Patent Application
20070281570
For a complete understanding of the objects, techniques and structure of the invention, reference should be made to the following detailed description and accompanying drawings, wherein:
Referring now to the drawings and in particular to
The vehicle 10 is constructed with an enclosing material that has many desirable properties. In general, these desirable properties are tear resistance, creep resistance, high strength, and light weight, which allows for an increase in payload size, and the ability to withstand extreme temperature and pressure variations. In view of these wide temperature and pressure variations the material also needs to be flexible in many conditions. It is also desirable that the laminate material be ozone and ultraviolet light resistant and have the necessary gas permeability characteristics. Resistance to tearing caused by bullets, punctures and the like is beneficial. It is desirable for the laminate material to have high altitude capabilities. It is believed that the constructions presented herein allow the vehicle 10 to operate at altitudes of within the troposphere and stratosphere. In certain embodiments, the enclosing material of vehicle 10 exhibits good thermal management and shear modulus, and is able to dissipate static electricity and provide lightning protection.
As best seen in
A straight ply monofilament yarn layer 25 forms the interior surface 22. An optional bias ply monofilament yarn layer 35 may be adhered to straight ply layer 25 with optional adhesive layer 30. When optional bias ply monofilament layer 35 is present, film layer 45 is adhered to bias play layer 35, and adhesive layer 40 is applied between bias ply layer 35 and a film layer 45. In one embodiment, film layer 45 is metallized. In other words, a metal coating may be applied to film layer 45 to form metal coating layer 50. In one embodiment, metal coating layer 50 may be adhered to the outer facing surface of film layer 45. In another embodiment, metal coating layer 50 may be adhered to the inner surface of film layer 45. In yet another embodiment, metal coating layer 50 may be adhered to both the inner and the outer surfaces of film layer 45. Reflectance enhancing layer 52 may be adhered to metal coating layer 50. Optionally, a clear film cover layer 55 may be adhered to metal coating layer 50, or to reflectance enhancing layer 52. Cover layer 55 may also form the exterior surface 24.
In another embodiment, shown in
In both embodiments, layer 25 may be described as a straight ply. By “straight ply” it is meant that the yarns are oriented at about 0 and 90 degrees to each other, and substantially parallel with the circumferential and axial directions of the airship hull. In certain embodiments, straight ply layer 25 provides the primary strength requirements for the airship structure.
The type of monofilament yarn employed in layer 25 is not particularly limited. Commercially available monofilament yarns include polyamides, polyesters, aramids, liquid crystal polymers, carbon, polybenzoxazole, and ultrahigh molecular weight polyethylene. In certain embodiments, a high tenacity yarn such as carbon, or those designated as M5® (DuPont), Vectran,® Zylon,® Dyneema,® and Spectra® may be employed. In one embodiment, the liquid crystal polymer fiber of layer 25 includes Vectran® or an equivalent material.
In one or more embodiments, straight ply layer 25 includes a woven fabric that has warp and fill yarns much like a cloth material. The liquid crystal polymer fiber yarns are advantageous in that they are strong yet light weight. A wide range of strengths are possible. Indeed, in one embodiment, the warp direction of straight ply layer 25 has a tensile strength of from about 200 to about 2000 lbs. per inch and in the fill direction a tensile strength of from about 120 to about 1200 lbs. per inch. The liquid crystal polymer fiber material has also excellent creep resistance and flex fatigue resistance. The weave pattern may provide intermittent gaps or periodic groups of bundled yarns for the purpose of reducing the overall weight of the laminate and to stop tearing in the event a bullet or other projectile punctures the laminate.
The at least one monofilament yarn layer may be woven or non-woven. Therefore, in another embodiment, straight ply layer 25 is non-woven. For example, the warp and fill yarns of layer 25 are layered and stitched, or knitted, together, rather than woven together.
