AU2009235992B2

AU2009235992B2 - Covering Fabric for Aircraft in General Aviation

Info

Publication number: AU2009235992B2
Application number: AU2009235992A
Authority: AU
Inventors: Siegfried Lanitz
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-05-11
Filing date: 2009-11-10
Publication date: 2011-01-06
Anticipated expiration: 2028-05-08
Also published as: AU2009235992A1

Description

- 1 Australian Patents Act 1990 - Regulation 2.3 Original Complete Specification, Standard Patent Invention Title: Covering fabric for aircraft in general aviation The following statement is a full description of this invention, including the best method of performing it known to the applicant: Technical Field The invention relates to a covering fabric for aircrafts in general aviation and also a method of manufacture for the covering fabric, in addition to a method for covering such aircraft with the fabric. 5 Background Art In order to reduce weight, designs are still used in aircraft manufacture in general aviation, and in the building of remote-controlled aircraft, whereby the entire body of the aircraft, or parts thereof, are made of spars and ribs. These can be made of metal, wood and/or plastic and must be covered. The covering relates preferably to foils or fabrics that are 10 applied to the structure. WO 96/14208 Al discloses a foil that is suited for the covering of aircraft. This deals with a multilayer material comprising a polyester carrier foil, onto which a polymer layer, based on polyurethane polymers, is applied, in addition to a pressure-sensitive adhesive layer, which is applied to the polymer layer on the side facing away from the carrier foil. 15 This publication discloses a foil for covering aircraft constructions but not a fabric that is suited for covering. US 20060084336 Al discloses a multi-layer, flexible covering fabric for aircraft construc tions. This fabric is constructed of laminated layers and distinguishes itself through espe cially low gas permeability. Therefore this fabric is especially intended for the construc 20 tion of Zeppelins. Furthermore, covering fabrics made of linen, cotton and polyester are known for the use of covering aircraft. These fabrics are applied with nitrocellulose adhesive or chlorinated rubber adhesive to the parts of aircraft that need to be covered, and once the adhesive dries -2 tension is induced in the fabric. To do so the polyester fabrics are shrunk with heat and painted with a varnish. After various coats of varnish, one to two layers of silver varnish are applied for UV protection. Finally the finishing varnish is applied. In DE 849 051 a covering of aircraft is disclosed, which consists of at least two fabric 5 sheets lying on top of one another, with their warp threads running at an angle to one an other. Each fabric sheet is individually stretched, and then connected by a treatment with resin. The fabric sheets are treated with solvent-containing impregnations and after being stretched are treated with tension inducing varnish. The disadvantage of the fabrics and methods for their processing known in the prior art is 10 that in the use of polyester fabrics, although the fabric fibres are covered by nitrocellulose adhesive, the adhesive does not bind with the fibres. Furthermore, nitrocellulose adhesives and varnishes harden further over time, which leads to the embrittlement of the entire adhesion and covering. Through this the covering be comes vulnerable to mechanical damage and it is possible that parts of the covering be 15 come unattached without external force. Lastly, when using the solutions for covering aircraft known in the prior art, a new covering is required after some years. A further disadvantage of the prior art solutions for the covering of aircraft lies in the un controlled gain of weight through the colour painting and layers that are applied. In weighing a square metre of the fabric disclosed in the prior art a gram weight variability 20 of 100 to 400 g/m 2 was measured. Furthermore, polyester fabrics with solvent-based surface covering are known from model plane building, whereby the heat sealable adhesive is applied to the backside. The cover ing can comprise of a resin solution made of polyurethane or a PVC/PVA co-polymer according to GB 2 215 746 A, whereby the resin could be added in combination with a 25 cross-linking agent and catalyst colorant or metal pigment. Furthermore, polyester fabrics for aircrafts with a solvent-based surface covering are known, which are distinguished by high strength, but low shrinkage and low further rip resistance. These products are ad hered through heat-activatable adhesives that have the disadvantage that under high tem peratures they can become soft, the covering loses tension and can even become wrinkled, 30 or the covering can start to float on the adhesive, which significantly limits their useful properties.

