Well, the R70 will knife-edge spin once in a while, when my thumbs work right; now that my CG is where it should be, it flat spins beautifully (better upright than inverted). I don't think the edffective dihedral on the R90 is any more than on the R70. I'll be interested in seeing how the R90 flies, but i will not be able to wring it out for a while. New DLE55RA, so I'll have to take it a bit easy for a gallon or so.