[001] TECHNICAL FIELD

[002] Present disclosure generally relates to the field of Airborne vehicles. Particularly, but not exclusively, the present disclosure relates to Unmanned Aerial Vehicles (UAVs). Further, embodiments of the present disclosure disclose a UAV of hybrid type having engine and electrically driven propellers for propulsion, maneuver and control.

[003] BACKGROUND

[004] An Unmanned Aerial Vehicle, as the name implies, is an autonomous airborne vehicle which finds application in variety of technical and non-technical domains. One of the important application areas is the field of defence where UAVs are extensively used for measurements, surveillance, transportation of artilleries and equipment, secret services, civil purposes, etc. UAVs are gaining utmost popularity and prominence these days owing to its swiftness, light weight configuration, enhanced degree of freedom in terms of manoeuvring and control, compactness and so on. UAVs are also extensively used in other applications such as aerial surveying, precession agriculture, healthcare and emergency medical services, geological studies, investigation of ecosystems where direct human access is close to impossible or treacherous, communication relay, reconnaissance support during natural disasters, scientific research, weather studies, logistics and so on.

[005] UAVs are particularly useful where usage of manned vehicles is not feasible. Thus, long endurance and high altitude flying abilities are desirable characteristics of an UAV. Another important characteristic is ability of the UAV to communicate with control stations, especially at higher altitudes and locations which are not-so-easily interactable with. A bigger challenge is devising a UAV which not only has long endurance and high altitude flying capabilities, but also has satisfactory payload carrying capacity. In simple terms, a higher payload to weight ratio for a UAV is well desired. Based on these requirements, UAVs are broadly classified into multiple rotor helicopters, popularly known as multicopters, and fixed wing aerial vehicles. Multicopters have two or more propellers (rotors), each propeller driven by a separate power source like an electric motor. They generate lift force similar to a helicopter rotor. Fixed wing aircrafts, on the other hand, use fixed wings to generate lift force like airplanes. Multicopters are gaining increasing prominence because of several advantages over the fixed wing counterparts. One of the advantages is vertical take-off and landing ability (VTOL) of multicopters which eliminates need of an air-strip (runway) to take off and land like fixed wing aircrafts. However, multicopters have limited payload bearing capacities than fixed wing aircrafts, as propellers of multicopters have to generate lift forces to overcome weight. Thus, designing a multicopter especially with swift VTOL abilities to carry payloads is extremely challenging. Operational endurance and altitude of multicopters are determined by several factors such as operational battery life, type of motors, and environmental conditions such as wind which may influence battery life.

[006] Fuel based propellers have also been proposed instead of electric propellers to operate UAVs. Engine driven single propeller UAV has been widely used. Single propeller UAVs however have several shortcomings such as large propeller size which results in compromise with compactness of the UAV. A large propeller also indicates a small payload to weight ratio which interferes with the endurance and altitude of flight. Another limitation of single propeller engine-based UAV is requirement of complex mechanical systems, for example, gear drives or auxiliary mechanical drives to control the engine output. To overcome these shortcomings, a combination of engine and electric motors i.e., a hybrid rotor configurations have been proposed. One such multi-propeller design for UAVs is presented in US Publication No: US 2017/001541, Bishop et. A1 [hereafter referred to as ‘541] ‘541 pertains to a VTOL UAV having two counter-rotating rotors for primary thrust generation and three other rotors for lift, stability and direction control. All the propellers are motor driven, with motors being powered by onboard batteries, on board fuel cells or onboard engine driving one or more alternators. Another hybrid configuration is discussed in US Publication US20200223544A1, Kelly et. A1 [hereafter referred to as ‘544] ‘544 provides a multicopter having a frame fitted with propulsion units such as turboprop engines, jet engines or electric motors, and a pair of wings attached on diametrical ends of the multicopter. The wings are pitch controlled to alter angle of attack for lift optimization.

[007] Although prior arts unveil several solutions to mitigate complications associated with endurance and payload carrying capabilities of UAVs, a satisfactory solution aimed at improving energy output for a given weight of the UAVs is not evident or disclosed.