-3 It is an aim of the present invention to provide a covering material for aircraft that avoids the disadvantages of the prior art. Summary of the Invention In one broad form, the present invention provides covering fabric for aircraft in general 5 aviation, comprising a polyester- or poly-ether-ether-ketone-fabric. In one embodiment, the fabric is coated with a crosslinked heat-resistant anionic aliphatic polyester polyurethane dispersion. Preferably, the coating is produced through cross-linking an anionic aliphatic dispersion with a preferred OH-number of < 0.5 with a hydrophilic aliphatic polyisocyanate, prefera 10 bly based on hexamethylene diisocyanate, with a preferred NCO-value of 17 to 18. A covering fabric that has been coated in the manner described above exhibits an initial coat. Further layers can be applied to the initial coat and such an initial coating is de scribed as the primer-coat herein. In another embodiment, the fabric is woven from fibers or filaments or ring yams, fila 15 ment yarns or twine, that are coated beforehand with a crosslinked heat-resistant anionic aliphatic polyester-polyurethane dispersion. Preferably, the coating of the fibers or filaments, respectively ring yams, filament yams or twine, is produced through cross-linking an anionic aliphatic dispersion with a preferred OH-number < 0.5 with a hydrophilic aliphatic polyisocyanate, preferably based on hexa 20 methylene diisocyanate, with a preferred NCO-value of 17-18. The fibers or filaments can be processed to ring yam, filament yam or twine before weav ing. It would be apparent to one skilled in the art that the invention also expressly relates to the coating of the processed fibers or filaments. Provided the fibers or filaments, respectively ring yams, filament yams or twine, are 25 coated before the weaving process, coloured pigments can be added to the heat-resistant anionic aliphatic polyester-polyurethane dispersion. It can also come solely to the use of a colour-pigmented dispersion. Coloured pigments are also intended to encompass coloured preparations comprising titanium dioxide and colouring agents.

-4 The fabrics can be produced with coated fibers and filaments, respectively ring yams, fila ment yams or twine, in addition to the coating of fabrics produced from either coated or uncoated fibers and filaments, respectively ring yams, filament yams or twine. In each case, the addition of coloured pigments, hydrophobic substances, UV-protection and/or 5 substances to impede combustibility is envisaged. In an alternative embodiment of the covering fabric of the present invention, the anionic aliphatic dispersion can be coloured or pigmented. Preferably, the pigment consists of alu minium particles or further additives that stabilize the fabric against UV rays or other rays that could accelerate the aging of the fabric. Furthermore, it is intended that hydrophobic 10 substances can be added to the coating of polyester fabrics. If the primer-coat comprises added aluminium particles, additives for UV-stabilisation and hydrophobic substances, then the coat will be long lasting and durable due to the protective additives. Such a coating is especially resistant against aging processes through environ mental influences. 15 In a preferred development of the covering fabric according to the invention, it is intended that at least one, preferably two further coats of colour are applied to the covering fabric. It is preferable that these coats consist of an anionic aliphatic polyester polyurethane disper sion as described above, whereby coloured pigments are added to the dispersion. A covering fabric coated as described above thus exhibits an initial coat (primer-coat), and 20 a second coat that contains coloured pigments. The second coat can also be designated as a colour-coat herein. In a further preferred embodiment of the covering fabric of the present invention, an addi tional coat is intended that has electrically conducting pigments to discharge electrostatic charges and/or an additional coat of a conductive material is applied. In both cases the oh 25 mic value of the electrical conducting coat is preferably between 10-7 und 10~8 n. Through such coats it is possible to discharge electrical charges without damage to the covered parts. In particular, lightening strikes can be prevented or electrical charges can be dis charged. The invention may also encompass the addition of a conductive pigment to the primer-coat.

