4 Creating the VLM geometry

1. In the navigation bar, click 'Geometries'.
2. In the tree, select the right project.
3. Click 'Add a new geometry'.

 

1. Enter a name for the geometry, 'testplane-VLM'.
2. At the bottom set the center of gravity position: we set the maximum take-off mass configuration, 199 / 0 / 89 [mm].
3. For this case, we will work in mm, check the units are properly set.
4. Then we must create the fuselage, wings, horizontal tail and vertical tail. let's start with the wings, click 'Add a part'.

 

Modeling the wings

A popup window will appear for you to set parameters for the new part. for the wings:

• At the top set the name 'WINGS'
• Skip all parameters in the middle of the page, the default settings are okay.
• Edit the sections to obtain a table similar to the one given below

 

This surface will mainly model the wings, but should also model vertical force effects of the fuselage. We will use two tricks to obtain a more realistic aerodynamic result:

1. For the first section, click 'options' button, then the 'CLaf param.' tab and set a CLaf parameter of 0.01. This can be done to decrease the lift generated on the very center of the wing, were the fuselage is, as generally the fuselage doesn't generate as much lift as a continuous wing portion would.
2. Then click on the 'CDCL param.' tab, and add values as shown in the following image. This will add a drag value that is a function of the lift value for the wing. Here it used to model an increase of form-drag when the angle of attack is increased. We place this function on the wing, but it is meant to model a drag increase for the whole aircraft.

Click 'OK to validate the optional parameters.
 
NB: The CLaf parameter should only be used on the Y=0 section. The CLCD parameters can be used for all section of this wing surface. This parameters will not be used for the other surfaces.
 

You may click '3D view of the part' if you want to open an AVL window of the part geometry. Use the spacebar to close this window.
 

Finally, click 'Ok' to validate the part.
 

Modeling the horizontal empennage We will now add another surface to model the horizontal tail. Proceed similarly to the wings surface, but without adding any optional parameters. Here is the sections table:
 

Modeling the vertical empennage Add another part for the vertical tail, using the following sections table:
 

NB: The symmetry parameter must be switched to 'No', as this is a vertical surface placed on the Y-normal plane.
 

Modeling the fuselage The lift generated by the fuselage has been modeled with the wing, but not the lateral forces that can be generated in case of sideslip angle. To do that we need to create a vertical surface.
 

NB: The symmetry parameter must be switched to 'No', as this is a vertical surface placed on the Y-normal plane.
 

Now that you have the 4 parts, click 'Create' at the bottom to validate the geometry.