With the help of Witold Kalita, the prototype was constructed in Poland and first flown on July 30, 1970. It weighed 286 lbs empty, and was constructed mostly of wood with a steel tube frame and fabric covering. Wings were constructed with one-piece ribs and a plywood covered leading edge "D-section". Power was provided by a two cylinder 23 hp "Saturn 500B" engine which was also designed by Janowski and constructed by S. Polawski.

The easy availability of the VW engine in the West prompted Janowski to redesign the structure to support added weight and power. The wing span was slightly reduced and the steel tube frame eliminated at this time. The resulting configuration was designated the J-1B and could be constructed in either wood or composite (foam & glass) versions. J-1B plans were initially made available in the U.S. by Andrew J. Baracz, and are currently available from Alpha Aviation Supply in Greenville, TX.