Propeller Design Analysis

[flatWorld]

First, I want

http://www addresses

on online engineering forums which they will answer-solve related engineering problems,quickly and accurately.

Second, " A propeller for a lightwave speedboat capable for been used in inland waters or at sea is currently made out of brass (a copper alloy).In service, the blades are deflecting too much a high rotational speeds i.e(it is not stiff enough).Use a chart of Young's modulus (stiffness) against density to choose three alternative metals which are stiffer, but which will not lead to a heavier component, i.e(they are not greater in density than brass).If possible mention briefly the relative advantages and disadvantages of the alternatives, bearing in mind the service conditions.

Please if you can't help me on the appropriate problem give me

http://www addresses

for engineering forums which they can help me on similar problems (on-line).

yours,
Vorissi Aikaterini(UK) [sig][/sig]

 

[socrates]

Vorissi: I would have thought that such a prop would be made of stainless steel. However brittleness, durability, and ability to resist rusting are undoubtedly factors in the choice of brass. Prob technology is well understood and I would imagine that such information would be available at any school of naval architecture or speed boat consortium.
Sincerely, Socrates

 

[LTD]

Sounds very much like a school project...

School projects are to make YOU solve the problem, the school couldn't care less about propellers. They care about training you how to think.

If it's not a school problem, stainless steel propellers can be made in a thinner blade cross section, and with the resulting cupped and curved geometry are quite stiff for their weight due to the reduced volume of metal made possible by the thinner cross sections.

Aluminum is the obvious choice here. Many grades are very stiff and strong.

Design the blades to flex and reduce the pitch of the blades for quicker starts - the blade will not be bent as much at speed, and will revert to it's steep pitch which could be efficent at speed. Fatigue life is a factor... Carbon fiber blades?

Berylium ! You just don't get any better in the "specific" stiffness game ! Great corrosion resistance too! Just don't do any sanding or grinding on it... It's dust is evil for your lungs. Very very evil.

Stainless is the real option form medium size / high speed.
Aluminum is great for either small or medium large
Bronze is still king for larger non-military, due to costs.

 

[arunmrao]

There is no substitute for copper base alloys as far as this application is concerned. However you may consider some of the high strength stainless steel which are precipitation hardened or CA6NM stainless steel which is extensively used in hydro turbines.

Dr Arun RAo

 

[TCrush]

Another Material you might look at is a B-Al composite. Not sure how it would stand up to the stress though, I have not been able to locate any specific information on it, but I know it is used by NASA for some of there structural stuff (very light and very strong), and if anyone has this info I would greatly appreciate it....Good Luck