A craft includes a hull, a wing, a hydrofoil, and a control system. The wing is configured to generate upwards aero lift as air flows past the wing to facilitate wing-borne flight of the craft. The hydrofoil is configured to generate upwards hydrofoil lift during a first mode of operation as water flows past the hydrofoil to facilitate hydrofoil-borne movement of the craft through the water. While the craft is hydrofoil-borne, the control system is configured to determine the upwards aero lift generated by the wing. The control system is further configured to control the hydrofoil to generate downwards hydrofoil lift to counteract the upwards aero lift generated by the wing that maintains the hydrofoil at least partially submerged in the water while the determined upwards aero lift is below a threshold lift.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the claims, are incorporated in, and constitute a part of this specification. The detailed description and illustrated examples described serve to explain the principles defined by the claims.

FIG.1A-1Gillustrate various views of a craft, in accordance with example embodiments.

FIG.2illustrates a battery system of a craft, in accordance with example embodiments

FIG.3illustrates a main hydrofoil deployment system of a craft, in accordance with example embodiments.

FIG.4Aillustrates a rear hydrofoil deployment system of a craft, in accordance with example embodiments.

FIG.4Billustrates the rear hydrofoil deployment system of a craft, in accordance with example embodiments.

FIG.5illustrates a control system of a craft, in accordance with example embodiments.

FIG.6Aillustrates a craft in a hull-borne mode of operation, in accordance with example embodiments.

FIG.6Billustrates a craft in a hydrofoil-borne maneuvering mode of operation, in accordance with example embodiments.

FIG.7Aillustrates a craft in a hydrofoil-borne takeoff mode of operation, in accordance with example embodiments.

FIG.7Bis a graph that illustrates various lift forces acting on a craft, in accordance with example embodiments.

FIGS.8A-8Gillustrate example aspects of articulation of a hydrofoil of a craft, in accordance with example embodiments.

FIG.9Aillustrates example operations that facilitate transitioning a craft to a wing-borne mode of operation, in accordance with example embodiments.

FIG.9Billustrates additional example operations that facilitate transitioning a craft to a wing-borne mode, in accordance with example embodiments.

FIG.10illustrates a craft in a wing-borne mode of operation, in accordance with example embodiments.

FIG.11is a table that summarizes aspects of some procedures that facilitate foil-borne takeoff operations, in accordance with example embodiments.

FIG.12illustrates example operations performed by a craft, in accordance with example embodiments.

DETAILED DESCRIPTION

Various examples of systems, devices, and/or methods are described herein. Any embodiment, implementation, and/or feature described herein as being an “example” is not necessarily to be construed as preferred or advantageous over any other embodiment, implementation, and/or feature unless stated as such. Thus, other embodiments, implementations, and/or features may be utilized, and other changes may be made without departing from the scope of the subject matter presented herein.

Further, terms such as “A coupled to B” or “A is mechanically coupled to B” do not require members A and B to be directly coupled to one another. It is understood that various intermediate members may be utilized to “couple” members A and B together.

Moreover, terms such as “substantially” or “about” that may be used herein, are meant that the recited characteristic, parameter, or value need not be achieved exactly but that deviations or variations, including, for example, tolerances, measurement error, measurement accuracy limitations and other factors known to skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

A wing-in-ground effect craft is a craft capable of moving over a surface (e.g., earth or water) by gaining support from the reactions of the air against one or more surfaces of the craft. When such a craft hovers relatively close to the surface, the drag experienced by the craft is reduced. For example, the drag on a WIG aircraft is reduced when its distance from the ground is within about half the length of the aircraft's wingspan.

Some WIG craft include fixed hydrofoils that create additional upward lift while the WIG is waterborne to reduce the wetted surface area on the vehicle's hull at intermediate speeds prior to takeoff. However, because WIGs need to fly at very low altitudes when wing-borne, the fixed hydrofoils need to be very short to avoid colliding with the water during flight. As a result, the fixed hydrofoils in these WIGs do not lift the hull of the vehicle above the water waves during waterborne operation. As such, these vehicles cannot (a) operate in rough seas or (b) operate at medium speeds (e.g., between the low speeds of a hull-borne operational mode and the high speeds of a wing-borne flight mode) in crowded harbors.

Disclosed herein are various examples of WIG craft that overcome these and other drawbacks of prior WIG craft. Some examples of these WIG craft correspond to seagliders and include and implement features disclosed in U.S. patent application Ser. No. 17/570,090, filed Jan. 6, 2022 (herein after '090 application), and U.S. patent application Ser. No. 17/845,480, filed Jun. 21, 2022 (herein after '480 application). The '090 and '480 applications are incorporated herein by reference in their entirety. The '090 application describes, among other things, a seaglider that includes a pair of retractable hydrofoils (e.g., front and rear hydrofoils) that facilitate a hydrofoil-borne operation, described further below. The '480 application describes, among other things, a seaglider that implements a bi-plane tail.

Some examples of these craft are configured to transition through several operating modes when preparing for takeoff. For instance, an example of such a craft operates in a hull-borne mode while near docks or in no-wake zones. While in this mode, the hull of the craft is in the water, and the craft may move at low speeds (e.g., less than 20 mph). The craft next transitions to a hydrofoil-borne mode of operation. While in this mode, the craft is supported by the hydrofoils, and the hull is substantially lifted out of the water. The craft may operate in this mode while traveling through harbors and crowded waterways and may move at increased speeds (e.g., between 20-45 mph). The craft next transitions to a wing-borne mode of operation. While in this mode, the craft is urged out of the water by the lift generated by the wings. The craft may operate in this mode while in open waters and at further increased speeds (e.g., between 45 mph). It should be understood that the example parameters and characteristics (including operating heights and speeds) provided herein are provided for purposes of example and explanation only and should not be taken as limiting.

The hydrofoil-borne mode of operation allows for a wide range of benefits. For instance, operating in hydrofoil-borne mode facilitates a high degree of maneuverability and greater speed while in harbors and crowded waterways. Additionally, the one or more hydrofoils help address the challenges faced by other WIG craft that transition directly from a hull-borne mode to a wing-borne mode of operation. These WIG craft experience significant hull-induced drag while taking off. Such drag is not experienced by the craft disclosed herein because the craft are hydrofoil-borne during takeoff.

An ability for a craft to take off from the hydrofoil-borne mode is desirable for several reasons. For instance, the craft would be expected to be operating in hydrofoil-borne mode prior to initiating a takeoff procedure (e.g., while navigating a crowded harbor). Therefore, transitioning back to the hull-borne mode of operation prior to takeoff could be uncomfortable for passengers. Further, taking off while in the hydrofoil-borne mode of operation minimizes disturbances that would otherwise be felt by passengers due to choppiness/turbulence of the water waves, which can be exacerbated at higher speeds.

Thus, some examples of successful take-off procedures of the craft generally involve, when initially in a hull-borne borne mode of operation, causing the craft to increase speed over water. Once the craft reaches a sufficient speed, the craft enters the hydrofoil-borne mode of operation and continues to accelerate. Once sufficient lift is generated by the wings of the craft (e.g., lift corresponding to the weight of the craft or within some margin thereof), the craft transitions to a wing-borne mode of operation.

In general, to sustain takeoff and accomplish flight, the aero lift, LW, generated by the wings of the craft and/or lift generated by other aspects of the craft such as, for example, tilted rotors that provide vertical thrust, should exceed the weight, WCRAFT, of the craft. (SeeFIG.7A). A variety of factors impact the magnitude of aero lift, including, for example, the size and shape of the wings of the craft, the angle at which the wings meet the oncoming air (angle of attack or “AOA”), the speed at which the wings move through the air, the density of the air, etc. Of particular importance are those factors that are controllable through the course of a takeoff procedure, e.g., the speed of the craft and the pitch of the craft (corresponding to the AOA of the wings). (Note, while the lift, LF, generated by the hydrofoil can be positive, this lift does not generally contribute to the lift of the craft once in flight because (a) the hydrofoil is no longer in the water and (b) as described further below, the hydrofoil is eventually retracted into (or towards) the craft once the craft is operating in wing-borne mode.)

During takeoff procedures for a conventional land-based craft, the craft gradually increases speed, thereby gradually increasing the aero lift, LW, prior to take-off and flight. Once the craft has achieved sufficient speed, the AOA of the craft is increased, e.g., by pitching the nose of the craft upward. This further contributes to an increase in the aero lift, LW, and eventually causes the craft to take off and maintain flight.

Conceptually, the takeoff procedure of the example craft disclosed herein are similar in some respects. For instance, in one example, the craft gains the speed needed to obtain the required aero lift, LW, while the craft is in the hydrofoil-borne mode of operation (i.e., traveling through water vs over the water). In some examples, additional lift can be generated, for example, using tilted rotors or the like that provide vertical thrust/lift. However, transitioning from the hydrofoil-borne mode of operation to the wing-borne mode of operation is complicated and/or may be interrupted or frustrated due to the effect/force on the craft by the hydrofoil in the water.

As noted above, hydrofoils, like wings, generate an associated lift, LF, due to the force of water passing under the hydrofoils as the craft gains speed. In a normal/standard arrangement, the net lift, LNET, is positive. That is, the lift is upward and urges the craft out of the water. In this respect, LFand LWnormally act in concert to urge the craft out of the water as the craft increases in speed. Some approaches to takeoff might involve attempting to increase the speed of the craft sufficiently while in the hydrofoil-borne mode of operation to eventually take off and gain flight. Moreover, such approaches might involve, at some point during takeoff, increasing the pitch of the craft, leading to increased wing AOA, to assist in increasing LW(and/or perhaps LF) to contribute to increased lift and achievement of flight.

However, there are several challenges with such approaches. For instance, in testing this approach, applicants found that craft were unable to take flight after the speed of the craft was ramped towards a threshold lift speed at which the combination of LWand LFwould theoretically exceed the weight of the craft. When the craft reached the threshold lift speed, and the AOA was increased, both the nose of the craft and the hydrofoil rotated upward. However, the positive lift provided by the hydrofoil, LF, became negligible after the hydrofoil breached the surface of the water, and the remaining aero lift, LW, was insufficient to sustain flight as LWwas not equal or great to the mass of the craft. As a result, once the hydrofoil left the water, the craft came back down into the water, thereby disrupting and/or frustrating and ultimately preventing takeoff from hydrofoil-borne operation to wing-borne operation. In other testing, applicants found that the angle of attack of the craft would abruptly increase. This, in turn, induced a stall condition in the craft, which prevented the craft from sustaining flight.

The example craft disclosed herein address these issues by modifying and improving the takeoff procedures described above to ensure that the aero lift, LW, is sufficiently large prior to the point in the procedure at which the hydrofoils are to be removed from the water to facilitate allowing the craft to become wing-borne.

In some examples, an additional “negative” lift, LF, is introduced via the hydrofoil while the craft is increasing in speed in anticipation of takeoff to “hold” the hydrofoils and, therefore, the craft in the water. As a result, the craft can further increase in speed and generate greater overall aero lift, LW, without causing the craft to take flight and/or pitch up such that the front hydrofoil breaches the surface of the water (possibly leading to the failure described above).

In some examples, at an appropriate time after the “negative” lift, LF, is introduced (e.g., when LWexceeds or is within some margin of the weight, WCRAFT, of the aircraft according to some predetermined threshold), the negative lift, LF, implemented via the hydrofoil can be “released,” and the craft can, as a result, proceed to take off and gain sustained flight. These aspects are discussed in more detail below.

In some examples, the “hold” is not released. Rather, as the craft accelerates, the hydrofoil lift, LF, generated by the hydrofoil increases to a maximum amount, which can be a predetermined maximum amount and/or a maximum amount achievable due to the control capabilities of the hydrofoil. Afterwards, as the aero lift, LW, generated by the wings continues to increase, the aero lift, LW, pulls the craft from the water, because the aero lift LWis greater than the mass of the vehicle prior to takeoff. This can also help prevent an abrupt increase in the AOA of the craft, which can, in some instances, “throw” the craft out of the water and cause the craft to stall, thereby frustrating further takeoff procedures.

To implement aspects of the above-described take-off procedures, some examples of the craft comprise a control system configured to coordinate and control the transition of the craft from waterborne to hydrofoil-borne operation and from hydrofoil-borne to wing-borne operation. For instance, some examples of the control system are configured to cause one or more hydrofoils of the craft to extend and retract as needed (e.g., extend prior to taking off and retract when the craft is wing-borne). Some examples of the control systems are configured to control the actions of various control surfaces of the craft (e.g., flaps, ailerons, elevators, rudders, etc.) to stabilize the craft and control the altitude of the craft when near the water surface, etc.

Some examples of the craft are configured to control the articulation of the one or more hydrofoils and/or the various control surfaces of the one or more hydrofoils which can modify the amount of downwards hydrofoil lift, LF, generated by the one or more hydrofoils when the craft is in hydrofoil-borne mode. For instance, some examples of the hydrofoils comprise one or more flaperons, flaps, ailerons, elevators, etc. The control system is configured to adjust respective deflection angles of one or more of these components to thereby control the downwards hydrofoil lift, LF, generated by the hydrofoils. In some examples, the control system is configured to control the overall angle of attack of one or more of the hydrofoils to thereby control the hydrofoil lift, LF, generated by the hydrofoils.

In some examples, while the craft is hydrofoil-borne, the control system is configured to control one or more of the hydrofoils to generate a downwards hydrofoil lift, LF, that maintains the hydrofoil at least partially submerged in the water after the lift generated by the main wing of the craft reaches a threshold lift, while maintaining the desired ride height on the hydrofoil. In some examples, the threshold lift is greater than or equal to an amount of lift required to be generated by the main wing to allow the craft to transition from hydrofoil-borne movement through the water to wing-borne flight in the air. By controlling the hydrofoil to generate downwards lift that counteracts the upwards aero lift generated by the main wing until the amount of upwards aero lift exceeds the threshold amount of upwards aero lift, the control system prevents the craft from leaving the hydrofoil-borne mode of operation until after the main wing generates enough lift to facilitate the transition of the craft to the wing-borne mode of operation, from which the craft can proceed to gain altitude.

In some examples, the hydrofoil is controlled to generate an actively derived, predetermined, or fixed amount of downwards hydrofoil lift that is sufficient to keep the hydrofoil submerged after the main wing produces sufficient lift to sustain wing-borne flight after the craft leaves the water. For instance, in some examples, the downwards hydrofoil lift generated by the hydrofoil is sufficient to keep the hydrofoil at least within a margin of distance below the surface of the water until after the lift generated by the main wing is sufficient to sustain wing-borne flight. Afterward, the hydrofoil breaches the surface of the water and no longer exhibits any appreciable downwards hydrofoil lift. In some examples, the control system is configured to control the hydrofoil to increase the downwards hydrofoil lift generated by the hydrofoil in proportion to an increase in the lift generated by the main wing.

