Abstract:
An erosion protection system and method applicable to foils or aerodynamic surfaces. Single element erosion protective elements having joggles are provided, each single element being alignable with the next to provide a contiguous erosion protection layer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to erosion protection systems and methods and more specifically to erosion protection systems and methods for airfoils or other aerodynamic surfaces. 
         [0002]    Foils and other aerodynamic surfaces are typically susceptible to erosion. For example, the rotor blade of an aircraft can be subject to sand erosion and wind erosion. It is for this reason that that a protective abradable layer is usually applied to leading edges of foils and other such aerodynamic surfaces. 
         [0003]    The abradable or protective surfaces can usually be applied as an adhesive to the leading edge of the foil or can be a high polymeric material that is sprayed on or otherwise applied to the leading edge area. To apply the erosion protection layer, a user typically needs to mark the foil leading edge so that the erosion protection layer is aligned with the foil leading edge. U.S. Army application TB-1-1615-351-23 generally discloses procedures for marking out and affixing tape to form an erosion protection layer. 
         [0004]    It is not unusual for a user to spend significant amounts of time marking the foil leading edge. A user can also inaccurately mark the foil leading edge due to fatigue, inexperience or other factors. 
         [0005]    Such an inaccurate marking can affect the performance and mass balance of the aerodynamic system. In turn, mass balance errors and aerodynamic changes often result in increased engine/rotor testing on the ground and in flight to track and balance the system. 
         [0006]    Erosion protection layers or materials often become abraded or become worn out over time. In such a case, the aerodynamic system or aircraft is returned to the maintenance base where the user or specialist removes the abraded erosion protection tape. Alternatively, the the foil or rotor can be removed from the aircraft and returned to the maintenance depot where the specialist can then remove the abraded erosion protection layer in its entirety. 
         [0007]    It is within the above-described context that a need for the present invention has arisen. Consequently, there is a need to address one or more of the foregoing disadvantages of conventional systems and methods, and the present invention meets this need. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    Various aspects of an erosion protection system and method can be found in exemplary embodiments of the present invention. 
         [0009]    In a first embodiment, the erosion protection system of the present invention is applicable to the leading edge of foils or aerodynamic surfaces to provide a protective abradable layer. The erosion protection system includes one or more single protective elements that can be mated to each other laterally to provide a contiguous erosion protection layer. 
         [0010]    Each protective element includes a female joggle at a proximal end and a male joggle at a distal end. In this manner, the male joggle of one protective element and the female joggle of an adjacent protective element are aligned and mated to provide a contiguous protective layer. Thus, unlike conventional systems, the entirety of the erosion protection layer need not be removed when a particular section is eroded. Further, users need not spend significant amounts of time marking the foil leading edge thus avoiding inaccurate marking of the leading foil edge, which in turn avoids detrimental effects on performance and mass balance of the aerodynamic system. 
         [0011]    A further understanding of the nature and advantages of the present invention herein may be realized by reference to the remaining portions of the specification and the attached drawings. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, the same reference numbers indicate identical or functionally similar elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates a generic foil on which an erosion protection system can be applied according to an exemplary embodiment of the present invention. 
           [0013]      FIG. 2  illustrates an erosion protection layer according to an exemplary embodiment of the present invention. 
           [0014]      FIG. 3  illustrates an erosion protection layer according to an exemplary embodiment of the present invention. 
           [0015]      FIG. 4  illustrates an erosion protection layer according to an exemplary embodiment of the present invention. 
           [0016]      FIG. 5  illustrates a male protective element and a female protective element completely mated and applied to leading edge of a foil according to an exemplary embodiment of the present invention. 
           [0017]      FIG. 6  illustrates an erosion protection layer according to an exemplary embodiment of the present invention. 
           [0018]      FIG. 7  illustrates two protective elements relative to a transverse cross section of a main rotor blade. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Reference will now be made in detailed embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as to unnecessarily obscure aspects of the present invention. 
         [0020]      FIG. 1  illustrates generic foil  100  on which an erosion protection system can be applied according to an exemplary embodiment of the present invention. 
         [0021]    In  FIG. 1 , among other components, generic foil  100  comprises foil leading edge  102 , aero/hydrodynamic surface  104  and foil trailing edge  106 . Generic foil  100  has curved surfaces providing a favorable ration of lift to drag. 
         [0022]      FIG. 2  illustrates erosion protection layer  200  according to an exemplary embodiment of the present invention. 
         [0023]    In  FIG. 2 , erosion protection layer  200  comprises a plurality of protective elements: namely, male protective element  202  and female protective element  204 . These elements are applicable to foil leading edge  102  ( FIG. 1 ) to provide an abradable surface that provides erosion protection to foil leading edge  102 . Male protective element  202  and female protective element  204  can be aligned to form a contiguous erosion protection layer as further described with reference to the figures below. 