[008] Present disclosure is directed to overcome one or more limitations stated above, or other such limitations associated with the prior arts. [009] SUMMARY OF THE DISCLOSURE

[010] One or more shortcomings of conventional unmanned aircrafts are overcome, and additional advantages are provided through the UAV as claimed in the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

[011] In one non-limiting embodiment of the disclosure, an Unmanned Aerial Vehicle (UAV) is disclosed. The UAV includes a frame and an internal combustion engine mounted to the frame. A first propeller is coupled to the internal combustion engine, where the internal combustion engine drives the first propeller to provide a substantial portion of thrust to lift the UAV. The UAV further includes a plurality of arms, each coupled to the frame and a plurality of second propellers, where each of the plurality of propellers is connectable to one of the plurality of arms. The plurality of second propellers is configured to provide remaining thrust to lift and manoeuvre the UAV. Further, at least one pair of yaw propellers is removably coupled to the frame, where the at least one pair of yaw propellers is configured to control an adverse yaw motion created by the first propeller of the UAV.

[012] In an embodiment of the disclosure, the frame comprises an upper disc and a lower disc. Further, one end of each of the plurality of arms is movably connected between the upper disc and the lower disc of the frame, and another end opposite to the one end of each of the plurality of arms is structured to accommodate one of the plurality of second propellers.

[013] In an embodiment of the disclosure, yaw propellers and each of the plurality of second propellers is actuated by a rotary actuator.

[014] In an embodiment of the disclosure, a fuel tank is fluidly coupled to the internal combustion engine. The fuel tank is mounted on the upper disc of the frame.

[015] In an embodiment of the disclosure, the UAV comprises a power source electrically interfaced with the plurality of second propellers and also with at least one pair of yaw propellers. The power source is mounted on the upper fuel tank. [016] In an embodiment of the disclosure, the first propeller generates a thrust equal to 70% - 80% of weight of the UAV, and the plurality of second propellers collectively generates a thrust equal to remaining 20%-30% of the weight of the UAV.

[017] In an embodiment of the disclosure, the UAV comprises a control unit communicatively coupled to the plurality of second propellers. The control unit is configured to selectively regulate at least a pair of second propellers of the plurality of second propellers to control maneuverability of the UAV. The maneuverability control includes control of surge, sway, heave, rolling, pitching and yawing of the UAV.

[018] In an embodiment of the disclosure, the control unit is also configured to regulate speed of each of the plurality of second propellers through the rotary actuators to control altitude, stability and heading of the UAV.

[019] In an embodiment of the disclosure, the control unit is further configured to adjust speed of the-at least one pair of yaw propellers in proportion to internal combustion engine output to compensate the adverse yaw motion generated by the first propeller of the UAV.

[020] In an embodiment of the disclosure, the UAV further comprises a Global Positioning System (GPS) module communicatively coupled with the control unit. The GPS module is configured to communicate with a control station which monitors the UAV. Further at least one telemetry unit is mounted on the frame for real-time interaction with the control station. The UAV further comprises a transducer, optionally a beacon for transmitting beacon signals, and one or more auxiliary modules.

[021] In an embodiment of the disclosure, the UAV comprises one or more sensors communicatively coupled with a control unit, the one or more sensors are configured to detect internal combustion engine output conditions and one or more physical conditions of the UAV.

[022] In an embodiment of the disclosure, the frame of the UAV includes at least one compartment structured to accommodate payload.

[023] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. [024] BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

[025] The novel features and characteristics of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an embodiment when read in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, with reference to the accompanying drawings wherein like reference numerals represent like elements and in which:

[026] FIG. 1 illustrates a perspective view of the Unmanned Aerial Vehicle (UAV) in accordance with embodiments of the present disclosure.

[027] FIG. 2 illustrates a front view of the UAV depicted in FIG. 1.

[028] FIG. 3 is a top view of the UAV of FIG. 1 illustrating operation of the yaw propellers. [029] FIG. 4 illustrates a side view of the UAV depicted in FIG. 1.

[030] FIG. 5 illustrates maneuverability control operations of the UAV using second propellers, in accordance with some embodiments of the present disclosure.

[031] FIG. 6 is a graphical illustration of variation of outputs of the first propeller, the second propellers and the yaw propellers, according to some embodiments of the present disclosure.

[032] FIG. 7 illustrates a block diagram

[033] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the Unmanned Aerial Vehicle illustrated herein may be employed without departing from the principles of the disclosure described herein.

[034] DETAILED DESCRIPTION

[035] While the embodiments in the disclosure are subject to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular form disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.