-5 If a conducting coat is present in the covering, conducting rods need to be attached to the outer ends of the aircraft after the covering (transition zone, trailing edge/wing tip and also ailerons, in addition to the elevator/horizontal rudder and optionally the vertical stabi lizer/vertical rudder) against the air. The conducting coat should be exposed at the point of 5 connection between the coat and the conduction rod and an intimate connection formed between the coat and the rod. For example, this can take place with the help of a conduc tive copper paste. The conducting rods are attached where appropriate in the direction of flow on the underside. Furthermore a covering fabric may be provided, upon which a surface layer is applied. The 10 surface layer consists of an anionic aliphatic polyester-polyurethane dispersion as de scribed above and is intended to be used with a UV-blocker or -adsorber and/or hydropho bic substances. The covering fabric according to the present invention may have optionally - independent from the intended purpose - multiple coats, whereby not all coats need be applied to the 15 covering fabric, and a single coat can be obtained through multiple applications of the cor responding compound. To increase the adhesiveness of the coat to be applied to the fabric, the present invention may include an optional plasma-, or corona-, treatment of the surface of the fabric onto which the coats should be applied. The adhesiveness of the coats be tween each other can also be optimised through plasma-, or corona-, treatment. 20 As already described, a multi-layer coating of the fibers and filaments, respectively ring yarns, filament yams or twine, is intended, whereby a coating system can consist of a primer-coat, a colour-coat and a surface-coat. Fibers or filaments, respectively ring yarns, filament yarns or twine, that are coated in such a manner are then worked into a fabric that can also be coated again as described above. 25 In one embodiment of the present invention, a covering fabric comprising a polyester- or poly-ether-ether-ketone-fabric is intended as a short-lived covering fabric for aircraft, whereby the fabric is coated solely with a cross-linked colour-pigmented heat-resistant anionic aliphatic polyester-polyurethane dispersion. The coating is produced through cross linking an anionic aliphatic colour-pigmented dispersion with a preferred OH-number < -6 0.5 with a hydrophilic aliphatic polyisocyanate, preferably based on hexamethylene diiso cyanate with a preferred NCO-value of 17 to 18. A short-lived covering fabric is also provided whereby the fabric to be coated comprises fibers or filaments, respectively ring yams, filament yams or twine, that were coated before 5 weaving with a cross-linked colour-pigmented heat resistance anionic aliphatic polyester polyurethane dispersion. Preferably, the covering fabrics have a fineness of gauge 30 - 350 dtex according to DIN 53830 T3. In this context DIN is the abbreviation for the ,,Deutsche Industrienorm", or German industry norm, according to the German institute for standardisation. These na 10 tional industry norms can be checked in a directory and represent defined standards. In the following passages the DIN numbers will refer to the demonstrated norms. It is further intended that the uncoated gram weight, or grammage, of a covering fabric of the present invention according to DIN EN 12127 exhibits a weight per unit area between 30 g/m 2 to 250 g/m 2 . 15 In a further embodiment of the invention, the number of single filaments, of which the threads are comprised, in warp and weft is preferably between 15 and 80, and the number of threads according to DIN EN 1049-2 is preferably 15-60 in the warp and 15-60 in the weft. Furthermore, the invention may use covering fabrics whereby the warp-threads or warp- and weft-threads are finished. Through the finishing, the single filaments lying par 20 allel to each other are combined, which can influence the ductility. To achieve a high strength of the warp-threads and/or weft-threads of the covering fabric, single filaments of the warp-threads can be twisted with one another to form a filament bundle. The shrink of the fabric is preferably about 10% longitudinally and transversely at a pre 25 ferred temperature of 150'C. Through this measure an optimal processing of the covering fabric is made possible. It is also intended that a transverse shrinkage of preferably about 10% is achieved, respec tively retained, during the drying of the coating in a drying channel by stretching on a frame.

