Technical field

The present invention relates to a system for piloting aircraft towed by sails stationed in the stratosphere. In particular, but not exclusively, the present system is applicable to aircraft for telecommunications and Internet connectivity.

State of the art

The stratosphere is a part of the Earth's atmosphere of interest to different technological sectors including telecommunications and Internet connectivity. With the need to make telecommunications and Internet connectivity available even in remote areas of the planet, systems called high-altitude platform station (HAPS) have been developed.

HAPS systems are typically unmanned aircraft and/or airships that are kept at altitude for a very long period of time in order to reduce take-offs and landings, operations that subject the system to great stress. To maintain them at defined altitudes and latitudes during use, such systems are normally powered by means of batteries and/or motors. In addition, batteries and motors are also used to power the connectivity and telecommunications devices that the systems have on board. However, these forms of power supply have limitations in terms of duration; in fact, they need to be recharged or refuelled, reducing the system's stay at altitude.

One solution for powering HAPS systems that has been implemented as an alternative to batteries and motors involves using solar cells. This solution, however, has the disadvantage of adding mass to the system's own mass, requiring more energy to keep them in the stratosphere.

Document US 9 611 025 B2 describes a system for long duration operations at altitude comprising two airships connected by a cable. For stationing at altitude, each airship may have deflectors integrated with the airship and creating an air channel with it. One or more propulsion elements in the form of deflectors, parachutes and/or parafoils may be attached to the cable and/or the airship itself. Although the connection cable of the airship may reach considerable lengths, in such a solution the propulsion elements (deflectors, parachutes, parafoils) have limited freedom of movement to catch the winds at different altitudes.

Patent document US 2012/312918 A1 describes a system comprising two aircraft connected by a respective connection cable. A sail may be attached to each aircraft, where each sail may be controlled to produce lift by increasing the tension in the connection cable and/or to make the aircraft to which it is attached increase in altitude.

Summary of the invention

An object of the present invention is to realize a piloting system for aircraft that enables more precise and faster maneuvering and piloting operations in the stratosphere. Another object is to allow greater freedom of maneuver by offering the possibility of piloting an aircraft in directions other than the directions of the winds in the stratosphere.

The above and other objects and advantages, which will be better understood below, are achieved according to the present invention having the characteristics set forth in independent claim 1. Preferred embodiments of the invention are set forth in the dependent claims.

In summary, the present invention discloses a piloting system for aircraft stationed in the stratosphere comprising an aircraft configured to reach a first altitude and immersed in a first wind, at least two sail towing means bounded to the aircraft, at least two nodal devices, at least one connection cable connecting the aircraft to the sail towing means, first and second sensor means, and a control unit. The two sail towing means each comprise at least one sail, are orientable and are configured to reach a second and third altitude to capture a respective wind and exploit its propulsive force to adjust the altitude of the aircraft and/or pilot the aircraft in a desired direction. A nodal device is arranged on each sail towing means, which is connected to a sail of the sail towing means to enable it to change orientation. The first sensor means, arranged on the aircraft, acquire data on the aircraft's altitude and a direction and speed of the first wind, while the second sensor means, arranged on the sail towing means, acquire data on the sail towing means’ altitude and a direction and speed of the wind. The control unit is configured to acquire data on altitude, wind speeds and directions from the first and second sensor means, acquire command data indicative of a desired direction or destination, correlate and process the acquired data, and generate command signals that are provided to the nodal devices to adjust the orientation of the relevant sails.

Brief description of the drawings

The features and advantages of the present invention will be evident from the following description, which is given by way of example and not limitation. Reference is made to the accompanying drawings, in which:

Figure 1 is a perspective view of the piloting system of the present invention;

Figures 2A and 2B are, respectively, a perspective view and a frontal view of an embodiment of a sail towing means;

Figures 3A and 3B are, respectively, a perspective view and a frontal view of an alternative embodiment of a sail towing means;

Figure 4 is a perspective view of an alternative embodiment of the piloting system of the present invention;

Figure 5 is a perspective view of an alternative embodiment of the piloting system in Figure 4;

Figure 6 is a perspective view of a piloting system of the present invention with a communication device and a wind generator;

Figure 7 is a perspective view of the orientation adjustment of sail towing means; and

Figure 8 is a perspective view of an alternative embodiment of the piloting system of the present invention.

