diff --git a/HySoP/hysop/operator/drag_and_lift.py b/HySoP/hysop/operator/drag_and_lift.py
index fd5064228b39754c754034c89f0ddaabf5f56cca..66aa09314b92fbd13e7d868317fe6bbfd059b879 100644
--- a/HySoP/hysop/operator/drag_and_lift.py
+++ b/HySoP/hysop/operator/drag_and_lift.py
@@ -18,7 +18,7 @@ class DragAndLift(Computational):
     The present class implements formula (52) of Plouhmans2002.
     Integral inside the obstacle is not taken into account.
     """
-    def __init__(self, velocity, subsets, formula=DragAndLift.Momentum,
+    def __init__(self, velocity, subsets, formula=None,
                  vorticity=None, **kwds):
         """
         @param velocity field