Hey guys I'm brand new. My son so spent his birthday money to get a RTF launch set. It says to use B4-4 for first flight. Which was fine because that's the only engine the store I went to had in stock. Now I saw a few almost ready and E2X on sale for $7 so I picked them up. I don't have the engines for 1st flight but I do have engines listed on the box how important is the first flight engine? And can you continue to use the first flight engine size over and over after the first flight?