Airborne vehicle having v-tail mounted propellers

Abstract

A seaplane is configured to land and take off in the water and includes a hull or fuselage including a cabin configured for transporting people and / or cargo, a main wing connected to the hull or fuselage in a mid-section thereof, and a tail portion disposed at a rear section of the hull or fuselage, wherein the tail portion includes a first tail element and a second tail element that form a V-tail and further wherein the first tail element and the second tail element carry a first propeller and a second propeller, respectively.

Description

AIRBORNE VEHICLE HAVING V-TAIL MOUNTED PROPELLERSRELATED APPLICATION

[0001] This application claims priority from, and incorporates by reference, U.S. Provisional Patent Application No. 63 / 550,279, entitled “MONOHULL AIRBORNE VEHICLE CAPABLE OF TAKEOFF AND LANDING ON WATER”, filed on February 6, 2024.TECHNICAL FIELD

[0002] Some embodiments of the subject matter disclosed herein generally relate to seaplanes, and, more specifically, to seaplanes having propellers mounted on tail elements at an angle relative to a horizontal, e.g., a V-tail, as well as methods for manufacturing same.BACKGROUND

[0003] Seaplanes, i.e. , powered planes that can land and take off in water, were initially developed in the early 1900s but saw extensive use in World War II. This category of planes includes so-called float planes (wherein the plane has floats attached thereto that are the primary contact with the water) and so-called flying boats (where the plane has a hull configured to be the primary contact with the water). Seaplanes can also have landing gear that enable them to land and takeoff from land-based airstrips (i.e., amphibious planes). For this document the term “seaplane” refers to all of these types of planes (and others) that can land and takeoff in water. An example of a conventional seaplane 100 is shown in the Background Art of Figures 1 (a) and 1 (b), described in more detail below.

[0004] Conventional seaplanes continue to have many uses today, particularly in coastal and island regions worldwide. However, conventional seaplanes suffer from high fuel burn and corrosion-related maintenance because of their heavy, draggy, aluminum airframes. Typically, seaplanes place their propulsion units high above the wing to increase water clearance, which necessitates extra structure and frontal area, increasing the vehicle's aerodynamic drag. In addition, hull features such as chines and conventional transverse steps used to create stable takeoff and landings increase the vehicle's aerodynamic drag. For float planes, adding struts and connecting devices between the main airframe and floats increases the vehicle's aerodynamic drag. Finally, the aluminum construction of the airframes results in high corrosion-related maintenance when seaplanes operate in saltwater environments.

[0005] Accordingly, designing and producing seaplanes that overcome these and other drawbacks and problems would be desirable.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:

[0007] Figures 1 and 1 B depict a side view and a front view, respectively, of a conventional seaplane with a V-tail;

[0008] Figures 2-4 generally illustrate a seaplane according to an embodiment having a V-shaped tail with propulsion units mounted thereon;

[0009] Figures 5A-5E depict aspects of the propulsion elements and control / deflection surfaces affixed to the V-tail elements according to embodiments;

[0010] Figure 6 is a block diagram illustrating a control system and propulsion elements according to embodiments;

[0011] Figure 7 is a flow diagram depicting a method of manufacturing a seaplane according to an embodiment; and

[0012] Figure 8 shows another tail portion of a seaplane according to an embodiment having a V-tail.SUMMARY

[0013] According to these embodiments, seaplanes, according to an embodiment, include a structure configured to land or take off from the water, including a V-shaped tail with propellers mounted on at least two tail elements that form the V- shaped tail. The propellers are powered by electric motors, the weights of which are balanced to provide for a center of gravity disposed at a predetermined location on the structure by locating at least a portion of a powertrain that powers the electric motors within a front section of the seaplane.

[0014] According to another embodiment, a seaplane is configured to land and take off on the water and includes a hull or fuselage including a cabin configured for transporting people and / or cargo, a main wing connected to the hull or fuselage in a mid-section thereof, and a tail portion disposed at a rear section of the hull or fuselage, wherein the tail portion includes a first tail element and a second tail element that form a V-tail and further wherein the first tail element and the second tail element carry a first propeller and a second propeller, respectively.

[0015] According to another embodiment, a method of manufacturing a seaplane includes fabricating a tail portion of the seaplane that includes a first tail element and a second tail element that form a V-tail; wherein the first tail element and the second tail element are configured to carry a first propeller and a second propeller, respectively.

[0016] According to another embodiment, a seaplane configured to land and take off on the water includes: a hull or fuselage including a cabin configured for transporting people and / or cargo; a main wing connected to the hull or fuselage in a mid-section thereof; and a tail portion disposed at a rear section of the hull or fuselage; wherein the tail portion includes a first tail element and a second tail element that form a V-tail;wherein the first tail element and the second tail element carry a first propeller and a second propeller, respectively; wherein the first tail element and the second tail element also have at least one movable control / deflection surface disposed thereon such that air moved by the first propeller is either (a) blown over or (b) pulled over a respective movable deflection / control surface and air moved by the second propeller is either (a) blown over or (b) pulled over a respective movable deflection / control surface.DETAILED DESCRIPTION

[0017] The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The embodiments to be discussed next are not limited to the configurations described below but may be extended to other arrangements, as discussed later.

