# Mini Glider Design and Implementation with Wing-Folding Mechanism
## 4 Experimental Work
### Safety of Folding Mechanism  
As the final step in the folding mechanism, the strength of the mechanism when the glider is hovering should be determined. To make (1\({}^{\circ}\)) circular motion on the wings, spring should be elongated by \(\delta_{x}=1.7452\) mm. Spring force, \(F_{s}\), is calculated as \(F_{s}=0.263\) N. All the forces that are acting on the glider could be examined in two parts, which are the gravitational force of the wings, \(F_{G}\), and the drag forces, \(F_{D}\). For a 144 g glider, maximum \(F_{G}\) could be obtained when the critical angle of attack is reached or exceeded. \(F_{D}=0.383\) N, \(F_{G}=0.071\) N and \(F_{m}=11.46\) N can be used to calculate total maximum force that is acting on the glider's wing slot. Because the wing-folding system can not ossilate due to the magnets, by taking \(F_{m}\) as the maximum testing force, fatigue of the wing-folding mechanism can be calculated. Tensile strength of the Acrylonitrile butadiene styrene (ABS) plastic, which is used in wing's slot section, is 42.5 MPa and the balsa wood tensile strength, which is used in the wing, is also 7.6 MPa. Accordingly, it should be checked whether these materials are safe or not according to result from COMSOL(r) analysis. Calculated maximum test force acting on the glider is determined as \(F_{m}=F_{t}=11.46\) N, which applies to both the slot and wing sections. First, slot part analysis under this force could be seen in Figure 15. In this figure, 11.46 N is applied as an impulse signal from the wing slots, where the magnets are located, to the center of the magnet. As expected, this part is fixed to the glider body on the \(z\)-axis so that the tensile strength is seen on the same surface with the magnets. Possible deformations in this region will prevent the wings from aligning themselves in a parallel position after opening. Therefore, it appears that only a deflection of 4.308 \(\upmu\)m appears in the wings for the maximum test force. Figure 14: Wings are deployed in 98 ms. left: picture of instant position; middle: during the deployment; right: picture of the completed deployment of the wings. Since tensile stress of ABS is almost 50 times greater than obtained 0.82 MPa, the design and the components are safe to be used. Furthermore, ABS slot could be cracked only if 87.92 (N) is applied; however, this force is not exceeded in the design. As a second part of the safety test, the wing is analyzed under the same test force and this analysis can be seen in Figure 16. In this figure, the wing profile is strengthened by applying epoxy on the surface with approximately 100 \(\upmu\)m thickness. The structure shows a highly strengthened profile. Stress can be seen more on the trailing edge corner and l-bracket part on the wing connection. Due to the l-bracket having a length of 20 mm, it (shown in Section 3, Figure 7 rotational axis) is not attached to whole wing structure, which is 200 mm. Thus, stress can been seen more on the leading and trailing edge corners where the l-bracket is attached to the wing. The force required to detach an l-bracket from its wing connection point is determined as 97.32 (N) by COMSOL(r) analysis. These results show that the chosen wing-folding mechanism is totally safe and reliable. Finally, the wings are deployed by releasing the folding position 25 times in succession for both configurations. During this test, wing motion is recorded on a 240 fps camera(Yi 4K, Shanghai Xiao Yi Technology Co. Ltd, shanghai, China). For the first configuration with only a spring, the first closing position time (1); the first oscillation movement position time (2); and complete closure time (3) along with only the full closure time (4) for the second configuration with magnets are shown in Figure 17.  
Figure 16: Maximum deflection is obtained 13.89 \(\upmu\)m on the wing’s corner edge. Maximum stress point 0.16 MPa is seen as the same as wing slots. Since the wings are indirectly influenced by the test force during deployment, there is not as much tension as the wing slots.