Originally Posted by
riff_raff
Lastly, one change I would like to see the FAA implement is for every certified gearbox design in production to undergo a formal design review every few years using the most current analysis tools/techniques available.
That is probably a good idea from a safety perspective. But:
- It would be quite expensive: Who pays for it?
- It probably wouldn't have caught this one. Using the planetary gears as bearing outer races is not an immediately visible safety hazard. It becomes one since material properties of a gear and a bearing race are somewhat similar but in detail not identical. A planetary gear with a separate bearing race inside could similarly break apart, e.g. if the bearing fails. Admittedly the latter design would put one more layer between potential problem and disaster. In that way a review of the redundancy concept might indeed have caught this design as lacking one layer of redundancy.
It is a bit sad to see that both manufacturers of the two only available (competitive) Types in this Heli category used technical trickery in order to shave weight. Sikorsky used a clever paragraph in order to circumvent the necessity for a more massive MGB/Gears that would have the mass to run dry for 30 minutes. AH tried to squeeze every ounce of the MGB by using the gears as outer races and putting the lift load through a mere 3 suspension bars.
Might be the downside of the cut- throat nature of competition in the O&G industry.