Optional layer 35 may be described as bias ply. By “bias ply” it is meant that the warp and fill yarns are oriented at an angle of from about 30 to about 60 degrees to the warp and fill yarns of straight ply layer 25. In certain embodiments, bias ply layer 35 provides shear modulus and tear strength for the airship structure.
The type of monofilament employed in bias ply layer 35 is not particularly limited, and may be selected from any of the monofilaments described hereinabove for straight ply layer 25. In one embodiment, layer 35 includes Vectran® or an equivalent material.
In certain embodiments, bias ply layer 35 includes a woven or non-woven fabric that has warp and fill yarns as described for straight ply layer 25. In one embodiment, bias ply layer 35 may be stitch-bonded or knitted to straight ply layer 25 to eliminate the need for adhesive layer 30. It will be appreciated that the layers 25 and 35 may use any warp/fill pattern that maximizes strength while minimizing weight. Moreover, the layers 25 and 35 are not enclosed or embedded in any type of carrier material that would otherwise limit the flexibility, tear, or strength properties of the yarns used in the layers.
Barrier film layer 45 may include any high modulus film, such as polyamide, liquid crystal polymer, polyethylene teraphthalate (PET), polyethylene napthalate (PEN), and polyimide films. Examples of polyimide films include Kapton® or equivalent material. In general, modulus is a measure of resistance to extension of the fiber or the ratio of change in stress to the change in strain after the crimp has been removed from the fiber. An easily extensible fiber or film has low modulus. In certain embodiments, the high modulus film exhibits a tensile modulus of at least about 218,000 psi, in other embodiments, the tensile modulus is at least about 261,000 psi, in other embodiments, the tensile modulus is at least about 290,000 psi.
In one or more embodiments, high modulus barrier film layer 45 provides excellent bias modulus and is also an excellent gas barrier material to hold the preferred lighter-than-air material, such as helium, within the hull construction. In one embodiment, high modulus film layer 45 functions as a gas barrier for retaining helium or the like.
The thickness of barrier film layer 45 is not particularly limited. In one embodiment, film layer 45 is from about 0.3 to about 2 mils in thickness.
In one embodiment of the present invention, barrier film layer 45 includes reinforcing filler. Examples of reinforcing filler include carbon black, fumed silica, carbon nanotubes, carbon nanofibers, nanoclay, and the like. The amount of reinforcing filler added to the barrier film is not particularly limited, so long as it is an effective amount to increase the modulus of the barrier film layer. In one embodiment, barrier film layer 45 includes reinforcing filler in an amount of at least about 2 weight percent (wt. %), based upon the total weight of barrier film layer 45. In another embodiment, barrier film layer 45 includes reinforcing filler in an amount of at least about 5 weight percent (wt. %), based upon the total weight of barrier film layer 45. In certain embodiments, the barrier film includes reinforcing filler in an amount of from about 1 to about 20 wt. %, based upon the total weight of barrier film layer 45. In one or more embodiments, barrier film layer 45 includes reinforcing filler in an amount of from about 2 to about 10 wt. %, based upon the total weight of barrier film layer 45.
Metal coating layer 50 is adhered to the outer surface of high modulus film layer 45. Suitable metals include highly reflective metals such as silver, aluminum, gold, and copper. In one or more embodiments, metal coating layer 50 includes aluminum. Aluminum coated polyimide films are commercially available from Sheldahl Technical Materials of Northfield, Minn. Alternatively, high modulus film layer 45 may be coated with metal films and foils via processes generally known in the art. Processes to apply metals to Kapton® without adhesives are known, for example by vacuum metallization and sputtering techniques.
The thickness of metal coating layer 50 is not particularly limited, but should be sufficient to prevent transmittance of solar radiation. The coating may be in the form of a thin foil, vapor deposited film or sputtered film. In one embodiment, the thin foil is from about 0.2 to about 1 mil in thickness. In one or more embodiments, metal coating layer 50 is applied to a thickness of from about 800 to about 1200 angstroms, and in one embodiment, metal coating layer 50 is applied to a thickness of about 1000 angstroms.
