# Fast Airfoil Selection Methodology for Small Unmanned Aerial Vehicles
## 1 Introduction  
Unmanned Aerial Systems (UAS), are being used increasingly over the years, compared to manned air vehicles, in order to accomplish certain aerial missions. The main advantage of the unmanned type of flight is the reduced cost of usage [1]. Specifically, the Small Unmanned Aerial Vehicles (SUAV) category is of special interest, because it can be used in a plethora of short-range aerial missions, such as in meteorological applications [2], forestry applications [3], agricultural applications [4], or in general purpose security surveillance and reconnaissance applications. The current airfoil selection methodology is a result of the <<Euclid>> SUAV development, which has a primary role of executing security surveillance and reconnaissance missions. The UAV's classification can be completed considering various criteria, such as (i) the presence of a main wing or not, (ii) the mass of the vehicle, (iii) the vehicle's maximum altitude, (iv) the vehicle's range and endurance, and (v) the nature of the mission that the vehicle is designed to execute [5]. Qualitative and quantitative widths, and also the naming of the UAV's categories, are not strictly defined bibliographically, resulting in a mixed classification between various authors and organizations worldwide [6]. For example,the <<Small>> prefix in front of the UAV acronym, used in the title of the present article, is interpreted as a UAV of mass between 0.1-150 kg according to Australia's Civil Aviation Safety Authority (CASA), and a UAV of mass \(\leq\) 20 kg according to the Civil Aviation Authority (CAA) of Great Britain [7]. In order to be more precise in the current article, the <<Small>> prefix relates to the Reynolds numbers that the main wing of the vehicle faces. These numbers, of course, are, respectively, in analogy with the physical dimensions and overall performance characteristics of the UAV. The airfoil, or the different type of airfoils, that will be placed in the main wing of an aircraft, can be either selected among a plethora of well-known geometries, or they can be designed from scratch. Usually, for the purpose of the design of a small aircraft such as a small UAV, the airfoil selection procedure is preferred, in order to preserve resources, as well as to reduce the complexity and development times [8]. For general information about the airfoil design procedure, the reader can refer to the textbook [9]. For the recent advances in the field, the reader can refer to scientific journal articles [10; 11; 12]. This study focuses on the airfoil selection means of obtaining an airfoil, which is an absolutely critical procedure for the final performance of the final product [13; 14]. Different airfoil selection procedures are available when selecting an airfoil for other purposes, such as wind turbines [15; 16; 17], various propellers [18], special purpose airfoils such as supersonic airfoils [19], unique flying machines such as flapping wings [20], etc. Figure 1 depicts the contribution of the current study within the broadest context, following the path with the green marking. Before the discussion of the details of the novelty of the current study, all of the possible internal processes of Figure 1 are discussed in detail, along with the necessary recent literature review. When following the airfoil selection route, the designers have to decide if they are willing to apply a strict airfoil selection methodology which can be obtained from the international aviation literature textbooks, or to attempt applying a custom method. Various  
Figure 1: Possible routes to result with an aircraft airfoil and the exact spot of current’s study contribution. Main airfoil selection procedure for this study is based on [8; 21]. well known authors in the aviation design field, describe analytical methodologies in their textbooks [21; 22; 23]. In the following paragraphs, a literature review is undertaken among recent scientific journal articles where an airfoil selection procedure is taking place.