[036] It is to be noted that a person skilled in the art would be motivated from the present disclosure and modify various features of an assembly, a system, a device, or a method, without departing from the scope of the disclosure. Therefore, such modifications are considered to be part of the disclosure. Accordingly, the drawings show only those specific details that are pertinent to understand the embodiments of the present disclosure, so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skilled in the art having benefit of the description herein. Also, the Unmanned Aerial Vehicle of the present disclosure may be employed in several applications such as defense, medical and healthcare, research, surveying, agriculture, weather studies, package delivery and the like. However, all the sub-systems of the unmanned aerial vehicle are not illustrated in the drawings of the disclosure for the purpose of simplicity.

[037] The terms “comprises... a”, “comprising”, or any other variations thereof used in the disclosure, are intended to cover anon-exclusive inclusion, such that an assembly, a system, a device, or a method comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such an assembly, a system, a device, or a method. In other words, one or more elements in the assembly, the system, the device, or the method proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the assembly, the system, the device, or the method.

[038] Embodiments of the present disclosure disclose an Unmanned Aerial Vehicle (UAV) of hybrid type. Throughout the description and claims, the abbreviation UAV is used for simplicity. Nonetheless, the UAV is alternately referred to as “unmanned aircraft”, “drone” and so on throughout the description, all of which pertain to the same UAV which are discussed in the embodiments of the present disclosure. The UAV of the present disclosure is configured to optimize operational endurance, altitude of flight and maneuverability while providing structural robustness and reduced weight, all provided through features described in detail in the forthcoming paragraphs. [039] One of the problems faced by UAVs known in the art is compromise with endurance and/or altitude of flight owing to number of reasons like limited battery capacities, constraints due to overall weight of the UAV and so on. Fuel based engine-powered propellers have high energy to weight ratio which provides sufficient output to the propellers to sustain high altitude, long endurance flights. However, they suffer from several practical constrictions such as difficulty in control, requirement of complex mechanical and/or electrical systems for operation, auxiliary drives including but not limited to gear drives for amplification/truncation of torque and speed, and so on. Electrically driven propellers, despite their incredible controllability, face shortcomings with respect to prolonged endurance due to low energy output and limitations associated with power source capacities. Also, to produce larger thrusts, heavy duty motors will be mandatory, adding to overall weight of the UAV, which is already occupied with numerous modules for communication, processing, sensing and so on.

[040] The UAV disclosed in the embodiments of the present disclosure serves to alleviate shortcomings charted above. The UAV of the present disclosure, as stated earlier, is of a hybrid configuration having both engine and electric actuators as drive devices. The UAV includes a frame acting as main supporting structure for rest of the components and sub-systems. The frame supports an internal combustion engine connected to it, for example, to its lower side. The internal combustion engine receives fuel from a fuel tank mounted above the engine. Combustion of charge viz. air-fuel mixture inside the internal combustion engine results in mechanical output which is used to drive a first propeller associated with the UAV. The engine driven first propeller is configured to provide a substantial portion of thrust to lift or raise the UAV, as well as to continuously generate lift necessary to keep the UAV at required heights during flight. In an embodiment, the thrust generated by the first propeller is about 70% -80% of overall weight of the UAV. This means that about 70-80% of total thrust required to lift, hover and head the UAV relative to weight of the UAV is provided by the internal combustion engine.

[041] The UAV further includes a plurality of arms essentially in the form of cantilever bars or beams coupled to the frame. The frame may have an upper disc and lower disc between which the plurality of arms may be movably connected, as shown in figures. In an embodiment, the arms may be removably secured to the frame through fasteners, hinges, etc., to facilitate movement of the arms relative to the frame. The arms are referred to as cantilever because one end of each of the arms may be coupled to the frame, while the other end opposite to said one end may carry loads, such as rotary actuators coupled with second propellers. The second propellers connected to the free ends of the arms are also configured to generate thrust to lift and move the UAV. The thrust generated by the second propellers is about 20-30% of the overall weight of the UAV. To attain this, each of the second propellers is coupled to a rotary actuator, including but not limited to an electric motors, such as AC and DC motors, stepper motors, variable speed servo drives, and so on. A rotary actuator may be accommodated in the free end of each arm of the plurality of arms such that each second propeller projects outwards perpendicularly to the plane of the arms to generate aerodynamic lift. Combined thrust generated by the second propellers coupled to rotary actuators and the first propeller coupled to the internal combustion engine is used to lift, hover and head the UAV. With this configuration viz. combined thrust of first and second propellers, advantages associated with both engine based propellers and rotary actuator driven propellers may be realized. Precisely, engine based propellers result in higher endurance, enhanced altitude and range, swift take-off capabilities and so on, while rotary actuator (Electric motor) based propellers result in enhanced maneuverability, speed regulation, landing capabilities, and so on. In an embodiment, maneuverability includes movements along 6 basic degrees of freedom i.e., surge, sway, heave (3 transverse degrees of freedom) along with roll, pitch and yaw (3 angular degrees of freedom). In an embodiment, the rotary actuators are powered by a power source, including but not limited to a battery, fuel cell etc. The power source may be mounted on the fuel tank and optionally may be secured to the frame.

