RU2541574C1 - Helicopter rotor and production of rotor from composites - Google Patents

Abstract

FIELD: aircraft engineering.

SUBSTANCE: structurally, this blade features frameless configuration with foam plastic core over the entire chord length and work skin. Foam plastic core is made of isotropic cellular structure material while skin represents a sandwiched shell of polymer composite enveloping said foam plastic core. Shell features variable-depth of outline in radius of rotor and blade chord while its outer plies form the blade airfoil. Blade nose part between shell plies accommodates sections of balancing weight and anti-erosion rubbing bar is fitted over outer ply. In terms of technology, this blade is produced by wet laying-out of shell plies and single-step hot pressing jointly with foam plastic core in the mould. Said shell and foam plastic core are polymerised to produce solid integral structure to ensure stable geometrical parameters of the blade root.

EFFECT: decreased amount of tooling and stable resilience and weight.

6 cl, 11 dwg

Description

The invention relates to the field of aeronautical engineering, namely, the design of blades made of polymer composite materials, and a method for manufacturing such blades.

Known designs of blades made of polymer layered composite materials with a contour (multi-contour) structure of power elements along the length of the blade, the so-called contour and multi-contour spars, and methods for manufacturing such structures.

Patent RU 2043953 dated 09/20/1995 describes a method for manufacturing blades with a variable number of contours (spars) along the length of the blade using sealed elastic bags with an expandable device inside the bag to form the inner contour of the spar.

The disadvantages of this method are:

- a multi-step procedure for assembling the blade structural elements, which requires preliminary crimping of packages of sheets of layered composite material at each step, which increases the complexity of the manufacturing process of the blade;

- instability of glueing the inner contour of the spar during serial production of the blades due to the extremely low resource of elastic bags, requiring frequent replacement and, as a result, the difficulty of ensuring pressure stability in the elastic bag during the polymerization of the assembled spar in the mold.

In addition, a significant drawback of the known technical solutions for the manufacture of the blades are the need for the manufacture of tail sections in separate specialized molds and their subsequent docking (gluing) to the said spar in a special slipway. Together, this method of manufacturing the blades increases the fleet of equipment, does not ensure the stability of the linear mass characteristics in the batch of manufactured blades.

The technical solution according to the patent RU 2230004 dated 06/10/2004 partially eliminates the disadvantages of the method of manufacturing the blades according to the patent RU 2043953. In particular, from the sheets of the layered composite material, as an initial step, the outer package of the open contour of the blade is cut along the entire length of its chord, thereby forming the outer surface the blades. Then, a prefabricated nose compartment with anti-abrasive shackle and centering weight is installed on the outer side of the bow of the outer package. And pre-prepared bags with elastic bags and expansion devices for forming the contours of the side members are sequentially installed in the inner cavity of the outer package.

In such an assembly, the blade is placed in a mold, subjected to a polymerization process, and at the output, the blade is obtained in the final aerodynamic configuration.

However, the aforementioned drawbacks associated with the multi-step procedure for assembling the blade structure and the negative aspects from the use of elastic bags with expanding devices remain.

A technical solution is known for a blade with a contour spar according to the patent EP 2222553 of 09/01/2010, in which the blade throughout the aerodynamically profiled part consists of a C-shaped spar turning into a closed contour in the butt part of the blade. The spar is mainly made of fiberglass.

The blade sheathing is solid throughout the chord, made of epoxy composite material with reinforced fibers, covers the spar, and is joined along the trailing edge of the profile by means of an insert of the same material.

The inner surface of the C-shaped spar is reinforced with a multilayer contour made of epoxy composite material closed in the cross section of the blade, and between the spar and the tail insert the blade contains a foam core made of closed-cell material. In the butt part of the spar there are built-in attachment points of the blade to the rotor hub spaced along the longitudinal axis of the blade.

A method of manufacturing the aforementioned blades is carried out with sequentially stacking upper and lower parts in the mold of the blade chord, respectively, of the outer skin packs, multilayer spar packs and tail liner.

A foam core of a slightly larger cross section is manufactured separately than its final size in the finished blade.

Separately, an assembly of a closed multilayer contour is carried out using an elastic bag mounted on a mandrel.

