The present invention belongs to the field of transport aircraft. More particularly, the invention relates to an aircraft having a wing and horizontal empennages rearward and forward of the wing and propelled by motors driving propellers placed in the vertical plane of symmetry of the fuselage. In the field of aircraft, the problem of choosing an aerodynamic architecture and that of the integration of the propulsion means are generally the result of compromise between the operational capabilities desired for the aircraft, its performance and its operating costs. . These aspects are further constrained by security and certification requirements. For transport aircraft, the aerodynamic configuration most commonly used consists of an elongated fuselage in the axis of the aircraft on which is fixed a wing ensuring the main lift and tail empennages, attached to the fuselage at the rear of the aircraft. wing, to meet the needs of longitudinal stability and control, in depth or yaw, of the aircraft. To overcome some disadvantages rear horizontal stabilizers, in particular the creation of a negative lift in some maneuvers, it is known to use for the longitudinal control in depth of the front empennages or empennages duck, located on the fuselage in front of the aircraft. 'wing. According to a known architecture, for example EP 0030053 or patent EP 0680877, an aircraft comprises a rear tail and a front duck empennage so as to combine certain advantages of each of the horizontal tail types in terms of stability and control longitudinal. Such an architecture has actually been implemented on the aircraft Avanti P150, architecture described in patent EP 0084686, the manufacturer Piaggio Aero, in which the propulsion is performed by two turboprop engines fixed on the wing of the aircraft on each side fuselage and driving pushing propellers placed near the trailing edge of the wing. In a manner similar to the other examples cited, propulsion engines, reactors or propeller engines, are, on such aircraft combining rear and front horizontal stabilizers, fixed on the wing in a conventional manner in a symmetrical arrangement with respect to the fuselage of the aircraft. so that interferences between the horizontal empennages and the motors are avoided. When a propulsion integration solution is sought which induces the minimum of side effects, particularly in the event of engine failure, it is also known to look for solutions in which the engines are placed close to the engine. fuselage axis of the aircraft, or at least close to the plane of vertical symmetry of the aircraft. In particular when the propulsion must be provided by propellers, it is known to put a propeller at the front of the fuselage, propeller operating to fire, and a propeller at the rear of the fuselage, propeller operating to push. Such an aircraft architecture, known from D0335 model manufacturer DORNIER and taken over by Skymaster model CESSNA manufacturer, however, remains associated with simple propellers and aerodynamically to a conventional rear horizontal tailplane architecture. To improve the possibilities of the known solutions and to allow an efficient integration of a propfan propulsion to fast transport aircraft, an aircraft comprising an elongated fuselage, a wing attached to the fuselage in a median portion along a length of said fuselage and a stabilizer forming a substantially horizontal aerodynamic surface, tailplane or tail duck tail as is known to implement to achieve stabilization and longitudinal control of the aircraft depth, comprises: a first engine fixed to the fuselage, at the rear end of the fuselage, the first motor comprising a turbine driving in rotation about the same axis two contrarotating propellers arranged to produce a pushing force oriented substantially in a longitudinal direction X of the aircraft and directed towards the front following a direction of flight in flight of the aircraft; a second engine fixed to the fuselage, at the front end of the fuselage, this second engine comprising a turbine driving in rotation about a same axis two counter-rotating propellers arranged to produce a pulling force oriented substantially in the longitudinal direction X and directed forward according to a direction of flight in flight of the aircraft. It is thus possible to integrate propellers with fast propellers to a transport plane, in a mechanically easy way, with a minimum of aerodynamic penalty, in particular by maintaining a disturbed flow along the fuselage due to counter-rotation. the two propellers of each engine, and improving the maneuverability conditions of the aircraft especially in the event of engine failure. In one embodiment, the aircraft includes both a front duck tail, attached to the fuselage in front of the wing and behind the second engine, and a rear tail attached to the fuselage in a portion of the fuselage located behind the fuselage. 'wing. Thus, an improved lift distribution is obtained which makes it possible to avoid creating negative lift on the tail tail, to reduce the necessary area of the wing to provide lift and to limit variations in the airplane's longitudinal attitude. especially during the take-off or landing phases. By fixing the tail empennage, when the aircraft is provided with a drift itself attached to the fuselage in a part of the fuselage, behind the wing and in front of the first engine, it is possible to limit interference between the aerodynamic flow disturbed by the tail empennage and the first engine. In one embodiment, the tail tail is fixed to the fin above the fuselage at a height such that the aerodynamic wake of the tail tail passes when the aircraft is in flight, at least in certain phases of flight, at the above the propellers of the first engine. Because, in this situation, the lack of significant interaction of the propellers of the first engine with the wake of the tail empennage, the noise level of the propellers is substantially decreased, their improved yields and fatigue in terms of blade structure decreased. Advantageously, the first motor is fixed to the fuselage so that the axis of the propellers of this first motor is located above a longitudinal axis of the fuselage. Thus the rear propellers have their distance to the ground when the aircraft is on the ground increased and the aircraft is able to take a longitudinal pitch attitude also increased when the wheels of the main landing gear are on the ground. To prevent the propellers of the first engine from approaching too close to the ground, for example during the take-off or landing phases, the flight control laws of the aircraft include limitations of the longitudinal attitude of the aircraft. aircraft, at least when wheels of a main landing gear touch the ground, so as to maintain a desired positive ground clearance of the propellers of the first engine.
