The SF 40 is a two-seat low-wing ultralight monoplane with a fixed tricycle landing gear. It has a fabric-covered steel-tube fuselage with fabric-covered glass-fibre wings. The first SF 40 powered by a Sauer four-stroke engine flew in 1995 but after five were built it was replaced in 1997 by an improved variant, the SF 40C. The SF 40C is powered by a Rotax 912 engine with a two-bladed propeller, a shorter wing span than the original with increased fuel capacity. The SF 40C was awarded a type certificate in May 1998.