Oh yeah, and here are the fans I'm using.
They are computer fans. 6cm diameter, 1cm thickness.
I got 5 of them for about $8 on ebay.

They are rated for a 12V power supply (eek!), but they kick on
at a lower speed with a voltage of 6V (four regular AA batteries).
This means that I'll probably be carying 6-8 batteries on my plane,
which will be on a seperate circuit to run the fans. It would be
standard to use AA cells, but I'm going to try AAA's because there
are significant weight savings and they have the same voltage rating.
It just means that I will have less run time.

The fans run on a current of 120 mA, while rechargable AAAs are
usually rated at about 1000 mAh. So to run 3 fans should get about
2.7 hours of run time. Do you guys concur?

(3)(120mA) / (1000 mAh) = 2.7 hour

Each rechargable AA or AAA gives 1.25V each.
Non-rechargable AAs and AAs give 1.5V each.
So an 8-pack of rechargable AAAs will deliver 10V