RE: 21x14 or 20x13???
I wasnt directly thinking about a spesific prop, but was trying to get som input if a smal prop with hirger rpm or bigger with lower rpm was the best choise. I have today a Himax 210 in a Spark using both a Falcon 21x14(wery good and silent until I rolled the plane out and one blade hit the ground..silly me) but change to a Apc 21x14 , this does the job but have some noise from vibration.
In the new plane I thinking maybe using a Q80 13 xs(I think that is correct "name") that are with is it 220 kw, this should be a nice combo with a 20x13, but will it be better with a 21x14 and lower kw.