Long-range electric transport aircraft system with air-to-air battery swapping mode and its use method

Abstract

This invention belongs to the technical field of new energy aircraft design and new energy electric power systems, specifically relating to an in-flight battery-swapping mode long-range electric transport aircraft system and its usage method. It utilizes a multi-aircraft formation flight mode with two types of aircraft. The lead aircraft, a towing aircraft, primarily provides power for cruising; one or more aircraft can be replaced mid-flight. The rear aircraft, a transport aircraft, primarily undertakes the task of loading cargo (passengers or goods), storing only a portion of backup power for safety, and has no cruising power at all; all cruising power comes from the lead towing aircraft. The two types of aircraft are connected by a detachable power cable. This significantly reduces the aircraft's energy costs, carbon emissions, and pollutant emissions during operation.

Description

Technical Field

[0001] This invention belongs to the technical field of new energy aircraft design and new energy pure electric or hydrogen-electric hybrid power systems, specifically relating to an in-flight battery swapping mode long-range electric transport aircraft system and its usage method. Background Technology

[0002] Currently, electric aircraft powered solely by batteries have attracted widespread attention due to their zero carbon emissions during operation and extremely low energy costs (calculated according to this invention, energy costs can be reduced by more than 80%). If used in civil aviation, they would have a cost advantage that would overwhelm existing high-speed rail and civil aviation. However, for the foreseeable future, the mass and volumetric energy density of batteries are extremely low compared to conventional aviation kerosene, resulting in a range of approximately 300km for battery-powered electric aircraft. Limited by advancements in battery energy density, the current mass energy density of batteries is generally in the range of 300Wh / kg, less than 1 / 10 of that of aviation kerosene, which greatly affects the market application of such electric aircraft.

[0003] Hydrogen-powered electric aircraft emit no carbon emissions during their operational phase. However, the market price of green hydrogen fuel is relatively high. Hydrogen-powered aircraft also face challenges such as the low volumetric energy density of hydrogen fuel, the need for extremely low-temperature storage which significantly consumes valuable commercial space, the low power density of hydrogen fuel cells leading to serious safety issues with hydrogen-powered engines, and the need for extensive modifications to major aircraft components like the cabin and wings. Furthermore, there are no adequate safety guarantees or solutions regarding the physical and chemical explosions of hydrogen and hydrogen embrittlement of load-bearing metal components. Even hydrogen-powered aircraft converted from existing aircraft will have limited range due to the low volumetric energy density of hydrogen fuel.

[0004] In existing technologies, glider towing is primarily used during the takeoff phase. The tow rope provides the pull for takeoff. Current aerial refueling tankers and receiver aircraft only form a short formation for towing during refueling. The towing device only transfers room-temperature liquid fuel and cannot transmit electrical energy. Aircraft formations, on the other hand, cruise for longer distances with relatively close spacing, but are not physically connected. Existing glider towing in the air or during takeoff relies on load-bearing connections; the tow rope provides the pull for takeoff and cruise, and does not transmit electrical energy. Aerial refueling tankers only transfer room-temperature liquid fuel and cannot transmit electrical energy. A schematic diagram of the existing technology is shown below. Figure 1 , Figure 2 As shown. Summary of the Invention

[0005] The purpose of this invention is to design an in-flight battery-swapping long-range electric transport aircraft system and its usage method. The aim is to significantly extend the range of existing pure electric and hydrogen fuel cell aircraft, making their range comparable to and a practical substitute for conventional aviation fuel aircraft.

[0006] To solve this technical problem, the technical solution of the present invention is as follows:

[0007] A long-range electric transport aircraft system with an in-flight battery swapping mode is provided. The aircraft system is powered by either pure battery energy or hydrogen energy, and the system comprises two parts:

[0008] Transport aircraft are equipped with a pure electric propulsion system and power batteries for takeoff, landing, and backup energy, but not with power batteries for storing cruise energy or hydrogen storage and power generation devices. Excess mass and space are reserved for commercial use, including the cabin, wings, takeoff and landing and backup power batteries, commercial cargo bays (cargo hold, passenger cabin, and cockpit), and aerial formation towing and docking equipment. The aircraft's outer wings are designed with a pair of split-type drag rudders to balance the yaw moment during lateral towing. The lateral force generated during lateral towing is offset by a slight roll deflection of lift. "Slight" here refers to a roll deflection of no more than 3 degrees, 1 degree, 2 degrees, or 3 degrees. Generally, the lift is perpendicular to the horizontal plane, and a small deflection along the fuselage axis also deflects the lift, creating a small lateral force to offset the lateral force caused by towing.

