SEBASTIAN KAWA

Attie and Uys Jonker began to dream of their own glider from the time as children when they helped their father in the construction of a glider [the Miller Tern]. They are an example of how dreams can transform into reality. Their ambition was to fly in the WGC in their own design of glider, and with the confident knowledge that it would be the best glider in its class.

Working from a clean sheet it took them 14 years to complete the Type Certification in South Africa and they have created a factory that now provides work for fifty people.

Attie works at NorthWest University based in Potchefstroom and has access to NWU’s supercomputing network and a wind tunnel, allowing optimisation and validation of designs. His main job at the university is the development of aircraft structures.

Uys is a part of the management of the project, and has conducted most of the development and certification flight testing, becoming the most experienced glider test pilot in South Africa.


This is a new company which is gaining in experience. What captivated us was the openness and acceptance to take comments about the sailplane. The fact is that they do not have anything to be ashamed of - on the contrary, there is every reason to be proud. They are aware that it is difficult to immediately create a perfect product, so carefully collect and analyse observations and experiences, listening carefully to the suggestions from pilots. Since the first flight of the prototype [in 2006] as many as 33 design changes have been made.

The effects are visible. The latest glider, which only left the factory a few days ago, goes much better than the prototype and the ergonomics of the cockpit and the quality of handling are greatly improved. Changes include refined mylar gap sealing, a reduction in the height of the fin, more space for handling the controls, improved handles and levers in the cockpit, and adding flap fences. Increased opening of wheel doors gives more ground clearance. On the fuselage behind the canopy there is a patented cockpit air extractor which is very effective in improving ventilation.

It weighs 300kg, but this is not a major obstacle, as a well-designed, modern aerofoil profile compensates for this inconvenience. During the climb in the thermals the greater weight of the glider is not felt. The problem may be the addition of a heavy motor and hence the work on a lighter [sustainer] design using a jet. On the other hand VNE is very high at 290kph.

The glider does not feel at all flimsy or have the feel of a flabby or weak construction.

The performance of the JS1 Revelation matches its name - outstanding. In comparison with the best competitors in Hungary it performed very well, and while flying at Tswalu we could try different serial numbers and confirm the performance. Compared to the LS6c-18 [flying at Tswalu] there is already an abyss [between the performance levels]. The fact is that with the lighter wing loading the LS6 gained a bit in the climb, but in the difference in the cruise was huge. The JS1 is very good at speeds of 200kph when compared to major competitors, despite the slightly lower [maximum] wing loading.

The thinner profile does the trick. Such was the experience about performance evaluated by our pilots during the WGC. The excellent L/D at high speeds is measured by the LX as 1:33 to 1:34. In practice, it makes no sense to fly slower. At optimal speed could start the final glide assuming an L/D of around 53 ... and this is the best L/D in its class.

The glider is very pleasant and easy while thermalling. When fully loaded, or even overloaded over 600kg, there are no problems. In this respect, it is easier than the ASG29, which for an advanced pilot is also very enjoyable and is a top performer, but the handling requires some practice. Zbyszek estimated that the South African glider is easier to fly. If someone is persistent enough to stall the glider, it is possible, but even then it is controllable and easy to recover.

The question remains the extent to which problems will appear with unstable wing surfaces which appear on all wings with spars. At this time the surface deformation on the oldest prototype is minimal and JS is experimenting with heating in a post-curing oven in order to minimise problems in the future.

I must admit that the JS1 is very successful and easy to fly, and in terms of performance beats the competition. We did not expect such a revelation from people with no experience who fourteen years ago started from scratch. Such beautiful results are not accidental but the result of the university link, development finance, helpful aviation authorities but above all, the passion that propels JS to creativity. I wish them further successful designs.

Sebastian Kawa [March 2011]
Translation using Google Translate
Original article can be found here



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