and rear edge of a blade it has substantially the same outline as the adjacent part of the associated blade and in a middle region between the front and back edge is wider by an approximately constant amount than the adjacent part of the blade application_number US 55349605 A description in the figures that follow the same reference characters are used in each case for identical or identically functioning components incremented by 100 if applicable e g 122 instead of 22 and these components are usually described only once fig1 shows an equipment fan 10 of ordinary design the present invention can be realized implemented in an axial fan and alternatively in a diagonal fan fan 10 depicted in fig1 has an external housing 12 at the four corners of which respective mounting openings 14 are provided and which defines in its interior an air conveying conduit 16 which conduit is limited toward the outside by a rotation surface 17 and in which conduit is rotatably mounted via struts 18 the central hub 20 of a fan wheel 22 that in operation is rotated about a central axis 25 fig4 and 5 by an electric motor arranged inside this hub 20 in fig1 hub 20 rotates counterclockwise in the direction of an arrow 24 the air flow is such that the air is blown out over struts 18 i e through the back or u201c delivery u201d side of fan 10 with reference to fig1 as fig1 to 5 show five fan blades 26 labeled 26 a to 26 e are mounted on outer periphery 27 of hub 20 in this exemplifying embodiment the angular distance beta fig2 from front edge 28 a of fan blade 26 a to front.