The Plan for Everloft I

With the lessons learned from our initial prototype, we are ready to move to the next phase. The goal for Everloft I is to prove that unstable flight possible on a more realistic and optimized solar plane, not just on a test platform. It will allow us to prove our optimization methods, measure accurate flight test data and verify our simulations. Despite it being an early prototype, Everloft I will already be capable of all-day and potentially all-night flights.

Design Optimization:

All the primary sizing variables for Everloft I are optimized in a single python script. This includes masses of all relevant components, solar panel area and wing geometry. Integrated optimization allows us to capture the interaction between these design variables. The script is integrated with xflr5 for whole-aircraft simulation, simulating the plane through multiple day-night cycles. The performance is scored according to a predetermined scoring system, which is used for an evolution-based optimization algorithm.

For other parts of the design, separate optimization scripts are used:

• The airfoil geometry used has a significant impact on the aerodynamic efficiency of the plane. Airfoil selection is handled by a separate script, using XFOIL to simulate the performance of every geometry in a database of over 22500 airfoils. This allows us to find the optimal airfoil for our operating conditions.
• The efficiency of the motor-propeller combination is simulated using propeller data from the UIUC Propeller Data site, as well as motor efficiency data. With this, the optimal motor-propeller combination for our operating point is found.
• Structural calculations are performed in a separate python script, allowing us to size the main structure based on strength and stiffness constraints.

Simulation:

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Main Design Decisions:

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• Limit the wingspan to 3m. This ensures that the aircraft remains easy to handle and transport, and is sufficient to reach the goals we set for Everloft I.
• Use straight carbon fiber tubes for the main structure. The high stiffness of carbon fiber is necessary to prevent excessive deflection, and tubes perform best in the load cases expected. Making the tubes, and therefore the wing, straight greatly simplifies and lightens the structure while having a negligible effect on aerodynamic efficiency. (here, straight means that the wing has no sweep, twist or dihedral)
• 3D-Print the wing sections from Lightweight PLA. This allows for a complex wing shape while keeping weight low. []
• Use 4 control surfaces. []
• Use two motors and implement differential thrust. []
• Use 21700 cells for the battery. We have access to sufficient 21700 cells from a previous project, which gives us a low-cost way to build our battery pack
• Launch with a launch rail and land in a net. []

Building Process:

The building process is [add text, add photos]

More detailed articles on the specific optimization methods and subsystems are coming soon.