I flew the 21 X 10.5PN this afternoon. In short - Perfect match for the 185cdi. The Valiant is just under 5kg's, so it isn't a light weight model either.
I used the exact same setup as for the 20.5 X 10PN. I didn't even have to adjust the mixtures, which probably means I was still a bit too rich on both.
Idle is a rock steady 1700, which is similar to the 20.5 X 10 but more stable. Throttle trim position is unchanged also. Top RPM was 7300 for the 20.5 X 10. The 21 X 10.5 killed 500 RPM and now sits at 6800. Noise at full throttle is noticeably less which is a result of the reduced revs. It's a much more pleasant throaty roar.
As far as flying, well, it just does it better than the 20.5 X 10. The plane tracks better and requires less throttle stick movement, which means a reduced work load. I pull into a vertical the same as with the 20.5 and feed on the power as usual. There's no need to throttle up earlier. The difference is I stop at around 5/8ths throttle and just leave it there. It doesn't slow down at all, just keeps pulling until it's time to push over or whatever. Throttle control for the figure 9 with 4 point roll up also uses the same technique. Basically set and forget. Down lines are more constant speed as well.
With the 20.5, I had to be more aware of throttle control coming down the back side of loops as the engine rpm would increase noticeably. With the 21 X 10.5 it doesn't do this.
This prop makes really good use of the mid range torque that the cdi produces.
I have a gut feeling that fuel consumption is less also. It's certainly no worse. Really looking forward to getting some more flights with it over the next few days.
Last edited by drac1; 10-23-2015 at 01:41 AM.