[0018] Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification does not necessarily refer to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0019] Figures 1 A and 1 B illustrate a conventional seaplane 100 that is configured to land and take off in the water, which includes a structure, i.e., a hull or fuselage, 102 (e.g., when the seaplane 100 is configured such that the structure 102 is designed to contact the water 101 , the structure 102 can be referred to as being (or having) a hull, alternatively when the seaplane 100 is configured such that the structure 102 is not intended to (primarily) contact the water it can be referred to as being a fuselage). Seaplanes are, therefore, capable of two operational modes: an airborne mode and a waterborne mode. Note that seaplanes are distinguishable from Wing-In-Ground (WIG) crafts, amongst other reasons, in that seaplanes can fly out of the ground effect whereas WIGs cannot.

[0020] Structure 102 includes cabin 104, configured to transport people and / or cargo. Structure 102 includes a main wing 106 connected to the hull or fuselage in a midsection 108 and a tail section 110 disposed at a rear section 1 12 of structure 102. As mentioned in the Background Section, conventional seaplane 100 is powered to provide variable thrust for takeoff, climbing, cruising altitude propulsion, descent, and landing functionality by a propeller 120 and engine 122 (collectively a “propulsion unit” 124) in conjunction with the main wing 106 and various control elements (not shown) which are known in the art. Also shown in Figures 1 A and 1 B are retractable floats 126 and 128, which those skilled in the art will appreciate may also be fixed rather than retractable. Likewise, conventional seaplanes 100 may have tail configurations other than a V-tail, e.g., a T-tail configuration.

[0021] As mentioned above, positioning the propulsion unit 124 as shown in Figures 1 (a) and 1 (b) results in various performance issues for the seaplane 100. Also note that when the propeller 120 is mounted to the main wing 106 as shown in Figures 1 A and 1 B, the pylon that connects the propeller 120 to the main wing (shown but unnumbered in Figures 1A and 1 B) is typically much thicker (Figures 1 A and 1 B not to scale), thus requiring extra surface area and / or frontal area to support the propeller.

[0022] On each wing or tail element, one or more control surfaces may be attached, comprising a movable hinged or tracked surface that deflects the air passing over them. Control surfaces may be deflected upward or downward generating aerodynamic moments around the aircraft that provide stability and control. Additionally, the tail elements may be combined with their respective control surface to enable allmoving tail elements.

[0023] Unlike the conventional seaplane 100, embodiments (e.g., seaplane 200 illustrated in Figures 2-6, and 8 sometimes just referred to herein as an “aircraft”) described herein have propellers 202 and 204 mounted on the tail section 210. More specifically, according to this embodiment, the propeller 202 is mounted on starboard tail element 206 and propeller 204 is mounted on port tail element 208. Each propeller 202 and 204 has a plurality of propeller blades. Note that although only two propellers 202 and 204 are illustrated in the Figures associated with these embodiments, those skilled in the art will appreciate that other embodiments may include two or more propellers mounted on each tail element 206, 208 and / or on other locations on airplane 200.

[0024] Like seaplane 100, seaplane 200 according to this embodiment is also configured to land and take off in the water and includes a structure, i.e., a hull or fuselage, 212 (e.g., a “hull” when the seaplane 200 is configured such that the structure 212 is designed to contact the water and the structure 212 can be referred to as being (or having) a hull, alternatively when the seaplane 200 is configured such that the structure 212 is not intended to (primarily) contact the water it can be referred to as being a “fuselage”). The structure 212 includes a cabin 214 configured to transport people and / or cargo. The structure 212 also includes a main wing 216.

[0025] The main wing 206 can include a starboard-wing element and a port-wing element (when viewed from a front section of the seaplane 200). Those skilled in the art will appreciate that the designations of a “front section”, a “mid-section”, and a “tail section” are arbitrary and not to scale but are instead used to orient the placement of various seaplane components relative to one another along the structure 212. Unlike the conventional seaplane 100 of Figures 1 A and 1 B, the starboard-wing element and the port-wing element need not include one or more respective propeller elements,although these embodiments do not preclude the provision of propellers and motors on the main wing 216. However, in some embodiments, the propellers 202 and 204 that are mounted on respective tail elements 206 and 208, respectively, are the only propellers provided on the seaplane 200 to provide variable thrust to the seaplane 200 for takeoff, climbing, cruising altitude propulsion, descent, and landing functionality in conjunction with the main wing 216 and various control elements (e.g., movable control surfaces shown in Figures 4-8).

[0026] Figure 2 also shows seaplane 200 with retractable floats 218 connected to the main wing 206 in their retracted position. Figure 3 shows another view of seaplane 200 with floats 218 in their extended position. In this view it can, for example, be seen that tail elements 206, 208 form a generally V-shape (seen also in Figures 1 A and 1 B, albeit without propellers mounted thereon unlike embodiments described herein). This tail portion 210 is commonly referred to as a “V-tail”, which nomenclature is used herein.

[0027] For example, a V-tail 210 can be described as having first and second tail elements 206, 208 having angled surfaces with both vertical and horizontal projected areas that have their base at an aft portion of the hull or fuselage 212. An angle between each tail element 206, 208 from the horizontal position can, for example, be between 25 and 75 degrees to create the generally V-shaped look of V-tail 210.

[0028] According to various embodiments, and as indicated by nacelles 400 and 402 in Figure 4, seaplane 200 can include electric motors (see Figure 5C for more detail) to power the propellers 202 and 204. As will be appreciated by those skilled in the art, an electric motor includes a rotor and a stator, one of which carries magnets and the other of which carries conductors through which a supply current flows. Interaction between the rotor and the stator causes the motor shaft to rotate, as compared withcombustion engines, which combust fossil fuels to generate energy converted to mechanical force.

