@sh.add_function(dsp, outputs=['curb_mass'])
def calculate_curb_mass(unladen_mass, fuel_mass):
"""
Calculate unladen mass [kg].
:param unladen_mass:
Unladen mass [kg].
:type unladen_mass: float
:param fuel_mass:
Fuel mass [kg].
:type fuel_mass: float
:return:
Curb mass [kg].
:rtype: float
"""
return unladen_mass - fuel_mass