Patent Description:
The propulsion device comprises at least two coaxial propellers, comprising a first propeller and a second propeller.

Propulsion devices of this type are known in the art.

It is also known to use intubed propellers in which the propulsion devices have sets of rotors and stators to achieve better propulsive characteristics.

This intubed propeller solution is widely used for fixed wing aircraft and VTOL aircraft and, in addition to achieving larger propeller efficiencies, also has the feature of reducing the noise emitted.

Document <CIT> discloses a counter-rotating propulsion device in which two coaxial propellers having fixed and different pitch from each other are optimized respectively for take-off and vertical flight and for horizontal cruise flight.

During the cruise flight, the propeller with a smaller pitch, optimized for vertical flight, is stopped and the blades are feathered to minimize air resistance.

Feathered blades, however, still exert air resistance and the propulsion device disclosed in the document is quite noisy.

<CIT> discloses a dual mode turbofan engine that includes a jet engine portion having a compressor, a turbine disposed aft of the compressor, and a shaft coupled to the compressor and the turbine. The jet engine portion is configured to produce an exhaust. The system further includes an auxiliary turbine having a plurality of auxiliary turbine blades. The auxiliary turbine is disposed aft of the turbine and decoupled from the shaft. The system also includes a diverter disposed between the turbine and the auxiliary turbine. The diverter is configured to selectively direct the exhaust to an inner flow path bypassing the plurality of auxiliary turbine blades or to an outer flow path engaging the plurality of turbine blades. A plurality of propeller blades is hingedly connected to the auxiliary turbine.

There is therefore a need not met by the state of the art for a propulsion device that allows the overall efficiency to be increased, the aerodynamic resistance of the blades when inactive to be decreased, and weight and noise to be decreased.

The present invention aims to achieve these objects and to overcome the drawbacks of the devices known to the state of the art with a device as disclosed at the beginning, which includes a cylindrical duct comprising a fixed part and a rotating part. Said first propeller consists of said rotating part and a plurality of blades arranged externally on said rotating part and said second propeller is intubed inside said cylindrical duct, wherein the blades of the first propeller are foldable on the outer surface of the duct. The first propeller is driven by a first electric motor and the second propeller is driven by a second electric motor.

The use of different propellers is particularly advantageous for optimizing thrust and propulsive performance in two critical flight regimes:.

The first propeller, external to the duct, is designed for stationary flight or vertical flight, such as take-off and landing. The second propeller, inside the duct, is designed for the range of thrusts and speeds necessary for cruising, optimising its performance.

The presence of a propeller intubed in the duct and a propeller arranged radially on this duct enables there to be a concentric counter-rotating propulsion device with the thrust flows generated well separated from each other, which therefore do not generate turbulence that can adversely affect the operation of the individual propellers in a crosswise manner.

The intubed propeller solution also guarantees good performance, such as a larger diameter non-intubed propeller, and above all a considerable reduction in noise.

The outer blades in the folded position precisely approximate the aerodynamic shape of the duct and do not increase its resistance. This ensures that the efficiency during flight is higher than that of two free propellers, one of which has feathered blades.

In one exemplary embodiment, the blades of the first propeller are hinged on the rotating part of the cylindrical duct in such a way that the blades of the first propeller are arranged radially with respect to the rotation axis when the rotating part is in motion and fold on the outer surface of the duct when the rotating part is stationary.

Advantageously, therefore, when the rotating part of the cylindrical duct is rotated, the blades open in an active condition by positioning themselves radially and exerting thrust on the air; when the rotating part of the cylindrical duct is stopped in the cruise flight phase, the blades, when inactive, are closed by the aerodynamic resistance, positioning themselves along the side surface of the cylindrical duct.

According to one embodiment the first electric motor comprises an annular stator fixed on the fixed part of the duct and an annular rotor fixed on the rotating part, so as to rotate the rotating part with respect to the fixed part.

The electric motor of the first propeller is advantageously fully integrated into the cylindrical duct, greatly reducing the weights of the motorization allowing a good reduction in the overall weight.

In one exemplary embodiment, the first propeller is advantageously multi-blade, preferably comprising seven blades, producing thrusts comparable to a larger diameter two-blade propeller. By providing a large number of blades, in fact, it is possible to reduce the overall diameter of the first propeller. This means that the first propeller has a reduced diameter and consequently produces less noise.

In one embodiment, said propellers are driven in a counter-rotating manner.

One object of the present invention is also an aircraft provided with aerofoils for cruise flight, comprising at least one propulsion device as disclosed above.

