Abstract:
A Vertical Take-off and Landing (VTOL) aerial vehicle ( 1, 46 ), e.g. a rotorcraft with long range and high cruising speed capability. The aerial vehicle ( 1, 46 ) has a torus-type fuselage ( 2 ) with radial inside a duct ( 5 ) and at least one main rotor ( 13, 26 ). A pair of lateral wings ( 40 ) are attached opposed to each other outside the fuselage ( 2 ) and at least one engine ( 18 ) drives said at least one main rotor ( 13, 26 ) and at least two propulsion means ( 24 ) fitted to each of said wings ( 40 ). The invention relates as well to a method of operating such a VTOL aerial vehicle ( 1, 46 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to European patent application No. 12 400050.6 filed Nov. 30, 2012, the disclosure of which is incorporated in its entirety by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    (1) Field of the Invention 
         [0003]    The invention relates to a Vertical Take-off and Landing (VTOL) aerial vehicle, e.g., a rotorcraft with long range and high cruising speed capability according to the preamble of claim  1  and to a method of operating such a VTOL aerial vehicle according to the preamble of claim  20 . 
         [0004]    (2) Description of Related Art 
         [0005]    There have been numerous attempts to combine the efficiency and performance of fixed-wing aircrafts in forward flight and the advantageous hover and vertical take-off capabilities of helicopters. 
         [0006]    The compound helicopters and the convertiplanes are basically the most relevant concepts aiming to overcome the horizontal flight deficiencies of pure helicopters by introducing attributes of fixed-wing aircrafts. However, all concepts represent a compromise between both aircraft types which has always to be conveniently adapted to the planned mission profile of the aircraft. 
         [0007]    Compound helicopters are characterized by a lift compounding and a thrust compounding or by a combination of both. Compound helicopters basically aim to off-load the main rotor from its simultaneous lifting and propulsive duties to allow for higher forward speeds. 
         [0008]    A lift compounding entails adding wings to a pure helicopter hence enabling to increase the load factor of the aircraft and to reach a higher maneuverability. This improves the efficiency of the aircraft at moderately high speed but at the expense of reduced efficiencies at lower forward speeds and in the hover. 
         [0009]    A thrust compounding implies the addition of auxiliary propulsion devices. This has been typically accomplished either by means of a single or a pair of propellers being driven by drive shafts powered by main turbo-shaft engines or by the use of additional engines. 
         [0010]    A more extended configuration of a compound helicopter includes both the addition of wings and propulsion units. The lift during cruise is simultaneously provided by the main rotor—in powered condition—usually addressed as “hybrid helicopter”—or in autorotation (“autogyro”) modus—and wings. The compound helicopter hence overcomes the main rotor lift limits by means of the wings and the rotor thrust limits by means of the propulsion units. As a result, the benefit of a higher load factor is obtained along with potential for higher speed of the compound helicopter. The use of a pair of thrust propulsion units enables for a simultaneous torque correction. 
         [0011]    The document US 2009/0321554 A1 discloses a hybrid helicopter including firstly an airframe provided with a fuselage and a lift-producing surface, together with stabilizer surfaces, and secondly with a drive system constituted by: a mechanical interconnection system between firstly a rotor of radius (R) with collective pitch and cyclic pitch control of the blades of the rotor, and secondly two propellers with collective pitch control of the blades of the propellers; and at least one turbine engine driving the mechanical interconnection system. The outlet speeds of rotation of the at least one turbine engine, of the two propellers, of the rotor and of the mechanical interconnection system are mutually proportional, the proportionality ratio being constant. The disclosure of US 2009/0321554 A1 is integrated into the present application. 
         [0012]    A drawback of helicopter configurations is both the downwash generated by the main rotor which is hitting the fuselage and the interference of the flow produced by the rotor with the wings and/or the propellers used in the forward flight mode. The result of this condition is a loss of efficiency and an increased noise and vibration signature of the helicopter, both features which are detrimental to operate the helicopter for commercial purposes economically and efficiently. 