[0009] The aircraft is towing a vehicle equipped with a pure electric propulsion system and power batteries for takeoff, landing, and backup energy. It is equipped with its own cruise energy and power batteries or hydrogen fuel cells to supply cruise energy to the transport aircraft, as well as retractable power cables and power supply devices, but carries no commercial payload. This includes the cabin, wings, takeoff and landing and backup power batteries, battery compartments (using the cargo hold, passenger cabin, and cockpit to house power batteries or hydrogen fuel cells and hydrogen storage devices), power batteries can also be arranged inside components such as the wings, long-distance power supply devices, and automated retraction and deployment devices, etc.

[0010] Transport aircraft are connected to each other via a connection mechanism, which includes a power supply end and a power receiving end. The power supply end is a flexible cable with a conical sleeve at the end, and the power receiving end is a pointed conical plug. The conical sleeve of the power supply end facilitates the insertion of the power receiving end. The edge of the conical sleeve is an inflatable annular airbag that keeps the conical sleeve open after inflation and maintains a horizontal state using airflow to facilitate the insertion of the power receiving end.

[0011] The power supply cable is in a "non-load-bearing" state, meaning that the retractable power supply cable does not pull the transport aircraft. The transport aircraft is propelled by its own motor, and the power supply cable only provides electrical energy.

[0012] Depending on the different connection methods in the traction mode, the power supply end is installed at the tail or wingtip of the traction aircraft, and the power receiving end is installed at the nose or wingtip.

[0013] Both the traction aircraft and the transport aircraft adopt a triplane aerodynamic layout with a high aspect ratio and a support wing design. The high lift-to-drag ratio of the aerodynamic layout partially compensates for the insufficient mass energy density of the power battery and the volumetric energy density of the hydrogen fuel. Preferably, the aspect ratio is 13-25 and the lift-to-drag ratio is 16-25.

[0014] The tractor and transport aircraft are powered by propellers, using coaxial counter-rotating propellers with at least three pairs of propellers. All propellers are fully operational during takeoff, while during cruise (long-distance flight at a specified altitude and Mach number), only one or two pairs of coaxial counter-rotating propellers are operational, and the remaining coaxial counter-rotating propellers are powered off and their blades are folded under the resistance of the oncoming flow to reduce the overall aerodynamic drag of the aircraft.

[0015] The nose of the towing aircraft is designed to open for quick replacement of the internal energy module. Specifically, the nose can open upwards or to the side.

[0016] The traction aircraft can also use a hydrogen-electric hybrid mode, refueling with hydrogen on the ground instead of charging. Refueling with hydrogen is faster than charging, but the current price of hydrogen fuel is too high. The traction aircraft can be considered as a transport aircraft specifically designed to transport recharged power batteries.

[0017] The wingtips of both the tractor and transport aircraft are designed with a pair of drag rudders to accommodate the yaw moment caused by non-load-bearing traction at the wingtips. Roll deflection generates lift to create lateral forces that counteract these lateral forces. See Figure 6 The drag rudder has an opening angle range of 0–30°; it is installed at the outermost edge of the wing, preferably at 70%–90% of the wingspan; for example, opening to 10, 20, or 30 degrees. Specifically, it is located at the outermost edge of the wing, at 70%–90% of the wingspan.

[0018] The states of the towing and transport aircraft include: ground charging state, aircraft take-off and landing state, climb and descent state, in-flight docking state, in-flight detachment state, and towing flight state (i.e., the cruise state mentioned earlier).

[0019] When in mid-air docking mode, the distance between the towing aircraft and the transport aircraft ranges from 15 to 40 meters.

[0020] The towing aircraft can be manned or unmanned. When unmanned, the towing aircraft is controlled by the pilot of the transport aircraft.

[0021] The system also includes airport charging equipment: the airport charging equipment includes charging or hydrogen refueling equipment at airports used by transport aircraft and airports used by tractor aircraft.

[0022] The charging device is a replaceable, single-unit power battery; the hydrogen refueling device is a hydrogen storage device.

[0023] The charging or hydrogen refueling equipment is located underground to save airport surface space.

[0024] On the other hand, a method for using an in-flight battery-swapping long-range electric transport aircraft system is provided. This method involves reserving multiple non-load-bearing towing aircraft in segments along the transport aircraft's flight path, supplying power to the transport aircraft in stages, and conducting in-flight formation non-load-bearing towing flights. Each towing operation involves one or more non-load-bearing towing aircraft (e.g., two). The transport aircraft only takes off and lands once for the entire flight, but the towing aircraft take off and land multiple times. This relay-style non-load-bearing towing of the transport aircraft allows for uninterrupted flights of distances far exceeding those of conventional electric aircraft, such as the 2000km journey from Beijing to Guangzhou. On the return trip, the towing aircraft tows the transport aircraft back to its original towing airport.

[0025] Specifically, the traction modes in the method of use are divided into: single-machine non-load-bearing traction mode, dual-machine non-load-bearing traction mode and three-machine non-load-bearing traction mode.

