FR2859702A1 - Air supply system for aircraft e.g. missile, has duct sub-divided into two branches at continuously varying sections between rear and front sections, where walls of branches are partly covered internally with magnetic material - Google Patents

Abstract

The system has an air duct sub-divided into two branches (13, 14) at continuously varying sections between rear and front sections. The branches separate and then connect by going around an aerodynamically profiled masking obstacle with a maximal transversal section (S3) masking a base section with respect to air inlet section. The walls of the branches are partly covered internally with a magnetic material absorbing radar waves. An independent claim is also included for an aircraft including an air supply system.

Description

The present invention relates to the architecture of the air intake of a

Stealth aircraft, including missile.

  It is known that, when special precautions are not adopted at the design stage, the air intakes of aircraft, mainly those which supply air to the engines, generate radar echoes which contribute to make said aircraft detectable by the enemy radars. .

  These echoes originate mainly on two parts of the air supply system, namely: - on the scoop of the air intake which is often arranged projecting at the underside of the fuselage so as to capture the air frontally, with the exception of integrated air intakes, such as that described in the unpublished patent application filed by the Applicant on July 2, 1991 under No. 91-08218 for "Attacking Attack Aircraft". integrated air, including missile "; - on the engine or on moving or mechanical elements arranged in the bottom of the air intake duct, such as compressor blades, injectors, engine supports, etc ... The echoes returned by these parts result from an effect propagation of radar waves which are weakened weakly when they traverse the duct both in the incoming direction and in the outgoing direction.

  The object of the present invention is to provide an aircraft air supply system in which the radar waves are greatly weakened as they traverse the duct both in the inbound and outbound directions, while air traveling the same path in the incoming direction lose very little energy, so that the efficiency of the air supply remains very good.

  Partial solutions have already been made.

  Thus, the document FR-2.681.983 proposes to provide in the air flow obstacles orienting the waves to traps, but this results in significant pressure losses affecting the performance of the air supply.

  Document US-4,148,032 proposes to provide on the surfaces disturbances to attenuate the waves, but this is not sufficient to prevent direct access of the waves to the bottom of the conduit. In addition, lateral obstacles have the effect of intolerably reducing air circulation due to eddies that seem inevitable.

  These are therefore only partial solutions to the problem of the invention.

  The invention proposes for this purpose an air supply system for an aircraft comprising a fuselage portion having a longitudinal axis, a front portion and a rear portion, this air supply system comprising a supply duct having a a forward section located outside the forward fuselage portion and having a minimum cross section that determines an air intake section and a rear section located laterally inside the rear fuselage portion and whose section determines a section This system is characterized in that, between these front and rear sections, the duct is subdivided into two branches with continuously varying and progressively separating sections, then approaching progressively bypassing an aerodynamically profiled masking obstacle having a maximum cross section masking the bottom section vis-à-vis the air inlet section and vice versa, the walls of these branches it being at least partly covered internally with a material that absorbs radar waves.

  According to preferred teachings of the invention, possibly combined: the masking obstacle comprises a tapered leading end defining a wedge leading edge and a tapered rear end defining a wedge trailing edge, these ends being connected by means of lateral surfaces of slight curvature, - the wedged leading edge is inclined with respect to the air inlet section, - the wedged leading edge has an edge inclined towards the rear and towards the inside of the fuselage, - the trailing edge is substantially perpendicular to the longitudinal axis, the lateral surfaces of the masking obstacle are twisted between the leading edge and the portion of the obstacle having said maximum cross-section, - the surfaces from the leading edge, first converging towards the inside of the fuselage and then converging towards the outside of the fuselage, the branches are symmetrical with respect to a longitudinal plane. udinal passing through the longitudinal axis, - the branches have, parallel to a plane passing through the longitudinal axis and cutting the masking obstacle, a dimension which grows continuously, - the inlet section has a bean shape and the bottom section has a circular part, the front section of the duct is convergent-divergent, the front section of the duct has an outer edge extending forwards through a scoop having a triangular shape whose tip is directed towards the 'before and whose edges are connected to the front fuselage portion, the fuselage portions having a lower surface and an upper surface, the inlet section is formed in the lower surface, the branches have, in projection in a longitudinal plane passing through the longitudinal axis between these branches, an inclination at least approximately constant, so as to avoid bends, - the bottom section is oriented towards the inlet section having its normal which has, in projection in a pla longitudinal n passing through the longitudinal axis between these branches, an inclination of a few degrees with respect to this longitudinal axis, - the capture of air is achieved by twisted and convex connection surfaces forming a funnel to channel the lines as much as possible of inward airflow and improve aerodynamic performance for all aircraft attitudes.