         [0013]    In addition, the tail boom of helicopter configurations can give rise to vibration known to the person skilled in the art as “tail shake”. It should be observed that this “tail shake” phenomenon applies to rotorcraft only. In practice, the main rotor behaves like an aerodynamic exciter. Thus, its wake is turbulent. Turbulence corresponds to variations in pressure, speed, and angle of incidence of the slipstream, which variations are distributed over a rather wide range of relatively high frequencies. 
         [0014]    The document U.S. Pat. No. 5,152,478 A discloses an unmanned flight vehicle wherein two counter-rotating rotors are positioned within a toroidal shaped fuselage and in which rotor pitch solely is utilized to generate all required lift, pitch, roll, yaw and vibration and stress control for the vehicle. 
         [0015]    The document U.S. Pat. No. 6,270,038 B1 discloses an unmanned aerial vehicle that includes a fuselage with a partial toroidal forward portion and an aft portion. A duct is formed through the fuselage and extends from the top to the bottom of the fuselage. Two counter-rotating rotor assemblies are mounted within the duct for providing downward thrust through the duct. The rotor assemblies are supported by a plurality of support struts. At least one engine is mounted within the fuselage and engages with the rotor assemblies. A pusher prop assembly is mounted to the aft portion of the fuselage. The pusher prop assembly is designed to provide forward thrust along the longitudinal axis of the aerial vehicle. The pusher prop assembly includes a drive shaft that is engaged with the engine. 
         [0016]    A plurality of propellers are attached to and rotated by the drive shaft. A shroud is mounted to the aft portion of the fuselage around the propellers and is operative for channeling the air passing through the propellers in a substantially aft direction. A pair of wings is removably attached to the sides of the fuselage. Each wing preferably includes a fixed portion and a pivotal flaperon portion hinged to the fixed portion. Directional vanes are preferably mounted to the shroud downstream from the propellers and control flow out of the shroud. Deflectors may be mounted to the bottom of the fuselage across a portion of the duct to control flow of air into the duct. 
       BRIEF SUMMARY OF THE INVENTION 
       [0017]    The objective of the invention is to propose a VTOL aerial vehicle with long range and high cruising speed features, for passengers and cargo transportation, effectively and efficiently military and commercially. It is a further objective of the invention to propose a VTOL aerial vehicle having a low vibration and noise signature compared to any helicopter configuration and thus a vertical take-off and landing aerial vehicle securing a standard degree of comfort and safety. It is a further objective of the invention to propose a method of operating such a VTOL aerial vehicle. 
         [0018]    A solution is provided with a VTOL aerial vehicle, e.g. a rotorcraft with long range and high cruising speed capability with the features of claim  1 . A further solution is provided with a method of operating such a VTOL aerial vehicle with the features of claim  20 . 
         [0019]    According to the invention a vertical take-off and landing aerial vehicle comprises a torus-type fuselage with a front portion, and a rear portion, used as cabin to transport passengers and cargo. The fuselage is provided as an aerodynamically optimized shroud. Radial inside said torus-type fuselage a duct is formed through the fuselage and extends from a top to a bottom side of the fuselage. The front portion of the fuselage contains a cockpit and preferably a galley compartment. The cockpit layout has been configured to provide the pilots with an excellent work environment. The design of the windshields and windows result in a large, unobstructed field-of-view. The instrument panel and consoles are evolutions from state-of-the art technologies, providing clear displays and controls to the crew. Standard entry into the cockpit is through a passageway from the cabin. The rear portion of the fuselage houses an additional galley compartment, while lavatory compartments are located on each side of the fuselage. 
