Vehicles (level design)
Making a controllable brush vehicle.
First make your plane before you do anything. You're going to want to keep it balanced. If it's not it will keep dropping down on the heaviest side. SO keep it stays balanced like a real plane would or it will fly funky.
Select you whole plane and make it a func_physbox, then give it a name like  plane_01
You need a chair to sit in. You should use the  prop_vehicle_prisoner_pod (you could use a buggy or airboat but that would look lame) name the chair  plane_01_pod Also make sure the pod isn't clipping into the planes func_physbox anywhere or it will go crazy sometimes. (it's ok if it clips with a door or other non-phys objects, but not the func_physbox)
Next set the outputs to the  plane_01_pod like so.
http://www.1337gamer.com/tutorials/vehicle/plane_01_pod_outputs.gif
Now make some  phys_constrants to hold the  plane_01_pod to the plane_01.
http://www.1337gamer.com/tutorials/vehicle/plane_01_pod_constrants.jpg
You also might want to make a trigger system to make it easier for the player to get in the plane and one that will
teleport the player somewhere when exiting the pod so there is no getting stuck.
Make a  game_ui entity. Name it  plane_01_game_ui Set the outputs for the  plane_01_game_ui like so.
http://www.1337gamer.com/tutorials/vehicle/plane_01_game_ui_outputs.gif
Not you are going to need 3  logic_compare entities. One for each, pitch. yawn. roll. These will control your thrusters.
First make a  logic_compare near the front of the plane and name it plane_01_logic_comparey. Then set the outputs for
 plane_01_logic_comparey like this
http://www.1337gamer.com/tutorials/vehicle/plane_01_logic_comparey_outputs.gif
Make another  logic_compare on one of the wings. Name it  plane_01_logic_comparex and set the outputs like so
http://www.1337gamer.com/tutorials/vehicle/plane_01_logic_comparex_outputs.gif
Make another  logic_compare near the engines. Name it  plane_01_logic_fly and set the outputs like so
http://www.1337gamer.com/tutorials/vehicle/plane_01_logic_fly_outputs.gif
Now you need to setup the  phys_thruster
Place a  phys_thruster on the left end on the wing and name it plane_01_roll_clockwise. Set the parent to
 plane_01 set the force to 800 and set the direction of the force UP. Go into the flags and check ignore mass.
Place a  phys_thruster on the right end on the other wing and name it plane_01_roll_counter_clockwise. Set the parent to
 plane_01 set the force to 800 and set the direction of the force UP. Go into the flags and check ignore mass.
Place a  phys_thruster on the front of the plane and name it plane_01_up. Set the parent to
 plane_01 set the force to 800 and set the direction of the force UP. Go into the flags and check ignore mass.
Place a  phys_thruster on the front of the plane and name it plane_01_down. Set the parent to
 plane_01 set the force to 800 and set the direction of the force DOWN. Go into the flags and check ignore mass.
Place a  phys_thruster at the end of the left engine and name it plane_01_fly1. Set the parent to
 plane_01 set the force to 2000 and set the direction of the force to "14 0 0". Go into the flags and check ignore mass.
Place a  phys_thruster at the end of the right engine and name it plane_01_fly2. Set the parent to
 plane_01 set the force to 2000 and set the direction of the force to "14 0 0". Go into the flags and check ignore mass.
http://www.1337gamer.com/tutorials/vehicle/plane_01_finished_plane.jpg
-Rickler --Rickler 17:28, 4 Jan 2005 (EST)
You should now have a basic working plane that will probably need some adjustments here and there.
Example map done by tyrtill it is really crappy and basic bu here it is and it works:sdk_vehicles2.zip (offline !!!)
Edit by Price :
Here u have convert 2 planes, the fire is only for show its dont hurt 
plane_examples.zip