Hybrid propulsion system for high endurance fixed-wing vertical take-off and landing (VTOL) aircraft

Abstract

A hybrid propulsion system (102) for high endurance fixed wing vertically take-off and landing (VTOL) aircraft (100), comprising internal combustion (IC) engine (104) to provide propulsive power, electric motor (106) configured to provide supplemental propulsive power during climb phase, first propulsion unit (108) and second propulsion unit (114), and controller (110) configured to determine total propulsive power required during climb phase based on desired rate of climb, dynamically allocate total propulsive power between IC engine (104) and electric motor (106) during the climb phase based on power density of electric motor (106) being greater than power density of IC engine (104), enabling electric motor (106) to provide higher supplemental propulsive power, and changes in brake specific fuel consumption (BSFC) of IC engine (104) with varying throttle settings, and operate IC engine (104) alone at optimal throttle setting to provide propulsive power required to maintain desired airspeed during the cruise phase.

Description

[0001] HYBRID PROPULSION SYSTEM FOR HIGH ENDURANCE FIXED- WING VERTICAL TAKE-OFF AND LANDING (VTOL) AIRCRAFT

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to aircraft propulsion systems, specifically to a hybrid propulsion system for high endurance fixed-wing vertical take-off and landing (VTOL) aircraft.

[0004] BACKGROUND

[0005] In recent years, the aviation industry has seen a significant increase in the development and deployment of high endurance fixed wing vertically take-off and landing (VTOL) aircraft. The high endurance fixed wing VTOL aircraft require three times more thrust and power during the climb phase compared to the thrust and power required during the cruise phase. Even though the duration of the climb phase is very small compared to the cruise phase, the power source for the high endurance fixed wing VTOL aircraft has to be selected based on climb phase requirements, which typically increases the weight of the power source.

[0006] Conventional propulsion systems of high endurance fixed wing VTOL aircraft rely on either internal combustion (IC) engines or electric motors to provide power to the propulsion system. However, these conventional aircraft propulsion systems are not able to maintain high efficiency and deliver the required propulsion power, which reduces the overall endurance of the aircraft. Thus, there exists a technical problem of how to provide high propulsion power for high endurance fixed wing VTOL aircraft during vertical take-off and climb phase with reduced overall fuel consumption.

[0007] Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with the conventional aircraft propulsion system. SUMMARY

[0008] The present disclosure provides a hybrid propulsion system for high endurance fixed wing vertically take-off and landing (VTOL) aircraft. The present disclosure provides a solution to the existing problem of how to provide high propulsion power for high endurance fixed wing VTOL aircraft during climb phase with reduced overall fuel consumption.

[0009] An objective of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provides an improved hybrid propulsion system for the high endurance fixed wing VTOL aircraft.

[0010] One or more objectives of the present disclosure are achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.

[0011] In one aspect, the present disclosure provides a hybrid propulsion system for a high endurance fixed wing VTOL aircraft. Furthermore, the hybrid propulsion system includes an IC engine. Moreover, the IC engine is configured to provide propulsive power to the high endurance fixed wing VTOL aircraft. Furthermore, the hybrid propulsion system includes an electric motor configured to provide supplemental propulsive power to the high endurance fixed wing VTOL aircraft during the climb phase. In addition, the hybrid propulsion system further includes a first propulsion unit driven by the IC engine and a second propulsion unit driven by the electric motor. Moreover, the hybrid propulsion system includes a controller that is communicatively coupled to the IC engine and the electric motor. Furthermore, the controller is configured to determine the total propulsive power required during the climb phase based on a desired rate of climb for the high endurance fixed wing VTOL aircraft. Moreover, the controller is configured to dynamically allocate the total propulsive power between the IC engine and the electric motor during the climb phase. Moreover, the allocation is based on the power density of the electric motor being greater than the power density of the IC engine, enabling the electric motor to provide higher supplemental propulsive power per unit weight compared to the IC engine, and changes in brake specific fuel consumption (BSFC) of the IC engine with varying throttle settings, wherein BSFC improves at higher throttle settings. Additionally, the controller is configured to operate the IC engine alone at an optimal throttle setting to provide the propulsive power required to maintain a desired airspeed for the high endurance fixed wing VTOL aircraft during the cruise phase. Moreover, the hybrid propulsion system enables a reduction in the size and weight of the IC engine and the overall weight of the high endurance fixed wing VTOL aircraft, including the fuel required for the mission, while maintaining the desired rate of climb, efficiency, and endurance of the high endurance fixed wing VTOL aircraft.

[0012] Advantageously, by using the electric motor to supplement the IC engine during the climb phase, the hybrid propulsion system ensures that the high endurance fixed wing VTOL aircraft achieves the desired rate of climb without an oversized IC engine. Furthermore, the hybrid propulsion system allows for the use of a smaller, lighter IC engine, which in collaboration with the electric motor is configured to provide the high-power output required during the climb phase. Moreover, by reducing the weight of the IC engine and improving the fuel efficiency, the hybrid propulsion system enables the high endurance fixed wing VTOL aircraft to carry more fuel or payload, thereby increasing the endurance or utility of the high endurance fixed wing VTOL aircraft.

[0013] It is to be appreciated that all the aforementioned implementation forms can be combined. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof. It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.

[0014] Additional aspects, advantages, features, and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not too scale. Wherever possible, like elements have been indicated by identical numbers.

[0017] Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:

[0018] FIG. 1 is a diagram illustrating a hybrid propulsion system for a high endurance fixed-wing vertical take-off and landing (VTOL) aircraft, in accordance with an embodiment of the present disclosure;

[0019] FIG. 2 is a flow chart illustrating operations performed by the controller for the hybrid propulsion system, in accordance with an embodiment of the present disclosure;

[0020] FIG. 3 is a graphical representation that illustrates the variation of endurance of the high endurance fixed wing VTOL aircraft for different power divisions of the IC engine, in accordance with an embodiment of the present disclosure; and FIG. 4 is a graphical representation that illustrates the variation of the BSFC of the IC engine for different throttle of the high endurance fixed wing VTOL aircraft, in accordance with an embodiment of the present disclosure.

[0021] In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.

[0022] DETAILED DESCRIPTION OF EMBODIMENTS

[0023] The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.

