Large vertical takeoff and landing aircraft

Abstract

An aircraft 1 comprising: a fuselage1 ; a forward lifting wing 2 with a first wingspan; an aft lifting wing 4 with a second wingspan, where the second wingspan is larger than the first wingspan; a first and second proprotor 3 mounted at each wing tip of the forward lifting wing; a third and fourth proprotor 3 mounted at each wing tip of the aft lifting wing; and a fifth and sixth proprotor 5 mounted on the aft lifting wing between the fuselage and each of the third and fourth proprotors. A method of use is also disclosed wherein each proprotor is rotated at 90 degrees to a top surface of the forward and aft wings; the aircraft takes off vertically; each proprotor is rotated so that it is oriented in a direction which is parallel to the direction of flight and to the top surface of the lifting wings for forward flight; each proprotor is rotated so that it is orientated at 90 degrees to the top surface of the wings; and the aircraft lands vertically.

Description

Technical Field The present disclosure relates to the field of vertical take-off and landing (VTOL) aircraft. Technical Background Large urban areas are often difficult to navigate due to severe road congestion and inadequate ground-based public transport. The majority of trips required in this environment are less than 50 kilometres, and modern batteries have enabled electric aircraft that can fly this distance and more. Vertical take-off and landing (VTOL) allows for passenger transport within congested urban areas without the need for long runways. Combining electric propulsion with VTOL has enabled a new class of so-called eVTOL aircraft. Significant entrants into this class of aircraft include Volocopter, Joby, Archer, Supernal, Autoflight, and Vertical Aerospace, among others. The concept of urban air mobility relies on eVTOLs performing these missions commercially. All the above existing eVTOL aircraft are designed for 1-6 passengers, which can lead to relatively high operating costs per passenger-mile, similar to private aircraft or helicopters today. It is anticipated that a large proportion of proposed eVTOL aircraft journeys will be from a limited number of verbports, for example from downtown to the airport, and a much larger aircraft may enable significant cost reduction by carrying more passengers at a time, similar to the cost advantages of a bus over private cars. Furthermore, there are significant reductions in airspace congestion, and frequency of operation - which can be less obtrusive in a crowded urban area. At the same time the energy usage and subsequent environmental impact per passenger may be reduced. The current state of the art in the engineering technical design of such aircraft has experienced challenges and problems, including how to make a large eVTOL aircraft provide enough lift, efficiently, in helicopter mode (where the aircraft is moving vertically) to lift 20-50 passengers while also being compact enough to utilize existing ground infrastructure. In addition, it is preferable that the weight and acquisition costs be minimized, along with operating costs. To this end overall complexity and aerodynamic drag should be minimized and the aerodynamic interference of combination lift / propulsion units should be well managed. Summary Disclosed is an aircraft as claimed in claim 1. Preferred technical features are recited in the dependent claims. Also provided is a method of operating an aircraft, as claimed in claim 10. Brief Description of the Drawings Figure 1 shows an isometric view of the aircraft in helicopter mode, according to a preferred embodiment; Figure 2 shows a plan view of the aircraft in airplane mode, with the forward and aft wings and the wingbp and inboard propulsion units horizontal in order to provide forward thrust, according to a preferred embodiment; Figure 3 shows a left profile view of the aircraft in airplane mode, according to a preferred embodiment; Figure 4 shows a front view of the aircraft in airplane mode, according to a preferred embodiment; Figure 5 shows a plan view of the aircraft in helicopter mode, with the landing gear extended. The dp propulsion units are tilted up roughly 90 degrees, and the forward sections of the inboard propulsion units are also tilted, in order to provide vertical lift, according to a preferred embodiment; Figure 6 shows a left profile view of the aircraft in helicopter mode, according to a preferred embodiment; Figure 7 shows a front view of the aircraft in helicopter mode, according to a preferred embodiment; Figure 8a is a flowchart showing an operation of the aircraft, according to a preferred embodiment; and Figure 8b is a diagram showing the aircraft at each step of the flowchart of Fig. 8a. Detailed Description of Preferred Embodiments The preferred embodiment relates to a large eVTOL aircraft as shown in Figs. 1 and 2. This aircraft in Figs. 1 and 2 preferably includes a fuselage 1 (see Fig. 2) which accommodates between 20 to 50 passengers, supported on two lifting wings - a smaller forward wing 2 (Fig. 2) with a tilting propulsion unit 3 at each wing tip, and a larger aft wing 4 with similar wingtip propulsion units 3 and two additional propulsion units 5 mounted on the leading edge 9 (Fig. 2) of the aft wing 4, between the fuselage and the wing tip. Each propulsion unit 3 comprises a combination propeller / rotor (proprotor) with its electric motor and associated drive and control systems. The aircraft is shown in helicopter mode in Fig. 1, with the wingtip propulsion units 3 tilted up and the forward section of the inboard propulsion units 5 tilted up. In this configuration the aircraft will take-off and climb until clear of the ground infrastructure, at which point it will tilt some or all of the propulsion units down approximately 90 degrees to provide forward thrust and continue to climb to its cruise altitude (which is referred to here as the aircraft being in airplane mode). Upon approach to its destination, it will slow and descend and will tilt the proprotors back up into helicopter mode for its final approach and landing. The aircraft according to a preferred embodiment is shown in airplane mode in Fig. 2, which shows a fuselage 1 that accommodates between 20 and 50 passengers plus crew. It has internal hand baggage space and an externally-accessible baggage compartment for larger luggage. The forward wing 2 is mounted on the top of the fuselage and supports a propulsion