power sources <NUM> are more exposed to ambient air, and thus are cooled to a greater degree by the ambient air than power sources included within the fuselage. In some examples, the ambient air itself is sufficient to provide a desired level of cooling for the one or more power sources <NUM>, thus eliminating the need for cooling fans or other active cooling mechanisms. Thus, the cost and complexity of the aircraft <NUM> is reduced by positioning the one or more power sources <NUM> exterior to the fuselage <NUM>.

Further, by positioning the one or more power sources <NUM> below the forward and aft set of wings <NUM>, and specifically below the one or more support elements <NUM>, the one or more power sources <NUM> are more accessible to ground personnel. Thus, ground personnel may more easily and quickly replace, re-charge, and/or re-fuel the one or more power sources <NUM> as compared to other aircraft that include the batteries inside the fuselage <NUM>.

In still further examples, the one or more power sources <NUM> are configured to be selectively repositioned forward and aft (along the longitudinal axis <NUM>). In particular, the one or more power sources <NUM> are configured to be selectively repositioned forward and aft relative to the one or more support elements <NUM> and/or the forward and aft set of wings <NUM>. In some examples, the one or more power sources <NUM> are selectively repositioned forward or aft to adjust a center of gravity of the aircraft <NUM>.

To perform the repositioning, the aircraft <NUM> comprises one or more power source repositioning actuators (e.g., mechanical, hydraulic, pneumatic, and/or electronic actuators), in some examples, that are controlled either manually (directly by a user) or electronically (by a controller) to reposition the one or more power sources <NUM>. In yet further examples, the aircraft <NUM> does not comprise any repositioning actuators for the one or more power sources <NUM>, and the one or more power sources <NUM> are instead repositioned by hand by a user without the aid of any actuators. In some examples, the repositioning is performed responsive to user input. However, in other examples, the repositioning is performed autonomously according to one or more control schemes (e.g., a feedback loop). As one such example, a controller may adjust the position of the one or more power sources <NUM> based on one or more of takeoff weight, aircraft center of gravity, fuel consumption, passenger distribution, etc..

Thus, the aerodynamic stability of the aircraft <NUM> is increased by including repositionable power sources. That is, by configuring the one or more power sources to be selectively repositioned forward or aft, the aircraft may be more effectively balanced than other aircraft comprising fixed-position power sources, thus ensuring a safer, smoother ride.

In some examples, the aircraft <NUM> additionally comprises a controller <NUM> that is programmed to control various actuators of the aircraft <NUM> (e.g., the electric motors that power the rotors <NUM>, the tilt mechanisms that tilt the one or more tilt-adjustable rotors <NUM>, the actuators that adjust the one or more flight control surfaces <NUM>, the actuators that re-position the one or more power sources <NUM>, etc.). When included, the controller <NUM> includes a memory unit <NUM> and a processing unit <NUM>. The memory unit <NUM> stores computer-readable instructions (the software) and the processing unit <NUM> executes the stored computer-readable instructions to perform the various computing functions responsive to various inputs, such as to selectively tilt the one or more tilt-adjustable rotors <NUM> responsive to a desired change between hovering and cruising.

When included, the memory unit <NUM> comprises non-volatile (also referred to herein as "non-transitory") memory <NUM> (e.g., ROM, PROM, and EPROM) and/or volatile (also referred to herein as "transitory") memory <NUM> (e.g., RAM, SRAM, and DRAM), in some examples. The processing unit <NUM> comprises integrated circuits including one or more of field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), digital signal processors (DSPs), microprocessors, microcontrollers, programmable array logic (PALs), and complex programmable logic devices (CPLDs).

As will be described in greater detail below, the controller <NUM> is programmed to execute various methods, such as methods schematically represented in <FIG>. In particular, the controller <NUM> is programmed to one or more of: selectively tilt the one or more tilt-adjustable rotors <NUM>, selectively adjust the thrust generated by one or more of the rotors <NUM>, and selectively reposition the one or more power sources <NUM>.

