Frequency tests are the final stage before the aircraft takes to the air. They are necessary to avoid flutter — dangerous aeroelastic resonant vibrations.
The tests are conducted in three stages:
- studying the aircraft's vibrations in free flight conditions, with particular attention to the connections of units, the quality of assembly, and the operation of rudders and ailerons;
- testing the remote control system, including checking all control paths, sensors, actuators, and other units;
- testing the landing gear, aimed at preventing the shimmy effect during takeoff and landing, i.e., automatic wheel oscillations due to instability of straight rolling.
Frequency tests are a mandatory condition for aircraft type certification. They guarantee the safety and reliability of the aircraft in the air — in this case, the import-substituted SJ-100 — in operation. Their prototype of a fully domestic regional aircraft passed at the workshops of the "Yakovlev" production complex in Komsomolsk-on-Amur by the forces of TsAGI specialists.
Now the aircraft is waiting to be sent to the enterprise's flight test complex, from where it will make its first flight. However, it is currently on standby: Russian PD-8 engines are being refined. Certification of the import-substituted SJ-100 has been postponed and is now scheduled for 2025, with the first deliveries to customers in February 2026.
These engines passed bench tests perfectly. But, as Konstantin Timofeev, Managing Director of Tupolev JSC, said in June 2024, during the engine testing phase in a flying laboratory, "processes arose that could not be foreseen on the bench".
Currently, since the beginning of June, the first SJ-100 sample with import-substituted components is undergoing certification tests in Zhukovsky. However, it is performing flights on Franco-Russian SaM-146 engines to speed up certification. About thirty flights have already been successfully conducted, the last of which tested new Russian equipment providing radio communications.
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