Description:[0001] Title of the Invention
Split Doubler for Repair/ Reinforce The Damaged Skin in Inaccessible Places.

[0002] Field of the Invention
The present invention relates to split doubler customised to reinforce aircraft external skin, damaged due to various reasons such as bird hit, collision with ground vehicles airport installations, tool impact etc. on aircraft sub- assemblies like wing, stabiliser, air intakes, air channel, vertical/ventral fin etc. without removal of major structural components.

[0003] Background of the Invention
In the life span of aircraft there may be occasions of skin damages which needs to be repaired. Replacement of the damaged components may not be feasible in most of the cases considering the cost and assembly constraints and may require extensive dismantling. Replacement of the damaged component is exhaustive, time-consuming and labour intensive and may result in the structural integrity of the assembly. For few of the aircraft sub-assemblies, once build/ assembled are difficult to access the internal places. The damages in the accessible places can be repaired using conventional repair schemes. However, for repairs to be carried out on in inaccessible places require special tailor made repairs.

[0004] Brief Summary of the Invention
The present invention relates to installation of split doubler reinforcing the damaged area from internal side and cover plate from external side to flush with the surface of the aircraft skin maintaining the aerodynamic contour and structural integrity of the assembly. A doubler in two halves called as split doubler made from sheet, having length and width so as to insert through the cut out made on the external skin to remove the damages. The repair comprises of removing the damaged area i.e. puncture (8) and/or crack (10) on the external skin (4) by making a cut out (7) and (11) respectively and installing split doubler (12) from internal side customised to reinforce the nearby undamaged area of skin (4) and blanking the cut-out by installing cover plate (17) from external side. Split doubler (12) consists of cover plate (17), installed from external side on split doubler (13) and (20).Split doubler (13) (20) are installed on the undamaged portion of the skin (4) from internal side of inaccessible places in the area of cut out (7) and (11). Integrity of the split doublers is provided by reinforcement with additional plates (19) and (22). Split doubler and additional plates are secured by fasteners (31). Further details of the invention are elaborated in the following description and drawings.

[0005] Detail description of the drawings
The brief of the invention is better understood by reading the detail description and the accompanied drawings. The embodiment of invention is described with an example with reference to the accompanying drawings/ sketches in which:
Figure 1: view of damage (5) on external skin,
Figure 2: detail ‘A’ showing the cut out (7) and (11) for removing the puncture (8) and crack (10) on external skin,
Figure 3: installation of split doubler (12),
Figure 4: detail B shows the layout of split doubler (13) and (20), additional plate (19) and (22) and cover plate (17),
Figure 5: perspective view of split doubler (12)
Figure 6: cross section C-C,
Figure 7: cross section D-D,
Figure 8: cross section E-E,
Figure 9: cross section F-F,
Figure 10: installation of split doubler (13) and (20), additional plate (19) and (22) and cover plate (17) on external skin (4) using fastener (31).