<FIG> schematically shows the controller <NUM> included in an example electrical system <NUM> of the aircraft <NUM>. In particular, <FIG> shows an example of how the one or more power sources <NUM> and the controller <NUM> are electrically coupled to some of the various actuators (e.g., the tilt mechanisms of the rotors <NUM>) of the aircraft <NUM> to control operation of the actuators.

As schematically illustrated in <FIG>, electrical system <NUM> is an example of an electrical system that may be included in the aircraft <NUM>. Electrical connections between components are shown in dashed lines, and mechanical connections between components are shown in solid lines. Electrical system <NUM> comprises the one or more power sources <NUM>, the controller <NUM>, and the various actuators that are controlled by the controller <NUM>. In the example of <FIG>, only a tilt mechanism <NUM> configured to tilt the one or more tilt-adjustable rotors <NUM>, a motor <NUM> configured to power (e.g., spin) the rotors <NUM> to generate thrust, and a re-positioning mechanism <NUM> configured to re-position the one or more power sources <NUM>, are shown. However, the electrical system <NUM> comprises additional actuators (e.g., actuators for adjusting the one or more flight control surfaces <NUM>), in other examples.

The tilt mechanism <NUM> is configured to selectively tilt at least one of the one or more tilt-adjustable rotors <NUM>. As described above, the electrical system <NUM> comprises multiple tilt mechanisms in some examples. For example, the electrical system <NUM> comprises one tilt mechanism <NUM> for each of the one or more tilt-adjustable rotors <NUM>, such that each of the one or more tilt-adjustable rotors <NUM> has its own dedicated tilt mechanism <NUM>. Thus, the tilt mechanism <NUM> is configured to tilt at least one of the one or more tilt-adjustable rotors <NUM> between the first position <NUM> and the second position <NUM> responsive to command signals received from the controller <NUM>. The tilt mechanism <NUM> comprises one or more of an electromechanical, pneumatic, and hydraulic tilt actuator that is configured to be electronically controlled by the controller <NUM>. As examples, the tilt mechanism <NUM> may comprise one or more of a ring-and-pinion, piston-and-bell crank, ball-screw, harmonic drive, multi-link geometry and/or harmonic drive gearbox.

As shown in <FIG>, in some examples, the tilt mechanism <NUM> is configured to tilt both the motor <NUM> and one of the one or more tilt-adjustable rotors <NUM>. That is, both the motor <NUM> and the one of the one or more tilt-adjustable rotors <NUM>, which the motor <NUM> is configured to spin, are tilted together. However, in other examples, as is shown by the dash-dot line in <FIG>, the tilt mechanism <NUM> is configured to only tilt the one of the one or more tilt-adjustable rotors <NUM> and is not configured to tilt the motor <NUM>.

The motor <NUM> is configured to selectively spin (e.g., power) at least one of the rotors <NUM> about the axis of rotation (R-R) to generate thrust. As described above, the electrical system <NUM> comprises multiple motors in some examples. For example, the electrical system <NUM> comprises one motor <NUM> for each of the rotors <NUM>, such that each of the rotors <NUM> has its own dedicated motor <NUM>. However, in other examples, a single motor <NUM> is configured to power more than one of the rotors <NUM>.

The re-positioning mechanism <NUM> is configured to selectively re-position the one or more power sources <NUM> to adjust a center of gravity of the aircraft <NUM>. The re-positioning mechanism <NUM> comprises a linear actuator, or other actuator configured to move the one or more power sources <NUM> back and forth along a single axis (e.g., longitudinal axis <NUM>), in some examples. The re-positioning mechanism <NUM> comprises one or more of an electromechanical, pneumatic, and/or hydraulic linear actuator that is configured to be electronically controlled by the controller <NUM>. As one example, the re-positioning mechanism <NUM> comprises a ball-screw. As another example, the re-positioning mechanism <NUM> comprises a loop and pulley system.