In one embodiment, the first motor is fixed to the fuselage so that the axis of the propellers of the first motor is located above said fuselage, which has the advantage of maximizing the height of the propellers relative to the ground. with an aerodynamic flow always relatively homogeneous at the helices despite the presence of the fuselage upstream of the flow. When a ground attitude of the aircraft may lead to a contact of the rear fuselage with the ground, it is for example fixed to the fuselage in the contact zone a mechanical limitation of the plane of the plane when the plates The wheels of a main landing gear of the aircraft touch the ground, so as to maintain a positive ground clearance of the propellers of the first engine. The mechanical protection obtained is then an additional safety which is added, if necessary, to the flight attitude limitation protection of the flight controls. When equipped with the aircraft, the duck tail comprises a structure passing through the fuselage at or under a structure of a floor of a volume of the fuselage for receiving persons or goods to be transported. It is thus obtained a structure of the duck tail adapted to desired high lift with limited effects on the interior volume of the fuselage. In another embodiment, the duck tail structure passes through the fuselage in a lower part of the fuselage, close to the lower edge of the fuselage casing, so that the underside of the duck tail is substantially tangent to the outer surface of the fuselage. In another embodiment, the duck tail structure passes through the fuselage in an upper part of the fuselage, close to the upper edge of the fuselage shell, so that the upper surface of the duck tail 10 is substantially tangent to an outer surface of the fuselage. These embodiments make it possible, on the one hand, to obtain a different occupation of the interior volumes of the fuselage to meet the needs of arrangements and to disengage the duck tail from the accelerated flow by the propellers of the second engine and to avoid or less limit the aerodynamic penalties associated with this local acceleration of the flow. In one embodiment, the first motor and the second motor are identical to the pitch of the propellers so that the maintenance costs are reduced. The airplane according to the invention is described with reference to the figures which show schematically: FIG. 1: an overall perspective view of a first example of an airplane according to the invention; FIG. 2 is an overall perspective view of a second example of an airplane according to the invention comprising an engine raised at the rear and a duck empennage lowered at the front; Figure 3 is a partial view in perspective of the front part of the fuselage of a third example of aircraft according to the invention having a raised duck tail. For the purposes of the description, reference is made to three main directions of a conventional aircraft marker: a direction X parallel to a longitudinal fuselage axis oriented positively towards the front of the aircraft; a direction Z perpendicular to the direction X and parallel to a plane of vertical symmetry of the aircraft, oriented downwardly; a direction Y perpendicular to a plane XZ determined by the X and Z directions, oriented positively to the right of the aircraft. The terms or expressions "high", "low", "inside", "outside", "right", "left", "upward", "downward", "inward", "towards" "outside" ... will have unless otherwise specified the meaning that would be given to them by a person in the aircraft in a conventional flying position. An aircraft 10 according to the invention, as illustrated in FIG. 1, comprises a fuselage 11, a wing 12 attached to the fuselage in a median part of the fuselage 11, a horizontal rear stabilizer 13 fixed to the fuselage in a part of the fuselage. located at the rear of the wing 12, via a fin 14 in the case of the aircraft shown, a horizontal forward tail or tail duck 15 attached to the fuselage in a part of the fuselage located in front of the wing 12. Known manner rear tail 13 and duck tail 15 are substantially horizontal aerodynamic surfaces which provide longitudinal stability functions in trim and or longitudinal control in trim via control surfaces associated with said rear tailings and duck. The aircraft 10 also comprises a first motor 16 fixed to the fuselage 11, arranged substantially in a plane of vertical symmetry XZ of the aircraft, 25 at a rear end of said fuselage. The first motor 16 is of the "propfan" type, that is to say comprising a turbine 163, arranged according to a turboprop architecture, coupled to propellers 161, 162 fast. According to the terminology used and commonly accepted, a rapid propeller is a propeller whose characteristics: shapes, dimensions and number of blades, rotation speed ..., are adapted for the propeller to operate, with an acceptable propulsive efficiency on the propeller. a transport aircraft, with cruising flight speeds of at least about 0.7 mach. Propellers 161, 162, two in number, are