I don't know how anyone can say the RV-4 is anything but a fantastic flying airplane. I built mine with flaps and installed an OS .46FX. It will not go vertical forever, but it will do it for a pretty long time. Loops, rolls, snaps and even knife edge are possible. I couldn't be happier with mine. It's just necessary to take some care while building so the weight doesn't balloon. IMHO it's nice to have a model that actually looks like an airplane though.