Why no screens on Jet engines??

[e-tek]

Thought one of you know-alls would be able to answer this: Why don't they put screens over jet engines to avoid "bird-strikes" like occured today when the plane went into the Hudson??

 

[ddawg16]

The material technology is not there yet.

A screen strong enough to prevent a bird strike would be too heavy and most likely restrict the air flow too much.

The reality is that bird strikes happen so rarely...and when they do, it's rare that it causes an engine failure. They actually test the engines by shooting chickens at the engines while they are running. I believe the engines have to be able in ingest a 4.5 lb chicken without loosing power. And you also have to take into consideration that most birds are well below 4.5 lbs.

As far as I know, this is the first time that birds have taken out both engines on an aircraft.

 

[boiler7904]

I'd think that a screen would get sucked into the engine and do more damage than possible FOD. It would only be a matter of time before one sucked in a screen and destroyed itself.

I'm thinking that screens would throw the aerodynamics off too by creating a big pressure zone in front of each engine due to decreased airflow.

 

[e-tek]

The news stated that 200 people have been killed since 1980 due to bird strikes. 90% happen around airports. Not all that rare.

 

[willysman]

I won't qualify as a know-all, but I think ddawg16 is on the right track. I've heard the chicken story also. The engineers have been battling this for years, balancing safety with adequate performance and efficiency. I don't envy them.

On the airflow side, I do know that those turbine inlets require a uniform flow into the chamber. Think of the rpm at full throttle on takeoff. Balance is king. So a screen would upset it. Plus, traveling at about 250 mph, any screen has all it can handle keeping birds out. I think all it would do is plug the inlet, when most of the time the turbine just pulverizes the goose and keeps going. It's a hard thing, deciding how much protection to put on a piece of equipment without rendering it ineffective. Bottom line: that pilot had some skills. Very impressive.

Any turbine engineers out there want to comment?

Which brings me back to the ddawg16 chicken story. It's not hard to imagine the inlet blades getting really bent up on impact, even if you threw a roll of Charmin in there at 250mph you'd think there would be consequences.

I wonder how they wind those chickens up to 250mph in the lab. Setting aside for a moment the obvious gravity of the LaGuardia situation - from a pure engineering viewpoint, being tasked with getting a chicken to travel 250mph is what makes engineers get out of bed in the morning. Whoever was asked to make that happen has the best job in the world.

 

[e-tek]

This is the second bird strike causing double engine failure in a short time span. November 2008 a Boeing 737 from Fankfurt suffered dual engine failure due to a flock of birds. They also landed the plane without deaths (to humans).

 

[boiler7904]

Willy,

One of the shows on the Discovery Channel a couple of years ago showed them testing airplane windshields by sending frozen chickens at the plane using an air cannon. Seems like they'd test the engines the same way.

 

[willysman]

I think you'll find that, of the 200 in the past 28 years, the vast majority of them were in small craft: ultralights, Cessna 172's, etc., where you have the unfortunate combination of light craft, single engines, inexperienced operators and surprise.

Most of the turbine craft have min 6-8 passengers, up to 350 passengers on large jets. If you examine the 7 or-so-per-year (200/28) death rate, it supports that argument. If that USAir flight had a less skilled pilot over Manhatten, we'd have nearly doubled the score in one afternoon.

Today was a very serious, "Lightning strikes twice" event with miraculous intervention. I think we'll learn more in the next several days.

 

[Stuart in MN]

I wonder how they wind those chickens up to 250mph in the lab. Setting aside for a moment the obvious gravity of the LaGuardia situation - from a pure engineering viewpoint, being tasked with getting a chicken to travel 250mph is what makes engineers get out of bed in the morning. Whoever was asked to make that happen has the best job in the world.

As it happens, I used to work with one of the guys who invented the chicken gun. http://en.wikipedia.org/wiki/NASA_Chicken_Gun

 

[Gabriel J]

I wonder how they wind those chickens up to 250mph in the lab. Setting aside for a moment the obvious gravity of the LaGuardia situation - from a pure engineering viewpoint, being tasked with getting a chicken to travel 250mph is what makes engineers get out of bed in the morning. Whoever was asked to make that happen has the best job in the world.

