Andrzej Jeziorski/SWIDNIK
POLISH HELICOPTER manufacturer PZL-Swidnik is anticipating a second-quarter debut for its SW-4 light helicopter after rotor and vibration problems delayed the programme by more than a year.
The first prototype of the four- to five-seat helicopter was completed at the end of 1994, and was due for its first flight in January 1995. Ground tests showed, however, that the static strength of the composite rotor blades was inadequate, and structural vibration levels excessive.
According to Swidnik research and development director Ryszard Kochanowski, the first rotor blades failed at 110% of the standard maximum operational load, against a requirement for 130%. Vibration levels were found to reach unacceptable limits beyond 97% of nominal RPM, and needed improved damping.
New rotor blades were completed in October 1995, and have since been under test. Working together with Wroclaw-based hydraulics specialist PZL-Hydral, Swidnik has been able to reduce vibrations "to an acceptable level", according to Kochanowski.
The first two SW-4 prototypes have been relegated to ground testing, while the third prototype will be the flight test vehicle. It will be powered by a single 355kW (475hp) Allison 250-C20R, while later models may also be offered with the option of a 460kW Pratt & Whitney Canada PW206.
Company president Mieczyslaw Majewski says that the earlier target date for the first flight was "normal engineering optimism," and hesitates to set a new firm deadline. He says, however, that it will "possibly" happen in the second quarter.
Majewski says that the maiden flight of the now-successful W-3 Sokol helicopter in 1979 was followed by a two-year gap for modifications to the rotor, and he wants to avoid such problems in future.
Source: Flight International
