You might search this forum for topics on location of the mean aerodynamic chord, or MAC. I believe the tools sticky at the top of this forum has some calculators. Also, search for neutral point, or NP. For a flying wing, the neutral point is at 25% of the MAC. I've built several flying wings, including a delta, and I have had success by locating the cg at a point that is 5% (of the MAC) ahead of the neutral point. Others may use a bit more or less, but that has worked for me, fwiw.