         [0020]    A main rotor is located adjacent the duct through the circular torus-type shroud type fuselage with an axis of rotation in common with a central axis rectangular to a mid-plane through said fuselage. The main rotor is mounted to its hub above or within the duct such that for a stalled main rotor the blade tips are within the profile defined by the fuselage. Pitch control of the rotor blades provide all flight control requirements of the inventive aerial vehicle including lift, pitch, roll and yaw control, by varying flow pattern through the duct. The main rotor is driven by at least one turbo engine, preferable a pair of turbo engines, housed in a power plant assembly unit. 
         [0021]    A mechanical interconnection system is provided between the main rotor and the at least one turbo engine within the power plant assembly unit in the center of the torus-type fuselage. The power plant assembly unit is supported by a plurality of support struts respectively fixed to the fuselage at one end and to the power plant assembly unit at the other end. The mechanical interconnection system connects the main rotor to the at least one turbo engine. 
         [0022]    The toroidal fuselage is closed radially around its duct. The supporting struts are hollow to house fuel tanks, cargo and/or passenger and/or aviation and navigation equipment including the required mechanical and service lines mandatory to enable the inventive aerial vehicle to safe flight and control operation. The torus-type fuselage and the supporting struts are fabricated of composite material or metal to have a strong and light weighted structure. 
         [0023]    At least two wings are attached symmetrical with regard to a longitudinal axis through the central axis and the mid of the cockpit. Said at least two wings are attached to a periphery of the torus-type fuselage to provide additional lift to the inventive aerial vehicle in high-speed flight. Each of said wings at least partly includes a fixed front portion and a pivotal portion. Said pivotal portion of the wing is used as pitch elevator, hinged to the fixed front portion. Essentially vertical stabilizers are located at a tip of each wing, consisting of a fixed front portion and a steering control surface, capable to provide additional means of yaw control. 
         [0024]    Propulsion means (e.g., turboprops or propellers) mounted at each wing generates thrust along the longitudinal axis of the inventive aerial vehicle. Said propulsion means in combination with the wings and torus-type fuselage give the high-speed capability in flight to the inventive aerial vehicle. The mechanical interconnection system connects the at least one turbo engine to the propulsion means for driving said propulsion means. Possible nose up pitching moments induced by the ducted rotor during forward flight of the inventive aerial vehicle are reduced by the wings mounted to the rear portion of the torus-type fuselage according to the present invention by creating a lift component on the rear portion of the inventive aerial vehicle. 
         [0025]    The inventive aerial vehicle includes the advantages of both airplanes and helicopters, featuring vertical take-off and landing with long range and high cruising speed capability on one side and equipped with a passengers and cargo compartment, which allows the inventive aerial vehicle to be operated at the same way effectively and efficiently for military and commercially services on the other side. 
         [0026]    The torus-type fuselage around the main rotor of the inventive aerial vehicle increases rotor efficiency, as the air flow is able to pass undisturbed through the duct without the disadvantageous effects of the downwash stream interfering with the fuselage as it would be the case for a conventional helicopter configuration. 
         [0027]    Moreover, the torus-type fuselage with a ducted shroud, particularly at the inlet and the outlet of the air flow through the duct, provide further system lift capabilities and selective distribution between the main rotor and the fuselage or shroud, i.e. at the front portion of the inlet to increase flow speed through the outlet of the ducted shroud, said ducted shroud having diffuser characteristics. At least a part of the duct is shaped as a diffuser. Said diffuser part of the duct ends at the bottom of the duct with a maximum cross section at least equal to the cross section of the at least one main rotor. Said diffuser has a minimum cross section defined by a ratio of 0.7 to 0.8 to 1 for minimum cross section/maximum cross section. The diffuser characteristics of the duct add to acceleration of the flow speed through the outlet of the ducted shroud for increased thrust and system lift capabilities of the inventive aerial vehicle. 
         [0028]    According to an important feature of the invention the blade cyclic pitch of the at least one main rotor is utilized to affect the pattern and velocity of any air flow entering the inlet of the fuselage duct to thereby selectively control the lift generated by the fuselage to affect the control of pitch, roll or yaw of the inventive aerial vehicle. In conjunction with the forces and moments of the fuselage induced through velocity of air flow into the aerodynamically shaped torus all required flight controls for the aerial vehicle are provided. 
