you better use this my friend, you will see more than you expected :wink:
If you want more specialized answers, you can also use its forums. It is active and supoorted by some professors
http://www.theottomans.org/english/index.asp
basic armor theory here.
this:
and the fact that even if penetrated, the relative armor thickness is higher if penetrated in an angle. same solution the soviets introduced with their t-34.
less plate diameter resulting in less weight @ higher relative plate diameter concerning the most obvious blow direction.
Think it's best said that it could be used to deflect blows, in a dynamic sense. But being unique to a certain culture, much like all armor is, it's subject to the trends of that culture. In short, many armors are based off of art...in this case Islamic art. Many of these arms and armors were formed off of Islamic iconography, including vegetal patterns, figural representation, and calligraphy.
One thing about this helm in particular was that this helmet was not only seen as just armor, but signified as a kind of religious insignia, the fighter of a Holy War. To answer your question about the disadvantages in melee combat, the turban helmet was mostly intended for heavy cavalry.
So to sum it up, the geometry of the helm is widely based on the art, religion, and effectivity as a defensive helm. Also like it was proposed before, it largely displayed the wearer, who would have been mounted on a large Arabian warhorse, decked out in a vivid display of armor. The conical, bulbous shape is also very characteristic with the Islamic mosques, further signifying cultural and religious influence, showing that geometry was also another important part in Islamic iconography.
This is my personal opinion derived from factual sources, including the metropolitan museum of art's webpage. I also read a book, of which I can't remember the name :(, that was a history of armor and it's dynamic and cultural relevance.
Below is a picture of a Islamic foot soldier, noticeably without the turban helm that is in discussion.
A turban helmet, like the one that is featured in cRPG.