L-39NG continues test campaign, expands flight envelope

Aero Vodochody has further expanded the flight envelope of its new L-39NG light jet trainer – the latest variant of the company’s Albatros family.

In opening the envelope further, the L-39NG reached new altitudes and speeds during its flight test campaign, achieving 580mph (934.4km/h or Mach 0.82) with a full integral tank in the so-called wet wing, and operating at a height of 38,000ft (11,580m). Flight testing continued to assess the aircraft’s flight qualities and performance, focusing on take-offs, landings, rates of climb, G-loads and fuel consumption, among other things.

Jaromír Lang, chief designer of the L-39NG, said: “The L-39NG project team has completed a crucial and very challenging phase of the flight testing. After a series of ground tests, we successfully proved the airframe strength during the flight without any critical case. Thanks to these tests, we confirmed that the L-39NG design has exceptional robustness and stability.”

Before the L-39NG’s flight envelope was expanded, the prototype aircraft went through a series of flutter tests to ensure its resistance to damp spontaneous oscillations, which are induced by external aerodynamic forces during flight. During these tests, the aircraft’s structure oscillations were initiated by small rockets attached to the wingtips or by impulses to the flight control system by the test pilot. The company then analysed the vibration measurements, with the L-39NG operating at different altitudes and speeds.

During the flutter tests – which were performed by the first flight prototype, serial 7001 – a total of 192 rockets were fired. Of these, 144 were launched in flight and 48 were fired on the ground.

Dieter John, president and CEO of Aero Vodochody Aerospace, said: “We [have] achieved significant progress in ground and flight testing so far. With two L-39NG flying prototypes in the air since the middle of April [2019] plus our technical demonstrator, we are very well prepared for our remaining journey to certify the aircraft in the third quarter of 2020.”

In recent months, the L-39NG has achieved additional successful results in ground testing. Aero Vodochody has run static strength tests since the middle of last year at the Czech Aerospace Research Centre (VZLÚ) in Beranoých. Strength tests of the wing took place on the second prototype, serial 7002, which were completed with no damage. According to Aero Vodochody, these tests took place with a “combined load of torsion plus bending was done up to 100% of the ultimate load (150% of the limit load)”. The wing strength test until structural failure is scheduled to take place in the first half of this month at the VZLÚ. The L-39NG has already undergone a destructive strength test of the fuselage, which the company states was completed successfully.