"RCE" wrote in message
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"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
But Aluminum will still crack evnentually with any flex. Some of the Alloyw
are much stronger, but they will still crack with flex. 5086 is probably
the stongest of the aluminum alloys for boat building, stronger and more
sal****er resistant than 5082, but can not be formed like 5082 without more
cases of cracking.