-7 Furthermore it is intended that the weave takes place as a plain weave or Ripstop. The coating of the covering fabric can be based on an aqueous polyurethane system. This measure serves environmental grounds and leads to the avoidance of CO 2 emissions during production. Nevertheless the invention also encompasses coatings based on solvent 5 containing systems. In a preferred embodiment of the present invention, the covering fabric consists of one or more of the described coatings, which additionally can be coated with an adhesive that consists of a thermo-activatable heat-crosslinking adhesive substance based on an aqueous, anionic dispersion of a high molecular weight polyurethane with a preferred OH-number < 10 0.5 with a preferred 15% hardening formulation made of encapsulated isocyanates, whereby at a heat-input of more than 40'C the polyurethane adhesive becomes crosslinked. There is also disclosed a method of manufacture for a covering fabric for aircraft in general aviation, whereby a polyester- or poly-ether-ether-ketone-fabric with a primer-coat is pro duced, in that a cross-linked heat-resistant anionic aliphatic polyester-polyurethane disper 15 sion is produced through cross-linking an anionic aliphatic polyisocyanate with a preferred OH-number < 0.5 with a hydrophilic aliphatic polyisocyanate, preferably based on hexa methylene diisocyanate with a preferred NCO-value of 17 to 18, and subsequently a poly ester or poly-ether-ether-ketone-fabric is then coated with the coating described above. Alternatively, fibers or filaments, respectively ring yams, filament yams or twine, are proc 20 essed to form a polyester- or poly-ether-ether-ketone-fabric, whereby the fibers or fila ments are coated with a cross-linked heat-resistant anionic aliphatic polyester-polyurethane dispersion before being processed into a fabric, whereby the coating is produced through cross-linking an anionic aliphatic dispersion with a preferred OH-number of < 0.5 with a hydrophilic aliphatic polyisocyanate preferably based on hexamethylene diisocyanate with 25 a preferred NCO-value of 17 to 18. The fabric, or fibers or filaments, respectively ring yarns, filament yarns or twine, from which the fabric is produced, can be coated solely with a cross-linked and colour pigmented heat-resistant anionic aliphatic polyester-polyurethane dispersion. Furthermore, fabrics or fibers or filaments, respectively ring yarns, filament yarns or twine, 30 can be additionally coated with an adhesive, which consists of a thermo-activatable heat crosslinking adhesive substance based on an aqueous anionic dispersion of a high molecu- -8 lar weight polyurethane, preferably with an OH-number < 0.5 with a preferably 15% hard ening-formulation made of encapsulated isocyanates. A pigmented anionic aliphatic dispersion can be used which is pigmented preferably with aluminium particles. 5 In the coating of the fabric, additional hydrophobic substances can be added or a hydro phobic layer can be applied before application of the primer-coat to fabric, fibers or fila ments. If a colourisation of the covering fabric is to be achieved, then at least one, preferably two colour-coats can be applied additionally to the fabric or fibers or filaments, respectively 10 ring yams, filament yarns or twine, out of which the covering is made. These coats can have differing colours, so that patterns, numbers and also letters can be applied as mark ings. In order to discharge lightning strikes or electric charges, an additional coat can be applied, preferably comprising an anionic aliphatic polyester-polyurethane dispersion as described 15 above, with at least one electrically conducting pigment, and/or an additional coat compris ing of an electrically conducting material can be applied. The discharge of charge carried out by such a coat is effected by conducting rods against the air. In order to improve the longevity of the covering produced through the manufacturing process, a surface layer can be applied, preferably comprising an anionic aliphatic polyes 20 ter-polyurethane dispersion as described above, that is intended to comprise UV-blockers or -adsorbers and hydrophobic substances. A fabric can be used that has preferably a fineness from 30 - 350 dtex according to DIN 53830 T3. Furthermore, this fabric can exhibit an uncoated gram weight with a weight per unit area between 30 g/m 2 to 250 g/m 2 according to DIN EN 12127, whereby threads can 25 be used in which the number of single filaments, of which the threads are comprised, in warp and weft is preferably between 15 and 80. In a preferred embodiment, a fabric can be used whereby the shrinkage of the fabric at a temperature of about 150'C is approximately 10% longitudinally and transversely, and/or a transverse shrinkage of preferably about 10% can be achieved during the drying of the 30 coating in a drying channel by stretching on a frame.

-9 In order to prevent destruction of the resulting fabric, or structures to be covered by the fabric, it is intended that a self-extinguishing coat can be additionally applied. Furthermore, every coat of the covering fabric, or the last applied coat, is preferably calen dered for hardening and improving the adhesion of the coat. 5 In another broad form, the present invention provides a process for covering aircraft in general aviation, especially aeroplanes, comprising the following steps: a. a covering fabric of the invention is brought into contact with an adhesive in the area in which the fabric is to be joined to a structure, the adhesive com prising a heat-activatable, heat-crosslinking adhesive substance based on an 10 aqueous, anionic dispersion of a high molecular weight polyurethane with a preferred OH-number < 0.5 with a preferred 15% hardening-formulation made of encapsulated ioscyanates, whereby the structure is also coated or painted with the adhesive, and b. after drying the adhesive, the covering fabric is ironed onto the structure, 15 and c. the areas where the covering fabric has been ironed onto the structure are heated by an appropriate heat source (iron) to about 95 - 105*C, preferably 100 C, and d. when the adhesive has cooled, all covered areas are tensed by a suitable heat 20 source (for example a quartz radiator or hot air gun) at approximately 150'C surface temperature, whereby e. the seams and overlaps, in addition to concave pieces, are at this stage not heated over about 1 00 0 C surface temperature, in order to prevent activation of the adhesive, through which otherwise the seams and overlaps could re 25 lease themselves from the concave pieces. The adhesive is therefore also intended for a separate coating from the described coated covering fabric. For processing, the adhesive can be sprayed onto the structure that is to be covered. This can also occur in an area where the covering fabric is to be stuck to the struc ture.

