In reply to a message from Ed Nantes sent Fri 14 Nov 2014:
The blades are at uneven angles to prevent a phenomenon
known as beating or wake chopping, where the blade passing a
stationary object like a hose or even the fanbelt causes a
noise, so uneven spacing breaks up the frequency and the fan
should be quieter.
Modern plastic fans are also unevenly spaced.
Here is a study by Hyundai.
http://papers.sae.org/2008-01-0569/
The electric Bosch auxiliary fan on my 120 has uneven blades.–
XK120 FHC, Mark V saloon, XJ12L Series II, S-Type 3.0
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