Each part (upper and lower) of the outer skin packages is pre-pressed and then uncured packages of the corresponding parts of the spar and tail liner, as well as a foam core and a closed multilayer contour with an elastic bag on the mandrel, are laid on them in a mold.

The mold closes, i.e. its two halves dock, pressure is applied to the elastic bag, and the mold heating temperature rises at the same time. There is a process of crimping and subsequent curing of all components of the composite materials of the blade.

The method provides an automated process of individual operations for stacking the spar packets and the outer skin.

In the known technical solution, the previously mentioned disadvantages associated with the use of elastic bags to form a multilayer closed loop in the C-shaped spar remain.

In addition, in the patent EP 2222553 the design of the blade does not contain such important elements as a centering load and anti-erosion forging, without which, on the one hand, it is impossible to obtain the necessary balancing of the blade to prevent critical frequencies of flexural-torsional vibrations of the “flutter” type, and on the other, - ensuring "aerodynamic integrity" of the blade profile in operation.

A known rotor blade of a helicopter made of composite materials (see US Pat. No. 4,935,277 of June 19, 1990), including a structural core consisting of a C-shaped spar in the nose of the profile and a Z-shaped spar in the central part of the profile made of organic wire harnesses or inorganic fibers connected by a polymerized synthetic resin, and a rigid shell made of a fabric package containing carbon fiber, covering the side members and joined along the trailing edge of the profile. The cavity between the side members and the cavity behind the Z-shaped side member are filled with synthetic porous foam material.

A centering load is placed in the bow of the profile contour, between the bearing shell and the C-shaped spar.

The outer skin, which repeats the aerodynamic profile of the blade, is non-load-bearing and is made of a rigid thermoplastic resin with an anti-erosion outer layer and a foam sublayer.

A method of manufacturing a blade includes the following steps.

1) The manufacture of the structural core by pre-forming the spars and the bearing shell, followed by their connection with a polymerizable synthetic resin and filling the cavities with synthetic porous material.

2) Laying on the structural core of the outer skin, followed by thermocompression molding in the mold.

The aforementioned method of manufacturing a blade requires a variety of specialized tooling for the manufacture of each type of spars, a tool for assembling them into a structural core, which increases the complexity and cost of manufacturing the blade.

Known sparless design of the blades of the rotor blades made of composite materials.

So, in patent EP 0378839 from 12/21/1989, the blade contains a core of solid porous material such as foam, located along most of the profile chord over the entire span of the blade, forming the technological core of the blade.

Outside, a core made of packets of organic or inorganic fibers of variable width is laid on the core, forming a stepped relief of the cross section of the shell with a thickening to the leading edge of the blade profile. The outer layer of the shell corresponds to the aerodynamic profile of the blade and may have a polyurethane coating.

In aggregate, a foam core with a multilayer shell (the layers are connected by a polymerized synthetic resin) form a self-supporting structure with high mechanical strength.

The nose of the blade contains a casing with an anti-erosion coating, which can be made of ceramic fiber composite material. A centering load is placed in the bow of the aerodynamic profile of the blade.

One way to obtain a molded blade of a fiber composite structure in combination with a cellular polymer as the core of the blade profile is described in US Pat. No. 4,335,182 of June 15, 1982.

In the known patent, a solid polyvinyl chloride foam foam deformable when heated is used as a core.

The essence of the method of manufacturing the blade is to pre-mechanically seal the core preform under pressure equivalent to the pressure of forming the blade, and then treat the core preform mechanically to give the core the desired shape.

Then, coating layers of thermosetting synthetic material reinforced with organic or inorganic fibers are laid on the core and placed in a mold.

In the mold, temperature and pressure exert external effects on the coating layers, polymerizing them, and at the same time, the temperature activates the tendency of the pre-compacted core to expand elastically inside, exerting pressure on the inner layers of the coating, thereby ensuring deep adhesion of the coating layer to the core.

EP 0378839 does not set forth a method for manufacturing a member-free blade structure from composite materials. And in the patent US 4335182 there is no design of the blade itself, to which the above method is applicable.

Known for the design of the sparless blade and method for its manufacture from composite materials according to patent EP 2256034 from 12/14/2011.

