Field of the invention The present invention relates to aircraft, in particular to personal air mobility aircraft and to drones. The invention also relates to an annular propeller unit that can be used in an aircraft of this type, as well as a boat using this of annular propeller unit. Prior art

In recent years, various types of drones and small aircraft have been proposed for personal air mobility. A common drawback in the solutions that have appeared to date lies in the poor efficiency of the propulsion rotors, in the constructive complication of the motor systems for driving the rotors, and in the relatively reduced autonomy.

Pietro Perlo, one of the present inventors, has been working since many years on studies and investigations aimed at achieving high efficiency propulsion rotors. For example, the document EP 1 524 189 A1 relates to a micro-aircraft that can be associated with a mobile phone, and comprising a substantially planar structure wherein four ducted propulsion rotors are incorporated, which are substantially coplanar with each other. Each of the four propulsion rotors comprises a rotating ring rotatably mounted within a cylindrical opening with a vertical axis, formed through the planar structure, and defines a guiding duct for the airflow generated by the rotor. Each of the four rotors comprises at least one blade, which extends radially from the body of the rotating ring towards the central axis of the rotor. The known solution described above was developed for an aircraft of microscopic dimensions and, therefore, did not involve the solution of the far more significant problems encountered in the case of a self-driving drone, intended for example for transporting loads (for example, for delivering parcels), or an aircraft for personal air mobility.

One example of application of the concepts set out above to a personal air mobility aircraft has already been proposed by the same Applicant in document WO 2020/261102. An aircraft having the characteristics indicated in the preamble of claim 1 is known from US 2020/062385A1. The aircraft described in this document has a rotor driven by toothed wheels or rollers in frictional engagement with the outer surface of one or more belts applied around the rotor.

A belt transmission for driving a helicopter rotor is schematically illustrated in JP2001097288A, however, without any explanation as to how this solution can be concretely implemented.

Other known solutions are illustrated in US 2006/196991 A1 and US 2018/178898 A1.

Object of the invention

The object of the present invention is to improve the solution proposed in WO 2020/261102.

In particular, an object of the invention consists of producing a personal air mobility aircraft, or a drone that has a drive system of the propulsion rotors characterized by high efficiency, in particular, in terms of the high thrust/weight ratio for the same value as the diameter of the propulsion rotor.

Another object of the invention is to propose an aircraft of the type specified above wherein the drive system of the propulsion rotors is characterized by an extremely low noise level.

Another object of the invention is to provide an aircraft of the type specified above wherein the drive system of the propulsion rotors is constructively simple and of low cost, and at the same time reliable.

Still another object of the invention is to propose a series of preferred configurations for an aircraft for personal air mobility aircraft having extremely high lift characteristics and anti-stall characteristics.

Summary of the invention

In order to achieve one or more of the aforesaid objects, the invention relates to an aircraft having the characteristics indicated in claim 1.

Further preferred characteristics and advantages of the invention are indicated in the dependent claims.

The invention also relates to an annular propeller unit according to claim 39. The annular propeller unit according to the invention can be used in any type of vehicle and, in particular, also in a boat.

Detailed description of the invention

The invention will now be described with reference to the attached drawings, provided purely by way of non-limiting example, wherein:

- Figure 1 is a partially cross-sectioned perspective view of a wing of an aircraft according to the invention,

- Figure 2 illustrates a variant of Figure 1.