One purpose of the metal coating is to reflect solar radiation for thermal management. Other purposes of the metal coating are to dissipate static charge buildup, reduce helium permeability, and reduce damage from lightning strikes.
Reflectance enhancing layer 52 may be adhered to metal coating layer 50. Reflectance enhancing layer 52 may include a polymer film such as 3M photonic filter films, or dielectric materials such as titanium dioxide, silicon dioxide, or hafnium dioxide. Layer 52 may enhance reflectance and/or provide a notch reflector for a specific band width of solar radiation. When employed, the polymer or dielectric coating 52 may be applied to a quarter-wavelength optical thickness (QWOT) or increments thereof. QWOT techniques include the process of applying successive layers of materials of differing refractive indexes, thereby increasing the reflectivity of the coating. The materials in the layers, the thicknesses of the layers, and the indices of refraction of the layers may be chosen to selectively reflect solar radiation within a certain wavelength range.
Optionally, clear film cover layer 55 is adhered to metal coating layer 50. When reflectance enhancing layer 52 is present, clear film cover layer 55 may be adhered to reflectance enhancing layer 52. Clear film cover layer 55 may include any film that is resistant to ozone and ultraviolet radiation. Useful films also include corrosion protector films. Examples of suitable films include polyvinylidene fluoride.
By “clear” it is meant that the film does not contain substantial amounts of pigments or solid materials that would cause the film to appear cloudy or opaque, or otherwise decrease the reflectivity of the metal coating layer.
In one or more embodiments, film cover layer 55 further includes a fluorescent dye. Any fluorescent dye that does not make the film cloudy or opaque, or otherwise detrimentally affect the properties of the film, may be used. Examples of fluorescent dyes include commercially available optical brighteners. In one embodiment, the fluorescent dye can be used in an inspection of film cover layer 55 to detect imperfections or damage in the cover layer. For example, ultraviolet or black light can be directed onto the laminate material. Areas that do not fluoresce indicate possible gaps or discontinuities in the cover layer.
Film cover layer 55 may be adhered to metal coating layer 50 or reflectance enhancing layer 52 by use of an adhesive, such as a thermoplastic or thermoset adhesive. Alternatively, film cover layer 55 may be directly cast onto metal coating layer 50 or reflectance enhancing layer 52. Therefore, in one or more embodiments, no adhesive layer is necessary between film cover layer 55 and metal coating layer 50 or reflectance enhancing layer 52. In one or more embodiments, the film cover material provides excellent ultraviolet and ozone protection while allowing reflectance of solar radiation from metal coating layer 50.
In certain embodiments, film cover layer 55 also enhances thermal control of the vehicle and reduces its infrared signature. In other words, metal layer 50 reflects about 85-95% of solar radiation in the ultraviolet, visible, and near infrared regions of the solar spectrum, while film cover layer 55 acts as an emitter in the mid to far infrared region to minimize heat build-up in the fabric hull material.
One or more layers 25, 35, 45 and 55 are bonded to one another with adhesive layers. Suitable adhesives include thermoplastic and thermosetting adhesives. Specific examples of adhesives include polyurethane adhesives that retain flexibility at low temperatures.
The adhesive material bonds the layers to one another and may fill in any pin holes or gaps that may be encountered. In one or more embodiments, the straight ply and bias ply layers are laminated such that penetration of the adhesive into the layers is minimized, and fabric stiffness or reduction in fabric tear strength is avoided. More specifically, the adhesive may be laid onto the surface of the yarn layers and is not embedded into the yarn.