         [0029]    According to a further important feature of the inventive aerial vehicle the plurality of support struts extending between fuselage and power plant unit assembly house pitch control servos, the drive shaft between the power plant assembly unit housed engine and the main rotor(s) and other equipment, such as stability gyroscopes. 
         [0030]    It is an important advantage of the invention that the shroud enclosing the at least one main rotor within the torus-type fuselage prevents the formation of tip vortices and thus improves efficiency of the at least one main rotor. It is a further important advantage of the invention that the shroud enclosing the at least one main rotor within the torus-type fuselage obstructs the free radiation of sound waves and thus reduces the noise emitted by the inventive aerial vehicle. As the at least one main rotor is protected by the shroud in flight mode, the stability of the inventive aerial vehicle is increased; noise and vibration signatures are reduced. On ground or other contact with the environment, the safety is increased by protecting operating personnel near the inventive aerial vehicle from inadvertently being struck when the at least one main rotor is running 
         [0031]    It is still a further important feature of the invention that the control moments produced by the application of cyclic pitch to the main rotor(s) are amplified by control moments generated by the fuselage as a result of said application of cyclic pitch. 
         [0032]    The at least one main rotor with its plurality of blades with collective and cyclic pitch control is rotated by a drive shaft connected mechanically via the mechanical interconnection system to the propellers attached to each wing of the inventive aerial vehicle. Collective pitch control of the blades of the propellers provides for additional thrust in forward flight along the longitudinal axis of the inventive aerial vehicle, giving in combination with the wings and torus-type fuselage to the inventive aerial vehicle the high-speed capability in flight. The pitch control of the at least one main rotor, the aerodynamically shaping of the shrouded fuselage and the additional introduction of wings and stabilizers allow generation of all required lift, pitch, roll, yaw forces and moments of the inventive aerial vehicle. 
         [0033]    The inventive aerial vehicle uses differential thrust between the wing mounted propulsion means, e.g. propellers, to provide counter torque when the at least one main rotor is operated by a power source. 
         [0034]    A smooth and safe vertical landing is provided by means of a hover cushion structure on the bottom surface of the inventive aerial vehicle. Said hover cushion structure is suitable to improve a diffuser characteristic of the shrouded duct defined by the torus-type fuselage. 
         [0035]    The circular shape of the fuselage of the inventive aerial vehicle allows a plurality of entrances, to embark and disembark the aircraft efficiently for greater service speed. The circular shape of the fuselage of the inventive aerial vehicle also provides better conditions of visibility. 
         [0036]    According to a further preferred embodiment of the invention two coaxial, counter rotating main rotors with in between an axial distance of 1 m to 2 m are provided. With two coaxial, counter rotating main rotors the wing mounted propulsion means can be optimized for higher horizontal speed of the inventive aerial vehicle. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0037]    The invention and its advantages appear in greater detail from the following description of embodiments given by way of illustration and with reference to the accompanying figures, in which: 
           [0038]      FIG. 1  shows a top view (a), a front elevation view (b) and a side elevation view (c) of an aerial vehicle in accordance with the invention, 
           [0039]      FIG. 2  shows cross-section views along a line A-A and along a line B-B of the aerial vehicle in accordance with the invention, 
           [0040]      FIG. 3  shows a schematic representation of aerodynamics of the aerial vehicle in accordance with the invention in hover (a) and forward flight (b) configuration mode, 
           [0041]      FIG. 4  shows cross-section views along a line A-A and along a line B-B of an alternative aerial vehicle in accordance with the invention, and 
           [0042]      FIG. 5  shows a top view (a), a front elevation view (b) and a side elevation view (c) of the alternative aerial vehicle in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    According to  FIG. 1   a,    1   b,    1   c  and  2  an aerial vehicle  1  comprises a torus-type or toroidal fuselage  2  with a front portion  3  and a rear portion  4 . A generally horizontal plane of the aerial vehicle  1  is defined by a longitudinal  6  and a transversal axis  7  with a central axis  8  perpendicular to said plane. A duct  5  is formed through the torus-type fuselage  2  and extends essentially coaxial to said central axis  8  from a top  9  to a bottom  10  radial inside of the torus-type fuselage  2 . The torus-type fuselage  2  is aerodynamically formed like a shroud in order to provide an optimum airflow stream through the duct  5  and around the fuselage  2 . 
