Something to crow about: Rooster Booster proves old-fashioned ingenuity needn't be high-tech.
Although Arnold Engineering Development Center (AEDC) uses some of the most sophisticated technologies in the world to test aerospace systems before flight, it's been using one system for 24 years that's about as simple as instant mashed potatoes and Stovetop Stuffing."It's about as low-tech as you can get," said Randal Watt, a project manager at the Arnold Air Force Base, Tenn., test center's Bird Impact Test Facility. "Most people who tour AEDC are surprised we haven't developed a more sophisticated test technique. But it's really common sense, a very simple thing. If you are trying to simulate a bird hitting the windshield of an aircraft, the easiest and best way to do it is to catch a bird, accelerate it to the desired speed, and have an aircraft windshield in its path."
Bird strikes can cause extensive damage to aircraft and serious injuries to their crews. At worst, they can be deadly confrontations. The Air Force estimates that planes hit about 3,000 birds every year, causing damages of $50 million and sometimes loss of human life. In a bird-strike accident in September 1995, 24 AWACS crew members were killed after takeoff from Elmendorf Air Force Base, Alaska. So for more than 20 years, Watt and his colleagues at AEDC have been helping the Air Force upgrade and certify aircraft windshields and canopies for bird-strike resistance.
"Birds have been a hazard ever since there has been an airplane," Watt said. "But the situation didn't become really critical until planes starting flying very fast and close to the ground."
A serious problem in Vietnam
The critical period began during the height of the Vietnam War, Watt said. F-111 aircraft--equipped with terrain following radar that allowed them to zip along a few hundred feet off the ground--were hitting a lot of birds. So an office set up at Wright-Patterson Air Force Base, Ohio, received a tasking to do something about the bird-impact hazard.
People at Wright-Patt knew AEDC had gun range experience, so they asked what it would take to develop some sort of bird-strike test. With some scrap hardware, including an old 8-inch Naval gun, and a little design and fabrication, engineers at AEDC hatched a plan. They assembled a simple air gun, and gave the world what people at Arnold now commonly call the Rooster Booster, or the Chicken Gun.
"The gun has a 60-foot-long barrel and a 10-foot, 3-inch chamber that can be pressurized with air," Watt said. "to operate the system, the chicken carcass is placed into a balsa wood container called a sabot (French for "shoe") and loaded into the barrel. Between the barrel and the air chamber is a thin plastic diaphragm, which isolates the sabot from the high pressure air until shot time. "Firing" of the gun is accomplished by rupturing the diaphragm, permitting the air to push the sabot and bird down the launch tube toward the test article, which sits in an outdoor shed area."
As the sabot and chicken exit the launch tube, a tapered and threaded section strips the sabot away, permitting the bird to continue in flight to the target. The sabot stops before the end of the section.
Good for tests, or Sunday dinner
Watt said AEDC buys whole 4-pound chicken carcasses, feathers and all, from a local chicken farmer.
"These are the same chickens that would end up on your Sunday dinner table," Watt said. They're kept in a freezer until needed for testing, when they're thawed. Though the American Society for Testing and Materials Standard for bird-impact testing will permit using imitation birds, Watt said the Air Force typically requires a real bird carcass.
The preference of most of the System Program Offices (SPOs) is to simulate the event as close to reality as possible, Watt said. "The best thing to sue to simulate a bird strike is a bird. And chickens are the easiest to come by."
Aircraft and bird encounters occur thousands of times each year. The Air Force alone has approximately 3,000, according to the Windshield Systems office at Wright-Patterson Air Force Base, Ohio. Since 1972, when AEDC's Bird Impact Range began operating, a representative transparency from nearly every type of U.S. military aircraft has been bird-strike tested. This testing has helped save untold lives and millions of dollars.
In the 20 years Watt has been associated with the chicken gun, he's seen some real advancements in windshield and canopy technology.
"Our first shot was in October 1972 on an F-111 escape module. Back then the windshields were basically glass," Watt said. "Because they were designed strictly for aerodynamic loads, with no consideration whatsoever to bird impacts, they failed at very low speeds, under 70 knots or so. They just punched right through, which would result in a fatality and the loss of an expensive aircraft."
The Air Force went to various windshield manufacturers and asked them to develop stronger windshields. Moving away from glass to more modern plastics such as acrylic or polycarbonate, a high-strength plastic, developers went to laminated designs, which are stronger and more flexible. Since its inception, AEDC's chicken gun has tested the windshields and canopies of the majority of aircraft flying in the Defense Department's inventory, including the A-7, A-10, F-15, F-1, F/A-18, F-111, T-37, B-1, and C-130.
Watt warns that not all windshields and canopies fail to qualify simply because they shatter. On an early F-16 test, Watt recalled, viewing the test with the naked eye showed the windshield withstood the impact just fine.
"We had our high-speed cameras running inside the cockpit photographing the bird coming in and the canopy deflecting into the cockpit area. It looked like the surf coming in--just a big wave running through it."
So in addition to integrity tests, Watt is also interested in how much deflection occurs. "Even if the windshield or canopy survives, if it hits the pilot in the head, he's dead. And sometimes the pilot's head is within an inch or two of that bubble canopy."
Still another consideration is temperature. Because a windshield's or canopy's properties will change according to the temperatures they are exposed to, developers must consider how windshields and canopies will respond to severe weather.
"One scenario is the plane sitting in the desert in the middle of the day that has to suddenly go into the air and hits a bird as it's taking off," Watt said. "That windshield is probably going to be very hot. So to simulate that condition, we heat the test area up to 200 degrees Fahrenheit.
"The other case is the aircraft sitting on the runway in Alaska in the middle of winter and it's 30 degrees below zero. Again, if that plane has to go airborne, its windshield will be very cold, so by putting a thermal enclosure around the test area and supplying cooled gaseous nitrogen, we can cool the area down to 30 or 40 degrees below zero."
Watt expects the chicken gun will be in use for years to come, including 40-plus firings a year.
Editor's Note: The Ballistic Impact Range A.K.A. "The Rooster Booster" was born out of necessity and has served the flying community well since then making aircraft components and canopies safer in the event of a bird strike. Although the need for impact testing has lessened over the past few years since this article was published, aircrews continue to reap the benefits of this unique testing program that's strictly for the birds.
Reprinted Courtesy of Leading Edge, AFMC Public Affairs
by Stephen A. Calatrello, Arnold Engineering Development Center, Public Affairs, Arnold AFB, Tn.
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| Author: | Calatrello, Stephen A. |
|---|---|
| Publication: | Combat Edge |
| Article Type: | Reprint |
| Geographic Code: | 1USA |
| Date: | Aug 1, 2005 |
| Words: | 1263 |
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