{
  "revision": "subframe-study-v5",
  "status": "Provisional space and weight study; no member or connection has been load-rated",
  "axes": "meters; X aft from bus midpoint, Y passenger side, Z above ground",
  "donor": {
    "length_m": 12.446,
    "width_m": 2.4384,
    "height_m": 3.2004,
    "wheelbase_m": 6.9342,
    "front_axle_x_m": -3.81,
    "rear_axle_x_m": 3.1242,
    "rail_center_y_m": 0.43,
    "rail_center_z_m": 0.65,
    "rail_length_m": 12.146,
    "rail_section_m": [
      0.244475,
      0.0762,
      0.00635
    ],
    "basis": "490 in long / 273 in WB scenario retained from donor model, not identified from VIN/photo. 96 in width, 126 in height and 9-5/8 x 3 x 1/4 in C rail section are period Blue Bird family specifications. Rail spacing, elevation and cut length are unverified inherited assumptions."
  },
  "stations": [
    {
      "id": "A",
      "x_m": -4.75,
      "purpose": "Behind door / head-support interface",
      "verify": "Stepwell, front suspension and head load transfer"
    },
    {
      "id": "B",
      "x_m": -3.0719,
      "purpose": "Just behind front wheelwell",
      "verify": "Actual arch, suspension, luggage bay and speaker brackets"
    },
    {
      "id": "C",
      "x_m": -0.85,
      "purpose": "Ahead of generator envelope",
      "verify": "Tank, driveshaft, generator service and body mounts"
    },
    {
      "id": "D",
      "x_m": 2.3861,
      "purpose": "Just ahead of rear wheelwell",
      "verify": "Actual arch, suspension and rear speaker brackets"
    },
    {
      "id": "E",
      "x_m": 4.45,
      "purpose": "Rear deck / rump interface",
      "verify": "Rear engine, cooling and service access"
    },
    {
      "id": "F",
      "x_m": 5.55,
      "purpose": "Rear deck edge / rump interface",
      "verify": "Rear engine, cooling, service hatch and stair interface"
    }
  ],
  "upright_y_m": 1.2811,
  "permanent_top_z_m": 3.15,
  "deck": {
    "length_m": 11.396,
    "width_m": 2.6984,
    "surface_z_m": 3.4004,
    "plywood_thickness_m": 0.01905,
    "joist_max_spacing_m": 0.4064
  },
  "sections_m": {
    "upright": [
      0.0508,
      0.1524,
      0.003175
    ],
    "crossbearer": [
      0.0762,
      0.1524,
      0.0047625
    ],
    "header": [
      0.0762,
      0.1016,
      0.003175
    ],
    "longitudinal": [
      0.0762,
      0.1524,
      0.003175
    ],
    "joist": [
      0.0508,
      0.0762,
      0.003175
    ],
    "brace": [
      0.0381,
      0.0381,
      0.003175
    ]
  },
  "section_basis": "Trial rectangular tube outside width x depth x wall for interference and mass budgeting ONLY, not engineering selections. Square corners assumed. 7850 kg/m3 steel, 600 kg/m3 plywood. No claim of minimum weight or capacity for 20 occupants.",
  "sources": [
    "https://kirkmanbussales.com/wp-content/uploads/2017/01/AM-AARE-1109.pdf",
    "https://pictures.dealer.com/birdbussales/aaf83ec20a0d028a00eabd2f4f128ce3.pdf"
  ],
  "open_items": [
    "Donor wheelbase and overall length",
    "GVWR, GAWR and loaded axle weights",
    "Actual rail spacing/profile/elevation and chassis torsional movement",
    "OEM-compatible mounting brackets; no drilling or welding specified",
    "Underfloor equipment and suspension envelopes",
    "Loads from dancers in motion, head, shell wind, equipment and lifting",
    "Connection strength, deck stiffness, fatigue and rollover stability",
    "Cassette attachments and removable module weights/assembly sequence",
    "Field-measure maximum body/rub-rail width; verify station clearance under chassis twist. Current 2-inch transverse posts plus pads still exceed standard 102-inch transport width.",
    "2x6 candidate requires biaxial bending, local buckling, connection and lateral stability analysis; trial 1/8-inch wall is not selected."
  ],
  "alternative_to": "subframe-study-v4",
  "layout_name": "Six stations \u2014 2 \u00d7 6 in rectangular upright candidate",
  "wheelwell_radius_m": 0.6,
  "wheelwell_post_clearance_m": 0.0619,
  "comparison_basis": "Same six longitudinal station locations as v4. Replace 3x3 uprights and removable caps with 2x6 oriented 2 inches across the bus; retain provisional 6 mm rub-rail clearance. Other trial sections remain unchanged; recalculate transverse spans and weights.",
  "side_fit": {
    "body_half_width_m": 1.2192,
    "modeled_rub_rail_projection_m": 0.0305,
    "provisional_clearance_m": 0.006,
    "previous_upright_y_m": 1.2938,
    "inward_move_per_side_m": 0.0127,
    "bare_station_width_in": 102.874015748,
    "zero_clearance_station_width_in": 102.401574803,
    "basis": "Clearance to approximate modeled rub rails, not a field measurement or verified movement allowance. No intended bearing on bus skin or rails."
  },
  "upright_orientation": "2 inches transverse (bus width), 6 inches longitudinal (fore-and-aft); 1/8-inch nominal trial wall"
}