Why would lift coefficent change with weight on swept-wing aircraft? Today I encountered a problem. There is a book saying, "Why does the lift coefficient of a swept-wing airplane decrease with the increase in the weight of the airplane?" I cannot think of the reason. Isn't the lift only coefficient related to the state of the wing?
A swept wing has less torsional strength than a straight wing, ie there's less structure at 90d to the root supporting the tip of a swept wing. 
Thus a swept wing twists when it's loaded, which unloads the tips and thus generates less lift at higher weights.