In one embodiment, the aircraft is of the vertical take-off type and may be provided with means for tilting the axis of rotation of said propellers from a vertical position for take-off and vertical flight or stationary flight, to a horizontal position for cruise flight.

Once the take-off has been carried out, in which the first propeller is actuated, the tilting of the propulsion device is progressively varied from a vertical position to a horizontal position. The first propeller is then stopped and the blades close on the cylindrical duct, while the second propeller is operated. The thrust is thus now exerted solely by the second propeller intubed for cruise flight and the lift is exerted by the wings of the aircraft.

Both propellers can be operated simultaneously during take-off or vertical flight. Alternatively, the second propeller is operated only during tilting of the propulsion device or when the propulsion device has reached the horizontal position.

These and other features and advantages of the present invention will become clearer from the following disclosure of some non-limiting examples illustrated in the accompanying drawings, wherein:.

A preferred example of an aeronautical propulsion device according to the present invention is shown in the figures. The propulsion device is applied in an aircraft provided with aerofoils for cruise flight, in particular an EVTOL, i.e. an electrically powered vertical take-off and landing aircraft.

The propulsion device comprises a first propeller <NUM> and a second propeller <NUM>, positioned coaxially and independently rotatable with respect to each other.

The first propeller <NUM> is driven by a first electric motor <NUM> and the second propeller <NUM> is driven by a second electric motor <NUM>, as can be seen in <FIG> and described in detail below.

The motors <NUM> and <NUM> respectively drive the first and second propellers <NUM> and <NUM> so that the latter are, preferably but not exclusively, counter-rotating with respect to each other.

The aircraft is also provided with means for tilting the axis of rotation of the propellers <NUM> and <NUM>, in particular the entire propulsion device, from a vertical position for take-off and vertical or stationary flight to a horizontal position for cruise flight. It is possible to rotate only the propulsion device or to constrain the propulsion device to the wings, or to a part of them, and rotate the entire wings, or that part of them. It is also possible to provide a tail-sitter aircraft, in which the entire aircraft changes inclination between take-off or landing phase and cruising phase.

The propulsion device comprises a cylindrical duct <NUM> in which the second propeller <NUM> is comprised, which is therefore an intubed propeller.

The cylindrical duct <NUM> preferably has an aerodynamic profile, with a leading edge rounded in the forward direction of the propulsion device, and an inner diameter that progressively decreases and then increases again towards the rear end. However, other intubed propeller geometries can be provided.

The cylindrical duct <NUM> comprises a fixed part <NUM> and a rotating part <NUM>, the rotating part <NUM> being rotatably coupled to the fixed part <NUM> and rotatably driven by the first motor <NUM> with respect to said fixed part <NUM>. The rotating part <NUM> is positioned in front of the fixed part <NUM>. However, it is possible to alternatively provide a rotating part positioned externally with respect to the fixed part.

The first propeller <NUM> consists of the rotating part <NUM> and of a plurality of blades <NUM> arranged externally on the rotating part <NUM>. There are preferably seven blades <NUM>.

The blades <NUM> of the first propeller <NUM> are foldable on the outer surface of the duct <NUM>. In the example of the figures, the seven blades <NUM> of the first propeller <NUM> are hinged on the rotating part <NUM> of the cylindrical duct <NUM>.

As illustrated in <FIG>, when the rotating part <NUM> is rotated with respect to the fixed part <NUM> by the first motor <NUM>, each blade <NUM> of the first propeller <NUM> rotates about its own coupling hinge to the rotating part <NUM>. The blades <NUM> are thus arranged radially with respect to the axis of rotation, placing themselves in an active condition. In this active condition, the first propeller <NUM> exerts a propulsion. This is the case for take-off or landing, or vertical or stationary flight.

As shown in <FIG> and <FIG>, when the rotating part <NUM> is stopped with respect to the fixed part <NUM>, the blades <NUM> rotate on the hinges for coupling to the rotating part <NUM> and fold onto the outer surface of the duct <NUM>. This is the case in the cruise flight phase, where lift is provided by the wings of the aircraft.

A system may be provided for locking the rotating part <NUM>, which is alternatively held stationary by the non-powered motor <NUM>.

At take-off, the entire rotating part <NUM> of the duct <NUM> rotates and the blades <NUM> of the first propeller <NUM>, constrained to the rotating part <NUM>, open providing the necessary thrust for vertical flight. For cruising flight the rotating part <NUM> stops rotating and the blades <NUM> of the first propeller <NUM> fold over the outer profile of the duct pushed by the aerodynamic air resistance. Alternatively, it is possible to provide active means for moving the blades <NUM> from the active condition to the inactive condition and vice versa.

