RE: OS FS 91 is it capable ?
10 pounds is my absolute limit on the 91 four strokes, and I am a lot happier with them when the weight is 8 pounds or less.
It all depends on what you want out of the plane.
At 14 1/2 pounds the 91 will probably be able to fly the plane but you will have to fly on the wing 100% of the time and to do loops you will have to dive first to pick up enough speed to get over the top.
What kind of ballast is required to balance the plane ?
If it is taking nose weight I would bolt on what ever engine would eleminate the ballast.