         [0024]    Each protective element might be a film surface or tape that is machined, polymeric or polyurethane tape element. This layer is attached by a high sheer strength adhesive that permits flexure of the layer for conform or fitment to the substrate. 
         [0025]    The substrate can be a wing, an aerodynamic surface or foil such as a rotor blade that allows for the removal of the layer after use. Protective elements  202  and  204  include a plurality of inverse V-shaped ends  206  along transverse edge A as well as a plurality of inverse V-shaped ends  208  along an opposing transverse end B. Male protective element  202  includes a male joggle  210  while female protective element  204  includes a female joggle  212  as further described with the diagrams below. 
         [0026]      FIG. 3  illustrates erosion protection layer  300  according to an exemplary embodiment of the present invention. 
         [0027]    In  FIG. 3 , erosion protection layer  300  includes protective elements  302 ,  304 ,  306  and  308 . As shown, protective elements  302 ,  304 ,  306 ,  308  have been aligned and mated so that they form a single contiguous erosion protection layer  300 . 
         [0028]    Male joggle  310  and female joggle  312  are observable at either end of erosion protection layer  300 . Specifically, male joggle  310  is observable at a distal end C while female joggle  312  is observable at a proximal end D. Erosion protection layer  300  also includes a plurality of vent/rip stop  312  that provides venting to the erosion protection layer as well as prevents the erosion protection layer from premature ripping. 
         [0029]    In  FIG. 3 , the exemplary length from transverse end A to transverse end B given by x can be 115 mm in length, tolerance+ or −1 mm. Ripstop  314  has an exemplary length of 18 mm (millimeters). 
         [0030]    The spanwise length y might be 300 mm+ or −1 mm. Exemplary thickness c of erosion protection layer can be 0.370 mm. Here again, as in the previous embodiment, erosion protection layer  300  can be elastomeric material such as polyurethane or other comparable materials. In this exemplary embodiment, the calculated mass of erosion protection layer  300  is 11.9 grams. 
         [0031]      FIG. 4  illustrates erosion protection layer  400  according to an exemplary embodiment of the present invention. 
         [0032]    In  FIG. 4 , application of erosion protection layer  400  on generic foil  406  is illustrated. Specifically, application of erosion protection layer  400  onto leading edge  407  of generic foil  406  is illustrated. Generic foil  406  might be that of an A016-X rotor blade. 
         [0033]    As shown in  FIG. 4 , erosion protection layer  400  includes male protective element  402  and female protective element  404 . Male protective element  402  includes male joggle  408  at a distal end and female joggle  410  at a proximal end. Female protective element  404  includes female joggle  412  and male joggle  414 . As previously noted, generic foil  406 , as shown, is the leading edge of a rotor blade. 
         [0034]    An advantage of the present invention is that erosion protection layer  400  is separated into component elements, i.e., male protective element  402 , female protective element  404  and additional protective elements not shown. The separate components permit replacement of a single separate component that is damaged without requiring additional work on the other elements or without requiring tracking and balancing. 
         [0035]    In operation, a user begins by applying male protective element  402  onto the leading edge  407  of generic foil  406 . Preferably, both male protective element  402  and female protective element  404  are both transparent although other nontransparent, semi-opaque, opaque or matte materials may be used. 
         [0036]    If leading edge  407  has a small radius, no marking is required. Here, the user begins by contacting male protective element  402  onto leading edge  407  so that a clear line mark (not shown) is visibile in the adhesive. The clear line mark is a reverse transfer image deposited on the adhesive. The clear line mark can then provide target alignment marks relative to female joggle  410  and and male joggle  408 . If a user requires an opaque element as opposed to a transparent element, leading edge  407  is initially marked, and the opaque element is aligned using the leading edge markings against the joggles. 
         [0037]    Use of transparent protective elements is advantageous because it permits the contact point on the surface of leading edge  407  to be visually observed. Once male protective element  402  is firmly in contact and pressed onto leading edge  407 , female protective element  404  is then mated with male protective element  402 . Mating is accomplished by aligning male joggle  408  of female protective element  402  with female joggle  412  of female protective element  404  in the direction of arrow E as shown until male joggle  408  and female joggle  412  are completely butted. 
         [0038]    Male joggle  408  and female joggle  412  permit male protective element  402  and female protective element  404  to be vertically aligned and positioned on leading edge  407 . The lateral position of the joggles also provides an exact alignment point for the contact point of male protective element  402  and female protective element  404  on leading edge  407 . 
         [0039]    An advantage of the present invention is that not only is vertical alignment accomplished in the first instance, lateral positioning for the adjoining elements based on the joggles on both lateral extremities of the protective elements is accomplished. The joggles provide skew alignment along the lateral extent. 
