ON A 95-DEGREE MID-SEPTEMBER DAY IN THE FLORIDA PANHANDLE, a Raytheon Hawker Horizon business jet taxied up to a hangar at Eglin Air Force Base, a joint-use facility whose civilian side is the Okaloosa Regional Airport. The “Hawk,” as it is called at Raytheon, is a glossy new eight-passenger bizjet to which the Federal Aviation Administration granted a provisional type certificate in December 2004. However, a bit of additional testing was necessary to gain final FAA approval, so the aircraft was towed inside the hangar, where technicians hooked up its two Pratt & Whitney turbofan engines to a pair of exhaust ducts, ran instrumentation cables to a sound-protected, temperature- and humidity-controlled observation booth, and chained the aircraft to a set of anchors embedded in the concrete floor.
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The next morning it was –40 degrees inside the hangar, which had been sealed against the outside. The Raytheon test crew entered the aircraft, started the Hawk’s engines, and, after a short countdown, slammed them to full power. The engines boomed for about an hour at various power settings as the hot exhaust streamed through ductwork and out the rear of the hangar; nevertheless, the indoor temperature remained a steady and crisp –40. By rights, two jet engines running at high speed inside a closed space should have created a vacuum that would have collapsed the hangar and drawn the debris through the engine intakes. The reason that didn’t happen is just one of the technological marvels of the McKinley Climatic Laboratory, the world’s largest torture chamber for aircraft in search of FAA or military certification.
The McKinley lab can create just about every weather condition imaginable, and some that are unimaginable. “We can make it rain up to 25 inches per hour,” says lab director Kirk Velasco. Using the type of snow machines found on ski slopes, lab workers can produce whiteout blizzards in the chamber. They can create fog, wind, and icing, generating a layer of “unlimited ice thickness” over your entire aircraft (along with icicles that hang from the ceiling, some weighing 200 pounds), then follow such a display with a scorching burst of simulated solar radiation. They can vary the relative humidity between 10 percent and 100 percent. Moreover, they can do this for aircraft of any size, including a Boeing B-29, a Northrop B-2, a Lockheed C-5A, a Lockheed Martin F-22, a Boeing 747, general aviation airplanes, and helicopters, all of which have been run at full power (and the helicopters at full collective) through McKinley’s weather gantlet. The only airplane too big to pass between the lab’s dual 15-inch-thick, stainless steel, 200-ton hangar doors is the forthcoming Airbus A380 airliner, whose wingspan is about 10 feet too long. “They’ll have to chase the weather,” says Velasco of the Airbus testers. “We’re not the only game in town: Mother Nature also provides. You can chase icing clouds to find icing conditions. It just takes a lot more time, and you do a lot of flying around.”
Over its nearly 60 years, the McKinley lab has tested every military aircraft in the current U.S. inventory, plus many civilian craft, not to mention a gaggle of missiles, bombs, Humvees, tanks, trucks, howitzers, ground-support equipment, hard- and soft-walled shelters, and even cars and snow tires, among other things. For smaller items and more specialized climatic cruelties, the McKinley lab has five test cells in addition to the cavernous Main Chamber. The Salt Fog Chamber can produce an oven-like 149 degrees and a jungle-like 100 percent humidity, together with a corrosive fog solution consisting of five percent sodium chloride in water. The Sun, Wind, Rain, and Dust Chamber can blast various commercially available grades of sand at a test item for hours at a time.
Recently, Velasco and his group subjected a 25-mm Gatling gun from a Lockheed AC-130U “Spooky” gunship to conditions perhaps encountered regularly in the Gobi desert. “We did a major sand test,” he says. “I mean we beat the crap out of it with sand—40-mile-an-hour windblown sand—for six hours.” Afterward, when lab workers aimed the Gatling gun at an in-house bullet catcher and fired, the weapon still worked.
Concern about the effect of cold weather on aircraft led the U.S. Army Air Corps to establish the Cold Weather Detachment at Ladd Field, Alaska, in 1940, and place it under the command of Lieutenant Colonel Ashley C. McKinley, a former dirigible pilot who had photographed American explorer Richard Byrd’s expedition to the Antarctic in 1928 and ’29. After a short stint at Ladd, however, McKinley realized that instead of flying each prototype aircraft to Alaska and back, it would make more sense, and cost the military much less, to create weather on demand, mechanically, at a geographic point that was easy to get to. McKinley also thought it reasonable that all U.S. combat aircraft be required to operate at –65 degrees.
In 1943, the U.S. Army Air Forces directed that an immense climate-controlled hangar be built at Eglin Field in Florida. Four years later, in May 1947, the Eglin Climatic Hangar was in operation, and within 50 years it had run its heavy weather conditions across more than 300 aircraft and 2,000 pieces of equipment. Between 1994 and 1997, the facility underwent a ground-up renovation, which created the lab that is in place today.
Although the principles of refrigeration are comparatively simple and relatively ancient (the first U.S. patent for mechanical refrigeration was granted in 1851), the scale and complexity of the cooling system at McKinley boggle the mind. The Main Chamber has two basic refrigeration modes (plus a heating mode), the first for cold-soaking the aircraft when its engines aren’t running. The setup here is a closed-loop system, the same in principle as that found in a home refrigerator or window air conditioner: Cool a refrigerant, send it through a set of coils, and then blow air over the coils. Doing this on the vast proportions of McKinley’s three-million-plus cubic feet of airspace is a simple matter of scaling up all the components: gigantic, screaming compressor pumps, huge squirrel-cage fans, monster cooling coils, and massive jolts of power. (McKinley has its own electrical substation so that when the system starts running, lights don’t dim in the surrounding community. As it is, the lab’s electric bill averages between $100,000 and $200,000 a month.)
During closed-loop operation, fans withdraw ambient air from inside the chamber, blow it over the cooling coils, and send the cold air up into ceiling ducts that distribute it through large circular diffusers. The same air is recycled through the system again and again, reducing the chamber’s temperature incrementally with each pass. (For high-temp tests, steam is run through the coils.)
The situation changes, however, when an aircraft’s jet engine is running, something that cannot happen in a closed system due to the process of combustion, which sucks in copious amounts of hangar air and forces it out through the engine exhaust system. All that air must be replaced at the precise rate at which it is being consumed. Plus, with the engines and exhaust ductwork radiating heat into the hangar, the incoming air must be cold enough to maintain the target temperature. Keeping up with all that heating and venting requires a whole new dimension in cooling and airflow management, which at McKinley is a masterpiece of engineering called the air makeup system.