The final and most important question, which was left out of Compressor Stall 2... is answered here. A Boeing training video about Compressor Stall : • Boeing Compressor Stal...
Don’t get old! 25 years ago I was waterskiing,playing hockey, working out, giving blood, riding bike and working 50+ hours a week, 10 years ago I was riding bike and working 50+ hours a week, these days I hope to do some of those things again someday and work 40 hours a week. By the way compressors stall because shit wears out!
"Don't get old" is good advice bur inevitable. I just turned 70 last October and am going in for a left hip overhaul next month. Believe me, keep your carcass in shape, whatever it takes.
You want to know my my old man at the first job said? I sat down. Put his lunch box on the table and took out his sandwiches. He looked at it and took a bite. 'Not cheese again;' I asked who made them. He did.
Remember my days in Cold Lake as a tech on CF-5's. J85 a great little engine but for some reason was prone to compressor stalls when fitted to this bird. Good thing it had 2 because it seemed like there wasn't a day went by without a 'bell' alarm as a result of a pilot calling in a stall on an engine. Double stalls were very rare & most of the time the pilots were able to get relights, so few crashes as a result. It was a busy time with many prospective fighter pilots from various NATO countries besides our own in their last phase of training to be full-fledged fighter jocks. So in the end it was probably a combination of engine inlet design of the aircraft along with hot shot rookies diddling with throttle position during various flight envelopes that caused so many stalls. The Tutors flown by the Snowbirds rarely suffer compressor stalls, same engine without afterburner..... Kind of makes one wonder about an engine being fine tuned on a stand in a test cell vs being installed in an aircraft with different intake geometries.... Not generally a thing with airliners as they mostly hang from the wings without lengthy intake tunnels.
Another feature i found interesting in school is that the compressor doesn’t stall all at once, when one blade stalls it perturbs the flow around it and can propagate or form waves and other nasty things
I have a quote for you. "Old age isn't so bad when you consider the alternative." This is attributed to the famous French entertainer, Maurice Chevalier. There's also a book, 'Gettin' Old Ain't for Wimps' - and I've got the big Eight-Oh coming up in August. Now I'll get back to answers on compressor surge/stall on the previous video.
You are an asset to this channel. You really are a part of it now, since you've also had to endure some attacks by the dunning-Kruger brigade, as they feel the need to "correct" you. I always feel like I should apologize when some moron thinks he's going to set you straight.
Had a 79 in 1989 that when you snapped the throttle from mil to max would over temp due to nozzle not opening fast enough. The engine would over temp and drive the speed below 87%, that would take the engine out of A/B then the speed would recover and the A/B would light again and start the cycle again. NAC had an internal failure.
Excellent example of how a malfunctioning component can affect the operation of the engine. We can all learn from this... but some out there will choose not to.
When I was an aircraft welder at Langley AFB in Virginia I was watching a mass takeoff of all our flyable F15s going in pairs, side by side when one infrint if me in full afterburner suffered a conoressor stall and lost lift. The wingman dropped his throttle and stayed next to him as he recovered very quickly and still took off, just used up a few hundred more feet of runway. Kept going and did not return to base as pilot didn't see any reason to return.i couldn't believe how quickly that engine recovered tho. I would say no more than 5 seconds and he was at full throttle again. F100 Pratt & Whitney engines.
Yes, one way a compressor can stall is if the rotation speed increases so quickly it gets a little "in front of" the resultant airspeed through it. Backing off and reapplying throttle a bit more gently cures it.
A word that was used a fair amount by one of my college profs that seems particularly apt in this case: You take a perfectly running engine then "perturb" it. Kick it, run a goose through it or volcanic ash - you perturb it. A manufacture will do this in a controlled manner but once your engine is out in the wild; what perturbs it is no longer controlled. The prob was fond of kicking things to perturb them. :^) Spinning tops, excessive voltage - you get the idea. Anyway, I also grew fond of the word.