[0024] FIG. l is a diagram illustrating a hybrid propulsion system for high endurance fixed- wing vertical take-off and landing (VTOL) aircraft, in accordance with an embodiment of the present disclosure. With the reference to FIG. 1, there is shown a hybrid propulsion system 102 for a high endurance fixed wing VTOL aircraft 100. The hybrid propulsion system 102 further includes an IC engine 104, an electric motor 106, a first propulsion unit 108, a second propulsion unit 114, a starteralternator 116, a power management unit 118, a battery 112, a VTOL propulsion unit 120, and a controller 110.

[0025] The hybrid propulsion system 102 for the high endurance fixed wing VTOL aircraft 100 is configured to integrate the IC engine 104 and the electric motor 106 to maintain the required propulsion power. The IC engine 104 provides the required propulsive power, while the electric motor 106 supplements the power during the climb phase, thereby optimizing the rate of ascent of the high endurance fixed wing VTOL aircraft 100. The controller 110 is configured to determine the total power needed for the high endurance fixed wing VTOL aircraft 100 to climb, leveraging the higher power density and efficient operation of the electric motor 106 at varying throttle settings. Moreover, during the cruise, the IC engine 104 operates at optimal settings to maintain the desired airspeed, enhancing fuel efficiency. Additionally, the size and weight of the IC engine 104 are reduced while preserving the overall climb rate, efficiency, and endurance of the high endurance fixed wing VTOL aircraft 100.

[0026] The IC engine 104 refers to a heat engine in which the combustion of a fuel occurs with an oxidizer, where the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. Furthermore, the IC engine 104 is operated by converting the energy from fuel into mechanical work. In an implementation, the IC engine 104 is a gasoline engine, a diesel engine, a turbine engine, or a rotary engine. Moreover, the versatility of choosing different types of the IC engine 104 allows the hybrid propulsion system 102 to fulfil specific performance needs, thereby enhancing the overall efficiency and effectiveness of the high endurance fixed wing VTOL aircraft 100. For example, the gasoline engine provides a high power-to-weight ratio ideal for quick response, the diesel engine offers superior fuel efficiency for long- endurance flights, the turbine engine delivers consistent high power suitable for high-speed operations, and the compact design of the rotatory engine is advantageous for the high endurance fixed wing VTOL aircraft 100 that are involved in space-constrained related applications.

[0027] The electric motor 106 is configured to convert electrical energy into mechanical energy. The electric motor 106 is configured to drive the propellers of the high endurance fixed wing VTOL aircraft 100. In an implementation, the electrical motor 106 is a brushless direct current (BLDC) motor. In such an implementation, the BLDC motor operates without brushes, which reduces the overall friction and wear of the electric motor 106, resulting in an increased lifespan with reduced maintenance. Moreover, the controller 110 is configured to manage the operation of the electric motor 106, such as by switching the flow of current through the motor windings. As a result, by using the BLDC motor, the overall efficiency of the hybrid propulsion system 102 is enhanced with reduced energy losses, leading to an increased battery life and extended flight time of the high endurance fixed wing VTOL aircraft 100.

[0028] The first propulsion unit 108 refers to a unit that is configured to generate thrust in order to move the high endurance fixed wing VTOL aircraft 100 in a forward direction. Furthermore, the first propulsion unit 108 includes a power source, such as the IC engine 104 , which is configured to generate thrust by rotating a propeller or a propulsive nozzle.

[0029] The second propulsion unit 114 refers to a unit that is configured to generate thrust in order to move the high endurance fixed wing VTOL aircraft 100 in a forward direction. Furthermore, the second propulsion unit 114 includes a power source, such as the electric motor 106, which is configured to generate thrust by rotating a propeller or a propulsive nozzle.

[0030] The VTOL propulsion unit 120 refers to a unit that is configured to generate thrust in order to move the high endurance fixed wing VTOL aircraft 100 when the high endurance fixed wing VTOL aircraft 100 is in the VTOL phase, i.e., while taking- off and landing vertically. Furthermore, the VTOL propulsion unit 120 includes power source, which is configured to generate thrust by rotating propeller or propulsive nozzle.

[0031] The starter-alternator 116 refers to an integrated component of the electrical system in the high endurance fixed-wing VTOL aircraft 100. The starter-alternator 116 combines the functionalities of the starter, which cranks the IG engine 104, and an alternator, which generates electrical power. The stater-alternator 116 also includes the power management unit (PMU) 118, which manages and regulates the electrical power generated by the alternator. The PMU 118 is configured to perform the rectification process, converting the alternating current (AC) generated by the alternator into direct current (DC), which is required by the electrical systems of the high endurance fixed-wing VTOL aircraft 100. Furthermore, the PMU 118 also ensures that the voltage levels are appropriate for operating the onboard avionics and other electrical components of the the high endurance fixed-wing VTOL aircraft 100.

[0032] The power management unit 118 refers to a component that oversees the distribution and regulation of electrical power within the hybrid propulsion system 102 of the high endurance fixed wing VTOL aircraft 100. The power management unit is configured to manage the interplay between the IC engine 104, the electric motor 106, and the electrical systems of the high endurance fixed wing VTOL aircraft 100, ensuring that power is allocated efficiently during various phases of flight. The power management unit 118 is also configured to optimize the use of energy sources to maintain optimal performance, reduce fuel consumption, and enhance the overall endurance of the high endurance fixed wing VTOL aircraft 100.

[0033] The battery 112 refers to an onboard energy storage component that provides electrical power to the electric motor 106 and electrical systems. The battery 112 stores energy that can be used during the climb phase to supplement the IC engine 104 or to power the electric motor 106 independently during certain phases of flight. The battery 112 is configured to optimize the overall efficiency and performance of the hybrid propulsion system 102 by enabling the use of electric power when needed, reducing fuel consumption, and enhancing the endurance of the high endurance fixed wing VTOL aircraft 100.

[0034] The controller 110 refers to a computational element that is configured to control the high endurance fixed wing VTOL aircraft 100. Furthermore, the controller 110 may refer to one or more individual processors, processing devices, and various elements associated with a processing device that may be shared by other processing devices. Additionally, the one or more individual processors, processing devices, and elements are arranged in various architectures for responding and processing the instructions that drive the high endurance fixed wing VTOL aircraft 100. Examples of the controller 110 may include but are not limited to a central processing unit (CPU) in a computer or a microcontroller in electronic devices, a programmable logic controller (PLC) in industrial automation systems, a digital signal processor (DSP), and the like.