One or more adhesive layer may include reinforcing fibers or inorganic fillers to enhance mechanical properties. Inorganic fillers include carbon black, fumed silica, carbon nanotubes, carbon nanofibers, nanoclay and the like. Advantageously, the addition of reinforcing filler may increase the strength and modulus of the laminating adhesive without significantly increasing its weight. In one or more embodiments, the greater strength contributed by the reinforced adhesive layer allows a reduction the monofilament yarns of bias ply layer 35, and this results in a reduced weight of bias ply layer 35.
Typically, a bias ply layer in a hull fabric for LTA vehicles has a weight of about 1.5 ounces per square yard (oz/yd2). Advantageously, the weight of bias ply layer 35 may be reduced according to the present invention. In one embodiment, the weight of bias ply layer 35 is from 0 to about 1 oz/yd2. In one embodiment, the weight of bias ply layer 35 is reduced by about 50%, or to less than about 0.75 oz/yd2. In another embodiment, the weight of bias ply layer 35 is completely eliminated.
In these or other embodiments, the laminated fabric including a reinforced adhesive layer and reduced bias ply layer has a higher strength to weight ratio than laminated fabric having a conventional bias ply layer but no reinforcing filler in the adhesive layers. In one embodiment, a conventional laminated fabric including a bias ply layer and having a strength to weight ratio of about 194 is modified by adding reinforcing filler to the barrier layer and reducing the weight of the bias ply layer by about 50 percent. The resulting strength to weight ratio is about 218. In another embodiment, the conventional laminated fabric is modified by eliminating the bias ply layer and adding reinforcing filler to the barrier film layer and the adhesive layer between the straight ply layer and the barrier layer. The resulting strength to weight ratio is about 259. In certain embodiments, the reinforcing filler in the adhesive layer improves adhesion to cloth layers, increases seam strength, or provides more even distribution of load around broken or damaged yarns.
In embodiments where barrier film layer 45 includes reinforcing filler, the weight of bias ply layer 35 may be reduced, while maintaining good strength. In certain embodiments, bias ply layer 35 and adhesive layer 30 may be completely eliminated, and the weight of the laminated hull fabric may be reduced by up to about 30 percent. In one embodiment, the weight of laminated hull fabric 20 is less than about 6.75 oz/yd2, and in another embodiment, the weight of laminated hull fabric 20 is less than about 5.1 oz/yd2 In one or more embodiments, the strength to weight ratio of hull fabric 20 is from about 218 to about 259.
As will be appreciated, the hull 12 and fins 14 are typically not made of a single piece of the laminate material 20. Accordingly, strips or patterns of the material are adjoined to one another while still providing all the properties of the laminate material. The method of joining strips is not particularly limited. In one or more embodiments, a butt joint configuration is used, such as that described in copending U.S. patent application Ser. No. 10/388,772, which is hereby incorporated by reference in its entirety. In other embodiments, other methods are used, such as sewing, splicing, adhesive tape, and the like.
Based on the foregoing, the advantages of the present laminate material construction are readily apparent. In particular, the present constructions provide for high strength and low weight characteristics which allow for maximum altitude of the lighter-than-air vehicle while providing light weight construction to increase the amount of payload that can be carried by the vehicle 10. Indeed, the preferred laminate or material weighs less than 8 ounces per square yard. The combination of the materials provides excellent permeability to retain the lighter-than-air gas. The present invention is also advantageous in that the materials are flexible and can withstand wide temperature variations ranging anywhere from −130° F. to +158° F. In certain embodiments, the barrier layer is reinforced to improve shear modulus of the fabric laminate, while the bias ply layer is reduced or eliminated to reduce fabric weight. In other embodiments, and adhesive layer includes reinforcing filler that improves shear modulus and tear strength of the fabric laminate.
Thus, it can be seen that the objects of the invention have been satisfied by the structure and its method for use presented above. While in accordance with the Patent Statutes, only the best mode and preferred embodiment has been presented and described in detail, it is to be understood that the invention is not limited thereto or thereby. Accordingly, for an appreciation of the true scope and breadth of the invention, reference should be made to the following claims.
