Atlas-C Project Highlights
Duration: Winter 2023 – Present
Tools Used:
- SOLIDWORKS for CAD design
- 3D printing for rapid prototyping
- Basic FEA for structural analysis
Project Summary:
Atlas-C is a flying wing unmanned aircraft designed within 24 hours as a challenge to leverage the capabilities of 3D printing. The aircraft features compliant mechanisms that reduce the part count, making it easier to assemble and more suitable for production in challenging environments.
Highlights and Insights Gained:
- Improved skills in using compliant mechanisms to simplify design and reduce complexity.
- Gained insight into rapid prototyping and testing under time constraints.
- Applied engineering principles to develop functional components with minimal resources.
- Enhanced experience in using 3D printing for aerospace applications.
The use of 3D printing
Multi-Filament Printing: The BambuLab P1S 3D printer allowed the use of multiple filaments within a single component, optimizing the performance of airfoils and control surfaces.
Layer Adhesion Strategy: To prevent shear failures, parts were printed with three layers of regular PLA at the base and top, sandwiching ultralight PLA for better structural integrity.
Improved Edge Durability: The layering technique not only enhanced bed adhesion but also reduced the risk of edge fraying, ensuring more durable parts.
Complexity of Ultralight PLA Printing: Ultralight PLA required specific printing conditions and customized G-code due to its expansion during printing. Testing with sample parts was necessary to refine these settings and ensure optimal structural integrity.
Increased Ductility: Ultralight PLA is significantly more ductile than traditional PLA, making it an ideal material for the compliant mechanisms used in the aircraft.
Higher Strain Capacity: The enhanced ductility of ultralight PLA allowed it to endure higher levels of strain before entering plastic deformation or failing, which was crucial for maintaining the functionality of the compliant mechanisms.
Balanced Layer Configuration: The number of wall layers for the compliant mechanism was carefully chosen to strike a balance between flexibility and rigidity, ensuring optimal performance.
Testing and Selection: After testing various configurations, a setup of three to five layers around the pivot point was selected for its ability to maintain structural integrity while allowing sufficient bendability.
Durability Through Cyclic Testing: The chosen layer configuration demonstrated excellent durability, showing no signs of wear or failure even after 50,000 cycles of loading.
Testing and Analysis
Focused Component: The FEA analysis primarily targeted the compliant mechanism of the control surface, as the rest of the airframe did not require such testing due to the lower loading conditions.
Load Distribution Optimization: The analysis ensured that the bending spring mechanism was designed to distribute load evenly across the spring, preventing potential failure points and optimizing the thickness and connection points of the spring.
Design Refinement: Various spring configurations were tested through FEA to identify the best design that minimized high strain areas within the coil, resulting in a more reliable and efficient control surface mechanism.
Testing Procedure: Cyclic testing involved moving the control surface's compliant mechanism between its operational extremes, from negative 25 degrees to positive 25 degrees, repeatedly for approximately 43,000 cycles over 12 hours. Initially, the three-layer configuration began to exhibit cracking and failures after about 8 hours, or 29,000 cycles.
Performance Metrics: The testing didn't focus on specific load measurements but rather on the operational angles the control surface would experience during flight. The control surface was tested within the peak deflection angles expected in real-world use, ensuring that the mechanism could perform reliably under those conditions.
Design Improvement: Based on the observed failures in the three-layer configuration, the design was adjusted to a four-layer setup, which successfully withstood the entire 43,000-cycle test without any signs of wear or failure, confirming its improved durability.
FEA Model Refinement: Collaboration with professors at SDSU is underway to develop more advanced FEA models. These models will be used to cross-reference expected outcomes with actual test results, focusing on the load testing of control surfaces .
Fluid Dynamics Study: Its planed to start building fluid dynamic analysis to better understand airflow interactions with the compliant mechanism. This analysis will be compared with wind tunnel results to determine whether the less smooth surface of the mechanism negatively impacts aerodynamic efficiency, potentially indicating the need for additional coverings.
Cross-Referencing Results: Both the refined FEA models and fluid dynamics studies will be cross-referenced with real-world data, ensuring that any discrepancies between theoretical and practical outcomes are identified and addressed before proceeding to full flight tests.
Atlas-C Project Summary
The Atlas-C Project involved designing a flying wing aircraft within a 24-hour timeframe, with a strong emphasis on the use of 3D printing. The challenge was to create an aircraft that could be almost entirely 3D printed, leveraging the accessibility and efficiency of 3D printers compared to larger, more complex manufacturing systems typically required for carbon fiber or foam aircraft. This design approach is particularly advantageous in scenarios where traditional manufacturing resources are limited, such as military applications, remote areas, or resource-constrained environments.
The aircraft’s design integrates several engineering features to maximize performance while maintaining simplicity and manufacturability. The primary innovation in the design is the use of compliant mechanisms at the trailing edge of the airfoil. These mechanisms are crafted in a coiled configuration, which spreads the bending forces across a larger area of material, significantly reducing localized stress. This allows the control surfaces to move smoothly and responsively without imposing excessive strain on the servos or the structure itself. The careful balance achieved here ensures that the control surfaces are neither too loose nor too stiff, providing precise maneuverability without compromising structural integrity.
The choice of a flying wing configuration was driven by the need to minimize weight and simplify the structural load distribution. Unlike traditional aircraft designs, which involve separate fuselage, wings, and tail sections, the flying wing offers a more unified structure, reducing the complexity of stress points. The primary load is distributed evenly across the wing, supported by strategically placed carbon fiber spars. These spars provide the necessary stiffness while allowing for flexibility where needed, enhancing the overall aerodynamic efficiency of the aircraft.
The 3D printing process was optimized to produce components with varying densities and thicknesses, tailored to the specific structural demands of different parts of the aircraft. Thicker sections were printed in high-stress areas, such as around the carbon fiber spars, while thinner, lighter sections were used in less critical areas to minimize weight. This approach not only enhances the strength-to-weight ratio but also ensures that the aircraft can be assembled quickly and efficiently.