HIGH ALTITUDE AIRCRAFT WING GEOMETRY

Abstract

An unmanned high altitude aircraft operating above 15 km with transmitting and/or receiving antennas, enclosed or more than half enclosed on a projected area basis normal to the plane of the antenna(s), in a wing structure where the chord length of the wing section enclosing the phased arrays or horn antennas is at least 30 percent greater than the mean wing chord length, and the wing surface adjacent to the antenna(s) in the path of the electromagnetic radiation being received or transmitted by the antenna(s) is substantially composed of material relatively transparent to this radiation.

Claims

1. An unmanned high altitude aircraft operating above 15 km with transmitting and/or receiving antennas, enclosed or more than half enclosed on a projected area basis normal to the plane of the antenna(s), in a wing structure where the chord length of the wing section enclosing the phased arrays or horn antennas is at least 30 percent greater than the mean wing chord length, and the wing surface adjacent to the antenna(s) in the path of the electromagnetic radiation being received or transmitted by the antenna(s) is substantially composed of material relatively transparent to this radiation.

2. The aircraft according to claim 1, wherein the transmitting and/or receiving antennas comprise one or more phased array or horn antennas.

3. The aircraft according to claim 1 where the wing span is greater than 30 m.

4. The aircraft according to claim 1 where the wing span is greater than 50 m.

5. The aircraft according to claim 1, where the beam axis or axes from the antenna(s)when the aircraft is in level flightis within 20 degrees of the vertical.

6. The aircraft according to claim 1, with two or more antennas where the beam axis from some or all of the antennas is at more than 20 degrees to the vertical, when the aircraft is in level flight.

7. The aircraft according to claim 1, with separate antennas used for transmitting and for receiving electromagnetic radiation.

8. The aircraft according to claim 1, with one or more additional antenna(s) operating at a higher frequencynormally at least 30%, preferably at least 100% greater than the mean operating frequency of the other antenna(s)but sufficiently small to fit into the wing structure without the encumbered wing section chord length of the additional antenna(s) being greater than 10% of the chord length of the minimum unencumbered wing section chord length adjacent to the transition sections of the additional antenna(s).

9. The aircraft according to claim 1, where the integral of the velocity field around the wing section containing the antenna is within 30% of an elliptical shape within one antenna's width along the wing at the cruising speed of the aircraft at its elevated operating altitude or a particular airspeed chosen to maximise the aircraft endurance.

10. The aircraft according to claim 1, where the integral of the velocity field around the wing section containing the antenna is within 30% of that within one antenna's width along the wing at the cruising speed of the aircraft at its elevated operating altitude or a particular airspeed chosen to maximise the aircraft endurance.

11. The aircraft according to claim 1, with the ability to vary additional flaps along the trailing edge of various sections of the aircraft wing in order to keep the circulation along the wing more elliptical and thereby reduce aerodynamic drag over a range of airspeeds at a particular altitude.

12. The aircraft according to claim 11 where the various elevator chord lengths vary by at least 10% along the wing to allow even more constant circulation for a variety of airspeeds.

13. The aircraft according to claim 1, where the lift to drag ratio of the aircraft at its operating altitude above 15 km is greater than 30:1.

14. The aircraft according to claim 1, where the aircraft wing span is at least 55 m.

15. The aircraft according to claim 1, which is used for communication to ground based user equipment such as mobile phones, computers, wearable devices, and vehicles, including both land and sea based equipment.

16. The aircraft according to claim 1, which is used for communication to aircraft based user equipment.

17. The aircraft according to claim 1, which is used for communication to satellite based user equipment.

18. The aircraft according to claim 1, carrying one or more circular, elliptical, polygonal or indented phased array antennas or antennas whose perimeter follows closelyto within 20% of the radial distance from the antenna centroid of any of the antenna shapes described.

19. The aircraft according to claim 1, which comprises a processing system operatively connected to the at least one antenna and adapted to receive external instructions via an antenna to modify additional signals for communication and not for radar.

20. A fleet of aircraft according to claim 19, working cooperatively to communicate together with a user antenna on user equipment at lower altitude than the aircraft.

Description

[0036] This is illustrated in the following figures and examples.

[0037] FIG. 1 shows in plan and side elevation an aircraft with two circular phased arrays with an approximately constant chord length for some distance from the aircraft fuselage. The wing design is similar to the design of high performance modest Reynolds number aircraft for high performance manned gliders. The Reynolds numberfamiliar to those skilled in the artis a measure of the ratio of turbulent to viscous forces concerning the relevant fluid flow. The plane thrust is provided by a plurality of propellers (1), supported by a long thin wing (105). The main wing section is of a chord length sufficiently great to accommodate the two antennas (2 and 3): it can simplify the antenna electronics and improve signal processing discrimination to have one antenna transmitting and one antenna receiving particularly if both transmission and reception are required at the same time.