[042] The UAV is further equipped with at least one pair of yaw propellers removably coupled to the frame. The at least one pair of yaw propellers are provided to control/balance out adverse yaw motion generated by the first propeller driven by the engine [also known as yaw compensation]. The yaw propellers may be mounted on the upper disc of the frame, and are intended to produce couple (equal and opposite moments of forces which are parallel to each other) which may counteract (balance) the adverse yaw motion arising due to first propeller. In an embodiment, the yaw propellers are driven by rotary actuators powered by the power source. In another embodiment, the output of yaw propellers may be regulated proportionally to the output of the engine so as to counteract adverse yaw motion of the UAV generated by the first propeller. A control unit is associated with the UAV to regulate output of the yaw propellers and the plurality of second propellers for yaw compensation and maneuverability. The control unit regulates speed of each of the plurality of second propellers which may assist in take-off, landing, hovering, maintaining desired altitude, stability and heading/advancing of the UAV.

[043] The UAV of the present disclosure also includes communication modules like Global Positioning System (GPS) for tracking and communication with a control station monitoring the UAV. The GPS module may be interfaced with the control unit associated with the UAV. At least one telemetry unit may be secured to the frame of the UAV for the purpose of real time interaction and transmission/reception of data with the control station. Apart from these, the UAV may include generic communication units such as a transducer, a beacon for generating visual indications (like beacon signals), and auxiliary modules a generic unmanned aerial vehicle may include for telecommunication and operation purposes. The frame of the UAV may also include a compartment for accommodating payloads, for example, artilleries, medical equipment, surveillance equipment, research apparatus and so on. One or more sensors may also be integrated with electronics of the UAV for the purpose of detection of certain physical conditions associated with the UAV, such as engine output conditions, wind direction, wind speed, battery status, fuel status and the like. In an embodiment, the power source may be a Lithium-Ion (Li-ion) battery which powers the plurality of second propellers and yaw propellers. Li-Ion batteries serve as better replacements for conventional Lithium-Polymer batteries owing to their extended energy capacities which improves the flight endurance of the UAVs. However, battery types other than Li-ion batteries may also be integrated. Furthermore, as compared to fully electric UAV counterparts, the Li-Ion battery employed in the UAV of the present disclosure has to supply only 20-30% of energy required by the second propellers, which results in substantial extension of Li-ion battery life.

[044] The following paragraphs describe the present disclosure with reference to FIGS 1 to 6. In the figures, the same element or elements which have similar functions are indicated by the same reference signs. With general reference to the drawings, an unmanned aerial vehicle (UAV) is designated with the reference numeral (100). The exterior of the UAV (100) may be shown operatively without explicit illustration or explanation on innate components, for example, inside of the engine, inside of the actuators, communication modules, etc.

[045] The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. It is to be understood that the disclosure may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices or components illustrated in the drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions or other physical characteristics relating to the embodiments that may be disclosed are not to be considered as limiting, unless the claims expressly state otherwise. Hereinafter, preferred embodiments of the present disclosure will be descried referring to the accompanying drawings. While some specific terms of “upper,” “lower,” “below”, “above”, “right,” or “left”, “on”, “under”, “front”, “behind” and other terms containing these specific terms and directed to a specific direction will be used, the purpose of usage of these terms or words is merely to facilitate understanding of the present invention referring to the drawings. Accordingly, it should be noted that the meanings of these terms or words should not improperly limit the technical scope of the present invention.

