Originally Posted by
turboshafts
This is what Nadar wrote. I asked a question, wether it is clearly known if there are no HUMS readouts, or no abnormal readouts.
Thatīs is why there is an immense amount of durability testing of components.
I would tend to agree with you if it was a completely new design, but this design has operated for years with 1000's flying hours. If you look at the failure modes and
wear prior to failure modes, you are able to accurately predict the life of components, adding a safety factor to it.
The accelerometers are able to measure vibration frequency. As I understood
monitoring a given treshold for the frequency should tell you if it is abnormal operation. It might be the case, exceeding my knowledge, if the G-REDL
and LN-OJF has different positioning of the accelerometers?
Read the REDL report closely. The length of the spalling close to where the crack started is very similar on the two gears
If you look at the outer ring gear of the secondary stage planet,
you will clearly see that on G-REDL it is broken on the same place as on LN-OJF.
What is different as I see it is the fair amount of teeth crushing on the sun gear of the LN-OJF.
In both cases the outer ring is cracked open.
In both cases 1 gear is cracked into several pieces.
Such a failure is fairly stochastic. If there was a piece of the failed gear that
broke and jammed between itself and the sun gear on LN-OJF which cracked
open the case and on G-REDL it jammed between itself and the outer ring gear.
Turbo shafts
Re the prediction of remaining gear life with spalling present, I was referring to your assertion that the gear should have lasted 300 hours, not the ability of the design team to predict residual life based on certification testing.
The use of case mounted accelerometers to measure deterioration in epicyclic planet gears is close to impossible, the planet system is inherently noisy, any defect in a planet race and hence the signature it produces is constantly changing position in relation to a fixed accelerometer, the planet rotates around the ring gear and it is also rotating about its mounting point. HEnce current research programs to try to develop a monitoring system that can defect epicyclic deterioration.
The REDL report clearly states that no spalling was present on the bits of the failed gear recovered, if there was spalling it would have been on the 25% of the gear not recovered. The only evidence of spalling was the particle recovered on 25 March and the evidence it gave.
Jamming means that a section of the gearbox monentarily stopped rotating, If you read the REDL report there is no suggestion of jamming and the latest AH report into OJF says that there is no evidence of jamming. The REDL report talks about debris being "entrained" between the remaining planets and ring gear.