Detailed description

Referring to the drawings, the reference numeral 10 denotes as a whole a piloting system for an aircraft 12 stationed in the stratosphere comprising, in addition to the aircraft 12, at least two sail towing means 14, 16 bounded to the aircraft 12, at least two nodal devices 20, 22, at least one connection cable 24, 26, first and second sensor means 28, 30 and a control unit 32 (Figure 1).

The aircraft 12 does not have a propulsion motor, but is connected to propulsion means, in the form of sail towing means 14, 16, capable of adjusting the altitude of the aircraft, to keep it at a predetermined altitude or vary its altitude, and/or to move it in a desired direction, to vary the geographical coordinates of its position.

The aircraft 12 may be rigid or at least partially rigid, or it may be flexible. For example, the aircraft 12 may be in the form of an aerostat, such as a balloon or airship, or it may be in the form of an aerodine, such as a glider, a kite, an hang-glider, or it may be another unmanned aerial vehicle, such as a “leading edge inflatable kite”, a “ram-air kite”, and is stationed in the stratosphere at a first altitude q1 and immersed in a first wind v1.

In order to be able to be stationed for long periods in the stratosphere, the aircraft 12 may be without a pilot on board and be controlled in its stationing and movements by means of the piloting system 10 as described below.

The sail towing means 14, 16 may be in a closed or folded form, or they may be in a permanently open form. When in open form they are capable of capturing a wind and exploiting its propulsive force to hold the aircraft 12 at an altitude or piloting it in a desired direction.

Each sail towing means 14, 16 may comprise a sail of canvas or other flexible material; alternatively, the sail may comprise a flexible wall having a given thickness and texture, capable of assuming a concave shape to capture the wind. According to other embodiments, the sail towing means may be in the form of a shell comprising a rigid or semi-rigid wall having a concave surface.

Preferably, each sail towing means 14, 16 includes at least one sail 18 (Figures 2A and 2B), which may be made, for example, in the form of a parachute or parafoil or “ram-air” or “power-kite”.

A sail configured as a “ram-air” (Figures 2A and 2B) may be advantageous and more performing for going upwind, i.e. to windward, which will be the typical pace of the upper sail towing means 14.

The sail 18 of the sail towing means 14, 16 may be made of polyester to resist ultraviolet rays and the stresses exerted on it by the wind, and to maintain a low weight.

Optionally, sail towing means 14, 16 may comprise a rigid or semi-rigid frame 48 (Figures 3A and 3B), adapted to hold the relevant sail deployed, made of strong, lightweight materials, such as carbon fiber or Kevlar; alternatively, the frame may be hollow and filled with, for example, air or polyurethane foam.

The frame 48 may include one or more fixed or articulated elements 50 to form an articulated mechanism, for example an articulated polygon. When sail towing means 14, 16 incorporate a frame 48 they may, for example, be in the form of a kite.

Overall, the shape of the sail towing means 14, 16 may be substantially flat or concave, as required, to increase or optimize wind capturing capacity or the surface area of the sail in contact with the wind. Furthermore, the sail towing means 14, 16 may have the same shape and size in relation to each other or different shapes and/or sizes with respect to each other. Each sail towing means 14, 16 is tensile strength and may indicatively weigh between about 5 kg and about 30 kg.

The frame 48 may allow the sail 18 to deploy and remain open while the piloting system 10 is stationed in the stratosphere, thereby increasing its stability. Furthermore, the frame 48, when in the form of an articulated mechanism, may be adjustable so as to adjust the opening width of the sail 18 to better exploit the propulsive force of the wind.

In an embodiment, the sail towing means 14, 16 may each comprise at least two tie rods 38, 40 (Figures 1, 2A and 3 A) acting on the sail 18 and adjustable in length. Preferably, each sail towing means may include three tie rods, each of which may be adjusted in length to define a direction of the relevant sail towing means. For example, two tie rods may be arranged laterally and a third tie rod may be arranged centrally on the sail towing means to adjust its lateral and frontal inclination, respectively.

Said tie rods 38, 40 may be connected at one of their distal ends 38a, 40a to the sail 18 of the sail towing means 14, 16 or may be connected to the frame 48 of the sail towing means 14, 16, or any combination thereof. In particular, each tie rod 38, 40 may be connected at a relative distal end 38a, 40a to a different point of the sail towing means 14, 16.

The sail towing means 14, 16 are orientable and configured to reach a second q2 altitude and a third q3 altitude respectively. Different modes of piloting or maneuvering the aircraft are possible, which may be selected according to requirements and weather conditions.

