Absolutely. I got 3 in this afternoon using the 18.1x10. I don't think I ever got above half throttle. To be fair, half throttle on my set-up opens the butterfly about 70%. In other words, half throttle is more than half power, more like 3/4. Regardless, the prop is just not enough load. Quite loud compared to glow (same prop). A good break in prop tho, for a piped set-up in a pattern plane.
Top speed in the air had to be at least 8400. It was ripping pretty good. The plane is a very light load compared to what I've been running the SAP in, both in terms of weight and in terms of drag. And BTW, today was pretty warm down here, around 90F and more muggy than we have ever run the engine in before. No problems I could tell...handled great
One good suggestion from today's gallery was to use a 3 bladed prop. I think I have a 15.75x13 3B stock. Worth a try. I need to quiet this thing down
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Regards,
MattK
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.