[BRENT in 10-uh-C]

Over the years I have personally known quite a few folks who have joined the 'Failed Two-Blade Fan Fraternity' but has anyone ever done a study to see exactly why they failed?

Since I was a little kid, I have always been told that it was because they rusted from the inside but is this a "he said~she said" myth or fact?

Another theory I have been told is that the length of the blade is incorrect and the tips spin in a harmonics stage that fatigues the metal. While this may indeed be true, it is never the ends or tips that you see the crack. (I might add that it has been said that if ½" is removed from the tip of the fan blades, that they still cool just the same but the blade tip speed is slower and out of the harmonics area.)

So has anyone ever researched this enough to make factual statements why they fail? Your theory is, ...and 'why'??