The controller <NUM> is in electrical communication (e.g., wired and/or wireless communication) with the one or more power sources <NUM>, the tilt mechanism <NUM>, the motor <NUM>, and the re-positioning mechanism <NUM>. Electrical connections between components are shown in dashed lines in <FIG>. The controller <NUM> receives electrical power from the one or more power sources <NUM>, and distributes the electrical power provided by the one or more power sources <NUM> to the tilt mechanism <NUM>, the motor <NUM>, and the re-positioning mechanism <NUM> according to a control scheme. In particular, the method described below in <FIG>, describes an example control scheme that may be utilized by the controller <NUM> to regulate the amount of electrical power supplied to one or more of the tilt mechanism <NUM>, the motor <NUM>, and the re-positioning mechanism <NUM>.

More generally, the controller <NUM> sends command signals (e.g., digital signals) to one or more of the tilt mechanism <NUM>, the motor <NUM>, and the re-positioning mechanism <NUM> to adjust operation thereof. As described above, the controller <NUM> is programmed to perform various actions (e.g., control the actuators described above) based on received input. In particular, the controller <NUM> includes computer-readable instructions stored in non-transitory memory <NUM>, wherein the computer-readable instructions comprise instructions for controlling one or more of the tilt mechanism <NUM>, the motor <NUM>, and the repositioning mechanism <NUM> based on received input. The processing unit <NUM> is configured to execute the stored computer-readable instructions to control operation of one or more of the tilt mechanism <NUM>, the motor <NUM>, and the re-positioning mechanism <NUM>.

<FIG> and <FIG> show an illustrative, non-exclusive example of the aircraft <NUM>. Where appropriate, the reference numerals from the schematic illustrations of <FIG> and <FIG> are used to designate corresponding parts of the examples of <FIG> and <FIG>; however, the example of aircraft <NUM> of <FIG> and <FIG> is non-exclusive and does not limit the aircraft <NUM> to the illustrated example of <FIG> and <FIG>. That is, the aircraft <NUM> is not limited to the specific example of <FIG> and <FIG>, and the aircraft <NUM> may incorporate any number of the various examples, configurations, characteristics, properties, etc. of the aircraft <NUM> that are illustrated in and discussed with reference to the schematic representations of <FIG> and <FIG> and/or the example of <FIG> and <FIG>, as well as variations thereof, without requiring the inclusion of all such examples, configurations, characteristics, properties, etc. For the purpose of brevity, each previously discussed component, part, portion, example, region, etc. or variants thereof may not be discussed, illustrated, and/or labeled again with respect to the example of <FIG> and <FIG>; however, it is within the scope of the present disclosure that the previously discussed features, variants, etc. may be utilized with the examples of <FIG> and <FIG>.

<FIG> and <FIG> show isometric side views of aircraft that are examples of aircraft <NUM> in different flying configurations. Specifically, <FIG> shows an example aircraft <NUM> in an example hover mode <NUM> configured for vertical flight, and <FIG> shows the example aircraft <NUM> in an example cruise mode <NUM> configured for horizontal flight. The <FIG> and <FIG> illustrate examples of how the rotors <NUM> are operated in the two modes, and specifically how the one or more tilt-adjustable rotors <NUM> are tilted differently in the two modes.

As shown in <FIG>, example aircraft <NUM> is an example of aircraft <NUM> in an example hover mode <NUM>. In the example hover mode <NUM> shown in <FIG>, the one or more tilt-adjustable rotors <NUM> are tilted to the first position <NUM> to generate thrust in a vertical direction. Further, in the example of <FIG>, the first position <NUM> is the horizontal position in which an axis of rotation (R-R) of the one or more tilt-adjustable rotors <NUM> is orthogonal to the pitch of the example aircraft <NUM>. The one or more fixed-tilt rotors <NUM> are also positioned such that their axis of rotation is orthogonal to the pitch of the example aircraft <NUM>. Thus, all of the rotors <NUM> are parallel in <FIG>.

Because the example aircraft <NUM> has a pitch of approximately zero (the longitudinal axis of the example aircraft <NUM> is substantially parallel to the longitudinal axis <NUM>) in <FIG> and <FIG>, the axis of rotation (R-R) of the one or more tilt-adjustable rotors <NUM> is orthogonal to longitudinal axis <NUM> and parallel to vertical axis <NUM> (and thus parallel to gravity). As mentioned above, the pitch of aircraft refers to the angle between the aircraft's longitudinal axis (e.g., front <NUM> of the example aircraft <NUM>) and the longitudinal axis <NUM>. Thus, changes in pitch refer to rotation of the aircraft <NUM> about the transverse axis <NUM>, relative to the longitudinal axis <NUM>.

