ORIGINAL: cmoulder
It'll be interesting to see how the 3-blade works out. I suspect it is too much pitch and less efficient, but it will be much quieter. The drop in dB's between the 18.1x10 and the 15.5x12W is quite significant.
Regarding props, I ordered a couple more of the 15.5x12W's from GravesRC because they seem to be an unusual size and therefore perhaps hard to find in the future. Also ordered a 16x12 pattern from Tower to test, which is probably a much more common species that is going to be around a while. If the 16x12 is just not quite the ticket (think ''Goldilocks Principle'') I will stock up with several more of the 15.5x12W's while they are available.
For the throttle, I started off trying to outsmart the set-up with mechanical differential by setting the servo arm at 90 degrees to the linkage at idle, reasoning that most of the movement of the butterfly would occur at the low end with much less at the high end, where the linkage and the servo arm ended up in a straight line with each other. Then I fiddled around with expo to try to tweak it, mainly because I couldn't figure out how to program a 5-point throttle curve on my 9caps despite much head banging. Sounded fine in theory, but never could get rid of that jump at about 1/3 throttle.
Finally just set it up ''normally'' with pretty much even arc on either side of the servo range, tweaked the expo a little and for some reason the transition is damned-near perfect with the 15.5x12W. The prop load must be juuuuust right!
You can't beat serendipity.
Bob,
I've loaded the engine down on purpose, basically to see what it will do. I am with you on this...I definitely have found the outside of the envelope. Just because the engine can turn this size prop at high rpm doesn't mean it is "happy" doing so. That's one key reason throttle response has been so non-linear
Unloading the engine to a degree will probably allow it to handle the way Todd originally designed it. Reason why Sport fliers are turning the small props. Engine is certainly happier and responds more linearly. Focus and Temptress are very similar lighter loads so they don't need a whole lot of prop to fly right. Backing off on prop size ma be the right thing to do
Only have 11 runs on the new engine so far and it is coming along nicely. I feel the compression developing the way it should as the surfaces wear in properly. Hoping to get some flight time today. I'll fly the 17x12 today which is practically the same load as the 18.1x10. I don't expect the throttle to behave any differently but do expect the noise to reduce. I have not found the 15 3/4x13 3B so I am back to well known performers like the 17x12 which is an all around great performing prop for Pattern planes