The second propeller <NUM> is intubed inside the duct <NUM> and, by means of the drive of the second motor <NUM> rotating preferably in the opposite direction to the first motor <NUM>, produces the necessary thrust during the cruising phase. The second propeller <NUM> can also be active during take-off and can be designed to generate the thrust necessary for vertical take-off in the event of failure of the first propeller <NUM> and/or the first motor <NUM>. The second propeller <NUM> has a plurality of blades <NUM>, e.g., two or more, in particular seven.

During the cruise flight, the first propeller <NUM> is stopped and only the second intubed propeller <NUM> is operated.

It is possible to operate only the first propeller <NUM> during take-off and landing, or to operate the first propeller <NUM> and the second propeller <NUM> simultaneously.

Similarly, in an emergency it is possible to operate only the second propeller <NUM> during take-off and landing.

In this case, the power of the second motor <NUM> and the sizing of the second propeller <NUM> must allow the necessary thrust to be delivered for take-off and landing.

As can be seen in <FIG>, the second propeller <NUM> is driven by the second motor <NUM> housed in the hub <NUM>, which hub <NUM> is connected to the fixed part <NUM> of the duct <NUM>, in a central position to the duct <NUM> itself, by means of four radially arranged spokes <NUM>.

<FIG> illustrates a sectional view of the device, with the blades <NUM> of the first propeller <NUM> placed in an inactive condition and folded over the duct <NUM>.

The first electric motor <NUM> comprises an annular stator <NUM> fixed on the fixed part <NUM> of the duct <NUM> and an annular rotor <NUM> fixed on the rotating part <NUM>. Activation of the first motor <NUM> rotates the rotating part <NUM> with respect to the fixed part <NUM> and then drives the first propeller <NUM>.

As can be seen in <FIG>, the first motor <NUM> is fully integrated into the wall of the cylindrical duct <NUM>.

In the example of the figures, the rotating part <NUM> is rotatably coupled to the fixed part <NUM> by means of a stator stage <NUM> for coupling to the hub <NUM>.

The stator stage <NUM> is pivotably fixed on the hub <NUM> by means of bearings, not shown in the figure, in an intermediate tubular portion <NUM> of the hub <NUM>. The first motor <NUM> can also be positioned on the hub, near said tubular part <NUM>. However, the positioning of the first motor <NUM> in the thickness of the walls of the duct <NUM> allows a large diameter of the first motor <NUM> to be obtained, allowing sections of the stator <NUM> and the rotor <NUM> to be reduced, with a decrease in weight and overall size.

The second motor <NUM> is placed behind this tubular part <NUM>, whereas the second propeller <NUM> is placed in front, the second propeller <NUM> being driven by the second motor <NUM> by means of a drive shaft passing through said tubular part <NUM>.

The stator stage <NUM> is provided with blades inclined opposite to the blades <NUM> of the second propeller <NUM>, to straighten the rotating air flow generated by the second propeller <NUM>.

The combination of thrust from the second propeller <NUM>, the residual thrust of the stator stage <NUM> and the pressure variation due to the profile of the duct <NUM> generates the propulsion of the intubed propeller.

During the rotation of the first propeller <NUM> and the rotating part <NUM>, the stator stage <NUM> contributes to the thrust by acting as a further propeller. The large diameter of the first propeller <NUM> allows low-speed rotations. In this way, even during rotation, the stator stage <NUM> acts as a stator. When the first propeller <NUM> and the rotating part <NUM> are stopped, the stator stage <NUM> contributes to the thrust only as a flow rectifier.

Claim 1:
Aeronautical propulsion device for an aircraft provided with aerofoils for cruise flight, the propulsion device comprising at least two propellers (<NUM>, <NUM>) coaxial to one another, comprising a first propeller (<NUM>) and a second propeller (<NUM>), wherein the aeronautical propulsion device includes a cylindrical duct (<NUM>) comprising a fixed part (<NUM>) and a rotating part (<NUM>), wherein said first propeller (<NUM>) consists of said rotating part (<NUM>) and a plurality of blades (<NUM>) arranged externally on said rotating part (<NUM>) and said second propeller (<NUM>) is intubed inside said cylindrical duct (<NUM>), wherein the blades (<NUM>) of the first propeller (<NUM>) are foldable on the outer surface of the duct (<NUM>),
characterized in that the first propeller (<NUM>) is driven by a first electric motor (<NUM>) and the second propeller (<NUM>) is driven by a second electric motor (<NUM>).