They freeze them and shoot them out of an air cannon. No i'm not lying. sometimes they also thaw them and shoot them out of the cannon. I watched the videos during my Aviation Technician training in the Coast Guard.

 

[Gabriel J]

Wow everyone stole my thunder while I slowly typed my response....

Bird engine strikes are a somewhat common occurance. Very rarely does it bring a plane down. 200 deaths from bird strikes in 28 years..not a whole lot considering I would say turbine engines are ingesting birds and safely completing their flight on a daily basis around the U.S.

-Gabe

 

[MXtras]

Were any of the birds wearing towels on their heads?

 

[kartracer55]

Haha interestingly enough, my friends girlfriend was commuting back from the city tonight and noticed a large crowd of boats in the hudson, and wondered "what the heck are all those boats doing"


Sorry, no point, just thought that was kind of ironic.

 

[kartracer55]

Were any of the birds wearing towels on their heads?

hahahahah thats classic. I give it a day before somebody complains about this post tho lol

 

[willysman]

Well I 'd have to say Stuart in MN brings the trump card with the NASA gun. Unbeleivable. And maybe a little bit funny. Midly sick, but funny. Well, you know what I mean...mostly funny....

Stuart, I'm guessing you're a Honeywell engineer. Or Alliant Tech? I'm in the Twin Cities also, I'll send you a message.

 

[wantedabiggergarage]

90% happen around airports. Not all that rare.

I wonder what percent happen around airplanes? LOL

Now the serious question, what is the MAXIMUM altitude, they think for strike possibilities?

 

[Nuit Damnant]

Quick search yield 1318 deaths from 1980-1995 due to lightning. So I'd say 200 from then till now is rather uncommon. Less likely than getting hit by lightning anyways

 

[Rory Bellows]

I think the Concord was brought down by a bird. They are out of business now maybe because of it.

 

[Thomarann]

I wonder what percent happen around airplanes? LOL

Now the serious question, what is the MAXIMUM altitude, they think for strike possibilities?

Well, since you asked.

"Question - What is the highest flying bird?
----------------------------------------
I am not aware of any documentation for regularly occurring highest flying
species; the greatest altitude documented as of the mid 1980's was a
Ruppell's griffon, an African vulture, struck by an airliner at 37,000 feet.
Another vulture, a lammergeyer was seen over "its mountain home" at 25,000
feet over Mt. Everest; alpine choughs have been recorded nesting at 27,000
feet on Mt. Everest. A mallard was struck by an airliner at 21,000 feet over
Nevada. Records of smaller birds, also from hitting airplanes, are mostly
from 7,000 to 12,000 feet."

from here.

 

[Kapt]

I agree that the pilot and crew did a great job protecting life. But has anyone thought about this scenario: Birds take out #1 (left) engine causing a fire and numerous cockpit alarms. Tons of confusion in the cockpit and the non flying pilot shuts down the wrong engine. Too low on altitude to restart it, so they ditch the airplane. It's very unlikely for birds to take out both engines and shutting down the wrong engine does happen.

I hope after the investigation concludes, that the pilot is truly the hero everyone is calling him.

 

[IHI]

OMG, the US just declared war on Canada!!!!!

They determined it was canadian geese that brought this plane down, FN terrorists birds anyways

 

[Kevin54]

I just watched the evening news and they were interviewing a guy in Dayton, Ohio tha tis contracted to shoot objects at objects to see how the stand up. He was saying that bird strikes are a common thing and happens almost on a daily basis. The thing is though that the designs of engines are made to withstand one or two birds hitting it and not a flock of birds. Redesigns are always considered, but alloys, weights, etc, play the huge part of it. It also stated on the news that the worst injury was one woman had two broken legs. They said when the plane hit was about the same impact as getting rearended in a car. Lucky people. I can't imagine being in that frigid water as cold out as it is.

 

[wantedabiggergarage]

I think the Concord was brought down by a bird. They are out of business now maybe because of it.

I thought it was the tire blowing and flames following the plane up on takeoff a few years ago now (I think the second to last flight of any Concorde).

