Defines the default units to be used for various modules.

default_area_units = 'ft**2' #square feet

default_avgas_units = 'lb' #pounds

default_density_units = 'lb/ft**3' # pound per cubic feet

default_length_units = 'ft' #feet

default_power_units = 'hp' #horsepower

default_press_units = 'in HG' # inches of mercury

default_speed_units = 'kt' #knots

default_temp_units = 'C' #celcius

default_weight_units = 'lb'

default_vol_units = 'ft**3'