It'll take a small plane like that 20-40 feet to become airborne. Tarps could work, but thier light weight would make them less than ideal. Used outdoor carpet would be better. You'll still need a flat spot of ground to do this on.

Now, that said, why not just level an area and mow the runway very short? We regularly fly small (36-45") 'leccy's from our grass field. The best use of a runway at this scale is in landing, not so much in taking off, for which a hand launch is easier. Landing takes vastly more runway. I figure a couple hours with regular lawn and garden tools, or less with a tractor, would have a suitable surface ready. Roll it for now, grass comes with time (if you seed!).

J