Bird screen will not work on jet engine
June 14, 2009
Q. In January, 150 people were lucky to escape with their lives when bird strikes caused a plane to ditch in the Hudson River. Why can’t they install a heavily reinforced steel shield over the engine intakes to prevent the birds from being sucked into the engine?
– Stephen Krause, of Collinsville
A. Here’s another interesting question: Why do you even need a shield? Why can’t a modern jet engine, which can weigh up to five tons and produce 100,000 pounds of thrust, grind a 15-pound Canada goose into so much pate without so much as a squeak?
Consider the physics involved. Have you ever thought about the force exerted when a plane flying at even 150 mph strikes such a bird? The Bird Strike Committee USA, formed in 1991 to reduce wildlife hazards to aircraft, has. They compare it to a 1,000-pound weight being dropped from a height of 10 feet — and we all remember what happened when those wacky folks at “WKRP” dropped turkeys out of a helicopter, don’t we? Oh, the humanity!
If the plane is flying faster, the impact is even harder. Run into a flock of birds and it’s easy to understand how the repeated bombardment can shut down even the most powerful engines.
At the front of such an engine are compressor blades, says Dale Olderman, an associate professor of aviation technology at Purdue University. These blades aren’t very big, but if a bird-strike breaks one off, it can be like shrapnel going through the engine.
The results can be devastating. According to the Bird Strike Committee, 219 people have died worldwide since 1988 because of plane-bird collisions; such accidents cost aviation an estimated $1.3 billion annually.
Yet there’s not much pilots can do when they suddenly run into a flock. Jet engines take in air as if they were in the neck of a funnel, so if they encounter birds, the planes can suck in the creatures from an area far larger than even the opening of the engine.
It’s not a problem the government has ignored. Depending on the size of the plane, engines must be certified to withstand hits from a bird of 4 to 8 pounds, according to the Federal Aviation Administration. Unfortunately, there are some 36 species of birds in North America that weigh more. And, even some smaller birds — like starlings, which are called “feathered bullets” because of their density — can cause problems.
Some type of shield would seem a common-sense solution. Unfortunately, the idea just doesn’t fly, experts say.
For one thing, the shield would have to be far more substantial than, say, something like chicken wire. A bird hitting something flimsy with such force would likely break off pieces of the shield, too. That could fowl up the engine even worse.
Adding something sufficiently sturdy would add a great deal of weight to the plane. Not only that, it also would reduce the flow of air into the engine, which would hurt performance and increase fuel consumption.
“So the idea gets dismissed quickly because it is not practical from an engineering point of view,” concluded John Downer, an expert in risk management at the London School of Economics who wrote a paper in 2007 entitled “When the Chick Hits the Fan.”
So, the only practical solutions are relatively primitive: scaring birds from runway approaches and plotting flight paths that avoid heavy migration routes.