In some examples, the control system is configured to control the hydrofoil to decrease the downwards hydrofoil lift generated by the hydrofoil after the lift generated by the main wing reaches the threshold lift. For instance, in an example, the downwards hydrofoil lift generated by the hydrofoil is initially selected so that when the lift generated by the main wing reaches the threshold above, the hydrofoil is some distance below the surface of the water. At this point, the control system controls the hydrofoil to decrease or release the downwards hydrofoil lift. This, in turn, causes the craft to rise, bringing the hydrofoil out of the water so that the craft can transition from hydrofoil-borne to wing-borne operation. In some examples, the angle of attack/pitch of the craft, deflection angles of one or more control surfaces of the wings, etc., can be adjusted to generate additional aero lift.

In some examples, as the craft accelerates, the control system is configured to control the hydrofoil to increase the hydrofoil lift, LF, generated by the hydrofoil to a maximum amount, which can be a predetermined maximum amount and/or a maximum amount achievable due to the control capabilities of the hydrofoil. Afterwards, as the aero lift, LW, generated by the wings continues to increase, the hydrofoil is elevated out of the water so that the craft can transition from hydrofoil-borne to wing-borne operation. In some examples, the angle of attack/pitch of the craft, deflection angles of one or more control surfaces of the wings, etc., can be adjusted to generate additional aero lift.

Some examples of the control system are configured to determine the lift generated by the main wing based at least in part on one or more of the speed of the craft, an angle of attack of the main wing, a sensed load force imparted on the hydrofoil, etc.

In some examples, the craft comprises at least one hull, at least one wing, at least one hydrofoil, and a control system. The at least one wing is configured to generate upwards aero lift as air flows past the wing to facilitate wing-borne flight of the craft. The at least one hydrofoil is configured to generate upwards hydrofoil lift during a first mode of operation as water flows past the hydrofoil to facilitate hydrofoil-borne movement of the craft through the water. While the craft is hydrofoil-borne, the control system is configured to determine the upwards aero lift generated by the at least one wing. The control system is further configured to control the at least one hydrofoil to generate downwards hydrofoil lift that maintains the hydrofoil at least partially submerged in the water while the determined upwards aero lift is below a threshold lift.

In some examples, the craft comprises at least one hull, at least one wing, at least one hydrofoil, at least one processor system comprising one or more processors, and tangible, non-transitory computer-readable media. The at least one wing is configured to generate upwards aero lift as air flows past the at least one wing to facilitate wing-borne flight of the craft. The at least one hydrofoil is configured to generate upwards hydrofoil lift during a first mode of operation as water flows past the at least one hydrofoil to facilitate hydrofoil-borne movement of the craft through the water. The tangible, non-transitory computer-readable media comprises program instructions executable by the one or more processors to configure the craft to, among other features, (i) determine the upwards aero lift generated by the at least one wing as the craft accelerates over the water while in hydrofoil-borne operation, (ii) adjust downwards hydrofoil lift generated by the at least one hydrofoil based on the determined upwards aero lift (generated by the at least one wing) to maintain the at least one hydrofoil at least partially submerged in the water, and (iii) after determining that the upwards aero lift is above some predetermined threshold (e.g., in an example, a predetermined threshold that may be selected according to an amount of aero lift that is sufficient to allow the craft to sustain flight), decrease the amount of downwards hydrofoil lift generated by the at least one hydrofoil to allow the hydrofoil to exit the water. In operation, controlling when the hydrofoil exits the water allows the craft to improve control of the transition of the craft from hydrofoil-borne movement through the water to wing-borne movement through the air.

In some examples, a method for operating the craft comprises determining upwards aero lift generated by at least one wing of the craft as the craft accelerates while the craft is operating in a hydrofoil-borne mode over water. The method further comprises adjusting, based on the determined upwards aero lift (generated by the at least one wing), downwards hydrofoil lift generated by at least one hydrofoil of the craft to maintain the at least one hydrofoil at least partially submerged in the water, thereby causing the craft to remain in hydrofoil-borne operation. The method further comprises, after determining that the upwards aero lift is sufficient to allow the craft to sustain flight (or determining that the upwards aero lift generated by the at least one wing is above some threshold amount of upwards aero lift), decreasing the amount of downwards hydrofoil lift generated by the hydrofoil to allow the hydrofoil to exit the water, thereby transitioning the craft from hydrofoil-borne operation to wing-borne operation.

II. Example Wing-In-Ground Effect Vehicles

FIGS.1A-1Dillustrate different views of an example of a craft100. As shown, some examples of the craft100include a hull102, a main wing104, a tail106, a main hydrofoil assembly108, and a rear hydrofoil assembly110.

Some examples of the craft100operate in a first waterborne mode for an extended period of time, during which the hull102is at least partially submerged in water. As such, some examples of the hull102are configured to be watertight, particularly for surfaces of the hull that contact the water during this first waterborne operational mode. Further, some examples of the hull102, as well as the entirety of the craft100, are configured to be passively stable on all axes when floating in water. To help achieve this, some examples of the hull102include a keel (or centerline)112, which provides improved stability and other benefits described below. Some examples of the craft100include various mechanisms for adjusting the center of mass of the craft100so that the center of mass aligns with the center of buoyancy of the craft100. For instance, in some examples, a battery system (described in further detail below in connection withFIG.2) of the craft100is electrically coupled to one or more moveable mounts. Some examples of the mounts are moved by one or more servo motors or the like. In some examples, a control system of the craft100is configured to detect a change in its center of buoyancy, for instance, by detecting a rotational change via an onboard gyroscope, and responsively operate the servo motors to move the battery system until the gyroscope indicates that the craft100has stabilized. Some examples of the craft100include a ballast system for pumping water or air to various tanks distributed throughout the hull102of the craft100. The ballast system facilitates adjusting the center of mass of the craft100so that the center of mass aligns with the center of buoyancy of the craft100. Other example systems may be used to control the center of mass of the craft100as well.

Additionally, or alternatively, some examples of the hull102are configured to reduce drag forces when both waterborne and wing-borne. For instance, some examples of the hull102have a high length-to-beam ratio (e.g., greater than or equal to 8), which facilitates reducing hydrodynamic drag forces when the craft100is under forward waterborne motion. Some examples of the keel112are curved or rockered to improve maneuverability when waterborne. Further, some examples of the hull102are configured to pierce the surface of waves (e.g., to increase passenger and crew comfort) by including a narrow, low-buoyancy bow portion of the hull102.

B. Wing and Distributed Propulsion System

As shown inFIGS.1A-1D, some examples of the main wing104include an outrigger114at each end of the main wing104. The outriggers114(which are sometimes referred to as “wing-tip pontoons”) are configured to provide a buoyant force to the main wing104when submerged or when otherwise in contact with the water, which improves the stability of the craft100during waterborne operation.

As shown inFIG.1D, some examples of the main wing104have a gull-wing shape such that the outriggers114at the ends of the main wing104are at the lowest point of the main wing104and are positioned approximately level with (or slightly above) a waterline of the hull102when the hull102is waterborne.

Some examples of the main wing104have a high aspect ratio, which is defined as the ratio of the span of the main wing104to the mean chord of the main wing104. In some examples, the aspect ratio of the main wing104is greater than or equal to five, or greater than or equal to six, but other example aspect ratios are possible as well. Such wings tend to have reduced pitch stability and maneuverability due to lower roll angular acceleration. These issues are ameliorated by various mechanisms described below. On the other hand, such wings tend to have increased roll stability and increased efficiency resulting from higher lift-to-drag ratios. Further, high aspect ratio wings provide a longer leading edge for the mounting of a distributed propulsion system along the wing.

As shown in the figures, some examples of the main wing104include a number of electric motor propeller assemblies116distributed across a leading edge of the main wing104. This arrangement corresponds to a blown-wing propulsion system. Arranging the propeller assemblies116in this manner increases the speed of air moving over the main wing104, which increases the lift generated by the main wing104. This increase in lift allows the craft100to take off and become wing-borne at slower vehicle speeds. This facilitates, for example, taking off on water which can be difficult at higher speeds due to the various forces that would otherwise act on the craft100.

The electric motor propeller assemblies116tend to be much lighter, less complex, and smaller than the liquid-fueled engines used on conventional craft. Some examples of the electric motor propeller assemblies116are controlled by an electronic speed controller and powered by an onboard battery system (e.g., a lithium-ion system, magnesium-ion system, lithium-sulfur system, etc.). Some examples of the electric motor propeller assemblies116are controlled by a fuel cell or a centralized liquid-fueled electricity generator. In some examples, the onboard electrical supply system includes multiple systems for supplying power during different operational modes, such as a first battery system configured to deliver large amounts of power during takeoff and a second system with a higher energy density but lower peak power capability for delivering sustained lower power during cruise operation (e.g., during hydrofoil waterborne operation or during wing-borne operation, each of which are described in further detail below).

In some examples, the positioning of the electric motor propeller assemblies116along the leading edge of the main wing104is determined based on a variety of factors including, but not limited to, (i) the required total thrust for all modes of operation of the craft100, (ii) the thrust generated by each individual propeller of the propeller assemblies116, (iii) the radius of each propeller in the respective propeller assemblies116, (iv) the required tip clearance between each propeller and the surface of the water, and (v) the additional freestream speed over the main wing104required for operation.

As shown in the figures, in some examples, the number of propeller assemblies116is symmetrical across both sides of the hull102. In some examples, the propeller assemblies116are identical. In some examples, the propeller assemblies116have different propeller radii or blade configurations along the span so long as the configuration is symmetrical across the hull102. The different radii facilitate adequate propeller tip clearance from the water or vehicle structure. In some examples, the different propellers are optimized for different operational conditions, such as wing-borne cruise. The propeller placement and configuration may vary to increase the airflow over the main wing104or tail system106to improve controllability or stability. While eight total propeller assemblies116are illustrated, the actual number of propeller assemblies116can vary based on the requirements of the craft100.

In some examples, the propeller assemblies116have different pitch settings or variable pitch capabilities based on their position on the main wing104. For instance, in some examples, a subset of the propeller assemblies116have fixed-pitch propellers sized for cruise speeds, while the remainder of the propeller assemblies116have fixed-pitch propellers configured for takeoff or can allow for varying the propeller's pitch.

In some examples, different propeller assemblies116are turned off or have reduced rotational speeds during different modes of operation. For instance, during waterborne operation, one or more of the propeller assemblies116may be turned off or have reduced rotational speeds in a manner that generates asymmetrical thrust. This may create a yawing moment on the craft100, allowing the craft100to turn without large bank angles and increasing the turning maneuverability of the craft100. For instance, in order to yaw right, the craft100may increase the rotational speeds of the propellers of one or more of propeller assemblies116e-hwhile decreasing the rotational speeds of the propellers of one or more of propeller assemblies116a-d. Similarly, to yaw left, the craft100may increase the rotational speeds of the propellers of one or more of propeller assemblies116a-dwhile decreasing the rotational speeds of the propellers of one or more of propeller assemblies116e-h.

Similarly varying rotational speeds or propeller pitches may be used to yaw or roll the aircraft in flight or while foiling due to varied forces and lift distributions imposed over the wing and its control surfaces or in general used to tailor the lift distribution across the wing for optimized efficiency.

In some examples, the propeller assemblies may tilt to vector thrust either to provide directly more vertical lift or to change how the wing is blown depending on the mode of operation so as to tailor the blown lift distribution.

Some examples of the main wing104include one or more aerodynamic control surfaces, such as flaps118and ailerons120. Some examples of these controls comprise movable hinged surfaces on the trailing or leading edges of the main wing104for changing the aerodynamic shape of the main wing104. Some examples of the flaps118are configured to extend downward below the main wing104to reduce stall speed and create additional lift at low airspeeds, while some examples of the ailerons120are configured to extend upward above the main wing104to decrease lift on one side of the main wing104and induce a roll moment in the craft100. In some examples, the ailerons120are additionally configured to extend downward below the main wing104in a flaperon configuration to help the flaps118generate additional lift on the main wing104, which, in some examples, is used to either create a rolling moment or additional balanced lift depending on coordinated movement of both ailerons. Some examples of the flaps118and ailerons120include one or more actuators for raising and lowering the flaps118and ailerons120. Within examples, the flaps118include one or more of plain flaps, split flaps, slotted flaps, Fowler flaps, slotted Fowler flaps, Gouge flaps, Junkers flaps, or Zap flaps. Further, in some examples, the flaps118(and the ailerons120when configured as flaperons) are positioned to be in the wake of one or more of the propeller assemblies116. In some examples, the ailerons120are positioned so that they are in the wake of one or more of the propeller assemblies116to increase the effectiveness of the ailerons at low forward velocities. Some of the propeller assemblies116are positioned so that no ailerons120are in their wake to increase thrust on the outboard wing during a turn without inducing adverse yaw. For example, in a left turn, a normal airplane would have adverse yaw to the right as the right aileron is deflected down, increasing drag. In the present disclosure, however, the right propeller assembly outboard of the right aileron may have its thrust increased relative to the respective left propeller assembly, initiating a turn without adverse yaw.

C. Tail System

As illustrated inFIGS.1A-1D, some examples of the tail106include a vertical stabilizer122, a horizontal stabilizer124, and one or more control surfaces, such as elevators126. Similar to the flaps118and ailerons120, some examples of the elevators126comprise movable hinged surfaces on the trailing or leading edges of the horizontal stabilizer124for changing the aerodynamic shape of the horizontal stabilizer124to control a pitch of the craft100. Some examples of the horizontal stabilizer124are combined with the elevator126, creating a fully articulating horizontal stabilizer (e.g., a stabilator). Raising the elevators126above the hinge point creates a net downward force on the tail system and causes the craft100to pitch upward. Lowering the elevators126below the hinge point creates a net upward force on the horizontal stabilizer124and causes the craft100to pitch downward. Some examples of the elevators126include actuators, which are operated by a control system of the craft100to raise and lower the elevators126.