  In other words, the invention essentially proposes that the air duct be equipped with a solid or hollow aerodynamically profiled hollow, arranged across the duct, and that the surfaces of the mast as well as the internal surfaces of the duct, led are made of an absorbent material for radar waves.

  The interest of this invention is to achieve a stealthy air intake which has a very good aerodynamic performance in cruising flight and cornering.

  Stealth is achieved by eliminating radar echoes from the scoop and the bottom of the air duct.

  Since the air intake is stealthy, it is not necessary to mask all or part of it by the surface of the fuselage, which optimizes the aerodynamic efficiency by combining three main effects: - arrange the air intake in the most favorable zone for the air supply of the engine, that is to say on the underside of the aircraft to benefit from the positive impact of the aircraft during the flight, and in the advanced position to reduce the thickness of the boundary layer in front of the air inlet; - capture as much air as possible in all the aircraft's attitudes; - Make the internal profile of the air inlet so as to eliminate the detachment of the flow and local vortices which are the cause of the pressure drops.

  The invention also proposes an aircraft comprising a power system of the aforementioned type connected to an engine, the branches of the duct having, in projection, in a longitudinal plane passing through the longitudinal axis between these branches, at least one inclination approximately constant , so as to avoid bends and the axis of the motor having, in projection in this plane, an inclination of a few degrees with respect to this longitudinal axis towards the inlet section.

  The shapes of the mast and the air duct make it possible to satisfy all or part of the following design rules: the trajectories of the waves (which can be likened to light rays) which penetrate into the duct while passing through the so-called capture section ( opening of the air intake), can not reach the bottom of the duct without being reflected at least once on the surface of the mast or duct. This is obtained by the massive transverse section of the mast in its central part and by the gradual spacing, then by the also progressive convergence, of the walls of the pipe on either side of the mast, which have the effect of interrupting the trajectories. rectilinear radar waves, while allowing the air streams to pass on curves curved weakly so as to optimize the aerodynamic efficiency of the air intake; the trajectories of the waves reflected on the surfaces of the mast and the duct can not enter and exit in the duct without undergoing at least a second reflection as soon as the edge of the mast is inclined relative to the normal to the nets of air and by taking advantage of the geometric masks that may be the scoop of air intake; - the mast and duct surface elements, with the exception of the leading edge members of the mast, are oriented so as to deviate slightly from the direction of the velocity vector and not to exhibit discontinuities or on the surface itself, or on the orientations of adjacent surface elements, outside the mast and duct connection; - the connection of the scoop, the fuselage and the air duct, located in the capture zone of the air intake, is realized in order to minimize the SER (Effective Backscattering Section) (avoid any frontal surface in sector before) and promote a healthy capture. All that is needed is for the air streams to be channeled following a twisted, convex, funnel-shaped surface so as to obtain maximum efficiency for capturing the air; - The duct has, in different successive cross sectional plans, an area for the passage of air streams which is approximately constant or follows a continuously increasing law from captation to the motor.

  Absorbent surfaces are made according to the known rules of the art. It is possible to use the technique of structural absorbent materials or the technique of absorbent coatings bonded to a structure of metal or structural composite material.

  It is advisable to choose an effective absorbent solution when the waves illuminating the surface at oblique incidence (bistatic reflections) correspond to the incidence of waves reflected multiple times in the conduit.

  Optionally, it is possible to obtain a satisfactory absorption rate by combining reflective surfaces and absorbent surfaces on the mast and on the conduit.

  In this case, it is advisable to: place the absorbent surfaces in the zones where the waves are most frequently reflected, especially near the leading edge of the obstacle; or - to optimize the surfaces and the thicknesses of materials so as to obtain a good absorption efficiency for a minimum overload in mass and volume.