[0035] There is provided the hybrid propulsion system 102 for the high endurance fixed wing VTOL aircraft 100 that includes the IC engine 104 configured to provide propulsive power to the high endurance fixed wing VTOL aircraft 100. Moreover, the IC engine 104 is configured to work either independently or in conjunction with some other power sources, such as the electric motor 106 depending on the flight phase. In an example, during the climb phase, the IC engine 104 is configured to provide propulsive power to the high endurance fixed wing VTOL aircraft 100 in conjunction with another power source, such as the electric motor 106. In another example, during the cruise phase, the IC engine 104 is configured to provide propulsive power to the high endurance fixed wing VTOL aircraft 100 independently. Therefore, the inclusion of the IC engine 104 in the hybrid propulsion system 102 offers a reliable and robust source of propulsion, which is necessary for sustained flight and efficient operation of the high endurance fixed wing VTOL aircraft 100.

[0036] Furthermore, the hybrid propulsion system 102 includes the electric motor 106 configured to provide supplemental propulsive power to the high endurance fixed wing VTOL aircraft 100 during a climb phase. Furthermore, the inclusion of the electric motor 106 in the hybrid propulsion system 102 offers an additional power to the high endurance fixed wing VTOL aircraft 100, when the high endurance fixed wing VTOL aircraft 100 requires an extra thrust, such as during the climb phase. Moreover, during the climb phase, the electric motor 106 works alongside the IC engine 104 to provide the additional propulsive force, reducing the load on the IC engine 104 and improving the overall power output of the high endurance fixed wing VTOL aircraft 100. Advantageously, the IC engine 104, along with the electric motor 106, are used to fulfil the need for high power during the climb phase without the drawback of carrying a heavier engine throughout the entire flight. By optimizing power distribution between the IC engine 104 and the electric motor 106, the hybrid propulsion system 102 enhances the performance of the high endurance fixed wing VTOL aircraft 100 by ensuring an efficient and effective climb with reduced load on the IC engine 104 with reduced fuel consumption.

[0037] Furthermore, the hybrid propulsion system 102 includes the first propulsion unit 108, driven by the IC engine 104 and the second propulsion unit 114, driven by the electric motor 106. The hybrid propulsion system 102 integrates the outputs from the IC engine 104 and the electric motor 106, allowing both power sources to work concurrently or independently as per the requirement of the high endurance fixed wing VTOL aircraft 100. In an implementation, the IC engine 104 is configured to provide primary power for steady flight, while the electric motor 106 is configured to supplement the power of the IC engine 104 during the different phases (i.e., the cruise phase and the climb phase) of the flight. Moreover, the IC engine 104 is configured to provide thrust during long-duration cruise flight, while the electric motor 106 is configured to deliver additional thrust. As a result, such a combination of the IC engine 104 and the electric motor 106 optimizes the overall aircraft performance, thereby reducing the requirement of a large and heavy engine to meet peak power demands of the high endurance fixed wing VTOL aircraft 100.

[0038] Furthermore, the hybrid propulsion system 102 includes the controller 110 communicatively coupled to the IC engine 104 and the electric motor 106, configured to determine the total propulsive power required during the climb phase based on a desired rate of climb for the high endurance fixed wing VTOL aircraft 100. Moreover, the controller 110 calculates the total propulsive power needed by the high endurance fixed wing VTOL aircraft 100 during the climb phase, which is essential to ensure the high endurance fixed wing VTOL aircraft 100 achieves the desired rate of climb efficiently and safely. As a result, by precisely calculating the power needed for the climb, the controller 110 ensures the power demands are met efficiently without overloading the power source. Moreover, such dynamic allocation optimizes performance and prevents excessive fuel consumption with efficient power distribution during the climb, maximizing the use of both the IC engine 104 and the electric motor 106, which enhances the overall performance of the hybrid propulsion system 102 and reduces the overall fuel consumption. In addition, the controller 110 is configured to monitor and compare the current rate of climb of the high endurance fixed wing VTOL aircraft 100 to the desired rate of climb by calculating the total propulsive power required to achieve the desired rate of climb continuously to meet the power demand of the high endurance fixed wing VTOL aircraft 100 during the climb phase.

[0039] Furthermore, the controller 110 is configured to dynamically allocate the total propulsive power between the IC engine 104 and the electric motor 106 during the climb phase. The dynamic allocation of the propulsive power is required to optimize the performance and efficiency of the hybrid propulsion system 102 during the climb phase of the high endurance fixed wing VTOL aircraft 100. The controller 110 continuously assesses the power requirements and availability of power resources. Thereafter, based on the assessed power requirements, the controller 110 is configured to adjust the distribution of propulsive power between the IC engine 104 and the electric motor 106 in real-time or in near real-time. Advantageously, by effectively utilizing both power sources, such as the IC engine 104 and the electric motor 106, the controller 110 contributes to improved manoeuvrability and operational flexibility of the high endurance fixed wing VTOL aircraft 100. By virtue of actively managing power distribution, the controller 110 helps to maximize the endurance of the high endurance fixed wing VTOL aircraft 100 and enhance the mission capabilities of the high endurance fixed wing VTOL aircraft 100, making the high endurance fixed wing VTOL aircraft 100 well-suited for demanding VTOL operations where precise power management is required in order to successfully complete the mission. For example, during a mission in mountainous terrain, the high endurance fixed wing VTOL aircraft 100 is used to perform vertical take-offs and landings in confined areas and sustain long-duration flights over rugged landscapes. The dynamic power allocation by the controller 110 ensures efficient climb performance and optimal fuel usage, enabling the high endurance fixed wing VTOL aircraft 100 to carry additional equipment or supplies essential for the mission, thereby increasing the chances of a successful operation. Furthermore, the allocation is based on the power density of the electric motor 106 being more significant than the power density of the IC engine 104, enabling the electric motor 106 to provide higher supplemental propulsive power per unit weight compared to the IC engine 104. Moreover, the controller 110 is configured to calculate the power density of both the electric motor 106 and the IC engine 104, and then allocates more propulsive power to the electric motor 106, especially during phases like climb where additional power is required to the high endurance fixed wing VTOL aircraft 100. Therefore, by maximizing the use of the electric motor 106, which provides more power per unit weight, the hybrid propulsion system 102 reduces the overall weight of the high endurance fixed wing VTOL aircraft 100 while maintaining the overall performance of the high endurance fixed wing VTOL aircraft 100 during the climb phase.