As illustrated inFIGS.1A-1D, some examples of tail106include a rudder128. Some examples of the rudder128comprise a movable hinged surface on the trailing edge of the vertical stabilizer122for changing the aerodynamic shape of the vertical stabilizer122to control the yaw of the craft100when operating in an airborne mode. In some examples, the rudder128additionally changes a hydrodynamic shape of the hull102to control the yaw of the craft100when operating in a waterborne mode. To facilitate such hydrodynamic control, in some examples, the rudder128is positioned low enough on the tail106that the rudder128is partially or entirely submerged when the hull102is floating in water. For instance, the rudder128is positioned partially or entirely below the waterline of the hull102. Some examples of the rudder128include one or more actuators, which are operated by a control system of the craft100to rotate the hinged surface of the rudder128to the left or right of the vertical stabilizer122. Actuating the rudder128to the left (relative to the direction of travel) causes the craft100to yaw left. Actuating the rudder128to the right (relative to the direction of travel) causes the craft100to yaw right. As such, the rudder128may be used in combination with any of the other mechanisms disclosed herein for controlling the yaw of the craft100, including in combination with the ailerons120during airborne operation and in combination with varying the rotational speeds of different ones of the propeller assemblies116to help improve the maneuverability of the craft100during waterborne operation.

As illustrated inFIGS.1E-1G, some examples of the tail106include one or more vertical stabilizers122a,122b,122n, one or more horizontal stabilizers124a,124b, one or more control surfaces, such as elevators126, and one or more tail flaps127a,127bfor enhanced pitch control configured to exert enhanced net downward force on the tail system. It should be understood that althoughFIGS.1E-1Gshow only two horizontal stabilizers and two tail flaps, it is contemplated that more than two of each can be used within the scope of the present teachings. In some applications, it has been found that the transition from waterborne operation to airborne or wing-borne operation can require a larger pitching moment to overcome the larger drag forces existing between the hull102and/or the hydrofoil assemblies108,110and the water. This phenomenon can further occur in wheeled aircraft configured for short takeoff and landing (STOL) operations. In this way, at low airspeeds, aerodynamic forces in conventional designs fail to produce sufficient downward force to permit sufficient pitching moment. To provide sufficient pitching moment to pitch the craft100upward, a conventional solution would be to increase the span of the tail so that the elevator generates more force; however, a resultant consequence of increasing the span of the tail is that the entire tail must be stronger and heavier, which can result in undesired reduction of payload and efficiency. However, the present configuration provides improved performance by providing a tail106having a first horizontal stabilizer124aand a second horizontal stabilizer124b. It should be understood that one or more additional horizontal stabilizers can be used.

In some examples, a first horizontal stabilizer124ais a lower horizontal stabilizer relative to a second horizontal stabilizer124b. However, it should be appreciated that the horizontal stabilizers in some examples can be interchanged for performance purposes (e.g., the disclosed structure of the first horizontal stabilizer124acan be incorporated in the upper horizontal stabilizer and the disclosed structure of the second horizontal stabilizer124bcan be incorporated in the lower horizontal stabilizer). In some non-limiting examples, the structure, shape, and/or performance of each horizontal stabilizer can be tailored as desired such that the lower horizontal stabilizer (in this example, the first horizontal stabilizer124a) is more likely to experience aerodynamic effect from being in the wake of the blown-wing propulsion system disclosed herein or associated wake produced by alternative propulsion systems. In this way, greater aerodynamic control and/or downwards lift can be generated during desired phases of operation.

Some examples of the horizontal stabilizers124a,124binclude one or more aerodynamic control surfaces, such as tail flaps127and elevators126, which may comprise movable hinged surfaces on the trailing or leading edges of the horizontal stabilizer124for changing the aerodynamic shape of the respective horizontal stabilizer124. It should be recognized that at least one of the horizontal stabilizers124a,124bcan be sized, shaped, and/or spaced relative to a second of the horizontal stabilizers124a,124bto enhance or minimize the aerodynamic effect on the adjacent stabilizers. In this way, the aerodynamic flow, pressures, and/or forces can be used to improve the efficiency or effectiveness of the adjacent stabilizer. In some examples, at least one of the horizontal stabilizers124a,124bcan be actuated in an opposing direction. In some embodiments, at least one of the horizontal stabilizers124a,124bcan define a ratio of a surface area of the first horizontal stabilizer to a surface area of the second horizontal stabilizer in the range of 0.9 to 1.6. In some non-limiting example configurations, the surface area of the first horizontal stabilizer is 5.7 m2, the surface area of the second horizontal stabilizer is 3.9 m2, both have a chord of about 1 m and a vertical separation of 1.8 m. In some embodiments, a vertical separation distance between the first horizontal stabilizer and the second horizontal stabilizer is in the range of 0.25 to 0.75 of the lower horizontal stabilizer span. In some examples, a vertical separation distance can be dependent on the required rudder authority and thus elevator size (driven by, e.g., yaw stability, or the need to counteract asymmetric thrust following powerplant failure). In some examples, a sweep offset moves the center of pressure further aft from the center of gravity, thus allowing the airfoil of the horizontal stabilizer to have less surface area overall, thus being smaller and lighter. In some examples, a dihedral in the bottom surface of the horizontal stabilizer adds stability. In some examples, the box tail design itself increases the efficiency due to the elimination of wingtip vortices of a typical tail. In some embodiments, a lower horizontal stabilizer may have approximately a 15% thickness-to-chord ratio to support the weight of the upper components, whereas the vertical and upper surfaces may be thinner, such as, for example, 10% thickness-to-chord ratio due to reduced structural load requirement, which enables the upper horizontal stabilizer to be more efficient (lower drag). It should be appreciated that the left and right elevator surfaces126can be controlled independently and/or differentially to create a rolling moment, thereby enabling the wing ailerons120to be made smaller. The smaller wing ailerons120further enable larger flaps118. It should be appreciated that in some embodiments, using the vertical control surfaces128a,128b,128ncan change the pressure distribution across the elevator126, for example, commanding a left 5 degree deflection in the left vertical control surface may move the mean pressure distribution left/right by a percentage of the elevator width.

Some examples of the tail flaps127are configured to selectively extend upward above the horizontal stabilizer124for changing a surface area, camber, aspect ratio, and/or shape of the horizontal stabilizer124. The tail flaps127may include, for example, one or more of plain flaps, split flaps, slotted flaps, Fowler flaps, slotted or double-slotted Fowler flaps, Gouge flaps, Junkers flaps, or Zap flaps. That is, in some examples, tail flaps127serve to change an angle of attack of the horizontal stabilizer124, change a chord line of the horizontal stabilizer124, change a surface area of the horizontal stabilizer124, and/or otherwise increase the net effective downwardly directed lift of the horizontal stabilizer124. Such configurations effectively reduce the speed at which the horizontal stabilizer124becomes aerodynamically effective by creating additional net downward force at low airspeeds to aid in exerting a nose-up pitching moment of the craft100. The elevators126may be configured for changing the aerodynamic shape of the horizontal stabilizer124to further control or vary a pitch of the craft100.

In some examples operations, the tail flaps127are deployed (e.g., extended as depicted in127aand127bwith dashed lines inFIG.1G) for takeoff (e.g., transition from hydrofoil-borne mode to airborne mode) and landing (e.g., transition from airborne mode to hull-borne mode) to generate additional downforce on the tail system when additional pitch-up moment is required. Tail flaps127can be stowed (e.g., retracted as depicted inFIGS.1E-1F) for other phases of operation, such as hull-borne mode, to reduce downforce on the tail system and reduce drag.

In some examples, the elevators126are additionally configured to extend upward above the horizontal stabilizer124in a flaperon-like configuration (yet with elevators, rather than ailerons) to help the tail flaps127generate additional downward force on the horizontal stabilizer124, which may be used to either create a pitching moment or additional balanced downward force. The tail flaps127and elevators126may each include one or more actuators125for raising and lowering the tail flaps127and elevators126, singly or in combination. The actuators125can comprise any system configured to selectively actuate the associated system, such as but not limited to a flap track system (integrated into vertical stabilizers122a,122b,122n, which can reduce complex hinge systems or external arms, thereby reducing wetted area and excrescences drag), an electric servo motor mounting within the vertical stabilizers122a,122b,122nand/or horizontal stabilizers124a,124b, and/or a central vertical strut system generally mounted in the hull102or the fuselage of the craft100(to provide the potential for reduced cross-sectional area and associated drag).

Further, in some examples, as depicted inFIG.1G, the elevators126and/or the tail flaps127are positioned so that they are in the wake129of one or more of the propeller assemblies116of main wing104. The elevators126and/or the tail flaps127may be positioned so that they are in the wake129of one or more of the propeller assemblies116to increase the effectiveness of the elevators at low forward velocities. In some examples, the propeller assemblies116are positioned so that no elevators126and/or tail flaps127are in the wake129to ensure consistent and/or predictable aerodynamic forces, independent of power application, are exerted during critical operational phases. In some examples, the propeller assemblies116are positioned so that the elevators126are in their wake129and the tail flaps127are not in the wake129(e.g., above the wake129) and are exposed to clean air131. It should be understood that positioning of the tail flaps127in the second horizontal stabilizer124b, or at a distance above the center of gravity of the craft100, will have the added unexpected benefit of creating additional nose-up pitching moment as a result of induced drag acting about the center of gravity causing the craft100to pitch upward.

Similar to the flaps118and the ailerons120of the main wing104, some examples of the elevators126comprise movable hinged surfaces on the trailing or leading edges of the horizontal stabilizer124for changing the aerodynamic shape of the horizontal stabilizer124to control a pitch of the craft100. The horizontal stabilizer124may be combined with the elevator126, creating a fully articulating horizontal stabilizer (e.g., a stabilator). Raising the elevators126above the hinge point creates a net downward force on the tail system and causes the craft100to pitch upward. Lowering the elevators126below the hinge point creates a net upward force on the horizontal stabilizer124and causes the craft100to pitch downward. The elevators126may include actuators, which may be operated by a control system of the craft100in order to raise and lower the elevators126.

In some examples, the tail106includes one or more rudders128a,128b,128n. The rudders128a,128b,128nmay each comprise a movable hinged surface on the trailing edge of the corresponding vertical stabilizers122a,122b,122nfor changing the aerodynamic shape of the vertical stabilizer122to control the yaw of the craft100when operating in an airborne mode. It should be understood that rudders128a,128b,128ncan operate independently or in combination as desired. Moreover, in some examples, rudders128a,128b,128ncan be used as redundant systems, particularly useful in the event of one or more failures.

In some examples, the rudders128a,128b,128nadditionally change a hydrodynamic shape of the hull102to control the yaw of the craft100when operating in a waterborne mode. In order to facilitate such hydrodynamic control, the rudders128a,128b,128nmay be positioned low enough on the tail106that one or more of the rudders128a,128b,128nis partially or entirely submerged when the hull102is floating in water. Namely, the rudders128a,128b,128nmay be positioned partially or entirely below a waterline of the hull102. The rudders128a,128b,128nmay include one or more actuators, which may be operated by a control system of the craft100in order to rotate the hinged surface of the rudders128a,128b,128nto the left or right of the vertical stabilizer122. Actuating the rudders128a,128b,128nto the left (relative to the direction of travel) causes the craft100to yaw left. Actuating the rudders128a,128b,128nto the right (relative to the direction of travel) causes the craft100to yaw right. As such, the rudders128a,128b,128nmay be used in combination with any of the other mechanisms disclosed herein for controlling the yaw of the craft100, including in combination with the ailerons120during airborne operation and in combination with varying the rotational speeds of different ones of the propeller assemblies116to help improve the maneuverability of the craft100during waterborne operation.

As depicted inFIG.1F, it should be understood that the fundamental shape of tail106, having one or more vertical stabilizers122a,122b,122nand one or more horizontal stabilizers124a,124b, can result in a box-like assembly, wherein the vertical stabilizers are generally coupled to the horizontal stabilizers to form a reinforced box-like construction. This box-like construction provides enhanced structural integrity that enables tail106of some examples to be lighter and/or smaller than otherwise constructed.

While not shown inFIGS.1A-1G, some examples of the craft100include a distributed propulsion system on the tail106, which may be similar to the distributed propulsion system of propeller assemblies116on the main wing104. Such a distributed propulsion system may provide similar benefits of increasing the freestream velocity over the control surfaces (e.g., the elevators126and/or the rudder128) to allow for increased pitch and yaw control of the craft100at lower travel speeds. When determining the number and size of propeller assemblies to include on the tail106, one may apply the same factors described above when determining the number and size of propeller assemblies to include on the main wing104.

As noted above, some examples of the craft100include a main hydrofoil assembly108and a rear hydrofoil assembly110. In some examples, the main hydrofoil assembly108is positioned proximate to the middle or bow of the craft100, and the rear hydrofoil assembly110is positioned proximate to the stern. For instance, some examples of the main hydrofoil assembly108is positioned between the bow and a midpoint (between the bow and stern) of the craft100, and some examples of the rear hydrofoil assembly110is positioned below the tail106of the craft100.

The main hydrofoil assembly108and the rear hydrofoil assembly110are configured to facilitate the breaking of contact between the hull of the craft and the water surface during takeoff, which, as noted above, can otherwise be challenging in some conventional craft designs. Some examples of the main hydrofoil assembly108and the rear hydrofoil assembly110are configured to be retractable, large enough to lift the entire craft out of the water and not impact the water surface, and to enable sustained operation in the hydrofoil-borne mode (where the entire weight of the craft is supported by the one or more hydrofoil assemblies).

Some examples of the main hydrofoil assembly108include a main hydrofoil130, one or more main hydrofoil struts132that couple the main hydrofoil130to the hull102, and one or more main hydrofoil control surfaces134. Similarly, some examples of the rear hydrofoil assembly110include a rear hydrofoil136, one or more rear hydrofoil struts138that couple the rear hydrofoil136to the hull102, and one or more rear hydrofoil control surfaces140.

Some examples of the main hydrofoil130and the rear hydrofoil136take the form of one or more hydrodynamic lifting surfaces (also referred to as “foils”) configured to be operated partially or entirely submerged underwater while the hull102of the craft100remains above and clear of the water's surface. In operation, as the craft100moves through water with the main hydrofoil130and the rear hydrofoil136submerged, the hydrofoils generate a lifting force that causes the hull102to rise above the surface of the water. In general, the lifting force generated by the hydrofoils must be at least equal to the weight of the craft100to cause the hull102to rise above the surface of the water. The lifting force of the hydrofoils depends on the speed and angle of attack at which the hydrofoils move through the water, as well as their various physical dimensions, including the aspect ratio, the surface area, the span, and the chord of the foils.

The height at which the hull102is elevated above the surface of the water during hydrofoil-borne operation is limited by the length of the one or more main hydrofoil struts132that couple the main hydrofoil130to the hull102and the length of the one or more rear hydrofoil struts138that couple the rear hydrofoil136to the hull102. In some examples, the main hydrofoil struts132and the rear hydrofoil struts138are long enough to lift the hull102at least five feet above the surface of the water during hydrofoil-borne operation, which facilitates operation in substantially choppy waters. Struts of other lengths may be used as well. For instance, in some examples, longer struts that allow for better wave-isolation of the hull102(but at the expense of the stability of the craft100and increasing complexity of the retraction system) are utilized.

