The recent letters on fixed pitch props noted that metal props are more
efficient at the tips because they can have thinner sections.
Flying thru rain favors metal props as well.
What would be involved in making an aluminum prop?
I see the pre WWII props were sometimes twisted from a comparatively thin
piece of stock, then profiled thinner toward the tips.  Today props appear to be
aluminum forgings.
Could a piece of aluminum bar stock be CNC milled, then hand finished at a
competative price?
What effects determine the alloy and heat treat of the bar stock? (toughness
vs hardness etc.)
What harmonic frequencies would be an issue, and how do you tune the prop to
avoid them?
What other questions should be asked?

The problem with aluminum is the low fatigue life.
Back in WW II they made hollow props out of pressed sheet steel brazed
or welded at leading and trailing edge. Heat treated 4130 steel sheet
has four or five times the fatigue stress limit as aluminum.
Some go as far to say that aluminum will eventually fracture no
matter how low the stress if it is allowed to flex.

I think the best material to use is carbon fiber.

Paul Lamar
 
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