[0040] Furthermore, Table 1 represents the relationship between the weight of the electric motor 106, the weight of the IC engine 104, and the weight of the fuel with the endurance of the high endurance fixed wing VTOL aircraft 100 for various configurations of the hybrid propulsion system 102 corresponding to same overall power. Moreover, the first column of Table 1 shows the weight of the electric motor 106 in kilograms (kg), ranging from 0 to 2.519 kg, and the second column of Table 1 shows the weight of the IC engine 104 in kilograms (kg), ranging from 17.223 to 6.028 kg. In an example, the weight of the electric motor 106 is 0 kg and the weight of the IC engine 104 is 17.223 kg. In another example, the weight of the electric motor 106 is 2.519 kg and the weight of the IC engine 104 is 6.028 kg. In yet another example, the weight of the electric motor 106 is 1.163 kg and the weight of the IC engine 104 is 12.056 kg. Additionally, the third column represents the endurance of the high endurance fixed wing VTOL aircraft 100 in hours (hr) for each combination of the weight of the electric motor 106 and the weight of the IC engine 104. Furthermore, the highest endurance of 13.36 hours is achieved when the electric motor 106 weighs 2.519 kg and the IC engine 104 weighs 6.028 kg. However, further increases in the weight of the electric motor 106 beyond the highest endurance point (i.e., when the weight of the IC engine contributes 65% of the total weight) result in a diminishing return in terms of endurance, as the IC engine 104 will be too small to sustain the cruise phase of the flight by own. Furthermore, the weight of the fuel in the high endurance fixed-wing VTOL aircraft 100 is carefully balanced to ensure that the overall weight of the high endurance fixed-wing VTOL aircraft 100 remains constant. Moreover, the strategic balance in the weight of fuel allows the high endurance fixed-wing VTOL aircraft 100 to achieve maximum endurance without compromising the structural integrity or performance capabilities. In the initial configuration, where the electric motor weighs 0 kg, the IC engine weighs 17.223 kg, and the weight of fuel is is 22.777 kg, the aircraft achieves an endurance of 5.63 hours. The high endurance fixed-wing

[0041] VTO1 aircraft 100 reaches the maximum endurance of 13.36 hours, when the weight of fuel is also maximized at 31.345 kg. As the weight of the IC engine is increased, the weight of fuel increases, which results in the decrease in the weight of electric motor. Thus, the weight of fuel is decided in such a way that overall weight of the high endurance fixed wing VTOL aircraft 100 remains the same.

[0042] Table 1

[0043] Advantageously, by utilizing the electric motor 106 to provide a portion of the power required during the climb phase, the high endurance fixed wing VTOL aircraft 100 can achieve a higher endurance compared to relying solely on the IC engine 104. Furthermore, by leveraging the electric motor 106 to assist with the power requirements during the climb phase, the size and weight of the IC engine 104 can be reduced. Additionally, by optimizing the power division and reducing the size and weight of the IC engine 104, the hybrid propulsion system 102 enhances the overall efficiency and performance of the high endurance fixed wing VTOL aircraft 100.

[0044] Furthermore, the allocation is based on changes in brake specific fuel consumption (BSFC) of the IC engine 104 with varying throttle settings. For example, during a mission requiring prolonged loitering at a specific altitude, the hybrid propulsion system 102 adjusts the power distribution based on the BSFC of the IC engine 104 in order to ensure that the IC engine 104 operates at the most efficient throttle setting during the cruise phase thereby conserving fuel while the electric motor 106 provides additional power as per the requirement. Moreover, such power distribution and power allocation allow the high endurance fixed wing VTOL aircraft 100 to remain in the air for extended periods, enhancing the effectiveness of the mission. In addition, the controller 110 is configured to monitor the BSFC of the IC engine 104 in real-time as the IC engine 104 operates at different throttle settings. The controller 110 continuously monitors the throttle settings and corresponding BSFC of the IC engine 104. During the climb phase, the controller 110 dynamically allocates power between the IC engine 104 and the electric motor 106, thereby optimizing the throttle setting of the IC engine 104 for fuel efficiency while the electric motor supplements the required additional power. Furthermore, the higher throttle settings result in a better BSFC, and the controller 110 allocates more power to the IC engine 104. Conversely, when the throttle setting is less efficient, the controller 110 is configured to shift more power demand to the electric motor 106. Therefore, by operating the IC engine 104 at an optimal BSFC range, the hybrid propulsion system 102 reduces the overall fuel consumption and improves overall efficiency, allowing the high endurance fixed wing VTOL aircraft 100 to perform longer missions with less fuel.

[0045] In accordance with an embodiment, the controller 110 adjusts the division of propulsion power to maintain optimum BSFC and provide excess power from the electric motor 106 during the climb phase. The maintenance of the optimum BSFC ensures that the IC engine 104 operates at the most fuel-efficient point with reduced fuel consumption. Furthermore, by providing excess power from the electric motor 106 during the climb phase, the hybrid propulsion system 102 is configured to ensure that the high endurance fixed wing VTOL aircraft 100 achieves the necessary performance without overloading the IC engine 104. For example, the high endurance fixed wing VTOL aircraft 100 engaged in a mission across rugged terrain requires frequent maneuvers in mountainous regions, where precise power management is crucial for mission success. The hybrid propulsion system 102, integrating the IC engine 104 and the electric motor 106 is used to balance the IC engine 104 and electric motor 106 outputs to meet varying power demands, especially in environments where air density affects engine efficiency. The controller 110 is configured to continuously monitor the operating parameters of the IC engine 104 and adjusts the power output between the IC engine 104 and the electric motor 106. Moreover, based on the monitored BSFC throttle setting, the hybrid propulsion system 102 dynamically adjusts the power distribution of the power sources of the high endurance fixed wing VTOL aircraft 100. During the climb phase, when the BFSC of the IC engine 104 crosses a threshold level, the controller 110 compensates by providing additional power from the electric motor 106 to ensure that the IC engine 104 operates within a most efficient range while still delivering the necessary power for the climb. Advantageously, by maintaining the IC engine 104 at an optimum BSFC and supplementing the IC engine 104 with the electric motor 106, the hybrid propulsion system 102 reduces an overall fuel usage and enhances performance.