[0026] The single-unit non-load-bearing traction mode has three connection forms:

[0027] I) The towing aircraft is connected to the nose of the transport aircraft by its tail, and the two aircraft are arranged to cruise at the same altitude.

[0028] II) The towing aircraft is connected to the nose of the transport aircraft by the left or right wingtip, and the two aircraft are arranged at the same altitude for cruising.

[0029] III) Lateral cruising at the same altitude, with the left wingtip of the towing aircraft connected to the right wingtip of the transport aircraft, or the right wingtip of the towing aircraft connected to the left wingtip of the transport aircraft. In this case, the towing aircraft must use the drag rudder of the corresponding outer wing to balance the yaw moment, and roll to deflect lift to generate lateral force to counteract the lateral force.

[0030] The dual-machine non-load-bearing traction mode has two connection methods:

[0031] I) Dual-engine traction includes the tails of two tractors being connected to the left and right wingtips of the transport aircraft, respectively;

[0032] II) The right wingtip of the left tractor is connected to the left wingtip of the transport aircraft, and the left wingtip of the right tractor is connected to the right wingtip of the transport aircraft. In this mode, the tractor must use the drag rudder of the corresponding outer wing to balance the yaw moment, and roll deflection lift to generate lateral force to counteract the lateral force.

[0033] The three-machine non-load-bearing traction mode has two connection forms:

[0034] I) All three tractors are connected to the nose, left wingtip, and right wingtip of the transport aircraft via their tail sections;

[0035] II) The middle towing aircraft is connected to the nose of the transport aircraft via its tail, and the two side towing aircraft are connected to the corresponding wingtips of the transport aircraft via their respective wingtips. In this case, the towing aircraft must use the drag rudder of the corresponding outer wing to balance the yaw moment, and roll to generate lift to create lateral force to counteract the lateral force. This is the same as the form II of the dual-aircraft towing mode.

[0036] The technical specifications of the tractor and transport aircraft are as follows:

[0037] The wing aspect ratio is 15–22, the cruising altitude is 10,000–16,000 meters, the cruising Mach number is 0.55–0.65, the cruising lift coefficient is 0.8–1.2, and the maximum lift coefficient is 1.6 (used only during takeoff and landing, not during cruise). Cruise altitude density, cruise altitude speed of sound, cruise altitude air pressure, and cruise altitude temperature are determined by standard atmospheric pressure and altitude. Cruise altitude velocity pressure and takeoff velocity pressure are determined by atmospheric conditions and Mach number. The wing area is determined by velocity pressure, aircraft gross weight, and cruise lift coefficient.

[0038] The beneficial effects of this invention are: the advantage and goal of in-flight battery swapping mode is to enable multiple automated in-flight battery swaps for extended flight, allowing electric transport aircraft to carry payloads continuously for longer distances. Specifically, it has the following technical effects:

[0039] 1) The use of aerial formation and battery-swapping modes enables electric aircraft to carry a certain amount of commercial payload over long distances (2000km and above), solving the major problem that the range of electric aircraft is significantly shorter than that of gasoline-powered aircraft. The flexible hose connection device in the aerial battery-swapping mode allows for the separate handling of the aircraft's main energy supply components from the commercial payload transport components, ensuring a sufficient and effective supply of electrical energy to the transport aircraft.

[0040] 2) The drag rudder of the traction aircraft and transport aircraft of the present invention is designed to open at an angle of 0 to 30° and is installed on the outermost side of the wing to adapt to the yaw moment caused by non-load-bearing traction at the wingtip, and the roll deflection lift generates lateral force to counteract the lateral force.

[0041] 3) The connection mechanism in this invention includes a power supply end, a power receiving end, and a control device to ensure the distance between the two aircraft and the length of the power transmission cable. The aerial power transmission connection can take various forms; the connection between the power supply end and the power receiving end can be a tail-to-nose connection, a tail-to-wingtip connection, or a wingtip-to-wingtip connection. The ratio of towing to transport aircraft can be one-to-one or two-to-one. Depending on the connection form, the power supply device and the power receiving end are installed at the tail or wingtip, etc. Attached Figure Description

[0042] Figure 1 A schematic diagram of aerial refueling using a refueling probe in existing technology;

[0043] Figure 2 A schematic diagram of multi-aircraft formation aerial refueling in existing technology;

[0044] Figure 3 This is a schematic diagram of a foldable nose cone for a towing aircraft; where (a) is a schematic diagram of a nose cone that can be opened to the side, and (b) is a schematic diagram of a nose cone that can be opened upwards.

[0045] Figure 4 This is a schematic diagram of the components used to tow an aircraft.