Axis system <NUM> is shown in <FIG> and <FIG> for reference. The three axes are orthogonal to one another. The vertical axis <NUM> is antiparallel to gravity, and the transverse axis <NUM> and the longitudinal axis <NUM> define a plane (e.g., the horizon) that is orthogonal to gravity and parallel to level ground. Rotation about the transverse axis <NUM> is referred to as pitch, and rotation about the longitudinal axis is referred to as roll. Rotation about the vertical axis <NUM> is referred to as yaw. In <FIG> and <FIG>, the aircraft <NUM> is substantially parallel to the horizon and thus has approximately zero pitch and zero roll.

In the example hover mode <NUM> shown in <FIG>, all of the rotors <NUM> are powered on to generate thrust. Because the rotors <NUM> are all oriented with their axis of rotation parallel to gravity, and because the rotors <NUM> face up (antiparallel to gravity), the rotors <NUM> generate thrust in a positive vertical direction, antiparallel to gravity. Thus, in the example hover mode <NUM> of <FIG>, the example aircraft <NUM> is configured for vertical flight, and a speed of the example aircraft <NUM> in the vertical direction is controlled by adjusting the speed (and thus the amount of thrust produced by) the rotors <NUM>.

In the examples of <FIG> and <FIG>, the aircraft <NUM> optionally comprises three rows of four rotors. Thus, the example aircraft <NUM> comprises four of the one or more tilt-adjustable rotors <NUM>, four of the one or more forward fixed-tilt rotors <NUM> and four of the one or more aft fixed-tilt rotors <NUM>. Further, the example aircraft <NUM> comprises one or more wheels <NUM> configured to support the example aircraft <NUM> on the ground. The fuselage <NUM> also comprises a cockpit windshield <NUM> configured to provide the crew with a view of the outside environment, in some examples.

As seen in <FIG>, example aircraft <NUM> is shown in an example cruise mode <NUM>. In the example cruise mode <NUM> shown in <FIG>, the one or more tilt-adjustable rotors <NUM> are tilted to the second position <NUM> to generate thrust in a horizontal direction. In the example of <FIG>, the second position <NUM> is the vertical position in which the axis of rotation (R-R) of the one or more tilt-adjustable rotors <NUM> is parallel to the pitch of the example aircraft <NUM>. The one or more fixed-tilt rotors <NUM> remain in the fixed position of <FIG>, such that their axis of rotation is orthogonal to the pitch of the example aircraft <NUM> in the cruise mode <NUM>. Thus, the axis of rotation of the one or more tilt-adjustable rotors <NUM> is orthogonal to the axis of rotation of the one or more fixed-tilt rotors <NUM> in <FIG>.

Because the example aircraft <NUM> has a pitch of approximately zero (the longitudinal axis of the example aircraft <NUM> is substantially parallel to the longitudinal axis <NUM>) in <FIG> and <FIG>, the axis of rotation (R-R) of the one or more tilt-adjustable rotors <NUM> is parallel to longitudinal axis <NUM> and orthogonal to vertical axis <NUM> (and thus orthogonal to gravity). Further, in the example cruise mode <NUM> shown in <FIG>, only the one or more tilt-adjustable rotors <NUM> are powered on to generate thrust. The one or more fixed-tilt rotors <NUM> are powered off.

Thus, because the one or more tilt-adjustable rotors <NUM> are oriented with their axis of rotation orthogonal to gravity, and because the one or more tilt-adjustable rotors <NUM> face forward, the one or more tilt-adjustable rotors <NUM> generate thrust in a forward direction (positive longitudinal direction). Thus, in the example cruise mode <NUM> of <FIG>, the example aircraft <NUM> is configured for horizontal flight, and a speed of the example aircraft <NUM> in the horizontal direction is controlled by adjusting the speed (and thus the amount of thrust produced by) the one or more tilt-adjustable rotors <NUM>.

<FIG> schematically provides a flowchart that represents illustrative, non-exclusive examples of methods according to the present disclosure. In <FIG>, some steps are illustrated in dashed boxes indicating that such steps may be optional or may correspond to an optional version of a method according to the present disclosure. That said, not all methods according to the present disclosure are required to include the steps illustrated in solid boxes. The methods and steps illustrated in <FIG> are not limiting and other methods and steps are within the scope of the present disclosure, including methods having greater than or fewer than the number of steps illustrated, as understood from the discussions herein.

In some examples, controller <NUM>, described above, is programmed to perform one or more of the methods and steps illustrated in <FIG>. In particular, instructions for performing the various steps and/or methods described in <FIG> are stored as computer-readable instructions in the non-transitory memory <NUM> of the controller <NUM>. The processing unit <NUM> of the controller <NUM> is configured to execute the computer-readable instructions to perform the one or more steps and methods described in <FIG>.

As seen in <FIG>, a method <NUM> includes operating in a hover mode at <NUM>, operating in a cruise mode at <NUM>, and transitioning between the hover mode and the cruise mode at <NUM>. Methods <NUM> may be described as methods of operation an aircraft, methods of enhancing operation of an aircraft, and/or methods of improving operation of an aircraft.

In one example, a VTOL aircraft (e.g., aircraft <NUM>) operates in the hover mode during take-off and landing. Thus, in the hover mode, the VTOL aircraft is configured to fly vertically, not horizontally. As such, the operating in the hover mode at <NUM> optionally comprises one or more of: tilting one or more tilt-adjustable rotors (e.g., one or more tilt-adjustable rotors <NUM>) to the horizontal position at <NUM>, powering on all rotors (e.g., rotors <NUM>) at <NUM>, and providing thrust in only a vertical direction (antiparallel to gravity) at <NUM>. As explained above, the horizontal position is a position where the axis of rotation of the rotors is antiparallel to gravity. However, in other examples, the rotors are adjusted to a position that is at an angle with respect to gravity and thus lift is generated in both vertical and horizontal directions (not antiparallel to gravity).

The operating in the hover mode at <NUM> may be conducted responsive to user inputs via a user input mechanism (e.g., joystick, throttle, touchscreen, button, etc.) and/or may be automated (e.g., cruise control) responsive to a start-up sequence which may be activated by a user (e.g., pressing of a start button).

However, in some examples, not all of the rotors are powered on while operating in the hover mode at <NUM>. In some such examples, only some of the rotors are powered on to conserve energy and/or reduce vertical speed of the aircraft. As one such example, at least one of the one or more tilt-adjustable rotors is powered off in the hover mode.

In other examples, the operating in the hover mode at <NUM> additionally comprises adjusting the amount of vertical thrust generated by the rotors by adjusting an amount of power supplied to the motors (e.g., motor <NUM>) of the rotors. In particular, the power supplied to the rotors may be adjusted to adjust the vertical speed of the aircraft. In other examples, the operating in the hover mode at <NUM> comprises providing maximum power to all of the rotors and/or providing maximum power to all of the one or more fixed-position rotors.

In further examples, the operating in the hover mode at <NUM> additionally or alternatively comprises repositioning one or more power sources (e.g., one or more power sources <NUM>) at <NUM> to adjust a center of gravity of the aircraft. In particular, the one or more power sources may be repositioned before takeoff to adjust the center of gravity of the aircraft. However, in other examples, the repositioning is performed mid-flight, after takeoff. In some examples, the repositioning comprises moving the one or more power sources forward or aft (longitudinally) relative to one or more of: one or more wings (e.g., one or more wings <NUM>), one or more support elements (e.g., one or more support elements <NUM>), and a fuselage (e.g., fuselage <NUM>). A technical effect of increasing the stability and energy efficiency of the aircraft is achieved by adjusting the center of gravity of the aircraft via the repositioning of the power sources.