In practice, hydrofoils have a limited top speed before cavitation occurs, which results in vapor bubbles forming and imploding on the surface of the hydrofoil. Cavitation not only may cause damage to a hydrofoil but also significantly reduces the amount of lift generated by the hydrofoil and increases drag. Therefore, it is desirable to reduce the onset of cavitation by designing the main hydrofoil130and the rear hydrofoil136in a way that allows the hydrofoils to operate at higher speeds (e.g., ˜20-45 mph) and across the entire required hydrofoil-borne speed envelope before cavitation occurs. For instance, in some examples, the onset of cavitation is controlled based on the geometric design of the main hydrofoil130and the rear hydrofoil136. Additionally, in some examples, the structural design of the main hydrofoil130and the rear hydrofoil136is configured to allow the surfaces of the hydrofoils to flex and twist at higher speeds, which may reduce loading on the hydrofoils and delay the onset of cavitation.

Further, in some examples, the distributed blown-wing propulsion system described above further facilitates the delay of onset of cavitation on the main hydrofoil130and the rear hydrofoil136. Cavitation is caused by both (i) the amount of lift generated by a hydrofoil and (ii) the profile of the hydrofoil (which is affected by both the hydrofoil's angle of attack and its vertical thickness) as it moves through water. Reducing the amount of lift generated by the hydrofoil delays the onset of cavitation. Because the blown-wing propulsion system creates additional lift on the main wing104, the amount of lift exerted on the main hydrofoil130and the rear hydrofoil136to lift the hull102out of the water is reduced. Further, because the main hydrofoil130and the rear hydrofoil136do not need to generate as much lift to raise the hull102out of the water, their angles of attack may be reduced as well, which further delays the onset of cavitation. In some examples, combining the blown-wing propulsion system with the hydrofoil designs described herein facilitates operating the craft100in a hydrofoil-borne mode at speeds above 35 knots before cavitation occurs.

As shown inFIGS.1A-1D, some examples of the main hydrofoil130have a flattened V-shaped design in which a center portion of the main hydrofoil130is substantially flat, and the ends of the main hydrofoil130extend upward toward the hull102of the craft100. This flattened V-shape design facilitates passive regulation of the distance between the hull102and the surface of the water (also referred to as “ride height”) while also allowing for passive roll-moment control. The passive regulation of ride height is achieved by having the tips of the V-shaped hydrofoil breach the surface of the water, reducing the lifting surface that is underwater. If the ride height is too low, the increased hydrofoil surface area under the surface of the water will create a net force greater than the weight of the craft100, causing the hydrofoil to rise higher. If the ride height is too high, the hydrofoil lifting area under the surface of the water will be insufficient to prevent the craft100from descending into the water. The passive roll stability is due to one side of the V-shaped hydrofoil breaching further out of the water than the other side. This creates a stabilizing roll moment when the craft100is rolled to (for example) the left because the left side of the V-shaped hydrofoil will have more surface under the water surface, allowing it to generate more lift than the right side. In some examples of the craft100(e.g., as shown inFIGS.1E-1G and3), the shape of the main hydrofoil130is different (e.g., flat, curved, etc.).

As noted above, some examples of the main hydrofoil assembly108and the rear hydrofoil assembly110include one or more main and rear hydrofoil control surfaces134,140, respectively. Some examples of the main hydrofoil control surfaces134include one or more hinged surfaces on a trailing or leading edge of the main hydrofoil130as well as one or more actuators which are operated by the control system of the craft100to rotate the hinged surfaces so that they extend above or below the main hydrofoil130. Some examples of the main hydrofoil control surfaces134on the main hydrofoil130are operated in a similar manner as the flaps118and ailerons120on the main wing104of the craft100. In some examples, lowering the control surfaces134to extend below the main hydrofoil130changes the hydrodynamic shape of the main hydrofoil130in a manner that generates additional lift on the main hydrofoil130, similar to the aerodynamic effect of lowering the flaps118. In some examples, asymmetrically raising one or more of the control surfaces134(e.g., raising a control surface134on only one side of the main hydrofoil130) changes the hydrodynamic shape of the main hydrofoil130in a manner that generates a roll force on the main hydrofoil130, similar to the aerodynamic effect of raising one of the ailerons120.

Likewise, some examples of the rear hydrofoil control surfaces140include one or more hinged surfaces on a trailing or leading edge of the rear hydrofoil136as well as one or more actuators, which are operated by the control system of the craft100to rotate the hinged surfaces so that they extend above or below the rear hydrofoil136. In some examples, the rear hydrofoil control surfaces140on the rear hydrofoil136are operated in a similar manner as the elevators126on the tail106of the craft100. In some examples, lowering the control surfaces140to extend below the rear hydrofoil136changes the hydrodynamic shape of the rear hydrofoil136in a manner that causes the craft100to pitch downwards, similar to the aerodynamic effect of lowering the elevators126. In some examples, raising the control surfaces140to extend above the rear hydrofoil136changes a hydrodynamic shape of the rear hydrofoil136in a manner that causes the craft100to pitch upwards, similar to the aerodynamic effect of raising the elevators126.

In some examples, one or both of the main hydrofoil control surfaces134or the rear hydrofoil control surfaces140include rudder-like control surfaces similar to the rudder128on the tail106of the craft100. For instance, some examples of the main hydrofoil control surfaces134include one or more hinged surfaces on a trailing edge of the main hydrofoil strut132as well as one or more actuators, which are operated by the control system of the craft100to rotate the hinged surfaces so that they extend to the left or right of the main hydrofoil strut132. Similarly, some examples of the rear hydrofoil control surfaces140include one or more hinged surfaces on a trailing edge of the rear hydrofoil strut138as well as one or more actuators, which are operated by the control system of the craft100in order to rotate the hinged surfaces so that they extend to the left or right of the rear hydrofoil strut138. In some examples, actuating the main hydrofoil control surfaces134or the rear hydrofoil control surfaces140in this manner changes the hydrodynamic shape of the main hydrofoil strut132or the rear hydrofoil strut138, respectively, which facilitates controlling the yaw of the craft100when operating in a waterborne or hydrofoil-borne mode, similar to the effect of actuating the rudder128of the craft100, as described above.

In some examples, instead of (or in addition to) actuating hinged control surfaces on the main hydrofoil130and/or the rear hydrofoil136, a control system of the craft100actuates the entire main hydrofoil130and/or the entire rear hydrofoil136themselves. In some examples, the craft100includes one or more actuators for rotating the main hydrofoil130and/or the rear hydrofoil136around the yaw axis. In some examples, the craft100includes one or more actuators for controlling the angle of attack of the main hydrofoil130and/or the rear hydrofoil136(i.e., rotating the main hydrofoil130and/or the rear hydrofoil136around the pitch axis). Some examples of the craft100include one or more actuators for rotating the main hydrofoil130and/or the rear hydrofoil136around the roll axis. Some examples of the craft100include one or more actuators for changing a camber or shape of the main hydrofoil130and/or the rear hydrofoil136. Some examples of the craft100include one or more actuators for flapping the main hydrofoil130and/or the rear hydrofoil136to help propel the craft100forward or backward. Other examples are possible as well.

Further, some examples of the craft100dynamically control an extent to which the main hydrofoil130and/or the rear hydrofoil136are deployed based on an operational mode (e.g., hull-borne, hydrofoil-borne, or wing-borne modes) of the craft100. For instance, in some examples, during hull-borne mode, the rear hydrofoil assembly110is partially deployed or retracted to increase turning authority. The amount of partial deployment or retraction may be a function of the desired overall vehicle draft when operating in a shallow water environment. In some examples, during hydrofoil-borne mode, the main hydrofoil assembly108is partially retracted to reduce the distance between the hull of the vehicle and the water's surface. This increases the amount of lift generated by the main wing104by operating the wing closer to the surface of the water, increasing the effects of the aerodynamic ground effect.

As noted above, some examples of the main hydrofoil assembly108and rear hydrofoil assembly110interface with a deployment system that facilitates retracting the respective hydrofoil assemblies108,110into or toward the hull102for hull-borne or wing-borne operation and for extending the respective hydrofoil assemblies108,110below the hull102for hydrofoil-borne operation. As described further below, in some embodiments, the deployment system is used in connection with extending, retracting, and/or otherwise controlling the positioning of the hydrofoil assemblies108,110during takeoff when the craft is transitioning from hydrofoil-borne operation to wing-borne operation.

E. Battery System

FIG.2illustrates an example of an onboard battery system. In some examples, the battery system200is arranged in a protected area202of the hull102below a passenger seating area204. Some examples of the battery system200are separated from the passenger seating area204by a firewall206to protect the passengers from harm if a thermal runaway occurs. In this regard, some examples of the craft100include a battery management system comprising voltage, current, and/or thermal sensors for detecting thermal runaway or some other fire detection system for detecting a fire in the protected area202.

Some examples of the craft100include one or more mechanisms for flooding the battery system200(e.g., with an inert gas fire, with water, etc.) upon detecting a thermal runaway or a fire in the protected area202. For instance, some examples of the hull102comprise one or more valves or other controllable openings. The control system of the craft100is configured to open the valves and/or controllable openings upon detecting a fire in the protected area202or thermal runaway in the battery system200to allow water to enter the protected area202and to extinguish or prevent a fire in the protected area202.

In some examples, the battery system200is configured to be jettisoned through one or more of the controllable openings in the hull102described above. In this regard, in some examples, the weight of the battery system200is sufficient to jettison the battery system200out of the hull102when the hull102is opened. In some examples, the craft100comprises an actuator or the like configured to jettison the battery system200out of the hull102.

In other examples, the craft100may take measures to become waterborne in response to detecting a fire in the protected area202or thermal runaway in the battery system200. Some examples of the control system of the craft100determine a fire suppression operation to perform based on the operational state of the craft100(e.g., operating in hull-borne, hydrofoil-borne, or wing-borne mode). For instance, when operating in hull-borne mode and upon detecting a thermal runaway or a fire in the protected area202, some examples of the control system are configured to flood the battery system200as described above. When operating in hydrofoil-borne or a wing-borne mode, the control system is configured to cause the craft100to transition to hull-borne mode upon detecting a thermal runaway or a fire in the protected area202and then flood the battery system200.

F. Hydrofoil Deployment Systems

FIG.3illustrates an example of a main hydrofoil deployment system300that facilitates retracting and extending of the main hydrofoil assembly108. As shown, some examples of the main hydrofoil deployment system300take the form of a linear actuator that includes one or more brackets302that couple the main hydrofoil assembly108(by way of the main hydrofoil struts132) to one or more vertical tracks304. Some examples of the brackets302are configured to move vertically along the tracks304, such that when the brackets302move vertically along the tracks304, the main hydrofoil assembly108likewise moves vertically. Some examples of the brackets302are coupled to a leadscrew306that, when rotated, causes vertical movement of the brackets302. Some examples of the leadscrew306are rotatable by any of various sources of torque, such as an electric motor coupled to the leadscrew306by a gear assembly308.

Some examples of the main hydrofoil deployment system300further include one or more sensors310configured to detect a vertical position of the main hydrofoil assembly108. As shown, the sensors310include a first sensor310athat senses when the main hydrofoil assembly108has reached a fully retracted position and a second sensor310bthat senses when the main hydrofoil assembly108has reached a fully extended position. However, the main hydrofoil deployment system300may include additional sensors for detecting additional discrete positions or continuous positions of the main hydrofoil assembly108. Some examples of the sensors310are included as part of, or otherwise configured to communicate with, the control system of the craft100to provide the control system with data that indicates the position of the main hydrofoil assembly108. Some examples of the control system use this data to determine whether to operate the electric motor to retract or extend the main hydrofoil assembly108.

In some examples, such as examples where the linear actuator is not a self-locking linear actuator, the main hydrofoil deployment system300includes a locking or braking mechanism for holding the main hydrofoil struts132in a fixed position (e.g., in a fully retracted or fully extended position). An example of the locking mechanism corresponded to a dual-action mechanical brake that is coupled to the electric motor, the leadscrew306, or the gear assembly308.

While the above description provides various details of an example main hydrofoil deployment system300, it should be understood that the main hydrofoil deployment system300illustrated inFIG.3is for illustrative purposes and is not meant to be limiting. For instance, the main hydrofoil deployment system300may include any of various linear actuators now known or later developed that are capable of retracting and extending the main hydrofoil assembly108.

FIGS.4A and4Billustrate an example of a rear hydrofoil deployment system400that facilitates retracting and extending the rear hydrofoil136. As shown, some examples of the rear hydrofoil deployment system400include a pulley system403that couples an actuator405to the rear hydrofoil strut138. When actuated, the actuator405causes the pulley system403to raise or lower the rear hydrofoil strut138by causing the rear hydrofoil strut138to slide vertically along a shaft407. While not illustrated inFIGS.4A and4B, in some examples, the rudder128is mounted to the shaft407such that, when the actuator405raises the rear hydrofoil strut138, the rear hydrofoil strut138retracts at least partially into the rudder128. Additionally, some examples of the rear hydrofoil deployment system400include one or more servo motors configured to rotate the rear hydrofoil strut138around the shaft. In this respect, in some examples, the rear hydrofoil strut138is rotated around the shaft to act as a hydro-rudder when submerged in water or to act as an aero-rudder when out of the water. Further, because the rudder128is mounted to the same shaft407as the rear hydrofoil strut138and the rear hydrofoil strut138can be retracted into the rudder128, the same servo motor can also be used to control the rotation of the rudder128.

The actuator405of the rear hydrofoil deployment system400may take various forms and may, for instance, include any of various linear actuators now known or later developed that are capable of retracting and extending the rear hydrofoil assembly110. Further, in some examples, the actuator405has a non-unitary actuation ratio such that a given movement of the actuator405causes a larger corresponding induced movement of the rear hydrofoil assembly110. This can help allow for faster retractions of the rear hydrofoil assembly110, which may be beneficial during takeoff, as described in further detail below.

Some examples of the main hydrofoil assembly108and/or the rear hydrofoil assembly110are configured such that, when fully retracted, the hydrofoil assembly is flush, conformal, or tangent to the hull102. For instance, some examples of the hull102include one or more recesses configured to receive the main hydrofoil assembly108and/or the rear hydrofoil assembly110. In this regard, some examples of the main hydrofoil assembly108and/or the rear hydrofoil assembly110have a shape such that when the main hydrofoil assembly108and/or the rear hydrofoil assembly110are fully retracted into the recesses of the hull102, the outer contour of the hull102forms a substantially smooth transition at the intersection of the hull102and the main hydrofoil assembly108and/or the rear hydrofoil assembly110.