coaxial, therefore rotated about a common axis on separate rotating shafts. They are also contrarotative the direction of rotation of a propeller being opposite to that of the other propeller of the engine, and operate in push mode by creating a force oriented in a direction corresponding to the direction in which the aircraft is. relative to the propellers 161, 162 of the first motor 16. The aircraft 10 further comprises a second motor 17 fixed to the fuselage 11, arranged substantially in a plane of vertical symmetry XZ of the aircraft, at a front end of said fuselage. The second motor 17 is also of the "propfan" type, that is to say comprising a turbine 173 arranged according to a turboprop architecture coupled to fast propellers 171, 172. Propellers 171, 172, two in number, are coaxial like the propellers of the first motor 16. They are also counter-rotating and operate in pull mode by creating a force directed in a direction opposite to the direction in which the propeller is located. relative to the propellers 171, 172 of the second engine 17. The propellers 161, 162 of the first motor 16 and the propellers 171, 172 of the second engine 17 thus exert on the aircraft 10 propulsion forces oriented in the same direction , in normal flight to the front of the aircraft. In one embodiment, the two motors are identical to minor details of embodiment and symmetry of the blades of the propellers close so as to produce the thrust of each of the propellers in the desired direction. The architecture of the aircraft 10 has many advantages. It allows an installation of motors 16, 17 whose geometry both turbines and propellers at the front and rear ends of the elongated shape of the fuselage 11 integrates with the geometry of said fuselage. It should be noted that in terms of mechanical integration it is more complex to fix the engines to the wing whose shape is totally different from that of the engine, especially since it is desired to disturb at least the 2 993 859 8 forms of the wing whose aerodynamic performance is very sensitive to local disturbances of its forms. The architecture of the aircraft 10 therefore allows a wing lighter and more efficient aerodynamically. In particular the position of the propellers resulting from the architecture of the aircraft 5 10 is adapted to the homogeneous aerodynamic flow, generally axisymmetric, around the fuselage. This results in an improved performance of the propulsion, a decrease in the level of the noises generated by interactions between the propellers and the aerodynamic flow around the aircraft, a decrease in the blade fatigue loads.
These advantages are particularly sensitive because of the remoteness of the propellers 161, 162 of the first motor 16 located relatively far behind the wing by their extreme positions at the rear of the fuselage 11. This position has the effect that a wake of the wing, connected to the vortex web detaching from a trailing edge of the wing 12, goes, given its natural deviation downwards, pass below the said propellers of the first engine 16. In in addition to the use of two contra-rotating propellers allows on the one hand, with a fixed diameter, to increase the power of the propulsion and on the other hand to produce, behind a set formed by the two propellers considered, a flow not or slightly twisted compared to that resulting from the use of a simple propeller. In this configuration of the aircraft 10 the second engine 17 located at the front of the fuselage 11 keeps a less disturbed flow on the fuselage 11 and due to the axial symmetry, not twisted, the flow back propellers 171, 172 of the second motor 17 maintains a symmetrical aerodynamic flow at the rear wing 12, regardless of the speed and power developed by the second motor 17. It is thus avoided asymmetrical setting of the half wing left and right, as well as for the empennage duck 15 for the same reasons, to take into account a mean twist of the flow. It is also avoided yawing drift 14 which would be necessary to compensate for a twisted flow that would wind around the fuselage in the case of a single propeller. By avoiding these wedges of the wing and empennages, wedges which are never adapted to all phases of flight and require further compensation actions via control surfaces in particular of roll and yaw, the aerodynamic drag of the plane 10 is decreased. The architecture of the aircraft 10 also allows, by using the tail tail 13 and the tail duck 15 together, to act on the total lift of the aircraft (lift of the wing 12 + lift of the aircraft). rear stabilizer 13 + lift of the tail duck 15) and on its longitudinal balance. The various lift modifications that are necessary in flight to ensure the attitude changes and the control of the aircraft are made by a combination of actions on control surfaces of the different aerodynamic bearing surfaces that are the tail empennage 13, the wing 12 and the duck tail 15. The patent EP 0680877 already cited gives an example of implementation of an aircraft having such an aerodynamic configuration.
