# Mini Glider Design and Implementation with Wing-Folding Mechanism
## 1 Introduction  
The demand is increasing for Mini-Gliders that weigh less than 1 kg, are small in size and can also communicate with each other in order to achieve desired functionality while also being reliable, having low power usage and low cost [1, 2]. In aviation, there are specialized systems that are capable of conducting field surveys by carrying multiple air vehicles such as rockets and dropping them on the target locations [3, 4, 5, 6]. For such specialized systems, reducing the weight and size while also deploying the maximum amount of payload is crucial. Accordingly, selecting the suitable materials for the glider and finding the design parameters allow multiple gliders to be transported at the same time. For this reason, different methods such as wing-folding mechanisms have been successfully applied to reduce the volume of miniature air-vehicles in the former designs [7, 8, 9, 10]. The international CanSat competition is a design-build-launch competition. The concept is somehow identical to a typical gun-launched air-vehicle system [11]. The air-vehicles are required to meet predefined volume restrictions of a container that is built in a rocket launcher. The wing-folding structure of the air-vehicle allows it to be contained in a small volume, and thus to be placed in a protective fixed-size container [12]. Recent research and industrial works related to gun-launched drones are principally focused on foldable fixed-wing configurations [13, 14]. Our goal in this work is to ensure that the wing-folding mechanism is opened quickly and reliably immediately after separating from the rocket. It must fulfill its assigned tasks successfully according to the competition regulations [15]. It is expected that the designed glider will descend from 400 m in helical orbit in around 120 s. For this purpose, the wing structure must have a fast deploying mechanism even in low air pressure and rough wind conditions and stabilize quickly. There are many different wing models used in literature for fixed-wing aerial vehicles, and use of Eppler and National Advisory Committee for Aeronautics (NACA) type wing structures is relatively more common [8; 16]. The Eppler-793 type wing structure appears to be fit for mini-gliders and speed-critical applications, where thickness, camber, and \(C_{L}/C_{D}\) (efficiency) ratio are crucial. Since the maximum \(t/c\) thickness ratio is in the 12-16% band, 2-5% camber is the best choice for desired operational speed [17]. Eppler wing structure allows easy assembly and easy folding by virtue of not being excessively cambered. The other selection criteria to choose an Eppler wing is to have more linear behavior in the desired (previously found via simulations) alpha operational range AoA (angle of attack). In order to gather information about the atmosphere, there are fixed-wing and larger-sized heavier systems [18] or measurements with different approaches [19; 20] instead of foldable wing systems. As a matter of fact, in many control applications, in order to find an optimal solution for a stable glider flight, Proportional-Integral-Derivative (PID), Adaptive and Neural network are widely used. Our glider mechanism does not have any motors attached to it; therefore, the phugoid flight mode is a necessity [21]. To achieve passive mechanical control, our aim is to combine all electronic equipment such as telemetry devices, communication devices, and sensors into a small PCB (Printed Circuit Board) while maintaining a light and compact design. According to research on related topics, our glider's \(C_{L}\) is higher at the same mass while also being smaller [19], and the wing-folding mechanism is also faster [9]. Moreover, there are designs whose stowed configurations are better than our glider and occupy %75 less volume and %75 less width than their deployed form. However, our primary aim is not a only wing-folding mechanism; our designed glider, which is able to land in a controlled manner via phugoid mode, can also collect data during its descent.