[0046] Furthermore, the controller 110 is configured to operate the IC engine 104 alone at an optimal throttle setting to provide the propulsive power required to maintain a desired airspeed for the high endurance fixed wing VTOL aircraft 100 during the cruise phase. The controller 110 is configured to monitor and adjust the throttle setting of the IC engine 104 based on real-time flight conditions and operational requirements. Thereafter, the controller 110 is configured to calculate the necessary propulsive power to sustain the desired airspeed during cruise phase operations. Moreover, such operation is crucial to maintain the desired airspeed of the high endurance fixed wing VTOL aircraft 100 during the cruise phase. By running the IC engine 104 at an optimal throttle setting, the hybrid propulsion system 102 is configured to ensure efficient fuel consumption and optimal performance throughout extended flight durations.

[0047] In accordance with an embodiment, the distribution of propulsion power between the IC engine 104 and the electric motor 106 during the climb phase is dynamically adjusted based on prior measurements of the weight of the high endurance fixed wing VTOL aircraft 100 and atmospheric conditions. Furthermore, the hybrid propulsion system 102 adjusts the distribution of propulsion power based on prior estimation of the weight of the high endurance fixed wing VTOL aircraft 100 and the atmospheric conditions, such as air density and temperature. In an implementation, when the high endurance fixed wing VTOL aircraft 100 needs to ascend rapidly to reach a remote location, the hybrid propulsion system 102 detects the current weight due to payload and fuel, as well as atmospheric conditions like air density and temperature. As a result, by dynamically adjusting power distribution, the hybrid propulsion system enhances the climb performance of the high endurance fixed wing VTOL aircraft 100 while minimizing energy consumption, increasing operational flexibility, and improving overall mission capability by adapting to changing flight conditions in real time. Furthermore, the data received from sensors in real-time is processed by the controller 110 to determine the optimal power distribution between the IC engine 104 and the electric motor 106. In addition, during the climb phase, the controller 110 adjusts the power output of the IC engine 104 based on the current weight of the high endurance fixed wing VTOL aircraft 100 and atmospheric conditions to maintain an efficient and effective propulsion. Therefore, by dynamically adjusting the power distribution between the IC engine 104 and the electric motor 106 based on real-time data, the hybrid propulsion system 102 is configured to ensure that the high endurance fixed wing VTOL aircraft 100 reduces the overall fuel consumption with an extended flight endurance of the high endurance fixed wing VTOL aircraft 100.

[0048] Furthermore, the hybrid propulsion system 102 enables a reduction in the size and weight of the IC engine 104 and the overall weight of the high endurance fixed wing VTOL aircraft 100, including the fuel required for the mission, while maintaining the desired rate of climb, efficiency, and endurance of the high endurance fixed wing VTOL aircraft 100. By utilizing the hybrid propulsion system 102, the size and weight of the IC engine 104 is reduced significantly. Moreover, such reduction is achieved due to the electric motor 106 that supplements the IC engine 104 during high-power-demand phases such as take-off and climb. During such phases, the electric motor 106 provides additional power, allowing for the selection of a smaller and lighter IC engine 104 that operates at optimal efficiency during cruise phases. During the climb phases, the controller 110 dynamically adjusts the power allocation based on the weight of the high endurance fixed wing VTOL aircraft 100 and environmental conditions. Moreover, such optimization ensures that the high endurance fixed wing VTOL aircraft 100 maintains the required rate of climb while minimizing fuel consumption and maximizing endurance with enhanced overall efficiency and extends the operational range and endurance of the high endurance fixed wing VTOL aircraft 100, crucial for missions requiring prolonged flight times or variable power demands.

[0049] In accordance with an embodiment, the distribution of power between the IC engine 104 and the electric motor is 106 predetermined for different phases of flight based on simulations to optimize overall aircraft performance. Furthermore, various simulations are used to determine the best power distribution between the IC engine 104 and the electric motor 106 for each phase of flight, which considers various factors, such as the weight of the high endurance fixed wing VTOL aircraft 100, atmospheric conditions, and the IC engine 104 performance characteristics. Therefore, by using simulations to predetermine the power distribution between the IC engine 104 and the electric motor 106, the hybrid propulsion system 102 can ensure that the IC engine 104 operates within the optimal range, reducing fuel consumption and emissions.

[0050] In accordance with an embodiment, the controller 110 is configured to operate the IC engine 104 at a reduced throttle setting below rated power output during the descent phases of flight. The controller 110 is configured to continuously monitor the flight phase and determines when the high endurance fixed wing VTOL aircraft 100 is in the descent phase. Moreover, during the descent phase, the controller 110 adjusts the throttle setting of the IC engine 104 to a level that is sufficient to maintain controlled descent. Furthermore, the adjustment of the throttle setting of the IC engine 104 is automated and based on real-time data, the hybrid propulsion system 102 is configured to ensure that the IC engine 104 operates at an optimal efficiency level. Additionally, by running the IC engine 104 at an adjusted throttle setting, the mechanical stress and wear of the IC engine 104 is reduced, thereby potentially increasing the operational life of the IC engine 104 and decreasing maintenance requirements of the IC engine 104.