         [0044]    Inside the torus-type fuselage  2  is a cabin to transport passengers and cargo. The front portion  3  of the fuselage  2  contains the cockpit  31  and galley  32  compartments. Windshields and windows  11  of the cockpit  31  result in a large, unobstructed field-of-view for pilots inside the cockpit  31 . A standard entry (not shown) into the cockpit  31  is through a passageway (not shown) from the cabin. The rear portion  4  of the fuselage  2  houses an additional galley  33  compartment, while lavatory compartments  34 , are located on each side of the fuselage  2 . 
         [0045]    The aerial vehicle  1  is conceived for an operating empty weight of about 38 tons +50/−10%, a maximum take-off weight of about 55 tons +60/−10% for 60 to 130 passengers. The height of the aerial vehicle  1  is about 5 m. Between the front portion  3  and the rear portion  4  of the fuselage  2  is on both sides a passageway  30  with a width of up to 0.6 m to 1 m and with a height allowing a passenger to pass without obstructions. 
         [0046]    The aerial vehicle  1  has a main rotor  13  with five or alternatively up to eight blades  14  mounted to a rotor hub  15  positioned therewith in the central axis  8  of rotation 0.8 m next to the top  9  above the duct  5 . Said duct  5  has an inlet at the shrouded top  9  of the torus shaped fuselage  2 . The main rotor  13  provides lift by creating downward flow of air from the inlet through the duct  5  to an outlet at the shrouded bottom  10  with diffuser characteristics. Each blade  14  of the main rotor  13  is linked to a laminated spherical bearing through a sleeve (not shown). A hinge hub architecture involves the laminated spherical thrust bearings providing the pitch, flapping and drag hinges for the eight blades  14 . These bearings counteract the centrifugal forces of the rotating blades  14 , and transmit the thrust, torque and bending moments from the blades  14  to the rotor hub  15 . Lead lag frequency adapters (not shown) are fitted between the rotor hub  15  and each sleeve. The damper characteristics of the lead lag frequency adapters are set to adapt the blades  14  lead lag frequency and damping to avoid any instability in flight with the fuselage  2  or on the ground with a landing device, such as a hover cushion structure  16  or a three point landing gear. 
         [0047]    The main rotor  13  is independently controlled through a separate conventional swash plate assembly  17  which selectively articulates the main rotor  13 . Motion of the swash plate assembly  17  along the rotor axis  8  will cause the rotor blades  14  of the main rotor  13  to vary pitch collectively and tilting of the swash plate assembly  17  with respect to the rotor axis  8  will cause the rotor blades  14  to vary pitch cyclically. The swash plate assembly  17  is controlled by a separate electronic servo mechanism (not shown) which selectively and independently articulates the swash plate assembly  17  for both, cyclic blade change and collective blade change of the main rotor  13 . 
         [0048]    The rotor hub  15  of the main rotor  13  is driven by a pair of turbo engines  18  by means of a mechanical interconnection system (not shown). The turbo engines  18  are located in a central power plant assembly unit  19 . A conventionally applied drive shaft  20  with appropriate clutch, drive and gearing means transform the power generated by the turbo engines  17 , to drive the main rotor  13  about the central axis  8  of the fuselage  2 . Air enters a housing of the power plant assembly unit  19  through inlets  12 . 
