I am not to sure about a car filter, it may be a bit restrictive and make tuning the heli hard. Also it may be hard to fit it under the fan. I use a metal screen type filter from Century. I have used them for years with no ill effects. You can also try a small piece of panty hose to keep the dirt out if it's real dusty. Whenever I take my engine out of my heli I notice little blades of grass and other weeds on the filter screen so i know it's working.