  Objects, features and advantages of the invention will become apparent from the description which follows, given by way of nonlimiting example, with reference to the appended drawings, in which: FIG. 1 is a partial schematic view in vertical axial section of a missile having on the underside an air intake duct according to the invention, moving to the left, - Figure 2 is a view from below, - Figure 3 is a sectional view of the missile according to the invention. III-III of Figure 1, - Figure 4 is a side view of the air intake duct, taken separately, without its scoop, - Figure 5 is a view from above, - Figure 6 in 5 is a sectional view along line VII-VII of FIG. 5, FIG. 8 is a sectional view along line VIII-VIII of FIG. FIG. 5, where the mast is of maximum width, FIG. 9 is a sectional view along the line IX-IX of FIG. 5, at the end of the duct, and - Figure 10 is an approximate curve giving the evolution of the passage section of the duct when going from its entrance to the bottom thereof.

  The figures show the architecture of an air supply system 10 for a stealth aircraft 1, here a missile, associating an aerodynamically profiled central mast and surfaces that absorb radar waves.

  More precisely, this air supply system 10 comprises: a fuselage portion having a longitudinal axis X-X, a front portion 1A and a rear portion 1B; the front portion has in practice a lower section than the rear portion to allow the capture of air; an air supply duct 12 having a front section 12A situated laterally outside the front portion of the fuselage IA and whose minimum section determines an air inlet section Si, and a rear section 12B located at the inside of the rear fuselage portion 1B and whose section determines a bottom section S2; two feed branches 13 and 14 whose sections vary continuously, with small curvatures and without discontinuities, which progressively separate from the section before 12 A and then progressively approach one another until they become confused in the rear section 12B; these branches are substantially symmetrical vis-à-vis a longitudinal plane passing through the X-X axis (this plane is perpendicular to the plane of Figure 5); the walls of these branches which are closest to this plane of symmetry constitute an aerodynamically profiled masking obstacle 15 whose maximum section S3 is chosen so as to mask the bottom section vis-à-vis the section of entry, and vice versa; the duct and in particular the walls of the branches are at least partly covered internally with a material absorbing radar waves.

  In fact, we can also consider that the branches result from the establishment in a divergent duct and then converge of a central mast forcing a separation of the air streams; this is the reason why the masking obstacle can also be called central mast.

  The masking obstacle 15, here hollow, is aerodynamically profiled in that it has a tapered front end, defining a wedge leading edge 16, a tapered rear end defining a wedge 17 trailing edge and weak curvatures between these edges 16 and 17.

  The leading edge 16 is advantageously inclined with respect to the inlet section 12A. This corner 16 is preferably oriented towards the front of the fuselage and towards the longitudinal axis, that is to say that its edge is inclined towards the rear and towards the X-X axis.

  The trailing edge 17 may instead be substantially transverse to the X-X axis.

  The side surfaces 18 and 19 of this masking obstacle 15 have, at the leading edge, an orientation defined by the orientation of the corner leading edge 16. In the example shown, they are first, in cross section (see Figure 7), converging towards the inside of the fuselage. Advantageously, they are then, especially near and beyond the portion of the mast 15 which has the largest section, converging towards the outside (see Figures 5 and 8). These side surfaces are twisted.

  The air passage section varies slowly from the inlet section S1 to the bottom section S2.

  By way of example (see Figure 10), the passage section remains approximately constant first (approximately until approaching the maximum section obstacle portion) and then increases continuously. Preferably, the passage section increases from the beginning substantially linearly.

  It can be noted in FIGS. 4 and 5 that the dimension of the branches, parallel to their plane of symmetry, increases continuously (FIG. 4), even if, perpendicularly to this plane, this dimension seems to decrease (FIG. 5).

  It can be shown that if L is the distance between the sections S1 and S2, and if P is the distance between the sections S3 and S2, and if D1, D2 and D3 are the dimensions of the sections S1, S2 and S3 in the plane of FIG. 5, the obstacle 15 ensures reciprocal masking of sections S1 and S2 if one has: L.D3 = D1.P + D2 (L-P) In fact, this condition is not a necessary condition given the difference in shape of the inlet and bottom sections (the inlet section has, in Figure 6, a bean shape, while the bottom section has, in Figure 9, a circular portion surmounted secondary capture).