[046] For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the disclosure illustrated therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

[047] FIG. 1 is an embodiment of the present disclosure which illustrates perspective view of the UAV (100). The UAV (100) includes a frame (1) which serves as basic supporting structure to all the components and sub-systems of the UAV (100). The frame (1) may be fabricated to include several sub-assemblies joined through conventional and non-conventional manufacturing processes. The frame (1) may include a downwardly oriented dome (lc) to resemble a cage like structure as shown clearly in FIGS. 1, 2 and 4. The dome (lc) may manifest as an enclosure to some constituents of the UAV (100). Further, the dome (lc) may serve the purpose of safeguarding the components enclosed within it through the structural properties. In an embodiment, the dome (lc) may include openings or recesses to facilitate circulation of air for purposes including but not limited to cooling of mechanical and electrical systems, as well as to ensure air circulation for thrust generation by a first propeller (2), which will be explained later. The dome (lc) may terminate at a lower disc (lb) as shown in FIG. 1. The lower disc (lb) may accommodate a body conforming upper disc (la) above it connected through arms (4). A plurality of legs (12) as shown clearly in FIGS. 2 and 4 may secured to underside of the dome (la) to assist in landing and halt of the UAV (100) on ground. The frame (1) of the UAV (100) may also include a compartment for accommodating payloads, for example, artilleries, medical equipment, surveillance equipment, research apparatus and so on.

[048] The frame (1) may further include a cross-member (Id) [depicted clearly in FIG. 3] secured rigidly to the upper disc (la). In an embodiment, the cross-member (Id) may resemble “plus” shape whose free ends are secured to the circumference of the upper disc (la). The cross-member (Id) accommodates and secures certain modules over it. An internal combustion engine (3) [referred to as “engine” throughout the description for sake of simplicity], like a typical gasoline, diesel or gas engine may be secured to the cross-member (Id). In an embodiment, the engine (3) is secured to underside of the cross-member (Id) so that the output shaft [not shown] of the engine (3) is oriented downwards to have vertical axis of rotation. A first propeller (2) is coupled to the engine output shaft [not shown] rotating about the vertical axis. Intricate details of engine, engine shaft, and the manner in which a propeller is coupled to a shaft is well-known, and is not explained in detail in this disclosure. A fuel tank (8) is mounted on top of the cross-member (Id) to supply fuel to the engine (3) for combustion. Fuel lines and air supply lines are inherently present along with a facility to initiate combustion of the air-fuel mixture (charge) inside the engine, depending on nature of the engine (3). Combustion of charge results in rotation of the shaft, and in turn, the first propeller (2). Rotation of the first propeller (2) in accordance with engine (3) speed generates thrust to lift the UAV (100) from ground for take-off. As engine (3) operation continues, the first propeller (2) continues to generate thrust to keep the UAV in continuously levitated state at a desired altitude, for example, 250 m, 500 m and so on. In an embodiment, the output power of the engine (3) contributes to 70%-80% of total thrust required to lift the UAV relative to weight of the UAV (100), at full engine capacity. In another embodiment, engine (3) produces constant output power so that the first propeller (2) generates constant thrust ranging from about 70% to about 80% of the total weight of the UAV (100). Thus, engine (3) carrying the first propeller (2) creates substantial portion of the lift required to take-off, levitate and hover the UAV (100) at desired altitude.

[049] The frame (1) of the UAV (100) further includes a plurality of arms (4) in the form of cantilever bars or beams. Each of the plurality of arms (4) may have an end (4a) movably attached between the upper disc (la) and the lower disc (lb) [shown clearly in FIG. 2] In an embodiment, each arm (4) may be hinged or pinned at a point of the upper disc (la) and lower disc (lb) of the frame (1) to facilitate movement of the arms (4) relative to the frame (1). The arms (4) are referred to as cantilever arms because the end (4a) of each of the arms (4) may be coupled to the frame (1), while the other end (4b) opposite to said one end (4a) may carry loads, such as rotary actuators (5) carrying a plurality of second propellers (6). The second propellers (6) connected to the free ends (4b) of the arms (4) are also configured to generate thrust to levitate the UAV (100). The free end (4b) of each arm (4) may have provisions to secure the rotary actuators (5).

