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Faro
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Useful Lives Of Different Engine Components

Sat Jan 09, 2010 2:02 pm

It was mentioned somewhere on a previous thread that some high-time turbofans have only the production plate as original equipment remaining from their ex-factory state; all other components had been replaced.

In the same line of thinking, how long can a modern high-bypass turbofan operate before having to change the following:

- the reversers;
- the bypass duct;
- the nozzle;
- the fan;
- the LP & HP compressor stages & stators;
- the combustion chamber; and
- the LP & HP turbine stages & stators.

What life-limiting factors are involved in each case?

Faro
The chalice not my son
 
tdscanuck
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RE: Useful Lives Of Different Engine Components

Sat Jan 09, 2010 6:58 pm



Quoting Faro (Thread starter):
In the same line of thinking, how long can a modern high-bypass turbofan operate before having to change the following:

- the reversers;
- the bypass duct;
- the nozzle;
- the fan;
- the LP & HP compressor stages & stators;
- the combustion chamber; and
- the LP & HP turbine stages & stators.

The reversers and bypass duct, on most planes, are the same part and are on-condition maintenance. In other words, they don't have explicit life limits, you just run them until they die. Normally, that happens due to wear in the non-replaceable moving parts (e.g. slides), then you pull them for overhaul. The structure is essentially infinite life.

The nozzle and fan are usually similar; you do regular inspections and repair as necessary. Nozzles usually succumb to sonic-fatigue cracking eventually, and fans to FOD or wear. However, you usually do fan's on a blade-by-blade basis, so you're unlikely to change an entire fan at once.

Compressors eventually wear out (abrasion) and, depending on the engine, may be life-limited by fatigue or on-condition limited by allowable blade wear. Stators don't fatigue, but do wear.

Combustion chambers and turbine stators undergo thermal cycling fatigue, and ablation/abrasion...they're basically slowing wearing away from the day they were made and eventually hit their life-limits, which is supposed to occur before they fail.

Turbine rotors have all the wear problems of the stators, plus ferocious fatigue problems due to the high loads. As far as I know, they're all life limited by fatigue, if they don't fail due to wear (increasing EGT) first.

Tom.
 
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Faro
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RE: Useful Lives Of Different Engine Components

Sat Jan 09, 2010 9:14 pm

Thanx a million Tom, much obliged.

Faro
The chalice not my son
 
MarkC
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RE: Useful Lives Of Different Engine Components

Sun Jan 10, 2010 11:29 am

Depends on the engine, and more importantly, how often you maintain it. I'm assuming that you are talking about a part needing replacement, and not just overhaul intervals. How about a 94" 4000:

First 3 are not engine parts.
Majority of rotating parts (disks, hubs, shafts, but not blades) are life limited to 20,000 cycles by the manufacturer. Technically, nothing else is life limited, only limited to condition.
Major cases should easily last the life of the engine. Realistically, HPT blades and vanes are not going to last more than 10,000 cycles. LPT, fan, and compressor blades a bit longer. All other vanes should be good for life. Combustion chambers should be good for life, but realize that these are just sheetmetal, and can be extensively "repaired". The chamber may have very little original sheet pieces left.

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