unit 3 at each wing tip. The aft wing 4 has a greater wingspan and supports a propulsion unit 3 at each wing tip, and in addition has two inboard propulsion units 5 mounted on the wing leading edges between the fuselage and the tip-mounted units. As shown in Fig. 1, the aft wing 4 is preferably up to twice as large in wingspan as compared to the forward wing 2. For example, in the preferred embodiment, where the aircraft can seat 30 people, the aft wing 4 has a span of 17.5m from wing tip to wing tip, whereas the forward wing 2 has a span of 10.0m. A preferred range for these lengths can be between 15m and 20m for the aft wing 4 and between 8m and 12m for the forward wing 2, depending upon the number of passengers. Each propulsion unit comprises a proprotor which has a diameter and number of blades that will vary with the exact size of the aircraft. For example, in a preferred embodiment, where the aircraft can seat 30 people, each proprotor has a diameter of 4.5m and has between 5 and 7 blades. A preferred range for the diameter can be between 4m and 6m. Each proprotor has an electric motor(s) that may drive the proprotor directly or via a gearbox, and also has the electronics required to drive the motors from a battery supply. The nominal lateral extent of the proprotors is illustrated by the dashed lines 6 in Fig. 4. The wing taper ratio, dihedral, and leading-edge sweep angles are subject to variation as deemed appropriate for specific sizing and applications. For example, in the preferred embodiment where the aircraft is designed to seat 30 people, the proposed values for these are: taper ratio: forward wing 2 - 0.55, aft wing 4 - 0.4; both wings' dihedral - 0 degrees; both wings' leading-edge sweep - 0 degrees. Preferred ranges for each of these are as follows: taper ratio; forward wing 2 - between 0.4 and 0.6, aft wing 4 - between 0.35 and 0.55: both wings' dihedral; between -2 and +3 degrees; both wings' leading-edge sweep -between -5 and +5 degrees. The control surfaces on the wing trailing edges 7 (in Fig. 2) are shown in their airplane mode position. The locations of the wings 2 and 4 on top of the fuselage 1 are shown in profile in Figure 3, and in Figure 4 the relationship between the fuselage 1 and the wings 2 and 4 is most clear. The extent of each proprotor is indicated by the dashed circles 6. Note that the exact height of each wing above the fuselage may not be the same as the aerodynamic interference impact is established. For example, in the preferred embodiment, the heights of the wings 2 &4 may be the same. Preferred ranges for these values may be up to 0.5m different. The relationship between the 6 proprotors and the wings 2 and 4 and fuselage 1 is shown in Figure 5 and the propulsion units 3 and 5 are shown in the helicopter mode. Note that the relationship between the wings and rotors will be optimized to minimize the rotor downwash impact on the wings and thus optimize lift. Specifically note that the control surfaces 7 shown in Figure 2 are not visible in Figure 5 as they are folded down out of the way of the proprotor downwash. The profile view of the aircraft in helicopter mode is shown in Fig. 6, illustrating how the 4 wingtip propulsion units 3 rotate in entirety while only the forward section of the inboard units 5 tilts. This view also illustrates a notional landing gear configuration 8. As shown in Fig. 7, the front view of the aircraft in helicopter mode, shows the propulsion units 3 and 5 tilted up to provide lift and control in hover. The amount of inboard / outboard tilt will be optimized to minimize interference between rotors but will be in the region of 2 -5 degrees. Fig. 8a is a flowchart that shows the steps of a method of operating the described aircraft. A first step 81, pre-takeoff, at least two of the proprotors, preferably all 6 of the proprotors, are rotated so that their axes are oriented at, or approximately at, 90 degrees to the ground. In this position, the aircraft is in helicopter mode, where it will be loading passengers and baggage, and charging the batteries as required. At a second step 82, takeoff, where the aircraft is performing vertical take-off, the landing gear is retracted and the aircraft climbs vertically to a safe altitude. At a third step 83, cruise, at least two of the proprotors, preferably all 6 of the proprotors, are rotated so that they are oriented in a direction which is parallel or approximately parallel, to the direction of flight while the aircraft accelerates to cruise speed. In this position, the aircraft is in airplane mode, where the aircraft has reached its cruising altitude and moves horizontally to its destination. At a fourth step 84, approach &landing, at least two of the proprotors, preferably all 6 of the proprotors, are rotated so that they are oriented at, or approximately at, 90 degrees to the ground in helicopter mode, while the aircraft decelerates to enter a hover and extend the landing gear. At a fifth step 85, post landing, the aircraft has performed a vertical landing at the aircraft's destination. The aircraft taxis to the terminal to unload passengers and baggage and the batteries are plugged in to charge, if appropriate. Fig. 8b shows the aircraft at each step 81, 82, 83, 84, and 85 of the method, according to the flowchart of Fig. 8a. Accordingly, the present disclosure proposes a unique configuration for a VTOL aircraft, which is preferably an eVTOL, which addresses at least some of the above-described technical engineering challenges, as well as others. This configuration preferably features wings and proprotors sized for efficiency while minimizing download from the proprotor downwash onto the wings and retaining a compact footprint allowing it to access many verti ports. Control in airplane mode is provided by one or more hinged control surfaces 7 on each wing. In helicopter mode control is provided by one or more rotors having variable blade cyclic and / or collective pitch and variable RPM (revolutions per minute). The hinged control surfaces 7 may be displaced downward approximately 90 degrees under the rotors to minimize the download from the tip rotors' downwash. Although a battery-electrically powered aircraft is used in the preferred embodiment, the aircraft could also be powered by other means, such as standard fuels or hydrogen fuel cell. The aircraft disclosed preferably relates to a 20-50 passenger battery-electric aircraft capable of vertical take-off and landing.