[0029] The compact and high power-to-weight properties of electric motors used in these embodiments, e.g., compared to typical fuel-burning engines used on existing seaplanes, unlocks the ability to mount propellers 202, 204 on the tail elements 206, 208 at the rear of the aircraft 200 as described above, which would have otherwise been prohibited by weight and balance problems caused by heavy combustion engines in the rear. The mechanical simplicity of electric motors used in these embodiments decreases the weight required to mount propulsion units on the tail element by removing the need for complicated and heavy transmission mechanisms and fuel delivery systems required to power a fuel burning propulsion unit. Figure 4 also shows two of the control / deflection surfaces 506, 508 associated with tail element 206 that are described in more detail below.

[0030] Figure 5A shows a top isometric view of seaplane 200 including control / deflection surfaces 500, 502 on tail element 206, as well as control / deflection surfaces 504, 506 on tail element 208. These control / deflection surfaces 500-506 are movable to control the flight path of the seaplane 200 by virtue of their position and the air blown over the control / deflection surfaces 500-506 by their respective propulsion units, as described in more detail below. Figure 5B depicts an exploded view of the elements associated with the port tail element 208’s propulsion and control, including propeller 204, electric motor nacelle 402, and control / deflection surfaces 500, 502. The electric motor nacelle 402 also covers internal structure required to connect the propeller shaft and motor to the tail element 208. Figure 5C shows a similar view as that of Figure 5B but also including electric motor 510 as well as inverters 512, 514 for converting thesupplied power from DC to AC. Elements 204, 510, 512, and 514 can be considered a“propulsion unit” 516. Although AC electric motors 510 are preferred for some embodiments, it is also possible to implement motors 510 as DC motors for other embodiments.

[0031] Regarding the location of the propulsion units 516 relative to the tail elements 206, 208, propeller(s) 202, 204 can be placed in front of (as seen in the embodiment of Figures 2-5C), or behind (not shown), the aerodynamic surfaces of the tail elements 206, 208 and the rotational axis 530 of the propeller 204 can be placed above or below the chord 532 (see Figure 5D) of its corresponding wing or tail surface . The rotational axis 530 of the propeller 204 may also be aligned with, or offset by an angle 534 relative to, the chord 532, also referred to herein as a “cant” of the propulsion unit 516 (see, e.g., Table 1 below and corresponding discussion). The electric motor 510 spinning each propeller 204 may be placed inline with the axis of rotation 530 of the propeller 204 or offset in angle 534 relative to the axis of rotation of the propeller 204 and coupled to the electric motor 510 with a transmission mechanism (not shown in Figure 5D).

[0032] . For example, according to some embodiments, the propulsion units 516 can be positioned anywhere between 0 and 2 nacelle radii (i.e., multiples of the radius of the nacelle 507) above or below the tail element 206, 208 surfaces and angled between 0 and 10 degrees above or below the tail element chord line 532, shown in Figure 5D as the vertical offset distance 536. The selected positioning and angling of the propulsion units 516 are used to shift the position and direction of the airflow induced by those units 516 on the tail elements 206, 208, and associated control surfaces 500-506. Furthermore, the positioning and angle of the rotational axis 530 of the propulsion units516 enable the thrust generated by each propulsion unit 516 to affect both the forces and moments imparted on the vehicle 200 in both airborne and waterborne operational modes to enhance stability and control. For example, a combination of propellers 202, 204 placed in different locations on the tail elements 206, 208 with rotational axes canted in different directions would allow the propellers 202, 204 to impart different moments on the aircraft 200 while maintaining the same level of overall thrust.

[0033] In some embodiments, the tail element 206, 208 is free to extend past the position of the outboard most propulsion unit 516 and can extend outwards at angles different than sections of the tail element 206, 208, which are inboard of the outboard most propulsion unit 516. In some cases, a generally horizontal element 250 connecting (see, e.g., connecting element 250 in Figure 5E) the two tail elements 206, 208 of the V- tail 210 can be added to improve the ability of the tail structure 210 to resolve aerodynamic and propulsive loads. The connecting element 250 can also be used to improve the longitudinal stability and control of the aircraft 200. Propellers may also be mounted to this connecting element 250. The connecting element 250 can also include control surfaces. The connecting element 250 can, according to some embodiments, be a horizontal wing with an airfoil shape. The connecting element 250 can, for example, be a horizontal lifting surface with an airfoil cross-section. The lifting surface can have a twist and camber distribution with a chord similar to the other two surfaces that form the V-tail as described above. The connecting element 250, if provided according to some embodiments, can be located at various positions between the tail elements 206, 208 (one of which is illustrated in Figure 5E) or even mounted on top of the tail elements 206,208.

[0034] Among other things, by placing the propellers 202 and 204 (and their corresponding electric motors 510) on the tail elements 206 and 208 as described in the embodiments herein, the propeller 202 and 204 according to these embodiments have more water clearance than if the propellers 202, 204 were placed on the main wing 216. Moreover, placing the propellers 202 and 204 on the V-tail 210, according to embodiments increases the dynamic pressure over the tail surfaces when thrust is produced, increasing the effectiveness of the tail control surfaces (e.g., control surfaces 500-506) at low speeds. According to these embodiments, the V-tail 210 also allows propellers 202, 204 to be placed laterally away from the aircraft centerline, allowing differential thrust to generate yaw moments on the aircraft 200. The blown V-tail 210 (i.e. , with the propeller 202, 204 disposed on a leading edge of respective tail elements 206 and 208, respectively, propellers 202, 204 blow air across the control surfaces 500-504) combines the impact of blown surfaces and differential thrust to improve attitude control during operation on water, including during harbor maneuvering. Note that although these embodiments depict a blown configuration, the propellers 202 and 204 could, alternatively, be disposed on the control surfaces or on a trailing edge of respective tail elements 206, 208 to provide embodiments wherein air is instead pulled across the respective control surfaces.