[0046] Figure 5 This is a schematic diagram of the coaxial counter-rotating propeller principle;

[0047] Figure 6 This is a schematic diagram of a split-type drag rudder, where (b) is a cross-sectional view along line A in (a);

[0048] Figure 7 This is a schematic diagram of the connection mechanism of the present invention;

[0049] Figure 8 This is a schematic diagram of the cone sleeve in the power supply terminal;

[0050] Figure 9 This diagram illustrates three connection methods for a single-unit, non-load-bearing traction mode.

[0051] Figure 10 This diagram illustrates two connection methods for a dual-machine non-load-bearing traction mode.

[0052] Figure 11 This diagram illustrates two connection methods for a three-machine non-load-bearing traction mode.

[0053] In the diagram, 1 is the foldable nose cone, 2 is the replaceable energy module, 3 is the retractable power supply device, and 4 is the drag rudder. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] The long-range electric transport aircraft system of the present invention, powered by pure electric battery energy or hydrogen energy and driven by in-flight battery swapping mode, comprises two parts: (1) a transport aircraft, equipped with a pure electric propulsion system and a power battery for takeoff, landing, and backup energy, but not equipped with a power battery for storing cruise energy or a hydrogen storage and power generation device, with excess mass and space reserved for commercial use; (2) a towing aircraft, equipped with a pure electric propulsion system and a power battery for takeoff, landing, and backup energy, and equipped with a power battery or hydrogen fuel cell for its own cruise energy and the cruise energy supplied to the transport aircraft, as well as a retractable power line and power supply device, but not carrying any commercial load. Here, the power line is in a "non-load-bearing" state, meaning that the retractable power line does not play a role in pulling the transport aircraft, the transport aircraft relies on its own electric motor for propulsion, and the power line only provides electrical energy.

[0056] Multiple non-load-bearing towing aircraft are reserved in segments along the transport aircraft's route. Power is supplied to the transport aircraft in stages for aerial formation non-load-bearing towing flights. Each towing operation involves one or more non-load-bearing towing aircraft (e.g., two). The transport aircraft only takes off and lands once for its entire journey, but the towing aircraft take off and land multiple times. This relay-style non-load-bearing towing transport aircraft continuously completes long-distance flights far exceeding those of conventional electric aircraft, such as the 2000km journey from Beijing to Guangzhou. On the return trip, the towing aircraft tows the transport aircraft back to its original towing airport.

[0057] Because the power battery and payload are relatively heavy, and the hydrogen storage and power generation system are also relatively heavy and large in volume, it is not suitable to adopt the overall aerodynamic design of vertical take-off and landing, tilt-and-turn, or tail-seat vertical take-off and landing aircraft. The thrust-to-weight ratio of such aircraft must be significantly greater than 1, thus limiting the payload capacity and losing the economic efficiency of transport aircraft (including those used to tow batteries).

[0058] Because civil aviation airports are classified into different levels, such as Shijiazhuang Airport being a 4E-level airport and Beijing Capital Airport being a 4F-level airport, 4E-level airports only allow aircraft with a wingspan of less than 65 meters to take off and land, while 4F-level airports allow aircraft with a wingspan of 80 meters to take off and land. However, some aircraft can take off and land at undeveloped airports, which only have dirt runways. In this invention, the towing aircraft can take off and land at lower-level airports (such as airports with dirt runways or higher-level airports) and standby for charging and battery swapping (or hydrogen refueling and tank swapping) because it does not need to carry any cargo. Meanwhile, the transport aircraft takes off and lands at higher-level airports (4E-level or other civil aviation airports) and loads and unloads cargo or passengers, thereby reducing overall costs. The towing aircraft is similar to a portable "power bank" for the transport aircraft. The key component of the towing aircraft is a retractable long-distance power cable, such as about 20 meters long.

[0059] Transport aircraft: cabin, wings, take-off and landing and backup power batteries, commercial cargo compartment (cargo hold and passenger cabin, cockpit), aerial formation towing and docking equipment, etc. The outer wings of the aircraft are designed with a pair of split drag rudders to balance the yaw moment during lateral towing. The lateral force generated during lateral towing is offset by the lift deflection caused by a slight roll.

[0060] Towing aircraft: Includes the fuselage, wings, takeoff and landing / backup power batteries, battery compartments (using the cargo hold, passenger cabin, and cockpit to house power batteries or hydrogen fuel cells and hydrogen storage devices), and power batteries can also be housed inside components such as the wings. It also includes long-distance power lines, power supply devices, and automated deployment and retrieval systems. Towing aircraft can also employ a hydrogen-electric hybrid mode, refueling with hydrogen on the ground instead of charging. Refueling with hydrogen is faster than charging, but the current price of hydrogen fuel is too high. Towing aircraft can be considered as transport aircraft specifically designed to transport recharged power batteries.

[0061] Long-distance power lines refer to power transmission cables and their end caps, receiving plugs, and automated cable recovery devices.