         [0049]    A plurality of supporting struts  22  extend from the radial inner surface at the bottom  10  of the fuselage  2  radial inwardly to support the central power plant assembly unit  19 . The support struts  22  are aerodynamically shaped and rigidly connected to the fuselage  2 . Smooth and safe vertical take-off and landing is provided by means of the hover cushion structure  16  at the bottom  10  of the aerial vehicle  1 . The hover cushion structure  16  is conceived to contribute to the diffuser at the bottom  10  of the aerial vehicle  1 . 
         [0050]    The torus-type fuselage  2  and the supporting struts  22  are hollow and therefore capable to carry fuel tanks, cargo compartments, passenger compartments and aviation and navigation equipment mandatory to enable safe on flight and control operation for the aerial vehicle  1 . The fuselage  2  and the struts  22  are made of composite material and/or metal to have a strong and light weighted structure. Moreover the torus-type fuselage  2  is closed to produce maximum strength. A fuselage inlet protection screen  23  is positioned so as to cover the inner circumference of fuselage  2  to protect the cabin of the aerial vehicle  1  from any fractioned parts of the blades  14  in case of a structural failure. 
         [0051]    At suitable forward speeds the aerial vehicle  1  has additional lift, to the lift provided by the main rotor  13 , with a pair of wings  40  on each outside of the rear portion  4  of the fuselage  2  in a rear half of said fuselage  2 . Said wings  40  provide horizontal stabilizer with a fixed front wing portion  43  and a pitch control surface  45  movable relative to the front wing portion  43 . Vertical stabilizer elements  41  are located at the lateral end of said wings  40  for steering and stability purposes. The vertical stabilizers  41  comprise a fixed front portion of a fin  44  and a movable rear portion or rudder  21  for yaw control. 
         [0052]    The aerial vehicle  1  is propelled by two propulsion means, i.e., turbojets or propellers  24 . The propulsion means  24  are driven by said turbo engines  18  by means of a mechanical interconnection system supplying drive not only to the main rotor  3  in rotation, but also supplying drive to said turbojets  24  in rotation using mechanical transmission. The said turbojets  24  are located at each of the outer lateral ends of the wing  40  in front of said vertical stabilizer elements  41  arranged in a respective fairing  42 . The supporting struts  22 , the fuselage and the wings  40  are conceived to house at least parts of the mechanical transmission of the mechanical interconnection system e.g. for supplying drive to said turbojets  24 . 
         [0053]    The aerial vehicle  1  is fitted with an integrated drive system that comprises said turbine engines  18 , the main rotor  13 , the two turbojets  24  and the mechanical interconnection system between these elements. Said integrated drive system is designed and operated according to the disclosure of US 2009/0321554 A1. To avoid repetition reference is made to the disclosure of US 2009/0321554 A1 for the description of said integrated drive system. 
         [0054]    According to  FIG. 3   a, b  corresponding features are referred to with the references of  FIG. 1   a - 2 . According to  FIG. 3   a  in hover configuration mode the aerodynamics of the aerial vehicle  1  are conditioned by the main rotor  13  in operation under collective pitch only. Lift forces F R  are generated by the main rotor  13  and lift forces F F  are generated also at the duct inlet  25  of the torus shaped fuselage  2 , because as the main rotor  13  rotates, it draws air into and across the inlet  25  of fuselage  2  at a high velocity, thereby inducing suction along the top  9  of the fuselage  2  so as to produce lift by means of the fuselage  2 . Thus, additive lifts F R  and F F  are generated by the main rotor  13  by means of the shrouded fuselage  2 . The inlet  25  of the fuselage  2  and an offset of 0.8 m+/−50% for the main rotor  13  from the top surface  9  of the fuselage  2  are conceived to selectively share the lift contribution, e.g. with an approximate equal sharing. 
         [0055]    In hover configuration mode of the aerial vehicle  1  the propulsion means  24  provide exclusively counter torque to the main rotor  13 . 
