Is there any way to determine what the minimum and optimum amount of lift is for a give spaceplane mass in stock? Currently, when I try and design a new plane and take it for a test flight, I have no idea if the poor performance is due to insufficient lift, too much lift/drag, or not enough thrust/power (moar boosters!). I am sure this all depends on each individual craft design, but is there any general rule of thumb people use? Edit: changed to answered. Thanks to all who responded.