A Canadian plane in emergency, live !

Word is that it has landed safely.



Yes, fortunately, it has landed without consequences for anyone. When I read that one of the engines would have introduced elements that came off the landing gear, I asked again (once again, it is a recurring thought every time there is a problem with the turbines, for example when they fail because they " gobble "birds)

Why in the turbines can not put a metal mesh like those that protect tweeters?

(Yes, they would be much bigger ........) :D

Can someone explain it to me ?
 

Attachments

  • D3004-602000.jpg
    D3004-602000.jpg
    121.8 KB · Views: 178
Why in the turbines can not put a metal mesh like those that protect tweeters?

(Yes, they would be much bigger ........) :D

Can someone explain it to me ?

To be useful, the mesh grid size would need to be relatively small. But putting a small grid mesh on a high bypass turbine would result in a stagnation point in the air immediately beyond the mesh due to the turbulance caused by the mesh. The engine performance (ultimate efficiency) will suffer from the choke point created by the air trying to get through the mesh.

Think of a busy railway station when a train unloads and the flood of people are passing through the gates. Even if they slow momentarily at the gate, the upstream flow chokes up.

Bird strikes (in large commercial aircraft) occur in the first or last few minutes of a flight because the vast majority of the time the aircraft is at an altitude above which birds can inhabit. This means that any performance degradation is incurred during the ~90% of the operations where the mesh is not required. This results in higher operating cost / higher emissions which are both undesirable consequences to the commercial operation and environment.

Another reason is that often birds are ingested without incident. Smaller birds are soft and squishy compared to the titanium alloy turbine blades (think strawberry versus blender). There are a few rare incidents which are very visible (Hudson River landing for example) but the total aircraft fatal accident frequency rate is around 0.3% of all accidents. Furthermore, there are significantly more airframe strikes than engine strikes (4.6 to 1) and the prime cause of accident is from windscreen penetration.

Helicopters do employ methods of air screening - For example, the EC145 can be fitted with a barrier filter kit (rather large K&N filters) and larger aircraft can be fitted with an optional 'Engine Air Particle Separator' kit. The EAPS systems create a centrifugal vortex that throw large particles, such as stones, outside of the main intake airflow and overboard. These methods have an efficiency cost of around 3-5%. A lot of helicopters just have an intake screen which is grid sized to the smallest nut / bolt in the air intake area. But..the big mincer on the top usually collects any birds before they get anywhere near the engines.

The actual reason is that the mesh would ice over.

Ah yes there is also the problem of icing. I remember reading a good article about that last year:

Analysis and modelling of icing of air intake protection grids of aircraft engines - ScienceDirect
 
Last edited:

H713

Member
2017-11-24 11:21 pm
Madison WI
Someone with more experience in aerospace engineering can correct me on this, but given the insane flow of air through a turbine I can only imagine that the forces on this "mesh" would be absolutely immense. I suspect that it would be extremely loud as well.

6L6 is right about the icing, and given the amount of airflow, it'd probably be nearly impossible to keep it hot enough to keep the ice off.
 
I worked for a short time at Rolls Royce, just out of school age. The Test Sheds were something else, even if just from the outside of the "armed patrol" boundary.

I don't have many concerns about icicles or birds causing ballistic damage when sucked into the first turbine. I'm not sure why that's a concern.

Where I work now, an aero testing house uses one of the buildings on the site, and have tested a fair few Rolls turbines, as well as other manufacturers. The latest was the 9X for the 777 if I recall.

They fire foot long slugs of ice through the turbine, at speed; or install ballistics to destroy a blade or group of blades, also when at speed.

The depth or breadth of testing is far greater than just my simple understanding, but testing is about as exhaustive as it can get!

Hail, freak weather, global weirding...when flying...THAT worries me!
 
Last edited:
In the case of the OP plane, there was talk of solid parts, not birds, that damaged an engine ....

The huge suction of the turbine would not defrost ice from a mesh?

Why the grid should be small, you can design a special with aerodynamic shapes and large sections with respect to the mouth of the turbine ....
I think that since the statistics are favorable, it does not "merit" to innovate in that regard.
Perhaps if the story had been different, with an end not so happy for the passengers of the Airbus that landed in the Hudson, it would begin to look for a solution ....
I only speak from my ignorance, huh!
 
Someone with more experience in aerospace engineering can correct me on this, but given the insane flow of air through a turbine I can only imagine that the forces on this "mesh" would be absolutely immense. I suspect that it would be extremely loud as well.

6L6 is right about the icing, and given the amount of airflow, it'd probably be nearly impossible to keep it hot enough to keep the ice off.

Ice protection system - Wikipedia

Engine antifreeze system
The motor system can also be affected by icing. If the freezing of any sector of the motor inlet occurs, it can cause an obstruction of the motor, which results in a loss of thrust. This can get worse if the ice formation reaches the blades of the "fan" or the compressor.

In general, you can differentiate between:

Antifreeze of the engine shield: performed by a flow of hot engine air that is carried to the leading edge of the engine air intake.
Antifreeze of the inlet guide vanes: performed by purging hot engine air and taken to the inside (hollow) of the blades, protecting them against ice.
 
....

It's an obvious concern so if it was practical to implement, it would have been already, right?

.......

Yes, it should not be practical to implement. Extreme measures in the security sector always have a high price, just because they are not "practical". What does not remove that can not be done. I just can't find a definitive explanation, the ice seems to be discarded, here it is not mentioned:


Screens Not the Answer to Keep Birds Out of Jet Engines - NYTimes.com

"According to experts, blah blah ..."

RR will have done studies about the feasibility of that implementation? The airlines will have requested it?
I don't think so, the deaths of birds (be they Canadian geese or any other specimen) do not enter the equation, and judging from the unfortunate accidents of the 737 Max, the proper training of pilots for a new automated flight system did not enter the equation at that time .. You know the story, much has been discussed here in another thread.
 
Last edited: