ORIGINAL: dick Hanson
I have used some props in 30 and 34" diameters on up to 20 hp motors ( ZDZ 160 and 210 to be specific)
the rated pitch on the best ones is 14". the 45 lb model on th 210 pulls vertically from a stop at 1/2 throttle and about 1/2 max rpm (well a bit more )
Watching the performance of the relatively narrow and almost symmetrical foil blades is an eye opener. the best ones - have extremely thick hub and a very pronounced twist right from the hub
These pull like a tractor even at low rpm ,yet provide excellent speed.
The material is one reason - all carbon fibre,
hollow for weight considerations and stiff as possible.
The "Clark Y" shape is really not used tho the backside is flatter than the face. These run in the 2000-6000rpm range
If you look at the blades (back a few posts) on my current selections of props for EFlite 15 thru 60 electric motors for 3d and some speed setups you see the extreme twist at base of many APC
These guys do have it figured out -based on results
A friend has some smaller ,excellent wooden props from Czech Republic which also work well The big props I mentioned are ZM which are also Czech prop designs
One thing we foundfor certain
the thin wooden props which flex when working, are for us-
worthless.
or worse
A properly designed and constructed prop will be effective through out the rpm range. APC is excellent for lower power (maybe up 5 HP). What these guys got right is blade area distribution and proper material choices for thin yet very stiff blades. They reduced area from the 70% station out to the tips, removing unecessary tip vortex amplitude which does nothing more than rob power to produce drag and noise.
I am doing the same thing with wood and refinishing with carbon cloth. Most wood props I have seen are just too thick for stiffness and have too large an area at the tips. I start with larger than needed and rework the blades to get better twist profile than the original, more closely resembling APCs. Depitching the tips of woodies is also desirable to unload the engine. A wood/carbon prop is a very good compromise and at a favorable weight to APC
Reccommended reading: Propellers, the first and final explanation by Jack Norris. At least it's reccommended if you are interested in theory, design and practice of why props do what they do. It's actually two books in one; the second he calls the Logic of flight, the thinking man's way to fly. The book is cheap considering what he gives you. We spend more on one prop. And BTW, the stuff I do to woodies I gleaned from Norris.
MattK