According to a possible piloting mode (figure 1), the sail towing means 14, 16 may reach different altitudes from each other and different from that of the aircraft 12, i.e. one sail towing means 14 may be placed at a higher altitude q2 and the other sail towing means 16 may be placed at a lower altitude q3 than the aircraft 12. For example, the components of the piloting system may be arranged as follows: with the aircraft at an altitude q1 of less than 20000 m, a first sail towing means 14 may reach an altitude q2 of about 26000 m, a second sail towing means 16 may reach an altitude q3 lower than the aircraft's altitude, for example at about 18000 m. In this piloting mode, the sail towing means 14, 16 may be subject to winds (v1, v2, v3) with different speeds and directions.

According to a different mode of maneuvering or piloting the aircraft (Figures 4 and 5), the second altitude q2 reached by a sail towing means 14 may be similar to the altitude q1 of the aircraft 12 and the third altitude q3 reached by the other sail towing means 16 is lower than the altitudes q1 of the aircraft 12 and the altitude q2 of the sail towing means 14. For example, the components of the piloting system may be arranged as follows: the aircraft and a first sail towing means 14 may reach an altitude below 20000 m and a second sail towing means 16 may reach an altitude below that of the aircraft. In this mode of operation, the aircraft 12 and a sail towing means 14 are subjected to the same wind having a given wind speed and direction, which is different from the wind speed and direction to which the other sail towing means 16 is subjected.

The sail towing means 14, 16 may have different dimensions between each other. For example, the sail towing means 14 at altitude q2, i.e. the one arranged at the upper altitude, may have a larger size than the sail towing means 16 arranged at the lower altitude q3.

Preferably, the sail towing means 14 at the upper altitude q2 is provided with a frame 48 so as to be more rigid than the lower sail towing means 16. Alternatively or additionally, the sail towing means 14 may have a sail of rigid or semi-rigid consistency.

In an embodiment (not illustrated), a back-up sail towing means may be provided on board the aircraft 12 to be deployed in the event of an emergency, for example if a sail towing means 14, 16 suffers structural damage.

Reaching altitudes q2, q3 allows the sail towing means 14, 16 to capture at least a second wind v2 and a third wind v3, present at altitudes q2 and q3 respectively, and exploit their propulsive force in order to adjust the aircraft's altitude and/or piloting it in a desired direction and possibly different from the directions of the winds present at that time, thus offering considerable freedom in piloting and maneuvering the aircraft.

At least two nodal devices 20, 22 are also associated with the system (Figures 1, 4 and 5), each arranged on a respective sail towing means 14, 16 and also connected to a sail 18 of the respective sail towing means 14, 16. The nodal devices 20, 22 may be connected indirectly to aircraft 12 (Figure 1), or at least one nodal device 20 may be connected directly to aircraft 12 (Figures 4 and 5). The nodal device 20, 22 may be connected directly to the sail 18 of the sail towing means 14, 16, or may be connected to the frame 48 of the sail towing means 14, 16, or to the tie rods 38, 40 connected to the sail towing means 14, 16. Each nodal device 20, 22 may be arranged on the respective sail towing means 14, 16 in one of the positions described above.

The nodal devices 20, 22 are configured to allow a variation in orientation of the respective sail 18. In an embodiment (Figure 1), the nodal devices 20, 22 may comprise first winding and unwinding means 42, for example winches or rollers, to adjust the length of each tie rod 38, 40 connected to the sail towing means 14, 16 and consequently vary the orientation of the sail 18.

In an alternative embodiment, the nodal devices 20, 22 may be configured to adjust the orientation of the sail 18 by modifying the shape of the frame 48 when in the form of an articulated mechanism or polygon, for example by opening and widening, or by narrowing or closing the frame 48.

In an embodiment, illustrated in Figure 1, the piloting system 10 may include at least two connection cables 24, 26 connecting the aircraft 12 respectively to the at least two sail towing means 14, 16, i.e. each sail towing means 14, 16 may be connected to the aircraft 12 by means of a respective connection cable 24, 26 such that each sail towing means 14, 16 may be independently controlled with respect to the others, thus being able to reach altitudes q2, q3 different from each other and different from the altitude q1 and capturing different winds v2, v3. In addition, each sail towing means 14, 16 may be individually oriented with respect to the wind v2, v3 by means of the respective nodal device 20, 22.