Other examples of the main hydrofoil assembly108and/or the rear hydrofoil protrude slightly below the hull102when retracted. These examples of the main hydrofoil assembly108and/or the rear hydrofoil assembly110are configured to have a non-negligible effect on the aerodynamics of the craft100. Some examples of the craft100are configured to leverage these effects to provide additional control of the craft100. For instance, in some examples, when the main hydrofoil assembly108and/or the rear hydrofoil assembly110are retracted but still exposed, the exposed hydrofoil is manipulated in flight to impart forces and moments on the craft100similar to an aero-control surface.

Some examples of the hydrofoil assemblies108,110disclosed herein are mounted on a pivot that is locked underwater but is unlocked to allow the hydrofoil to move around the pivot in the air. At that point, the control surfaces act like trim tabs and are able to effect movement of the entire unlocked, pivoting hydrofoil, which would otherwise require impractically large and heavy servo motors. This configuration facilitates unlocking and moving of the hydrofoil using a slow servo and/or a combination of control surface movement combined with forward movement through water, and then re-locked such that the hydrofoil is at a selected angle of incidence.

As noted above, some examples of the main hydrofoil assembly108are configured to be retractable. Some examples of the hull102include openings through which the struts132of the main hydrofoil assembly108are retracted and extended. Some examples of the hull102are configured to isolate water that enters through these openings (e.g., when the hull102contacts the water surface) and to allow for the water to drain from the hull102after the hull102is lifted out of the water. For instance, some examples of the hull102include pockets142on each side of the hull102aligned above the struts132. Some examples of the pockets142are isolated from the remainder of the interior of the hull102so that water that accumulates in the pockets142does not reach any undesired areas (e.g., the cockpit, passenger seating area, areas that house the battery system200, components of the control system of the craft100, etc.). Further, some examples of the pockets142include venting holes or other openings located at or near the bottom of the pockets142. The venting openings are configured to allow water that enters the pockets142to vent out of the pockets142when the hull102is lifted out of the water.

Some examples of the main hydrofoil assembly108and/or the rear hydrofoil assembly110include one or more propellers for additional propulsion when submerged underwater. For instance, in some examples, one or more propellers are mounted to the main hydrofoil130and/or the rear hydrofoil136. In some examples, the propellers are configured to provide additional propulsion force to the craft100during hydrofoil-borne or hull-borne operation.

In some examples, propellers are mounted to the hull102. The propellers are submerged during hull-borne operation. In some examples, the propellers are configured to provide additional propulsion force to the craft100during hull-borne operation.

Some examples of the main and/or rear hydrofoil assemblies108110include various failsafe mechanisms in case of malfunction. For instance, in some examples, when one or both of the main and rear hydrofoil deployment systems300,400cannot be retracted due to a malfunction, the craft100is configured to jettison the malfunctioning assembly. In this regard, some examples of the main and/or rear hydrofoil assemblies108,110are coupled to the hull102by a releasable latch. Some examples of the control system of the craft100are configured to identify a retraction malfunction (e.g., based on data received from the positional sensors310) and responsively open the latch to release the connection between the hull102and the malfunctioning hydrofoil assembly. In some examples, the weight of the malfunctioning hydrofoil assembly is sufficient to jettison the malfunctioning hydrofoil assembly out of the hull102when the latch is opened. Some examples of the craft100include an actuator or some other mechanism to jettison the malfunctioning hydrofoil assembly out of the hull102. In some examples, the main and/or rear hydrofoil assemblies108,110are configured to break in a controlled manner upon impact with water. For instance, in some examples, a joint between the main hydrofoil struts132and the hull102and/or a joint between the rear hydrofoil struts138and the hull102is configured to disconnect when subjected to a torque significantly larger than standard operational torques at the joints. Other designs for providing controlled breaks are possible as well.

G. Control System

FIG.5illustrates an example of a control system500of the craft100. As shown, some examples of control system500include one or more processors502, data storage504, a communication interface506, a propulsion system508, actuators510, a Global Navigation Satellite System (GNSS)512, an inertial navigation system (INS)514, a radar system516, a lidar system518, an imaging system520, various sensors522, a flight instrument system524, and flight controls526. In some examples, some or all of these components communicate with one another via one or more communication links528(e.g., a system bus, a public, private, or hybrid cloud communication network, etc.)

Some examples of processors502correspond to or comprise general-purpose processors (e.g., a single- or multi-core microprocessor), special-purpose processors (e.g., an application-specific integrated circuit or digital-signal processor), programmable logic devices (e.g., a field-programmable gate array), controllers (e.g., microcontrollers), and/or any other processor components now known or later developed. Further, while the one or more processors502are illustrated as a separate stand-alone component of the control system500, it should also be understood that the one or more processors502could comprise processing components that are distributed across one or more of the other components of the control system500.

Some examples of the data storage504comprise one or more non-transitory computer-readable storage mediums that are collectively configured to store (i) program instructions executable by the one or more processors502such that the control system500is configured to perform some or all of the functions disclosed herein, and (ii) data that may be received, derived, or otherwise stored, for example, in one or more databases, file systems, or the like, by the control system500in connection with the functions disclosed herein. In this respect, the one or more non-transitory computer-readable storage mediums of data storage504may take various forms, examples of which may include volatile storage mediums such as random-access memory, registers, cache, etc. and non-volatile storage mediums such as read-only memory, a hard-disk drive, a solid-state drive, flash memory, an optical-storage device, etc. Further, while the data storage504is illustrated as a separate stand-alone component of the control system500, it should also be understood that the data storage504may comprise computer-readable storage mediums that are distributed across one or more of the other components of the control system500.

Some examples of the communication interface506include one or more wireless interfaces and/or one or more wireline interfaces, which allow the control system500to communicate via one or more networks. Some example wireless interfaces provide for communication under one or more wireless communication protocols, such as Bluetooth, WiFi (e.g., an IEEE 802.11 protocol), Long-Term Evolution (LTE), WiMAX (e.g., an IEEE 802.16 standard), a radio-frequency ID (RFID) protocol, near-field communication (NFC), and/or other wireless communication protocols. Some example wireline interfaces include an Ethernet interface, a Universal Serial Bus (USB) interface, CAN Bus, RS-485, or similar interface to communicate via a wire, a twisted pair of wires, a coaxial cable, an optical link, a fiber-optic link, or other physical connection to a wireline network.

Some examples of the propulsion system508include one or more electronic speed controllers (ESCs) for controlling the electric motor propeller assemblies116distributed across the main wing104and, in some examples, across the horizontal stabilizer124. Some examples of the propulsion system508include a separate ESC for each respective propeller assembly116, such that the control system500individually controls the rotational speeds of the electric motor propeller assemblies116.

Some examples of the actuators510include any of the actuators described herein, including (i) actuators for raising and lowering the flaps118, ailerons120, elevators126, main hydrofoil control surfaces134, and rear hydrofoil control surfaces140, (ii) actuators for turning the rudder128, the main hydrofoil control surfaces134positioned on the main hydrofoil struts132, and the rear hydrofoil control surfaces140positioned on the rear hydrofoil strut138, (iii) actuators for retracting and extending the main hydrofoil assembly108and the rear hydrofoil assembly110, and/or (iv) actuators for performing the various other disclosed actuations of the main hydrofoil assembly108and the rear hydrofoil assembly110. Each of the actuators described herein may include any actuators now known or later developed capable of performing the disclosed actuation. Some examples of the actuators correspond to linear actuators, rotary actuators, hydraulic actuators, pneumatic actuators, electric actuators, electro-hydraulic actuators, and mechanical actuators. Some examples of the actuators correspond to electric motors, stepper motors, and hydraulic cylinders. Other examples are contemplated herein as well.

Some examples of the GNSS system512are configured to provide a measurement of the location, speed, altitude, and heading of the craft100. The GNSS system512includes one or more radio antennas paired with signal processing equipment. Data from the GNSS system512may allow the control system500to estimate the position and speed of the craft100in a global reference frame, which can be used for route planning, operational envelope protection, and vehicle traffic deconfliction by both understanding where the craft100is located and comparing the location with known traffic.

Some examples of the INS514include motion sensors, such as angular and/or linear accelerometers, and rotational sensors, such as gyroscopes, to calculate the position, orientation, and speed of the craft100using dead reckoning techniques. In some examples, one or more of these components are used by the control system to calculate actuator outputs to stabilize or otherwise control the vehicle during all modes of operation.

Some examples of the radar system516include a transmitter and a receiver. The transmitter may transmit radio waves via a transmitting antenna. The radio waves reflect off an object and return to the receiver. The receiver receives the reflected radio waves via a receiving antenna, which may be the same antenna as the transmitting antenna, and the radar system516processes the received radio waves to determine information about the object's location and speed relative to the craft100. This radar system516may be utilized to detect, for example, the water surface, maritime or wing-borne vehicle traffic, wildlife, or weather.

Some examples of the lidar system518comprise a light source and an optical receiver. The light source emits a laser that reflects off an object and returns to the optical receiver. The lidar system518measures the time for the reflected light to return to the receiver to determine the distance between the craft100and the object. This lidar system518may be utilized by the flight control system to measure the distance from the craft100to the surface of the water in various spatial measurements.

Some examples of the imaging system520include one or more still and/or video cameras configured to capture image data from the environment of the craft100. Some examples of the cameras correspond to or comprise charge-coupled device (CCD) cameras, complementary metal-oxide-semiconductor (CMOS) cameras, short-wave infrared (SWIR) cameras, mid-wave infrared (MWIR) cameras, or long-wave infrared (LWIR) cameras. Some examples of the imaging system520are configured to perform obstacle avoidance, localization techniques, water surface tracking for more accurate navigation (e.g., by applying optical flow techniques to images), video feedback, and/or image recognition and processing among other possibilities.

As noted above, some examples of the control system500include various other sensors522for use in controlling the craft100. Examples of such sensors522correspond to or comprise thermal sensors or other fire detection sensors for detecting a fire in the hull102or for detecting thermal runaway in the battery system200. As further described above, the sensors522may include position sensors for sensing the position of the main hydrofoil assembly108and/or the rear hydrofoil assembly110(e.g., sensing whether the assemblies are in a retracted or extended position). Examples of position sensors may include photodiode sensors, capacitive displacement sensors, eddy-current sensors, Hall effect sensors, inductive sensors, or any other position sensors now known or later developed.

Some examples of the sensors522facilitate determining the altitude of the craft100. For instance, some examples of the sensor522include an ultrasonic altimeter configured to emit and receive ultrasonic waves. The emitted ultrasonic waves reflect off the water surface below the craft100and return to the altimeter. The ultrasonic altimeter measures the time for the reflected ultrasonic wave to return to the altimeter to determine the distance between the craft100and the water surface. Some examples of the sensor522include a barometer for use as a pressure altimeter. The barometer measures the atmospheric pressure in the environment of the craft100and determines the altitude of the craft100based on the measured pressure. Some examples of the sensor522include a radar altimeter to emit and receive radio waves. The radar altimeter measures the time for the radio wave to reflect off of the surface of the water below the craft100to determine a distance between the craft100and the water surface. In some examples, these sensors are placed in different locations on the craft100to reduce the impact of sensor constraints, such as sensor deadband or sensitivity to splashing water.

Some examples of the control system500are configured to use one or more of the sensors522or other components of the control system500to help navigate the craft100through maritime traffic or to avoid any other type of obstacle. For example, some examples of the control system500determine the position, orientation, and speed of the craft100based on data from the INS514and/or the GNSS512, and the control system500may determine the location of an obstacle, such as a maritime vessel, a dock, or various other obstacles, based on data from the radar system516, the lidar system518, and/or the imaging system520. Some examples of the control system500determine the location of an obstacle using the Automatic Identification System (AIS). Some examples of the control system500are configured to maneuver the craft100to avoid collision with an obstacle based on the determined position, orientation, and speed of the craft100and the determined location of the obstacle by actuating various control surfaces of the craft100in any of the manners described herein.

Some examples of the flight instrument system524include instruments for providing data about the altitude, speed, heading, orientation (e.g., yaw, pitch, and roll), battery levels, or any other information provided by the various other components of the control system500.

Some examples of the flight controls526include one or more joysticks, thrust control levers, buttons, switches, dials, levers, or touch screen displays, etc. In operation, a pilot may use the flight controls526to operate one or more control surfaces (e.g., flaps, ailerons, elevators, rudder, propulsion props, etc.) of the craft100to thereby maneuver the craft100(e.g., control the direction, speed, altitude, etc., of the craft100)

In some examples, the combinations of control surfaces on the craft100used by the control system500to control operations of the craft100depends on the mode of operation of the craft100and is determined based at least in part on aspects such as vehicle position, speed, attitude, acceleration, rotational rates, and/or altitude above water. Table 1 summarizes an example of the relationship between the control surfaces and the operation mode.

In some examples, the propulsion control surfaces in the table include the propeller assembly116, as well as any propellers mounted to the hull102, main hydrofoil assembly108, or rear hydrofoil assembly110. In some examples, the aerodynamic elevator control surfaces include elevator126, the aerodynamic ailerons include ailerons120, the aerodynamic rudder includes rudder128(when not submerged), the aerodynamic flaps include flaps118, the hydrodynamic elevator includes rear hydrofoil control surfaces140, the hydrodynamic flaps include main hydrofoil control surfaces134, and the hydrodynamic rudder includes rudder128(when submerged).

In some examples, when actuating the control surfaces in the various example, operational modes identified in Table 1 above, the control system500executes different levels of stabilization along the various vehicle axes during different modes of operation. Table 2 below identifies examples of stabilization controls that the control system500applies during the various modes of operation for each axis of the craft100. Closed-loop control may comprise feedback and/or feed-forward control.

Further, in some examples, the control system500is configured to actuate different control surfaces to control the movement of the craft100about its different axes. Table 3 below identifies example axial motions that are affected by the various control surfaces of the craft100.

TABLE 3Control SurfaceAxis Control FunctionPropulsion(a)accelerate and decelerate the vehicle(b)turn the vehicle about yaw axis(c)create a rolling momentAerodynamic Elevator(a)create a pitch up or pitch down momentAerodynamic Ailerons(a)create a rolling moment(b)increase lift on aerodynamic wing(c)create a pitch-down momentAerodynamic Rudder(a)create a yawing momentAerodynamic Flaps(a)increase lift on aerodynamic wing(b)create a pitch-down momentHydrodynamic Elevator(a)create a pitch moment(b)generate heave force on rear hydrofoilHydrodynamic Flaps(a)generate heave force on main hydrofoilHydrodynamic Rudder(a)create a yaw moment

III. Example Modes of Operation

FIG.6Aillustrates an example of the craft100when the craft100is operating in a hull-borne mode. During this mode, the craft100is docked and floating on the hull102, with the buoyancy of the outriggers114providing for roll stabilization of the craft100. While docked, the battery system200of the craft100may be charged. In some examples, rapid charging is aided by an open or closed-loop water-based cooling system. In some examples, the surrounding body of water is used in the loop or as a heat sink. In some examples, the craft100includes a heat sink integrated into the hull102for exchanging heat from the battery system200to the surrounding body of water. In other examples, the heat sink is located offboard in order to reduce the mass of the craft100.