[0035] The improved on-water and harbor maneuvering brought by propellers 202, 204 mounted on the tail section 210 according to embodiments reduces dependency on a water rudder (not shown in the Figures described above, see description below), typically required for on-water and harbor maneuvering. Propellers 202, 204 placed on the tail section 210 also result in significantly reduced cabin noise by being located behind the cabin 214, where passengers are seated, and brings increased safety of operation by moving propellers 202, 204 away from passengerentry and exit locations, away from cargo doors, and avoiding propellers 202, 204 sweeping over docks when docking the airborne vehicle 200 with the wing over a dock. However, these benefits associated with embodiments come with additional challenges. Placing the propellers 202, 204 on the tail section 210 requires a stronger structure at the tail of the aircraft 200 to support the thrust loads generated by the propellers 202, e.g., relative to the tail section 1 10 of conventional seaplane 100 which has no propellers. The strengthened structure, along with the weight of the motors 210 and propellers 202, 204, requires careful balancing to ensure that the center of gravity of the aircraft is appropriately placed. Finally, it is useful according to some embodiments to properly characterize the main spray blister created by the hull 212 during takeoff and landing to ensure that it does not intersect with the propeller’s plane to prevent undue maintenance.

[0036] One aspect of embodiments associated with placing propulsion units 516 on the tail elements 206, 208 is that the propulsion units 516 enhance the effectiveness of the tail element and associated control surfaces (e.g., in the “blown tail” embodiments described above). The additional airflow increases the dynamic pressure over each tail element 206 and 208 and respective control surface(s), i.e., 500, 502, 504, and 506, thereby increasing the magnitude of moment applied to the aircraft 200 per unit of control surface deflection or per unit of pitch of the aircraft 200. This impact is most relevant for seaplanes 200 during low-speed operations, such as harbor maneuvering, on-water taxiing, and takeoff. At typical on-water maneuvering speeds of 5-30 knots and during takeoff, the embodiments provide a 1 .5-10 times increase in moment per unit control surface deflection compared to an unblown surface at the same operating condition. For example, according to some embodiments e.g., when coming into a dock, seaplanes 200 can (at essentially zero speed) have some moment associated with propeller washthat can enable fine maneuvering of the vehicle 200 which cannot be achieved with conventional seaplanes 100.

[0037] Furthermore, the additional airflow generated by these embodiments energizes the fluid boundary layer on control surfaces 500-506 and decreases the local angle of attack of airflow, delaying aerodynamic stall on both the stabilizer and control surface, i.e., the additional airflow prevents separation at higher angles of attack. The increased control surface effectiveness can also improve the aircraft’s ability to maintain control in the event asymmetric thrust is produced, such as during a motor failure on one side of the aircraft 200. In this case, control surfaces 500-506 blown by the propellers 202 or 204 that are still operational will continue to benefit from increased airflow over the control surfaces 500-506, allowing the aircraft 200 to compensate for moments created by asymmetric thrust with less control surface deflection compared to an equivalent tail without blown surfaces.

[0038] According to embodiments, the position of the propeller is selected such that the propeller wash generated appropriately enhances tail element and control surface effectiveness in both undeflected and deflected configurations. As seen in Figure 5D, the propulsion units 516 can be placed over a range of positions and angles relative to the chord of the tail elements 206, 208. The size (diameter) and number of the propellers 202, 204 are selected for various embodiments by balancing the need for increased effectiveness of the tail elements 206, 208 and control surfaces 500-506, the efficiency of the propellers 202, 204 during the cruise phase, propeller noise requirements, maintenance, part count requirements, and clearance to the water, spray, and docks. For example, smaller faster spinning propellers 202, 204 can drive higher airflow velocity over the tail elements 206, 208 and associated control surfaces.However, each of the small propellers 202, 204 will only provide increased airflow velocity over a small fraction of the respective tail element, requiring more propellers 202, 204 to be placed on the tail elements 206, 208. By way of contrast, larger slower spinning propellers 202, 204 do not increase the airflow velocity over the tail elements 206, 208 as much as small faster spinning propellers. However, the larger, slower, spinning propellers decrease the noise generated by the propellers and provide increased airflow over a larger fraction of the tail element, thereby decreasing the number of propellers 202, 204 required.

[0039] Another impact of propeller size is control bandwidth provided by differential thrust. Smaller propellers tend to have smaller rotational inertias, allowing motors to more quickly adjust the rotational speed of the propellers and thus the thrust produced, leading to wider control bandwidth. Conversely, larger propellers will typically lead to narrowing control bandwidth. In any case, a blade pitch control mechanism can be added to achieve required control bandwidth if thrust control with rotational speed variation is limited by propeller inertia and would not provide adequate control response.

[0040] Another aspect associated with placing propellers 202, 204 on the tail for seaplanes 200 according to some embodiments is that the propulsion units 516 are elevated without necessitating the use of vertical pylons to connect the propulsion units 516 to lifting surfaces. This eliminates the need for vertical pylons to raise propellers 202, 204 to achieve sufficient water and dock clearance. This is especially true in aircraft configurations requiring large diameter propellers, which potentially enable benefits such as high propeller efficiency and low propeller noise. For example, configurations that mount propulsion units 516 on the wings or directly on the fuselage side would typically require separate pylons to raise propellers to meet clearance requirements. Largerpropellers would require longer pylons, which increase aerodynamic drag and structural weight. Compared to other traditional tail configurations, such as the T-tail and cruciform tail, the V-shape of the tail elements 206, 208 according to these embodiments also eliminates the need for joints in the tail that would have otherwise been required to resolve thrust loads for tail mounted propulsion units 516 and provides increased effectiveness from the propulsion units 516 for both directional and longitudinal stability.