The blade contains a foam core placed along the chord of the blade over its entire span. Packets of strips, each ≈0.3 mm thick, made of flat unidirectional fibers of various widths, forming a multilayer shell with a variable thickness along the cross section of the profile contour, increasing towards the profile toe, acting as a spar, are laid on the core.

On top of the shell and the remaining chord-free part of the foam core, a skin is laid that forms the aerodynamic profile of the blade. The casing is made of multidirectional fabric, as one of the options is fiberglass with the direction of the fibers at an angle of ± 45 degrees.

An erosion cuff is installed in the nose of the blade, under which a centering load is placed.

A method of manufacturing a blade of composite materials according to the aforementioned patent is carried out by laying out dry packages of reinforced fabric, followed by impregnation with a binder resin, supplied under pressure.

The manufacturing process of the blade includes the following steps.

1) Manufacturing by mechanical means of a foam core of the required configuration.

2) Installation of protective linings from a material similar to the skin material on the nose and tail of the foam core.

3) Cutting and laying successively pre-sour cream dry packages of the upper and lower canvases of the casing and shell.

As an alternative option - the use of thermoplastic binders in the process of estimation.

4) Prepared packages of sheathing and sheath cloths are laid out on a foam core, already equipped with protective pads, in one of the halves of the open mold.

5) A prefabricated and assembled anti-erosion shackle with a centering weight placed in it is installed in the nose, assembled in the mold of the structure.

6) The mold is closed and a binder is introduced under pressure.

7) After completion of the polymerization process, the product (blade) is removed from the mold.

On the basis of the distinguishing features, the technical solution according to patent EP 2256034 is taken as a prototype.

One of the disadvantages of the known method of manufacturing the blade remains a multi-step procedure for assembling structural elements with the possible use of thermoplastic binders in the process of bagging when laying them out, which increases the complexity of the assembly process of the structure before it is polymerized in the mold.

In addition, it is problematic to control the quantitative content of the binder in the tissue fibers in the cross sections of the blade profile in terms of scope due to the concentration of injection channels for supplying the binder only in the nose of the profile, which, in turn, can lead to local non-sticking of composite materials, and considering the complex dynamics of the behavior of the blade - the separation of composite packets and the possible destruction of the blade.

As for the design of the blade, the patent EP 2256034 does not contain such an important element as the butt portion of the blade, the pattern of formation of the butt in the context of the overall design of the blade, the method of its manufacture and possible solutions of the attachment points of the blade to the rotor hub. This aspect in the design and manufacture of the blade occupies an equal position in assessing the deformed state of the blade under the action of high cyclic loads in operation, because peak shear stresses in the butt are comparable to stresses when evaluating the fatigue life of a blade.

The technical task of the claimed design of the blade and the method of manufacturing it from composite materials is to reduce the cost of manufacturing the blade due to the one-step technology of forming its profile and minimizing the amount of equipment used, ensuring uniform adhesive bonding over the entire area of the structure and obtaining stability of the elastic-mass characteristics of the blade.

The technical result is achieved by the fact that the blade containing a foam core, placed on most of the chord along the entire length of the blade, a multilayer shell of the nose of the foam core, multilayer sheathing with the fibers in different directions, layers reinforcing the trailing edge of the blade, anti-erosion forging of the blade toe and alignment load, that the said multilayer shell in the butt part of the blade is reinforced with liners of at least two, made in the form of orthotropic plates, placed between the layers of the sheath covering the upper and lower surfaces of the foam core in the area of the attachment points of the blade to the sleeve, and the multilayer sheathing is made of a single sheet covering most of the surface of the blade, has a variable thickness in the cross section of the profile of the blade with thinning to its trailing edge, while the foam the core is made of a material having a predominantly isotropic cellular structure, and a cavity in the bow along the length of the blade between the shell and the casing, where there is no centering load, filled with a simulated insert made of a material of the same type as the foam core material, in addition, the element reinforcing the trailing edge of the blade has a V-shaped cross section, with the possibility of attaching a metal plate to it as a trimmer, and the blade attachment nodes are made in the form of holes of different diameters spaced along the longitudinal axis of the blade so that the hole of a smaller diameter is located closer to the butt end of the blade.

