"RCE" wrote in message
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"Calif Bill" wrote in message
nk.net...

"RCE" wrote in message
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"Forrest" wrote in message
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I can't picture an aluminum prop continuously flexing without breaking.
A good one for "Mithbusters". What are you using the boat for? Do you
want to zoom from one side of the lake to the other as fast as you can
... or pull the kids around on a sled or a skier ... maybe tow a
dingy? I would just stick with the cheaper aluminum and increase the
pitch. How much depends on the above. Good luck


Better stay out of airplanes. Those aluminum wings flex big time. If
they didn't, the wings would break off the first time the plane hit some
turbulence.

Metal will flex without breaking as long as it does not exceed it's
yield strength. The yield strength of aluminum alloys is similar to
that of carbon and stainless steel.

RCE


Not true. There is no B-50 bearing type rating for aluminum. As long as
you stay below the yield strength in the flex in steel, that is true, but
aluminum wants to crack anyway. Airplanes just keep track of any cracks
and when they exceed a defined amount the part is replaced. I would
assume the airframe is designed so a single part failure is not
catastrophic.


I said aluminum alloys. Any of the structural aluminum alloys will flex
to their yield strength number without cracking. The internal monocock
frame structure of a modern jetliner flexes a foot or more over the length
of the wing. Next time you fly, note the relative position of the wingtip
to the fuselage while the plane is on the ground. Then, watch as you take
off and note the position of the wingtip.

Note table 1 at the following link. There are several aluminum alloys
that exceed the carbon steel yield strength of 60 ksi. The 5000 series
alloys are of particular interest for sal****er marine use.

http://elvis.engr.wisc.edu/UER/uer99...1/content.html

RCE


Another quick comment on aluminum. Although there are some high strength
alloys, the yield strength and ultimate strength (where it permanently takes
on a new shape or fails) are very close to each other, unlike steel.

RCE