diff --git a/flow360/component/simulation/translator/solver_translator.py b/flow360/component/simulation/translator/solver_translator.py
index 8fc250127..9afafe1b6 100644
--- a/flow360/component/simulation/translator/solver_translator.py
+++ b/flow360/component/simulation/translator/solver_translator.py
@@ -958,7 +958,7 @@ def bet_disk_entity_info_serializer(volume):
     }
 
 
-def bet_disk_translator(model: BETDisk):
+def bet_disk_translator(model: BETDisk, is_unsteady: bool):
     """BET disk translator"""
     model_dict = convert_tuples_to_lists(remove_units_in_dict(dump_dict(model)))
     model_dict["alphas"] = [alpha.to("degree").value.item() for alpha in model.alphas]
@@ -975,7 +975,6 @@ def bet_disk_translator(model: BETDisk):
         "omega": model_dict["omega"],
         "chordRef": model_dict["chordRef"],
         "nLoadingNodes": model_dict["nLoadingNodes"],
-        "bladeLineChord": model_dict["bladeLineChord"],
         "twists": model_dict["twists"],
         "chords": model_dict["chords"],
         "sectionalPolars": model_dict["sectionalPolars"],
@@ -985,8 +984,16 @@ def bet_disk_translator(model: BETDisk):
         "ReynoldsNumbers": model_dict["reynoldsNumbers"],
         "tipGap": model_dict["tipGap"],
     }
-    if "initialBladeDirection" in model_dict:
-        disk_param["initialBladeDirection"] = model_dict["initialBladeDirection"]
+
+    if is_unsteady:
+        # Unsteady BET Line
+        disk_param["bladeLineChord"] = model_dict["bladeLineChord"]
+        if "initialBladeDirection" in model_dict:
+            disk_param["initialBladeDirection"] = model_dict["initialBladeDirection"]
+    else:
+        # Steady BET Disk
+        disk_param["bladeLineChord"] = 0
+
     return disk_param
 
 
@@ -1499,6 +1506,7 @@ def get_solver_json(
             bet_disk_translator,
             to_list=True,
             entity_injection_func=bet_disk_entity_info_serializer,
+            translation_func_is_unsteady=isinstance(input_params.time_stepping, Unsteady),
         )
 
     if has_instance_in_list(input_params.models, ActuatorDisk):
diff --git a/tests/simulation/translator/test_betdisk_translation.py b/tests/simulation/translator/test_betdisk_translation.py
new file mode 100644
index 000000000..d0e035704
--- /dev/null
+++ b/tests/simulation/translator/test_betdisk_translation.py
@@ -0,0 +1,72 @@
+import pytest
+
+import flow360.component.simulation.units as u
+from flow360.component.simulation.primitives import Cylinder
+from flow360.component.simulation.services import clear_context
+from flow360.component.simulation.translator.solver_translator import get_solver_json
+from flow360.component.simulation.unit_system import imperial_unit_system
+from tests.simulation.translator.utils.xv15_bet_disk_helper import (
+    createBETDiskSteady,
+    createBETDiskUnsteady,
+    createSteadyTimeStepping,
+)
+from tests.simulation.translator.utils.xv15BETDisk_param_generator import (
+    create_param_base,
+    createUnsteadyTimeStepping,
+)
+
+
+@pytest.fixture(autouse=True)
+def reset_context():
+    """Clear user variables from the context."""
+    clear_context()
+
+
+def _create_test_cylinder():
+    return Cylinder(
+        name="bet_zone",
+        center=(0, 0, 0) * u.inch,
+        axis=[0, 0, 1],
+        outer_radius=150 * u.inch,
+        height=15 * u.inch,
+    )
+
+
+def test_betdisk_unsteady_excludes_internal_fields():
+    rpm = 588.50450
+    params = create_param_base()
+    bet_disk = createBETDiskUnsteady(
+        cylinder_entity=_create_test_cylinder(), pitch_in_degree=10, rpm=rpm
+    )
+    params.models.append(bet_disk)
+    params.time_stepping = createUnsteadyTimeStepping(rpm)
+
+    translated = get_solver_json(params, mesh_unit=1 * u.inch)
+    assert "BETDisks" in translated and len(translated["BETDisks"]) > 0
+    bet_item = translated["BETDisks"][0]
+
+    assert "initialBladeDirection" in bet_item
+    assert "bladeLineChord" in bet_item
+
+
+def test_betdisk_steady_excludes_internal_fields():
+    rpm = 588.50450
+    params = create_param_base()
+    bet_disk = createBETDiskSteady(
+        cylinder_entity=_create_test_cylinder(), pitch_in_degree=10, rpm=rpm
+    )
+    bet_disk = bet_disk.model_copy(
+        update={
+            "blade_line_chord": 25 * u.inch,
+            "initial_blade_direction": (1, 0, 0),
+        }
+    )
+    params.models.append(bet_disk)
+    params.time_stepping = createSteadyTimeStepping()
+
+    translated = get_solver_json(params, mesh_unit=1 * u.inch)
+    assert "BETDisks" in translated and len(translated["BETDisks"]) > 0
+    bet_item = translated["BETDisks"][0]
+
+    assert "initialBladeDirection" not in bet_item
+    assert "bladeLineChord" in bet_item and bet_item["bladeLineChord"] == 0