Serafim, I'd guess you could almost fly a 1/4 scale Cub with a .90. It would be at the lower end of the power spectrum, but would work. 1/4 scale comes out to 108 inch wing. I have a 1/5 scale L-4, 84.5 inch wing, weighs ten pounds. I have a .65 Saito in it and it is plenty. The plane will cruise at 1/4-1/3 throttle, and does a nice scale, extended roll takeoff at 1/2 throttle. At full throttle it comes off the ground in about 20 feet. The .65 is enough to turn a scale prop (14 inch). An 18 is scale for a 1/4, and the .90 should be able to spin that okay. I don't know where you could find an ARF that size, the biggest one I know of is the Dave Patrick Super Cub, but I think it needs more than the .90. Next down , as far as I know, is the large GP .60 size, or the Hangar 9, which flies just fine with a .56. But hey- that's why they put throttles on these things