New L-39NG trainer jet successfully passed the fuselage strength test

New L-39NG trainer jet successfully passed the fuselage strength test
Author: Aero Vodochody, VZLU|Caption: L.39NG during the test
09 / 03 / 2020, 10:00

In February 2020, the most important test of the L-39NG (serial number 7002) airframe hull strength test series was conducted at the Aeronautical Research and Testing Institute in Prague (VZLÚ). A successful static test is an important milestone on the road to full airplane certification. L-39NG is the latest addition to the famous Czech trainer and light attack jet family. The first pre-serial L-39NG made its first flight on 22nd December 2018.

The purpose of the tests was to verify the strength of the hull according to the requirements of the EMACC European military regulation. During previous tests, the strength of the torso exposed to bending, from the engine and also from the horizontal tail has been verified. The last realized and at the same time the most critical case was the combined bending load of the horizontal and vertical tail surfaces.

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In this test, the airplane fuselage was first equiped with the operational load corresponding to the maximum possible airplane load in flight, which showed that there were no permanent deformations. The airframe was then subjected to a numerical load (150% of the operational load) and the fuselage was deliberately loaded with even greater forces leading to a structural failure that occurred at 110% of the numerical load. The difference between the numerical and operational load of 1.5 represents the standard safety factor worldwide in aviation.

"The load test is the culmination of a campaign of tests that define the fuselage structure's load-bearing capacity," Pavel Henzl, Head of Technical Analysis, AERO Vodochody AEROSPACE, said. As to the result of the test, he notes: “The test turned out as it should. The structure responded to our expectations and reached the limit we needed. The design failures and reactions correspond to the calculations, so we are completely satisfied with the test. ”

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Tests of a similar scale are carried out in the Czech Republic especially when a new type of aircraft is needed and their preparation will take months, sometimes years. For each airplane it is necessary to design a unique method of experimental verification of airplane properties. This was an important event for the staff of the Aeronautical Research and Testing Institute. David Novotný from VZLÚ added: “The intention was for the test piece to withstand the load corresponding to the maximum numerical load. This proved the strength of the structure. In the course of the test we reached 110% of the numerical load, then the first deformations appeared, which prevented further continuation without the risk of complete damage to the test piece. At the same time, we achieved the necessary failure condition and therefore the test passed successfully. ”

But the path of the second prototype produced does not end there. The hull with the number 7002 will undergo further tests. “We will continue with pilot seat tests and the test of engine bed destruction in the front and rear direction, which is actually an emergency case,” adds David Novotný.

As part of the L-39NG certification, another important step has been taken. But it's not yet done. "Now we have a campaign to try out wing limit states, then we have another partial test and at the moment we are basically launching a campaign of fatigue experiments at VZLÚ, which is another big part of the certification process," Pavel Henzl from Aera Vodochody Aerospace concludes.

Source: Aero Vodochody Aerospace

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