diff --git a/CHANGELOG.md b/CHANGELOG.md
index 532b0816..76b6fa40 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,24 @@
 # Changelog
 
+## Unreleased
+
+### Fixed
+
+- `ObjWing` fills the mesh-derived fields of the `Wing` it returns again:
+  `gamma_tip`, `radius`, `le_interp`, `te_interp`, `area_interp`,
+  `inertia_tensor` and `T_cad_body`. Building the wing through
+  `ObjAdapter.obj_to_yaml` + `Wing(yaml)` in v4.0.0 left all seven at their
+  empty defaults, so a caller reading the spanwise geometry off an OBJ wing —
+  `wing.le_interp[i](gamma)` is how a bridle is placed on one — hit
+  `nothing`, and the wing's inertia silently fell back to point masses. The
+  values are in the mesh's own coordinates, the frame `obj_to_yaml` cuts its
+  sections in, and `test/ram_geometry/test_kite_geometry.jl` asserts that.
+- `ObjWing` hands the `Wing` it builds the `crease_frac` it generated the polars
+  about, instead of leaving it at the default 0.75, and its
+  `spanwise_distribution` defaults to `LINEAR`. `UNCHANGED` keeps whatever
+  sections the geometry file carries, so asking for more panels than it has
+  sections threw a `BoundsError` out of `compute_refined_panel_mapping!`.
+
 ## VortexStepMethod v5.1.1 2026-09-12
 
 ### Fixed
diff --git a/docs/src/private_functions.md b/docs/src/private_functions.md
index d7807c42..16d9ccc3 100644
--- a/docs/src/private_functions.md
+++ b/docs/src/private_functions.md
@@ -246,6 +246,7 @@ find_circle_center_and_radius
 march_edges
 calculate_inertia_tensor
 center_to_com!
+seed_mesh_geometry!
 airfoils_from_yaml
 write_geometry_yaml
 resolve_aero_geometry
diff --git a/src/obj_adapter/obj_geometry.jl b/src/obj_adapter/obj_geometry.jl
index 0a5ac73a..4f49789c 100644
--- a/src/obj_adapter/obj_geometry.jl
+++ b/src/obj_adapter/obj_geometry.jl
@@ -370,3 +370,29 @@ function calc_inertia_y_rotation(I_b_tensor)
 end
 
 
+"""
+    seed_mesh_geometry!(wing, obj_path; mass=1.0)
+
+Fill the mesh-derived fields of a [`Wing`](@ref VortexStepMethod.Wing) built from
+`obj_path`: the `radius` and `gamma_tip` of the arc fitted through the mesh, the
+`le_interp`, `te_interp` and `area_interp` interpolations over that arc, the
+thin-shell `inertia_tensor` about the centre of mass for a wing of `mass` [kg],
+and `T_cad_body`, the centre of mass negated. Positions are in the mesh's own
+coordinates, the frame [`obj_to_yaml`](@ref) writes its sections in.
+"""
+function seed_mesh_geometry!(wing, obj_path; mass=1.0)
+    vertices, faces = read_faces(obj_path)
+    com = -center_to_com!(copy.(vertices), faces; prn=false)
+    circle_center_z, radius, gamma_tip = find_circle_center_and_radius(vertices)
+    le_interp, te_interp, area_interp =
+        create_interpolations(vertices, circle_center_z, radius, gamma_tip)
+    wing.mass = mass
+    wing.inertia_tensor = calculate_inertia_tensor(vertices, faces, mass, com)
+    wing.T_cad_body .= -com
+    wing.gamma_tip = gamma_tip
+    wing.radius = radius
+    wing.le_interp = le_interp
+    wing.te_interp = te_interp
+    wing.area_interp = area_interp
+    return wing
+end
diff --git a/src/yaml_geometry.jl b/src/yaml_geometry.jl
index 11da48ac..6a542626 100644
--- a/src/yaml_geometry.jl
+++ b/src/yaml_geometry.jl
@@ -443,6 +443,16 @@ polars; the default is `AirfoilAero.NeuralFoilSolver()`.
 
