I began with an iFlight I, which, as other fliers have found, tended to oscillate (pitch up, stall, dive, recover, and pitch up again. On advice of an iFlight I Vented flier, I photographed his to get the exact dimensions of the vent, and cut a vent in my unvented iFlight I. That cured the problem. Now, with the delightful, easy, slow glide of my iFlight II, I hardly ever touch the iFlight I any more.