The prototype, type SL-1, was powered by a Velie M-5 engine but this was replaced in production SL-2s by a LeBlond 60-5D. Both were five cylinder radial engines. Behind the engine the fuselage was a steel tube structure with fabric covering, flat-sided but with raised, rounded decking. The Skylark had two open cockpits in tandem, one close to the leading edge and the other over the rear of the wing.