In said embodiment, the piloting system 10 may also comprise an intermediate connection cable 60 that connects the at least two connection cables 24, 26 to the aircraft 12, as illustrated in Figure 8. The intermediate connection cable 60 may have a first end tethered to the aircraft 12 and a second end, remote from the aircraft 12, that is respectively connected to the two nodal devices 20, 22 by the respective connection cables 24, 26. The intermediate connection cable 60 may be advantageously used to minimize or dampen undesirable and/or excessive traction of the sail towing means 14, 16 on the aircraft 12.

In an alternative embodiment, illustrated in Figures 4 and 5, a sail towing means 14 may be directly connected to the aircraft 12 by means of tie rods 38, 40 and the other sail towing means 16 may be connected to the aircraft 12 by means of a connection cable 26. In this embodiment, the tie rods 38, 40 may have a length of between 20 and 30 meters. The connection cables 24, 26 may, for example, be made of high-molecular- weight synthetic fiber materials, e.g. Gel Spun Polyethylene (Dyneema®) with low weight and high tensile strength. When fully deployed, the connection cables 24, 26 may reach long lengths of, for example, up to 10000 m.

A distal end 24a, 26a of the connection cable 24, 26 may be connected directly to the sail 18 of the sail towing means 14, 16, or to the nodal device 20, 22, or to the frame 48, or to the tie rods 38, 40 of the sail towing means 14, 16. It is to be understood that each connection cable 24, 26 may be associated with the sail towing means at any of the indicated points.

In an embodiment, the connection cable 24, 26 may comprise second winding and unwinding means 44, for example winches or rollers, used to adjust its length in use by bringing the sail towing means 14, 16 closer to or further away from the aircraft.

In particular, the second winding and unwinding means 44 may be arranged on the aircraft 12 and may be associated with a proximal end 24b, 26b of the connection cable 24, 26 (Figure 1). Alternatively, the second winding and unwinding means 44 may be arranged on the sail towing means 14, 16 or the nodal device 20, 22 and may be associated with the distal end 24a, 26a of the connection cable 24, 26.

In an alternative embodiment, the connection cable 24, 26 may have a fixed length in which its proximal end 24b, 26b may be directly connected to the aircraft 12 and its distal end 24a, 26a may be directly connected to the nodal device 20, 22, or to the sail 18, the frame 48, or the tie rods 38, 40 of the sail towing means 14, 16. Possibly, in such an embodiment the connection cable 24, 26 may be folded during the launch of the aircraft 12 and deployed in its full length once the aircraft 12 reaches the desired altitude.

According to one embodiment, a piloting system 10 comprising an aircraft 12, at least two sail towing means 14, 16, each comprising at least one sail 18, at least two tie rods 38, 40 each having one end tethered to one of the sails, at least two nodal devices 20, 22, and at least one connection cable 24, 26 is proposed. The two nodal devices 20, 22 may both be bounded to the aircraft 12 and may each be associated to one of the sail towing means 14, 16. Each nodal device may comprise respective first winding and unwinding means 42 for adjusting the length of each tie rods 38, 40 and consequently varying the orientation of the sail 18. The at least one connection cable 24, 26 may be interposed between the aircraft 12 and at least one of said nodal devices 20, 22 to connect at least one of the nodal devices 20, 22 to the aircraft 12.

Preferably, at least two connection cables 24, 26, each interposed between the aircraft 12 and a respective nodal device 20, 22 are provided to connect the nodal devices 20, 22 to the aircraft 12.

Optionally, at least one of the nodal devices 20, 22 is connected to the aircraft 12 directly and not by a connection cable.

Installed on board the aircraft 12 are the first sensor means 28 (Figure 1), which are configured to acquire data on the altitude q1 at which aircraft 12 is located and on a direction dl and a speed si of the first wind v1 present at that first altitude q1.

The second sensor means 30 are installed on the sail towing means 14, 16 (figure 1) and are configured to acquire data on the altitude q2, q3 at which the sail towing means 14, 16 is located and on a direction d2, d3 and wind speed s2, s3 present at altitude q2, q3.

In the embodiment in which one sail towing means 14 is directly connected to the aircraft 12 by means of tie rods 38, 40 and the other sail towing means 16 is connected to the aircraft

12 by means of a connection cable 26, the second sensor means 30 may only be arranged on the sail towing means 16 connected to the aircraft 12 by means of the connection cable 26.

First and second sensor means 28, 30 may for instance include GPS systems.

The first sensor means 28 may be arranged in a front area 12a, or in a rear area 12b, or at the top 12c of the aircraft 12, or in a combination of said positions, consistent with the shape of the aircraft 12 itself. Preferably, the first sensor means 28 are arranged on an external surface

13 of the aircraft 12 so as to be able to intercept the wind v1 in which the aircraft 12 is immersed.