Additionally, in some examples, the propeller assemblies116are folded in a direction away from the dock while the craft100is docked to help avoid collision with nearby structures or people. This folding may be actuated in various ways, such as by metal spring force, hydraulic pressure, electromechanical actuation, or centrifugal force due to propeller rotation. Other examples are possible as well. Further, in some examples, the main hydrofoil assembly108and the rear hydrofoil assembly110are retracted (or partially retracted) to avoid collisions with nearby underwater structures.

In some examples, when the craft100is ready to depart, the craft100uses its propulsion systems, including the propeller assemblies116and/or the underwater propulsion system (e.g., one or more propellers mounted to the hull102, the main hydrofoil130, and/or the rear hydrofoil136), to maneuver away from the dock while remaining hull-borne. In some examples, the main hydrofoil assembly108and the rear hydrofoil assembly110remain retracted (or partially retracted) during this maneuvering to reduce the risk of hitting underwater obstacles near docks or in shallow waterways. However, when there is a limited risk of hitting underwater obstacles, the craft100may partially or fully extend the main hydrofoil assembly108and/or the rear hydrofoil assembly110. With the main hydrofoil assembly108and/or the rear hydrofoil assembly110extended, the craft100actuates the main hydrofoil control surfaces134and/or the rear hydrofoil control surfaces140to improve maneuverability as described above.

In some examples, at low speeds during hull-borne operation, the control system500controls the position and/or rotation of the craft100by causing all of the propeller assemblies116to spin at the same idle speed, but with a first subset spinning in a forward direction and a second subset spinning in a reverse direction. For instance, in some examples, the control system500causes propeller assemblies116a,116c,116f, and116hto idle in reverse and propeller assemblies116b,116d,116e, and116gto idle forward. In this arrangement, the control system500causes the craft100to make various maneuvers without having to change the direction of rotation of any of the propeller assemblies116. For instance, to induce a yaw on the craft100, in some examples, the control system500increases the speed of the reverse propeller assemblies on one side of the main wing104while increasing the speed of the forward propeller assemblies on the other side of the main wing104and without causing any of the propeller assemblies to transition from forward to reverse or from reverse to forward. For example, idling the propellers at a nominal RPM may allow for a faster response in generating a yaw moment on the craft100because the propellers required for generating the yaw moment do not have to increase from zero RPM to the desired RPM value. They can spin from the idle RPM to the desired RPM value.

FIG.6Billustrates an example of the craft100when the craft100is operating in hydrofoil-borne maneuvering mode. During this mode, the craft100is configured to, for example, move through harbors and crowded waterways at speeds generally between 20-45 mph. In this regard, the craft100may extend the main hydrofoil assembly108and the rear hydrofoil assembly110(if not already extended) (not shown inFIG.6B) and accelerate using the previously described propulsion system towards a desired takeoff speed. During acceleration, the craft100reaches a speed at which the main hydrofoil assembly108and the rear hydrofoil assembly110alone support the weight of the craft100, and the hull102is lifted above the surface of the water (e.g., by 3-5 ft) so that the hull is clear of any surface waves. After the hull102leaves the surface of the water, the drag forces exerted on the craft100drop significantly, and the amount of thrust required to maintain acceleration can be reduced. Therefore, in some examples, after the hull102has left the water, the control system500reduces the speed of the propeller assemblies116to lower the thrust of the craft100.

Some examples of the control system500sustain this operational mode by actively controlling the pitch and speed of the craft100so that the main hydrofoil assembly108and the rear hydrofoil assembly110continue to entirely support the weight of the craft100. In this regard, some examples of the control system500actuate the main hydrofoil control surfaces134and/or the rear hydrofoil control surfaces140and/or the propulsion system to stabilize the attitude of the craft100to maintain the desired height above the surface of the water, vehicle heading, and vehicle forward speed. In this regard, some examples of the control system500are configured to detect various changes in the yaw, pitch, or roll of the craft100based on data provided by the INS514and to make calculated actuations of the main hydrofoil control surfaces134and/or the rear hydrofoil control surfaces140to counteract the detected changes.

FIG.7Aillustrates an example of the craft100when the craft100is operating in hydrofoil-borne takeoff mode. During this mode, the craft100is configured to, for example, move through open waters and obtain speeds generally between 40-50 mph to facilitate generating the lift required to become wing-borne.

Referring toFIG.7A, aero lift, LW, generally represents the lift generated by the main wing104of the craft100but can also include the lift generated by other surfaces such as the tail wing, hull, or propulsive devices such as props, rotors, jets, etc. LFgenerally corresponds to the lift generated by one or more hydrofoils130,136of the craft100, where LFFcorresponds to the lift generated by the front foil and the LFRcorresponds to the lift generated by the rear foil. WCRAFTcorresponds to the force of gravity exerted on the craft100and is also referred to as the weight of the craft. During steady state operation, WCRAFTgenerally corresponds to LW+LFR+LFFwhich also corresponds to LNET. Throughout the description, the term LFis generally understood to correspond to LFR+LFF.

As previously noted, some experimental craft developed by Applicant that include aero foils were unable to achieve the lift required to sustain flight. In these experimental craft, in an attempt to become airborne, the craft100would ramp up to a speed at which point the hydrofoil would breach the surface of the water, as WCRAFT<LWLF, and LF>0, resulting in LW<WCRAFT. However, in order to takeoff from the water's surface, the aero lift must be greater than or equal to the weight of the craft, however prior to takeoff, the hydrofoils are still under the water's surface, and up until takeoff, have been generating lift as the aerodynamic lift has been insufficient for takeoff up until this point. If the hydro lift and the aero lift sum to greater than the weight of the craft, the vehicle will accelerate upwards and potentially create a premature takeoff condition (prior to condition C0inFIG.7B) as the aero lift, LW, generated by the wings, etc., of the craft100would be insufficient to sustain flight, and, as a result, the craft100would come back down and breach the water, ultimately preventing takeoff. The techniques disclosed below ameliorate these problems by controlling the hydrofoil lift vector, LF, specifically by generating downward forces of one or more hydrofoils130,136of the craft100to keep the hydrofoils130,136submerged until after the upwards aero lift, LW, is sufficient to allow the craft100to sustain flight.

In some examples, the lift LFis in the downward direction, and is introduced via the hydrofoil(s) as LWincreases beyond WCRAFTwhile the craft100is increasing in speed in anticipation of takeoff. This allows the craft100to generate a greater overall aero lift, LW, prior to actual takeoff than would otherwise be possible. Then, at the appropriate time (e.g., when LWreaches some predetermined threshold such as the weight of the craft100or some margin thereof), the negative lift, LF, can be “released” from the craft100, and the craft100can, as a result, proceed to become wing-borne.

FIG.7Bis an example of a graph700that relates these aspects. The relationships shown in the graph700and the ways in which various lift forces, thresholds, etc., are depicted are merely examples and are provided to aid understanding of the various operations and procedures described herein. As shown, the net lift, LNET, on the craft100initially corresponds to the combination of the aero lift, LW, generated by the wing (e.g., main wing, tail wing, etc.) and the lift, LF, generated by the hydrofoils130,136(e.g., LNET=LW+LF). On the left side of the graph700, the speed of the craft100is such that LNETis sufficient to allow the craft100to operate in hydrofoil-borne maneuvering mode but is insufficient to allow the craft100to become wing-borne. Moving to the right of the graph700as speed increases, LWincreases with increased craft100water speed. To maintain ride height and prevent the hydrofoils130,136from breaching the water surface, LFis reduced in proportion to an increase in LW. For example, LFis adjusted with the speed of the craft100to maintain LNETat a margin equal to the weight, WCRAFT, of the craft100, or small deviations about equal to control ride height. The overall lift provided by the hydrofoils130,136may decrease at the same rate at which lift from the wing is increased towards zero or even become negative with increased speed. For example, just before the speed of the craft100reaches the speed associated with condition C0, LFmay be reduced to zero. The conditions at C0(e.g., speed of the craft100, angle of attack of craft100, deflection angles of control surfaces, angle of incidence of hydrofoils, etc.) may be such that LFmay be zero or close to zero. At C0, the aero lift, LW, generated by the main wing105may be expected to be able to transition the craft100to a wing-borne mode of operation if the downwards hydrofoil lift, LF, were to be removed as LW=WCRAFT. Accordingly, at some time and/or increased speed after this point (e.g., speed associated with condition C1) where LW>WCRAFT, LFmay be gradually or abruptly removed/released. This, in turn, allows LNETto approximately equal to or greater than WCRAFTwhich allows the craft100to take off and become wing-borne.

While not shown in the graph, in some examples, LFis not removed/released as described. Rather, as the craft100continues to accelerate, the downwards hydrofoil lift, LF, increases to a maximum downwards amount (e.g., a predetermined maximum amount and/or a maximum amount achievable due to the limitations of the control capabilities of the hydrofoil). As the aero lift, LW, generated by the main wing105continues to increase past this maximum amount of downwards hydrofoil lift, LF, LNETincreases in the upwards direction beyond WCRAFTand the craft100is pulled from the water. This, in turn transitions the craft100to a wing-borne mode of operation.

FIGS.8A-8Gillustrate examples of ways in which one or more of the hydrofoils130,136of the craft100can be articulated to control the lift, LF, generated by the hydrofoils130,136. The hydrofoil130in the figures represents the main hydrofoil130. However, the aspects described herein apply to the rear hydrofoil136or other hydrofoil configurations that use a different number of hydrofoils. Further, additional/alternative aspects may be capable of further controlling the lift generated by the hydrofoils, and such aspects may be implemented additionally or alternatively to the specific aspects described in connection withFIGS.8A-8G.

FIGS.8A-8Cillustrate the articulation of one or more control surfaces134of the hydrofoil130of the craft100to control the lift, LF, generated by the hydrofoil130. As noted above, some examples of the hydrofoils130,136include one or more control surfaces134,140that are hingedly connected to trailing edges of the hydrofoils130,136. These control surfaces134,140operate in a similar manner as the flaps118, ailerons120, and/or elevators on the main wing104of the craft100and the elevators126on the tail106of the craft100. Some examples of these control surfaces134,140are operated via one or more actuators which are in turn controlled by the control system500. As the craft100accelerates through the water, the control system500can adjust/maintain the ride height of the craft100(e.g., the height of the craft100above the water surface) by adjusting the respective position (e.g., deflection angles) of the control surfaces134,140. For example, as shown inFIGS.8A-8C, a control surface134of the main hydrofoils130can be rotated from the initial position shown inFIG.8Ato the upward direction shown inFIG.8Bto generate negative lift, LF(or reduce positive lift, LF). The control surface134of the main hydrofoil130can be rotated in the downward direction shown inFIG.8Cto generate positive lift, LF(or reduce negative lift, LF).

FIGS.8D-8Eillustrate the articulation of the angle of incidence of the hydrofoil130of the craft100to control the lift, LF, generated by the hydrofoil130. As previously noted, some examples of the craft100include one or more actuators for controlling the angle of incidence of the main hydrofoil130and/or the rear hydrofoil136(i.e., rotating the main hydrofoil130and/or the rear hydrofoil136around the pitch axis). As shown inFIG.8D, the angle of incidence of the main hydrofoil130can be reduced by rotating the main hydrofoil130clockwise from the initial position shown inFIG.8A(i.e., rotated downward in the direction of travel) to generate negative lift, LF(or reduce positive lift, LF). As shown inFIG.8E, the angle of incidence of the main hydrofoil130can be increased by rotating the main hydrofoil130counterclockwise from the initial position (i.e., rotated upward in the direction of travel) to generate positive lift, LF(or reduce negative lift, LF).

FIGS.8F-8Gillustrate the articulation of the angle of the strut132of the hydrofoil130of the craft100to control the lift, LF, generated by the hydrofoil130. As previously noted above, some examples of the craft100include one or more actuators for controlling the angle of main hydrofoil struts132and the rear hydrofoil struts138that couple the corresponding main hydrofoil130and/or the rear hydrofoil136to the hull102, respectively. As shown inFIGS.8F and8G, the angle of incidence of the main hydrofoil130can be increased or decreased by rotating the main hydrofoil130counterclockwise as shown inFIG.8F(i.e., rotated upwards in the direction of travel) or clockwise as shown inFIG.8G(i.e., rotated downwards in the direction of travel) from the initial position shown inFIG.8Ausing these actuators to generate positive lift, LF(or reduce negative lift, LF) or to generate negative lift, LF(or reduce positive lift, LF), respectively. While the various ways in which the main hydrofoil130can be articulated are shown separately inFIGS.8A-8G, it should be understood that any combination of these articulation procedures can be used to control the lift, LF, generated by the main hydrofoil130and/or the rear hydrofoil136.

FIGS.9A and9Billustrate examples of operations900,950performed by the craft100when operating in the hydrofoil-borne takeoff mode. In some examples, the control system500of the craft100is configured to control various components of the craft100to facilitate performance, by the craft100, of these operations.

The operations900inFIG.9Afacilitate transitioning the craft100to a wing-borne mode of operation without “holding” the craft100in the water. That is, the overall lift, LF, generated by the hydrofoils130,136tends to remain in the upward/positive direction so that the craft is not “held” in the water past the point at which the craft100can take off based on the natural amount of lift generated by the wings of the craft100, which will lift the craft100out of the water due to the net upwards force.

Referring toFIG.9A, the operations at block905involve accelerating the craft100. For instance, the propulsion system508of the craft100is controlled to begin to accelerate the craft100to a sufficient speed to transition to wing-borne operation.