- 10 After drying the covering is ironed on the structure. After that, all ironed regions are heated to approximately I 00 0 C with a hot air gun, a radiant heat source or an iron in order to en sure a secure crosslinking of the adhesive, in that the encapsulated isocyanates change their aggregate condition and thus crosslink the polyurethane adhesive. After cooling of the ad 5 hesive all covered areas are tensed with a hot air gun, respectively heat source, at approxi mately 150*C. Particularly advantageous is that the fabric, due to its layering, already encompasses all the individual coats that could otherwise be applied. The task of applying many layers, as for particular varnishes or colour coats, does not apply here because the fabric is already 10 intended to contain a colour-pigmented coat. Use of the dispersion described herein allows an environmentally friendly covering in comparison to evaporating solvents. The present invention however also encompasses the use of adhesives and covering systems based on solvents. A secure and temperature-independent connection between the covering and the structure 15 is ensured through use of the adhesive. In contrast to the solutions described in the prior art, an increase in temperature does not lead to a softening of the adhesive or to the fabric wrinkling, whereby the fabric could begin to float on the soft adhesive. The reaction of the adhesive is reversible at temperatures >100*C, which can only be achieved by the extreme addition of heat in order to provide the possibility of specific 20 removal of the covering for revision or repair purposes. Thus the adhesive as used in the present invention ensures an ongoing durable strength. Due to the substances that are intended as additives for the coatings, the ageing process of the covering fabric, for example through UV-rays or other natural factors, is significantly slowed. 25 In coating the fabric a production plant with an adjustable stretching frame may be used, so that the fabric can be stretched cross-wise on the frame during the drying in order to achieve and maintain the preferable approximate 10% transverse shrinkage of the fabric. The present invention also provides a kit for the covering of aircraft, comprising a covering fabric of the invention and an adhesive for coating the fabric, which comprises a thermo 30 activatable, heat-crosslinking adhesive substance based on an aqueous anionic dispersion - 11 of high molecular weight polyurethane with an OH-number < 0.5 with a 15% hardening formulation made of encapsulated cyanates. Additionally the kit can contain serrated belts or tapes and/or reinforcement tapes. Such a kit provides all the means that are necessary to cover an aircraft, whether it be an 5 aeroplane or a model aeroplane, with the covering fabric of the present invention. Overall the covering fabric and adhesive according to the present invention lead to the fact that considerably less weight is attached to the aircraft which is to be covered. This is par ticularly advantageous when applied to small or light aircraft such as remote controlled aircraft, unmanned reconnaissance aircraft, ultra-light aircraft and category-E aircraft. 10 It is to be noted for the coating of a fabric that the coat is applied and does not permeate the fibers or filaments, respectively ring yarns, filament yarns or twine. The depth of coating of the fabric should only amount to approximately 1/3 of the fabric thickness, in order to protect the fabric from the permeation of water or other liquids and to produce an airtight coat. 15 A further advantage of the coating of the fabric according to the present invention is that the fabric itself maintains elasticity. In the methods known in the prior art the fabric was soaked in resin. This represents an encroachment in the structure of the fibers or filaments of which the fabric is made. The drying of the resin or other liquids in which the fabric is soaked leads to a loss of elasticity of the fabric. Through this, the danger of damage to the 20 covering through the forces present in the operation of an aircraft is increased, especially on the wings. Such a soaking also negatively influences the rip-resistance. Detailed Description of Preferred Embodiment(s) Example 1 Covering fabric for ultra-light aircraft of up to approximately 600kg takeoff weight. In 25 order to produce a covering fabric of the above-mentioned specifications, the following was undertaken: For the warp: One can create a warp with approximately 43 threads for every cm. For crea tion of the warp a high-strength polyester thread is applied with a residual shrinkage of 5 12%. The total weight of the raw fabric without coating should lie between 70 and 100 30 g/m 2 . In order to obtain this weight, filament yarn with approximately 70 DETEX and a - 12 diameter of approximately 0.15 - 0.20 mm is used. In order to control the elasticity of the fabric the filaments could be additionally twisted. The twisting influences the E-module of the fabric, respectively the elastic components in the fabric. As weft yarn, threads of an identical material are used. In this example ap 5 proximately 32 threads are deployed for the weft. However these numbers can by all means vary to a significant extent. In weaving it must be ensured that the weave occurs without stress or warping. In using certain finishes in the fibers, particularly with Skybon, a washing after the weaving is not essential, as the Skybon coats can be simultaneously deployed as a contact-area between the coating and fibers. 