Ferram Aerospace Research includes aerodynamics fixes that simulate realistic lift and drag, modelling interaction between various aerodynamic parts, effects of Mach Number, and aerodynamic instabilities, making airplane, spaceplane and rocket designs perform more realistically in KSP.
Simple stability augmentation systems are added to make airplane flight easier and assist in controlling unstable aircraft. An editor GUI is included to calculate aerodynamic performance prior to flight.
More information can be found in the KSP Forums thread here:
A note: If you designed any planes prior to installing this plugin, they will probably need redesigning after installation; the changes in the aerodynamics are sweeping enough to force the change.
Copy EVERYTHING in the GameData folder in the zip over to your GameData folder. You MUST have a copy of ModuleManager.dll (included) in the GameData root for the mod to run properly.
The Ships folder includes example crafts to provide assistance acclimating to the new aerodynamics.
The Source folder includes the source files for the plugin in C#; they do not need to be copied over for the plugin to function properly.
How to use
Aerodynamic fixes automatically take effect after installation. However, specifying whether control surfaces should act as ailerons, elevators, rudders, flaps or some combination does not occur automatically. You must go into the editor and use the FAR Control Systems GUI to limit their control axes, and any flaps will have to be added to an action group to increase or decrease their deflection to make them function. The same GUI can be used to estimate your plane's aerodynamic performance.
In flight, the GUI displays Mach Number and air density, as well as giving access to the Flight Assistance Systems GUI, which is somewhat self-explanatory, and the Flight Data GUI, which provides various aerodynamic parameters in-flight. Help dialogs exist to explain each parameter.
More information can be found in the FAR Thread
on the KSP Forums.