Rotate a twisted section's chord fully about the spanwise axis - #263
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_apply_refined_section_thetas! built the twisted TE point from cos(theta)*chord - sin(theta)*(chord x local_y), which is the Rodrigues rotation with its axial term k(k.c)(1-cos(theta)) dropped. That term vanishes only when the chord is perpendicular to the twist axis, so a swept or dihedral section had its along-span chord component scaled by cos(theta): the chord shortened and tilted out of the twist plane, both growing as theta^2. On the 2-plate kite of SymbolicAWEModels the chord runs 7.4 deg off the plane normal to the local span, and the deformed VSM chord left the structural chord it is meant to track by 0.065 deg at 7.7 deg of twist and 2.4 deg at 48 deg. Restoring the axial term takes both to 1e-13 deg, and the chord length is now preserved to machine precision. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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_apply_refined_section_thetas!built the twisted TE point fromcos(theta)*chord - sin(theta)*(chord × local_y)— the Rodrigues rotation withits axial term
k(k·c)(1 - cos(theta))dropped. That term vanishes only when thechord is perpendicular to the twist axis, so a swept or dihedral section had its
along-span chord component scaled by
cos(theta): the chord shortened and tiltedout of the twist plane, both errors growing as
theta^2.The result was not a rotation at all —
|TE - LE|changed under twist.Impact
On the 2-plate kite of SymbolicAWEModels.jl the chord runs 7.4° off the plane
normal to the local span. The deformed VSM chord left the structural chord it is
meant to track by:
With the axial term restored both drop to ~1e-13° and machine epsilon.
Changes
_apply_refined_section_thetas!adds the axial Rodrigues term.Full test suite passes.
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