Method for manufacturing a preform made of woven reinforcement fibers having a variable cross-section

A method for manufacturing a preform of reinforcing fibers woven along a longitudinal direction to be impregnated with resin to form a longilineal element having an evolutive transverse section, the manufacturing method comprising:

• simultaneously a reduction or an increase in a width of the preform, and
• an increase or a reduction in the height of the preform,
• the evolutive transverse section including on a length of the warp yarns (C) in constant number which are continuous, disposed in height along layers,
• wherein, for a reduction in the width, performing a change of weave introducing additional weft yarns (T) which thus increase a number of layers and simultaneously, tightening teeth of a longitudinal settling comb (P) in order to reduce a space between columns of warp yarns, and conversely, for an increase in the width, reducing a number of weft yarns (t) which decreases the number of layers and simultaneously, spreading the teeth of the longitudinal settling comb (P).