         [0056]    According to  FIG. 3   b  in forward flight configuration mode the aerodynamics of the aerial vehicle  1  are conditioned with the main rotor  13  in operation and under cyclic pitch application to the blades  14  of the main rotor  13 . After vertical take-off of the aerial vehicle  1 , both, collective and cyclic pitch are applied to the main rotor  13 . Again the fuselage  2  generates lift forces F F  and the main rotor  13  generates additive lift F R . Supplementary the main rotor  13  generates a pitching moment M R  and the shrouded fuselage  2  generates a pitching moment M F . A substantial amount of the total moment M R  and M F  is produced by the shrouded fuselage  2 , as compared to the moment M R  produced by the main rotor  13 . Changes in main rotor lift F R  produce changes in the fuselage lift F F  and the pitching moments M R  and M F . Therefore main rotor control results in amplification for the forward flight characteristics of the aerial vehicle  1 . 
         [0057]    The free stream velocity in forward flight V 0  is additive to and serves to increase the suction velocity of the main rotor  13  over the forward section of the torus-type fuselage  2 . The free stream velocity in forward flight V 0  serves to decrease correspondingly the inlet velocity over the aft section. The resulting inflow velocity towards the duct  5  at the forward section  3  is therefore substantially larger than the velocity of the air entering the duct  5  of fuselage  2  over the rear section  4 . The air velocities during forward flight result in a pressure or lift distribution differential with a lift F F  substantially larger at the forward section  3  than at the rear section  4  of the fuselage  2 , thus producing a nose-up moment M F  for the aerial vehicle  1  in forward flight. 
         [0058]    In forward flight and with both collective and cyclic pitch applied to the main rotor  3  the lift or moment creating characteristics of fuselage  2  are usually tuned to produce a nose-up moment M F . Cyclic pitch of the main rotor  3  may as well be tuned so as to cause the flow of inlet air into the shrouded duct  25  to have a maximum at the rear section  4  of fuselage  2 , thus creating a counteracting nose-down moment M F  on the fuselage  2  which co-acts with the nose-down moment M R  produced by the main rotor  3 . 
         [0059]    According to  FIG. 4 ,  5  corresponding features are referred to with the references of  FIG. 1   a - 3 . Additional to the main rotor  13  a co-axial rotor  26  is provided for an alternative aerial vehicle  46 . Said co-axial rotor  26  is counter rotating with regard to the main rotor  13 . Said co-axial rotor  26  is mounted to the drive shaft  20  inside the duct  5  with an axial distance of 1 m to 2 m, preferably 1.5 m below the main rotor  13  to avoid collision of the blades  14  of the main rotor  13  with the further blades  27  of the co-axial rotor  26 . 
         [0060]    Method of Operating the VTOL Aerial Vehicle  1 ,  46   
         [0061]    The turbo engines  18  of aerial vehicle  1 ,  46  continuously drive the main rotor(s)  13 ,  26  in rotation by means of the mechanical interconnection system. The speeds of rotation of the outlet from the pair of turbine engines  18 , of the propellers of the pair of propulsion means  24 , of the main rotor(s)  13 ,  26  and of said mechanical interconnection system are mutually proportional, with the proportionality ratio being constant whatever is the flying configuration of the aerial vehicle  1 ,  46 . 
         [0062]    For vertical take-off or landing and for hovering of the aerial vehicle  1 ,  46  lift is provided by means of said main rotor(s)  13 ,  26 . With counter rotating main rotors  13 ,  26  of the aerial vehicle  46  the counter torque can be supplied without any supplemental propulsion means  24 . If only one main rotor  13  is provided differential horizontal thrust for counter torque is provided by means of said two propulsion means  24  arranged laterally outside said fuselage  2  of the aerial vehicle  1  i.e. the differential thrust is created by a difference between the thrusts exerted by the respective turbojets  24 , i.e., in vertical flight, turbojet  24  on the left outside of the fuselage  2  exerts thrust towards the rear of the aerial vehicle  1  while the opposed turbojet  24  on the right outside of the fuselage  2  produces thrust towards the front, assuming that the main rotor  13  rotates anticlockwise seen from above. 