- Figure 3 is a cross-sectional view of the annular propeller illustrated in Figures 1 , 2,

- Figure 4 illustrates an enlarged detail of Figure 3,

- Figure 5 illustrates a variant of Figure 3,

- Figure 6 illustrates the same cross-section of Figure 3 according to a different embodiment,

- Figure 7 is a perspective view of the wing equipped with an annular propeller made according to the embodiment of Figure 6,

- Figure 8 is a partial perspective view of a leaf spring used in the annular propeller of Figure 7,

- Figures 9, 10 are a side view and a plan view of the leaf spring of Figure 8,

- Figure 11 is a partial perspective and enlarged-scale view of a cup spring used in another embodiment of the invention,

- Figure 12 is an additional partial perspective view of the bup springiRssi] of Figure 11 ,

- Figure 13 illustrates a variant of Figure 12,

- Figure 14 illustrates a cross-section of the annular propeller in the embodiment using the cup spring of Figure 12, in the condition wherein the rotor ring is stationary,

- Figure 15 illustrates the same cross-section as Figure 14 in the condition wherein the rotor ring is in motion,

- Figure 16 is an overall view of the annular propeller using the cup spring of Figure 12,

- Figure 17 is a partially cross-sectioned perspective view of a ball support of the type used to support the rotor ring in rotation in another embodiment of the invention, - Figure 18 is an enlarged scale view of a detail of a cross-section of the rotor ring in an embodiment using horizontally oriented ball supports of the type illustrated in Figure 17,

- Figure 19 is a variant of Figure 18,

- Figure 20 is a view of another embodiment of an annular propeller used in the aircraft according to the invention,

- Figure 21 is a partial cross-sectional view of the annular propeller of Figure 20,

- Figure 22 illustrates an enlarged detail of Figure 21 ,

- Figure 23 illustrates a variant of Figure 21.

- Figure 24 illustrates a variant of Figure 21.

- Figure 25 is a perspective view of another embodiment of a propeller used in the aircraft according to the invention,

- Figure 26 is a cross-sectional view of the propeller of Figure 25,

- Figure 27 is a view, on an enlarged scale, of a detail of Figure 26,

- Figure 28 is a perspective view of another embodiment of the propeller used in the aircraft according to the invention,

- Figure 29 is a cross-sectional view of the propeller of Figure 28,

- Figure 30 illustrates a wing of an aircraft according to the invention provided with two propellers driven by the same motor unit,

- Figures 31 , 32 are two perspective views of a first configuration of the aircraft according to the invention,

- Figures 33-37 are perspective views of additional configurations of the aircraft according to the invention,

- Figure 38 is a perspective view of a variant wherein the same rotor is driven by two electric motors by means of the same transmission belt,

- Figure 39 is a perspective view of another variant wherein the rotor is driven by an electric motor by means of a transmission belt, which also engages an auxiliary pulley located on the opposite side of the rotor with respect to the motor,

- Figures 40, 41 show additional variants of the propulsion system of the aircraft rotors according to the invention,

- Figures 42, 43 show the flight attitude and take-off/landing attitude of a further embodiment of the aircraft of the invention,

- Figures 44, 45 show the flight attitude and take-off/landing attitude of a further embodiment of the aircraft of the invention,

- Figures 46, 47 are two alternative diagrams of the connection circuit between the photovoltaic cells of the aircraft and the on-board electric batteries,

- Figure 48 is a schematic cross-sectional view showing the layering of the laminar structure, incorporating photovoltaic solar cells, which is applied to the surfaces of the aircraft.

- Figure 49 is a perspective view of an embodiment example of a boat using two annular propeller units according to the invention,

- Figures 50, 51 are two additional perspective views of the boat of Figure 49 with retracted and extracted hydrofoil, respectively,

- Figure 52 is another perspective view of the boat of Figure 49, which transparently shows the battery pack for electrically powering the electric drive motors driving the propeller units,

- Figure 53 is a schematic perspective view of the propulsion system and hydrofoils of the boat of Figure 49,

- Figure 54 is a rear view of the boat, and

- Figure 55 illustrates an enlarged detail of Figure 54.

With reference to Figures 1-4, an embodiment example of the aircraft according to the invention comprises a wing 1 in which an annular propeller 2 is incorporated. As can be seen in detail in Figure 4, the annular propeller 2 comprises a rotor ring 2A mounted rotatably within a stationary ring 2B defined by the structure of the wing 1. The rotor ring 2A carries one or more blades 3 (the example refers to the case of three blades), which extend radially from the rotor ring 2A towards the axis 4 of the propeller 2. In a preferred embodiment, the blades 3 are of the variable pitch type, with a variable angle of attack. The pitch may also become negative, to obtain a reversal of the thrust (reversible propeller).