The second sensor means 30 may be arranged on the sail 18, or on the frame 48, or on the tie rods 38, 40 of the sail towing means 14, 16, or in a combination of the preceding positions according to the shape of the sail towing means 14, 16 to maximize the wind v2, v3 detected by the second sensor means 30. In an alternative embodiment, the second sensor means 30 may be arranged on the nodal device 20, 22 associated with the respective sail towing means 14, 16.

The piloting system 10 also comprises a control unit 32 which may be arranged on the aircraft 12 (Figure 1) or on the ground. The control unit 32 may communicate with the first sensor means 28, the second sensor means 30, the nodal devices 20, 22 and/or with a programmable memory (not illustrated) provided on board the aircraft.

The control unit 32 is configured to acquire data relating to the first altitude q1 of the aircraft 12, the second and third altitudes q2, q3 of the sail towing means 14, 16 and the speeds s1, s2, s3 and directions d1, d2, d3 of the winds v1, v2, v3 from the first and second sensor means 28, 30. Such data acquisition may be made in real time or the acquisition may be made at a predetermined sampling rate.

In addition, the control unit 32 is configured to acquire command data indicative of a desired direction or destination. Such command data may be a signal transmitted from the ground or may be provided in the programmable memory on board the aircraft 12 supplied in real time or at a specified frequency.

In an embodiment, the control unit 32 may be configured to acquire data (speeds and directions) of winds at altitudes other than q1, q2 and q3 such that winds present in surrounding areas may be mapped and captured by the sail towing means 14, 16 to move the aircraft 12 to a desired destination. Such data may be provided to the control unit 32 by aerostatic devices, disposed in the stratosphere, which are not part of the present invention, or by probes (not illustrated) connected to the sail towing means 14, 16 by means of a cable. When the acquired data is available, the control unit 32 correlates and processes said data and based on the results generates control signals which are supplied to the nodal devices 20, 22 to adjust the orientation of the respective sails 18. The orientation of the sail towing means 14, 16 may be done as described above by means of the adjustment of the tie rods 38, 40 or by means of the adjustment of the frame 48.

Alternatively or additionally, when the acquired data is available, the control unit 32 generates command signals which are provided to the second winding and unwinding means 44 to adjust the length of the connection cable 24, 26, bringing the sail towing means 14, 16 closer to or further away from the aircraft 12 itself.

The control signals to the nodal devices 20, 22 for adjusting the orientation of the sail towing means 14, 16 and those to the second winding and unwinding means 44 for adjusting the length of the connection cable 24, 26 of the sail towing means 14, 16 allow the adjustment of each sail towing means 14, 16 which may quickly reach the respective altitude q2, q3 and capture the wind v2, v3 to piloting the aircraft 12 in the desired direction.

The piloting system 10 may also comprise a plurality of transmission means 46 which may be operatively associated with the first and second sensor means 28, 30, for transmitting data acquired by said sensor means to the control unit 32, for example, by means of wireless data transmission.

In an alternative embodiment, when the control unit 32 is arranged on board the aircraft, it may be contemplated that the first sensor means 28 transmit the acquired data to the control unit 32 by means of a wired connection and that transmission means 46 are arranged for wireless communication between the second sensor means 30 and the control unit 32.

Preferably, the aircraft 12 may be provided with a communication device 34 (Figure 6) for receiving and transmitting signals or data.

The signals and/or data transmitted by the communication device 34 may be radio-frequency signals, such as for Internet connectivity and/or Earth observation. Advantageously, the communication device 34 may be arranged on the aircraft 12 in such a way as to have greater stability or be subject to gradual shifts and/or minimal oscillations in operation.

In addition, the aircraft 12 may also be provided with a wind generator 36 (Figure 6) for generating electricity by harnessing the wind v1 in which the aerostat 12 is immersed. The generated wind power may be used to power the communication device 34.

There are several possible ways of arranging the aircraft's piloting system 10 in the stratosphere, which may be used depending on the configuration of the aircraft 12 and the sail towing means 14, 16.

