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I thought the most interesting part of this was the part about the internal structure being classified. Naively I assumed that they were cast solid and then th

I thought the most interesting part of this was the part about the internal structure being classified. Naively I assumed that they were cast solid and then the surface machined to the exact shape, but it sounds like they either have internal passages or they're made of some sort of honeycomb to reduce weight? What else could be inside?

ars 8y ago
Some sort of sound deadening? Like how an empty and full can sound different?
Retra 8y ago
It could also just be material layering for stability, shaping, cavitation protection, noise reduction, strength, etc..
petee 8y ago
It could have been done like some jet engine blades, where a thin skin 'pocket' is pressured or vacuumed into shape during forging. Or perhaps simply, they are not made of metal anymore, albeit unlikely. You're probably closest with the internal passages though; if one of the primary issues is cavitation, there must be some solution to relieve that vacuum pressure from becoming too great, or absorbing the shock when it does
- dsfyu404ed 8y ago
  I would suspect that there's some internal structure made of a different material (steel, air, silly putty, whatever) that is tuned to act as a damper or allows the screw to flex in a certain way that changes its acoustic signature allowing it to be quiet at higher speeds like those crappy flex fans for car radiators. Casting in an internal pocket with sufficient accuracy(!) in a part so massive would have been very, very, very difficult/expensive if not impossible with the kinds of industrial process control that were available in the 1960s.
starbeast 8y ago
Could it be a bureaucratic reason where technically they have only declassified the shape, so therefore the inside could be said to still be classified and the Navy could waive it, but finds it funny to force civilians to lug the complete thing around for a while?

ars 8y ago

Some sort of sound deadening? Like how an empty and full can sound different?

Retra 8y ago

It could also just be material layering for stability, shaping, cavitation protection, noise reduction, strength, etc..

petee 8y ago

It could have been done like some jet engine blades, where a thin skin 'pocket' is pressured or vacuumed into shape during forging. Or perhaps simply, they are not made of metal anymore, albeit unlikely. You're probably closest with the internal passages though; if one of the primary issues is cavitation, there must be some solution to relieve that vacuum pressure from becoming too great, or absorbing the shock when it does

dsfyu404ed 8y ago
I would suspect that there's some internal structure made of a different material (steel, air, silly putty, whatever) that is tuned to act as a damper or allows the screw to flex in a certain way that changes its acoustic signature allowing it to be quiet at higher speeds like those crappy flex fans for car radiators. Casting in an internal pocket with sufficient accuracy(!) in a part so massive would have been very, very, very difficult/expensive if not impossible with the kinds of industrial process control that were available in the 1960s.

starbeast 8y ago

Could it be a bureaucratic reason where technically they have only declassified the shape, so therefore the inside could be said to still be classified and the Navy could waive it, but finds it funny to force civilians to lug the complete thing around for a while?