[0041] Typically, when tail elements 206, 208 are placed in a V-shape according to these embodiments, the propellers 206, 208 are placed at angles between 25-75 degrees when measured from the horizontal position (See, e.g., Figure 2). The implementation of a blown V-Tail onto a seaplane 200, from an aircraft stability and control perspective, is more challenging than onto conventional tail configurations. In conventional seaplane tail configurations, horizontal and vertical stabilizers contribute to longitudinal and lateral / directional stability independently. In contrast, the diagonal angle of each surface of the tail elements 206, 208 in the blown V-tail configuration according to these embodiments causes both surfaces to simultaneously affect longitudinal, lateral, and directional stability. Furthermore, the impact of varying dynamic pressure on the tail with different levels of propeller thrust may impact the stability of the aircraft 200 in the blown V-tail configuration according to embodiments, which does not occur for conventional seaplane configurations without tail mounted propellers.

[0042] The static and dynamic stability properties of the seaplane 200 are affected by the V-tail through the angle of the tail elements 206, 208 from horizontal, span, chord, and relative distance of the tail elements from the aircraft center of gravity. Increasing span, chord, and relative distance to center of gravity, all else held equal, generally improves stability at the cost of additional weight and drag as well as possibly decreasedmaneuverability. The increased tail area generates greater restorative moment towards a steady flight condition. This increases static stability by causing the aircraft to respond more stiffly to disturbances in attitude. Maneuverability may be decreased as greater control moment to maneuver the aircraft and hold attitude would be required, but the larger tail may accommodate larger control surfaces that can provide greater control moment. The resulting greater tail area could also increase aerodynamic damping, thus rendering the aircraft less agile. Because the tail surfaces are at an angle, adjusting the span, chord, and planform shape of either tail surface will simultaneously impact the longitudinal and lateral-directional stability and control of the aircraft. Similarly, varying the angle affects aircraft stability in multiple axes. Decreasing the angle, which moves the tips of each tail element 206, 208 surface downwards and further from each other, generally decreases lateral and directional stability but increases longitudinal stability. For the same span and chord of tail surface, this also increases the maximum distance that propulsion units 516 may be placed away from the center of gravity, improving the ability of differential thrust to contribute to on-water directional control. Lastly, while additional stability may result from the blown tail surfaces, each surface must also be sized to provide adequate stability if the propellers provide no thrust and thus no additional dynamic pressure over the surfaces above freestream velocity, such as during failure of motor(s) or during landing.

[0043] An additional constraint on the angle and length of the tail elements 206, 208 of avoiding the main spray blister of the hull 202 during takeoff and landing can be considered when applied to a seaplane 200 according to these embodiments. Predictions of the distribution of spray during takeoff and landing of the seaplane 200 are used by embodiments to ensure that the tail elements 206, 208 are angled such that the attached propellers 202, 204 generally do not come in contact with the spray blister.

[0044] According to embodiments, the individual deflections of control surfaces 500-506 and thrusts generated by each propulsion unit 516 can be commanded / controlled via a control system 600 to enable pitch, roll, or yaw movements for the seaplane 200. A block diagram of control system 600 is provided as Figure 6, which is under the control of one or more processor(s) 602 operating in conjunction with one or more memory devices 604. The memory device(s) 604 can store machine- readable instructions which, when executed by processor(s) 602, jointly operate to perform functions described herein.

[0045] The control system 600 may actuate the surfaces 500-606 and modulate the thrust of each propulsion unit 516 to create or enhance the stabilization of the vehicle 200 in all axes in both the waterborne and airborne modes. The thrust generated by each propulsion unit 516 can be controlled by a blade pitch effector 606 and / or a change in the rotational speed of the engine or motor 510 driving the propeller 202 or 204, e.g., by changing a voltage and / or frequency of the electric power provided to electric motor 510 via control signal 616 to a power modulation or power control unit 618, which adjusts power supplied by unit 620. The deflection of each control surface 500-506 is applied by an actuator (represented by arrows between blocks 606 and 500-506), such as a servo or cable linkage. According to embodiments, the control system 600, tail elements 206, 208, propulsion units 516, and control surfaces (e.g., 500-506) together enable enhanced forms of control of the seaplane 200 both on water and in the air. On the water, differential thrust produced by the propellers 202, 204 on starboard and port tail elements 205, 207 provides directional control. The blown tail effect enhances the effectiveness of the control surfaces at low speeds on the water, allowing them to contribute to the directional control of the seaplane 200. Although the enhanced control surface effectiveness of the blown tail would mean that a water rudder 622 is not necessary inmost conditions, in certain embodiments, the differential thrust of the propellers 202, 204 and the enhanced effectiveness of the control surface(s), e.g., 500-506, can be combined with a water rudder 622 for additional directional control.

