3d planes are able to fly on their control surfaces not just wing and stab. a 3d plane must be able to transition between standard flight and 3d smoothly - this is where light weight is important - heavy planes don't transition very well. engine needs to be just big enough to create necessary airforce to hold up the plane while it is stalled. an engine and big control surfaces are not required for 3d - you can do many 3d manuevers on a slope with 30 mph wind letting mother nature provide airforce/uplift for free.