Which Prop?

[JohnE]

I'm sure there are people out there that understand the advantages and disadvantages of different props. Let's just say I'm not one of them :) I'm flying a 60 size CAP 232 with a Saito91 and a 14x6 prop. This prop turns at 10K RPM. I went with the large prop to keep me slow, I didn't wan't to crash my new CAP the first day out!

Any idea what the ideal prop for this airplane would be? Should I stay with a 6 pitch prop and just change the diameter until I get the engine at it's peak RPM? I'm looking for a good balance between torque and speed. Any suggestions?

Thanks

John

[Dave Robelen]

Hi John,
I am a little sluggish in answering, sorry. My test for a prop match is to pull a large inside loop at full throttle. When the prop is well matched, I look to hear the mill slow just a little in the climb, and wind up a bit on the downhill. There are so many variables in the different brands of props, and the requirements of your plane, that it really is tough to be specific. If you really like the manuevers that favor the vertical, less pitch and more diameter are the way. The best match for good airspeed in rolling manuevers is usually a bit less dia. and more pitch. Often just changing the brand of prop will produce a nice match.
Regards, dave

[JohnE]

Thanks Dave, I guess I just need to buy a couple of props and test them to see which one I like. Looking at the manual for my Saito91 it has 3 catagories for prop sizes. Here they are:

Sport 12x8, 13x7, 13x8, 14x6, 14x8

Scale 13x7, 13x8, 14x5, 14x6, 15x4

Aerobatics 11x10, 11x11, 12x9, 12x10N (What is the "N" for?), 13x9

What is the difference in the catagories? Any idea what chriteria puts the prop in a specific catagory? Also am I correct in thinking the ordering in each catagory starts with the most speed and progresses to the most torque?

Thanks

John

[Dave Robelen]

Hello John,
As I read the chart, the emphasis for speed is on aerobatics, witness the 10" pitch. There is also a need to run the engine at lower rpm's in aerobatics, as noise from the prop and engine are taken into consideration in scoring. It appears that they put the emphasis for maximum thrust in the scale group, where many planes are heavy or draggy, or both. The sport group seems to split it down the middle. The "N" designator generally means a blade that is more narrow than normal.
Regards, Dave