Hello there.  I'm wondering if anyone could give me advice on doubling fans, piggybacking them.  If one fan pulls in a certain amount of air, what would the effect be if another identical fan were behind it, screwed to the back of it using the same 4 screws?  Would it double or triple the amount of air that pulls and and pushes out?  What effect would this have on noise?  Would it be overkill to daisy chain even 3 or 4 extra fans together  I tried looking up info by going to Yahoo and typing in (airflow,"air flow") (basics,"how to",how-to) but didn't get any good results.  Any feedback is appreciative.

Hi,
First of all, welcome to Macmod!
I don't know if you will find this info on a computer website.  But as a long time Radio control pilot with ducted-fan experience, I can tell you that:

A: the turbulence created by a second fan in the air stream will negate any added flow.
B: the only way to overcome this is to add stators after the first fan to straighten the flow before the second fan.
And C: This adds drag and starts to make the fan duct extremely long.

In the hobby we could have as many fans as we want being driven by a nitro burning engine, but early on it was discovered to lower efficiency. Here you can see a glow powered ducted fan set up:

http://www.jethangar.com/Ducted%20Fans/df.html

I hope this helps.