In addition to the increased possibilities of controlling the longitudinal attitude of the aircraft 10, the implementation of such an aerodynamic architecture makes it possible to achieve a longitudinal equilibrium of the aircraft with only surfaces having a positive lift, upwards, unlike the general case of planes without empennage duck. It is thus possible to reduce the surface of the wing 12 due to the absence of a negative lift component on the tail tail and because of the positive lift components on the rear stabilizers 13 and duck 15 which participate in the lift from the plane. Following the example of architecture of the aircraft 10 illustrated in Figure 1, the implementation of a rear tail 13 located in the upper part of the fin 14 makes a wake of said tail tail passes over the propellers 161, 162 of the first motor 16 with the same beneficial effects on the noise and fatigue of the propeller blades as in the case of the wing 12 whose wake passes below the propellers.
As illustrated in FIG. 1, the first motor 16 is offset upwards with respect to a longitudinal axis of the fuselage, in particular the axis of the propellers of the first engine, so that the aircraft 10 is able to have a pitch attitude when the wheels of a main gear 18 touches the ground, keeping a ground clearance of the propellers 161, 162 of the first motor 16. The longitudinal axis of the fuselage considered here is an axis substantially parallel to the lines generatrices of a cylindrical portion of the fuselage and substantially mid-height between a lower portion and an upper portion of the fuselage in the cylindrical portion. For example, if the cylindrical portion of the fuselage is of circular section, the axis of the fuselage is advantageously coincident with the axis of the cylinder passing through the centers of the circular sections. In the case of the example of arrangement of the first motor 16 illustrated in Figure 1, a physical contact of the propellers 161, 162 of the first motor 16 with the ground being possible in the event that the aircraft 10 could take the ground an excessive pitch attitude, control functions are introduced into the control means of the aircraft, in practice flight control laws, to limit the pitch attitude, at least on the ground, to a maximum value for which said propellers of the first engine retains a desired ground clearance. It should be understood on this point that the implementation of multiple airfoils (wing 12 + rear tail 13 + tail duck 15) provides the necessary lift to the aircraft 10 during the takeoff and landing phases with a reduced longitudinal attitude compared to a conventional airplane configuration. In another embodiment of the aircraft 10, the first engine is deported substantially above the fuselage 11, as illustrated by the variant of the aircraft 10 in Figure 2, so that the axis of the propellers of the first The engine is located above the fuselage. In this exemplary embodiment, the raised position of the first motor 16 allows the aircraft to take a nose-up attitude which is mechanically limited by the fuselage while maintaining a ground clearance of the propellers 161, 162 of the first engine 16. this case, in a known manner, a shoe is advantageously attached to the fuselage 11 in the area of said fuselage likely to touch the ground first, and or logical functions to limit the attitude are if necessary introduced into a flight control system . 2 993 85 9 11 The duck tail 15 is, because of the architecture of the aircraft 10, located behind the propellers 171, 172 of the second engine. As has already been described, the flow behind the torque of said propellers of the second engine is rectified and there is no major disadvantage that the tail duck 15 is secured to the fuselage 11 in a position intermediate height on said fuselage as shown in Figure 1. In this example a central structure of the duck tail is located at a cabin floor of the aircraft 10, or below the floor, which allows not to affect the adaptable volumes of the fuselage 11 for the transport of persons or goods. In this case the duck tail 15 is located, at least in part, in a breath of the propellers 171, 172 of the second engine in which the flow is accelerated. When it is desired to avoid this situation, for example to avoid a slight deterioration of the friction drag of the duck tail because of this acceleration of the local flow, it is possible to shift the height position on the fuselage. the duck tail, possibly at the cost of structural constraints that may affect the possibilities of development of the fuselage, either downwardly as in the embodiment of the aircraft 10 20 shown in Figure 2, or upwards as in the detail of realization of a front part of the fuselage 11 of the aircraft 10 as shown in Figure 3. In an alternative embodiment not shown, the aircraft 10 does not include duck empennage. In this case it will be preferred to implement a configuration of the aircraft for which the possibility of taking a longitudinal ground attitude sufficient to ensure takeoffs and landings. In this configuration without duck empennage, it will be if necessary uses flying laws allowing the aircraft to fly with a centering sufficiently rear to maintain a positive lift on the tail tail 13. In an embodiment not illustrated, the aircraft 10 does not have a rear tail. In this configuration without tail tail, the aircraft enjoys the benefits of the lift provided by the empennage duck.
Thus the aircraft of the invention benefits from propulsion by rapid propellers and improved performance.