The rotation of the rotor ring 2A is controlled by a motor unit P by means of a belt transmission 5. In the example of Figure 1 , the motor unit P is constituted by an electric motor M with radial flux or axial flux of a high torque motor.

In the example of Figure 2, the motor unit P comprises an electric motor M and a reducer unit R. In both cases, a pulley 6 is mounted on the output shaft of the motor unit P to engage a closed loop belt B, which is also engaged on the lateral surface of the rotor ring 2A. If the motor is of the "torque motor" type, the rotor can integrate the pulley itself. The stationary ring defined by the supporting structure 1 has one or more openings for the passage of the belt B. In the example of Figures 1-4, the stationary ring has an inner circumferential wall surrounding the rotor ring 2A, which is interrupted for an entire sector of the circumferential extension, so as not to interfere with the belt B.

As can be seen in detail in Figure 4, in the example illustrated, the lateral surface of the rotor ring 2A has a circumferential groove 7 for engaging the belt B. In one example, the transmission belt B has a body of elastomeric material and includes one or more metal wires (not shown).

In the example illustrated in the drawings, the belt B has a trapezoidal cross-section and the cavity 7 that receives it has a cross- section of corresponding shape.

As also visible in Figure 4, the stationary ring 2B has an inner circumferential wall defining a cylindrical duct surface of the annular propeller, which serves to guide the flow of air generated by the rotation of the rotor ring.

In the specific illustrated example, the structure of the wing 1 has an upper part 1 A and a lower part 1 B (see Figure 4). The parts 1 A, 1 B of the wing structure define a circumferential cavity within which the rotor ring 2A is rotatably mounted in such a way as to leave the lateral surface of the rotor ring 2A free, where it is engaged by the belt B.

Still with reference to Figure 4, the rotor ring 2A is rotatably mounted within a circumferential groove 9 defined by the structure of the wing 1. In particular, the circumferential cavity 9 is delimited by an upper wall 10A and a side wall 10B forming part of the upper portion 1A of the structure 1 , as well as by a lower wall 10C and a side wall 10D defined by the upper and lower portions 1A, 1 B of the wing structure 1. As can be seen in Figure 4, the side walls 10B, 10D are configured in such a way as to leave the central part of the side surface of the rotor ring 2A free for engaging the belt B.

Figure 4 does not show in detail the means that support the rotor ring 2A in rotation within the cavity 9, which will be described below.

Figure 5 illustrates the same cross-section as Figure 3 in the case of a solution wherein the axial dimension H2 of the propeller guiding duct is reduced with respect to the axial dimension H1 of the propeller guiding duct in the case of the solution of Figure 3.

Figure 6 illustrates a cross-sectional view corresponding to that of Figure 4, and shows an embodiment example of the means for supporting the rotor ring 2A in rotation.

As indicated above, the blades 3 are of the variable pitch type and - to this end - they are supported rotatably about their longitudinal axes, this rotation being controlled by an actuator device (not illustrated). These construction details are not illustrated here, since they can be made in any known way, and also to make the drawings simpler.

As in all the embodiments illustrated here, the inner circumferential surface 200 of the rotor ring 2A has a predetermined profile to guide the airflow generated by the propeller. Similarly, the inner circumferential walls 8A, 8B of the structure portions 1A, 1 B have profiles which extend on opposite sides of the profile of the inner surface 200 of the rotor ring, in such a way that the set of the circumferential surfaces 8A, 200, 8B defines the duct for conveying the airflow generated by the propeller.

In the embodiment illustrated in Figure 6, the rotating support of the rotor ring 200 is obtained by providing a seat on the upper circumferential surface 20A and on the lower circumferential surface 20B of the body of the rotor ring 2A, said seat receives a wavy leaf spring S.

