Why no screens on Jet engines??

[fattogatto]

I'm very curious why both engines died at once.. sure a bird will choke a engine to death but two at once. I'm suspious of the Airbus computer.. I'm betting it shut them down after the strikes threw the engines off balance.. When a Boeing operated engine plane would have had the pilot shut the engine down.. again I'm just wondering, I've never flown a Airbus.

Well, I have flown the Airbus . . . . for the last 8 years. And, your statement reflecting that the Airbus will shut down the engine on its own is about as inane as I have heard. There is no automatic shutdown . . . period. BTW, I also have flown Boeings for over 18 years.

Two birds . . . . two engines. What is so hard to understand?

 

[e-tek]

Well, I have flown the Airbus . . . . for the last 8 years. And, your statement reflecting that the Airbus will shut down the engine on its own is about as inane as I have heard. There is no automatic shutdown . . . period. BTW, I also have flown Boeings for over 18 years.

Two birds . . . . two engines. What is so hard to understand?

Good catch - sounds like Garage Dreamer was also dreaming that was a pilot!!

 

[e-tek]

This is nearly as stupid as the comment about the pilot shutting down the wrong engine. Why in the world would you shut automatically shut down an operating engine on a two engine plane if one failed. Big heavy planes fall out of the sky with no power

I agree with you - up 'til that last sentence....many big heavy planes have been set down smooth as silk without power (e.g. GILMLY).

 

[nissan_crawler]

I agree with you - up 'til that last sentence....many big heavy planes have been set down smooth as silk without power (e.g. GILMLY).

Yes, but almost all of them still have a glide ratio of a brick. When it gets quiet, you're riding an expensive lawn dart.

As for auto-shutdown, that could have drastic consequences.

 

[skrunks]

I was a military test pilot for many years -- the reason they don't put screens on the inlet of engines is for a variety of reasons

1) It changes the aerodynamics of the inlet air coming into the compressor section of the engine. Each compressor blade is a mini-airfoil and requires exact inlet airflow angles (called angle of attack). Turbine engines use inlet guide vanes or other techniques to get the right angle. Without the correct angle of attack from incoming air, the compressor could stall creating huge issues (complete engine failure). However, airflow issues in this case could be overcome by engineering design.

2) Icing -- a screen quickly ices over in rain/clouds. This would severely or completely restrict airflow. No air = engine failure

3) Strength of materials. Think about this, you are tooling along at 200 knots and encounter a flock of birds...no worries you have an inlet screen. Unfortunately, hit anything at 200 knots and it breaks, including your inlet screen. Now you have dead birds and broken screen in your engine inlet. Result? Catastrophic engine failure.

 

[JetLinkin]

^^^exactly what skrunks said.

 

[jkeyser14]

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.

A very large air cannon with a dead frozen bird loaded into it. They actually test to much higher velocities than that though, closer to mach 1 speeds (a regular commercial plane can travel up to 800 mph). In order to get the speed that high they also incorporate a few tricks. They put a cap over the end of the barrel and pull a vacuum inside of the barrel. Then they use helium as the propellant. Since the helium molecules are smaller they are able to expand more rapidly which gives it a large advantage over compressed air.

I'm an engineer who has personally seen one of these setups at Pratt and Whitney. The tour was related to research I was working on that was related to containment during a "blade out" which is when one of the turbine blades breaks off. The turbine housing must "catch" the titanium blade spinning at insane rpms to keep the blade from flying right into the fuselage of the plane and killing people.

 

[jkeyser14]

A very large air cannon with a dead frozen bird loaded into it. They actually test to much higher velocities than that though, closer to mach 1 speeds (a regular commercial plane can travel up to 800 mph). In order to get the speed that high they also incorporate a few tricks. They put a cap over the end of the barrel and pull a vacuum inside of the barrel. Then they use helium as the propellant. Since the helium molecules are smaller they are able to expand more rapidly which gives it a large advantage over compressed air.

I'm an engineer who has personally seen one of these setups at Pratt and Whitney. The tour was related to research I was working on that was related to containment during a "blade out" which is when one of the turbine blades breaks off. The turbine housing must "catch" the titanium blade spinning at insane rpms to keep the blade from flying right into the fuselage of the plane and killing people.

And I forgot to mention... The high speed video footage of the bird hitting the turbine blades is amazing. It puts those "will it blend" blentec videos to shame. You see a bird approaching the turbine blades at an insanely slow speed. The blades hit and there are no "chunks" of meat that get knocked off, only an instantaneous atomized red mist.

 

[Ron Lombardo]

I think its cheaper to control the birds around the air ports then engineer the technology to prevent this from happening ... I think they are using the laws of probabilty ...

On second thought they are fitting the Commercial Airlines with Decoys to prevent Air to Ground rockets so whats the Probabilty some terrorist takes a shot at a Jet and Decoys are deployed to prevent taking down a plane full or people ?

 

[usdemt]

Almost a 3 year thread revival....nice!

 

[Shadowdog500]

The screen would disrupt the airflow for one thing.


It would also be an ice magnet! Jet engine inlets have ice protection systems that heat the inlet to keep icing at bay. If you put a screen in front of the inlet it would collect ice extremely efficiently which would either block the airflow or would cause damage to the engine when chunks of ice break off and go into the engine.

Chris

 

[Garage5.9]

check this out

 

[kmacht]

Most of the comments are right except for disturbing air flow. I work for a jet engine manufacturer and we use large cone shaped screens over the front of the engines when being tested. This is just to keep debris that might be sucked into the test cell from being ingested into the engine. They do not cause the air flow to the engine to be disturbed nor does it restrict airflow. The reason that you don't see them on aircraft is because they are only strong enough for small debris that would be sucked in by a stationary engine. The amount of kinetic energy that a 30lb goose has when it is hit at a hundred to two hundred miles per hour is huge. There isn't much that could be put in front of an airplane let alone an engine that will stop the goose to the point where it won't cause any damage.

Keith

 

[MN BIANCHI]

Many years ago while serving in the US Navy as the assitant Legal Officer on board the USS independence I read an investigation of an accident that had occurred on board the ship during a night time maintenance test of an A7 Corsair aircraft. Seems they were doing high rev testing of the engine while the jet was chained to the deck. There was a load bang and spark flew out of the engine. It turned out that somebody walking by in the dark got sucked into the intake of the A7. They were not using intake screens as required because the Navy had not yet developed intake screens for the A7's. They do use intake screens on other aircraft, but only for staitionary engine tests.

 

[Virgil Cain]

Things bigger than birds get sucked in sometimes:

 

[Milton Shaw]

Back in the 60's there was a jet I think at Boston airport that was taken down by sea gulls. There were a lot of people killed. The new GE E90 engine that's being put on in two engine planes had to pass turkey's shot at it from air canon to get certification to fly over the Atlantic and the Pacific. I think that is a standard test for engines. The frozen turkey would not be encountered in real life so they used thawed turkeys as that's about the biggest bird there is 16 to 20 lbs is a lot of red fluff when it comes through the engine.

 

[Outlander]

Been in the aerospace industry for 30 years. Was told a story about a foreign object being analysed after landing. Turns out it was a fish. Likely cause was the fish was dropped by an eagle and ingested........

 

[plinker]

(going by memory from a PBS nova special), IIRC

On some Russian aircraft (MiGs and others I'm sure, have some type of screen on the intake but as I recall that was more) for runway debris then birds.