It’s a bird! It’s a plane! It’s… a collision?
Superman is the last thing pilots worry about. Birds, however, are a real concern. After all, it was a flock of birds that led to the ‘miracle on the Hudson.’ Airplanes are capable of taking a hit, but just how much they can withstand is a matter for engineers.
The survivability of bird strikes is the topic of a Technical Spotlight in the October edition of Advanced Manufacturing & Processes. According to the article, “Annually, approximately 10,000 strikes with civilian planes occur in the U.S. alone, with losses of more than $650 million for commercial and military aircraft.”
Jet engines are designed to survive bird strikes and contain catastrophic failures, but many other structural components, such as stabilizer or empennage structures must withstand the impact without failing.
To address the issue, aviation engineers are looking to increase strength without adding weight. How much strength is required may be surprising.
For example, if a 12 lb Canada goose is hit at 150 mph, it will generate the same amount of kinetic energy as a 1000 lb weight being dropped 10 ft.
Making structures lightweight and strong means balancing rigidity and ductility. Aircraft aluminum is able to handle impact well, but its density limits the component size. Composites are extremely rigid and lightweight for their strength, but they tend to be more brittle. Composites are also difficult to repair.
“We looked at a variety of material options for the vertical stabilizer, including all-composite and composite/metal hybrid versions,” says Ganthimathinathan Perumal, senior project manager in HCL’s engineering and R&D services department which works with the aerospace industry. “Each design iteration requires its own bird-strike analysis to meet appropriate safety regulations”
Those design iterations use to require building each design and shooting birds at them. This is where computer simulation has helped. Fairly recent advancements in simulation quality have enabled it to be used as a stand-alone method for testing.
Now many modifications of the design can be tested without such significant time and expense. For example, simulation revealed a 30-ply all-composite design (comprised of glass and Aramid fibers) survived an impact that a 20-ply design failed to. The 20-ply version could outperform the 30-ply if the outermost ply was replaced with a single aluminum layer (0.9 mm in thickness).
This hybrid design, when impacted by the model bird, incurred damage on the outer metal layer but protected underlying composite layers from severe or catastrophic damage. It is this rapid feedback that makes simulation so valuable.
Simulation and materials development can help accelerate the design process and produce a superior structure. When it comes to staying airborne after a bird strike, this is a very good thing. Unfortunately, there’s really no upside for the bird.
If you’re interested in the “old-fashioned,” chicken-cannon testing, the video below shows how a cockpit window can be tested.
Images courtesy of:
http://www.mnh.si.edu/highlight/feathers/ and Advanced Materials and Processes