I’m sure there is a simple answer to this, but why can’t jet engines have some type of screen attached to the front of them to keep a bird (or anything else that could cause damage) from being sucked in?
why is this even a problem?
Asked and answered earlier this week.
By darn, I congratulate you for having the courage and energy to ask that. I wondered the same thing myself, but then forgot about it.
My guess is that systems like that would be a combination of:
[ul]
[li]too heavy - it has to be strong enough to withstand the bird strike[/li]without collapsing into the intake.
[li]too expensive - all the parts of a commercial airliner engine are fine-tuned to achieve the right profit-margin, sad but true.[/li][li]too inefficient - it would decrease engine power, so that the engine would have to be heavier and larger for the same thrust, and burn more fuel.[/li][li]too ineffective - a system that overcame all the other objections wouldn’t do much to reduce bird strikes.[/li][/ul]
The Russians have systems on their fighters that prevent the inflow of dirt and rocks into the engine. This anticipates that aircraft will have to operate from unimproved airfields in wartime, something they discovered in WWII. These systems probably aren’t effective enough handle a bird strike.
Remember, too, that airliner engines are supposed to resist strikes of a certain effective speed/weight. The FAA has standards. Either this was an unusual occurrence, or something else was going on.
I can’t help thinking now of the scene from Indiana Jones and the Last Crusade where Sean Connery downs a German fighter plane by chasing a flock of seabirds into it.
Not exactly. That OP discussed different placement of the engines and additional engines, not my breakthrough screen idea!
Maybe I’m not seeing it but where does that thread talk about screens? It seems to be all about engine placement and number.
That idea was discussed in this thread. The most relevant post is #15:
[QUOTE=aerodave]
There is nothing practical you can do to prevent a commercial engine from ingesting a bird that is determined to enter the intake. Any screen more robust than some flimsy chicken wire will produce unacceptable pressure losses in the incoming flow. Airlines depend on wringing every last bit of efficiency possible from their engines, and the performance hit from a FOD* screen that could stop a goose would be massive.
Military aircraft may have certain FOD avoidance measures built in. But these usually rely on being able to take advantage of a certain length of inlet duct to help separate foreign objects from the air stream. Commercial airliners don’t have embedded engines with long inlet ducts to work with a FOD rejection system. That’s because, again, they need all the efficiency they can get. And a near zero-length inlet on a pod-mounted engine is the best way to wring maximum performance from your jet.
They do use FOD screens in ground testing of engines. You may see a conical mesh cover put over the inlet of an engine on a thrust stand. But those are meant to stop the relatively casual ingestion of a stray bolt or pebble. They are not what you would need to withstand a 10-lb bird hitting the engine face at 200 mph. It’s like fencing equipment. The mesh face mask will help stop a foil from hitting you in the eye, but it won’t do anything to keep you from being shot in the face with a .45.
So, because there’s no practical way to keep a bird from getting in the turbomachinery, the best the engineers can do is design the engine to be as tolerant as possible of ingesting such material. When you consider how complicated turbine engines are, they’re doing a remarkable job if they can have any success at all. The fact that an engine can ever withstand a birdstrike and keep operating is amazing to me. But they’re not bulletproof, so sometimes you have what happened yesterday. And geese are pretty damned big…so yesterday’s accident was hardly surprising (if it happened they way everyone thinks).
*Foreign Object Damage
[/QUOTE]
The Russian screens are folded up out of the way once the aircraft takes off, to prevent them from interfering with the airflow at normal flight speeds, as otherwise they would cause the problems noted above. Helicopters often have fixed screens on the engine intakes, as they spend a fair amount of time close to the ground, the rotorwash tends to increase the amount of crud blowing around in the air, and they have top speeds low enough the the bad effects of a fixed screen are not significant.
Me Bad.
Thanks Colibri. At least I didn’t get docked on the return fare.
What about a deployable screen, that is only used at low altitude, then folds away somehow, restoring engine efficiency?
Of course, you probably want all the efficiency you can get on take-off, so maybe not.
People get sucked in on engine ground tests. Happened right here a few years ago.
Yep…happens.
Here is a vid of a guy getting sucked into the engine of an A6 Intruder. Before you get mad at me for posting gross stuff understand that in this particular case the guy lived (really)! :eek:
Apparently he managed to wedge himself in the air intake with his face mere inches away from the turbine blades. His helmet gets sucked off though and goes through the engine.
I was once at an aircraft museum with a guy who had done jet maintenance in the Air Force well more than 30 years prior. Even though the decommissioned planes had visible covers over their intakes, he distinctly avoided the areas in front of them, was visibly cautious in their vicinity. He said that he had seen guys sucked in, and I guess his deeply ingrained habits were still there.
Since this has come up anyway, yes, people have been killed that way.
I was told a story once that, when it happened to an S-3 crewman on a carrier, the captain simply ordered the engine removed, covered with a flag, and buried at sea. He was allegedly disciplined later for destroying government property. When it happened the next time, the engine was sent to a training school for student mechanics to disassemble, without being told what had happened to it or what all the mess was.
I heard that right from somebody else so it must be true.
There is a well-known video of a guy on a carrier who is sucked in to the jet engine when the pilot applies power. The miracle is that the guy survived because his suspenders caught on something and he was prevented from going all the way inside. You see him sucked right into the engine but the blades must have been quite further back.
Psst, sailor, it was posted, like, four posts ago - by Whack-a-Mole.
OOps. The worst part is that I DID read the thread. Oh well…
so something like a titanium screen, strong and light, would cause significant drag and significantly higher fuel usage?
I’m thinking as long as the engine is sucking in the right amount of air, the safety aspect outweighs the extra fuel consumption. Which to me would be minimal if made of a light enough product.
Has any solution ever been tested?
My bolding. With any kind of screen over the intake, the engine can no longer suck in the right amount of air. Not only that but the airflow will be very turbulent after flowing through the screen which causes problems as well. I think the essence of the matter is that failure of all engines due to foreign object ingestion is so rare that the benefit is far outweighed by the cost. In a commercial company that is not acceptable.
[quote=“1920s Style “Death Ray”, post:18, topic:482255”]
My bolding. With any kind of screen over the intake, the engine can no longer suck in the right amount of air. Not only that but the airflow will be very turbulent after flowing through the screen which causes problems as well. I think the essence of the matter is that failure of all engines due to foreign object ingestion is so rare that the benefit is far outweighed by the cost. In a commercial company that is not acceptable.
[/QUOTE]
This is interesting to me. Is there any data that supports your claim? I can understand the cost aspect of your argument. However, based on your answer, they have already tested something like this. I’m curious to read anything that shows that a screen will cause turbulent air flow that would disrupt engine performance, as well as the screen keeping the right amount of air from flowing into the engine.
Related question:
How many sets of vanes ( for compressing air intake )are there in a jet engine for A320 ?? or for similar engines ??
An aircraft engine repair guy once told me something like 24 . ( from my memory) is this correct ?