  In this respect, it may be noted that the axis of the motor supplied by the duct 12 has an axis which, in FIG. 1, is inclined at an angle a of a few degrees (less than 5), in the plane of symmetry of the leads, forward and down. This has the advantage of reducing the curvatures of the branches in the plane of Figure 1 and thus improve the aerodynamic efficiency: indeed the inclination of the branches in Figure 1 is substantially constant.

  The front portion 12A of the conduit is preferably convergent-divergent, the air inlet section thus being preceded by a funnel area.

  The supply system 10 further comprises, forward of this front section 12A, a scoop 21 extending forwards the outer edge of this section 12A.

  This bailer preferably has a triangular shape, the tip 22 is directed forward, and whose edges are laterally connected to the front fuselage portion 1A.

  It can be noted in Figure 3 that the missile has a flattened section with a lower surface (below) and an upper surface (above). It is in the intrados that is arranged the air intake.

  It may be noted that the total inlet section S1 is divided into an integral or parietal portion A1, corresponding to the difference in section between the fuselage portion IA and the fuselage in front of the air intake, and an outer portion A2.

  The shapes of the mast and duct are defined so that the waves that enter the duct through the air intake section can not reach the bottom of the duct without being reflected at least once on the surfaces of the mast and the duct. .

  The mast has a leading edge inclined so that the reflected waves can not pass through the opening of the air intake without being reflected at least a second time on the surface of the duct.

  The scoop of the air intake in reverse arrow has the shape of a V whose point is directed towards the front and towards the outside of the fuselage (forming a projection) and whose two edges are connected on the fuselage so that the two arms of the V constitute the leading edges of two approximately rectilinear lips and which have the property of masking a large part of the surfaces of the mast and the interior of the duct, by returning the radar echoes, in the direction of the fuselage, or in lateral directions where the aircraft is less vulnerable to the conduct of enemy fire.

  The capture section of the air intake is semi-integrated (partially parietal). In the front view, the section of the air intake that protrudes from the fuselage is thus reduced, which makes it possible to reduce the master torque of the masking mast (that is to say its width in FIG. as a consequence the reduction of the elbow of the air duct to obtain a softer evolution of the local slopes.

  A fully parietal air intake (fully integrated) has been proposed in the aforementioned unpublished patent application for an "integrated air intake attack aircraft, including missile".

  The connection surfaces of the scoop on the fuselage and on the air duct located in the catchment area, particularly sensitive area for the operation of the air intake, are defined to minimize the RES and optimize the aerodynamic efficiency: - in front view of the connecting surface is minimized: all surfaces or portions of frontal surfaces, a source of specular reflection, are eliminated, - the twisted and convex connection surfaces form a funnel to channel the current lines as much as possible inwards to capture as much air as possible and allow the air streams to slide without detachment on the surfaces thus defined. The performance of the air intake is thus improved for all the attitudes of the aircraft: when cruising, when the aircraft is flying with a slight incidence and in a turn when the aircraft is flying with incidence and skid.

  The surface elements of the mast and the duct, with the exception of the leading edge elements of the mast and the scoop lips, are oriented so as to deviate slightly (not more than a few degrees) from the direction of the mast. local velocity vector of air streams and not to introduce discontinuities. Thus, the efficiency of the air intake is optimized by avoiding high local slopes, slope breaks or sharp edges that could give rise to vortices or cause flow detachments.

  The different planes of cross section of the conduit have an area for the passage of the air streams which follows a monotonous law with slow and constant growth from the opening to the motor bottom.

  The inner surfaces of the duct, as well as the surfaces of the mast, are coated with an effective absorbent material in oblique incidence, for example a magnetic material, of the bilayer magnetic elastomer type, or they are manufactured in structural material, for example a multilayer absorbent with carbon impregnated layers.

  The inner surfaces of the duct and the mast surfaces may possibly be only partially absorbent, the complementary parts being reflective, so as to maintain a sufficient absorption efficiency by limiting the overloads in mass and volume.

  The lips of the air inlet bailer are made according to the definition described in the unpublished patent application filed by the Applicant on July 8, 1993 under No. 93-08415 for a "stealthy leading edge". , so as to reduce the effects of reflection and diffraction that inevitably produce some echoes of low amplitude in the lateral directions where the aircraft is not vulnerable to enemy fire control systems.