Claims

1. An aircraft comprising:a fuselage;a forward lifting wing with a first wingspan;an aft lifting wing with a second wingspan, where the second wingspan is larger than the first wingspan, wherein the aft lifting wing has an aft lifting wing leading edge;a first and second proprotor mounted at each wing tip of the forward lifting wing;a third and fourth proprotor mounted at each wing tip of the aft lifting wing; anda fifth and sixth proprotor mounted on the aft lifting wing leading edge between the fuselage and each of the third and fourth proprotors.

2. The aircraft according to claim 1 where at least two of the proprotors tilt.

3. The aircraft according to claim 2 wherein at least two of the proprotors tilt by 90 degrees.

4. The aircraft according to claim 1 where at least two of the proprotors adjust collectiveblade pitch or RPM or both to control the proprotor thrust and thus the aircraft attitude.

5. The aircraft according to claim 1 where at least two of the proprotors have variable cyclic blade pitch.

6. The aircraft according to claim 1 wherein the aircraft is electrically-powered.

7. The aircraft according to claim 1 further comprising hinged control surfaces on each ofthe forward lifting wing and the aft lifting wing.

8. The aircraft according to claim 1 wherein each of the first, second, third, fourth, fifth, and sixth proprotors has a plurality of blades.

9. The aircraft according to claim 1 wherein each of the first, second, third, fourth, fifth, and sixth proprotors has an electric motor.

10. A method of operating an aircraft which comprises a fuselage; a forward lifting wing with a first wingspan; an aft lifting wing with a second wingspan, where the second wingspan is larger than the first wingspan, wherein the aft lifting wing has an aft lifting wing leading edge; a first and second proprotor mounted at each wing tip of the forward lifting wing; a third and fourth proprotor mounted at each wing tip of the aft lifting wing; and a fifth and sixth proprotor mounted on the aft lifting wing leading edge between the fuselage and each of the third and fourth proprotors; the method comprising steps of:(a) each of the proprotors is rotated so that it is oriented at 90 degrees to the top surface of the forward and aft lifting wings;(b) the aircraft takes off vertically;(c) each of the proprotors is rotated so that it is oriented in a direction which is parallel to the direction of flight and to the top surface of the forward and aft lifting wings for forward flight;(d) each of the proprotors is rotated so that it is oriented at 90 degrees to the top surface of the forward and aft lifting wings; and(e) the aircraft lands vertically.

11. The method according to claim 10 where at least two of the proprotors tilt.

12. The method according to claim 11 wherein at least two of the proprotors tilt by 90degrees.

13. The method according to claim 10 where at least two of the proprotors adjust collective blade pitch or RPM or both to control the proprotor thrust and thus the aircraft attitude.

14. The method according to claim 10 where at least two of the proprotors have variable cyclic blade pitch.

15. The method according to claim 10 wherein the aircraft is electrically-powered.

16. The method according to claim 10 further comprising hinged control surfaces on each of the forward lifting wing and the aft lifting wing.

17. The method according to claim 10 wherein each of the first, second, third, fourth, fifth, and sixth proprotors has a plurality of blades.

18. The method according to claim 10 wherein each of the first, second, third, fourth, fifth, and sixth proprotors has an electric motor.

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