how to disable air unit and brigades upgrade?

[Nelson007]

I want to disable air unit auto upgrade from propellerairplane to jet plane，how?
I donot find a clear upgrade tag in tech files or unit files

 

[MartinBG]

What game version/mod is that?
In DH Full interceptors and rocket interceptors are 2 different unit types that do not upgrade from one to the another on their own, but only if the player changes default upgrade path for each unit individually.
That can be disabled by removing this line from interceptor.txt:

upgrade = { type = rocket_interceptor upgrade_time_factor = 0.42 upgrade_cost_factor = 1.40 }

You can also remove this line from rocket_interceptor.txt:

upgrade = { type = interceptor upgrade_time_factor = 0.42 upgrade_cost_factor = 1.40 }

In DH Ligth/core there's no distinctive rocket_interceptor unit type, but those are incorporated into the regular interceptor models:

model = { # Advanced Interceptor - 4
	cost 					= 16
	buildtime	 			= 150
	defaultorganisation 		= 30
	morale					= 30
	manpower				= 1
	maxspeed				= 650
	surfacedetectioncapability	= 6
	airdetectioncapability		= 6
	surfacedefence				= 10
	airdefence				= 9
	airattack				= 15
	strategicattack				= 0
	softattack				= 2
	hardattack				= 2
	navalattack				= 1
	range					= 325
	supplyconsumption 			= 1.1
	fuelconsumption				= 1.9
	upgrade_time_factor = 0.5
	upgrade_cost_factor = 1.0
}
model = { # Basic Rocket Interceptor - 5
	cost 					= 20
	buildtime	 			= 150
	defaultorganisation 		= 30
	morale					= 30
	manpower				= 1
	maxspeed				= 1000
	surfacedetectioncapability		= 5
	airdetectioncapability			= 6
	surfacedefence				= 16
	airdefence				= 13
	airattack				= 18
	strategicattack				= 0
	softattack				= 0
	hardattack				= 0
	navalattack				= 0
	range					= 150
	supplyconsumption 			= 1.3
	fuelconsumption				= 2.2
	upgrade_time_factor = 0.5
	upgrade_cost_factor = 1.0
}
model = { # Improved Rocket Interceptor - 6
	cost 					= 25
	buildtime	 			= 150
	defaultorganisation 		= 30
	morale					= 30
	manpower				= 1
	maxspeed				= 1200
	surfacedetectioncapability		= 7
	airdetectioncapability			= 8
	surfacedefence				= 16
	airdefence				= 15
	airattack				= 20
	strategicattack				= 0
	softattack				= 0
	hardattack				= 0
	navalattack				= 0
	range					= 200
	supplyconsumption 			= 1.5
	fuelconsumption				= 2.5
	upgrade_time_factor = 0.5
	upgrade_cost_factor = 1.0
}
model = { # Basic Turbojet Interceptor - 7
	cost 					= 19
	buildtime	 			= 150
	defaultorganisation 		= 30
	morale					= 30
	manpower				= 1
	maxspeed				= 900
	surfacedetectioncapability		= 7
	airdetectioncapability			= 7
	surfacedefence				= 16
	airdefence				= 16
	airattack				= 22
	strategicattack				= 0
	softattack				= 2
	hardattack				= 2
	navalattack				= 2
	range					= 350
	supplyconsumption 			= 1.2
	fuelconsumption				= 2.1
	upgrade_time_factor = 0.5
	upgrade_cost_factor = 1.0
}

There's no simple way to "disable" those as more editing is involved and errors could be made along the way. Probably the fastest solution would be to edit techs that enable those models and comment-out lines that do so, effectively making those models unavailable for production and upgrade in new games.
secret_weapons_tech.txt:

  # Basic Rocket Interceptor
  application =
  { id        = 7010
...
    effects =
    { command = { type = new_model which = interceptor value = 5 }#REMOVE THAT LINE
    }
  }
  # Improved Rocket Interceptor
  application =
  { id        = 7020
....
    effects =
    { command = { type = new_model which = interceptor value = 6 } #REMOVE THAT LINE
    }
  }