 

[The Muffin Man]

My former high school robotics teacher has a brother that flew jets in the navy. Several hundred feet after taking off an aircraft carrier a pelican was sucked in by the engine of his jet. He eventually had to eject when the engine failed and would not restart.

 

[Kapt]

I thought it was the tire blowing and flames following the plane up on takeoff a few years ago now (I think the second to last flight of any Concorde).

They hit a piece of metal that had fallen off a Continental jet that had taken off before them. I still think the lawsuit against Continental is ongoing.

 

[tatra]

it all has to do with costs.........first ya put a screen on, then it has to be chrome cuz that's what united has on theirs.............then anodized, then the logos/branding by mr.gasket etal..........and then we might as well put a filter in there and then the top hat has to be inverted to make it sound mean when ya open it up..........and then ya need a snorkel to out cool the air canada boys , and it doesn't stop, ever............i'm sure nissan crawler can attest to the lengths pilots will go to outdo the others when it comes to cooling up on the others...............at least that is my guess knowing men and machines the way i do............

 

[nissan_crawler]

Thought one of you know-alls would be able to answer this: Why don't they put screens over jet engines to avoid "bird-strikes" like occured today when the plane went into the Hudson??

I've seen birds go through 1/8" aluminum, 1/4" glass, bend a .032 aluminum bracket out of the way, then dent a piece of .040 aluminum.

I saw an eagle strike that was 100% parallel with the airplane, hit just a little off center of the nose, and still smashed the nose in almost 2", even though it was hitting at damn near a 70% angle.

I've seen a bird strike shatter (but not lose pressurization) a glass window that's many layers about 3/4" thick.

That screen would have to be made of rebar.

I won't qualify as a know-all, but I think ddawg16 is on the right track. I've heard the chicken story also. The engineers have been battling this for years, balancing safety with adequate performance and efficiency. I don't envy them.

On the airflow side, I do know that those turbine inlets require a uniform flow into the chamber. Think of the rpm at full throttle on takeoff. Balance is king. So a screen would upset it. Plus, traveling at about 250 mph, any screen has all it can handle keeping birds out. I think all it would do is plug the inlet, when most of the time the turbine just pulverizes the goose and keeps going. It's a hard thing, deciding how much protection to put on a piece of equipment without rendering it ineffective. Bottom line: that pilot had some skills. Very impressive.

Any turbine engineers out there want to comment?

Which brings me back to the ddawg16 chicken story. It's not hard to imagine the inlet blades getting really bent up on impact, even if you threw a roll of Charmin in there at 250mph you'd think there would be consequences.

I wonder how they wind those chickens up to 250mph in the lab. Setting aside for a moment the obvious gravity of the LaGuardia situation - from a pure engineering viewpoint, being tasked with getting a chicken to travel 250mph is what makes engineers get out of bed in the morning. Whoever was asked to make that happen has the best job in the world.

Actually, 99% of the time, an engine won't even hiccup when it eats a bird. I've witnessed it on the ground, absolutely no ITT or N1 change, inspected the engine, not a scratch on it.

The chickens are encased in a foam block that's split in two and shoved down an air cannon. When it comes out of the cannon, the foam halves fall off, and you now have a bird hurtling at a plane.

Willy,

One of the shows on the Discovery Channel a couple of years ago showed them testing airplane windshields by sending frozen chickens at the plane using an air cannon. Seems like they'd test the engines the same way.

I believe there's some mis-information there. When they say they use frozen chickens, that's in reference to the fact they used to use LIVE chickens, feathers flying off and all. This was deemed cruel, so now they use "frozen" chickens, however, they are thawed before being shot at the plane. A frozen chicken would come out the other end, thawed ones do enough damage as is.

The only situation I'm aware of frozen birds being used is military aircraft to test canopies.

 

[Moose-LandTran]

Chicken Gun in action!

The first recorded use of a chicken gun was by the Royal Aeronautical (Aircraft) Establishment (RAE) in Farnborough, UK in 1961.

Woohoo! Go Britain!

 

[Moose-LandTran]

I'd love that job, just so i could go home and have the future wife ask "What did you do at work today, honey?" and i could say "I fired a chicken at 250mph into a jet engine at full-tilt."