[0051] In accordance with an embodiment, the electric motor 106 is powered by the battery 112, which provides sufficient energy for the electric motor 106 to assist in a predetermined number of climb phases, based on the expected mission profile of the high endurance fixed wing VTOL aircraft 100. Furthermore, the battery 112 is configured to match the expected energy requirements of the electric motor 106 during the climb phase. In an implementation, the controller 110 is configured to calculate the energy required for each phase, thereby ensuring that the battery 112 can deliver power consistently to the electric motor 106 as per the requirement of the high endurance fixed wing VTOL aircraft 100. Moreover, the capacity of the battery 112 is determined based on the mission profile, which includes factors such as the number of climbs, the duration of each climb, and the power required by the electric motor 106. In an example, the battery 112 can be a zinc -based battery. In another example, the battery 112 can be a lithium-based battery. In yet another example the battery 112 can be a lead-based battery. As a result, by providing a continuous source of power to the electric motor 106 through the battery 112 for a predetermined number of climb phases, the hybrid propulsion system 102 can meet the specific demands of the mission profile of the high endurance fixed wing VTOL aircraft 100. In another implementation, the high endurance fixed wing VTOL aircraft 100 requires a high rate of discharge from the battery 112 to run the powerful vertical take-off rotors. Even though the energy required for a VTOL phase, which takes only a few seconds, is minimal, a larger battery is necessary to meet the discharge rate requirements. Thus, the hybrid propulsion system 102 combines the power from the IC engine 104 with the power from the electric motor 106, allowing the high endurance fixed wing VTOL aircraft 100 to take advantage of the strengths of both power sources.

[0052] In accordance with an embodiment, the controller 110 is configured to selectively engage one or more electric motors during the climb phase based on the required total propulsive power, furthermore, the selective engagement of the electric motor 106 from one or more electric motors ensures that the high endurance fixed wing VTOL aircraft 100 provides the required thrust for a successful and efficient climb, thereby optimizing the overall performance and energy utilized by the high endurance fixed wing VTOL aircraft 100. Moreover, the controller 110 is configured to assess the total propulsive power needed during the climb phase on the basis of real-time flight data, such as altitude, vertical speed, and throttle settings and determines whether one or more electric motors should be activated. Therefore, by selectively engaging the electric motors based on the required power, the hybrid propulsion system 102 can efficiently allocate propulsion power and increase the overall flight time of the high endurance fixed wing VTOL aircraft 100. In accordance with an embodiment, the controller 110 adaptively engages and disengages the electric motor 106 based on flight conditions, providing smooth and seamless transitions between the IC engine 104 and the electric motor 106 while maintaining the overall propulsion power of the high endurance fixed wing VTOL aircraft 100. The controller 110 continuously monitors various parameters of the high endurance fixed wing VTOL aircraft 100, such as altitude, speed, engine performance, and power demand. Moreover, based on such parameters, the controller 110 is configured to decide when to engage or disengage the electric motor 106. In an example, during the take-off and climb, the controller 110 is configured to engage both the IC engine 104 and the electric motor 106 to provide maximum power. In another example, during the cruise phase, the controller 110 disengages the electric motor 106 to rely solely on the IC engine 104 to attain sustained efficiency. Therefore, by dynamically adjusting the power by engaging and disengaging the electric motor 106 during different phases of the flight, the high endurance fixed wing VTOL aircraft 100 can operate at optimal efficiency across all flight phases.

[0053] Advantageously, by using the electric motor 106 to supplement the IC engine 104 during the climb phase, the hybrid propulsion system 102 ensures that the high endurance fixed wing VTOL aircraft 100 achieves the desired rate of climb without an oversized IC engine 104. Furthermore, the hybrid propulsion system 102 allows for the use of a smaller, lighter IC engine, which in collaboration with the electric motor 106 is configured to provide the high-power output required during the climb phase. Moreover, by reducing the weight of the IC engine 104 and improving the fuel efficiency, the hybrid propulsion system 102 enables the high endurance fixed wing VTOL aircraft 100 to carry more fuel or payload, thereby increasing the endurance or utility of the high endurance fixed wing VTOL aircraft 100.

[0054] FIG. 2 is a flow chart illustrating operations performed by the controller of the hybrid propulsion system, in accordance with an embodiment of the present disclosure. FIG. 2 is described in conjunction with elements from FIG. 1. With reference to FIG. 2, there is shown a flowchart 200 illustrating the operations to be performed for distributing the power between the IC engine 104 and the electric motor 106 during different phases of the flight.

[0055] At operation 202, the controller 110 starts operating by performing various diagnostic checks, such as by receiving the data from multiple sensors, such as pressure sensors, air data sensors, fuel level sensors, vibration sensors and the like, and components of the high endurance fixed wing VTOL aircraft 100. Furthermore, the controller 110 is configured to determine the flight phase of the high endurance fixed wing VTOL aircraft 100. For example, the controller 110 is configured to monitor altitude, airspeed, throttle settings, vertical speed, and GPS data of the high endurance fixed wing VTOL aircraft 100 to identify whether the high endurance fixed wing VTOL aircraft 100 is in a VTOL phase, a take-off phase, a climb phase, a cruise phase, a descent phase, or in a landing phase. Moreover, the controller 110 also utilizes predefined flight plans and compares the real-time data against the predefined flight plans to accurately assess the current flight phase of the high endurance fixed wing VTOL aircraft 100.

[0056] Thereafter, at operation 204, the controller 110 is configured to determine if the high endurance fixed wing VTOL aircraft 100 is in the climb phase. Moreover, during the climb phase, the controller 110 is configured to monitor the vertical speed of the high endurance fixed wing VTOL aircraft 100, which indicates an upward trajectory, and check altitude data in order to confirm that the high endurance fixed wing VTOL aircraft 100 is gaining height. Additionally, the controller 110 assesses the throttle settings, as increased throttle is typically used during the climb phase. At operation 206, the controller 110 is configured to determine if the high endurance fixed wing VTOL aircraft 100 is in the cruise phase. Moreover, during the cruise phase, the controller 110 is configured to monitor the altitude of the high endurance fixed wing VTOL aircraft 100, which remains relatively constant during the cruise phase. In addition, the controller 110 is configured to check the horizontal speed of the high endurance fixed wing VTOL aircraft 100, thereby ensuring that the high endurance fixed wing VTOL aircraft 100 is in a steady position and is within the range required for cruising. Additionally, the controller 110 is configured to evaluate throttle settings that are generally set to a lower and stable level as compared to the other phases, such as climb or descent phases. Therefore, by considering all of the factors, along with the pre-defined flight plan and GPS data, the controller 110 is configured to identify and confirm that the high endurance fixed wing VTOL aircraft 100 is in the cruise phase.

