Abstract—— This paper introduces an new method to simulate a guidance algorithm running on Simulink that controls a fixed wing unmanned aircraft model running on the flight simulator X-Plane, which simulates the vehicle dynamics, sensors, and actuators. It presents the necessary settings for running simulations on small aircrafts in X-Plane and explains the UDP communication between the flight simulator and Simulink. The functions and codes to interpret X-Plane packets are explicated in details, and all codes are written in Matlab language in order to facilitate the development. As a final implementation we propose a guidance algorithm based on waypoints to validate the Software-In-the-Loop where the UAV needs to complete two missions that are also presented in this paper. I. INTRODUCTION couple of decades ago engineers and researchers would need to build a prototype of an airplane in order to investigate the effects of control laws or guidance algorithms that they have developed [1]. The prototype would be used as many times as possible, which eventually would cause an accelerated degradation, leading to manufacture another airplane. Besides the degradation, if the engineer decided to change a parameter in the wing, as an example, he would need to build another wing, consuming more time. Nowadays Hardware-In-the-Loop (HIL) and Software-In-the-Loop (SIL) simulations are commonly used to evaluate controls and algorithms, because it easily allows to change the model (which would be the prototype), permits a fast development, increases the safety because you minimize the experimental flights, reduces the number of peripheral people involved, and consequently decreases the final cost of the project [2, 3]. A. Bittar was with the Instituto Tecnológico de Aeronáutica, São José dos Campos, Brazil when this work was perfomed and now is with Denver University, Denver, USA. (adrianobittar@gmail.com) H.V. Figueiredo and A.C. Mendes are with the Instituto Tecnológico de Aeronáutica, São José dos Campos, Brazil. This paper presents all the steps that are needed to implement a SIL simulation, where the model of the airplane runs on X-plane and the control and guidance algorithm runs on Simulink. It is described the configuration that is required to operate small unmanned aerial vehicles (SUAV) on X-Plane and Simulink functions developed to interpret X-Plane packets. Instead of using C functions as in [4, 5, 6] all the code is presented in Matlab language to facilitate the development. The motivation of presenting this work is to help researchers that are starting working on simulations and wanted to go one step further on using a reliable mathematical model use a reliable flight simulator to visualize the behavior of the aircraft and test new control ideas. Since there is a lack of detailed information on how to integrate Simulink with X-plane in literature, this paper can be used as a reference for engineers and researchers, who want to start developing Software or Hardware-in-The-Loop systems. Neither the controls laws nor the aircraft’s dynamic’s equations are presented here, because the paper focuses on the integration of X-Plane and Simulink. The controls details for the architecture presented can be found at [7]. SUAV dynamic’s equation can be found at [8]. The paper is organized as follows. The next section introduces the flight simulator X-Plane and the characteristics of the SUAV model used during the simulations. The two following sections detail the setting on X-Plane and Simulink, respectively. The fifth section details the proposed guidance algorithm. The overview implementation of Software-In-the-Loop is described in Section 6. Section 7 presents the results obtained. The conclusion discusses the validity of proposed modifications, based on the results obtained, as Guidance Software-in-The-Loop Simulation Using X-Plane and Simulink for UAVs Adriano Bittar, Helosman V. Figuereido, Poliana Avelar Guimaraes and Alessandro Correa Mendes A 2014 International Conference on Unmanned Aircraft Systems (ICUAS) May 27-30, 2014. Orlando, FL, USA 978-1-4799-2376-2/14/$31.00 ©2014 IEEE 993