The operations at block907involve adjusting one or more control surfaces of the craft100to achieve and maintain a target pitch or angle of attack of the craft100for takeoff. In an example, the target pitch is between about 0-5 degrees. In some examples, the pitch of the craft100is actively monitored and controlled to maintain the pitch at the target pitch while craft100accelerates. In some examples, one or more control surfaces of one or more of the main hydrofoil130, the rear hydrofoil136, and the main wing104are adjusted relative to one another to maintain the pitch of the craft100at the target pitch as the craft100accelerates. The pitch target for the craft100while riding on the main hydrofoil130and the rear hydrofoil136can be actively adjusted to increase or decrease the angle of attack of the aero wing, and thus, control the aero lift, LW. In some examples, this is accomplished by adjusting the control surfaces on the main hydrofoil130and/or the rear hydrofoil136to create the same lift LFat a different operational angle of attack

The operations at block910involve adjusting one or more control surfaces of the craft100to maintain the ride height of the craft100while in the hydrofoil-borne mode of operation. For instance, as the craft100accelerates through the water, the control system500is configured to adjust/maintain the ride height of the craft100(e.g., the height of the craft100above the water surface) by adjusting the respective position (e.g., deflection angles) of the control surfaces134,140of the main hydrofoil130and/or rear hydrofoil136and/or the overall angle of attack of the main hydrofoil130and/or rear hydrofoil136, as shown and described above with reference toFIGS.8A-8G. For example, a control surface134of the main hydrofoil130can be rotated in the upward direction relative to the direction of travel to decrease the lift, LF, generated by the main hydrofoil130and can be rotated in the downward direction relative to the direction of travel to increase the lift, LF, generated by the main hydrofoil130. Similar operations can be performed by the rear hydrofoil136.

If at block915, the aero lift, LW, acting on the craft100has not reached a threshold level that is sufficient to allow the craft100to become wing-borne and sustain wing-borne flight, the operations repeat from block905. In some examples, the threshold level corresponds to the weight of the craft100, WCRAFT, or a margin above the weight of the craft100, WCRAFT(e.g., WCRAFT+10% to allow the craft to accelerate upwards away from the water's surface). In some examples, the control system500is configured to determine or infer the aero lift, LW, based at least in part on the speed of the craft100, an angle of attack of the main wing104, and respective positions of control surfaces (e.g., flaps118, ailerons120, elevator, rudder, etc.) of the main wing104(and/or the tail wing) of the craft100, the density of the air etc. In some examples, the control system500is configured to determine or infer the aero lift, LW, based at least in part on a sensed load force imparted on one or both of the hydrofoil assemblies108,110(e.g., sensed via one or more load sensors). In some examples, the control system500is configured to determine or infer the aero lift, LW, based at least in part on the speed of the craft100, an angle of attack of the main wing104, and respective positions of control surfaces (e.g., main foil control surfaces134) of the main hydrofoil108(and/or the rear hydrofoil110control surfaces140) of the craft100, the density of the water, etc. In some examples, the control system500is configured to determine or infer the aero lift, LW, based at least in part on an amount of unlock and/or back-drive current used to drive or maintain the main hydrofoil struts132and/or the rear hydrofoil struts138in a particular position. For instance, in some examples, an increase in the amount of current to actuators of the main hydrofoil struts132and/or the rear hydrofoil struts138indicates an increased load imparted on the main hydrofoil struts132and/or the rear hydrofoil struts138. In some examples, the control system500computes the aero lift, LW, acting on the craft100according to various functions, lookup tables, etc., that relate the aspects to the aero lift, LW.

If the aero lift, LW, acting on the craft100has reached the threshold level to become wing-borne and sustain wing-borne flight, then the operations at block920are performed. The operations at block920involve allowing the craft100to naturally take off based on the pitch that was targeted at block907. That is, the craft100can take off without changing the angle of attack/pitch of the craft100. In some examples, the articulations of the main hydrofoil130and/or rear hydrofoil136as configured at block910to maintain ride height are maintained as the craft100takes off. That is, the respective angles of incidence of the main hydrofoil130and/or rear hydrofoil136, deflection angles of the control surfaces134,140of the main hydrofoil130and/or rear hydrofoil136, etc., are not actively or passively adjusted to different positions as the craft100takes off from the water.

Alternatively, at block925, the angle of attack/pitch of the craft100can be actively adjusted to generate additional lift. (See block985and description thereof)

The operations950inFIG.9Bfacilitate transitioning the craft100to the wing-borne mode of operation by actively controlling one or more of the main hydrofoil130and rear hydrofoil136to generate a negative lift, LF, that “holds” the craft100within the water until the aero lift, LW, generated by the wings(s) is sufficient for the craft100to become wing-borne and sustain wing-borne flight. The operations950can be more clearly understood with reference to the graph700inFIG.7B.

Referring toFIG.9B, the operations performed at blocks955-960are generally the same as those operations performed at blocks905-910ofFIG.9A. For example, the operations at block955involve accelerating the craft100towards a takeoff speed (e.g., 45 mph). The operations at block957involve adjusting one or more control surfaces of the craft100to maintain a target pitch or angle of attack of the craft100. In an example, the target pitch is between about 0-5 degrees. The operations at block960involve maintaining the ride height of the craft100during hydrofoil-borne operation while the craft is accelerating during the process of transitioning from hydrofoil-borne operation to wing-borne operation.

The operations at block965involve determining whether the aero lift, LW, generated by the main wing104(and/or tail wing, hull, etc.) has reached a threshold level that is sufficient to allow the craft100to become wing-borne and sustain the wing-borne mode of operation. In some examples, the threshold level corresponds to the weight of the craft100, WCRAFT, or a margin above the weight of the craft100, WCRAFT, (e.g., WCRAFT+10% to accommodate passengers and cargo). In some examples, the control system500is configured to determine or infer the aero lift, LW, based at least in part on the speed of the craft100, an angle of attack of the main wing104, and respective positions of control surfaces (e.g., flaps118, ailerons120, elevator, rudder, etc.) of the main wing104(and/or the tail wing) of the craft100, the density of the air etc. In some examples, the control system500is configured to determine or infer the aero lift, LW, based at least in part on a sensed load force imparted on one or both of the hydrofoil assemblies108,110(e.g., sensed via one or more load sensors). In some examples, the control system500is configured to determine or infer the aero lift, LW, based at least in part on the speed of the craft100, an angle of attack of the main wing104, and respective positions of control surfaces (e.g., main foil control surfaces134) of the main hydrofoil wing108(and/or the rear hydrofoil110control surfaces140) of the craft100, the density of the water, etc. In some examples, the control system500is configured to determine or infer the aero lift, LW, based at least in part on an amount of unlock and/or back-drive current used to drive or maintain the main hydrofoil struts132and/or the rear hydrofoil struts138in a particular position. For instance, in some examples, an increase in the amount of current to actuators of the main hydrofoil struts132and/or the rear hydrofoil struts138indicates an increased load imparted on the main hydrofoil struts132and/or the rear hydrofoil struts138. In some examples, the control system500computes the aero lift, LW, acting on the craft100according to various functions, lookup tables, etc., that relate the aspects to the aero lift, LW.

If at block965, the aero lift, LW, has not reached the threshold level, the operations continue from block955. The left side of the graph700ofFIG.7B(i.e., left of C0) characterizes the state of the various lift forces acting on the craft100during the operations performed above. For example, as the craft100accelerates, the hydrofoil lift, LF, generated by one or more of the hydrofoils130,136is positive but is controlled to decrease the hydrofoil lift, LF, to counteract increases in the aero lift, LW, generated by the main wing104. This results in a net lift, LNET, that is sufficient to maintain the desired ride height of the craft100during hydrofoil-borne operation.

If at block965, the aero lift, LW, reaches the first threshold level, the operations at block970are performed. The operations at block970involve generating or increasing the negative lift, LF, generated by one or more of the main hydrofoil130and the rear hydrofoil136to prevent the craft100from becoming wing-borne due to the main wing104and other aerodynamic surfaces. For instance, as noted in block960, as the craft100accelerates through the water while hydrofoil-borne, the control system500is configured to adjust/maintain the ride height of the craft100(e.g., the height of the craft100above the water surface) by adjusting control surface deflections of the control surfaces134,140of the main hydrofoil130and/or rear hydrofoil136and/or the overall angle of attack of the main hydrofoil130and/or rear hydrofoil136, as shown inFIGS.8A-8G. As the speed of the craft100increases and the aero lift, LW, generated by the wing(s) increases beyond the point required to initially achieve wing-borne flight (e.g., the weight of the craft100, WCRAFT), the control system500causes one or more of the main hydrofoil130and the rear hydrofoil136to generate a force in the downward direction to maintain the proper force balance to maintain the desired ride height. At this stage, the deflection of one or more of the control surfaces134,140of the main hydrofoil130and/or the rear hydrofoil136and/or the overall angle of attack of the main hydrofoil130and/or rear hydrofoil136are configured to generate an overall negative lift, LF, that “holds” the hydrofoils130,136in the water, thereby forcing the craft100to remain hydrofoil-borne despite the wing(s) generating a lift force greater than the weight of the craft, WCRAFT, and thus sufficient lift to achieve wing-borne flight.

The portion of the graph700ofFIG.7Bbetween C0and C1characterizes the state of the various lift forces acting on the craft100during the operations performed in block970. For example, when the speed of the craft100reaches the speed greater than condition C0, the aero lift, LW, generated by the main wing104equals the weight of the craft, WCRAFT. Therefore, the craft100should be able to achieve flight. However, the hydrofoil lift, LF, is controlled to generate a negative lift, LF, such that the net lift, LNET, acting on the craft100keeps the craft100in hydrofoil-borne operation. Thus, the craft100is “held” in the water by the negative lift, LFat the desired ride height.

At block975, if the aero lift, LW, has not reached the second threshold level, the operations continue from block955. For example, referring toFIG.7B, if the aero lift, LW, has not reached the lift associated with condition C1, the operations continue from955. An example of the second threshold level corresponds to the weight of the craft plus some margin (e.g., WCRAFT+10% or some other margin). The aero lift, LW, acting on the craft100can be determined or inferred as described above with reference to block965and the first threshold level.

In some examples, the determination as to whether the threshold above has been passed is based on whether the speed of the craft is a particular margin higher (e.g., 10% higher or some relative amount higher) than the speed of the craft100associated with the first threshold level (e.g., fromFIG.7B, condition C1). In some examples, the determination as to whether the threshold above has been passed is based on the amount of time that has elapsed since the first threshold was passed (e.g., 10 seconds later after the first threshold passed). In some examples, the determination that the second threshold level has been reached is based on an indication from an operator (e.g., the pilot) of the craft100. That is, the operator can override any other determinations and indicate to the control system500whether the second threshold level has or has not been reached.

If at block975, the aero lift, LW, has reached the second threshold level, final takeoff operations are performed. Some examples of the final takeoff operations include the operations at block980and block985. The operations at block980involve decreasing the negative lift, LF, generated by one or more hydrofoils of the craft100. That is, the “hold” is gradually, passively, or abruptly released. In some examples, this involves actively controlling the deflection angles of one or more of the control surfaces134,140of the main hydrofoil130and/or the rear hydrofoil136and/or the overall angle of attack of the main hydrofoil130and/or rear hydrofoil136to gradually decrease the overall negative lift, LF. In some examples, this involves removing all control of the deflection angles of one or more of the control surfaces134,140of the main hydrofoil130and/or the rear hydrofoil136and/or the overall angle of attack of the main hydrofoil130and/or rear hydrofoil136to allow these components to passively move to their respective natural states to decrease the overall negative lift, LF. In some embodiments, allowing these hydrofoil components to passively move to their natural states to decrease the overall negative lift includes gradually reducing the power applied to the electric actuators that control the positions of the hydrofoil components.

The portion of the graph700ofFIG.7Bwhere to the right of condition C1characterizes the state of the various lift forces acting on the craft100during the operations performed in block980. For example, when the speed of the craft100reaches the speed associated with condition C1, the aero lift, LW, generated by the main wing104is more than sufficient to achieve sustained wing-borne flight. As such, the negative lift, LF, generated by one or more of the hydrofoils is gradually (in a controlled manner), naturally/passively, or abruptly (in a controlled manner) reduced to zero such that the net lift, LNET, acting on the craft100becomes equal to the aero lift, LW, and the craft100becomes wing-borne.

Additionally, at block985, the angle of attack/pitch of the craft100can be actively adjusted to generate additional lift. In this regard, in some examples, in addition to (or as an alternative to) gradually, passively, or abruptly releasing the “hold” generated by the one or more hydrofoils of the craft100, the angle of attack/pitch of the craft100can be actively adjusted to generate sufficient lift to overcome the “hold” created by the negative lift, LF, of the hydrofoil to bring the craft100airborne. In this regard, in some examples, once the control system500determines that the craft100has reached the desired takeoff speed or desired main wing lift has been achieved, the control system500deploys the flaps118(and the ailerons120if configured as flaperons), causing the main wing104to generate additional lift. In some examples, the control system500additionally actuates the rear hydrofoil control surfaces140and/or the elevators126to pitch the craft100upward and increase the angle of attack of the main wing104and the hydrofoil assemblies108,110. In this configuration, the main wing104and hydrofoil assemblies108,110create enough lift to accelerate the craft100upwards until the hydrofoil assemblies108,110breach the surface of the water and the entire weight of the craft100is supported by the lift of the main wing104.

In some examples, when performing this transition from hydrofoil-borne operation to wing-borne operation, the control system500quickly deploys the flaps118(and the ailerons120if configured as flaperons) over a very short period of time (e.g., in less than 1 second, less than 0.5 seconds, or less than 0.1 seconds). Quickly deploying the flaps118(and ailerons120) in this manner creates even further additional lift on the main wing104that helps “pop” the craft100out of the water and into wing-borne operation.

Additionally, in some examples, during the transition from hydrofoil-borne operation to wing-borne operation, the control system500actuates various control surfaces of the craft100to balance moments along the pitch axis. For instance, the propeller assemblies116, the flaps118, and the drag from the hydrofoil assemblies108,110all generate nose-down moments around the center of gravity about the pitch axis during the transition. To counteract these forces, in some examples, the control system500deploys the elevator126, and the rear hydrofoil control surfaces140to generate a nose-up moment and stabilize the craft100.

Alternative examples of the final takeoff operations that do not involve releasing the “hold” described in block980are described in block990.

The operations at block990involve maintaining the negative lift, LF, generated by one or more hydrofoils130,136of the craft100. That is, rather than releasing the “hold” (as described in block980), the respective articulations of the main hydrofoil130and/or the rear hydrofoil136(e.g., the deflection angles of the control surfaces134,140, the angles of incidence of the main hydrofoil130and/or the rear hydrofoil136, etc.) are maintained. As the craft100accelerates, the lift, LF, generated by the hydrofoils130,136reaches a constant/steady downward force that is maintained for the remainder of the takeoff procedure (e.g., the summation of the aero lift, LW, the weight of the craft, WCRAFT, and the hydrofoil lift, LF, equal zero). In an example, the “steady” downward hydrofoil lift, LF, is effectively a “maximum” amount of downward hydrofoil lift, LF, that is possible to be applied as a result of the control capabilities of the hydrofoils130,136. This conceptually means that the ride height of the craft100is maintained up to the point of takeoff. As ride height is maintained and the craft100is “held” in the water as speed is increased and aero lift, LW, on the wings is increased, until the ability to apply further maintenance/downward hydrofoil lift, LF, is “saturated.”