[0062] like Figure 3 As shown, the nose of the towing aircraft is designed to open upwards or to the side, facilitating rapid replacement of internal energy modules and accelerating the replenishment of electrical or hydrogen fuel. The aircraft's outer wings are designed with a pair of split-type drag rudders to balance the yaw moment during lateral towing, while the lateral force generated during lateral towing is offset by lift deflection caused by a slight roll.

[0063] In this invention, both the traction aircraft and the transport aircraft adopt a triplane aerodynamic layout with a high aspect ratio and a support wing design. The high lift-to-drag ratio of the aerodynamic layout partially compensates for the insufficient mass energy density of the power battery and the volumetric energy density of the hydrogen fuel. Triplane layout: refers to an aerodynamic layout in which the aircraft simultaneously has three lifting surfaces: wings, canards (nose position), and horizontal stabilizers (tail position). This type of layout has relatively strong pitch control capabilities.

[0064] The aircraft employs a triplane design, including a barrel-shaped fuselage, wings, canards, horizontal stabilizer, and vertical stabilizer. It has at least six electric coaxial counter-rotating propulsion units. In addition to conventional control surfaces, the outer sides of the wings are equipped with a pair of split-type drag rudders. Because the wings are designed for large-scale applications (aspect ratio of 13-25), there is sufficient spanwise space to accommodate the split-type main drag rudders. The canards and drag rudders are additional devices added to enhance the flight control capabilities of the aircraft in its connected configuration. Figure 5As shown, a coaxial counter-rotating propeller consists of two rotating drive shafts that drive two propellers. The counter-rotating effect eliminates circumferential airflow, concentrating propeller airflow energy in the axial direction, thus improving propulsion efficiency. The main power is applied to either the inner or outer shaft, and the two shafts are driven by planetary gears to achieve a coaxial counter-rotating state. Using coaxial counter-rotating propellers, each nacelle integrates two to three electric motors, used in parallel to increase total power. During takeoff, all propellers are fully operational, while during cruise (long-distance flight at a specified altitude and Mach number), only one or two pairs of coaxial counter-rotating propellers are engaged, with the remaining propellers powered off and their blades automatically folding under the resistance of the oncoming airflow to reduce overall aerodynamic drag.

[0065] Split-drag rudder: Unlike a traditional rudder surface which is a single unit, the split-drag rudder surface is split. See... Figure 6 Control surfaces increase or decrease aerodynamic drag by opening and closing. At the same time, these control surfaces are generally designed on the outer side of the wing, and their center has a large lever arm relative to the center of gravity of the aircraft, which makes it easy to generate yaw moment, that is, the moment that controls the left and right yaw of the nose.

[0066] See Figure 7 , Figure 8 The connection mechanism includes a power supply end and a power receiving end. The power supply end is a flexible cable with a tapered end, while the power receiving end is a pointed, tapered plug. The tapered design of the power supply end facilitates the insertion of the power receiving end. The edge of the tapered end is an inflatable, ring-shaped air bladder that keeps the tapered end open after inflation, while using airflow to maintain a horizontal position for easy insertion of the power receiving end.

[0067] The power transmission uses three-phase alternating current. The receiving end is a cone, and the two rear conductors that can be radially inserted and ejected are three conductive devices that transmit three-phase power. The two rear elastic devices are designed to withstand a certain amount of tension, and the aerodynamic resistance of the cone-shaped airbag at the power supply end must be greater than this tension threshold so that the receiving end can be inserted.

[0068] Since the connection between the power supply end and the power receiving end can only withstand a certain amount of tension, the distance between the two aircraft and the length of the power transmission cable must be strictly tested and designed. This is ensured by the aircraft spacing control device. Once the power transmission task is completed, the two aircraft need to be separated in the air. This can be achieved by forcefully pulling the power supply end and the power receiving end apart. This device can avoid excessive tension and drag between the two aircraft if the distance is too large. After all, the power transmission cable does not bear the task of dragging, and mutual dragging will cause flight control problems.

[0069] The spacing between the towing and transport aircraft is controlled by an aircraft spacing control mechanism. Since the power line and the transport aircraft are non-load-bearing, minor changes in spacing do not cause significant changes in the pulling force on either aircraft. The aircraft spacing control mechanism works as follows: if the ranging device detects that the spacing is too large, it reduces the speed of the leading aircraft or increases the speed of the trailing aircraft to reduce the spacing; if the ranging device detects that the spacing is too small, it increases the speed of the leading aircraft or decreases the speed of the trailing aircraft to increase the spacing. Both ranging and acceleration / deceleration are performed automatically under computer control.

[0070] Airport charging facilities include charging or hydrogen refueling equipment for transport aircraft and towing aircraft, or replaceable modular power batteries and hydrogen storage devices. These facilities are typically installed underground to save surface space at the airport.

