To be correct, the SR-71 did indeed have elevons...but they have nothing to do with the rudders. The -71 had regular "rudders...albeit full flying. Elevons are combined elevators and ailerons.

The -117 did have elevons...4 in total...two per side. The 117's "fins" as they are called are called "fins" because they supply rudder control and assisted roll control. All pitch control is supplied by the 4 elevons.

Just to make sure, I called a couple of my former DFW roommates, one who flew the -71 and the other who flew the -117.

Beave [8D]