Marty: This sounds like a really great idea. There were a number of times last summer, particularly waiting on a hot ramp for take off clearance, that I thought that there should be more air from those vents. If you open them full open, there is occasionally a little whiff of fresh air, but not enough to cool this pilot.
Some of the cooling ideas (two devices with ice and electric fans) are a little over the top, to my way of thinking and would take more effort than I would like (eg. where are you going to find a block of ice for such a device on a hot ramp somewhere?) but this one is really practical.
Have you looked at the possibility of using a smaller fan? If you could find a smaller one that would still move a reasonable amount of air, it would make the device more convenient to store. It seems like every computer parts catalog I get has dozens of fans of every type and size. With the engine running and headsets on the noise level of the fan is probably a non-issue. The current draw is likewise probably a non-issue. Some compact little fan with a round shape that really moves the air would seem to be the best for this application. Bill Dobson used a small fan with a very low current draw. For your application a small round fan that really moves the air would be best. I can’t seem to get to Bill Dobson’s original post, but I remember that he used some standard PVC adaptors to mount the fan with. That would make the project even simpler.
It may be that the proper fan is not something made for a computer but made for some electronic cooling application requiring very small size where plenty of power is available. I am not sure that you need any kind of finger guard, but if a round fan was used in a round plastic tube a recess of 1/2 inch or so would lessen the concern about contacting the blade. If you got the proper little screamer in there the blade speed and power could be a consideration.
The “muffin fan” type of fan is designed particularly for low noise level where a very compact size is not necessarily needed. A little round fan with a higher blade speed and power would seem best for this kind of application.
A number of “cottage industries” seemed to have sprung up among Cirrus drivers. If you are interested in producing such an item, I for one would be very interested.