I had the opposite happen..jump from cub flying to a jet (Consecutive flights) and I could not figure out why the jet was flying so crappy, all over the sky, etc.....it was my Cub thumb at work!! (jets do not need rudder when flying)

I've got a heavy overpowered 1/4 scale cub. It took a long while to get used to it, even though I have flown probably a dozen different cubs. Now I love it...and I get many comments on how realistic it flies...but it takes a lot of effort! When I'm up there I like to fly it on the ragged edge of the stall - keeping the wings level with the rudder..in a stiff breeze, it will have zero ground speed (I haven't managed backwards yet..

I had a H9 80" cub and wore it out..but I tell ya, the bigger 1/4 scale cubs fly three times better. I have to really, really work at getting it to snap or spin. It will taxi the length of the runway with the tail in the air, and will not nose over. Down side it is a pain getting it set up at the field....It's all good !

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On the ventral fin question..the real cub was STD'ed for at least two different floats (probably more now) One set required the use of a subfin for directional stability, the other did not...sorry, but I have forgotton the specific model numbers....so you can fly with it, or without it - your choice.