[0057] Moreover, at operation 208, the controller 110 is configured to determine if the high endurance fixed wing VTOL aircraft 100 is in the transition phase. The transition phase of the the high endurance fixed wing VTOL aircraft 100 occurs when the high endurance fixed wing VTOL aircraft 100 makes a transition from one phase to another, such as from the VTOL phase to the climb phase or vice-versa. At operation 210, the controller 110 is configured to determine if the high endurance fixed wing VTOL aircraft 100 is in the VTOL phase. The VTOL phase of the high endurance fixed wing VTOL aircraft 100 refers to the instant when the high endurance fixed wing VTOL aircraft 100 is taking off or landing in a vertical position.

[0058] Furthermore, at operation 212, the controller 110, after determining that the high endurance fixed wing VTOL aircraft 100 is in the climb phase, operates the IC engine 104 and the electric motor 106. Therefore, by operating the IC engine 104 and the electric motor 106 simultaneously, the hybrid propulsion system 102 maximizes the available thrust to ensure an efficient ascent of the high endurance fixed wing VTOL aircraft 100 with reduced overall fuel consumption. Furthermore, the combined operation of the IC engine 104 and the electric motor 106 helps the high endurance fixed wing VTOL aircraft 100 to achieve the desired climb rate quickly and smoothly, thereby optimizing the overall performance and fuel efficiency during the critical phase of the high endurance fixed wing VTOL aircraft 100. Furthermore, at operation 214, the controller 110, after determining the high endurance fixed wing VTOL aircraft 100 is in the cruise phase, operates the IC engine 104 individually in order to optimize the fuel efficiency and reduce wear on the electric motor 106. In addition, the controller 110 is configured to ensure that the electric motor 106 is conserved for other flight phases of the high endurance fixed wing VTOL aircraft 100, such as take-off, climb, and landing, where additional thrust and agility are required. At operation 216, the controller 110, after determining the high endurance fixed wing VTOL aircraft 100 is in the transition phase, operates the IC engine 104 and the VTOL propulsion unit 120 to provide the propulsion to the high endurance fixed wing VTOL aircraft 100. At operation 218, the controller 110, after determining the high endurance fixed wing VTOL aircraft 100 is in the VTOL phase, operates only the VTOL propulsion unit 120 to provide propulsion to the high endurance fixed wing VTOL aircraft 100.

[0059] Advantageously, the ability of the controller 110 to dynamically allocate power between the IC engine 104 and the electric motor 106 based on real-time data ensures that the high endurance fixed wing VTOL aircraft 100 operates within optimal parameters, thereby improving the overall safety and reliability of the high endurance fixed wing VTOL aircraft 100. Additionally, the controller 110 significantly enhances the performance, fuel efficiency, and overall mission effectiveness of the high endurance fixed wing VTOL aircraft 100 by intelligently managing the power distribution between the IC engine 104 and the electric motor 106 across different flight phases.

[0060] FIG. 3 is a graphical representation that illustrates the variation of endurance of the high endurance fixed wing VTOL aircraft for different power divisions of the IC engine, in accordance with an embodiment of the present disclosure. FIG. 3 is described in conjunction with elements from FIG. 1. With reference to FIG. 3, there is shown a graphical representation 300 that illustrates the endurance of the high endurance fixed wing VTOL aircraft 100 at different power divisions of the IC engine 104. The graphical representation 300 includes an X-axis 302 that represents the different power divisions of the IC engine 104 in percentage (%) and a Y-axis 304 that represents endurance in hours (hr).

[0061] In another words, the X-axis 302 represents the percentage of total power provided by the electric motor 106 during the climb phase, ranging from 0% to 100%. For example, at 0%, the IC engine 104 provides all the power required for the climb phase, while at 100%, the electric motor 106 provides all the power, and at 50%, both the IC engine 104 and electric motor 106 contribute equally to the total power required during climb. Similarly, the Y-axis 304 represents the endurance of the high endurance fixed wing VTOL aircraft 100 in hours (hr). Furthermore, the endurance is a measure of how long the aircraft can stay in the air, which is directly related to the amount of fuel the high endurance fixed wing VTOL aircraft 100 carries and the overall efficiency of the high endurance fixed wing VTOL aircraft 100.

[0062] Moreover, the graphical representation 300 shows that as the power division of the electric motor increases from 0% to approximately 60%, the endurance of the high endurance fixed wing VTOL aircraft 100 also increases, reaching a peak 306 of around 13.36 hours at the 65% power division point of the electric motor 106. Furthermore, the peak 306 of the graphical representation 300 indicates that the optimal power division between the IC engine 104 and electric motor 106 for maximum endurance occurs when the electric motor 106 provides about 65% of the total power required during the climb phase. In an implementation, beyond the 65% power division point of the electric motor 106, the endurance starts to decrease as the IC engine 104 takes on a larger share of the power requirements. Furthermore, such decline in the endurance can be attributed to the increased fuel consumption and reduced efficiency of the IC engine 104 at higher power settings, as well as in such cases the added weight of the larger IC engine required to provide the increased power. In such a case, the IC engine 104 will be too small to substain the cruise phase of the flight and the high endurance fixed-wing VTOL aircraft 100 will need to carry extra power supply to fly, thereby causing the weight of battery of the high endurance fixed-wing VTOL aircraft 100 to become more heavy and reduce the fuel capacity. In accordance with an embodiment, the hybrid propulsion system 102 is designed to maximise the endurance of the high endurance fixed wing VTOL aircraft 100 while minimizing the overall weight of the high endurance fixed wing VTOL aircraft 100 by minimizing the weight of the IC engine 104. In an implementation, the above data is for a particular engine, and the data will change for the different engines with different specifications.

[0063] Advantageously, by ensuring that the high endurance fixed wing VTOL aircraft 100 achieves optimal endurance when the electric motor 106 provides more power to the hybrid propulsion system as compared to the IC engine 104, for e.g., the electric motor provides 65% of the power for an optimal endurance for a particular type of IC engine, which is counter-intuitive to the traditional propulsion systems, the information helps identify the most efficient power distribution between the IC engine 104 and the electric motor 106 for maximizing flight duration of the high endurance fixed wing VTOL aircraft 100. Additionally, with the help of the above information, the hybrid propulsion system 102 can be designed to minimize the weight of the IC engine 104, optimize fuel usage, and enhance the overall performance and endurance of the high endurance fixed wing VTOL aircraft 100.

