I've never heard of Diagonal Fans before, they seem to have a huge advantage over axial fans in the static pressure department!. A Papst 127mm Diagonal fan is quoted at having static pressure of 120PF at 100CFM, 75FP at 130CFM!. compared to a lowely 40PF at 100CFM, 35 at 130CFM for a Papst 127mm Axial fan.
Axial fans are the ones we are common/familiar with are'nt they?...
Why don't we hear about Diagonal fans?. what is the design difference between them and Axial?, they look the same to me, except the motor body seems to be rounded or 'bowl' shaped, a bit like an areoplane 'nosecone'. they perform better than 'squirrel cage/crossflow' and 'centrifugal/radial' fans from the little I've read on Papst's site...
Papst English version