I tried "air dried" beef jerky last summer and it worked well.
We place a small fire, well more of a barely smoking fire under the frame and covered it with hazel bows and a tarp. We used oak and cherry to smoke the meat but as mentioned above the fire was only there to keep the bugs off and help smoke the meat.
We flavoured some of the meat in Chilli and garlic, the rest was just heavy salted. Its best to cut it as thin as you can as it will dry faster. In regards to how long, well you need a very dry day, light breeze and start it first thing in the morning and it will probably take all day - atleast..
bot the best pics but you will get the idea
Drying rack