Figure 7 illustrates an example wherein segments of wavy leaf S, separated from each other, are provided on the upper surface 20A and on the lower surface 20B of the body of the rotor ring 2A. Alternatively, a single wavy elastic leaf element S can be provided extending along the entire circumference of the rotor ring, both on the upper surface 20A and on the lower surface 20B.

Figure 8 shows a portion of a wavy elastic leaf element S, having a width di and a thickness si. Figure 9 shows a side view of the element S, and Figure 10 shows a plan view.

Both in the case of a single circumferential leaf and in the case of several leaf segments, in the static condition of the rotor ring, the rotor ring rests against the walls of the stationary ring that face the leaf S at the points of culmination, spaced apart from each other, of the successive undulations of the leaf. When the rotor ring is set in rotation by the motor unit, the wavy elastic leaf (or the wavy elastic leaves) stretches away from the rotor ring, which thus rotates on an air cushion. The leaf also performs an aerodynamic function by favoring the formation of a flow of air which keeps the facing surfaces of the leaf, or leaves, and the stationary structure separate. In other words, a sort of air support of the rotor ring during its rotation is achieved in this way.

Figures 11-16 illustrate another embodiment, wherein for the rotor support of the rotor ring 2A, the rotor ring is provided with a cup spring T, instead of the wavy elastic leaf S of Figures 8-10. In this case, both on the upper surface 20A of the body of the rotor ring 2A, and on the lower surface 20B, there is a cup spring T consisting of a single metal leaf, which extends circumferentially above the rotor ring 2A or of multiple leaf segments. As can be seen in Figure 11 , the metal leaf T has a distribution of notches 11 which define a plurality of separate leaf portions 12 which have a folded edge 13 on their radially inner side. The circumferential assembly of the folded edges 13 constitutes a cup spring, substantially conical in shape. Figure 12 illustrates the case wherein a single leaf T with circumferential extension is provided, while Figure 13 illustrates the case in which several leaf segments T1 are provided.

Figures 13, 14 show the configuration assumed by the cup spring T in the stationary rotor ring condition (Figure 14) and in the moving rotor ring condition (Figure 15).

In some additional embodiments, the rotor ring 2A can be supported in rotation by the stationary structure of the aircraft by means of rolling ball supports of the type illustrated in Figure 17.

Figure 17 shows a rolling ball support device, indicated overall with the reference number 14. The device 14 comprises a hollow cylindrical body 150, which in the example is shaped like a bellows, inside which a cylindrical casing 160 is slidably mounted, within which a metal ball 170 is freely rotatable, by means of auxiliary balls 180. The ball 170 is retained within the casing 160 and protrudes from one end of the casing. At the opposite end, the casing 160 is pushed by a helical spring 190 contained within the hollow body 150, which tends to keep the ball 170 in a stroke- end position protruding from the body 150. Figure 18 illustrates a first embodiment wherein two circumferential arrays of devices 14 for supporting rolling balls are provided, arranged horizontally, with the ball of each device 14 in contact with the outer lateral surface 20C of the stator ring 2A.

Figure 19 illustrates an alternative solution, wherein the two circumferential series of devices 14 are arranged vertically, with their respective balls in contact with the upper and lower surfaces 20A, 20B of the stator ring 2A.

Figure 20 is a variant of Figure 2 showing an alternative solution wherein the variable pitch blades 3 join at their inner ends in a hub 15, which is rotatably mounted on a support pin 16. The support pin 16 is rigidly connected at its ends to two beams 17, which extend diametrically through the space inside the annular propeller, and which have their ends rigidly connected to the stationary structure of the wing 1.

Figure 21 , and its detail illustrated in Figure 22, refer to the case wherein the support pin 16 extends vertically between the two crossbars 17, and the hub 15 is mounted in rotation on the pin 16 [RSS2]by means of a single rolling bearing 18, adjacent to the crossbar 17 located below.