Hello! While I understand your explanation of a compressor stall, i think it would be cool if you could assemble a hollow compressor case with the VIGVs actuating linkages intact and get a shot of them in action from the inside without the compressor in the way. Is such a setup possible for illustrative purposes? Thanks!
You've got to be kidding. You appear to know not what you ask. I have shown something similar in my T58 series. In my J79 test videos is an actuation of the vsv system, but from the outside.
Now you got me worried! Compressor stall is not that bad, it could be flown with no problem, even if flames are shooting out at both ends, everything is OK. The stall may just be due to little dings, or just ageing. And then I worry. This thing is damaged! Better go into another plane!
Just a coincidence. A lot of armchair experts are not really helpful. A stall is not an engine failure, nor an engine fire. Even a tailpipe fire is not an engine fire, and at no time was the aircraft "on fire". The crew were very calm, because they knew it was an annoyance, not an emergency.
@15:00 - talking about "the physical linkage" for VSVs and "it's can't detect a near-stall condition and back off" gave me an idea... You are probably aware of the existence of hydraulic lifters in piston-engine valve trains to modify the valve timing... i bet it would be possible to design a VSV ring linkage with a hydraulically-variable length to allow the FADEC to vary the pitch of individual VSV rings relative to each other.... It would be really interesting to see a modern airliner engine using such a system coupled with per-stage sensors to detect an oncoming stall and interrupt it by reducing the pitch of just the stage or stages experiencing critical airflow.
It would be interesting. The ultimate would be to have every variable stator equipped with its own sensor (RVDT: rotary variable digital transducer) and rotary actuator, to constantly monitor and adjust its position. But for that, it would also need an air speed sensor. That would add enormous complexity, considerable weight, and many millions of dollars to the overall cost, as well as many hours and dollars to maintenance. Maybe just having each stage independently controlled. But then, it's a solution to a problem that is so rare. Properly adjusted and maintained engines don't stall, until they are damaged. Do you want to spend billions on a fleet of engines only to avoid a stall once they are damaged? Would that save lives? How many people are hurt by airliner engines stalling?
I could be wrong here but I am under the impression that many compressors work best at a specific air ingestion rate. This has been told to me as the reason for needing the ramps and spaces between the fuselage intakes and engine intakes. Mt favorite example for this is the F-4 as it had two different engines EG the SPEY in RAF service. Apparently the intake ramp activation happened at the same IAS as the J-79 engine variant. I was told that since airlines should not hit transonic speeds so they do not need them. However in extremely turbulent air I'm guessing you could have a 100kt difference in airspeed which would give the compressor a really hard time. This is roughly what wiki says but TBH I do not 100% trust either source.
You've "been told" a lot of things. Many of them are not revelations, but are just things. You've mingled all of these normal and well understood principles into a bit of an interesting grouping here.
There's a well known video of 757 ingesting a crow on takeoff, engine stalls, with flames shooting out of it (why periodically?) until crew shuts it down, plane returns to airport.
Periodically because the ignitors are on continuously during takeoff but fuel can only ignite when it's mixed properly with oxygen. No oxygen, no fire. Usually the compressor makes there is lots of oxygenated air to mix with the fuel. If the compressor is damaged, there will not be enough air, and the fuel won't ignite until it spreads out by being blown out the back of the engine into the local air. Once it is spread out enough, it burns. Then all the fuel is gone, the ignitors stay on, the fuel keeps spraying, and the cycle repeats.
That's not correct. Under normal running conditions, only about 15 to 20% of the oxygen in the air in the combustors is used to burn the fuel. During a compressor stall the flame usually does not go out. Even if the ignitors are not activated.
You're interests interest me. But I could care less about compressor stalls because I am not a pilot and can do nothing about it. I love machinery and knowing how things work. I can understand motorcycles though, Like seeing the bikes. I work with turbine engines but only in the control and data acquisition realm..: peakier power plants. Still, the power plants are boring, the bikes are exciting.