In an embodiment (not illustrated), the piloting system 10 may be brought into the stratosphere by means of a motorized aircraft, such as an airplane, or the piloting system 10 may be brought by a motorized aircraft into the vicinity of a jet stream, exploiting which it may reach the desired altitude q3. Upon reaching the desired altitude q3, the piloting system 10 deploys a sail tow means 14 which opens and orients itself to capture the wind present at that altitude in the stratosphere. Then the aircraft 12 begins a descent to its operational altitude q1 by means of the towed motorized aircraft. Once the descent of the aircraft 12 to its operational altitude q1 is complete, the piloting system releases the other sail towing means 16 in closed form which lowers in altitude until it reaches a relative operational altitude q2 and then opens and orients to capture the wind present at that altitude in the stratosphere.

The operation of the piloting system 10 of the present invention is as follows. When the piloting system 10 reaches the stratosphere, it remains therein by exploiting the winds v1, v2, v3 present in the stratosphere itself at different altitudes. In particular, the aircraft 12 arranges itself at the first altitude q1 at which the first wind v1 is present. The aircraft 12 may arrange itself against the wind, for example when in airship or glider form. When in glider form, the aircraft may also arrange itself so as to receive the wind sideways. Advantageously, by arranging itself against the wind, the flow of air into the wind generators will be greater and, therefore, the energy produced will be greater. The sail towing means 14, 16, deployed reach the second altitude q2 and the third altitude q3 to capture the second wind v2 and the third wind v3 and are exploited in order to maintain the position of the aircraft 12 or to generate propulsion and piloting the advancement of the aircraft 12 in a desired direction or to maintain the position. The first wind v1, the second wind v2 and the third wind v3 may have a speed s1, s2, s3 between 20 km/h and 180 km/h. Preferably, the aircraft 12 is positioned at an altitude q1 where a wind v1 with a speed si of about 80 km/h is present.

The wind v1 to which the aircraft 12 is subjected, the second wind v2 and the third wind v3 to which the sail towing means 14, 16 are subjected may have directions that are concordant with each other or different, i.e. forming an angle.

When immersed in a wind v2, v3, the sail 18 of the sail towing means 14, 16 is subjected to an aerodynamic force that may be decomposed into aerodynamic resistance D, having a direction dD parallel to the direction d2, d3 of the wind v2, v3, and lift L having a direction dL perpendicular to the direction d2, d3 of the wind v2, v3 and allowing the sail 18 to change its altitude q2, q3 by rising or falling. Resistance D and lift L acting on the sail 18 of the sail towing means 14, 16 will have different intensities id, iL depending on the orientation of the sail towing means 14, 16 with respect to the direction d2, d3 of the wind v2, v3.

By appropriately defining direction dD, dL and intensity iD, iL of the drag D and lift L it is possible to pilot the sail towing means 14, 16. Indeed, by keeping the orientation of the sail towing means 14, 16 constant relative to the direction d2, d3 of the wind v2, v3 it is possible to maintain the altitude q2, q3 of the sail tow means 14, 16. By changing the orientation of each sail towing means 14, 16, by means of an adjustment of the lengths of the tie rods 38, 40 (figure 7), with respect to the wind v2, v3 to which it is subjected, it is possible to vary the intensities iD, iL of the resistance D and of the lift L and thus to make the altitude q2, q3 change to the sail towing means 14', 16', which will be at a greater or lesser altitude than the previous one. This change in altitude q2, q3 of the sail towing means 14, 16 occurs quickly as a result of its change in orientation, immersing the sail towing means 14, 16 in a wind different from the previous one. Each sail towing means 14, 16, arranged at an altitude q2, q3, exerts on the respective connection cable 24, 26 to the aircraft 12 a traction force which is transferred to the aircraft 12 itself. The aircraft 12, arranged at the first elevation q1, is then subjected to the wind v1 and a traction force received by each of the sail towing means 14, 16. By balancing the wind force v1 and the traction forces, it is possible to keep the aircraft 12 in a defined position, thus keeping it in equilibrium. Alternatively, by varying the contribution of the traction force that is transferred to it by at least one of the sail towing means 14, 16 it is possible to piloting the aircraft 12 forward towards a desired direction, for example by making movements at the same altitude, or it is possible to vary its altitude q1 by making it rise or lower. The presence, in the piloting system 10 for the aircraft 12, of at least two sail towing means 14, 16 which are independent of each other makes it possible to maneuver the aircraft 12 in the stratosphere quickly and precisely at desired points in the stratosphere.

While specific embodiments of the invention have been described, it must be understood that this disclosure is provided purely for illustrative purposes and that the invention is not to be limited in any way by it. Various modifications will become apparent to those skilled in the art in the light of the above examples. The scope of the invention is limited only by the appended claims.