10 It is recommended that before the coating, as a separate process or online, that the fabric is corona-treated or pre-treated with plasma in order to achieve an optimal anchoring of the coating composition to the filament yarn. The coating consists of polyurethane. Depending on the E-module to be achieved and the desired properties, polyester-, polyether- or poly carbonate-polyurethane, or mixtures thereof, can be applied. In order to optimize the proc 15 essing and performance characteristics the system must be crosslinked. Amongst other things, increased temperature stability, in addition to chemical and solvent strength, is obtained through the crosslinking. The crosslinking can also control the degree of hardness of the fabric in combination with the mixtures. Should the PU-system be based on solvents, it must contain sufficient OH-groups with an OH-number < 0.5 in order to 20 achieve the corresponding crosslinking; which is achieved with a hydrophilic, aliphatic polyisocyanate based on hexamethylene diisocyanate with a NCO-value of 17-18. When one binds the dispersion system at hand according to the present invention, the dispersion system reacts over urea formation as a secondary crosslinking to polyurethane. In this case a hydrophilic aliphatic polyisocyanate based on hexamethylene diisocyanate, with a pro 25 portion of 2.5 - 4.0 proportion by weight (NCO-value of 17 - 18), is also used as a crosslinker. In order to achieve a reasonable weight ratio the fabric is coated twice with the above mentioned color-pigmented coating composition. In the coating process it must be ensured that the shrinkage should not be removed from the fabric to be covered through the activi 30 ties in the drying channel. Should the shrinkage be about 5% or less, one can increase the shrinkage through the fixation temperature and relaxation ratio. After the colour coating at - 13 least one UV-protection system is applied. In order to enhance the value of the product, the fabric should be treated with at least two UV-coating procedures. One can also additionally add a hydrophobic substance to the UV-coating. The material produced as described is now applicable as a covering material for ultra-light aircraft. In a strength test the tensile 5 strength should be at or above 600N. Example 2 Covering fabric for light aircraft of up to approximately 3000kg takeoff weight. In order to produce a covering fabric of the above-mentioned specifications, the following was under taken: 10 For the warp: One can create a warp with approximately 27 threads for every cm. For crea tion of the warp a high-strength polyester thread is presented with a residual shrinkage of 5-12%. The total weight of the raw fabric without coating should lie between 70 and 100 g/m 2 . In order to obtain this weight, filament yarn with approximately 180 DETEX is used. In order to control the elasticity of the fabric the filaments could be additionally twisted. 15 The twisting influences the E-module of the fabric, respectively the elastic components in the fabric. As weft yarn, threads of an identical material are used. In this fabric class ap proximately 24 threads are deployed for the weft. However these numbers can by all means vary to a significant extent. In weaving it must be ensured that the weave occurs without stress or warping. In using certain finishes in the fibers, particularly with Skybon, 20 a washing after the weaving is not essential, as the Skybon coats can be simultaneously deployed as a contact-area between the coating and fibers. It is recommended that before the coating, as a separate process or online, that the fabric is corona-treated or pre-treated with plasma in order to achieve an optimal anchoring of the coating composition to the filament yarn. The coating consists of polyurethane. Depending 25 on the E-module to be achieved and the desired properties, polyester-, polyether- or poly carbonate-polyurethane, or mixtures thereof, can be applied. In order to optimize the proc essing and performance characteristics the system must be crosslinked. Amongst other things, increased temperature stability, in addition to chemical and solvent strength, is obtained through the crosslinking. The crosslinking can also control the degree 30 of hardness of the fabric in combination with the mixtures. Should the PU-system be based -14 on solvents, it must contain sufficient OH-groups with an