[0046] The freedom to position and cant each propulsion unit 516 and propellers 202, 204 independently, along with the blown tail effect, provides additional control power in the longitudinal and lateral axes compared to traditional tail designs and is an alternate way to affect aircraft longitudinal, directional or lateral control in the event certain aerodynamic surfaces cease to operate. Given that the control surfaces e.g., 500-506, affect all three axes of the seaplane 200 and the propulsion units 516 can be configured to provide additional control in all axes, see Table 1 below, the control system 600 can determine an optimal combination of deflection of the control surface 500-506 and thrust changes to the propulsion units 516 to achieve the desired control. Characterization of the blown effects of the propulsion on the tail elements 206, 208, and control surfaces 500-506 will assist in defining the optimal control allocation for the seaplane 200 both in the air and on the water. Additionally, under a failure condition of either a propulsion unit 516 or a control surface 500-506, the control system 600 may change the control allocation to use the other control surface(s) or propulsion units differently to maintain control of the aircraft 200 in all three axes. See, e.g., Table 1 below.Examples of Primary Axes of Control for Each Control Surface / ActuatorTable 1

[0047] As shown in Table 1 , by mounting the propulsion units 516 above the center of gravity (COG) of the seaplane 200, embodiments enable the control system 600 to readily change the pitch / attitude of the vehicle 200. Among other things shown in Table 1 , by providing a relatively small cant or angle of the propulsion units 516 relative to the chord 534, enables the embodiments to provide propeller access to (and control over) all three dimensions. Moreover, when embodiments include a ruddervator, the ruddervator deflection can also be used to change roll, pitch, and yaw of the vehicle 200, as well as to operate as speed brakes. As mentioned above, according to some embodiments, yaw control is provided at slow speeds, e.g., 0-30 knots.

[0048] Other control elements and sensors may be included in seaplane 200 to achieve the above-described functionality according to embodiments. For example, as shown in Figure 6, the components of the control system 600 may include control effectors / actuators 606, propulsions units 516, communication links (represented by the various arrows in Figure 6), an inertial navigation system (INS) and / or a global navigation satellite system (GNSS) 624, and other sensors 626. Communication links between the flight computer and the flight actuators can take the form of mechanical linkages, fly-by-wire systems wherein commands and information are transmitted between the flight computer and actuators and sensors through electrical signals, or optical systems. Sensors 626 providing data to the control system 600 may include one or more of: airspeed probes, angle of attack sensors, sideslip angle sensors, water / ground proximity sensors, aircraft attitude sensors, and acceleration sensors. These sensors 626 provide information regarding the state of the aircraft 200 that can be conveyed to the pilot or used by the control system 600 to decide how to actuate the vehicle controls.

[0049] Pilot controls 628 will enable the pilot or autopilot of the seaplane 200 to input commands in the control system 600. Controls 628 that the pilot has access to may include one or more joysticks, one or more thrust levers, switches, dials, and screens. The pilot may use these effectors to adjust power or thrust levels, switch between flight modes, or command the control surface actuators 606. Control surface actuation can either be directly commanded by control effector movement by the pilot, or the flight computer can interpret control effector movement by the pilot as commanding a vehicle attitude, rate, and / or acceleration and use data from sensors to decide how to command control surface actuators 606 to make the vehicle meet the pilot command.

[0050] Those skilled in the art will appreciate that embodiments could also include other elements such as landing gear, fairings, floats attached to the main wing, see, e.g., other aspects of embodiments described below, although some of these elements are not shown (at least in detail) in Figures 2-4.

[0051] As described above, and further described in the above-incorporated by reference provisional patent application reprinted below, the vehicle 200 according to embodiments and described in the renderings and graphics shown is a monohull airborne vehicle capable of takeoff and landing on water. The vehicle can be configuredwith additional capability for takeoff and landing on improved runways and / or unimproved runways. The renderings and graphics describe a vehicle with a wingspan between 40- 75 ft and a maximum takeoff weight between 8000-19000 lb. According to other embodiments, the sizes and takeoff weights of seaplanes 200 could be different to accommodate different applications. For example for resupply (e.g., food) missions, a seaplane 200 having a similar configuration to those described above can have a payload weight of 20-50 lb and wingspan of 6-15 ft. Such vehicles 200 can be configured as drones rather than having pilots. Similarly, other embodiments can include vehicles having a 200-500 lb of range of maximum takeoff weight or a 3000lb takeoff weight with a 30-45 ft wingspan.

[0052] The vehicle is driven by a hybrid-electric, battery-electric, hydrogenelectric, or combustion powertrain. The vehicle includes a main wing, a tail, a propulsion system with propellers placed on the main wing and / or on the tail, a hull to provide buoyancy, and, according to some embodiments, includes a water rudder, retractable tip floats configured to operate in: a) an extended configuration where the floats are intended to enter the water to provide a righting roll moment when the vehicle heels to one side and b) a retracted configuration where the floats rotate to the tip or into the interior of the wing, and retractable landing gear configured to operate in: a) an extended configuration where the landing gear is intended to contact ground for improved runway and / or unimproved runway landings and b) a retracted configuration where the landing gear is housed in an aerodynamic fairing to reduce aerodynamic drag. The aerodynamic fairing used to house the retractable landing gear also provides lateral stability during operation on the water when the landing gear is retracted or if the landing gear is removed.

[0053] The main wing has control surfaces to provide control authority such as ailerons or spoilers and, according to some embodiments, has high-lift systems such as slats, simple flaps, and slotted flaps. Providing control authority is defined as enabling the pilot or aircraft control systems to stabilize and control the motion of the vehicle. The high-lift systems enable a small, high aspect ratio, low-aerodynamic-drag wing to achieve sufficient aerodynamic lift at low speeds to enable safe takeoff and landing from the water and potentially short takeoff and landing capability on land. The high-lift systems are also configured to contribute to control authority.

