I have seen all manner of ducted fan units used to provide some kind of cooling affect. My personal opinion is that you get more cooling air from RAM air as the RC moves than you would get from a small electric fan. If you set up your body properly (ventilate it) and you run the right fuel to air mixture (needle settings), then your engine should be just fine. You add fans, you add weight and draw more juice from the batteries powering your receiver (unless you add a separate battery which becomes more weight). All in all, I think the bads out weigh any possible goods you could come up with for adding a fan.