[0071] The states of the towing and transport aircraft include: ground charging state, aircraft take-off and landing state, climb and descent state, in-flight docking state, in-flight detachment state, and towing flight state.

[0072] (1) Ground charging status

[0073] The ground charging / swapping or hydrogen refueling status of the towing aircraft, and the ground charging / swapping status of the transport aircraft.

[0074] (2) Aircraft takeoff and landing status

[0075] This includes the takeoff and landing status of transport aircraft and towing aircraft, both of which take off and land independently.

[0076] The takeoff phase consumes electrical energy, while the landing phase recovers electrical energy.

[0077] (3) Climbing and descending state

[0078] This includes the ascent and descent status of transport aircraft and tractor aircraft, both of which ascend and descend independently.

[0079] The ascent phase consumes energy, while the descent phase recovers electrical energy.

[0080] (4) Aerial docking status

[0081] During the aerial docking process between the power receiving device of the transport aircraft and the long-distance power supply device of the towing aircraft, the distance between the towing aircraft and the transport aircraft is relatively large, for example, about 20 meters. During the docking process, it must be ensured that the end of the power supply line does not come into contact with rotating parts such as the propeller or fan of the transport aircraft.

[0082] (5) Aerial disengagement state

[0083] During the in-flight disengagement process of the power receiving device of the transport aircraft and the long-distance power supply device of the towing aircraft, the distance between the towing aircraft and the transport aircraft is relatively large, for example, about 20 meters. During the disengagement process, it must be ensured that the end of the power supply line does not come into contact with rotating parts such as the propeller or fan of the transport aircraft.

[0084] (6) Traction Flight Status

[0085] The transport aircraft is in a cruise flight state powered by the traction power of the towing aircraft, because the transport aircraft does not carry any cruise power battery and must rely on the towing aircraft for power to cruise.

[0086] When in mid-air docking mode, the distance between the towing aircraft and the transport aircraft shall be greater than or equal to 20 meters.

[0087] The towing modes for transport and towing aircraft in this invention include: three single-aircraft non-load-bearing towing modes, two dual-aircraft non-load-bearing towing modes, and two triple-aircraft non-load-bearing towing modes, such as... Figure 9 , 10 As shown in Figure 11.

[0088] In this invention, there are two modes: the aircraft is connected by the tail and the nose, cruises at the same altitude front and rear, cruises at the same altitude laterally, and the left wingtip of the tractor is connected to the right wingtip of the transport aircraft, or the right wingtip of the tractor is connected to the left wingtip of the transport aircraft. In this case, the tractor must use the drag rudder of the corresponding outer wing to balance the yaw moment, and roll deflection lift to generate lateral force to counteract the lateral force.

[0089] The dual-aircraft towing configuration includes two towing aircraft whose tails are connected to the left and right wingtips of the transport aircraft, the right wingtips of the left towing aircraft connected to the left wingtips of the transport aircraft, and the left wingtips of the right towing aircraft connected to the right wingtips of the transport aircraft. The towing aircraft must use the drag rudder of the corresponding outer wing to balance the yaw moment, and roll deflection lift to generate lateral force to counteract the lateral force.

[0090] The three-aircraft towing mode includes the towing aircraft being connected to the nose of the transport aircraft by their tails, the middle towing aircraft being connected to the nose of the transport aircraft by its tail, and the two towing aircraft being connected to the corresponding wingtips of the transport aircraft by their respective wingtips. In this mode, the towing aircraft must use the drag rudder of the corresponding outer wing to balance the yaw moment, and roll to deflect lift to generate lateral force to counteract the lateral force.

[0091] Conceptual design of tractor and transport aircraft: Technical specifications are shown in Table 1 below.

[0092] Table 1

[0093]

[0094]

[0095] Example 1:

[0096] Taking the design of the pure electric transport aircraft system from Beijing Capital International Airport to Guangzhou Baiyun International Airport as an example, as shown in Table 2 below.

[0097] Table 2

[0098]

[0099]

[0100] Green electricity price: The green electricity price here is 0.3 yuan / kWh (off-peak electricity price). The actual market price of green electricity may be much lower than this price. If the battery swapping model is adopted, charging during off-peak hours (off-peak electricity price is less than 0.2 yuan / kWh in many parts of China), and considering the recycling of abandoned wind, solar and hydropower generation, the reduction in energy costs will be further increased. If dedicated wind and solar power stations are built near airports, the cost of purchasing electricity can be close to zero. The price of pure electric air transport energy is extremely low compared to aviation kerosene aircraft air transport.

[0101] Assuming energy costs account for 30%, the cost of transportation per person from Beijing to Guangzhou is 313 yuan (at a speed of 637 km / h). Assuming a 10% profit margin (compared to 3.1% for the global aviation industry), the ticket price could be set at 350 yuan per person. For comparison, a high-speed rail ticket costs 1000 yuan per person at a speed of 350 km / h; a passenger plane ticket costs 3500 yuan (full price) at a speed of 800 km / h. This demonstrates the significant competitive advantage of long-range electric aircraft in the market.

