Howdee
I wanted to toss in a responce to thermal coatings. Robin and S&S Turbines re-built our J-79 and updated the hot section with thermal coatings. We know first hand that these coatings work very well. The North American Eagle run our engine with kerosene and white gas to raise the BTU output and we can run the RPM's up to higher setting. This gives us more power through out the military throttle settings. Without these coatings the J79 would not handle the extra BTU output. We had an incident were excess fuel got into the liner area and lit off. We re-fired the engine and blew out the problem. After doing a check of the hot section it was determined that the coatings did their job and protected the metal. I do not recommend this procedure be done to often, but is go to know that with coatings there is a fudge factor and accident protection. We know all to well what happens to an un-protected engine, we over tempt and cooked an engine and even spit parts out, (not something I am proud of) the metal was exposed to 1200deg or more temp and the blades did not handle those temps. With the coatings Robine figures we could handle 1200deg maybe more. We run our engine in the dirt on the lake beds and the other thing coatings can do is protect the metal from erosion in this case the coating will ebrade away from the silt and sand ingestion. This does not cure the compressor blade erosion however ever little bit helps. I am a believer in thermal coatings!
The RB211 and GE90-90-100-115 use the theraml coatings to control heat related issues in turbine section. We have expirenced a few hot starts and shut down mistakes. Without thermal coatings we would be changing engines. Granted when over temps happen we do borescopes to verify possible damage. The old J79 does not have borescope capability's so we have to rely on visual inspections as best we can. The engine will be removed this winter and freshened at S&S Turbines. During this time we will look at how the enigne is holding up to the abuse.
WB