         [0040]    By using elastomeric materials, the present invention permits accurate butt joints to be obtained resulting in full protection of the extent of the leading edge  407  of the rotor/blade. The contact point of the transparent protective elements  402  and  404  provides visible witness mark in the adhesive. This mark is then used to align with the joggles or other surface markings on a protective element to achieve accurate registration of position. 
         [0041]    In an alternate embodiment, leading edge  407  may be marked to visually align with joggles  408 ,  410 ,  412  and  414  which are preferably transparent. Note transparent elements without joggles can be aligned visually with the surface by having a marking applied to either the upper or lower face of the element. 
         [0042]    In such a case, the contact point to the surface provides a witness mark in the adhesive that can be assessed for alignment against the markings on the element. An opaque element can be aligned with a substrate where the substrate has a marking that can be aligned with any of the joggles on the upper surface alignment mark on the element. 
         [0043]      FIG. 5  illustrates male protective element  402  and female protective element  404  completely mated and applied to leading edge  407  ( FIG. 4 ) according to an exemplary embodiment of the present invention. 
         [0044]    In  FIG. 5 , male protective element  402  and female protective element  404  form a single protective layer that is contiguous and that provides erosion protection to leading edge  407 . The spanwise alignment at F in  FIG. 5  is 0.00 mm, tolerance−0 mm+1 mm. This indicates that the spanwise alignment between male protective element  402  and female protective element  404  is 0 and that the two elements are tightly fitted using male joggle  408  and female joggle  412 . 
         [0045]    Protective elements  402  and  404  are adjacent and are aligned vertically via joggles  408  and  412 . As previously discussed, alignment of leading edge  407  markings against joggles  408 / 412  leaves a clear line (not shown) in the adhesive. Vertical alignment is indicated by the vertical error of the joggles to the clear line. The skew of protective element  404  relative to protective element  402  is indicated by the differential in vertical error of both joggles. 
         [0046]    For example, if joggle  408  has L+2 mm, R+2 mm, then the protective element is 2 mm low from the required location. Visually, this can be judged as the joggles are semicircles of say 3 mm diameter, and the human eye is effective at recognizing the shape difference between a part circle and a half circle. 
         [0047]    For example, if a joggle is L+1 mm, R+2 mm, the protective element is both low and skewed. The error need not be measured. The positioning is done by holding one end of the protective element in position while positioning the other end by the estimated error observed, then doing the same to the other end. Once the first element is located, then the next element is fixed in place at the adjacent end by the joggle and the butt joint of two elements. The remaining requirement is only to get the vertical position of the other end of the element to the blade&#39;s leading edge. 
         [0048]    An advantage of the present invention is that the location of the protective elements are accurate and faster. Unlike conventional systems the require wholesale replacements of tape, by using single elements, the present invention allows permit replacement of single components of an erosion protection system. The present invention reduces cost and maintenance time and increases asset availability. In addition, in situ repair of patches resulting in changes in a mass that then requires track and balancing of the rotor/blades is reduced. lability. 
         [0049]      FIG. 6  illustrates erosion protection layer  600  according to an exemplary embodiment of the present invention. 
         [0050]    In  FIG. 6 , erosion protection layer  600  has been applied to main rotor blade span  606 . Erosion protection layer  600  comprises five protective elements, namely protective element  602 , protective element  604 , protective element  606 , protective element  608  and protective element  610 . The elements are aligned to form single contiguous erosion protection layer  600 . 
         [0051]    Here, the exemplary spanwise length x of erosion protection layer  600  is 1,500 mm. Consequently, each protective element  602 ,  604 ,  606 ,  608  and  610  is 300 mm in length. Here, the length of main rotor blade span  606  is 3,835.40 mm. 
         [0052]      FIG. 7  illustrates protective element  702  and protective element  704  relative to a transverse cross section of main rotor  700 . 
         [0053]    In  FIG. 7 , main rotor  700  might be an A016 rotor. Exemplary dimensions for protective elements  702  and  704  as they relate to main rotor  700  are shown. Here, length h between the tip of leading edge  706  and bond line  708  is 24.56 mm. Protective element  702  is dimensioned to sufficiently cover this area as shown. 
         [0054]    Length j representing the distance between the tip of leading edge  706  and the forward extent of the valley  718  of protective element  702  is 28.70 mm. Length k between the tip of leading edge  706  and the outermost edge  720  of protective element  702  is 52 mm. Length m between the tip of leading edge  706  and OEM erosion paint rear edge  722  is 35.02 mm. 
         [0055]    The chord C of main rotor  700  is 183 mm. The transverse length q of protective element  704  from one transverse end T 1  to a second transverse end T 2  is 115 mm. One skilled in the art will understand that these exemplary dimensions and other dimensions consistent with the spirit and scope of the present invention can be utilized.