PEER REVIEW
20
th
Australian International Aerospace Congress, 27-28 February 2023, Melbourne
20th Australian International Aerospace Congress
ISBN number: 978-1-925627-66-4
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DSTG Planet Gear Rim Crack Propagation Test
David M. Blunt
1
, Wenyi Wang
1
, Lucinda Le Bas
2
, Riyazal Hussein
1
, Peter Stanhope
1
George Jung
1
, Elizabeth Hinchey
3
, Eric Lee
1
, Greg Surtees
1
, Nicholas Athiniotis
1
and Scott Moss
1
1
Platforms Division, Defence Science and Technology Group, 506 Lorimer Street, Port Melbourne, Victoria, 3207, Australia
2
Contractor, Defence Science and Technology Group, 506 Lorimer Street, Port Melbourne, Victoria, 3207, Australia,
3
Defence Graduate Program, Department of Defence, Australia
Abstract
The Defence Science and Technology Group (DSTG) recently conducted a planet gear fatigue
crack propagation test in a Kiowa 206B-1 helicopter main rotor gearbox (4-planet version).
This test was designed to explore the phenomenon of fatigue cracking in thin-rim helicopter
planet gears where the gear body incorporates the outer raceway of the planet bearing, and the
crack initiates at or near the raceway surface and propagates through the gear body instead of a
gear tooth. The crack was initiated from an electric discharge machined (EDM) notch in the
planet gear rim and propagated from one side of the gear to the other between two gear teeth.
This type of fault is challenging to detect reliably due to the lack of liberated wear debris, and
the relatively weak vibration signature (using classical vibration fault detection methods) until
the crack reaches across a large proportion of the gear body. As a result, this can lead to the
catastrophic failure of the main rotor gearbox. The details of the test, selected results, and other
issues are presented and discussed. A vibration dataset generated from this test was made
available to the participants of HUMS2023 conference for a data challenge competition.
Keywords: fatigue crack, fault detection, helicopter, planetary gearbox, planet gear.
Introduction
Helicopters usually have one or more epicyclic stages in the main rotor gearbox. This allows
the high torque load of the main rotor to be shared between multiple planet gears. Typically,
the sun gear is the input, the planet carrier is the output, and the ring (annulus) gear is stationary.
Detecting faults in epicyclic gears is difficult; particularly for those that do not shed metal, such
as fatigue cracks. This can lead to catastrophic failures, even in helicopters with relatively
sophisticated health and usage monitoring systems (HUMS). In two recent examples [1, 2], a
fatigue crack initiated at the inner bore surface of a planet gear (outer bearing raceway) and
propagated through the body of the gear until it fractured into pieces, with the resulting
secondary damage causing the separation of the main rotor from the helicopter.
The method most often used to detect fatigue cracks in gears is vibration analysis. Many
detection algorithms have been developed over the years and proven successful at detecting
cracks in fixed-axis gears [3-6]. However, these algorithms are typically less effective when
applied to epicyclic gear trains for three general reasons:
