Aircraft line profiles?

Hi!

First thank you all for these great plugins. I am new to Gimp and have been trying to spread the word.

Now I need some help please.

I am getting into Aircraft line profiles.

My main problem is the metalic sheen/shadows.

What I mean to achieve can be found here:
http://www.whatifmodelers.com/index.php/topic,26859.585.html
Here is part of a tutorial
http://robbievontrappsflyingcircus.com/?q=templateseries
Can anyone help me with a suggestion or better yet a plugin that that can create these effects?

Thanks in advance!