A method of manufacturing the proposed blade, including the manufacture of a foam core, cutting sheets to form multilayer shell and sheathing packages, manufacturing of erosion-resistant forging and centering weights, assembling the aforementioned elements on a foam core and laying it assembled in a mold, the polymerization process of composite elements in a press form, with the assembly of multilayer packages produced on a mandrel, repeating in cross section the surface of the foam core over most of the chord from the sock along the entire length of the blade, starting from the manufacture of the package of the open shell contour, laying in the butt part between the layers of open branches of the contour the prefabricated inserts, carry out preliminary crimping of the bag and, without removing it from the mandrel, the adhesive layer is rolled on its nose and pre-made sections of the centering load and simulation liners, on top of which a package of an open sheathing circuit is assembled, starting from sheets of smaller width, the assembled structure is subjected to preliminary op scaffolds on the mandrel to obtain the desired geometry of the nose of the blade, the above-mentioned structure is removed from the mandrel and a foam core is laid in the cavity formed, the surface of which is pre-treated with a bonding coating, the structure assembled on the foam core is laid in the mold, simultaneously installing an anti-erosion forging and an element reinforcing the trailing edge of the blade, close the mold, and the polymerization process is carried out with a gradual stepwise increase in the heating temperature ess forms with a step interval of exposure.

The essence of the proposed technical solution is illustrated by drawings,

where in Fig.1 is a General view of the blade in isometry;

figure 2 is a typical cross section of the blade in the area with the centering load;

figure 3 is a fragment of the cross section of the blade in the area without centering load;

figure 4 is a cross section of the butt part of the blade with installed liners and the mount (section along aa of figure 1);

figure 5 - plot of the stress concentration coefficients in the contour of the hole in the liner;

figure 6 is a profile of a typical section of the blade in accordance with figure 2 in a partially disassembled form;

Fig.7 - the skin sheathing;

on Fig is a diagram of the assembly of multilayer packages open loop contour and casing on the mandrel;

figure 9 is a fragment of the assembly package of the open contour of the shell and liners in the butt part of the blade;

figure 10 - scheme of laying the constructive blades in the mold;

figure 11 is a diagram of the crimping and polymerization of the blade in the mold.

The blade 1 according to the proposed technical solution is shown in figure 1, which shows the butt part 2 with the nodes 3, 4 of the attachment of the blade to the sleeve, the aerodynamically shaped part (feather of the blade) 5 and erosion control forging 6.

The design of the blade allows for various alternative solutions and forms, here is given for a better understanding of the invention a specific embodiment as an example.

A typical cross-sectional design of the blade 1 is shown in FIG. 2 and consists of a foam core 7 located over most of the chord along the entire length of the blade made of a material having a predominantly isotropic cellular structure, for example, 71 WF polymethacrylimide foam.

The multilayer casing 8 is made in the form of a solid web 9, covering most of the surface of the blade 1, forming its aerodynamic profile. Sheathing layers 8 are made with a multidirectional position of the fibers, mainly at an angle of ± 45 degrees to the longitudinal axis 10 of the blade 1, have a different width, forming a variable (step) thickness Δδ _i ; web 9, as a result of which the casing 8 in the cross section of the profile of the blade 1 is made thinning to its trailing edge 11. In accordance with a preferred embodiment of the present invention, such a formation of the casing 8 allows to increase its thickness in the direction of the bow and this can be varied, if necessary , not only by the position of the center of gravity of the blade profile, but also by local strength from the action of distributed aerodynamic loads on the profile surface. To harden the casing 8, increase its resistance, one of the outer layers can be made of fibers having high mechanical strength, for example, organoplastics fibers.

To strengthen the trailing edge 11, the sheathing 8 along the entire length of the blade 1 is joined with an element 12 made of the same material as the sheathing material, which has a V-shaped cross section ending in stringer 13 with the possibility of attaching a metal plate to it as a trimmer (not shown conditionally )

The foam core 7 in its nasal part is equipped with a multilayer shell 14 that performs at least three functions:

1 - protection of the foam core (its nose) from the action of Coriolis forces and resistance forces;

2 - the formation together with the multilayer sheathing of the power skeleton of the blade for the perception of alternating stresses acting in flight from the bending-torsional vibrations of the blade and inertial loads;

3 - ensuring local strength in the butt section of the blade along the site of its attachment to the rotor hub.

