diff --git a/examples/external_aerodynamics/external_aero_volume_data_processors.py b/examples/external_aerodynamics/external_aero_volume_data_processors.py
index 9c71aa7..f2854a7 100644
--- a/examples/external_aerodynamics/external_aero_volume_data_processors.py
+++ b/examples/external_aerodynamics/external_aero_volume_data_processors.py
@@ -122,8 +122,8 @@ def filter_volume_invalid_cells(
 
 def non_dimensionalize_volume_fields(
     data: ExternalAerodynamicsExtractedDataInMemory,
-    air_density: PhysicsConstantsCarAerodynamics.AIR_DENSITY,
-    stream_velocity: PhysicsConstantsCarAerodynamics.STREAM_VELOCITY,
+    air_density: float = PhysicsConstantsCarAerodynamics.AIR_DENSITY,
+    stream_velocity: float = PhysicsConstantsCarAerodynamics.STREAM_VELOCITY,
 ) -> ExternalAerodynamicsExtractedDataInMemory:
     """Non-dimensionalize volume fields."""