She's an animal lover, but still..

 

[Charles (in GA)]

The news stated that 200 people have been killed since 1980 due to bird strikes. 90% happen around airports. Not all that rare.

Worldwide possibly. Not just in the US however, the number is quite low.

A screen heavy enough to stop a goose would be a rather massive device. Anything at all in the inlet of the engine has a major effect on the airflow. I don't think its possible to design for such a situation. Its a calculated risk.

Charles

 

[AlanD]

One other reason you would not see screens in front of the engines is the cold at altitude would cause the moisture in the air to ice up and start clogging the screen. Once that happens the turbine would come apart internally as it will literally tear the blades out from the suction.

We use screens on the hovercraft I pilot to seperate the salt mist from the air to keep it out of the turbines. Any time the weather goes below 40 degrees we have to port hot air from the turbine around to the intake to keep it free of ice.

Al

 

[Bevis]

there's a new engine out or being tested that can ingest birds and still continue to run.

 

[JRW]

Any turbine engineers out there want to comment?

I'll comment late. Both reasons have already been identified, to prevent a canadian goose from entering the inlet the screen would have to be very heavy. The fan / compressor blades are suseptible to flow disturbances (inlet distortion) that can cause these parts to fatigue or the engine to surge. Ice acretion is another reason, the screen would have to heated to prevent ice buildup. Generally, the regulations assume 1 failure not multiple ones. A dual engine flameout due to bird strike is very rare.

 

[d110pickup]

The only aircraft I can think of with screens over the inlets is the F-117 and it has nothing to do with birdstrikes. Here's a photo during maintenence.
Mike

 

[ddawg16]

The F117 is a different animal....that grid in front of the engine is to prevent radar waves from reflecting off the engine blades. If you look at the latest stealth aircraft (B2, F35, etc) you will notice NO screen. Too many problems.

Kind of related to bird strikes...the below is the video of the blade off test for the Trent engine for the Airbus A380. The engine is supposed to contain all large fragments in the event that a blade comes off the shaft.

Trent Blade Off Test

Bottom line....don't worry about it....still a lot safer than driving.......

Lets see....what are the latest #'s? Over 42,000 people a year die in auto accidents (in the US alone)....and over 60% are not wearing seat belts? That's over 25,000/yr compared to about 200 over 20 years?

BTW.....the pilot on that plane 'earned' his paycheck yesterday.

 

[yhprum]

OK ,Turbine engineer here.
A screen would disrupt airflow and that would cause reduced thrust if made strong enough to protect against a birdstrike.
The comment about icing is very valid. In fact, fan blades routinely get damaged by ice that forms in the inlet or the spinner that sheds and makes contact with the fan blades.
A goose can weigh more than 30 pounds. I have seen photos where the goose has gone through the windscreen , or the aircraft structure. Not pretty.

Most airports have a bird control plan, but sometimes the birds dont follow the rules

 

[MXtras]

Most airports have a bird control plan, but sometimes the birds dont follow the rules

Especially when they are illegal immigrants....

 

[Stuey]

Throw on a screen and you get an instant deduction in airflow, without much benefit. As others mentioned, if a bird is headed for the engine, nothing's going to stop it.

I imagine that a cone-shaped screen might do a good job of deflecting head-on birds, but it would/could create too many aerodynamic complications.

A lot of people are injured each year due to hitting deer on the road, yet there are no specific deer-deflecting mechanisms on cars.

 

[TheShrine]

A lot of people are injured each year due to hitting deer on the road, yet there are no specific deer-deflecting mechanisms on cars.

Here in central Texas we call 'em bumpers. When I see the number of deer dead on the roads each morning, I'm thinking maybe "bumper" is the wrong term!

 

[Stuey]

Here in central Texas we call 'em bumpers. When I see the number of deer dead on the roads each morning, I'm thinking maybe "bumper" is the wrong term!

Yes, but the damage done to a pickup's bumper and that of a tiny 4 cylinder vehicle is pretty different. Even then, I've seen situations where deer have been directed into windshields. Most of a deer's mass is above their legs, which also happens to be above a lot of small cars' bumpers, or at least that's how I'm visualizing it right now - I could still be wrong.