# Design, Modeling, and Simulation of a Wing Sail Land Yacht
## 1 Introduction  
In the last decades a broad range of research has been conducted in autonomous systems, ranging from land to marine or aerial robots, since these vehicles are useful in a very broad spectrum of tasks, due to their ability to remove humans from dangerous environments, relieve them of tedious tasks, or simply go to locations otherwise inaccessible or inhospitable [1]. Diverse applications have been envisaged for these platforms, from exploration of remote places [2] to warfare [3]. In order to have truly autonomous systems, they must present not only control autonomy but also energy autonomy. A possibility for granting energy autonomy to land and marine vehicles is to make use of wind to propel the vehicle [4] and, eventually, to power its on-board systems [5, 6, 7]. To propel these vehicles, traditional fabric sails (the most common approach), rigid wing sails, and mechanical devices, such as Flettner rotors or vertical and horizontal axis turbines, or even more uncommon options, such as different sail concepts or towing kites [8], can be adopted. Sailing has been practiced all around the world for thousands of years and virtually all boats, apart from those in recent sailing history, used conventional fabric sails [4]. Although flexible fabric sails have a number of useful properties, especially when controlledby a human sailor, they also present a number of limitations and / or drawbacks which can be overcome by alternative sail types, in particular rigid wing sails [8]. Among the advantages of using rigid wing sails for autonomous systems are the fact that its control is easier to automate and their increased reliability [8]. Given these advantages, the use of rigid wing sails has been proposed, for example, for powering commercial ships [9]. The vast majority of robotic sailing research is focused on wind propelled water platforms--sailboats; however, there is a lesser common type of sailing vehicles--land yachts. As autonomous robotic platforms, land yachts can play an important role in the context of environmental monitoring, namely, in the case of open flat windy regions, such as iced planes or sandy shorelines. As a result, autonomous land yachts can be used to monitor river, lake or ocean shoreline environments, or even for planetary exploration [10]. Like a sailboat, a land yacht does not require motors for propulsion, as it uses the wind, resulting in a considerable increase in power autonomy [11; 12; 13]. Although the majority of the autonomous sailing research addresses sailboats, there are also works on land yachts. The latter include the contributions of:  
1. [PERSON] et al. [10; 14] propose the National Aeronautics and Space Administration (NASA) Zehpyr land sailing rover. It is intended to be used in Venus, a harsh, windy planet. The conceptual design uses a NACA0015 airfoil with a wingspan of 5.44 m, a lateral area of 12 m\({}^{2}\), and weight of 49 kg. The chassis has a triangular shape with three wheels and weighs 35 kg. 2. [PERSON] et al. [11] present the Autonomous Controlled Four-Wheeled Land Yacht concept. This land vehicle is propelled by a single wing sail with a symmetrical profile, 1 m wingspan, a lateral area of 0.25 m\({}^{2}\), a mass of 2.15 kg, and a rotation range of 0\({}^{\circ}\) to 360\({}^{\circ}\). The chassis is composed by an aluminium hull and two front and two rear wheels with a total mass of 19 kg. 3. [PERSON] et al. [15] propose the Multiple Wing Sail Land Yacht. It adopts a triple wing sail design to reduce the wind velocity required to start the vehicle motion. The remaining features are equal to those of the previous example. 4. [PERSON] et al. [13] adopt a free-rotating NACA0015 wing sail with a wingspan of 2.5 m and a lateral area of 1.25 m\({}^{2}\) design to rig a land yacht. The steel chassis has one front wheel and two rear wheels. Although not fully autonomous, the angle of attack of the free-rotating wing sail is set by controlling the tail flap, which induces torque on the wing sail. 5. [PERSON] et al.