An RC flight simulator is a computer program that allows pilots of radio-controlled airplanes to practice on a computer without the risk and expense of damaging a real model. Besides the obvious benefits of its use as a training tool, simulators are also used for practicing new aerobatics and evaluating a model before buying it, and of course for flying when it's dark and/or raining. Most simulators allow the importing of add-ons such as new models and landscapes. There are many websites dedicated to offering free content like this.