Fix lofted-airfoil rib placement for +spanwise section order - #256
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`airfoil_skin_geometry` chose which panel edge to loft each section's contour onto with `plus_edge = i <= n_panels ? !increasing : increasing`, where `increasing` tests whether the refined sections run along +spanwise. But panels are always built with `refined_sections[p]` as corner 1/2 and `refined_sections[p+1]` as corner 4/3 (`init_pos!`), independent of span order, so the correct edge is purely index-based: section `i` sits on panel `i`'s first edge for `i <= n_panels`, and on the last panel's second edge for the final section. For a wing whose sections run −y→+y (`increasing == true`) the old expression inverted every mapping, drawing each section's contour at its neighbour's station: the first-section tip got no rib and the last-section tip got a doubled (folded) rib, while the VSM panels rendered correctly. Replace it with `first_edge = i <= n_panels`, which reproduces the previous (correct) result for −spanwise wings and fixes the +spanwise case. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Problem
In the Makie extension, airfoil_skin_geometry draws one lofted airfoil rib per section by fitting the section's contour onto a panel edge. It picked the edge with:
where increasing tests whether refined_sections run along +spanwise.
Panels are always built with refined_sections[p] → corner_points col 1/2 and refined_sections[p+1] → col 4/3 (init_pos!), independent of span order. So the edge for section i is purely index-based:
The increasing term is spurious. It is a no-op for −spanwise wings (increasing == false) but inverts every mapping for +spanwise wings (increasing == true): each section's contour is lofted onto its neighbour's station. The result is a missing rib at the first-section tip and a doubled/folded rib at the last-section tip, while the VSM panels themselves render correctly.
Observed on an SK100 wing (sections ordered −y→+y): no lofted airfoil at the most-negative-y tip, a folded double airfoil at the most-positive-y tip.
Fix
This reproduces the previous (correct) output for −spanwise wings and fixes the +spanwise case. spanwise/increasing are no longer needed and are removed.
Notes
🤖 Generated with Claude Code