In one example, a VTOL aircraft (e.g., aircraft <NUM> described in <FIG>) operates in the cruise mode when flying horizontally (not during take-off and landing). As such, the operating in the cruise mode at <NUM> optionally comprises one or more of: tilting the one or more tilt-adjustable rotors to the vertical position at <NUM>, cutting off power to one or more fixed-tilt rotors (e.g., one or more fixed-tilt rotors <NUM>) at <NUM>, and providing thrust in only a horizontal direction (orthogonal to gravity) at <NUM>. As explained above, the vertical position is a position in which the axis of rotation of the tilt-adjustable rotors is orthogonal to gravity and parallel to the horizon. However, in other examples, the operating in the cruise mode at <NUM> comprises adjusting the tilt-adjustable rotors to a position that is at a slight angle with respect to the horizon (not orthogonal to gravity). In this way, thrust is provided in both horizontal and vertical directions during the cruise mode, in some examples.

Further, the cutting off power to the one or more fixed-tilt rotors at <NUM> comprises stopping the flow of electrical power to the motors that power/spin the one or more fixed-tilt rotors, in some examples. Thus, the one or more fixed-tilt rotors stop spinning and come to rest during the cruise mode in examples where power is cut off to the fixed-tilt rotors. However, in other examples, only some of the one or more fixed-tilt rotors are powered off when operating in the cruise mode at <NUM>. In still further examples, the power supplied to the one or more fixed-tilt rotors is reduced, but is not completely cut off when operating in the cruise mode <NUM>. Thus, the thrust generated by the one or more fixed-tilt rotors is reduced in the cruise mode, and in some examples, the one or more fixed-tilt rotors are powered off so that they do not generate any thrust. However, in other examples, at least one of the one or more fixed-tilt rotors is powered on during to the cruise mode to generate lift in the vertical direction.

In some examples, the operating in the cruise mode at <NUM> additionally or alternatively comprises differentially tilting at least one of the tilt-adjustable rotors to adjust the yaw of the aircraft at <NUM>. In particular, by independently selectively tilting at least one of the tilt-adjustable rotors on only one side of the aircraft away from the vertical position towards the horizontal position, the yaw of the aircraft is adjusted.

The operating in the cruise mode at <NUM> may be conducted responsive to user inputs via a user input mechanism (e.g., joystick, throttle, touchscreen, button, etc.) and/or may be automated (e.g., cruise control) responsive to reaching one or more threshold parameters (e.g., threshold altitude) and/or responsive to a cruise sequence activated by a user (e.g., user pressing of a cruise button).

The transitioning between the hover mode and the cruise mode at <NUM> comprises tilting the one or more tilt-adjustable rotors and/or adjusting the thrust of the one or more fixed-tilt rotors at <NUM>. As described above, the one or more tilt-adjustable rotors are positioned forward of the forward set of wings and the fixed-tilt rotors are positioned behind the forward set of wings. Thus, in such examples, the tilting the one or more tilt-adjustable rotors comprises tilting only the rotors positioned forward of the one or more wings and maintaining a fixed tilt angle of (i.e., not tilting) the fixed-tilt rotors positioned behind the one or more wings.

By tilting only the one or more tilt-adjustable rotors, a technical effect of reducing the total force required to tilt the one or more tilt-adjustable rotors is achieved relative to systems that tilt all of the rotors. Thus, tilting only the one or more tilt-adjustable rotors enables more facile, effortless transitions between the hover and cruise modes that reduces energy consumption.

In some examples, all of the one or more tilt-adjustable rotors are tilted simultaneously and/or to the same degree when transitioning between the hover mode and the cruise mode at <NUM>. In some such examples, the one or more tilt-adjustable rotors are tilted at substantially the same rate. However, in other examples, the one or more tilt-adjustable rotors are tilted at different rates. In still further examples, the one or more tilt-adjustable rotors are tilted at different times and/or to different degrees when transitioning between the cruise mode and the hover mode at <NUM>. That is, the one or more tilt-adjustable rotors are differentially tilted when transitioning between the hover mode and the cruise mode at <NUM>.