[0038] FIG. 2 shows in plan and side elevation an aircraft with two circular antennas (4, 5) utilizing the invention, where the diameter of the antennas is much greater than the average wing chord length. In this case, the vertical cross section where the antennas are located is also considerably greater than the average vertical cross section of the wing. There are two substantial transition sections (T) in addition to the encumbered (E) and unencumbered UE) wing sections.

[0039] FIG. 3 shows in plan and side elevation an aircraft with four circular antennas (4,5,6,7) utilizing the invention, where the diameter of the antennas is much greater than the average wing chord length. In this case, the vertical cross section where the antennas are located is also considerably greater than the average vertical cross section of the wing. There are also as in the aircraft shown in FIG. 2, two substantial transition sections (T) in addition to the encumbered (E) and unencumbered UE) wing sections.

[0040] FIG. 4 shows in plan and side elevation an aircraft with two circular antennas (8,9) utilizing the invention, where the diameter of the antennas is much greater than the average wing chord length and the transition section is short. In this case, the vertical cross section where the antennas are located is also considerably greater than the average vertical cross section of the wing.

[0041] FIG. 5 shows an aircraft with square antennas (10,11) utilizing the invention, rather than circular antennas otherwise similar to the aircraft shown in FIG. 4.

[0042] In FIG. 6 the relatively thin phased array (61) sits just below the bottom of the wing spar (62), which can be made of conducting materials being above the main electromagnetic radiation field entering or leaving the phased array (61). The wing surface (64) defines the aerofoil shape and should be of sufficiently low conductivity when situated below the phased array if the array is communicating downwards to avoid significant interference with the electromagnetic radiation transmitted or received by the antenna(s). The top of the wing spar (63) sits just below the upper surface of the wing.

[0043] FIG. 7 shows an aircraft with two separated antennas (73,74) to provide a more uniform mass distribution and reduce structural loads on the aircraft and/or to allow reduced electromagnetic interference between the antennas.

[0044] FIG. 8 shows a plane with a large pair of antennas (82,83) and a small pair of antennas (81,82). Such an arrangement can be optimal if the communication to small antennas on the ground is carried out at much lower frequencies than the backhaul frequenciescommunication to larger antennas on the ground linking the aircraft to a core ground based network.

[0045] FIG. 9 shows an example of a multiple antennas arrangement designed to allow an individual aircraft to communicate with a much larger area on the ground than would be possible with a flat almost horizontal phased array antenna(s). Typically, flat phased arrays only project and receive within a cone of around 60 degrees to axis of the array; normally the axis is at right angles to the plane of the array. Therefore communication to transmitters or receivers, or transceivers based at an angle more than sixty degrees to the axis of the array begins to be inadequate. This problem is exacerbated if the plane pitches or rolls and continuous communication is required. The arrangement shown is mirrored on both sides of the fuselage; the centerline of the plane (92) is shown horizontally.

[0046] A plan view and three sections (AA, BB, and CC) are shown. The encumbered (E) section (91) encloses all the antennas.

[0047] There are three sets of antennas: a single horizontal antenna (94) pointing directly down, a pair of antennas (95) allowing better communication from side to side, and a pair of antennas (93) allowing better communication forward and backwards. The antennas need usually to be sited to avoid significant interference with one another. Round, ellipsoidal or more complex shapes can be envisaged as well as an inverted saucer shape. The angles can be varied and larger or smaller numbers of sets of antennas can also be used.

[0048] For a given antenna projected sizethe area of the antenna when viewed normally to the main plane of the antennato minimize aerodynamic drag, the entire antenna should usually be enclosed by the wing structure. However in some instances, the design will benefit from a modest portion of the antenna or antenna casing being outside the aerofoil cross section of the wing rather than going to the expedient of increasing the aerofoil chord length(s) in the encumbered section(s) of the wing. This may be because of the particular antenna shape not readily fitting in with the aerofoil section, being for example square rather than elliptical or circular, or for particular attachments to pods containing other equipment or access points or for a variety of other reasons. Usually the encumbered section will enclose a substantial fraction being at least 50%, preferably 80% and more preferably all of the projected area of the antenna(s).