OH-number < 0.5 in order to achieve the corresponding crosslinking; which is achieved with a hydrophilic, aliphatic polyisocyanate based on hexamethylene diisocyanate with a NCO-value of 17-18. When one binds the dispersion system at hand according to the present invention, the dispersion 5 system reacts over urea formation as a secondary crosslinking to polyurethane. In this case a hydrophilic aliphatic polyisocyanate based on hexamethylene diisocyanate, with a pro portion of 2.5 - 4.0 proportion by weight (NCO-value of 17 - 18), is also used as a crosslinker. In order to achieve a reasonable weight ratio the fabric is coated twice with the above 10 mentioned colour-pigmented coating composition. In the coating process it must be en sured that the shrinkage should not be removed from the fabric to be covered through the activities in the drying channel. Should the shrinkage be about 5% or less, one can increase the shrinkage through the fixation temperature and relaxation ratio. After the colour coat ing at least one UV-protection system is applied. In order to enhance the value of the prod 15 uct, the fabric should be treated with at least two UV-coating procedures. One can also additionally add a hydrophobic substance to the UV-coating. The material produced as described is now applicable as a covering material for light aircraft up to 3000 kg. In a strength test the tensile strength should be at or above 850N. Example 3 20 Covering fabric for light aircraft of up to approximately 6000 kg takeoff weight. In order to produce a covering fabric of the above-mentioned specifications, the following was under taken: For the warp: One can create a warp with approximately 22 - 27 threads for every cm. For creation of the warp a high-strength polyester thread is presented with a residual shrinkage 25 of 5-12%. The total weight of the raw fabric without coating should lie between 110 and 130 g/m 2 . In order to obtain this weight, filament yarn with approximately 180 DETEX is used. In order to control the elasticity of the fabric the filaments could be additionally twisted. The twisting influences the E-module of the fabric, respectively the elastic components in 30 the fabric. As weft yarn, threads of an identical material are used. In this example ap proximately 18 - 22 threads are deployed for the weft. However these numbers can by all - 15 means vary to a significant extent. In weaving it must be ensured that the weave oc curs without stress or warping. In using certain finishes in the fibers, particularly with Sky bon, a washing after the weaving is not essential, as the Skybon coats can be simultane ously deployed as a contact-area between the coating and fibers. It is recommended that before the coating, as a separate process or online, that the fabric is corona-treated or pre-treated with plasma in order to achieve an optimal anchoring of the coating composition to the filament yarn. The coating consists of polyurethane. Depending on the E-module to be achieved and the desired properties, polyester-, polyether- or poly carbonate-polyurethane, or mixtures thereof, can be applied. In order to optimize the proc essing and performance characteristics the system must be crosslinked. Amongst other things, increased temperature stability, in addition to chemical and solvent strength, is obtained through the crosslinking. The crosslinking can also control the degree of hardness of the fabric in combination with the mixtures. Should the PU-system be based on solvents, it must contain sufficient OH-groups with an OH-number < 0.5 in order to achieve the corresponding crosslinking; which is achieved with a hydrophilic, aliphatic polyisocyanate based on hexamethylene diisocyanate with a NCO-value of 17-18. When one binds the dispersion system at hand according to the present invention, the dispersion system reacts over urea formation as a secondary crosslinking to polyurethane. In this case a hydrophilic aliphatic polyisocyanate based on hexamethylene diisocyanate, with a pro portion of 2.5 - 4.0 proportion by weight (NCO-value of 17 - 18), is also used as a crosslinker. In order to achieve a reasonable weight ratio the fabric is coated twice with the above mentioned pigmented-pigmented coating composition. In the coating process it must be ensured that the shrinkage should not be removed from the fabric to be covered through the activities in the drying canal. Should the shrinkage be about 5% or less, one can increase the shrinkage through the fixation temperature and relaxation ratio. After the colour coat ing at least one UV-protection system is applied. In order to enhance the value of the prod uct, the fabric should be treated with at least two UV-coating procedures. One can also additionally add a hydrophobic substance to the UV-coating. The material produced as described is now applicable as a covering material for light aircraft of up to 6000 kg. In a strength test the tensile strength should be at or above 1 IOON.

