What The ?

[Swamp Donkey]

Haven't heard that either...

maybe something to it...but even if you are at flight idle, there's still a lot of heat on the inside of that exhaust. The PT-6 needs it for the lip heat which is fed from the little intake in the output of the stack.

Maybe a little research is needed...hmmmm B)

 

[C-FCRA]

I've never heard of cracking the stacks. The ITT on the -66's are still around 600*c at idle. Near idle or idle descents are what we practice and have never seen it before. Anyone else heard of this cracking? :blink:

 

[co-joe]

I'll ask the boss what exactly happened. He told me we cracked one a few years ago "pre-maturely". I don't know the precise numbers of how long they're supposed to last, but this one developped cracks early. Apparently they're quite expensive?

The other thing I've heard is that "spikes" in ITT can lead to scoring inside the compressor section from the blades and the outer shell of the chamber expanding at different rates. Over time this can hurt your TBO costs. We fly a lot of short hops and usually run out of cycles before we run out of hours so keeping everything in good shape for trade in is important.

I try to fly it as if I were the one paying for maintenance. cj

 

[twotter]

co-joe,

Sounds like someone has been leading you down the garden path. While some exhaust stacks have a tendancy to crack occasionally, I don't think you will find that it's from shock cooling in flight. Starting will give you your biggest shock..

As for your other comment on the compressor, he may be talking about your CT wheel. Even that seems a little far fetched as once the engine is running the temperature is a lot more stable that at say, start-up.. Oh, did that come up again??

Happy New Years to all..

 

[Spinner]

saw a 99 come back with two six inch cracks in each exhaust on one engine.

might have had something to do with the overpressure and backfire when the compressor turbine blade went through and took out everything inside.

Guess the view from the cockpit was quite spectacular. 🙄

needless to say the cooling fan stopped pretty suddenly and all that could be
heard was the tinkling of metal against the fuselage. 🙁

thats the only time that I've seen them crack, in about 5000 hours of beech ops.