I have a soft spot for birds of prey, particularly eagles.
So earlier this week, when I read that officials of a wind power company had asked for a permit that would allow the company's wind turbines to kill a given number of golden eagles each year, I became concerned.
Bald and golden eagles are protected under the Bald and Golden Eagle Protection Act of 1940. It struck me as odd that representatives of a "green" industry would ask permission to violate that law a few times a year.
I certainly understand why: If the feds allow the company's turbines to kill some eagles, the feds then can't shut the company down unless the number killed exceeds the allowable limit. In other words, the company gets some leeway it otherwise might not get.
Anyway, thinking about eagles got me wondering how such sharp-eyed birds could ever fall victim to such enormous, seemingly slow-moving machines.
A little math explained how.
Wind turbine towers stand 200 to 300 feet tall, and their blades range from 100 to 150 feet in length. The blades rotate 10 to 22 times each minute.
Let's split the difference between the industry minimums and maximums and assume a turbine blade length of 125 feet. Double that to get the diameter of the circle the rotor tips describe, and multiply by pi (3.14159265359 ... OK, I'm a geek) to find out how far each blade tip travels per revolution. Answer: 785.39 feet.
Split the difference between minimum and maximum rotation rates to get an average rotation rate of 16 rpm. So each blade makes a complete circle in 3.75 seconds.