Full aerodynamic design development of the proposed fans for the enlarged primary ventilation system at Mount Isa Mines Limited was initiated before tender specifications were prepared. Theoretical and analytical design studies were made of many possibilities to determine the optimum proposal. Major considerations were efficiency, simplicity, standardization, and mechanical feasibility. Model testing and experimental work covered blading design, inlet shape, diffuser and tail fairing dimensions, instrumentation requirements, ancl noise studies.Theoretical and predicted performance estimates were prepared for the three 20 ft diameter vertically mounted axial flow fans.