Your friend doesn't own any air rights . And you can't fly over someone else's property with your models. I don't know if the neighbor has the right to shoot a modle that keeps over flying his house or property. If he threatens you it is assault. IF he threatens to shoot a real airplane, then he is in deep do do. He does have the right to tell you that you cannot fly your models over his property.
You should make amends. It sounds as though every party involved is slightly in the wrong; you for flying over this man's property without his permission, and he is as fault for making threatening comments. You need to approach him, apologize for getting off on the wrong foot and see if you can negotiate an agreement. He could very well shut down your model flying. Not only can you not over fly someones property without their permission, but the noise from your models can only measure so high, (ex. 90db) at the edge of his property. The sound levels vary from state to state and even from one community to another. Some places don't have defined sound levels and its left to the discretion of law enforcement. It is possible that you have already wrecked the situation and negotiations are not likely. Good luck.