Guy Norris/LOS ANGELES
INITIAL FLIGHT TESTS of a new wide-chord rotor blade on a Sikorsky UH-60L testbed show that the design produces substantially lower vibratory hub loads, in addition to other hoped-for improvements in payload, speed and manoeuvrability.
The "growth" main-rotor blade now being tested on the helicopter at Sikorsky's West Palm Beach flight-test site in Florida, is designed for the UH-60 product line and is aimed principally at a possible US Army blade-upgrade programme in the 1997-8 timeframe. The composite blade is 16% wider than the UH-60's standard titanium rotor and features an anhedral tip which is angled downwards at 20¡.
Sikorsky made two sets of prototype growth rotors: a minimum weight design and a low- vibration rotor design. The former was rejected after model tests and analysis showed that the design objectives for the other blade were achieved and offered substantially lower vibration levels.
Details of the design reveal that vibratory hub loads are reduced by placing a "lumped mass" inside the blade at mid-span. Tests show that increasing the mid-span mass causes vibratory hub loads to decrease further.
Source: Flight International
