A control system for forming a tapered structure includes a sensor providing feedback for a machine for forming a tapered structure including at least three rolls having at least one bend roll and at least two guide rolls. The guide rolls may include rollette banks having a plurality of rollettes. The machine may also include an adjustment mechanism to position at least one of the rolls, where a diameter of the tapered structure being formed is controlled by relative positions of the rolls. The machine may also include a joining element to join edges of a stock of material together as it is rolled through the rolls to form the tapered structure. The control system may also include a controller to receive feedback from the sensor and to send a control signal based on the feedback to the adjustment mechanism for positioning at least one of the rolls.

Apparatus (10) for forming a spirally wound conduit (14) from a flat strip (2) comprising: a forming device (6) comprising a bending section (7) configured to spiralling bend the strip (2) and a joining section (8) configured to join opposite longitudinal sides (2A,2B) of the strip (2) each other; a feeding device (11) of the strip (2) along a feeding direction (F) parallel to the longitudinal edges (9) of the strip (2); a cutting device (1) arranged upstream the forming device (6) comprising a cutting head (3) for cutting the strip (2) and moving means configured to move said cutting head (3) along a plurality of moving axes (X,Y,Z) orthogonal to each other; a control unit (18) configured to command said moving means according to diameter (D) of the conduit (14) to be realized and to the width (B) of the strip (2) so that said cutting head (3) realizes on the strip (2) a plurality of arrays (12) of holes (13) each one tilted with respect to one of the longitudinal edges (9) of the strip (2) by an angle () function of the width (B) of the strip (2) and of the diameter (D) of the spiral conduit (14) to be realized. The present invention relates also to a air conduit (14), a perforated strip (2) and a coil (19) of a perforated strip (2) comprising a plurality of said arrays (12) of holes (13) wherein said holes (13) comprise at least two different shapes.