The Jonker Sailplanes Evolution

By Luzanne Keyter (Photographs supplied by Jonker Sailplanes)

What started as a family's dream ended in the development of a high performance racing machine - the JS1 Revelation. A glider climbing well in the up currents, capable of flying slowly and then reaching extraordinary high speeds when finally touching the clouds.

In the 70's, Mr. Tienie Jonker started building a Tern (an American wood and fibreglass glider with a 15m wingspan) in the family home's garage in Bloemhof, soon getting his young sons, Attie and Uys, interested in the world of soaring. By the mid-80's the two siblings were flying wooden gliders under the watchful eye of their father and soloed shortly after their sixteenth birthday. Unfortunately, competition soaring was out of bounds for the brothers since racing gliders were sleek and fast, unlike the beloved Tern. After completing engineering degrees, Uys started working for Denel Aviation, South Africa's military aircraft manufacturer and Attie became a full time lecturer at the North West University. By the end of the 90's, both of them were lecturing at the university and got back into the competition arena, flying Cirrus sailplanes they rebuilt. Being chosen for the South African gliding team with the Cirruses, the Jonker's dream of building a perfect glider was born. Attie began design work and in the new millennium, the project took a turn for the best. These days, they are hardly novices in the sport of gliding. Between the brothers they have over 2000 gliding hours behind their names, both have been crowned national champions three times and have represented South Africa in the world championships various times.

What was born from a dream, the Jonker brothers, Attie and Uys, are slowly creating a legend in the world soaring community. At first they only thought of building one or two gliders for their own personal use. After 30 000 man-hours they produced the very first JS1 prototype. They predicted that the glider's work efficiency to be 6% higher than any other in its class and on a good day, cover a distance of 1000km within 6 hours. A week after the maiden flight on 12 December 2006, the Attie Jonker entered their first glider into the combined Open/18m class at the South African National Championships in Bloemfontein and to everyone's surprise, walked away victorious.

In 2001 the formal business operation, Jonker Sailplanes was established. Based on quality, innovation and unrivalled performance, this sailplane factory in Potchefstroom is the only one of its kind in the southern hemisphere. Jonker Sailplanes is not a one man show, involving many more than just the brothers. While Uys fills the role of project manager and Attie that of chief design engineer, Johan Bosman, an aerodynamicist, as well as an entire team at the factory also contributes hugely to the success of the JS1 and company as a whole. All executives are glider pilots and improves the operation based on the fact that they are directly involved. A huge passion for gliding and the industry also helps! Production has created over 70 jobs, and all employees are encouraged to take part in the process - innovation by all.

All 900 components used to build the glider are hand made and techniques are locally developed. A young technician at the Jonker Sailplanes facility, Lucky Kokwe, became the first licensed black South African glider pilot through AkaVlieg Potch (AVP), allowing Jonker Sailplanes staff members and many university students to become glider pilots. These days, Jonker Sailplanes produce over 12 gliders per year.

The JS1 Revelation, introduced 15 December, is an 18m class sailplane created using the most advanced methods in the layout and design. State of the art numeric computational and FEM design methods results in superior aerodynamics and the production moulds are manufactured in-house with the use of a CNC-milling machine. A lightweight structure and a unique double-hole blowing/suction system on the wing enabling very low drag allow the JS1 to reach a top speed of 290km/h. Another big plus for speed is water tanks in the wings, a small lift sacrifice for a big advantage.


Wing Span: 18m
Aspect Ratio: 28.8
Wing Area: 11.2m˛
Wing Loading (max): 53.3m˛
Wing Loading (min): 31.2m˛
Max all up Weight: 600kg
Max Speed (Vine): 290km/h
Maneuver Speed (Vb): 198km/h
Max Glide Ratio (L/D): 53

Andy Davis, 3 time world champion from Brittan flew the JS1 in 2007 and described it as “a fabulous looking sailplane, beautifully finished with impressive build quality” and that Uys and Attie should be very pleased with themselves and proud of their stunning achievement. The company's culture, dedication, capabilities, professionalism and love for the sport gives them the edge and has blossomed into a business that will put South Africa on the map as a premier supplier of competition sailplanes to the soaring community of the world.

Gliding in South Africa has become more popular over the last few years, and places like Gariep, Tempe, Potchefstroom, Parys, Brits and many others are always teeming with life. The Germans like to go to Gariep, an area for gliding and skies for the more hardcore pilots. Tempe on the other hand has a lot of infrastructure, families are welcome and there are more gliders for hire.

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