Missing faces when importing Blender Model into Game

[Leystryku]

Hey,
I'm trying to export my model into Unreal Engine || Source Engine, but at both of these engines faces ended up missing or only showing up if the model is viewed at by a certain angle.

Example:
[url]http://i.imgur.com/1zLvQxJ.png[/url]
[url]http://i.imgur.com/sXekQUZ.png[/url]

In Blender:
[url]http://i.imgur.com/j2uVFZN.png[/url]
[url]http://i.imgur.com/k4N6om5.png[/url]
[url]http://i.imgur.com/nVR4iOC.png[/url]
[url]http://pianova.com/images/products/eb95d96b-a29a-467f-9e68-b75522099949.jpg[/url]

Does anyone have an idea whats wrong?

Edit:
Alright, I managed to fix it by using Normals->Recalculate & Flip direction.
Isn't there an easier way to handle this automatically though?

Edit2:
Welp, whenever I rebuild the lights in unreal engine the model turns fully black