[0054] The tail will have control surfaces to provide control authority such as elevators, rudders, or ruddervators. According to some embodiments, the tail is configured as a T-tail (vertical surface with its base at the aft portion of the fuselage and with a horizontal tail surface mounted at its top). In other embodiments, the tail is configured as a V-tail (two angled surfaces with both vertical and horizontal projected area that both have their base at the aft portion of the fuselage and potentially a horizontal surface spanning between the angled surfaces and placed at a location between the base and the tip of the angled surfaces).

[0055] A water rudder is an actuated vertical surface placed on the hull of the vehicle such that some or all of the water rudder is submerged in water during operation on water. Actuation of the water rudder supplements directional control during operation on the water.

[0056] Propellers placed on the main wing increase the lift capability of the wing and also contribute to control authority by increasing the effectiveness of main wing control surfaces, especially at low speeds. Propellers placed on the tail increase the effectiveness of the tail control surfaces at low speeds, improving attitude control duringoperation on water and improving harbor maneuvering. The improved harbor maneuvering brought by propellers mounted on the tail reduces dependency on a water rudder, typically required for harbor maneuvering. Propellers placed on the tail also bring significantly reduced cabin noise by being behind where passengers are seated and bring increased safety of operation by moving propellers away from passenger entry and exit locations, away from cargo doors, and avoiding propellers sweeping over docks when docking the airborne vehicle with the wing over a dock.

[0057] According to some embodiments, the vehicle has a planing hull with a step. A planing hull is a hull where the surface on the bottom of the hull provides some or all of the hydrodynamic lift during the planing regime of water operation. Planing hulls typically have a step, which is a sharp and abrupt discontinuity used to separate water flow to reduce hydrodynamic drag and improve hydrodynamic stability. This step is required for planing hull airborne vehicles to achieve safe takeoffs and landings from water, but existing step designs and geometries incur high aerodynamic drag during airborne operation. The hull of the vehicle described by the renderings is designed for low aerodynamic drag during airborne operation. One of the methods of reducing hull aerodynamic drag is novel geometry and fairing of the step. The vehicle includes a novel step geometry and step fairing that achieves sufficient hydrodynamic stability while minimizing the aerodynamic drag during airborne operation. According to some embodiments, the hull of the vehicle is reinforced to enable hull-borne landings on surfaces other than water, such as snow or grass.

[0058] The retractable tip floats are attached with pylons to the main wing. An actuator housed in the main wing or in the pylon enables movement of the pylon and tip floats between extended and retracted configuration. In their extended configuration, thetip floats and potentially the pylon provide buoyancy when they enter the water. Thus, when the vehicle heels to one side and the tip float and potentially the pylon enter the water, they provide a righting moment. In the retracted configuration, the pylon is housed inside or just under the wing and the tip float is at the tip of the wing or is housed inside the wing. This retracted configuration can be used in airborne operation to reduce aerodynamic drag and can be used in waterborne operation to enable the main wing to sweep over a dock.

[0059] The retractable landing gear system includes either a main gear located behind the center-of-gravity and a nose gear located in front of the center-of-gravity or main gear located in front of the center-of-gravity and a tail gear located behind the center-of-gravity. One side of the main gear would be mounted on the port side of the fuselage, and the other side of the main gear would be mounted on the starboard side of the fuselage. In its extended configuration, the landing gear system provides the capability to land on improved runways and / or unimproved runways potentially including paved runways, gravel runways, dirt runways, and grass strips. The retractable landing gear can also be fitted with or replaced with auxiliary components such as skis to enable operation on snow, ice, or other surfaces. The retractable landing gear is capable of being deployed during operation on water to increase the ease of beaching the vehicle. In their retracted configuration, the main landing gear is housed in an aerodynamic fairing on either side of the vehicle fuselage, and the nose or tail gear is housed in the hull, empennage, or nose of the vehicle. The main gear housing, during operation on the water with the landing gear retracted or with the landing gear removed, provides buoyancy when the housing enters the water, providing a righting moment and improving lateral stability during operation on water.

[0060] Embodiments can also be expressed as methods of manufacturing seaplanes having configuration(s) as described above. For example, the aircraft 200 can be split into smaller sections (e.g., a few sections for the fuselage 212, a couple of sections for the wing 216 and V-tail 210) and assembled by attaching each of the sections together. Each of the sections would likely be individually cured in an autoclave and a bond would be formed between the sections. There may also be internal components like spars that are made as separate components and then integrated into the wings and tails.

[0061] Thus, as shown in Figure 7, a method of manufacturing a seaplane according to embodiments can include the step 700 of manufacturing a seaplane by fabricating a tail portion of the seaplane that includes a first tail element and a second tail element that form a V-tail; wherein the first tail element and the second tail element are configured to carry a first propeller and a second propeller, respectively.

[0062] Figure 8 shows another embodiment of a seaplane 800, which includes alternative features that may be individually or jointly included in the designs. For example, seaplane 800 has a riser 806, which connects the main wing to the structure 212, with differently shaped propeller blades on propeller units 802 and 804, as well as a fairing 808 into which retractable landing gear (not shown in Figure 8) can be stored when not in use and which adds to the stability of seaplane 800 while in the water.

[0063] According to these embodiments, it should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications, and equivalents, which are included in the spirit and scope of the invention. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensiveunderstanding of the invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

[0064] Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

[0065] This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.

Claims

WHAT IS CLAIMED IS:1 . A seaplane (200) configured to land and take off on the water comprising: a hull or fuselage (212) including a cabin (214) configured for transporting people and / or cargo; a main wing (216) connected to the hull or fuselage (212) in a mid-section thereof; and a tail portion (210) disposed at a rear section of the hull or fuselage (212); wherein the tail portion (210) includes a first tail element (206) and a second tail element (208) that form a V-tail; wherein the first tail element (206) and the second tail element (208) carry a first propeller (202) and a second propeller (204), respectively.

