Method of making composite material stiffeners

1. A method of making at least one stiffener element, the method comprising the steps of:

cutting out two substantially identical elongate flanks ( 2 , 4 ) from fiber plates, each flank presenting two lateral projections ( 10 , 14 ) on either side of a central portion ( 6 );

superposing the flanks ( 2 , 4 ) and stitching them together along two parallel lines ( 8 , 12 ) that mark the boundaries between the lateral projections and the central portions; and

folding the lateral projections ( 10 , 14 ) along the lines of stitching to either side of the assembly as formed in this way in order to form flanges ( 22 , 24 ),

wherein the central portions ( 6 ) of the flanks extend beyond the lateral projections in order to define at least at one free end ( 16 , 18 ) of the stiffener element.

2. A method according to claim 1 , wherein at least one reinforcing element ( 30 , 32 , 34 ) cut out from a fiber plate is stitched on the free end and is stitched at the free end.

3. A method according to claim 2 , wherein a plurality of reinforcing elements ( 30 , 32 , 34 ) are stitched on either side of the free end.

4. A method of making a stiffener element, the method comprising the steps of:

cutting out two substantially identical elongate flanks ( 2 a , 4 a ) from fiber plates, each flank presenting two lateral projections ( 10 a , 14 a ) on either side of a central portion ( 6 a );

superposing the flanks ( 2 a , 4 a ) and stitching them together along two parallel lines ( 8 a , 12 a ) that mark the boundaries between the lateral projections and the central portions in order to obtain a first stiffener blank ( 40 a );

cutting out two substantially identical elongate flanks ( 2 b , 4 b ) from fiber plates, each flank presenting two lateral projections ( 10 b , 14 b ), on either side of a central portion ( 6 b ), the flanks presenting at least one free end ( 16 b );

superposing the flanks ( 2 b , 4 b ) and stitching them together along two parallel lines ( 8 b , 12 b ) that mark the boundaries between the lateral projections and the central portions in order to obtain a second stiffener blank ( 40 b );

superposing the two stiffener blanks so that the free end ( 16 b ) of the second stiffener blank ( 40 b ) faces the central portion ( 6 a ) of the first stiffener blank ( 40 a );

stitching the free end ( 16 b ) of the second stiffener blank to the central portion of the first stiffener blank;

folding the second stiffener blank ( 40 b ) in such a manner that it extends transversely relative to the first stiffener blank; and

folding the lateral projections ( 10 a , 14 a , 10 b , 14 b ) at right angles along the lines of stitching ( 8 a , 12 a , 8 b , 12 b ) so that the lateral projections form flanges ( 22 a , 24 a , 22 b , 24 b ).

5. A method according to claim 4 , wherein reinforcing strips ( 52 a , 52 b ) cut out from a fiber plate are sewn onto the flanges.

6. A method according to claim 5 , wherein the reinforcing strips ( 52 a , 52 b ) cross at a junction of the stiffener element.

7. A method according to claim 4 , wherein a reinforcing cross ( 72 ) cut out from a fiber plate is sewn onto the flanges at a junction of the stiffener element.

8. A method of making a stiffened panel, the method comprising the steps of:

cutting a panel ( 60 ) out from a fiber plate;

making a stiffener element according to claim 1 or according to claim 5 ; and

placing the stiffener element on the panel and stitching the flanges of the stiffener element that face the panel thereto.