[0006] Detailed Description of the Invention
The present invention provides details of cut out (7) and (11) to remove damaged external skin (4), split doubler (13) and (20), additional plate (19) and (22) and cover plate (17). The following specification particularly describes the invention and the manner in which it is to be performed:
Fuselage of aircraft (1) consisting of longitudinal stringer (2), web of frames (3) with external skin (4) forming a closed inaccessible volume as represented in Figure 1 and Figure 3. External skin (4) fastened to the stringer (2) and web of frame (3) is the boundary of inaccessible/ closed compartment.
Mark the outline for making cut out (7) and (11) on external skin (4) with one axis (16) and other axis (18). Provide radius fillet (9) and (6) at the corners of the cut out as shown on Figure 2. Make a cut out of length (G) and width (N) as shown in Figure 4 on the external skin (4) to remove damage.
The invention consists of split doubler (13) and (20), additional plate (19) and (22), cover plate (17) and fastener (31). Split doubler (13) and (20) are installed on the external skin (4) from internal side in the zone of cut out (7) and (11). Split doubler are further reinforced with additional plate (19) and (22) installed on split doubler (13) and (20). Cover plate (17) is installed on split doubler (13) and (20), fit flush with the external skin surface (28) maintaining the aerodynamic contour.
Split doubler (13) and (20) extends on both side of the cut out (7) and (11) from the central axis (16) of cut out (9) and (7). Split doubler (13) and (20) with dimensions length (H) and width (M) are of same thickness and are installed on the internal side of external skin (4) with gap (P) between both the parts (refer Figure 6). The split doubler are provided with fillet radius (14) and additional plate (19) and (22) are provided with fillet radius (15).
Additional plate (19) and (22) with length (J) and width (L) are of same thickness provided with fillet radius (15) are installed on the split doubler from internal side on the edge of cut out (7) and (11).
Cover plate (17) with length (N) and width (G) and thickness same as of external skin (4), provided with fillet radius (23) is installed on the split doubler (13) and (20) maintaining gap (O) with cut out (7) and (11). Surface (27) of external skin (4) is flush with surface (28) of cover plate (17).
The method for installation of the split doubler (13) and (20), additional plate (19) and (22) and cover plate (17) using fastener (31) is described below:
Locate split doubler (13) & (20) and additional plate (19) & (22) from external side of cut out (7) and (11) on external skin (4). Drill pilot holes through the external skin, split doubler and additional plate. Insert additional plate (19) and (22) initially and then split doubler (13) and (20) through cut out (7) and (11). Align the pilot holes on external skin, split doubler and additional plate and hold the split doubler and additional plate using suitable fastener at initial drilled holes.
Zone (25) and (26) represents the external and internal side respectively of the inaccessible places on the aircraft.
Drill holes through external skin (4), split doubler (13) and (20) and additional plate (19) and (22) for installation of fastener (31) as shown in figure 10. Install split doubler (13) and (20) and additional plate (19) and (22) on external skin (4) by using fastener (31).
Locate cover plate (17) on split doubler (13) and (20) from external side matching with cut out (7) and (11) on external skin (4). Drill holes through cover plate (17) and split doubler (13) and (20). Install cover plate (17) on split doubler (13) and (20) using fastener (31).
, C , C , Claims:1. A split doubler (13) and (20) intended to repair the damaged area from internal side (26) and cover plate (17) from external side (25) to flush with the surface (27) of the aircraft external skin (4) maintaining the aerodynamic contour, structural integrity and strength of the assembly. Split doubler from inaccessible/ closed compartments of aircraft comprising:
a cut out (7) and (11) on external skin (4);
split doubler (13) and (20) extends on both side of the cut out (7) and (11) from the central axis (16) of cut out (7) and (11);
additional plate (19) and (22) with length (J) and width (L) of same thickness provided with fillet radius (15);
cover plate (17) with length (N) and width (G) and thickness, same as of external skin (4), provided with fillet radius (23);
fastener (31);
wherein cut out (7) and (11) on external skin (4) ensures the complete removal of puncture (8) and crack (10) by maintaining length (N) and width (G) with radius (9) and (6) at the corners;
wherein split doubler (13) and (20) with length (H) and width (M) are of same thickness installed on the internal side (26) of external skin (4), with radius (14) maintaining gap (P) between both doubler;
wherein additional plate (19) and (22) installed on the split doubler from internal side (26) on the edge of cut out (7) and (11) reinforcing the damaged inaccessible zone of fuselage of aircraft;
wherein cover plate (17) installed on split doubler (13) and (20) maintaining gap (O) with cut out (7) or (11) and surface (27) of external skin (4) flush with surface (28) of cover plate (17);
wherein all the parts namely split doubler (13) and (20), additional plate (19) and (22) are integrated to the external skin (4) using fastener 31;
where in cover plate (17) is integrated to the split doubler (13) and (20) using fastener 31; and
wherein thickness of cover plate (17) is same as thickness of external skin (4).

2. The split doubler (13) and (20) as claimed in claim 1, wherein the length (H) and width (M) of said split doubler (13) and (20) is more than length (N) and width (G) of cut out (7) and (11) and width (M) is less than the length of the diagonal of the cut out (7) and (11).

3. The split doubler (13) and (20) as claimed in claim 1, wherein said additional plate (19) and (22) length (J) is equal to (M) + (M) + (P) and width (L) equal to ((H)-(N)/2).

4. The split doubler (13) and (20) as claimed in claim 1, wherein gap (P) is maintained between the doubler for expansion and contraction of material during atmospheric effects.

5. The split doubler (13) and (20) as claimed in claim 1, wherein gap (0) is maintained between the cover plate and external skin (4) for expansion and contraction of material during atmospheric effects.

6. The split doubler (13) and (20) as claimed in claim 1, wherein cut out (7) and (11) on external skin (4) can be used for removal of components or for removal of Foreign Object, or for managing access for reworks in the inaccessible places.

7. The split doubler (13) and (20) as claimed in claim 1, wherein the steps for installation of split doubler (13) and (20), additional plate (19) and (22) and cover plate (17) using fastener (31) on external skin (4), comprising:
mark the outline of cut out (7) and (11) with length (N) and width (G) on external skin (4) with one axis (16) and other axis (18) encompassing puncture (8) and crack (10);
make cut out of length (L) and width (M) with corner radius (9) and (6) of the cut out;
locate split doubler (13) & (20) and additional plate (19) & (22) from external side (26) of cut out (7) and (11) on external skin (4);
locate cover plate (17) on split doubler (13) and (20) from external side (25) matching with cut out (7) and (11) on external skin (4).
drill pilot holes through the external skin (4), split doubler (13) & (20) and additional plate (19) & (22);
insert additional plate (19) and (22) initially and then split doubler (13) and (20) through cut out (7) and (11);
drill holes through external skin (4), split doubler (13) and (20) and additional plate (19) and (22) for installation of fastener (31);
Install split doubler (13) and (20) and additional plate (19) and (22) on external skin (4) by using fastener (31);
drill holes through cover plate (17) and split doubler (13) and (20); and
Install cover plate (17) on split doubler (13) and (20) using fastener (31).