Figure 23 illustrates a variant wherein the upper crossbar 17 is eliminated and the pin 16 has a reduced extension.

Figure 24 illustrates another variant wherein the blades 3 are rigidly connected to the pin 16, which has its ends supported in rotation by the two cross-members 17 by respective rolling bearings 18.

Figures 25-26 show another embodiment wherein the aforesaid support pin 16 has been eliminated. In this case, the supporting crossbars 17 are always provided. As can be seen more clearly in Figure 27, each support bar 17 may have an elliptical shape to minimize the aerodynamic field disturbance (this characteristic is also applicable to the previously described embodiments). Each of the two bars 17 carries a pin 19, on which a hub 21 is rotatably mounted by means of a bearing 20. Each of the two hubs 21 is connected by means of a plurality of spokes 22 to the stator ring 2A. As can be seen in Figure 25, the spokes 22 associated with the upper hub 21 and the spokes 22 associated with the lower hub 21 are coupled two by two, in the same radial position and converge with each other in the direction of the rotor ring 2A. The embodiment of Figures 28, 29 differs from that of Figures 25- 27, in that - in this case - the two hubs 21 are connected to each other by a central vertical pin 23 which is - in turn - connected to the rotor ring 2A by spokes 24. The blades with variable pitch in the representation of Figures 28-29 are free to vary their angle of attack with respect to the rotor ring 2A.

In the illustrated example, each annular propeller 2 has a crossbar 17 carrying a central pin on which a hub connected to the rotor ring 2A by means of spokes 22 is rotatably mounted. In this case, the blades 3 of each annular propeller may have their radially inner ends spaced apart from the central axis of the propeller.

Figure 30 shows another embodiment wherein two annular propellers 2 have their rotor rings 2A driven by a single motor unit T by means of two belts B gripped on two pulleys 6A, 6B, mounted in superimposed positions on the output shaft of the motor unit T.

Figures 31 , 32 show two perspective views of a first configuration of aircraft for personal air mobility aircraft, indicated overall with the reference number 100. The aircraft 100 has a passenger compartment 30 connected to a front wing 31 and to rear wings 32 in which four annular propellers 2 of any type described above are incorporated. The two annular propellers 2, arranged symmetrically at the two sides of the aircraft, are controlled in rotation in opposite directions by respective motor units, by means of respective belt transmissions (not shown), even if there is also the possibility of providing a motor unit to control multiple propellers via multiple belt transmissions. The aircraft has a tail with an annular propeller 2 with a vertical axis, also made in accordance with the present invention. The passenger compartment 30 is surmounted by a roof-wing 33 preferably discoidal in shape.

On both the lower and rear surfaces of the wings 31 , 32, and on the roof-wing 33 a distribution of photovoltaic cells 34 is preferably provided, distributed by independent groups in order to reduce the impact of shading and the malfunction of one or more of the cells. The partition by groups of cells makes it possible to minimize the length of the array of cells so that the voltage of each group of cells is contained to values lower than 48V, typically between 6V and 48V. A panel containing a group of photovoltaic cells is composed of a flexible multilayer laminar structure. The photovoltaic cells are of the type consisting of monocrystalline silicon (for example, marketed by SUNPOWER Corporation) with an efficiency in the order of 25%, or of the multi-joint type, for example, GaAs, with typical efficiencies higher than 30%, or of the perovskite type or of the organic type. The photovoltaic panel has the back layer replaced by a thin carbon fiber composite. The first layers of the photovoltaic panel may be directly integrated into the aircraft structure and contribute to its rigidity.

Figure 33 shows a variant with six annular propellers 2 for vertical thrust arranged on six respective wing surfaces.

Figure 34 shows the solution that still provides six annular propellers for vertical thrust arranged on a single wing surface 31. The horizontal thrust is obtained by means of a single annular propeller with a horizontal axis, as in the case of the embodiments described above.

