[1][2] The S-21 Outbound features a strut-braced high-wing, a two-seats-in-side-by-side configuration enclosed cabin accessed via doors, fixed tricycle landing gear or optionally conventional landing gear and a single engine in tractor configuration.

The sheet metal parts employ final-size matched holes to reduce builder errors and speed construction.

With full fuel of 31.75 U.S. gallons (120.2 L; 26.44 imp gal) the payload for the crew/pilot, passengers and baggage is 625 lb (283 kg).

[5][6] In a review for KitPlanes magazine writer Dave Prizio stated that aircraft amateur builders, "seem to want a high-wing utility plane they can use to knock around the backcountry.

It's nice to be able to get from here to there at 180 knots, but if there ends up being a 1200-foot dirt strip, an RV-8 doesn't look like the best choice for the trip.