This add-in imports airfoil coordinate data from .dat files and fits optimized splines to it. This reduces the number of control points considerably, thereby improving the performance and stability of subsequent surfacing operations. The generated splines are aligned to the selected sketch line. The result maintains smooth curvature and geometric continuity at the leading edge and can be used immediately for lofts, sweeps, and other CAD operations.

Features

Airfoil Data Import

• Automatic format detection: The loader analyzes coordinate patterns to determine the format. Currently, Selig and Lednicer are supported.
• Automatic normalization: Coordinates are translated, rotated, and scaled so the leading edge is atthe  origin and the chord lies along the X-axis

B-Spline Fitting

• Single-span Bézier curves: Uses degree = (control points - 1), creating true Bézier curves without internal knots to ensure compatibility with Autodesk® Fusion®. Based on Dev Rajnarayan et al. 2019 (https://arc.aiaa.org/doi/10.2514/6.2018-3949).
• Adjustable control point count: 4 to 19 control points per surface (upper/lower fitted independently)
• G1 continuity: Tangent continuity is always enforced at the leading edge between upper and lower surfaces
• G2 continuity (optional): Curvature continuity at the leading edge via constrained optimization
• G3 continuity (optional): Curvature derivative continuity at the leading edge
• Trailing edge tangency (optional): Enforces tangent direction at the trailing edge based on the original airfoil data
• Smoothness penalty: Adjustable regularization to balance accuracy vs. smoothness of the control polygon

Geometry Placement

• Chord line selection: Select any sketch line to define the chord position and length
• Automatic scaling: Airfoil is scaled to match the selected chord line length
• Rotation: Rotate the airfoil plane in 90° increments around the chord line (0°, 90°, 180°, 270°)
• Flip orientation: Reverse the nose-to-tail direction along the chord line
• Trailing edge thickness: Add symmetric trailing edge thickness with minimal distortion of the airfoil.

Output Options

• Adjustable splines (experimental): Creates geometry via DXF import to create control-point splines that can be edited in Fusion
• Fixed splines: Creates read-only splines directly through the Fusion-API
• Live preview: Preview is automatically shown when both chord line and airfoil file are selected
• Show input data: Optionally display the original airfoil coordinate points for comparison

Error Reporting

• Max deviation display: Shows the maximum fitting error for upper and lower surfaces in document units

Dependencies

The add-in requires the following Python packages:

1. numpy
2. scipy
3. ezdxf

Note: This app uses a custom installer (and not the standard App Store installer).