[050] FIG. 2 illustrates a front view of the UAV (100). Reference is made to FIG. 1 in conjunction with FIG. 2 to illustrate operational mode of the UAV (100) using the second propellers (6). The second propellers (6), each connected to its respective rotary actuator (5) as shown in FIG. 2, extends vertically downwards from the free end (4b) of the arm (4). This results in all the second propellers (6) have vertical axes of rotation which are parallel to vertical axis of rotation of the first propeller (2). The angular orientation of the second propellers (6) relative to the first propeller (2) results in optimization of lift of the UAV, preferably with even numbered second propellers (6), for instance, four number of second propellers, as illustrated. Each of the rotary actuators (5) may be an electric motor which drives each of the second propellers (6). In an embodiment, the combined thrust generated by all the second propellers is about 20% to 30% of the overall weight of the UAV. In other words, the second propellers (6) are configured to make up the remaining 20% to 30% of total thrust required by the UAV (100), with the initial 70%-80% of thrust being generated by the first propeller (2) via the engine (3).

[051] Combined thrust generated by the second propellers (6) and the first propeller (2) is used to lift, hover and head the UAV (1) at desired altitude. With this configuration viz. combined thrust of first and second propellers, advantages associated with both engine powered propellers and rotary actuator driven propellers may be realized. Engine based propellers offer higher endurance i.e., supports prolonged duration of flights without signs of performance drop. At the same time, engine based propellers provide other benefits such as enhanced altitude and range owing to high energy output, swift take-off capabilities due to instant full capacity operation, and so on. The engine (3) driven first propeller (2) provides all these benefits to the UAV (100) of the present disclosure. Further, the plurality of second propellers (6) driven by rotary actuators (Electric motor) result in enhanced maneuverability of the UAV (100), speed regulation for control/hovering, landing initiation, and so on. In an embodiment, maneuverability of the UAV (100) includes movements along/about 6 basic degrees of freedom i.e., surge, sway, heave (3 transverse degrees of freedom) along with roll, pitch and yaw (3 angular degrees of freedom). Surge and Sway movements are essentially translational movements along a plane parallel to plane of the ground at a fixed height, while heave is vertical upward and downward (ascent and descent) movement away and towards the ground, respectively. The manner in which second propellers (6) facilitate rolling, pitching and yaw motions i.e., 3 angular degrees of freedom of the UAV will be described in forthcoming paragraphs. In an embodiment, the second propellers (6) are operated at different operating conditions to effectuate surge, sway and heave movements of the UAV (100), which is not explained in detail in the present disclosure.

[052] The rotary actuators (5) may be powered by a power source (9) mounted on the fuel tank (8), including but not limited to a battery, fuel cell etc. In an embodiment, the power source (9) may be a Lithium-Ion (Li-ion) battery which powers the plurality of second propellers (6) through rotary actuators (5). Li-Ion batteries serve as better replacements for conventional Lithium-Polymer batteries or other batteries, owing to their extended energy capacities which improves flight endurance of the UAV (100). Furthermore, as compared to fully electric UAV counterparts, the Li-Ion battery employed in the UAV (100) of the present disclosure has to supply a thrust equal to only 20-30% of the UAV weight, which results in substantial extension of endurance with Li-Ion battery. The power source (9) may be optionally be secured to the frame. In an embodiment of the present disclosure, number of second propellers (6) are four, each second propeller (6) having equal angular orientations relative to the centrally located first propeller (2). For instance, for four number of second propellers (6), equidistant angular spacing between adjacent second propellers (6) would be 90 degrees. In an embodiment, a control unit (15) associated with the UAV (100) and communicatively coupled to the plurality of second propellers (6) via rotary actuators (5) may regulate the output of the second propellers (6) to control maneuverability of the UAV (100). To realize this, the control unit (15) may selectively operate a pair of second propellers out of the plurality of second propellers (6) at a time. For example, for a four numbered second propeller configuration, the control unit (15) may increase speed of a pair of second propellers to the right compared to the pair on the left to balance rolling, and so on. [053] Now, reference is made to FIG. 3 which illustrates top view of the UAV (100). As depicted in FIGS. 1 and 3, the cross-member (Id) may accommodate at least one pair of yaw compensators (7) on diametrically opposite ends [FIG. 1] relative to centrally located first propeller-engine combination. Yaw compensators (7) are strategically placed and fixed above the cross-members (Id) so as to counteract adverse yaw motion generated by the first propeller (2) driven by the engine (3). Yaw compensators (7) include yaw propellers (7a and 7b) having horizontal axes of rotation. As shown in FIG. 3, when the engine (3) drives the first propeller (2) in a given direction ‘FPD’ to generate thrust, say for instance counter-clockwise (CCW), the UAV (100) tends to experience an adverse yaw effect opposite to the direction of the first propeller (2). The adverse yaw direction of the UAV (100) is denoted by AYD, which is clockwise (CW) for the above instance. To counteract the clockwise acting adverse yaw motion (AYD), the yaw compensators (7) may be activated. The yaw compensators (7) include yaw propellers (7a and 7b) which are facing in the opposite directions and having horizontal axes of rotation, as clearly shown in FIG. 2. For example, in FIG. 2, the yaw propeller (7a) to the left is facing the reader, while yaw propeller (7b) to the right is facing away from the reader. Thus, when yaw compensators (7) are activated, the yaw propellers (7a and 7b) generate equal but opposite thrusts in the directions of arrows indicated by YCT. Equal and opposite thrusts YCT constitute a couple (torque), whose net effect rotates the UAV (100) counter-clockwise (CCW) to counteract the clockwise (CW) acting adverse yaw motion AYD. In an embodiment, the yaw propellers (7a and 7b) are powered by the power source (9), including but not limited to on-board battery (Li-ion), on-board fuel cell, on-board alternator which may be powered by the engine (3) and so on. In another embodiment, a control unit (15) associated with the UAV (100) changes the thrust direction of the yaw propellers (7a and 7b) based on direction of rotation of the engine (3) carrying the first propeller (2), so that adverse yaw motion is counteracted every time. In another embodiment, power output of the Li-ion battery which is usually maintained between 20-30% of the total power requirement by the UAV (100) may minimize interference with electronic components associated with the UAV (100). For example, electromagnetic interference associated with compasses, GPS, controllers may function without interference due to minimal output characteristics of the Li-ion battery.

