This is how I jack up my RV-3: I bought two automotive scissor jacks and bolted a 12" x 12" plywood base to the bottom of each. I drilled a hole in the top plate of each jack and installed an eyebolt that matches the size that can screw into your wing tie-down threads. One eyebolt goes into the wing, then use a short bolt/nut that will hold the eyebolt on the jack to the one in the wing. I use cinder/wood blocks to raise the jacks high enough. This method attaches the jack to the wing securely enough that you can climb into the airplane without worry. Also, no expensive aircraft jacks needed. If you position the eyebolts parallel to the fuse, you can also level the plane fore and aft. The scissor jacks allow you to easily level the wings as well. Just remember that if you're going to jack up both sides, you must secure the tail, as (at least on the RV-3 and RV-4) the empty CG is ahead of the tie down points, and the nose will tip over.
