Depends on the plane, but generally you put some linear or heavy RCS thrusters dotted around the fuselage, facing down. It\'s not a bad idea to put a couple retro thrusters in front to slow the plane so it can be perfectly vertical. It\'s trial and error, really, until you get a decently stable distribution of thrusters. Look at your RCS key mappings for translations - IJKLHN or whatever it is. Personally, I remapped it to the numpad and pg up/down. Translate the ship UP to provide a downward force. When you have the correct distribution, your plane should end up looking something like this when using translation