[0102] Example 2:

[0103] The design of the pure electric transport aircraft system from Beijing Capital International Airport to Urumqi Diwopu Airport is shown in Table 3 below.

[0104] Table 3

[0105]

[0106]

[0107] Green electricity price: The green electricity price here is 0.3 yuan / kWh (off-peak electricity price). The actual market price of green electricity may be much lower than this price. If the battery swapping model is adopted, charging during off-peak hours (off-peak electricity price is less than 0.2 yuan / kWh in many parts of China), and considering the recovery of abandoned wind, solar and hydropower generation, the reduction in energy costs will be further increased. If dedicated wind and solar power stations are built near airports for air transport, the cost of purchasing electricity can be close to zero. The price of pure electric air transport energy is extremely low compared to aviation kerosene aircraft air transport. Energy recovery technology during descent and landing has already been considered here.

[0108] Here, the power system uses three pairs of coaxial counter-rotating propellers, and each power nacelle integrates two to three electric motors, which are used in parallel to increase the total power. For example, three electric motors are used in parallel, and each electric motor has a rated power of 250kW. Currently, the power-to-weight ratio of automotive electric motors on the market has reached 4 to 6 kW / kg, which is close to the power-to-weight ratio of 3 to 5 kW / kg of general turboprop engines.

[0109] As the range increases, the energy cost of electric shipping systems increases, but the cost reduction relative to conventional aviation kerosene aircraft transportation is decreasing. If we take into account the further reduction in off-peak electricity prices and the comprehensive application of renewable energy curtailment, the energy cost of pure electric shipping systems can be further reduced.

[0110] The main obstacle to aircraft electrification lies in onboard energy storage. It must simultaneously meet practical requirements in both volumetric and gravimetric energy density, while also ensuring low energy prices. Direct energy storage fails to meet the design requirements for long-range flights in terms of both volumetric and gravimetric energy density, but it offers excellent advantages in terms of energy price and carbon emissions. In-flight battery swapping can avoid the first two problems and fully leverage the advantages of low cost and clean energy. Currently, hydrogen-electric hybrid systems face challenges due to high energy market prices, significant volumetric energy density issues requiring substantial aircraft modifications, and prominent hydrogen embrittlement and safety concerns. Sustainable aviation fuel (SAF) is primarily hampered by insufficient production and excessively high market prices.

Claims

1. An in-flight battery-swapping long-range electric transport aircraft system, characterized in that: The aircraft system is powered by either pure battery energy or hydrogen energy, and the system comprises two parts: The transport aircraft is equipped with a pure electric propulsion system and a power battery for takeoff, landing and backup energy, but it is not equipped with a power battery for storing cruise energy or a hydrogen storage and power generation device. The excess mass and space are reserved for commercial use. It includes the cabin, wings, takeoff and landing and backup power batteries, commercial cargo compartment, aerial formation towing and docking equipment, etc. The aircraft's outer wings are designed with a pair of split drag rudders to balance the yaw moment during lateral towing. The lateral force generated during lateral towing is offset by the lift deflection caused by a slight roll. The towing aircraft is equipped with a pure electric propulsion system and a power battery for takeoff, landing and backup energy. It is equipped with a power battery or hydrogen fuel cell for its own cruise energy and to supply cruise energy to the transport aircraft, as well as retractable power lines and power supply devices, but does not carry any commercial payload, including the cabin, wings, takeoff and landing and backup power batteries, battery compartment, and the power batteries are also arranged inside the wings. The tractor and the transport aircraft are connected by a connection mechanism, which includes a power supply end and a power receiving end. The power supply end is a flexible cable with a conical sleeve at the end, and the power receiving end is a pointed conical plug. The conical sleeve of the power supply end facilitates the insertion of the power receiving end. The edge of the conical sleeve is an inflatable annular airbag that keeps the conical sleeve open after inflation and maintains a horizontal state using airflow to facilitate the insertion of the power receiving end. When the power cable is in a "non-load-bearing" state, it means that the retractable power cable does not pull the transport aircraft; the transport aircraft is propelled by its own electric motors, and the power cable only provides electrical energy. Depending on the different connection methods in the traction mode, the power supply end is installed at the tail or wingtip of the traction aircraft, and the power receiving end is installed at the nose or wingtip.