In particular, to ensure local strength, the multilayer shell 14 in the area of placement of the blade attachment nodes 3, 4 is reinforced with liners 15, 16, at least two made in the form of orthotropic plates placed between layers 17.18 of the shell 14, covering the upper and lower surfaces of the foam core 7.

As is known (see R.A. Mikheev. Helicopter Strength.- M .: Mashinostroenie, 1984, pp. 104-105), large bending moment in the plane of rotation of the blade and centrifugal force, which are transmitted to the nodes, act in the butt part of the blade. blade mounts.

The transfer of these loads, as a rule, occurs through the bolts of the docking unit, and the concentration of the resulting total stresses for the blade made of composite materials is quite critical.

The main objective of the structural and technological solution of the blade attachment unit is to minimize the stress concentration in the composite material. And the liners 15, 16 of orthotropic plates in combination with metal sleeves 19, 20 mounted on the adhesive layer 21, as shown in figure 4, can reduce the stress concentration in the composite material:

- from the district load more than 4 times;

- from a radial load of 2-3 times.

In support of this conclusion, Fig. 5 shows the diagrams of the concentration coefficients of circumferential stresses K _σB and radial stresses K _rd on the contour of the hole in the orthotropic plate (analog of the liner) under the action of the load P in the presence of the sleeve - area "a" and without it - area "in ", Obtained experimentally (see." Technology for the production of products and integrated structures from composite materials in mechanical engineering "under the editorship of A. G. Bratukhin and others M., 2003, p. 338, 339, 342).

The implementation of the nodes 3.4 in the form of holes of different diameters spaced along the longitudinal axis 10 of the blade 1 so that the hole 3 of a smaller diameter is located closer to the end 22 of the butt 2, allowed us to optimize the stress concentration in the loop liners 15, 16 due to the redistribution of loads on the nodes 3 , 4 and form a profile in knot 2, adequate to the profile of the feather blade 5, which together improves the strength, technological and aerodynamic characteristics of the blade.

In the region of the blade 1, in the range of relative radii from approximately 0.5R-0.55R to 1.0R, where R is the radius of the rotor, a centering load 23 in the form of profiled metal sections is installed between the casing 8 and the sheath 14 in the bow of the blade (conventionally not shown). And in areas of the blade where there is no centering load 23, the cavity in the bow along the length of the blade 1 between the shell 14 and the casing 8 is filled with imitation liners 24 made of a material of the same material as the foam core 7.

In accordance with a preferred embodiment of the blade design described in the present invention, an example implementation of the proposed method of manufacturing a blade of composite materials includes the following operations:

1) the manufacture by mechanical means of a foam core 7 for the entire length of the blade 1 with a cross section subordinate to the blade structure;

2) cutting sheets of layered composite material in accordance with the cutting map and a given orientation of the fiber filler;

3) from the cut sheets on the mandrel 25, repeating the surface of the foam core 7 on the greater part of the chord, starting from the sock along the entire length of the blade, an open loop package 26 of the shell 14 is assembled, laying in the butt part 2 between the layers 17, 18 along the upper and lower surfaces mandrels pre-made liners 15, 16;

4) the assembled structure is subjected to preliminary crimping on the mandrel 25 at a temperature of 50 ... 60 ° C to ensure bonding of sheets in the package;

5) the adhesive layer is rolled onto the bow of the pre-pressed open-loop package 26, without removing it from the mandrel 25, and pre-made sections of centering weights 23 and simulation inserts 24 are installed;

6) then, from the cut sheets on the said mandrel, without removing the previously assembled and pre-pressed structure, an open loop package 27 is assembled from the web 9, the assembly of the package 27 begins with sheets of smaller width. The assembled structure is subjected to preliminary crimping on a mandrel in the aforementioned temperature mode to obtain the desired geometry of the nose 28 of the blade 1;

7) the pre-pressed structure is removed from the mandrel 25 and into the cavity formed, expanding the open branches of the packages of the open loop 26 and 27, put the foam core 7, the surface of which is pre-treated with a binder coating;

