Model Unvisable on some angles

[soldier101@]

I finally took a rather short modeling class for blender and decided to make a throw-able paper airplane add-on for blockland.
Right now it works fine, (*the code) But Ever since I exported the model to torque (*.dts)  the model kinda disappears on some angles. I have no idea whats causing this.
If anyone can help me fix the model, that'd be nice.
Its called Weapon_Dart cause I still haven't updated the name.
Download
IF you look into the code you'll see a lot of *dart class names. Forget about it.

[Ad Bot]

[Siberian Husky]

I assume you're refering to this? This is because back-face culling. Pretty much all game engines use it.
https://en.wikipedia.org/wiki/Back-face_culling

[PhantOS]

If your airplane is made entirely of flat faces, half of it will be invisible. Instead use thin rectangles