2. The system according to claim 1, characterized in that: Both the traction aircraft and the transport aircraft adopt a triplane aerodynamic layout with a high aspect ratio and a support wing design. The high lift-to-drag ratio of the aerodynamic layout partially compensates for the insufficient mass energy density of the power battery and the volumetric energy density of the hydrogen fuel. The aspect ratio is 13-25 and the lift-to-drag ratio is 16-25. The tractor and transport aircraft are powered by propellers, using coaxial counter-rotating propellers. There are at least three pairs of propellers. All propellers are fully operational during takeoff, while only one or two pairs of coaxial counter-rotating propellers are operational during cruise. The remaining coaxial counter-rotating propellers are powered off and their blades are folded under the resistance of the oncoming flow to reduce the overall aerodynamic drag of the aircraft.

3. The system according to claim 1, characterized in that: The nose of the towing aircraft is designed to open for quick replacement of the internal energy modules.

4. The system according to claim 1, characterized in that: The traction aircraft uses a hydrogen-electric hybrid mode, refueling with hydrogen instead of charging on the ground.

5. The system according to claim 1, characterized in that: The wingtips of the tractor and transport aircraft are designed with a pair of drag rudders to adapt to the yaw moment caused by non-loaded traction at the wingtips, and to generate lateral force by rolling and deflecting lift to counteract the lateral force; the opening degree of the drag rudders is 0 to 30°; the installation position is located on the outer side of the wing, at 70% to 90% of the span.

6. The system according to claim 1, characterized in that: The states of the towing and transport aircraft include: ground charging state, aircraft take-off and landing state, climb and descent state, in-flight docking state, in-flight detachment state, and towing flight state. When in mid-air docking mode, the distance between the towing aircraft and the transport aircraft ranges from 15 to 40 meters.

7. The system according to claim 1, characterized in that: The system also includes airport charging equipment: the airport charging equipment includes charging or hydrogen refueling equipment at airports used by transport aircraft and airports used by towing aircraft. The charging device is a replaceable, single-unit power battery; the hydrogen refueling device is a hydrogen storage device. The charging or hydrogen refueling equipment is located underground to save airport surface space.

8. A method of using the in-flight battery-swapping mode long-range electric transport aircraft system as described in claim 1, characterized in that: The method involves reserving multiple non-load-bearing traction aircraft in segments along the transport aircraft's flight path, supplying power to the transport aircraft in stages, and conducting non-load-bearing traction flights in aerial formation. Each traction operation involves one or more non-load-bearing traction aircraft. The transport aircraft only takes off and lands once during its entire flight, but the traction aircraft take off and land multiple times. The relay-type non-load-bearing traction transport aircraft continuously completes long-distance flights that far exceed those of conventional electric aircraft. On the return trip, the traction aircraft pulls the transport aircraft back to the original traction airport.

9. The method according to claim 8, characterized in that: The traction modes in the aforementioned usage method are divided into: single-machine non-load-bearing traction mode, dual-machine non-load-bearing traction mode, and three-machine non-load-bearing traction mode. The single-unit non-load-bearing traction mode has three connection forms: I) The towing aircraft is connected to the nose of the transport aircraft by its tail, and the two aircraft are arranged to cruise at the same altitude. II) The towing aircraft is connected to the nose of the transport aircraft by the left or right wingtip, and the two aircraft are arranged at the same altitude for cruising. III) Lateral cruising at the same altitude, with the left wingtip of the towing aircraft connected to the right wingtip of the transport aircraft, or the right wingtip of the towing aircraft connected to the left wingtip of the transport aircraft. In this case, the towing aircraft must use the drag rudder of the corresponding outer wing to balance the yaw moment, and roll to deflect lift to generate lateral force to counteract the lateral force. The dual-machine non-load-bearing traction mode has two connection methods: I) Dual-engine traction includes the tails of two tractors being connected to the left and right wingtips of the transport aircraft, respectively; II) In the mode where the right wingtip of the left towing aircraft is connected to the left wingtip of the transport aircraft, and the left wingtip of the right towing aircraft is connected to the right wingtip of the transport aircraft, the towing aircraft must use the drag rudder of the corresponding outer wing to balance the yaw moment, and roll deflection lift to generate lateral force to counteract the lateral force. The three-machine non-load-bearing traction mode has two connection forms: I) All three tractors are connected to the nose, left wingtip, and right wingtip of the transport aircraft via their tail sections; II) The middle towing aircraft is connected to the nose of the transport aircraft via its tail, and the two towing aircraft are connected to the corresponding wingtips of the transport aircraft via their respective wingtips. In this case, the towing aircraft must use the drag rudder of the corresponding outer wing to balance the yaw moment, and roll to deflect lift to generate lateral force to counteract the lateral force, which is the same as the form II of the two-aircraft towing mode.

10. The system according to any one of claims 1 to 7, characterized in that: The technical specifications of the tractor and transport aircraft shown are as follows: The wing aspect ratio is 15–22, the cruising altitude is 10,000–16,000 meters, the cruising Mach number is 0.55–0.65, the cruising lift coefficient is 0.8–1.2, and the maximum lift coefficient is 1.6.

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