Vertical and short takeoff and landing lift booster systems

Abstract

A propulsion system for a vehicle includes at least one generator, at least one ultracapacitor coupled to the at least one generator, at least one battery coupled to the at least one generator, at least one compressor coupled to the at least one generator, the at least one ultracapacitor, and the at least one battery, and at least one propulsion element coupled to the compressor.

Description

[Technical Field]

[0001] [Copyright Notice]

[0001] This disclosure is protected under U.S. and / or international copyright laws. ©2023 Jetoptera, Inc. All Rights Reserved. A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or patent disclosure as it appears in the Patent and / or Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. [Priority claim]

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 427,043, filed November 21, 2022, the contents of which are incorporated herein by reference as if fully set forth herein. [Background technology]

[0002]

[0003] Existing VTOL and STOL propulsion aircraft pose significant challenges in selecting the correct size or power of their propulsion systems due to the disparity between the power required for takeoff and cruise. Some systems involve rotary or tilting rotors or ducted fans, vectoring jets, or combinations of these known as hybrid helicopters, but they have poor lift-to-drag characteristics, lack high endurance, and are limited in speed. While aircraft such as the Harrier Jump Jet have proven excellent for vertical takeoff and landing, their propulsion systems have been oversized for the cruise speeds they can offer. Therefore, the challenge for any VTOL aircraft is the propulsion system selected, which typically ends up being a very large weight fraction of the overall aircraft, thus limiting payload, range, and endurance. Large turbine-based systems are sized for VTOL aircraft, and during cruise flight, when their operating point is far from the VTOL operating point, the turbines operate efficiently only during takeoff, for example, and are less efficient during cruise.

[0003]

[0004] Current propulsion systems for V / STOL aircraft in military and civilian applications rely on large tilting rotors, such as the V-22 Osprey or Agusta AW609, or large fixed ducted fans, such as the F-35 fighter. The challenge with the latter is that the fixed ducted fan becomes deadweight for 99% of the mission time during non-vertical flight segments. Given the fact that the weight displaced by the vertical takeoff fan limits the aircraft to vertical landings only, as fuel is consumed during the mission and the aircraft becomes lighter and can land vertically with the available onboard power, the F-35 is now known to no longer be called VTO, but STOVL. This also limits payload capacity and is extremely complex, making it unaffordable for smaller manned or unmanned applications. The challenge with V22 rotors is that they have a large footprint and must be tilted with high precision, yet their maximum speed is still limited by rotor tip speed limitations. The V22's development history also shows that it has significant flaws that have cost many lives. High-speed VTOL propulsion vehicles are needed—those capable of propelling aircraft at the high speeds or long endurance typical of intelligence, surveillance, and reconnaissance. Most eVTOL aircraft use highly efficient tilting propellers but rely on very heavy batteries, which have an energy density many times lower than jet fuel. Many of the hundreds of proposed eVTOL platforms use distributed, fixed propellers for vertical takeoff and a single thrust propeller for horizontal flight, which are also severely limited in speed. Therefore, a novel approach to propulsion is clearly needed that optimizes operation during cruise and is lighter than both battery-powered vehicles or the oversized VTOL turbines.

[0004]

[0005] Engineers have implemented highly complex and costly technologies to enable propellers to maximize their hovering efficiency, but today's smaller propellers suffer from low efficiency and high cost. Speeds for cargo drones and Urban Air Mobility flying cars (air taxis) are limited to low values, and the propellers are noisy and inefficient at their size.

[0005]

[0006] Most hybrid V / STOL aircraft may use hybrid systems, often referred to as range-extension systems, to address the very severe limitations on range and flight time typically experienced by all-electric aircraft. Again, this is due to the fact that these aircraft require massive batteries; therefore, hybrid systems involving generators are thought to extend the range of, for example, eVTOLs by doubling it. However, even when sizing onboard generators to generate the power that powers the electric motors that spin the fans or propellers, the impact on the aircraft is still more detrimental than a pure fuel-to-propulsion system due to the additional elements that must be added to the legacy system. Generators typically require inverters, conditioners, cooling, large cables, power transmission, electronics, and may require batteries, making the entire hybrid system, as one expert put it, “three times more expensive, twice as heavy, and 10% less efficient overall.” This arises from the fact that adding additional components that are far from 100% efficient themselves significantly reduces the thermal efficiency of the power plant, making the thrusters heavier, less efficient, and more costly to maintain and operate, not to mention replacing useful payload with components that were not present in the legacy system.

