# Design of a Human Muscle-Powered Flying Machine
## 6 Structural Development of the Human-Powered Aircraft
### Determination of Aerodynamic Characteristics  
Using the XFLR5 program, an analysis of the previously designed lifting surfaces (wing, vertical stabilizer, horizontal stabilizer) was conducted to examine their aerodynamic characteristics. The following analyzes were performed only to initially determine whether the construction of HPA was capable of flying. The assumed temperature of air was set to 20 \({}^{\circ}\)C and no wind was assumed.  
This analysis included studying the lift coefficient versus drag coefficient for various velocities (Figure 12a). The value of the lift force for the wing was also checked, without deflection (NO DEFL--marked with a blue line in the graph) and with the expected deflection (DEFL--red line in the graph) taken into account (Figure 12b). Based on the graph (Figure 12b), it was determined that with a bent wing, the decrease in lift force in relation to a straight wing is 46.6 N for a speed of 9.5 m/s. For the purposes of the project, the assumed lift force drop was 50 N.  
The next step was to indicate the total resistance force. The XFLR5 program does not allow the construction of high-level solids, so the 3 DExperience program was used. The first step was to create a simplified surface model of the muscle aircraft using the Generative Wireframe and Surface module (Figure 13a). Next, in the Scenario Creation module and using the Assistant function, preliminary analysis requirements were specified, including the dimensions of the bounding box, the surface area of the studied part, and the type of fluid flowing around, in this case, air. Then, the turbulence model was determined--the SST k-\(\omega\) model was chosen.  
In the next step, boundary conditions were established, where orange arrows indicated the inlet velocity of 9.5 m/s, and purple arrows indicated the pressure outlet (Figure 13b). The motion of the bottom wall (9.5 m/s) was set parallel to the airflow to simulate the aircraft flying over the ground, which helps capture the ground effect more accurately. In the next stage, the desired output values were specified (Figure 13c).  
In this case, it was the generated force. In the next step, the mesh parameters were set. The Hex-Dominant Mesh type was selected, with a maximum mesh size set to 150 mm and a minimum size of 15 mm. Additionally, three layers of 1 mm thickness were added, distributed around the model's surface (Figure 13d).  
The final step was to run the Model and Scenario Check function, which verifies the correctness of actions taken in the previous stages. Subsequently, the simulation was initiated. The graphical result of the simulation shows changes in velocity at the upper and lower edges of the wing (Figure 14a). Consequently, on the upper edge of the airfoil, pressure decreases, while it increases on the lower edge (Figure 14b). This results in the generation of lift force. To retrieve significant analysis results, the Sensor function was used, followed by reading the results in the Feature Manager window (Figure 14c).  
The results pertain to the design of the human-powered aircraft, which achieves a ceiling of 3.4 m (measured from the lowest point of the structure) and moves at a speed of 9.5 m/s. In this scenario, the drag force is 23.8 N, and the lift force is 971.8 N (accounting for wing flex). However, if the aircraft reaches a higher altitude (6.4 m), the drag force increases to 24.7 N, while the lift force decreases to 963.7 N. This confirms the occurrence of the ground effect.  
Figure 12: Graphs of (**a**) lift coefficient versus drag coefficient \(\mathrm{C_{1}}/\mathrm{C_{d}}\) for speed \(v\), (**b**) lift force \(F_{Z}\) versus speed \(v\).  
Figure 14: (**a**) Velocity distribution around the lift airfoil, (**b**) pressure distribution on the structure, (**c**) screenshot of the Feature Manager window.  
Figure 13: (**a**) Simplified surface model of the plane, (**b**) boundary conditions for the performed analysis, (**c**) screenshot of the Output window, (**d**) numeric grid with settings window.