- 16 The term "comprise" and variants of that term such as "comprises" or "comprising" are used herein to denote the inclusion of a stated integer or integers but not to exclude any other integer or any other integers, unless in the context or usage an exclusive interpreta tion of the term is required. 5 Reference to prior art documents or disclosures in this specification is not an admission that the prior art constitutes common general knowledge in Australia.

Claims

1. Covering fabric for aircraft in general aviation, comprising a polyester- or poly-ether-ether-ketone-fabric, characterised in that the fabric is coated with a crosslinked heat-resistant anionic aliphatic polyester-polyurethane dispersion.

2. Covering fabric for aircraft in general aviation, comprising a polyester- or 5 poly-ether-ether-ketone-fabric, characterised in that the fabric is woven from fibers or filaments or ring yarns, filament yarns or twine, that are coated be forehand with a crosslinked heat-resistant anionic aliphatic polyester polyurethane dispersion.

3. Covering fabric according to claim 1 or 2, characterised in that the fabric, fi 10 bers, filaments or ring yams, filament yams or twine are coated with one or more additional crosslinked heat-resistant anionic aliphatic polyester polyurethane dispersion coats.

4. Covering fabric according to one of the preceding claims, characterised in that the coating is produced though crosslinking an anionic aliphatic dispersion 15 with a preferred OH-number < 0.5, with a hydrophilic aliphatic polyisocyanate, preferably based on hexamethylene diisocyanate with a preferred NCO-value of 17 to 18.

5. Covering fabric according to one of claims I to 4, characterised in that the heat-resistant anionic aliphatic polyester-polyurethane dispersion contains ad 20 ditives, preferably colour-pigments, electrically conducting pigments, alumin ium particles, UV-blockers or -adsorbers, hydrophobic substances and/or sub stances to impede combustibility.

6. Covering fabric according to one of the preceding claims, characterised in that an additional coat is applied consisting of an electrically conducting material. 25

7. Covering fabric according to one of the preceding claims, characterised in that the fabric is additionally coated with an adhesive, which consists of a thermo activatable, heat-crosslinked adhesive substance based on an aqueous anionic 18 dispersion of a high molecular weight polyurethane, preferably with an OH number < 0.5, and preferably containing a 15% hardening-formulation made of encapsulated isocyanates.

8. Method for coating aircraft in general aviation, especially aeroplanes, charac 5 terised by the following method steps: a. A covering fabric according to one of claims 1 to 7 is brought into con tact with an adhesive in the area where it is to be attached to a structure, the adhesive comprising a thermo-activatable, thermal-crosslinking ad hesive substance based on an aqueous anionic dispersion of a high mo 10 lecular weight polyurethane, preferably with an OH-number < 0.5 with preferably 15% hardening-formulation made of encapsulated isocy anates, whereby the structure is also coated with the adhesive, and b. After drying the adhesive the covering fabric is ironed onto the struc ture, and 15 c. The areas in which the covering fabric is ironed onto the structure are heated by means of a suitable heat-source to approximately 95 - 100*C. d. when the adhesive has cooled, all covered areas are tensed by means of a suitable heat-source at approximately 150*C surface temperature, whereby 20 e. the seams and overlaps, in addition to concave pieces, are at this stage not heated over approximately 100*C surface temperature, in order to prevent activation of the adhesive, through which otherwise the seams and overlaps could release themselves from the concave pieces.

9. Kit for covering aircraft in general aviation, comprising a covering fabric ac 25 cording to one of claims I to 7 and an adhesive for coating the fabric, which is made of a thermo-activatable, heat-crosslinked adhesive substance based on an acqueous anionic dispersion of a high molecular weight polyurethane with a preferred OH-number < 0.5 with a preferred 15% hardening-formulation made of encapsulated isocyanates, whereby the polyurethane adhesive is crosslinked 30 by supplying heat of more than 40'C. 19

10. Kit according to claim 9, which additionally contains serrated belts or tape and/or reinforcement tapes.

11. Covering fabric according to one of claims 1 to 4, characterised in that an ali phatic polyisocyanate, based on hexamethylene diisocyanate, with a proportion 5 of 2.5 - 4.0 proportion by weight and an NCO-value of 17 - 18, is used as a crosslinker.

12. Covering fabric for aircraft, the covering fabric being substantially as described herein with reference to the examples.

13. A method for coating aircraft, the method being substantially as described 10 herein with reference to the examples.