Figures 35, 36 show variants of Figures 33, 34, wherein two annular propellers 2 with horizontal axis are arranged at the tail of the aircraft, for horizontal thrust. Both in the case of a single tail rotor and in the case of two tail rotors, the shape of the passenger compartment is designed in such a way that the airflow remains adjacent to the surface of the passenger compartment due to the Coanda effect, until it is conveyed mainly towards the center of the rotors. In the case of two rotors, the tail of the passenger compartment divides in two to direct the flow.

Figure 37 shows a single-wing configuration, wherein a single lower wing 31 has a discoidal shape, similar to the discoidal shape of the roof wing 33, preferably having a wider surface than the lower wing.

Figure 38 is a perspective view of a variant wherein the same rotor ring 2A is driven by two propulsion units P arranged on opposite sides with respect to the rotor ring 2A. In the example, each propulsion unit comprises an electric motor M and a reducer R. The propulsion units P drive two pulleys 6, which drive the rotor ring 2A by means of the same belt transmission 5, including a closed loop belt B, which engages the two pulleys 6 and the rotor ring 2A. The two electric motors M may be of equal power or of different power, and operate independently, that is to say, thanks to the properties of the electric motors, the speeds and torques of the two motors M self-adapt and synchronize without the need for specific control.

Figure 39 is a perspective view of another variant wherein the rotor ring 2A is driven by a single electric motor M by means of a transmission belt B, which also engages an auxiliary pulley 6’ located on the opposite side of the rotor ring 2A with respect to the electric motor M. The auxiliary pulley 6’ is mounted freely rotatable, by means of a ball bearing, on a support element (not illustrated), which is pushed by a spring (not illustrated) in a direction that tends to keep the belt taut. In this way, the pin carrying the auxiliary pulley 6’ by means of the respective bearing constitutes a belt-tensioning member, and also prevents translation of the rotor ring in the horizontal plane.

Both in the case of Figure 38 and in the case of Figure 39, the aircraft structure incorporates a substantially oval-shaped casing, which incorporates the annular propeller and the two electric motors (in the case of Figure 38) or the annular propeller, the electric motor and auxiliary pulley (in the case of Figure 39).

Figure 40 is another variant of the drive system of the annular propellers of the aircraft of the invention, useful, for example, for the aircraft configuration, which will be described below with reference to Figures 44, 45.

In the example of Figure 40, two electric motors M are designed to drive two pairs of rotor rings 2A axially spaced apart from the two electric motors M, above and below (with reference to the Figure) the two electric motors M.

The basic principle of this variant is also applicable to the case of a single rotor ring 2A driven by a single electric motor M. As illustrated, the pulley 6 that drives one rotor ring 2A is mounted at the end of a crankshaft 60 which has a predetermined length, so as to achieve the required spacing between the electric motor M and the plane of the rotor ring 2A and of the pulley 6.

In the example shown, each electric motor M has two crankshafts 60 extending from opposite sides of the electric motor (if necessary through a respective reducer) to drive respective pulleys 6 spaced above and below the electric motor. As already indicated, in this example, two electric motors are provided to drive two pairs of rotor rings 2A. Figure 41 illustrates a variant of the solution of Figure 40, wherein each electric motor M rotates the two rotor rings connected thereto in opposite directions, thanks to a gear transmission (in the example a pair of gears 61 , 62), which reverses the direction of rotation. In this way, in the example of Figure 41 , the two electric motors M drive the two upper rotor rings in one direction and the two lower rotor rings in the opposite direction.

Figures 42 and 43 show another embodiment of the aircraft according to the invention, respectively, in the flight attitude and in the take-off and landing attitude. In these Figures, the parts common or corresponding to those of Figures 31-37 are indicated by the same reference numbers. In this case, the aircraft has a passenger compartment 30 wherein the pilot and any passengers are each seated on a seat 70 supported with an entire interior cabin in a pivoting manner, and controlled by an actuator device using gravity and an inertial platform to automatically maintain the same attitude of the occupants when the aircraft attitude varies between the vertical attitude and the horizontal attitude.