         [0063]    The anti-torque function can as well be performed by a single turbojet  24 , i.e., the right turbojet  24  develops double thrust while the left turbojet  24  does not provide any thrust. The main rotor  13  must then be inclined towards the rear of the aerial vehicle  1  in order to balance the thrust from the right turbojet  24 . 
         [0064]    The main rotor(s)  13 ,  26  serve to provide all of the lift of the aerial vehicle  1 ,  46  during take-off, landing, vertical flight and some of the lift during cruising flight. The lift of the aerial vehicle  1 ,  46  is controlled by adapting the collective pitch of the blades  14 ,  27  of said main rotor(s)  13 ,  26 . 
         [0065]    After take-off lift with a horizontal component can be provided by selectively applying longitudinal cyclic pitch to the respective blades  14 ,  27  of said main rotor(s)  13 ,  26  to thereby produce pitch forces on both the main rotor(s)  13 ,  26  and the fuselage  2  of the aerial vehicle  1 ,  46 . Additional pitch forces can be provided by means of both of the pitch control surfaces  45  movable in the rear portion of the aerial vehicle  1 ,  46 . 
         [0066]    After take-off any roll of the aerial vehicle  1 ,  46  is controlled by selectively applying lateral cyclic pitch to the blades  14 ,  27  of said main rotor(s)  13 ,  26  as a function of flight conditions to thereby produce roll forces on both the main rotor(s)  13 ,  26  and the fuselage  2  of the aerial vehicle  1 . Additional roll forces can be provided by one of the pitch control surfaces  45  movable in the rear portion  4  of the aerial vehicle  1 ,  46 . 
         [0067]    After take-off any yaw control is provided to said aerial vehicle  1 ,  46  by applying differential thrust between said at least two turbojets  18  as a function of flight conditions to thereby produce the required torque differential for yaw control. Yaw forces can be provided as well by both of the movable steering rudders  21  of the vertical stabilizer  41  in the rear portion of the aerial vehicle  1 ,  46 . 
         [0068]    After take-off any nose-up moment created by the torus-type fuselage  2  during forward flight is abated by selectively applying cyclic pitch to said main rotor(s)  13 ,  26  to selectively vary the pattern of air flowing into said duct  5  to thereby produce a counteracting pitching moment on said torus-type fuselage  2  and to thereby reduce the total nose-up pitching moment created by the fuselage  2  in forward flight until the total nose-up pitching moment is substantially equal to the nose-down pitching moment created by the main rotor(s)  13 ,  26 . 
         [0069]    For forward flight the propulsion means  24  exert thrust towards the rear of the aerial vehicle  1 ,  46  for propulsion. The wings  40  contribute to provide part of the lift for supporting said aerial vehicle  1 ,  46 . 
       REFERENCE LIST 
       [0000]    
       
           1  aerial vehicle 
           2  torus shaped fuselage 
           3  front portion 
           4  rear portion 
           5  duct 
           6  longitudinal axis 
           7  transversal axis 
           8  central axis 
           9  top 
           10  bottom 
           11  window 
           12  inlet lip 
           13  main rotor 
           14  blades 
           15  rotor hub 
           16  hover cushion structure 
           17  swash plate assembly 
           18  turbo engines 
           19  power plant assembly unit 
           20  drive shaft 
           21  steering rudder 
           22  support strut 
           23  protection screen 
           24  propulsion means 
           25  duct inlet 
           26  co-axial rotor 
           27  further blade 
           30  Passageway 
           31  cockpit 
           32  galley 
           33  additional galley 
           34  lavatory compartments 
           40  wings 
           41  vertical stabilizers 
           42  fairing 
           43  front wing portion 
           44  fin 
           45  pitch control surface 
           46  alternative aerial vehicle