## 1 Introduction  
Atmospheric icing remains an extremely important topic of study today, as it affects many sectors such as power generation [1; 2], communications [3; 4] and transport [5; 6; 7]. [PERSON] et al. [1] published a comprehensive review on modelling icing in wind turbines, where they highlight the importance of paying special attention to the modelling of turbulence (as there is usually evidence of flow separation) and roughness. They also highlight the need for experimental studies to obtain reliable data to validate the models proposed in recent years, since these models have only been validated with other numerical results to date. However, they do note the difficulty in obtaining accurate experimental data and the need for the development of experimental measurement methods. In the communications sector, studies found in the literature address the problem of icing on overhead power transmission lines. These issues, as well as the main de-icing and anti-icing systems used in this field, can be found in recent reviews by [PERSON] et al. [3] and [PERSON] et al. [4]. Within the transport sector, although there are a considerable number of studies within the naval field, of which a summary of the main studies to date can be found in the review work of [PERSON] et al. [5], most studies belong to the aeronautics field [1]. Icing wind tunnels (IWTs) are complex facilities that allow the recreation of conditions such as those encountered in the icing that occurs during flight, and they are used both for more fundamental studies (to understand the underlying physics) and for more applied studies (the validation of de-icing and anti-icing technologies). An IWT differs from a general-purpose wind tunnel in that it has the ability to control temperature and misting conditions to simulate icing conditions, in addition to aerodynamic conditions relative to flight. It emulates velocity, temperature, water content and droplet or microdroplet size distribution, allowing it to reflect the specific conditions that are contained in CS-25 [35]. Appendices C and O, on which the STANAG standards for Unmanned Aerial Systems (UAS) [36; 37; 38] are based. There are many types of icing wind tunnels, more or less complex, but in general the functional parts that make up an IWT are as follows:  
* Wind tunnel, responsible for accelerating the air and stabilising the required velocity in the test section, where the test specimen will be housed;
* Cooling system, responsible for reaching and maintaining the temperature required for the test, below the freezing temperature of water and normally below ambient temperature;
* Misting system, which generates and ejects water in the required quantity and droplet-size distribution. There is a clearly defined classification according to the geometry of the wind tunnel and its associated cooling system: open-circuit tunnels inside freezing chambers or closed-circuit tunnels with a heat exchanger system. Figure 1 shows the two types of wind tunnels mentioned: the closed-circuit wind tunnel of the Alfonso X University (UAX), which currently has no cooling system and is therefore not an IWT (but the feasibility of converting it into an IWT could be studied in the future), and the current open-circuit IWT of INTA, with a test section of only 15 \(\times\) 15 cm\({}^{2}\) and therefore a limited capacity in terms of the models to be tested. INTA's current IWT is limited to studies of anti-icing coatings andicing sensors on small test specimens or reduced-size models, allowing no aerodynamic testing to obtain forces. Figure 1: UAX wind tunnel and INTA icing wind tunnel (IWT). In this context, the main objective of this paper is to show and describe the design process of a new low-cost open-circuit wind tunnel inside a freezing chamber, with a test section five times larger than the existing one at INTA, adapted for the evaluation of ice detection and ice protection systems in fixed-wing UAVs.