JS and M&D Jet Type certification a reality

In 2009 Jonker Sailplanes and M&D Flugzeugbau, started a 6-year long adventure, the JS1 JET. This project included the installation of the MD TJ 42 sustainer engine, with a radial flow compressor and a single stage turbine, into the JS1. This adventure took JS and M&D on a journey of more than 50 test engines, various endurance- and cycle tests, over 300 hours in-field testing and more than 200 flight tests. Finally, all the hard work has paid off, and the MD TJ 42 is EASA type certified, and the SACAA JS1 JET certification in the final stages of approval!

The Type certification involved severe analysis and testing combined with vigorous compliance verification. This demanding process acknowledges EASA to be the experts in glider certification. The standards for safety, reliability and consistent performance are particularly high. Through the cooperation between M&D and JS, this certification was completed, but not without a few hurdles.

One of these steeplechases was to run the engine for predetermined cycles at a specific temperature. The test required the engine to be run at a minimum temperature of -15°C at 103% of the maximum allowable RPM for 10^7 cycles. Here is where the high-density altitude and temperatures in Africa have contributed important insights for the development. A suitable test aircraft was luckily available at the JS Factory. These tests required a few modifications to the JS1 test aircraft.

It was essential that the testing aircraft had to carry enough fuel for the duration of the test. The fuel had to last for both the time required to climb, until reaching desired temperature, as well as completing the tests. The JS1 180L wing water ballasts became the integral fuel tanks. Sealant was used to slosh the tanks as a precautionary protection and fuel connectors were fitted to root ribs to connect the huge fuel tanks the fuselage tanks.

In addition to this modification, the wings were installed with forward facing vents, where normally the water tank vents are located. This installation caused an additional positive pressure in the ballast tanks to aid the flow of fuel to the main tanks. Temperature sensors were also fitted in front of the engine, just aft of the cockpit air extractor. The sensor ensured that temperature could be measured both inside and outside the cockpit and displayed to the pilot.

During the initial tests the wax in the diesel crystallized after being exposed to the low temperatures for long periods, resulting in a reduction in fuel flow until the engine starved. The problem could have been solved by using “Winter Diesel” or (without access to special diesel in mid-summer) by heating the fuel to 55°C overnight before filling the glider.

The JS1 Jet was towed with a Cessna 182 tug plane while jet power was gradually added to assist the climb. Around 15000ft, when the jet started to outperform the 182, the glider released and further climbing was under own power. The desired test temperature of -15°C was at reached only above 22 000ft AMSL, nearly two hours after take-off.

These were just some of the many obstacles that JS and M&D proudly overcame in their certification battle.

The EASA TC came with many impediments, a few headaches and even fewer nights of sleep, but finally, the thermal is climbed and JS and M&D can confidently glide into 2016 proofing again the legends vast growing likeliness.

 

   
   


 

 

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