8) in parallel, from the cut sheets, an element 12 is assembled using an individual wedge-shaped device, stacking the sheets so as to form a package of an open V-shaped contour, which is then subjected to preliminary crimping according to the above procedure;

9) the structure assembled on the foam core 7 is placed in the mold 29, orienting it with the nose 28 to the hinge assemblies 30 of the base 29 ₁ and the cover 29 _{2 of} the mold 29; at the same time, a prefabricated shackle 6 is installed with a bonding coating applied to its inner surface, and the prepared element 12, orienting its open V-shaped contour under the open branches of the open loop packet 27;

10. cover 29 _{2 of} the mold 29 is closed; raise the mold heating temperature gradually, stepwise up to + 150 ± 5 ° C with a speed of 1.0 ... 2.0 ° C / min and an intermediate exposure time of 25 ... 30 min. The process of polymerization of the blade in the mold takes 3 hours. ^{+ 5%}

The proposed design of the blade and the method of its manufacture allow qualitatively forming stable geometrical parameters of the blade feather, provide stable linear mass characteristics during serial production of the blade and, as a result, provide a single replacement of the blade in operation of the helicopter.

Due to the one-step procedure for thermal formation of the profile of the blade, uniformity of the polymerized composite material is achieved, ensuring the integral structure of the blade structure, thereby increasing its dynamic strength.

The proposed method of manufacturing a blade made of composite materials allows us to simplify the manufacturing technology of the blade, reduce the complexity and costs due to the rejection of complex formative tooling equipment for servicing such equipment and operations for monitoring the tightness of equipment.

Claims (6)

1. The blade of the rotor of the helicopter, containing a foam core, located on most of the chord along the entire length of the blade, a multilayer shell of the nose of the foam core, a multilayer sheathing with the fibers in different directions, an element that reinforces the trailing edge of the blade, anti-erosion centering sock cargo, characterized in that the multilayer shell in the butt part of the blade is reinforced with liners of at least two, made in the form of orthotropic plates placed between the layers shells covering the upper and lower surfaces of the foam core in the area of the attachment points of the blade to the sleeve, and the multilayer sheathing is made of a single sheet covering most of the surface of the blade, has a variable thickness in the cross section of the profile of the blade with thinning to its trailing edge. 2. The blade according to claim 1, characterized in that the foam core is made of a material having a predominantly isotropic cellular structure. 3. The blade according to claim 1, characterized in that the cavity in the bow along the length of the blade between the shell and the casing, where there is no centering load, is filled with a simulated insert made of a material of the same material as the foam core material. 4. The blade according to claim 1, characterized in that the element reinforcing the trailing edge of the blade has a V-shaped cross section with the possibility of attaching a metal plate to it as a trimmer. 5. The blade according to claim 1, characterized in that the attachment points of the blade are made in the form of holes of different diameters spaced along the longitudinal axis of the blade so that the hole of a smaller diameter is located closer to the butt end of the blade. 6. A method of manufacturing a blade made of composite material, including the manufacture of a foam core, cutting sheets to form multilayer shell and sheathing packages, manufacturing of erosion-resistant forging and centering weights, assembling the above-mentioned elements on a foam core, laying it in the mold and polymerizing the composite elements in the mold, characterized in that the assembly of multilayer bags is performed on a mandrel that repeats in cross section the surface of the foam plastic On the greater part of the chord from the toe along the entire length of the blade, starting from the manufacture of the package of the open shell contour, laying the prefabricated inserts in the butt part between the layers of open contour branches, the package is pre-pressed, then, without removing from the mandrel, they are rolled onto its nose the adhesive layer and install prefabricated sections of the centering load and imitation liners, on top of which collect a package of an open contour of the skin, starting with sheets of smaller width, assembled design the section is subjected to preliminary pressure testing on the mandrel to obtain the required geometry of the nose of the blade, the above-mentioned structure is removed from the mandrel and a foam core is laid in the cavity formed, the surface of which is pre-treated with a bonding coating, the structure assembled on the foam core is laid in the mold, while installing an anti-erosion forging and the element reinforcing the trailing edge of the blade closes the mold and the polymerization process is carried out with a gradual step ohm raising the heating temperature of the mold with a stepper exposure interval.

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