Scarebus03 From Ireland, joined Apr 2005, 303 posts, RR: 2
Reply 10, posted (8 years 4 months 4 weeks 10 hours ago) and read 2597 times:
normally during an engine surge in the H.P.C, airflow to the combustion chamber and turbine section stops for a period of time. There will be a massive temp. increase in the turbine as there is no air available for cooling resulting in hot section stress. The fuel will ignite alone as there is not enough airflow to allow normal expansion of the fuel/air mixture, too much fuel not enough air. When the airflow resumes in between surges it blows the ignited fuel out the exhaust much like a flamethrower, as the combustor now has too much fuel and too much air. I once saw an A320 lose a turbine on takeoff and there was no flame as it did not restrict the airflow. For large high bypass engines it would be unusual for the flame to come out the inlet but for smaller engines especially those with reverse flow combustors it is more likely to happen.
Good job by the U.S. crew in EHAM, the system works!!
Neilking From United Kingdom, joined Aug 2005, 101 posts, RR: 0
Reply 11, posted (8 years 4 months 3 weeks 6 days 22 hours ago) and read 2554 times:
Quoting Scarebus03 (Reply 10): The fuel will ignite alone as there is not enough airflow to allow normal expansion of the fuel/air mixture, too much fuel not enough air. When the airflow resumes in between surges it blows the ignited fuel out the exhaust much like a flamethrower
That was my understanding Scare which was why I posted the question. When I initially posted, I had not spotted that there were other threads on A.net suggesting there was a more fundamental problem with this engine than a compressor surge.
A compressor surge is not a "land immediately" event is it?
Many moons ago in 1971 when I was 7, I saw a big gob of flame come out the back of an engine on an SAA 707 at Heathrow when it was starting up. But it taxi-ed off and took off normally without delay. Would that have been a c/s at start up, do you think? What other conditions of turbojets cause momentary flaming but is obviously not so much of a problem that t/o is cancelled and/or immediate return to land is not required as on the US 767 in the pic?
TristarSteve From Sweden, joined Nov 2005, 3930 posts, RR: 34
Reply 12, posted (8 years 4 months 3 weeks 6 days 21 hours ago) and read 2544 times:
Quoting Neilking (Reply 11): I saw a big gob of flame come out the back of an engine on an SAA 707 at Heathrow when it was starting up. But it taxi-ed off and took off normally without delay. Would that have been a c/s at start up
No. in older engines, when they shut down the fuel remaining in the engine drains into the by pass case and ignites on the next start. Also if the engine is slow to ignite after fuel on a flame can come out of the jetpipe. Flames in the jet pipe are not bad, it is built for the temperatures, the pilots would not even know.
Scarebus03 From Ireland, joined Apr 2005, 303 posts, RR: 2
Reply 13, posted (8 years 4 months 3 weeks 6 days 19 hours ago) and read 2527 times:
a surge usually relates to a major problem in the gasflow path resulting from internal damage to a fan, compressor, or turbine. It can also happen when engine bleed valves, variable stator vanes, e.t.c. become defective. A surge will normally result in high vibration, high exhaust temp. and overspeed (more often than not overlimit). After an engine surge occurence, action has to be taken, normally an engine change as one or more limits will have been exceeded. And if you're lucky only a component change after troubleshooting provided no limits were exceeded
The compressor stall is a transient condition where one or two compressor stages become starved of air momentarily. Even when you hear a stall it's very loud but a surge is like standing beside a grenade as it goes off. Stalls normally clear with changes in power settings but after a surge happens it's normally too late. No pilot I know would dispatch after an engine surge,
FlyingColours From United Kingdom, joined Dec 2003, 2315 posts, RR: 10
Reply 15, posted (8 years 4 months 3 weeks 6 days 17 hours ago) and read 2505 times:
I have the FAA Training Video on engine failures, its really good I'll try and grab some screen shots of the surge, there were flames momentarily coming out the front of the engines both on the test bay and the test 747.
It also went on to say that even a failed engine can still produce thrust, so sometimes even if an engine is on fire you should leave it at thrust till you are out of the ground effect, whats your opinion on that guys?
Lifes a train racing towards you, now you can either run away or grab a chair & a beer and watch it come - Phil
Airgypsy From United States of America, joined Nov 1999, 130 posts, RR: 2
Reply 19, posted (8 years 4 months 3 weeks 3 days 14 hours ago) and read 2374 times:
"Passengers reported seeing flames from the engine exhaust when moving away from the gate." I told them to have the people up front turn around and see the flames coming out of the inlet.
When the EPA mandated reduction of "smoke" from aircraft exhaust the Pratts got an instant reputation for belching flames and banging to no ill effects. Passenger complaints to the FAA caused much of the research to control the problem and it resulted in MANY bleed control configurations. They have always been prone to "off idle" stalls.
I dispatched many aircraft after surges when they were trouble shot to a fault and fixed. I talked to many pilots of 727s that reported that the surges were "excessive" and maybe that #2 needed to go to the shop. They'd move it outboard and get another thousand hours out of it.
They were all Pratt and Whitney engines.
Early F-14s had Pratts and you had to close the canopy for engine run or get singed if the engine banged. It would shoot out a flame almost to the nose of the aircraft. Seen 747s shoot flames on the pad, get adjusted, and go to the gate.
A GE engine used to turn to junk with one good hard bang (I understand that thats been remedied in their latest models). A CFM-56 does not compressor stall as a rule nor do the CF-6s. If they do, there is a shop visit in the immediate future.
Essentially, Pratt builds stout stall tolerant compressors and GE builds very good controls. If we could just get them together. Mechanic heaven.