In some examples, the rate at which the one or more tilt-adjustable rotors are tilted is adjusted based on one or more aircraft operating conditions (e.g., wind speed, aircraft velocity, and/or aircraft acceleration). Further, in examples, where the one or more tilt-adjustable rotors are not tilted simultaneously when transitioning between the two modes, the sequencing of the tilting of different rotors (i.e. the delay between the tilting of different rotors) may be adjusted based on one or more aircraft operating conditions (e.g., aircraft pitch, aircraft altitude, wing speed, wind direction, etc.). That is, in some such examples, one or more of: some of the one or more tilt-adjustable rotors are tilted before others, some of the one or more tilt-adjustable rotors are only partially tilted while other tilt-adjustable rotors are fully tilted to the other orthogonal position, etc..

The transitioning between the hover mode and the cruise mode optionally comprises one or more of transitioning to the cruise mode at <NUM>, and transitioning to the hover mode at <NUM>. The transitioning to the cruise mode at <NUM> comprises tilting the one or more tilt-adjustable rotors towards the vertical position (i.e. away from the horizontal position). Thus, the method <NUM> at <NUM> comprises tilting the axis of rotation of the one or more tilt-adjustable rotors towards the pitch of the aircraft, away from the axis of rotation of thefixed-tilt rotors. Conversely, when transitioning to the hover mode at <NUM>, the method <NUM> comprises tilting the one or more tilt-adjustable rotors towards the horizontal position (i.e. away from the vertical position). Thus, the method <NUM> at <NUM> comprises tilting the axis of rotation of the one or more tilt-adjustable rotors towards the axis of rotation of the fixed-tilt rotors and away from the pitch of the aircraft.

The transitioning to the cruise mode at <NUM> optionally comprises reducing power supplied to the fixed-tilt rotors at <NUM>. The reducing the power supplied to the one or more fixed-tilt rotors at <NUM> comprises reducing electrical power to the motors of the fixed-tilt rotors to reduce the speed of the fixed-tilt rotors, and thus reduce an amount of thrust generated by the one or more fixed-tilt rotors. In some examples, power to the fixed-tilt rotors is evenly reduced However, in other examples, the power is differentially reduced, such that some of the fixed-tilt rotors are supplied with less power, and/or the power is reduced more quickly, than other rotors. Further, in some examples, the rate at which the power is reduced and/or the amount that the power is reduced may be adjusted based on aircraft operating conditions.

Conversely, the transitioning to the hover mode at <NUM> optionally comprises increasing power supplied to the fixed-tilt rotors at <NUM>. The increasing the power supplied to the one or more fixed-tilt rotors at <NUM> comprises increasing electrical power to the motors of the fixed-tilt rotors to increase the speed of the fixed-tilt rotors, and thus increase an amount of thrust generated by the fixed-tilt rotors. In some examples, power to the fixed-tilt rotors is evenly increased. However, in other examples, the power is differentially increased, such that some rotors are supplied with more power, and/or the power is increased more quickly, than other rotors. Further, in some examples, the rate at which the power is increased and/or the amount that the power is increased may be adjusted based on aircraft operating conditions.

In some examples, the power supplied to the fixed-tilt rotors is maintained while the tilt-adjustable rotors are tilted (towards the vertical position when transitioning to the cruise mode, and towards the horizontal position when transitioning to the hover mode), and the power supplied to the fixed-tilt rotors is only adjusted once the tilt-adjustable rotors reach the desired position (either the vertical position when transitioning to the cruise mode or the horizontal position when transitioning to the cruise mode).

Thus, in some examples, the reducing the power to the fixed-tilt rotors at <NUM> optionally comprises maintaining power while the one or more tilt-adjustable rotors are tilted towards the vertical position, and then cutting off power to the fixed-tilt rotors responsive to the one or more tilt-adjustable rotors reaching the vertical position. Conversely, the increasing the power to the.

fixed-tilt rotors at <NUM> optionally comprises maintaining power (e.g., keeping the rotors powered off) while the one or more tilt-adjustable rotors are tilted towards the horizontal position, and then increasing power to the one or more fixed-tilt rotors responsive to the one or more tilt-adjustable rotors reaching the horizontal position.

