Turbomeca help
Hi VF,
I am not going to hide behind the bush. I am a Turbomeca employee and would like to accomplish a number of things here:
a) first of all, congratulations for having 2 Arriel 2D having reached TBO already... that is pretty remarkable as a handful only have flown that much yet,
b) provide general info about difference between "creep limit" and "cycle life limit" as I think it might benefit all who have interest in this thread,
c) comment about the O/H cost difference question in general terms,
d) offer you to PM me if you want to contact me outside of the forum as an "official" Turbomeca person.
So for the creep counter, this "new" limit applied to the latest generation of Arriel 2 engines is only applicable to HP blades. It is essentially a continuous computation by the FADEC that takes into account the combined levels of rotational speed (N1 speed) and temperature (T45) the blades are subject to. The existence of this "new" live monitoring for HP blades has enabled Turbomeca to open some areas (think power rating capabilities) of the flight domain during certification. It is a tad different than the existing "Life Limit" defined in cycles (and mostly driven by variation of load based on rotational speed only... think of a cycle as one occurence of you loading the component by accelerating it from no load at all when engine is shutdown to some load as you accelerate it to say flight gate speeds... then you have partial cycles added when you lower the load and reinstall it before complete shutdown for whatever operational need that caused to significantly drop the collective and pull it back up later...) that has long existed on most engines for setting limit after which parts (mainly disks and similar rotating components + blades) have to be retired from service just like the creep. For info the Arriel 2D HP blades have both limits... creep and life in cycles as depending on how one operates, one or the other might be reached first. These 2 limits are aiming at controlling the risk of occurrence of 2 different components damaging modes.
For the O/H difference between the 2 engines the main reason why people must be gun shy to give you an estimate is mainly because there is very limited experience with return of 2D reaching O/H.
Now my 2cts is that if one engine has reached creep 250% while the other is only at 50% after roughly the same number of hours (4000hrs), that is probably because one has seen higher levels of N1 / T45 during its first TBO. I would venture to say that the cost of the O/H of the engine having seen the higher level of load may become higher if more heat related damage (cracking of NGV's or burner can) is found during inspection. The main difference though would be the set of HP blades IF the blades of the engine with only 50% creep are not rejected for other type of damage (like having lost the coating protection and starting to show signs of profile erosion for instance). Anyway, as you see there are lots of "if if if" in this and it is not to try not to answer you... It really is hard to completely predict prior disassembling the engine.
I hope this will help a bit. Please feel free to PM me if you wish to connect with me as an official Turbomeca person.
Safe and enjoyable flying to all