In this case there are two annular propellers 2, one front and one rear, placed on the same longitudinal axis (which is vertically oriented in the take-off and landing attitude (Figure 43)). The structural body 30 that contains the cabin has the shape of an ovaloid configured to favor and guide the airflow from one propeller to another. The cabin-passenger compartment, which contains the seats 70 and the driving control panel, rotates with respect to the ovaloid structural body by pivoting on reinforcing elements placed on the same ovaloid body.

Directional flaps 71 are associated with each annular propeller (for example, two pairs of flaps oriented orthogonally to each other), which may also have the function of support feet. In the example of Figures 42, 43, support feet 72 are provided, distinct from flaps 71 , which are operational when the aircraft is on the ground, in the attitude of Figure 43. In the parking phase, the rotors may also be kept on a horizontal plane and - in this case - the flaps are used so that the aircraft rises on one side until the rotors are arranged on a vertical axis and then begin the ascent. Preferably, two wings 33A, 33B are provided, always preferably of discoidal shape, spaced apart above and below the oval body of the passenger compartment 30 (with reference to the horizontal flight attitude shown in Figure 42). This configuration is made possible in that the aircraft lands and takes off in the vertical attitude of Figure 43. In flight, the aircraft has a biplane-type configuration. The two wings may differ in area and width (wingspan). In addition to the disc-shaped wings, the wings may be of a classic shape, usually used in biplanes, for example, straight wing with constant chord and zero arrow angle, or straight wing with reduced arrow angle and variable chord, or trapezoidal wing with strong arrow angle and variable chord. Flowever, it is also possible to provide a single wing. The profile of the wings is chosen based on the maximum design speed.

Once taken off in the attitude of Figure 43, the aircraft gradually moves into the attitude of Figure 42, by controlling the direction of the jet of the rotors by means of the flaps associated therewith.

Figure 44 shows a perspective view of an aircraft configuration with two front rotors 2 and two tail rotors 2, an upper wing 33A and a lower wing 33B with integrated groups of photovoltaic cells PV on both the upper and lower surfaces of each wing. The ovaloid structure is configured in such a way as to favor the directing of airflows between the rotors.

Figure 45 is a view of the aircraft of Figure 44 in take-off and landing attitude.

As can be understood, the configuration of the propulsion system of Figure 40 or of Figure 41 can be adopted and useful, for example, for an aircraft of the type illustrated in Figures 44, 45. In the case of the aircraft of Figures 42, 43, it is possible to adopt a propulsion system with a single electric motor equipped with two shafts extending on opposite sides to drive the pulleys 6 that drive the two rotors. Of course, the representations of Figures 42, 43 and 44, 45 are purely schematic. For greater simplicity of illustration, these Figures do not show the drive transmissions of the rotors, which can be made in accordance with the basic principle of the solutions of Figures 40 and 41 , and which can be contained within two housings (not shown), arranged at the two sides of the passenger compartment body 30.

For the same reason, these schematic Figures do not show the door, with an associated ladder, arranged in the body of the passenger compartment 30, for access to the passenger compartment.

With reference to the configuration of Figure 43, the typical dimensions are:

- height H: 270 - 300 cm;

- width W: 160 - 200 cm;

- length L in the case of a discoid wing: 250-300cm;

- length L in the case of a conventional wing: 500-700 cm.

The aircraft of the invention comprises independent groups of photovoltaic cells for recharging a main battery pack 201, for powering the electric motors of the aircraft, at low or medium voltages (for example, 48 - 120 V) up to higher voltages (usual in the automotive world) up to 800V, and possibly also an auxiliary electric battery 202, at relatively low voltage (for example 12V), for powering the on-board electrical circuit.

Figure 46 and Figure 47 illustrate two alternative schemes of the charging management system 200.