[0006]

[0007] Additionally, the power boost required for a V / STOL aircraft is typically only a small portion of the overall mission, perhaps at the beginning and end, making the decision in selecting the correct propulsion and energy storage combination even more difficult. For example, a VTOL aircraft may only need to operate for one to two minutes in a hover or vertical takeoff or landing, while it is then desirable to fly for several hours in cruise conditions (i.e., fixed wing). Summary of the Invention

[0007]

[0008] It is therefore of interest to create an architecture that allows a V / STOL aircraft to operate efficiently during cruise using a generator that operates very efficiently at its peak efficiency point, but benefit from some augmented power for lift generation during the vertical phase of the mission without the addition of heavy, poorly energy-dense systems such as batteries, motors, and auxiliary systems. Such a system would significantly optimize the operation of virtually any V / STOL aircraft. [Brief explanation of the drawings]

[0008] [Figure 1]

[0009] FIG. 1 is a schematic diagram of a hybrid vertical takeoff and landing system, according to one embodiment. [Figure 2]

[0010] FIG. 2 illustrates operation during vertical takeoff, according to one embodiment. [Figure 3]

[0011] FIG. 3 illustrates operation during transition to fixed wing, according to one embodiment. [Figure 4]

[0012] FIG. 4 illustrates operation in a fixed wing, according to one embodiment. [Figure 5]

[0013] FIG. 5 illustrates operation in a fixed wing that avoids battery use while recharging the battery, according to one embodiment. [Figure 6]

[0014] FIG. 6 illustrates an alternative fixed wing operation using an electric ducted fan, according to one embodiment. [Figure 7]

[0015] FIG. 7 illustrates an alternative fixed-wing operation using electrically driven propellers, according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009]

[0016] This application is intended to describe one or more embodiments of the present invention. It should be understood that the use of absolute terms such as "must" and "will," as well as specific quantitative quantities, should be construed as applicable to one or more of such embodiments, but not necessarily to all such embodiments. Thus, embodiments of the present invention may omit or include modifications of one or more features or functionality described in the context of such absolute terms. Additionally, headings in this application are for reference purposes only and do not in any way affect the meaning or interpretation of any embodiment of the present invention.

[0010]

[0017] The embodiments of the invention disclosed herein specifically relate to augmented propulsion systems that operate in conjunction with electric motors powering air compressors, fans, or propellers. Rather than sizing the aircraft's 100 propulsion system to generate a maximum force at least 20% greater than the aircraft's system weight for vertical takeoff, thus resulting in a heavier propulsion system during cruise, this approach involves the use of electric ultracapacitors or supercapacitors that can provide large amounts of power for short periods of time, thus enabling the aircraft to additionally power its onboard electrical components, enough to lift it off the ground or land vertically. Supercapacitors (SCs), also called ultracapacitors, are high-capacity capacitors with much higher capacitance values ​​but lower voltage limits than other capacitors, bridging the gap between electrolytic capacitors and rechargeable batteries. Unlike regular capacitors, supercapacitors do not use traditional solid dielectrics, but rather use a double-layer capacitance on one electrode and an electrochemical battery electrode as the other.

[0011]

[0018] One or more embodiments include a novel hybrid propulsion method that can be used without the drawbacks of propellers. The propulsor is designed around the principle of thrust augmentation using a specialized ejector and upper surface blown lift augmentation. Such ejectors may include those disclosed in U.S. Provisional Patent Application No. 62 / 213,465, filed September 2, 2015, and U.S. Patent Application No. 15 / 256,178, filed September 2, 2016, each of which is incorporated by reference herein as if fully set forth herein. The air supply may come from, for example, an electric turbocompressor, an electric turbofan, or any electric air compressor that produces an air supply with a pressure ratio of at least 1.5:1 in sufficient quantity and is electrically operated by at least two power sources: a generator and a series of ultracapacitors or supercapacitors.

[0012]

[0019] In FIG. 1 , which illustrates a VTOL configuration of one embodiment of the present invention, compressed air is generated by air compressors 101. These compressors 101 may be electric turbofans, bypass airflow, or any type of fan or compressor capable of generating large volumes of flow, specifically at a pressure ratio of at least 1.5 relative to ambient pressure. The air compressed by the compressors 101 may be routed to fixed-wing ejectors 108 and / or used for other purposes, including being directed to secondary nozzle inlets or used for cooling, thrust augmentation, cabin pressurization, or other uses. In various embodiments, the fixed-wing ejectors 108 may be positioned on or embedded within an aerodynamic surface, such as a wing 104. Similar to a typical turbocharger compressor, the compressors 101 may have a pressure ratio of preferably 2.5 or greater at peak operation. A valve may be present on the compressor discharge volute to direct compressed air to either a secondary compressor or external to a gas generator, as needed.

[0013]

[0020] The power supplied to the electric compressor 101 is provided in part by a generator 102 sized for the cruise condition of the aircraft. For example, if cruise requires half the power required at takeoff, then the generator 102 is sized exactly at its power rating to produce optimal power at the optimal operating point throughout the mission.

[0014]

[0021] The remaining power needed for takeoff, hovering, or vertical landing, or any time the compressor 101 needs to supplement propulsion, is provided by a series of ultra- or super-capacitors 110, which are much more capable than batteries of generating power in short bursts for limited durations and at high currents and voltages. An advantage of these ultra-capacitors 110 is also their ability to be rapidly recharged in flight from the generator 102 in just a few minutes. By appropriately sizing the system, the aircraft 100 can operate very efficiently in rapid vertical takeoffs and landings, and even hover for minutes, without the burden of large batteries that cannot provide the large power required by these flight scenarios, and without the risk of thermal runaway or serious thermal management issues that one skilled in the art will understand.

[0015]

[0022] In one embodiment, the aircraft 100 is a small unmanned system weighing 350 lbs, carrying, for example, 60 lbs of payload and 110 lbs of fuel. The generator 102, for example, a heat-recuperating gas turbine or a highly efficient piston engine, is continuously generating 15 kWe at a high efficiency and weighs 70 lbs. Three ultracapacitors 110, weighing no more than 45 lbs, provide a total of 90 kWe for up to two minutes, providing the balance of the power required for all motors driving compressors, fans, or propellers dedicated to the vertical takeoff and landing phase of flight. This, in turn, provides sufficient thrust for the aircraft to take off and land vertically. The generator 102 can remain "on" at all times to provide the 15 kWe of power required for forward flight (i.e., fixed-wing flight), when all thrust required is to overcome drag and lift is primarily generated by the wings 104. Additionally, the generator 102 can provide power to perform a variety of onboard functions, from navigation and communications to aircraft control to servos and payload, etc. A 350 lb aircraft has a large wing allowing a lift to drag coefficient of 20 for a forward speed of only 30 knots, the drag generated at this speed is only 350 lb ÷ 20 = 17.5 lbf, which can be overcome by using an electric compressor producing an 18 lbf jet at a modest pressure ratio of 1.1 feeding an ejector with an augmentation ratio of 2.5, consuming only 5 kWe. With increasing speed, and an L / D of, for example, 25, power requirements are therefore minimized and the turbogenerators can provide propulsion for the system, extending range and endurance, providing recharging for the ultracapacitors, and powering the aircraft for control, communications, navigation, etc. and the payload, while burning very little fuel, for example, for a total output of only 10 kWe - 0.6 lb / HP / h or 0.365 kg / kW / h for a highly efficient recuperated turbogenerator, so the aircraft becomes lighter as it burns fuel and can therefore conservatively fly for a considerable amount of time in fixed-wing flight, for example, 100 lb fuel ÷ (0.6 lb / HP / h × 13.4 HP) = 12.4 hours.Using the Breguet equation for range, assuming a true speed of 100 knots and using 100 lbs of fuel on board the aircraft, the resulting endurance is over 15 hours at an L / D of 25. The generator output would be equivalent to 13.4 HP (or 10 kWe) for the duration of the fixed-wing flight, allowing for a flight of nearly 16 hours and 1900 miles, an excellent endurance for a small aircraft with sufficient power for critical communications.

[0016]

[0023] Note that if a battery with an energy density of 150 Wh / kg and required to deliver 45 kWe for several minutes were used instead of the ultracapacitor 110, the weight imposed on the vehicle by the battery alone would be over 200 lbs, heavier than the generator 102 itself and incompatible with a 350 lb system where the combined weight of the generator and battery is 77% of the total aircraft weight. It would be impossible to discharge the battery in rapid succession, as the chemical reactions within the battery would be accelerated to the point where the battery would become useless or even explode. Only a massive battery could provide such an extra boost in power consumption for the short time required for takeoff, but this would significantly increase the vehicle's weight and would likely not provide a solution. The battery would also require a recharge time two orders of magnitude longer than that required by an ultracapacitor. This is why a hybrid system using capacitors and ultracapacitors uniquely enables V / STOL, as well as other applications.

[0017]

[0024] In another embodiment, a VTOL ejector 107, which may be rotatable through 360°, is used for VTOL flight for several minutes, supplied with air from an electric compressor 101 powered by an ultracapacitor 110. By the time the aircraft 100 is in fixed-wing flight, the ultracapacitor 110 is no longer providing electrical power, and the turbogenerator 102 is solely powering a single forward flight thruster, which may be a propeller, fan, ejector, or combination thereof.

[0018]

[0025] In another example, a 1 lb / s motive airflow is generated using a compressor, such as those typically used in turbochargers or electric compressors, operating at a maximum pressure ratio of 2.0:1 and an isentropic efficiency of over 85%; in this case, the input mechanical power or electrical power required to drive the air compressor is 38 horsepower (HP) or approximately 29 kW; this motive air is fed to a fluid propulsion system, actually a thruster-ejector, deployed on the wing or around the fuselage. When deployed across the wing in an upper-surface blown configuration with the correct tilt angle and over deployed flaps, the lift generated at speeds as low as 10 knots is doubled compared to when a clean wing is used at the same headwind velocity (10 knots) but with no thruster augmenter active or present. This would enable the aircraft to perform very short takeoff and landing (SSTOL) or, ultimately, to take off vertically into a headwind, for example, on the deck of a ship placed into the wind. A typical value of lift that can be obtained for a blown wing example with 10 knot headwind conditions and flaps extended can be about 200 lbf for an input of 38 HP, resulting in a ratio of 5.26 lbf / HP, which is a typical value for the hover efficiency of a tilt rotor such as a V22 Osprey or helicopter as explained by Maisel et al. - NASA SP-2000-4517, "The History of the XV-15 Tilt Rotor Research Aircraft: From Concept to Flight" (Bibliographic data) https: / / ntrs.nasa.gov / search.jsp?R=20000027499 (PDF) http: / / history.nasa.gov / monograph17.pdf.

[0019]

[0027] The result is that an aircraft may be able to generate, for example, multiples of 200 lbf of vertical thrust in a low-speed headwind by using multiple 38 HP electric compressors that may be powered by electric ultracapacitors or supercapacitors, in addition to generators minimized for cruise conditions that are also the power source for recharging the ultracapacitors during flight. Thus, a 380 HP load distributed across the aircraft and directed to electric compressors powered by a combination of Auxiliary Power Units plus lightweight ultracapacitors, combined with hydrodynamic thruster augmenters and blown wing flaps, can generate 2000 lbf of vertical force by using 10 lb / s motive airflow at a 1.8 pressure ratio to ambient, where the APU is sized for, for example, only 120 HP (90 kW) and weighs less than 150 lbs, and an additional 260 HP (200 kW) from the ultracapacitors weighing 100 lbs, sufficient for vertical takeoff and landing, albeit for short periods of time. With a permanent on-board battery doing the same job, a 500 lb battery would be needed to provide 200 kW, but not for such a short period of time.

[0020]

[0028] In that case, once levitated and gaining forward speed, the ultracapacitors would advantageously be immediately recharged.

[0021]

[0029] The system shown in Figure 1 includes several elements: an electric motor, a payload, navigation, communications, control, and a generator 102 that powers an ultracapacitor 110 sized for a VTOL aircraft. The turbogenerator 102 has a maximum output of 15 kWe, operates optimally at full load, and is preferably a regenerative type with an efficiency as high as 30%. This turbogenerator 102 may also be a piston engine generator type or any other generator that minimizes weight and maximizes efficiency, and preferably runs on jet fuel, diesel, or any other suitable fuel, including hydrogen. The generator 102 may be electrically connected to a series of electric compressors 101, a buffer battery 103, and a series of ultra- or supercapacitors 110. The battery 103 may also be connected to other components, such as a servo or fixed-wing propulsor, such as an electric motor driving an electric ducted fan 105, a propeller 106, another compressor 101 feeding air to a thruster-ejector 108, or an electric compressor 101 that may be used in dual role, feeding air to an ejector or simply expanding compressed air into the surroundings in the form of a jet. The ejector 108 may also be used in conjunction with the wing 104 to augment the wing during takeoff, or the ejector 108 in general. At takeoff, the generator generates 15 kWe, and the capacitor provides an additional 90 kWe for just a few seconds to up to a few minutes. After the aircraft transitions to forward flight (also known as fixed-wing flight), all power from the ultracapacitor 110 is disconnected, and for propulsion, the turbogenerator 102 feeds power only to one of the fixed-wing propulsor motors as needed for thrust. A propeller 106 driven by an electric motor consumes the least energy and allows for very high endurance, but is very noisy and easily detected from a distance. An electric ducted fan 105 is the least efficient, but is quieter from a distance and generates only high-frequency noise that is quickly absorbed at a distance. When a combination of a compressor embedded and silenced within the aircraft is used in conjunction with an FPS-type ejector 108, even lower noise can be generated, making the propulsion efficient and quiet without noise frequency peaks, but rather only broadband noise similar to wind.One, several, or all of these options may be used on a vehicle as needed, while the ultracapacitors can be recharged in seconds.

[0022]

[0030] In another embodiment, the hybrid propulsion system as described is utilized for an ultra-short takeoff and landing aircraft, similar to rocket-assisted takeoff (RATO) or jet-assisted takeoff (JATO) then used for 10 to 30 seconds, with the difference that the ultracapacitors are used for the same amount of time but for cleaner lift boost, then recharged on-board during flight and can be used again for thousands of cycles. The rockets used for JATO and RATO are single-use only. In this embodiment, the compressor is embedded within the wing and located near an ejector, such as an FPS ejector, which can work in conjunction with the wing via the FPS and upper surface blown wing to boost the aircraft faster, cleaner, and faster into the air. The lift coefficient can be significantly increased by double-digit levels thanks to the ability to repeatedly recharge the ultracapacitors thousands of times within seconds, and this process is repeated until the aircraft has risen very high.

[0023]

[0031] 2 illustrates operation of the air vehicle 100 during vertical takeoff, according to one embodiment. In such a configuration, the compressor 101 receives power from at least one of the generator 102, the capacitor 110, and the battery 103. The powered compressor 101, in turn, provides compressed air to the VTOL ejector 107, which is configured and oriented to provide thrust and lift to the air vehicle 100 to facilitate vertical takeoff.

[0024]

[0032] 3 illustrates operation of aircraft 100 during a transition to a fixed-wing configuration, according to one embodiment. In such a configuration, ultracapacitors 110 no longer provide electrical power, and turbogenerators 102 and / or batteries 103 alone power one or more forward flight propulsors, which may be, for example, propeller(s) 106, fan(s) 105, fixed-wing ejector(s) 108, or a combination thereof. In the example illustrated in FIG. 3 , the powered forward flight propulsors are fixed-wing ejector(s) 108, which receive compressed air from one or more compressors 101, which may be powered by generators 102 and / or batteries 103.

[0025]

[0033] 4 illustrates fixed-wing operation of the aircraft 100, according to one embodiment. In such a configuration, the ultracapacitors 110 no longer provide electrical power, and only the turbogenerators 102 and / or batteries 103 power one or more forward flight propulsors, which may be, for example, the propeller(s) 106, the fan(s) 105, the fixed-wing ejector(s) 108, or a combination thereof. In the example illustrated in FIG. 4 , the powered forward flight propulsors are the fixed-wing ejector(s) 108, which receive compressed air from one or more compressors 101, which may be powered by the generators 102 and / or the batteries 103. Additionally, the ultracapacitors 110 are recharged by the turbogenerators 102.

[0026]

[0034] 5 illustrates fixed-wing operation of aircraft 100 with avoiding battery use while recharging the batteries, according to one embodiment. In such a configuration, ultracapacitors 110 no longer provide electrical power, and turbogenerators 102 alone power one or more forward flight propulsors, which may be, for example, propeller(s) 106, fan(s) 105, fixed-wing ejector(s) 108, or a combination thereof. In the example illustrated in FIG. 5 , the powered forward flight propulsors are fixed-wing ejector(s) 108, which receive compressed air from one or more compressors 101, which may be powered by generators 102. Additionally, batteries 103 are recharged by turbogenerators 102.

[0027]

[0035] 6 illustrates an alternative fixed-wing operation of the aircraft 100 using electric ducted fans 105, according to one embodiment. In such a configuration, the ultracapacitors 110 no longer provide electrical power, and the turbogenerators 102 alone power the one or more fan(s) 105.

[0028]

[0036] 7 illustrates an alternative fixed-wing operation of the aircraft 100 using electrically driven propellers 106, according to one embodiment. In such a configuration, the ultracapacitors 110 no longer provide electrical power, and only the turbo-generators 102 power the one or more propeller(s) 106.

[0029]

[0037] One or more embodiments include a hybrid electric system comprised of a combination of an electric generator and an ultracapacitor that, when combined, produces a bulk power supply for an aircraft electric propulsion.

[0030]

[0038] In one or more embodiments, generators and ultracapacitors alternately power several types of electric propulsion units onboard an aircraft in a distributed arrangement.

[0031]

[0039] One or more embodiments include a propulsion system comprising: a battery connected to at least one generator, an ultracapacitor, and an electric motor; at least one electric compressor, a conduit, a thrust augmenter, and a valve with a nozzle; at least an electric motor directly connected to at least a propeller; and at least an electric motor powering at least a fan or rotor.

[0032]

[0041] In one or more embodiments, the ultracapacitor provides power for a limited time and then recharges from the generator.

[0033]

[0042] In one or more embodiments, the ultracapacitor provides power for a limited time and then recharges from the generator's starter battery.

[0034]

[0043] One or more embodiments include a method of flying an aircraft or hovercraft, the method comprising using electric motors to maximize the maximum power output of several thrust generating devices, electrically powering the thrust devices and modulating the power to the thrust devices, and balancing the attitude of the aircraft for as long as capacitors can provide power for vertical hovering, takeoff, and landing; returning to power from generators only when the capacitors are depleted, and recharging the capacitors while the aircraft is in horizontal flight.

[0035]

[0044] One or more embodiments include a method of flying an aircraft or hovercraft, the method comprising: maximizing the maximum power output of several thrust-generating devices using electric motors to power and regulate the thrusters, and for short takeoffs, counterbalancing the aircraft's attitude and providing lift for shorter takeoffs as long as the capacitors can provide power; reverting to power from a generator only when the capacitors are depleted and recharging the capacitors while the aircraft is in level flight; using the capacitors to provide lift or thrust with burst electric supply motors driving propulsors in flight to change the aircraft's attitude, speed, and altitude and for rapid maneuvering; maximizing the maximum power output of several thrust-generating devices using electric motors to electrically power the thrusters and regulate power to the thrusters, and for short or vertical landings, counterbalancing the aircraft's attitude and providing lift for shorter landings as long as the capacitors can provide power.

[0036]

[0045] While preferred embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the following claims.

Claims

1. 1. A propulsion system for a vehicle, comprising: at least one generator; at least one ultracapacitor coupled to the at least one generator; at least one battery coupled to the at least one generator; at least one compressor coupled to the at least one generator, the at least one ultracapacitor, and the at least one battery; at least one propulsion element coupled to the compressor; A system comprising:

2. The system of claim 1 , wherein the at least one propulsion element comprises a propeller.

3. The system of claim 1 , wherein the at least one ultracapacitor provides power for a predetermined period of time and then recharges from the at least one generator.

4. The system of claim 1 , wherein the vehicle comprises at least one wing, and the at least one propulsion element is coupled to the at least one wing.

Images