How to make airfoil profile with deflected flap, using XFOIL

The following post is intended to describe, how to generate a flap deflection on a given airfoil, using XFOIL software. The need for this kind of technique might be useful when modeling a wing profile together with a deflected trailing edge and you would like to have them as an integral part. It is easier therefore to create only one wing in your CAD model, based on the airfoil nodes that already contains the flap, for instance.

Application example: Vertical tail section with deflected rudder

(Please note, the part after the double slash symbol was used for comments only!)

Start opening XFOIL:

XFOIL c> naca0012 //This will load a typical airfoil from the XFOIL library.

It will display the following information about the loaded airfoil:

Max thickeess, Max camber, Buffer airfoil points (e.g.331points)

Panel parameters used...etc.

XFOIL c> gdes //Opens Geometry Design, to work with the buffer airfoil,

.GDES c> f //type "f" for flap definition,

Enter flap hinge x location  r> 0.6   //in this case 60% of chord,

Enter flap hinge y location (or 999 to specify y/t)  r> 999

//Here 999 is used to give y location in percentage of the total thickness,

Then it asks for that value:

Enter flap hinge relative y/t location  r> 0.5

Enter flap deflection in degrees (+ down) r> 10

After setting the deflection angle, you may look into PltLib window, where the airfoil with deflected flat is shown.

white: original airfoil, pink: deflected airfoil with 10 deg

Next command will be to execute it.

.GDES c> x

Current airfoil nodes set from buffer airfoil nodes (335)  //This tells the total number of the newly created nodes.

.GDES c> (hit enter to exit from GDES)

XFOIL c> save

Enter output filename s> naca0012_flap.dat (type a file name with or without extension)

Enter --> you may find the created *.dat file in your XFOIL working directory.