A group of photovoltaic cells PV1, PV2,..., PVn is connected to the main battery pack 201 or to a lower voltage portion thereof by means of DC-DC converters 203 controlled in a synchronized way by an electronic board 204 in order to power the pack battery 201 with charging current at the operating voltage of the battery pack 201 or in order to reduce the multiplication factor of the converter connected to a portion of the battery pack of lower voltage.

Another DC-DC converter 205 supplies current to the auxiliary battery 202 at the operating voltage of the auxiliary battery 202. The electronic card 204 is connected by means of BUS CAN 206 with the DC- DC converter 205, and by means of a BUS CAN line 207 with the battery pack management system 208 (BMS or Battery Management System). In the case of the diagram of Figure 47, there is also a selector switch 209, controlled by an electronic board 210, to control the charging current supply to the battery pack 201 and to the auxiliary battery 202.

The groups of photovoltaic cells are positioned on the aircraft in such a way as to minimize the possibility of being in shaded areas. The system includes an electronic board to control the connection of the photovoltaic cell groups with the main battery at relatively high voltage, for powering the electric motors, and with an auxiliary electric battery, at relatively low voltage, for powering the electrical circuit onboard.

The aircraft according to the invention has a transverse dimension lower than the limit of 255 cm allowed for road vehicles, so that it can travel on the road and be parked in car parks.

Preferably, the electric batteries are distributed on the bottom and on the top of the cabin, with reference to the attitude in horizontal flight, to facilitate balancing the weights in forward movement. Alternatively, the batteries are placed on the bottom with the driver's position shifted towards the front rotor to keep the center of gravity midway between the two rotors in horizontal motion.

The photovoltaic solar cells are distributed over the entire wing surface (on both sides) and over the entire surface of the cabin, leaving transparent areas upwards and downwards.

The photovoltaic cells PV are incorporated in a layered laminar structure (Figure 48), including an outermost layer comprising one or more layers of PET with a UV or ECTFE coating, two layers of a thermoplastic polyolefin material, above and below the cells, to encapsulate the cells, and a back layer of PET with UV coating, or preferably of carbon fiber. The thickness of each layer may vary from 300 to 450 microns, and the total thickness is approximately 1.5-2 mm, which contributes to the structural rigidity of both the wings and the ovaloid module containing the passenger compartment.

According to another aspect, the present invention is also directed to the annular propeller unit taken on its own, as indicated in the attached claim 39.

The invention also covers any other type of vehicle comprising one or more annular propeller units according to the invention.

Figures 49-55 show an example of application of the invention to a boat. In this example, two annular propeller units 2 are provided, made in accordance with the disclosures of the invention, which have been described above. Each annular propeller unit 2 is carried at a lower end of a upright 300 supported outboard at the stern of the boat, and configured to keep the respective annular propeller immersed in the water.

The stator ring 2B of each annular propeller unit 2 is carried by a lower end of the upright 300, and is arranged with its axis directed orthogonally to the upright 300. The motor unit P is carried at the upper end of the upright 300. The belt B of the belt transmission 5 is guided within the upright 300 by means of rollers 301 and is engaged both on a pulley 6 (see in particular Figures 53-55) carried by the shaft of the motor unit P and on the outer surface of the rotor ring 2A.

Each upright 300 can be oriented around its vertical axis, to consequently orient the thrust direction of the respective annular propeller unit 2. With reference in particular to Figures 50, 51 , the boat is provided with at least two front hydrofoils 302 and at least two rear hydrofoils 303, which can be moved by means of respective actuators of any known type between an inoperative position adjacent to the hull of the boat (Figure 50), and an operative position spaced downwards with respect to the hull (Figure 51). Above a certain navigation speed, the hydrofoils can be extracted to raise the hull above the water and kept in a position that minimizes energy consumption at each cruising speed of the vehicle.

With reference to Figure 52, a battery pack 400 is housed in the hull for electrically-powering the motor units P. Preferably, this battery pack is made according to the disclosures of the document WO2021070018A1 by the same Applicant.

Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to those described and illustrated purely by way of example, without departing from the scope of the present invention, as defined by the attached claims.