Tienie Jonker - More Than Just The Inspiration Of The JS1

By Juri Keyter

Building an aircraft from plans is an achievement but building it in 1970 must have been a triumph. The e-mail and internet ordering today probably makes the logistics of such a project the easiest part but in 1970 it was probably the most difficult. Tienie Jonker is one of those who through perseverance and commitment built and flew a glider in those days.

Tienie Jonker is the father of Uys and Attie Jonker, the creators of the Jonker Sailplanes JS1 and Tienie is therefore also known as the inspiration of the JS1. The JS1 is the talk of the world's glider fraternity with its exceptional quality and ability.

As a child Tienie saw a biplane slowly flying over their family farm in Bloemhof and enjoyed this sight so much that he tried to run after it and could not understand why he could not keep up with this aircraft appearing to be flying so slowly. This is where Tienie's passion for aviation started. In 1970 he and two partners bought a Slingsby T31 glider from Cape Town at a cost of R250 and refurbished it over a period of one year. Flight training started at Brits, then Randfontein and after the gliding club relocated to Orient, it is believed that Tienie was the first solo student at Orient. Tienie only flew the T31 twelve times before a transfer to Bloemhof forced him to sell his share in the T31.

In 1974 Tienie bought a set of Miller Tern glider plans and worked through it for a period of one year to ensure that he understood it, but most of all, to ensure that he ordered all the parts and hardware he required to complete the project. Re-ordering was simply not an option in those days and he had to get it right the first time round.

The project took a mere five years to complete with his sons, toddlers at the time, by his side for the entire duration.

Without improvising and coming up with extraordinary plans to manufacture some of the parts it would not have been possible to build an aircraft in those days. One simple example is the process of heating the Plexiglas to mould the canopy. The wooden crate used to ship all the parts he ordered was laminated with foil on the inside to slow the heat dissipation down while he blew heat into this box with a paraffin blowtorch. Once he estimated that the Plexiglas was worm enough, compressed air was pumped into the box to form the canopy. After the third attempt, Tienie was satisfied and the canopy is still on the Tern, 33 years later.

With only the primer on, the urge was simply too big and after 5 years the Tern was moved to the airfield and flew its maiden flight.

Through the years Tienie made some changes to the Tern such as retractable undercarriage which he designed and built but he and his sons had endless fun flying their creation.

Tiennie Jonker, you are truly a South African aviation pioneer and your passion for aviation did not only contribute to your own pleasure but also to the success of your sons and a legacy in our countries' aviation industry.

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