[054] Table 1 below illustrates an exemplary data of dynamic compensation of adverse yaw by yaw propellers, which is investigated experimentally based on engine output:

Table 1: Dynamic compensation of adverse yaw motion

In the above table, it can be inferred that if extent of adverse yaw generated by first propeller (2) is 50%, then the dynamic compensation achieved by providing yaw propellers (7a and 7b) is 40%, and so on. In an embodiment of the present disclosure, the output of yaw propellers (7a and 7b) may be regulated proportionally to the output of the engine (3) so as to counteract adverse yaw motion of the UAV (100) generated by the first propeller (2). The control unit (15) takes care of regulation of output of the yaw propellers (7a and 7b) in proportion to the engine (3) output.

[055] FIG. 4 shows a side view of the UAV (100) which illustrates communication modules and other electronic/electrical modules associated with the UAV (100). The control unit (15) associated with the UAV (100) may include discrete controllers like a flight controller (10a) and a speed controller (10b), both mounted on the power source (9). The speed controller (10b) may regulate speed of the second propellers (6) to maintain altitude, stability and heading direction. In an alternate embodiment, a single control unit (15) associated with the UAV (100) may regulate the second propellers (6) for maintaining altitude, stability and heading direction of the UAV (100), instead of discrete controllers. A flight controller (10a) which is essentially a module with intelligent electronics and software monitors and controls every activity of the UAV (100). The flight controller (10a) may receive input commands from various interfaces and may coordinate various internal functions within the UAV (100) using sequence of instructions/programs. The communication modules include a Global Positioning System (GPS) (11) for the purposes of tracking and establishing communication with a control station which monitors the UAV (100). The GPS module (11) may be interfaced with the control unit (15) associated with the UAV. The GPS module (11) may be configured such that the UAV (100) may be remotely navigated and located/traced in a real-time manner on coordinate basis from all over the globe. Waypoint GPS navigation allows the UAV (100) to fly on its own towards the destination with the coordinates preplanned and configured into the UAV’ s remote control navigation software. This autonomously updates the UAV (100) of the path the UAV (100) is supposed to traverse, the altitude of flight, speed of flight as well as hover at each waypoint. In an embodiment, the GPS module (11) facilitates Waypoint navigation of the UAV (100).