[0064] FIG. 4 is a graphical representation that illustrates the variation of the BSFC of the IC engine for different throttle of the high endurance fixed wing VTOL aircraft, in accordance with an embodiment of the present disclosure. FIG. 4 is described in conjunction with elements from FIG. 1. With reference to FIG. 4, there is shown a graphical representation 400 that illustrates the variation of the throttle of the high endurance fixed wing VTOL aircraft 100 with respect to the change in BSFC of the IC engine 104. The graphical representation includes an X-axis 402 representing the value of throttle and a Y-axis 404 representing the value of BSFC of the IC engine 104.

[0065] Furthermore, the graphical representation 400 illustrates the relationship between throttle settings and Brake Specific Fuel Consumption (BSFC) for an example of IC engine 104 in the high endurance fixed wing VTOL aircraft 100. The x-axis represents the throttle settings of the IC engine, ranging from 0 to 100%, while the y-axis shows the BSFC values, ranging from 0 to 0.8 (in g / Wh). At low throttle settings (below about 40%), the BSFC remains constant at its highest value of approximately 0.7, which indicates that the engine operates at its least efficient state when the throttle is low, consuming more fuel per unit of power produced. Moreover, as the throttle increases beyond 40%, a sharp decrease is depicted in BSFC, indicating a rapid improvement in fuel efficiency. The BSFC drops from about 0.7 to 0.5 as the throttle increases from 40% to 60%, which indicates that the engine becomes significantly more efficient as it's pushed to higher power outputs. From 60% throttle onwards, the BSFC remains relatively stable, hovering around 0.5 with slight fluctuations. Furthermore, there is a minor increase in BSFC (lower efficiency) around 80% throttle, followed by a steep decrease as the throttle approaches 100%.

[0066] Advantageously, the graphical representation 400 indicates that operating the IC engine at very low throttle settings should be avoided due to poor fuel efficiency. Thus, the system could be designed to keep the IC engine operating in its more efficient mid to high-throttle range, using the electric motor to provide additional power when needed or to allow the IC engine to operate at lower, less efficient settings only when absolutely necessary.

[0067] Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and / or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments" . It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.

Claims

CLAIMSWE CLAIM:

1. A hybrid propulsion system (102) for a high endurance fixed wing vertically take-off and landing (VTOL) aircraft (100), comprising: an internal combustion (IC) engine (104), wherein the IC engine (104) is configured to provide propulsive power to the high endurance fixed wing VTOL aircraft (100); an electric motor (106), wherein the electric motor (106) is configured to provide supplemental propulsive power to the high endurance fixed wing VTOL aircraft (100) during a climb phase; a first propulsion unit (108) driven by the IC engine (104) and a second propulsion unit (114) driven by the electric motor (106); and a controller (110) communicatively coupled to the IC engine (104) and the electric motor (106), wherein the controller (110) is configured to: determine a total propulsive power required during the climb phase based on a desired rate of climb for the high endurance fixed wing VTOL aircraft (100); dynamically allocate the total propulsive power between the IC engine (104) and the electric motor (106) during the climb phase, wherein the allocation of the total propulsive power between the IC engine (104) and the electric motor (106) during the climb phase is based on: a power density of the electric motor (106) being greater than a power density of the IC engine (104), enabling the electric motor (106) to provide higher supplemental propulsive power per unit weight compared to the IC engine (104), and changes in brake specific fuel consumption (BSLC) of the IC engine (104) with varying throttle settings, and operate the IC engine (104) individually at an optimal throttle setting to provide the propulsive power required to maintaina desired airspeed for the high endurance fixed wing VTOL aircraft (100) during the cruise phase; wherein the hybrid propulsion system (102) enables a reduction in the size and weight of the IC engine (104) and the overall weight of the high endurance fixed wing VTOL aircraft (100), including the fuel required for the mission, while maintaining the desired rate of climb, efficiency, and endurance of the high endurance fixed wing VTOL aircraft (100).

2. The hybrid propulsion system (100) as claimed in claim 1, wherein the controller (110) adjusts the division of propulsion power to maintain optimum BSFC and provide excess power from the electric motor (106) during the climb phase.

3. The hybrid propulsion system (100) as claimed in claim 1, wherein the distribution of propulsion power between the IC engine (104) and the electric motor (106) during the climb phase is dynamically adjusted based on prior measurements of weight of the high-endurance fixed wing VTOL aircraft (102) and atmospheric conditions.

4. The hybrid propulsion system (100) as claimed in claim 1, wherein the distribution of power between the IC engine ( 104) and the electric motor (106) is predetermined for different phases of flight based on simulations to optimize overall performance of the high endurance fixed wing VTOL aircraft (102).

5. The hybrid propulsion system (100) as claimed in claim 1, wherein the controller (110) is configured to operate the IC engine (104) at an optimum throttle setting during the different phases of the flight of the high- endurance fixed wing VTOL aircraft (102).

6. The hybrid propulsion system (100) as claimed in claim 1, wherein the electric motor (106) is powered by a battery (112) that provides sufficient energy for the electric motor (106) to assist the high endurancefixed wing VTOL aircraft (102) during climb phase and VTOL phase, based on the expected mission profile of the high endurance fixed wing VTOL aircraft (102).

7. The hybrid propulsion system (100) as claimed in claim 1, further comprises one or more electric motors, wherein the controller (110) is configured to selectively engage one or more electric motors during the climb phase based on the required total propulsive power.

8. The hybrid propulsion system (100) as claimed in claim 1, wherein the controller (110) is configured to adaptively engage and disengage the electric motor (106) based on flight conditions, providing smooth and seamless transitions between the IC engine (104) and the electric motor (106) while maintaining the overall propulsion power of the high endurance fixed wing VTOL aircraft (102).

9. The hybrid propulsion system (100) as claimed in claim 1, wherein the electric motor (106) is a brushless DC motor.

10. The hybrid propulsion system (100) as claimed in claim 1, wherein the IC engine (104) is a gasoline engine, a diesel engine, a turbine engine, or a rotary engine.

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