A couple of years ago I was surprised to see the aluminum blade of a four blade air conditioner fan develop a classic fatigue crack. If I had not noticed it in time it probably would have destroyed the condenser and triggered a $10,000+ replacement.

The odd looking 5 blade fan of a 1995 Ram is all steel with a stiffening rib.
Designed for low noise and maximum fatigue life?
I wish it was a split hub design that would make it three times faster to take off or remove.