[056] Further, at least one telemetry unit (16) may be coupled to the frame (1) of the UAV (100) for the purpose of real-time interaction and transmission/reception of data with the control station. Telemetry unit (16) may push the information such as health, position and related conditions/status pertaining to UAV (100). For example, the telemetry unit (16) may enable applications to have a live icon of the navigating UAV (100) displayed on a map. Apart from these, the UAV may include generic communication units such as a transducer (13a, 13b), essentially a transmitter-receiver pair having an antenna (13c) for transmission and reception of data, whose operation is not explained in detail. Optionally, a beacon [not shown] may be configured for generating visual indications (like beacon signals) which may go on and off in a timed manner. This may be provided as a safety feature as per air-traffic regulations to warn other air-vehicles. Several auxiliary modules may be configured within and on the UAV (100) for other purposes. One or more sensors [not shown] may also be integrated with electronics of the UAV (100) for the purpose of detection of certain physical conditions associated with the UAV (100), such as engine output conditions, wind direction, wind speed, battery status, fuel status and the like. The one or more sensors provide inputs regarding engine (3) output for example, engine speed, torque, power, throttle, etc., to the control unit (15), such that the control unit (15) adjusts the speed of the yaw propellers (7a, 7b) in proportion to the engine output detected by the sensors. The control unit (15) and its associated components/elements are shown as a block diagram in FIG. 7.

[057] FIG. 5 illustrates maneuver control of the UAV (100) of the present disclosure. The maneuver control is attained by different combinations of rotation of at least a pair of second propellers of the plurality of second propellers (6). We see that in all four cases, i.e., throttle, roll control, pitch control and yaw control, there are two counter rotating second propeller pairs. For example, in all four cases, diagonally opposite pairs rotating in same direction is seen. The counter-rotating pairs cancel out adverse yaw motion of the UAV (100) arising from the second propellers (6). To control throttle i.e., levitation of the UAV (100), all the four second propellers (6) may be rotated at equal but low speeds or at equal high speeds so that all the four second propellers 1, 2, 3 and 4 equally assist in lifting or lowering of the UAV (100) depending on whether the speed is low or high. Equal thrust of all the four second propellers for throttle control is indicated by equal sized arrows. Similarly, for roll control, the leftmost second propeller pairs i.e., 1 and 4 rotate with same speed, i.e., W1 = W4 = Wί, and rightmost second propeller pairs rotate at same speed, i.e., W2 = W3 = QR, with GR WI. For pitch control, frontmost second propeller pairs rotate at same speed W1 = W2 = GF, and rearmost second propellers rotate at the same speed W4 = W3 = WB, such that GF ¹ WB. Yaw control is achieved by rotating diagonally opposite pairs at same speeds, as apparent from FIG. 5. Variations of output of first propellers (3), yaw propellers (7a, 7b) and second propellers (6) are represented on a graph shown in FIG. 6. [058] Table 2 below shows load sharing between first propeller and second propellers relative to engine output and output of the power source, determined experimentally for a UAV (100) of 2.56 kg as an exemplary configuration. Table 2: Load sharing between first propeller and second propellers

[059] From table 2 it can be inferred that with the increase in throttle of the engine (3), the thrust produced by first propeller (2) increases which results in reduction of collective thrust produced by the second propellers (6). Minimization of thrust by second propellers (6) indicates lesser consumption of electric current. For example, transition from row 4 to row 5 of table data shows when engine throttle increases from 60% to 70% resulting in change of thrust of first propeller from 1.536 kg to 1.792 kg, the thrust contribution from second propellers (6) drops from 1.024 kg to 0.768 kg. A drop in current drawn by second propellers (6) from power source (9) may also be seen i.e., 8.1 A to 7.8A. [060] Further, Figure 7 discloses a block diagram of a system controlling UAV. The system includes a control unit communicatively coupled with one or more sensors, second propellers, yaw propellers, GPS, telemetry, transducers, auxiliary modules. In an embodiment, the system includes one or more data storage devices or memory operatively coupled to the control unit and is configured to store instructions for operating the UAV.

[061] Advantages:

[062] The UAV disclosed in the present disclosure provides number of advantages. One of the advantages is with the combined thrust of first propeller (engine driven) and second propellers (rotary actuator driven), advantages associated with both engine powered propellers and rotary actuator driven propellers may be realized. This ensures better maneuverability, control and stability without affecting endurance and altitude of flight. Another advantage is with the diametrically opposite positioned yaw propellers, adverse yaw arising due to engine based first propeller may be effectively compensated. A yet another advantage is yaw propellers are regulated depending on engine output, so that even minute extents of adverse yawing of the UAV can be detected and compensated by yaw propellers. Another advantage is improved payload to weight ratio due to small size in electrical actuators used compared to conventional fully-electric UAVs. Still another advantage is the ability of using higher energy - to-weight batteries such as Li-Ion batteries instead of commonly used Li-Polymer batteries due to small current consumption.

[063] Equivalents:

[064] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[065] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system) having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

[066] List of Reference Numerals: