Originally Posted by
Lonewolf_50
The cost differential riff mentioned is a non-trivial issue when considering whether to upgrade / replace. Any manufacturer for a civil or military contract has to account for lead times for exotic / specialty alloys, and the cost versus customer requirements (and regulatory requirements) -- a balancing act that goes into any final design or upgrade decision.
Lonewolf_50-
I think the subject of what upgrades/modifications can be made to existing gearbox designs that can provide significant improvement in loss of lube operation versus the cost involved is somewhat relevant to this thread, and is worth discussing a bit further. Your comment about OEMs making decisions that are a balance between manufacturing cost and regulatory requirements is correct. But I don't think the higher raw material cost of C64 is a major factor versus the benefit it provides.
Let's take a look at an example of where C64 gears may have made a huge difference. Consider the 2009 S-92 accident where the main gearbox TTO
spiral bevel pinion suffered catastrophic plastic failure of the gear teeth from elevated temperatures during loss of lube operation after just 15 minutes. One could argue that if the TTO spiral bevel gears were made of C64, with its much higher temperature capability, they might have continued to function long enough to prevent the crash.
Below is a table of the cost for replacement spiral bevel pinions/gears used in the UH-60 tail rotor drivetrain. The TTO pinion is $7291 and the gear is $9436. The difference in raw material cost between 9310 and C64 for the 25lb ring gear forging is probably around $250, or less than 3% of the total gear cost. In this example, raw material cost would not seem to be a significant factor. However, the total cost of manufacturing and retrofitting a dozen or more gears would likely run several hundred thousand dollars per gearbox. So the question becomes is that cost worth the added safety/reliability provided?
Here's a good
NASA technical paper on the subject of C64 gears if anyone is interested.