Multiblade fan

A multi-blade fan comprising:

• a spiral shaped housing including a bell-mouth orifice at one side, a sucking inlet and an exhausting outlet;
• an impeller disposed in the housing and including a plurality of blades supported by a main plate and a lateral plate at both axial ends of each one of the blades, said lateral plate located closer to the bell-mouth orifice than said main plate;
• and
• a motor for driving the impeller,
• wherein a cross section, cut along vertically with respect to a rotary shaft within a first given length, of each one of the blades has a given shape which allows a main air stream to flow along a back face of each one of the blades from a leading edge to a trailing edge of each one of the blades,
• wherein an axial length of each of the blades comprises a thin-walled section of a second given length and a thick-walled section of a third given length, said thick-walled section extending from said thin-walled section at a transition section so as to reach the trailing edge, the second given length being smaller than the third given length, a thickness of the thin-walled section being smaller than a thickness of the thick-walled section, said transition section oriented substantially perpendicular to the axial length of the blade.