2. The seaplane of claim 1 , wherein the generally V-shaped tail portion further comprises: the first and second tail elements have angled surfaces with both vertical and horizontal projected areas that have their base at an aft portion of the hull or fuselage.

3. The seaplane of claim 2, further comprising: a horizontal surface spanning between the angled surfaces and placed at a location between a base and a tip of the angled surfaces.

4. The seaplane of any of claims 1-3, wherein the first tail element and the second tail element further comprise: a first electric motor connected to the first tail element for powering the first propeller; and a second electric motor connected to the second tail element for powering the second propeller.

5. The seaplane of any of claims 1 -4, further comprising: a powertrain disposed within the hull or fuselage and configured to provide electric power to the first propeller and the second propeller.

6. The seaplane of claim 5, wherein the powertrain includes one or more of: a battery, a hydrogen fuel-consuming electrical power generating device, and / or a fossil fuel-consuming electrical power generating device.

7. The seaplane of any of claims 1 -6, wherein the main wing has a wingspan between 40-75 ft and a maximum takeoff weight between 8000-19000 lb.

8. The seaplane of any of claims 1 -7, further comprising:retractable tip floats configured to operate in: a) an extended configuration where the floats are intended to enter the water to provide a righting roll moment when the seaplane heels to one side and b) a retracted configuration where the floats rotate to the tip or into the interior of the wing.

9. The seaplane of any of claims 1 -8, further comprising: retractable landing gear configured to operate in: a) an extended configuration where the landing gear is intended to contact ground for improved runway and / or unimproved runway landings and b) a retracted configuration where the landing gear is housed in an aerodynamic fairing to reduce aerodynamic drag.

10. The seaplane of claim 9, wherein the aerodynamic fairing used to house the retractable landing gear also provides lateral stability during operation on water when the landing gear is retracted or if the landing gear is removed.

11. The seaplane of any of claims 1 -10, further comprising a water rudder implemented as an actuated vertical surface placed on the structure of the seaplane such that some or all of the water rudder is submerged in water during operation of the seaplane on water, and wherein actuation of the water rudder supplements directional control during operation of the seaplane on the water.

12. The seaplane of any of claims 1 -11 , wherein the first propeller and the second propeller can be positioned anywhere between 0 and 2 nacelle radii above or below their respective first tail element and second tail element surfaces.

13. The seaplane of claim 12, wherein the first propeller and the second propeller have a rotational axis between 0 and 10 degrees above or below a tail element chord line.

14. The seaplane of any of claims 1 -13, wherein the first tail element and the second tail element each carry a plurality of propellers.

15. A seaplane comprising: a structure (212) configured to land or take off from the water; the structure (212) including a V-tail (210) with propellers (202, 204) mounted on at least two tail elements (206, 208) that form at least a part of the V-tail 210; and electric motors (510), that power the propellers (202, 204), the weights of which electric motors (510) are balanced to provide for a center of gravity disposed at a predetermined location on the structure (212) by locating at least a portion of a powertrain that powers the electric motors (510) within a front section of the seaplane (200).

16. A method of manufacturing a seaplane comprising: fabricating a tail portion of the seaplane that includes a first tail element and a second tail element that form a V-tail; wherein the first tail element and the second tail element are configured to carry a first propeller and a second propeller, respectively.

17. The method of manufacturing a seaplane of claim 16, further comprising: fabricating a hull or fuselage of the seaplane including a cabin configured for transporting people and / or cargo, wherein the hull or fuselage is configured to take off and land from the water; fabricating a main wing and connecting the main wing to the hull or fuselage in a midsection thereof; and connecting the V-tail at a rear section of the hull or fuselage.

18. The method of either claims 16 or 17 including one or more of the features of claims 2-14.

19. A seaplane (200) configured to land and take off on the water comprising: a hull or fuselage (212) including a cabin (214) configured for transporting people and / or cargo; a main wing (216) connected to the hull or fuselage (212) in a mid-section thereof; and a tail portion (210) disposed at a rear section of the hull or fuselage (212);wherein the tail portion (210) includes a first tail element (206) and a second tail element (208) that form a V-tail; wherein the first tail element (206) and the second tail element (208) carry a first propeller (202) and a second propeller (204), respectively; wherein the first tail element (206) and the second tail element (208) also have at least one movable control / deflection surface (500-506) disposed thereon such that air moved by the first propeller (202) is either (a) blown over or (b) pulled over a respective movable control / deflection surface (500, 502) and air moved by the second propeller (204) is either (a) blown over or (b) pulled over a respective movable control / deflection surface (504, 506).

20. The seaplane of claim 19, further comprising the elements recited in any of claims 1 - 14.21 . The seaplane of claims 1 , 15, 19 or 20, wherein the first and second propellers (202, 204) are mounted on their respective tail elements (206, 208) in front of their respective at least one movable control / deflection surface(s) such that the air is blown over the movable control / deflection surfaces.

22. The seaplane of claims 1 , 15, 19 or 20, wherein the first and second propellers (202, 204) are mounted on their respective tail elements (206, 208) behind their respective at least one movable control / deflection surface(s) such that the air is pulled over the movable control / deflection surfaces.

23. The seaplane of any of claims 20-22, further comprising: a control system (600) including at least one processor and at least one actuator (606) associated with each of the at least one movable control / deflection surfaces (500-506)which are configured to enable positioning of the at least one movable control / deflection surfaces (500-506).

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