However, in other examples, the power to at least one of the fixed-tilt rotors is adjusted while the one or more tilt-adjustable rotors are tilted between the horizontal and vertical positions. For example, the power to at least one of the fixed-tilt rotors is reduced while the one or more tilt-adjustable rotors are tilted towards the vertical position at <NUM>. Conversely, the power to at least one of the fixed-tilt rotors is increase while the one or more tilt-adjustable rotors are tilted towards the horizontal position at <NUM>.

However, maintaining some level of power (even if it is reduced power) to one or more fixed-tilt rotors while tilting the one or more tilt-adjustable rotors during the transition between the hover mode and the cruise mode provides a technical effect of increasing the stability of the aircraft during the transition, thus making for a smoother transition. In particular, the spinning fixed-tilt rotors and the tilting tilt-adjustable rotors provide counterbalancing forces that minimize pitch fluctuations during the transition from hovering to cruising. In particular, during the transition from hovering to cruising, tilting the front row of rotors downwards produces a nose-down tendency in the aircraft. However, powering the fixed-tilt rotors during the transition provides an opposing nose-up tendency. Specifically, the spinning fixed-tilt rotors generate a flow field that convects towards the tail, causing a strong nose-up tendency. Thus, by powering on the fixed-tilt rotors while tilting the one or more tilt-adjustable rotors, the pitch of the aircraft may be more stably maintained, thereby reducing unwanted fluctuations in the aircraft's pitch during the transition. In this way, the aircraft of the present disclosure provides a smoother transition from hovering to cruising than tilt-rotor aircraft that tilt all of their rotors.

Further, powering only some of the rotors (e.g., the one or more tilt-adjustable rotors) in the cruise mode saves energy as compared to other tilt-rotor aircraft that tilt all of their rotors. In other tilt-rotors aircraft, all of the rotors are tilted to the vertical position during cruising, and all of the rotors are therefore powered during the cruising. But, cruising may require less thrust than takeoff. By reducing power (e.g., powering off) to the one or more fixed-position rotors in the cruise mode, the aircraft of the present disclosure conserves energy during cruising while still meeting the lower thrust demands required during such cruising. Further, by tilting the one or more tilt-adjustable rotors to the horizontal position and powering all of the rotors (both the fixed-tilt and tilt-adjustable rotors) in the hover mode, the one or more tilt-adjustable rotors are not a parasitic loss during hovering because they may be used to provide additional vertical thrust. In this way, the aircraft saves energy during the cruise mode while increasing the maximum vertical thrust of the aircraft during hovering. Thus, the aircraft is just as capable during takeoff as other tilt-rotor aircraft, and is more energy efficient during cruising.

In some examples, power to the one or more tilt-adjustable rotors is maintained (e.g., not adjusted) while tilting the one or more tilt-adjustable rotors when transitioning between the hover mode and the cruise mode at <NUM>. However, in other examples, power to the one or more tilt-adjustable rotors is adjusted while tilting the one or more tilt-adjustable rotors when transitioning between the hover mode and the cruise mode at <NUM>.

Further, the transitioning between the hover mode and the cruise mode at <NUM> comprises maintaining a tilt angle of (e.g., not tilting) the fixed-tilt rotors, since the fixed-tilt rotors are fixed and are not configured to be tilted.

As used herein, a controller may be any suitable device or devices that are configured to perform the functions of the controller discussed herein. For example, the controller may include one or more of an electronic controller, a dedicated controller, a special-purpose controller, a personal computer, a special-purpose computer, a display device, a logic device, a memory device, and/or a memory device having non-transitory computer readable media suitable for storing computer-executable instructions for implementing examples of systems and/or methods according to the present disclosure.

Claim 1:
An aircraft (<NUM>) comprising:
an airframe (<NUM>) comprising a forward set of wings (<NUM>) and an aft set of wings (<NUM>);
one or more tilt-adjustable rotors (<NUM>) wherein all of the one or more tilt-adjustable rotors are positioned forward of the forward set of wings;
a first set of fixed-tilt rotors (<NUM>) positioned between the forward set of wings and the aft set of wings; and
a second set of fixed-tilt rotors (<NUM>) positioned behind the aft set of wings.