A Cub can fly with just a stiff wind, they need almost no power, a nice rubber band would do it. I have flown giant Cubs with the G-23, today it's the G-26 but same thing. The 30cc would be great in it. Just for fun go look at the CRRC engines, I fly with a few guys using them with good results. I think they go from the 26 right to the 40 but if I had the choice between a 30 and 40 I would go with a 40 every time. I has more uses down the road in different planes. The yellow Sukhoi I posted uses the Brison 2.4 40cc gas engine, it's an 80 incher but very light for it's size, I built it from plans I bought in MAN and did the mods for the gasser, it was designed for the 1.20 FS glow. Most anything with an 80 inch wing I go right to about 40cc gassers. I have the Brisons and they are more high performance then the new gassers from China.