Courtney,
Now, we're all guessing, maybe too early to do so, but I would be far more interested to understand more about what happened, how to fix it and what may be the future issues.
What happened was a titanium fire, rare in modern day jet engines when it occurs forward of the HP compressor area, but in the colder area of the LP fan. The phenomena of a titanium fire involves subjecting a titanium part to a temperature above 1,600ºC (2912℉) and within 4 to 20 seconds a white hot fire starts which reaches a temperature of 3,300ºC (5972℉). The energy destroys surrounding materials by burning and melting. You can see in the photos provided by
kbrockman how it has burned a hole or holes in the aircraft skin. The fire once started is nearly impossible to put out. Common extinguishing agents don't work and some make the fire worse as well as their usual quantity being inadequate. An argon blanket type gas coverage in place of normal air that contains oxygen works the best. Titanium fires behave like magnesium fires, it is why there are no magnesium gearboxes on jet engines provided to the Navy for carrier operations.
Titanium is used in the front end of the engine where possible because of its high strength-to-weight ratio verses steel or nickel-base alloys. So what causes titanium fires in the case of a rotating inner seal?
- Bearing failure
- Rotor unbalance, or
- (rarely) high g-loading and flexing under certain flight maneuvers
BTW, these reasons were known in the 1960s and were published in 1979 in a report for the FAA by the National Engineering Laboratory. There is no guessing and the reason given by USAF General Bogdan was the third item above. So what do you do to avoid the problem?
Proper design processes:
- Mechanical stacking determination between stationary and rotating components
- Heat transfer and deflection analysis
- Transient heat transfer and deflection analysis under burst and chop conditions in both radial and axial directions
- Determination of transient stresses so LCF of the part can be assessed.
- Analysis of out of round instability caused by local rubbing
- Frequency analysis to prevent resonance to determine the acceptable margin
- Determination of damping requirements
- Determination side-slip instability of the rotor stator at low speed affecting fan and LP compressor seals.
But, if the design proves to not work, what do you do to fix it?
- Open up seal tolerances (performance loss and potential adverse affect on bearing life)
- Configuration and material changes (probable added weight)
- Strengthening support structures (added weight but preserves performance)
glad rag quote:
Saying that there are fixes coming is fine but, as I believe to be correct, the aircraft will never return to those original specifications for numerous reasons.
Which kinda makes you think the original specifications must have been completely unrealistic from the beginning.......<scratchchin>
I suspect most of this applies to the engine as well.