At this stage, continued acceleration of the craft100causes a natural increase (e.g., without further articulation of the main wing control surfaces) in the aero lift, LW, and, therefore, the angle of attack of the craft100. The gradual increasing of the angle of attack of the craft100further contributes to the “saturation” of the downward lift, LF. That is, the downward lift, LF, is reduced as the angle of attack of the craft100increases.

In some examples, the angle of attack of the craft100is actively adjusted to generate additional lift as described above in block985. The increase in the angle of attack of the craft100causes the craft to rise without further increasing the downwards lift, LF, generated by the hydrofoils130,136.

FIG.11is a table1100that summarizes some examples of the procedures described above and inFIGS.9A and9Bthat facilitate foil-borne takeoff operations and the ways in which different components of the craft100can be used in these procedures to facilitate foil-borne takeoff operations. All the procedures generally involve maintaining the ride height of the craft100using the control surfaces134,140of one or more of the hydrofoils130,136as the craft100accelerates (e.g.,FIG.9A, block907).

In procedure (A), downwards lift, LF, is not introduced using the control surfaces134,140of the hydrofoils130,136or by adjusting the angle of attack of the hydrofoils130,136. In this procedure, the speed of the craft100is increased using the aero lift, LW, generated by one or more wings of the craft100until the aero lift, LW, is greater than the weight, WCRAFT, of the craft100(e.g.,FIG.9A, block905-915). At that point, the craft100can “naturally” take off without otherwise increasing the angle of attack and/or pitch of the craft100because the aero lift, LW, alone is greater than the weight of the craft (e.g.,FIG.9A, block920).

In procedure (B), downwards lift, LF, is introduced using one or more control surfaces134,140of one or more hydrofoils130,136of the craft, but the angle of attack of the hydrofoils130,136is fixed (e.g.,FIG.9B, block960). In this procedure, as the craft100accelerates, aero lift, LW, is generated by one or more of the wings. When the aero lift, LW, exceeds the weight, WCRAFT, of the craft100, the control surfaces134,140of the hydrofoils130,136are adjusted to introduce a downwards lift, LF, or “extended hold” that holds the hydrofoils130,136in the water (e.g.,FIG.9B, blocks970-975). In some examples, when the perceived aero lift, LW, generated by the wings reaches a desired threshold (e.g., above “natural” takeoff lift by some margin), the hold on the hydrofoils130,136is “released” by adjusting the control surfaces134,140of the hydrofoils130,136to reduce the downward lift, LF, and takeoff is permitted to proceed (e.g.,FIG.9B, block980). In some examples, the downwards lift, LF, is not released and instead, as the craft100continues to accelerate, the downwards lift, LF, increases to a maximum downwards amount (e.g., a predetermined amount and/or a maximum amount achievable due to the limitations of the control capabilities of the hydrofoils130,136). As the aero lift, LW, generated by the wings continues to increase and overcomes this maximum amount of downwards lift, LF, the craft100takes off from the water (e.g.,FIG.9B, block990).

Procedure (C) is similar to procedure (B), except that the pitch of the craft100is increased during takeoff to generate additional upwards lift (e.g.,FIG.9B, block985).

In procedure (D), downwards lift, LF, is introduced using one or more of the control surfaces134,140of one or more of the hydrofoils130,136and by adjusting the angle of attack of one or more of the hydrofoils130,136(e.g.,FIG.9B, block960). In this procedure, as the craft accelerates, aero lift, LW, is generated by the wings. When the aero lift, LW, exceeds the weight, WCRAFT, of the craft100, one or more of the control surfaces134,140and the angles of attack of one or more of the hydrofoils130,136are adjusted to introduce a downwards lift, LF, that holds the hydrofoils134,140in the water (e.g.,FIG.9B, blocks970-975). In some examples, the perceived aero lift, LW, generated by the wings reaches a desired threshold (e.g., above “natural” takeoff lift by some margin), the hold on the hydrofoils130,136is passively “released” by allowing the control surfaces134,140of the hydrofoils130,136and the angles of attack of the hydrofoils130,136to passively return to their respective natural positions (e.g.,FIG.9B, block980). This, in turn, reduces the downward lift, LF, and takeoff is permitted to proceed. The procedure may further involve increasing the pitch of the craft100afterward to generate additional upwards lift (e.g.,FIG.9B, block985). In some examples, the downwards lift, LF, is not released and instead, as the craft100continues to accelerate, the downwards lift, LF, increases to a maximum downwards amount (e.g., a predetermined amount and/or a maximum amount achievable due to the limitations of the control capabilities of the hydrofoils130,136). As the aero lift, LW, generated by the wings continues to increase and overcomes this maximum amount of downwards lift, LF, the craft100takes off from the water (e.g.,FIG.9B, block990).

Procedure (E) is similar to procedure (D) except that when the perceived aero lift, LW, generated by the wings reaches a desired threshold (e.g., above “natural” takeoff lift by some margin), the hold on the hydrofoils130,136is actively “released” in a controlled manner by controlling the control surfaces134,140of the hydrofoils130,136and the angles of attack of the hydrofoils130,136to gradually or abruptly return to their respective natural positions (e.g.,FIG.9B, block980, such as zero deflection).

In some of the procedures above, the downwards lift, LF, that “holds” the craft100in the water is released when the aero lift, LW, reaches a particular takeoff threshold. In some other examples, the articulation of the hydrofoils130,136(e.g., the control surfaces134,140, respective angles of incidence, etc.) may not be released. In these examples, the amount of downward hydrofoil lift, LF, that can be generated by the hydrofoils130,136eventually saturates (e.g., reaches a maximum amount).

In some examples, continued acceleration of the craft100causes a natural increase (e.g., without further articulation of the main wing control surfaces) in aero lift, LW, and, therefore, the angle of attack of the craft100. The gradual increasing of the angle of attack of the craft100contributes to further “saturation” of the downward hydrofoil lift, LF, as the craft takes off from the water. In some examples, the angle of attack of the craft100is actively adjusted to generate additional aero lift, LW.

In some examples, when LWis greater than the weight, WCRAFT, of the craft100, the downward hydrofoil lift, LF, is released by initiating ventilation of one or more of the hydrofoils130,136which creates a loss of downward lift, LF, allowing the craft100to take off.

FIG.10illustrates an example of the craft100after becoming wing borne. In some examples, once the transition from hydrofoil-borne operation to wing-borne operation is complete, the control system500causes the main hydrofoil deployment system300and the rear hydrofoil deployment system400to respectively retract the main hydrofoil assembly108and the rear hydrofoil assembly110. In some examples, the control system500initiates this retraction as soon as the hydrofoil assemblies108,110are clear of the water to reduce the chance of the hydrofoil assemblies108,110reentering the water. The control system500may determine that the hydrofoil assemblies108,110are clear of the water in various ways. For instance, in an example, the control system500makes such a determination based on a measured altitude of the craft100(e.g., based on data provided by the radar system516, the lidar system518, and/or the other sensors522described above for measuring an altitude of the craft100). In another example, the sensors522may further include one or more conductivity sensors, temperature sensors, pressure sensors, strain gauge sensors, or load cell sensors arranged on the hydrofoil assemblies108,110, and the control system500may determine that the hydrofoil assemblies108,110are clear of the water-based on data from these sensors.

Once the craft100is clear of the water, the control system500continues to accelerate the craft100to the desired cruise speed by controlling the speed of the propeller systems116. In some examples, the control system500retracts the flap systems when the craft100has achieved sufficient airspeed to generate enough lift to sustain altitude without them and actuates various control surfaces of the craft100and/or applies differential thrust to the propeller systems116to perform any desired maneuvers, such as turning, climbing, or descending, and to provide efficient lift distribution. While in wing-borne mode, the craft100can fly both low over the water's surface in ground-effect or above ground-effect depending on operational conditions and considerations.

E. Return to Hull-Borne Operation

To facilitate transitioning from wing-borne to hull-borne mode of operation (SeeFIG.6A), the control system500determines that the hydrofoil assemblies108,110are fully retracted so that the craft100may safely land on its hull102. In some examples, the control system500additionally determines and suggests the desired landing direction and/or location-based on observed, estimated, or expected water surface conditions (e.g., based on data from the radar system516, the lidar system518, the imaging system520, or other sensors522).

The control system500initiates deceleration of the craft100, for instance, by reducing the speeds of the propeller systems116until the craft100reaches a desired landing airspeed. During the deceleration, the control system500may deploy the flaps118to increase lift at low airspeeds and/or to reduce the stall speed. Once the craft100reaches the desired landing airspeed (e.g., approximately 50 knots), the control system500reduces the descent rate (e.g., to be less than approximately 200 ft/min). As the craft100approaches the surface of the water (e.g., once the control system500determines that the craft100is within 5 feet of the water surface), the control system500further slows the descent rate to cushion the landing (e.g., to be less than approximately 50 ft/min). As the hull102of the craft100impacts the surface of the water, the control system500reduces thrust, and the craft100rapidly decelerates due to the presence of hydrodynamic drag, the reduction in forward thrust, and the reduction or elimination of blowing air over the wing which significantly reduces lift causing the vehicle to settle into the water. The hull102settles into the water as the speed is further reduced until the craft100is stationary.

In some examples, after the craft100is settled in the water, the craft100is transitioned back to hydrofoil-borne maneuvering mode (SeeFIG.6B) by extending the hydrofoil assemblies108,110to transition from hull-borne operation to hydrofoil-borne operation in the same manner as described above. In some examples, the control system500then sustains the hydrofoil-borne mode at the fifth stage and maneuvers the craft100into port while keeping the hull102insulated from surface waves. The control system500then reduces the thrust generated by the propeller assemblies116to lower the speed of the craft100until the hull102settles into the water, thereby transitioning that craft back to hull-borne operation at the sixth stage. The control system500then retracts the hydrofoil assemblies108,110and performs the hull-borne operations described above to maneuver the craft100into a dock for disembarking passengers or goods and recharging the battery system200.

IV. Examples of Operations

FIG.12illustrates examples of operations1200that facilitate operating a craft100according to some embodiments, including operating the craft100to facilitate transitioning from hydrofoil-borne to wing-borne modes. In some embodiments, a control system of the craft (e.g., control system500) performs one or more of the functions shown inFIG.12.

The operations at block1205involve determining upwards aero lift (FIG.7A, LW), generated by one or more wings104of the craft100as the craft100accelerates over the water while the craft100is in hydrofoil-borne operation. (See alsoFIG.9B, block965and description thereof).

The operations at block1210involve adjusting, based on the determined upwards aero lift, LW, downwards hydrofoil lift (FIG.7A, LF) generated by one or more hydrofoils130,136of the craft100to maintain the one or more hydrofoils130,136at least partially submerged in the water, thereby causing the craft100to remain in a hydrofoil-borne maneuvering mode of operation (FIG.6B) despite upwards aero lift, LW, generated by the wing(s)104that would otherwise cause the hydrofoil(s)130,136to breach the surface of the water and the craft100to become wing-borne. (See alsoFIG.9B, block970;FIG.11, procedures B-E; and description thereof).

The operations at block1115involve, after determining that the upwards aero lift, LW, generated by the wing(s)104is sufficient to allow the craft100to sustain flight, decreasing the amount of downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136to allow the hydrofoil(s)130,136to exit the water. (See alsoFIG.9B, block975;FIG.11, procedures B-E; and description thereof).

In some examples, adjusting the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136involves adjusting the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136to both (i) allow the hull of the craft100to lift above the water as the craft100accelerates and (ii) maintain the hydrofoil(s)130,136at least partially submerged in the water, thereby causing the craft100to remain in the hydrofoil-borne maneuvering mode of operation. (See alsoFIG.9B, block960;FIG.11, procedures B-E; and description thereof).

In some examples, adjusting the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136involves increasing the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136in proportion to an increase in the upwards aero lift, LW, generated by the wing(s)104. (See alsoFIG.9B, block970;FIG.11, procedures B-E; and description thereof).

In some examples, adjusting the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136involves increasing the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136to maintain a ride height of the craft100.

In some examples, determining the upwards aero lift, LW, generated by the wing(s)104involves determining a speed of the craft100and determining the upwards aero lift, LW, generated by the wing(s)104based at least in part on the determined speed of the craft100. (See alsoFIG.9B, blocks965and975;FIG.11, procedures B-E; and description thereof).

In some examples, determining the upwards aero lift, LW, generated by the wing(s)104involves determining an angle of attack of the wing(s)104and determining the upwards aero lift, LW, generated by the wing(s) based at least in part on an angle of attack of the wing(s)104. (See alsoFIG.9B, blocks965and975and description thereof).

In some examples, determining the upwards aero lift, LW, generated by the wing(s)104involves determining the angle of attack of one or more hydrofoils130,136, respective defections of one or more control surfaces134,140of the one or more hydrofoils130,136, a water speed of the craft100, and a density of water in which the craft100is moving.

In some examples, determining the upwards aero lift, LW, generated by the wing(s)104involves determining a sensed load force on the hydrofoil(s)130,136and determining the upwards aero lift, LW, generated by the wing(s)104based at least in part on a sensed load force on the hydrofoil(s)130,136. (See alsoFIG.9B, blocks965and975and description thereof).

In some examples, one or more of the hydrofoils130,136comprise one or more flaperons and/or ailerons and/or elevators. In some of these examples, adjusting the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136involves adjusting the respective deflections of the one or more flaperons and/or ailerons and/or elevators to thereby control the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136. (See alsoFIG.9B, block970;FIG.11, procedures B-E; and description thereof).

In some examples, one or more of the hydrofoils130,136are moveable. Some of these examples involve extending the hydrofoil(s)130,136below the hull of the craft100for submersion in the water and at least partially retracting the hydrofoil(s)130,136into the hull of the craft100after the craft is wing-borne. (SeeFIG.10and description thereof).

In some examples, respective angles of incidences of the one or more of the hydrofoils130,136are adjustable. (SeeFIGS.8D-8Gand description thereof).

In some examples, adjusting the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136involves adjusting an angle at which the hydrofoil(s)130,136extends below the hull to thereby control the downwards hydrofoil lift, LF, generated by the hydrofoil(s)130,136. (See alsoFIG.9B, block970;FIG.11, procedures D-E; and description thereof).

While the systems and methods of operation have been described with reference to certain examples, it will be understood by those skilled in the art that various changes can be made, and equivalents can be substituted without departing from the scope of the claims. Therefore, it is intended that the present methods and systems not be limited to the particular examples disclosed, but that the disclosed methods and systems include all embodiments falling within the scope of the appended claims.