diff --git a/ROSCO_toolbox/turbine.py b/ROSCO_toolbox/turbine.py
index 53c404d0b..4d28ea01f 100644
--- a/ROSCO_toolbox/turbine.py
+++ b/ROSCO_toolbox/turbine.py
@@ -82,6 +82,11 @@ def __init__(self, turbine_params):
         else:
             self.ptfm_freq = 0.0
 
+        if turbine_params['TSR_operational']:
+            self.tsr_operational = turbine_params['TSR_operational']
+        else:
+            self.tsr_operational = None
+
     # Allow print out of class
     def __str__(self): 
         '''
@@ -386,6 +391,11 @@ def __init__(self,performance_table, pitch_initial_rad, TSR_initial):
         performance_fine = f_performance(TSR_fine_ind)
         performance_max_ind = np.where(performance_fine == np.max(performance_fine))
         self.TSR_opt = float(TSR_fine[performance_max_ind[0]])
+        
+        # Save below-rated operational TSR
+        if not self.TSR_operational:
+            self.TSR_operational = self.TSR_opt
+
 
     def interp_surface(self,pitch,TSR):
         '''
diff --git a/ROSCO_toolbox/utilities.py b/ROSCO_toolbox/utilities.py
index 60fa4579f..ce93f31f3 100644
--- a/ROSCO_toolbox/utilities.py
+++ b/ROSCO_toolbox/utilities.py
@@ -484,7 +484,7 @@ def write_param_file(self, turbine, controller, param_file='DISCON.IN', txt_file
         file.write('{:<11d}         ! VS_n				- Number of generator PI torque controller gains\n'.format(1))
         file.write('{:<014.5f}      ! VS_KP				- Proportional gain for generator PI torque controller [1/(rad/s) Nm]. (Only used in the transitional 2.5 region if VS_ControlMode =/ 2)\n'.format(controller.vs_gain_schedule.Kp[-1]))
         file.write('{:<014.5f}      ! VS_KI				- Integral gain for generator PI torque controller [1/rad Nm]. (Only used in the transitional 2.5 region if VS_ControlMode =/ 2)\n'.format(controller.vs_gain_schedule.Ki[-1]))
-        file.write('{:<13.2f}       ! VS_TSRopt			- Power-maximizing region 2 tip-speed-ratio [rad].\n'.format(turbine.Cp.TSR_opt))
+        file.write('{:<13.2f}       ! VS_TSRopt			- Power-maximizing region 2 tip-speed-ratio [rad].\n'.format(turbine.Cp.TSR_operational))
         file.write('\n')
         file.write('!------- SETPOINT SMOOTHER ---------------------------------------------\n')
         file.write('{:<13.5f}       ! SS_VSGain         - Variable speed torque controller setpoint smoother gain, [-].\n'.format(controller.ss_vsgain))
diff --git a/Tune_Cases/DTU10MW.yaml b/Tune_Cases/DTU10MW.yaml
index 8ebae7500..de9409f03 100644
--- a/Tune_Cases/DTU10MW.yaml
+++ b/Tune_Cases/DTU10MW.yaml
@@ -19,7 +19,11 @@ turbine_params:
   max_torque_rate:    5000000.              # Maximum torque rate [Nm/s], {~1/4 VS_RtTq/s}
   rated_power:        10000000.             # Rated Power [W]
   bld_edgewise_freq:  4.519                 # Blade edgewise first natural frequency [rad/s]
-
+  # Optional 
+  TSR_operational:    # None                # Desired below-rated operational tip speed ratio (Cp-maximizing TSR is used if not defined)
+  # - should be defined if Fl_Mode = 1
+  twr_freq:           # None                # Tower natural frequency [rad/s]
+  ptfm_freq:          # None                # Platform natural frequency [rad/s]   
 #------------------------------- CONTROLLER PARAMETERS ----------------------------------
 controller_params:
   # Controller flags 
diff --git a/Tune_Cases/IEA15MW.yaml b/Tune_Cases/IEA15MW.yaml
index 8235d95fc..b3513f372 100644
--- a/Tune_Cases/IEA15MW.yaml
+++ b/Tune_Cases/IEA15MW.yaml
@@ -19,7 +19,9 @@ turbine_params:
   max_torque_rate:    4500000.              # Maximum torque rate [Nm/s], {~1/4 VS_RtTq/s}
   rated_power:        15000000.             # Rated Power [W]
   bld_edgewise_freq:  3.4164                # Blade edgewise first natural frequency [rad/s]
-  # Optional - should be defined if Fl_Mode = 1
+  # Optional 
+  TSR_operational:    9.0                # Desired below-rated operational tip speed ratio (Cp-maximizing TSR is used if not defined)
+  # - should be defined if Fl_Mode = 1
   twr_freq:           # None                # Tower natural frequency [rad/s]
   ptfm_freq:          # None                # Platform natural frequency [rad/s]         
 #------------------------------- CONTROLLER PARAMETERS ----------------------------------
diff --git a/Tune_Cases/NREL5MW.yaml b/Tune_Cases/NREL5MW.yaml
index 9b483ef65..06306a43d 100644
--- a/Tune_Cases/NREL5MW.yaml
+++ b/Tune_Cases/NREL5MW.yaml
@@ -8,7 +8,7 @@ path_params:
   # FAST_InputFile: '5MW_OC4Semi.fst'                                                                # Name of *.fst file
   # FAST_directory: '../Test_Cases/5MW_OC4_NR'                     # Main OpenFAST model directory, where the *.fst lives 
   # Optional
-  rotor_performance_filename:  'Cp_Ct_Cq.OpenFAST_5MW.txt'                                # Filename for rotor performance text file (if it has been generated by ccblade already)
+  rotor_performance_filename:  'Cp_Ct_Cq.NREL5MW.txt'                                # Filename for rotor performance text file (if it has been generated by ccblade already)
 
 # -------------------------------- TURBINE PARAMETERS ----------------------------------- 
 turbine_params:
@@ -21,7 +21,9 @@ turbine_params:
   max_torque_rate:    1500000.              # Maximum torque rate [Nm/s], {~1/4 VS_RtTq/s}
   rated_power:        5000000.              # Rated Power [W]
   bld_edgewise_freq:  6.2831853             # Blade edgewise first natural frequency [rad/s]
-  # Optional - should be defined if Fl_Mode = 1
+  # Optional 
+  TSR_operational:    # None                # Desired below-rated operational tip speed ratio (Cp-maximizing TSR is used if not defined)
+  # - should be defined if Fl_Mode = 1
   twr_freq:           0.4499                 # Tower natural frequency [rad/s]
   ptfm_freq:          0.2325                # Platform natural frequency [rad/s]              
 #------------------------------- CONTROLLER PARAMETERS ----------------------------------