Ok.......I think I'm on to something. I have two J-3 cubs and I've been having some battery problems. The lack of power would give me only 2-3 min of flight time so I'm looking into a lithium battery. However I started looking into changing the prop. So I'm in the hobby shop and then........THERE IT IS......Its a prop from megatech 4-bladed propeller for a P51D Mustang so I asked about it . They said it would work on the J-3. So $5.20 later I had alot more POWER. I tested it with out the wing and it wanted to jump out of my hand and thats with my bad battery. If anyone has battery INFO Please let me know.