round prop vs. pointed?

[dana]

whats the difference?

[Diegoboy]

???
My Octura V props are lifting props and they are very pointed.
http://www.offshoreelectrics.com/prodimages/small__04_04_2007_08_21_oct-v-series.JPG



Octura 17 series props are the highest lifting props.
http://www.offshoreelectrics.com/prodimages/small__04_04_2007_08_37_oct-17-series.JPG



On the other hand...
Octura 16 series props are high lift props and are rounded.
http://www.offshoreelectrics.com/catimages/octura-1640-cat.JPG



I have to assume it has nothing to do with lift. It looks like lift is directly related to pitch

[Diegoboy]

I recall hearing that the pointed props tend to cavitate before getting on plane, but have a faster top end. :confused1:

[dana]

Yes diegoboy I have to agree... But why even make a rounded prop if pointy are faster and not lift related?

[dana]

I guess if rounded props cavitate less, then they would be better for short courses

[m4a1usr]

whats the difference?

Blade shape does have certain effects related to performance. The 2 most common you pointed out are the tapered, or cleaver/straight edge, and the eliptical or rounded edge. If we look at real props used in aircraft we can see they fall into 2 catagories for performance. Rounded tip props are used when tip vortices are required to be at a minimum. So it has less to do with pitch and chord design. But its still important to consider blade shape and geometry. Now for cleaver or tapered props you see the rake angle different in comparison to keep the turbulance or drag minimized. And you will see blade face shape designed much differently. But both are subject to engineering design. What works for one does not work well for the other. In fact they are different critters.

I know that didnt answer your question but if you think about them from their design defferences it might be obvious in their applications. Riggers tend to like the eliptical design and monos/cats tend to like cleavers. My own opinion is that cleavers with cup designed into it produce the narrow thrust cones while reducing or not creating anymore lift. Eliptical blades, since they have more back edge require greater attention to cup location and do inccurr more lift or drag because the area to be cupped varies in relation to diameter. Thats just my opinion, not fact but if you look trailing edge design this has greater influences. Just my 2 cents, nothing more.