  The definition of the lips also makes it possible to satisfy the criteria of aerodynamics and mechanical strength according to the aforementioned patent.

  The present invention relates primarily to the engine air supply system, but it can also be used to avoid radar echoes in the air intake cooling or air conditioning of aircraft.

  It goes without saying that the above description has been proposed by way of non-limiting example and that many variants can be proposed by those skilled in the art without departing from the scope of the invention.

Claims (17)

  An air supply system for an aircraft (1) having a fuselage portion having a longitudinal axis (XX), a front portion (1A) and a rear portion (1B), said air supply system having a a supply duct (12) having a front section (12A) located outside the fuselage front portion and whose minimum section determines an air inlet section (Si) and a rear section (12B) located laterally inside the rear fuselage portion and whose section determines a bottom section (S2), this system being characterized in that, between these front and rear sections, the duct is subdivided into two branches (13, 14). ) with continuously varying and gradually separating sections ,. then approaching progressively bypassing an aerodynamically profiled masking obstacle having a maximum cross section (S3) masking the bottom section vis-à-vis the air inlet section and vice versa, the walls of these branches being at least partly internally coated with a radar-absorbing material.   2. Feeding system according to claim 1, characterized in that the masking obstacle (15) has a tapered front end defining a wedge leading edge (16) and a tapered rear end defining a trailing edge in corner (17), these ends being connected by side surfaces (18, 19) of low curvature.   3. Feeding system according to claim 2, characterized in that the wedge leading edge (16) is inclined with respect to the air inlet section (Sl).   4. Feeding system according to claim 3, characterized in that the wedge leading edge (16) has an edge inclined towards the rear and towards the inside of the fuselage.   5. Feeding system according to any one of claims 2 to 4, characterized in that the trailing edge (17) is substantially perpendicular to the longitudinal axis (X-X).   2859702 15 6. Feeding system according to any one of claims 2 to 5, characterized in that the side surfaces (18, 19) of the masking obstacle are twisted between the leading edge and the portion of the obstacle. having said maximum cross section.   7. Feeding system according to claim 6, characterized in that the lateral surfaces (18, 19) are, from the leading edge, first converging towards the inside of the fuselage and then converging towards the outside of the fuselage.   8. Feeding system according to any one of claims 1 to 7, characterized in that the legs (13, 14) are symmetrical with respect to a longitudinal plane passing through the longitudinal axis (X-X).   9. Feeding system according to any one of claims 1 to 8, characterized in that the branches have, parallel to a plane passing through the longitudinal axis (XX) and cutting the masking obstacle (15), a dimension that grows continuously.   10. Feeding system according to any one of claims 1 to 9, characterized in that the inlet section (Si) has a bean shape and the bottom section (S2) has a circular portion.   11. Fuel system according to any one of claims 1 to 10, characterized in that the front section (12A) of the duct is convergent-divergent.   12. Feeding system according to any one of claims 1 to 11, characterized in that the front section (12A) of the conduit has an outer edge extending forwardly by a scoop (21) having a triangular shape which the tip (22) is directed forward and whose edges are connected to the front fuselage portion.   13. Fuel system according to any one of claims 1 to 12, characterized in that the fuselage portions having a lower surface and an upper surface, the inlet section (Sl) is formed in the intrados.   14. Feeding system according to any one of claims 1 to 13, characterized in that the branches have, in projection in a longitudinal plane passing through the longitudinal axis between these branches, an inclination at least approximately constant, so that to avoid elbows.   15. Feeding system according to any one of claims 1 to 14, characterized in that the bottom section is oriented towards the inlet section having its normal which has, in projection in a longitudinal plane passing through the longitudinal axis between these branches, an inclination of a few degrees with respect to this longitudinal axis.   16. Feeding system according to any one of claims 1 to 15, characterized in that the capture of the air is achieved by twisted and convex connection surfaces forming a funnel to channel the maximum current lines of inward air and improve aerodynamic performance for all aircraft.   17. An aircraft comprising a power system according to any one of claims 1 to 16, and a motor connected to the bottom section, the branches of the duct having, in projection in a longitudinal plane passing through the longitudinal axis between these branches, an inclination at least approximately constant, so as to avoid bends and the axis of the motor having, in projection in this plane, an inclination of a few degrees with respect to this longitudinal axis towards the inlet section.