Oil-out conditions, or conditions
in which an aircraft is
operating without any oil in its
gearbox or transmission, are
devastating for an aircraft's
hardware. Even the sturdiest gears
usually can't last 30 minutes under such
conditions before they catastrophically
fail, and the whole system usually follows shortly after. That doesn't leave pilots with a whole lot of time to find a suitable location to land in the case of an oil-out emergency.
Following is a report on the R&D findings regarding remediation of high-value, high-demand spiral bevel gears for the UH–60 helicopter tail rotor drivetrain. As spiral bevel gears for the UH–60 helicopter are in generally High-Demand due to the needs of new aircraft production and the overhaul and repair of aircraft returning from service, acquisition of new spiral bevel gears in support
of R&D activities is very challenging. To compensate, an assessment was done of a then-emerging superfinishing method—i.e., the micromachining process (MPP)—as a potential repair technique for spiral bevel gears, as well as a way to enhance their performance and durability. The results are described in this paper.
Gear tooth wear and micropitting are very difficult phenomena to predict
analytically. The failure mode of micropitting is closely correlated to the lambda ratio. Micropitting can be the limiting design parameter
for long-term durability. Also, the failure mode of micropitting can progress to wear or macropitting, and then go on to manifest more severe failure modes, such as bending. The results of a gearbox test and manufacturing process development program will be presented to evaluate super-finishing and its impact on micropitting.
No matter how well gears are designed and manufactured, gear corrosion can occur that may easily result in catastrophic failure. Since corrosion is a sporadic and rare event and often difficult to observe in the root fillet region or in finely pitched gears with normal visual inspection, it may easily go undetected. This paper
presents the results of an incident
that occurred in a gear manufacturing
facility several years ago that resulted in pitting corrosion and intergranular attack (IGA).
The objective of this paper is to demonstrate that transmission gears
of rotary-wing aircraft, which are typically scrapped due to minor foreign
object damage (FOD) and grey staining, can be repaired and re-used with
signifi cant cost avoidance. The isotropic superfinishing (ISF) process is used to repair the gear by removing surface damage. It has been demonstrated
in this project that this surface damage can be removed while maintaining
OEM specifications on gear size, geometry and metallurgy. Further, scrap
CH-46 mix box spur pinions, repaired by the ISF process, were subjected to
gear tooth strength and durability testing, and their performance compared
with or exceeded that of new spur pinions procured from an approved
Navy vendor. This clearly demonstrates the feasibility of the repair and
re-use of precision transmission gears.
Results from the Technical University
of Munich were presented in a previous technical article (see Ref. 4). This
paper presents the results of Ruhr University Bochum. Both research groups
concluded that superfinishing is one of the most powerful technologies for
significantly increasing the load-carrying capacity of gear flanks.
This paper will present data from both laboratory and field testing demonstrating that superfinished components exhibit lower friction, operating temperature, wear and/
or higher horsepower, all of which translate directly into increased fuel economy.
This presentation is an expansion of a previous study (Ref.1) by the authors
on lapping effects on surface finish and transmission errors. It documents
the effects of the superfinishing process on hypoid gears, surface finish and transmission errors.
An experimental effort has been conducted on an aerospace-quality helical gear train to investigate the thermal behavior of the gear system. Test results from the parametric studies and the superfinishing process are presented.