 By default (`remake=false`) an existing `geometry.yaml` in `output_dir` is reused,
 skipping the expensive polar generation. Set `remake=true` to force regeneration.
+
+`spanwise_distribution` defaults to `LINEAR`, so a mesh cut into fewer sections
+than `n_panels + 1` is panelled into that many rather than kept as it is.
+`crease_frac` is the chordwise hinge the polars are deflected about, and the
+wing carries it.
+
+The mesh-derived fields a wing loaded from YAML alone leaves empty — `gamma_tip`,
+`radius`, `le_interp`, `te_interp`, `area_interp`, `inertia_tensor` and
+`T_cad_body` — are filled from the mesh by
+[`ObjAdapter.seed_mesh_geometry!`](@ref).
 """
 function ObjWing(obj_path, dat_path=nothing;
                  n_panels::Int=56,
@@ -451,13 +461,14 @@ function ObjWing(obj_path, dat_path=nothing;
                  delta_range=-5:1:20,
                  n_sections::Union{Nothing, Int}=nothing,
                  spanwise_direction=[0.0, 1.0, 0.0],
-                 spanwise_distribution=UNCHANGED,
+                 spanwise_distribution=LINEAR,
                  remove_nan::Bool=true,
                  aero_solver=AirfoilAero.NeuralFoilSolver(),
                  remake::Bool=false,
                  output_dir::String=mktempdir(),
                  crease_frac=0.75,
                  verbose::Bool=false)
+    (!endswith(obj_path, ".obj")) && (obj_path *= ".obj")
     yaml_path = joinpath(output_dir, "geometry.yaml")
     if remake || !isfile(yaml_path)
         n_sec = isnothing(n_sections) ? n_panels + 1 : n_sections
@@ -471,5 +482,7 @@ function ObjWing(obj_path, dat_path=nothing;
                                            crease_frac,
                                            verbose)
     end
-    return Wing(yaml_path; n_panels, spanwise_distribution, spanwise_direction, remove_nan)
+    wing = Wing(yaml_path; n_panels, spanwise_distribution, spanwise_direction,
+                remove_nan, crease_frac)
+    return ObjAdapter.seed_mesh_geometry!(wing, obj_path)
 end
diff --git a/test/ram_geometry/test_kite_geometry.jl b/test/ram_geometry/test_kite_geometry.jl
index 4c9fdc8d..37d269db 100644
--- a/test/ram_geometry/test_kite_geometry.jl
+++ b/test/ram_geometry/test_kite_geometry.jl
@@ -167,11 +167,45 @@ using Serialization
         @test R_b_p2 ≈ I(3)
     end
 
-    @testset "Converted-wing construction and deformation" begin
-        # TODO: redesign. These previously tested ObjWing internals (radius,
-        # gamma_tip, UNCHANGED distribution, obj deform\!) that were dropped when
-        # ObjWing was replaced by convert-then-load (obj_to_matrix_yaml -> Wing).
-        # Rebuild against ram_air_matrix_wing() geometry once its numerics are set.
-        @test_skip false
+    @testset "ObjWing carries the mesh geometry its sections are cut from" begin
+        gen_dir, _ = ram_air_matrix_dir()
+        obj = joinpath(dirname(dirname(@__DIR__)), "data", "ram_air_kite",
+                       "ram_air_kite_body.obj")
+        wing = ObjWing(obj; n_panels=20, spanwise_distribution=LINEAR,
+                       output_dir=gen_dir, verbose=false)
+
+        @test wing.gamma_tip > 0
+        @test wing.radius > 0
+        @test !isnothing(wing.le_interp)
+        @test !isnothing(wing.te_interp)
+        @test !isnothing(wing.area_interp)
+        @test wing.area_interp(wing.gamma_tip) > 0
+
+        vertices, faces = read_faces(obj)
+        com = -center_to_com!(vertices, faces)
+        @test wing.T_cad_body ≈ -com
+        @test wing.inertia_tensor ≈ wing.inertia_tensor'
+        @test all(>(0), diag(wing.inertia_tensor))
+
+        # The interpolations must be in the frame the sections are cut in: at the
+        # centre they land on the centre section, not a centre-of-mass away from it.
+        le_points = [section.LE_point for section in wing.refined_sections]
+        spacing = maximum(abs(le_points[i + 1][2] - le_points[i][2])
+                          for i in 1:length(le_points) - 1)
+        le_center = [wing.le_interp[i](0.0) for i in 1:3]
+        nearest = argmin(le_point -> abs(le_point[2] - le_center[2]), le_points)
+        @test norm(nearest - le_center) < spacing
+    end
+
+    @testset "ObjWing panels a coarser cut and flies the crease it generated" begin
+        gen_dir, _ = ram_air_matrix_dir()   # four sections
+        obj = joinpath(dirname(dirname(@__DIR__)), "data", "ram_air_kite",
+                       "ram_air_kite_body.obj")
+        wing = ObjWing(obj; n_panels=20, crease_frac=0.82,
+                       output_dir=gen_dir, verbose=false)
+
+        @test wing.n_unrefined_sections == 4
+        @test length(wing.refined_sections) == 21
+        @test wing.crease_frac == 0.82
     end
 end