[0049] High altitude long endurance planes fly quite slowly: typically at speeds lower than 100 m/s and more usually below 50 m/s and sometimes as slow as 15 m/s. At these velocities with the cold, low density, relatively viscous air encountered at high altitude, the wing Reynolds number is much lower than that encountered in conventional aircraft: gliders or powered vehicles. However, aerofoil sections designed for low Reynolds numbers are common in low altitude unmanned aerial vehicles, in wind turbines and other applications. Examples of such an aerofoils have been designed by for example Selig (see New Airfoils for Small Horizontal Wind Turbines, Giguere and Selig, Trans ASME, p 108, Vole 120, May 1998): particularly the aerofoils SG 6040, SG 6041, SG 6042, SG 6043, with thicknesses of respectively 16%, 10%, 10%, and 10%.

[0050] The aircraft designs described below in Table 1 show the advantages of utilizing the invention.

[0051] All cases tabulated are for the same weight of wing per unit wing area with the addition of a constant spar weight per unit width of wing. The aircraft design is for operation at a latitude of within 15 degrees of the equator, and the powers and speeds are calculated on the basis of midwinter conditions to allow station holding throughout the year. In the base case utilizing the invention, the encumbered section is designed on the basis of an SG 6040 cross section with a 16% thickness to chord length, two antenna of 1.6 m diameter with a weight of less than 6 kg/m.sup.2 (total weight of antenna+electronics=30 kg), can be fitted into the encumbered sections having a chord length of 2 m. The unencumbered sections are designed on the basis of an SG 6043 cross section.

[0052] Utilizing the invention results allows a plane of the same wingspan to either support a heavier payload and larger antenna with a similar operating speed (necessary for station-holding in many applications) than a conventional plane, or with a similar payload weight, the maximum operating speed is significantly increased.

TABLE-US-00001 TABLE 1 Comparison of classical wing and novel wing designs Novel Constant Constant design speed payload (with (classical (classical invention) design) design) Design variables Payload power (W) 350 350 350 Overall power train efficiency 70% 70% 70% Battery energy (Whr/kg) 350 350 350 Aircraft altitude (m) 18000 20000 18850 Wing span (m) 35 35 35 Wing area (m.sup.2) 43.5 56 70 Average wing chord length (m) 1.2 1.6 2.0 Overall lift to drag coefficient 43 38 37 Reynolds number of average 280,000 280,000 340,000 wing chord length Outcomes Payload weight (kg) 30 20 30 Aircraft speed (m/s) 28 28 23 Reduction in payload weight 32% Reduction in speed 18%

[0053] It can be seen that an aircraft utilizing the invention has a significantly higher payload weight (32%) than a conventional design with the same cruising speed, or a significantly higher cruising speed (18%) than planes of the same wing-span with conventional design and the same cruising speed.

[0054] This is a result of higher induced drag caused by the lower aspect ratio for wings of classical design, which reduces the energy available for the payload or results in lower aircraft speeds than would be desirable. The operating altitude has been optimized to reflect the different characteristics of the different designs.

[0055] It may also be desirable to maintain a similarity of circulation over a variety of airspeeds if for example low drag performance is necessary for high flying speeds as well as low.

[0056] In a third aspect of the invention additional wing flaps are provided in one or more of the encumbered, transitions or unencumbered sections that allow the circulation to maintained at a more elliptical level over the sections for a greater range of aircraft speeds.

[0057] In a fourth aspect of the invention the flap sections are of variable relative chord length along the wing allowing a more elliptical circulation and lower drag along the length of the wing. The relative flap chord length is defined as the distance from the leading edge of the flap to the trailing edge of the aerofoil referenced to the chord length of the aerofoil at a particular distance from the fuselage centerline. It is familiar to those skilled in aerofoil aerodynamics that deflection of an aerofoils flap results in a change to the effective local angle of attack, see Schlichting, Truckenbrodt Die Aerodynamik des Flugzeuges Bd II. Springer-Verlag 1969, p 439.

[0058] In a fifth aspect there are two main frequencies used on the plane: a relatively low frequency of between 0.5 and 5 GHz with large phased arrays which can provide uplink and down link to user equipment with a suitably long wavelength such that transmission and reception can be through rain and building walls of a reasonable thickness and secondly a higher frequency than the uplink/downlink utilizing a much larger bandwidth and smaller arrays that is used for backhaul to and from the plane. These phased arrays can have beam axes that are approximately vertical, or be made up of clusters of arrays whose axes are approximately vertical, or be clusters some of whose axes are approximately vertical and some of whom which are not.