“The air makeup system will take that outside air at 95 degrees, cool it down to –40 degrees, and dump it into the chamber at the exact same rate that the engines are using it,” says Velasco. The system has two primary components, the first of which is the air makeup building proper, which is a separate, free-standing, two-story structure housing an air-intake duct, one steam coil and two successive ranks of air conditioning coils, and an exhaust duct that pours a continuous volume of fresh-frozen air into the Main Chamber through a large square hole in the ceiling.
However, there is no way that even McKinley’s powerful compressors can produce the mass of cold air needed to balance a 747’s four engines running at cruise power for a solid hour. The solution: Chill a whole lot of coolant in advance and store it at low temperature until it’s needed. Accordingly, for two days prior to the Raytheon Hawker Horizon test, McKinley’s air makeup team has been cooling down the facility’s most potent refrigerant, R30, a.k.a. methylene chloride, to a temperature of –100 degrees, then shunting it into a 750,000-gallon cylindrical tank adjacent to the air makeup building. Big as a house, that tank of liquid frigidity is really the crux of the entire enterprise.
“This system can take outside air as hot as 105 degrees Fahrenheit and cool it down to minus 80 degrees Fahrenheit, at a rate of 1,000 pounds mass of air per second,” says Velasco. “So as long as your engines aren’t using more than a thousand pounds mass per second of air, we can maintain the conditions in there while those engines are operating.”
Lab personnel are kept informed of equipment functioning by the Facility Monitoring and Control System, a room that runs 24/7 to keep tabs on the facility’s hundreds of valves, miles of piping and electrical circuitry, and compressor pumps, steam boilers, heat exchangers, evaporators, condensers, nozzles, ducts, fans, backflow dampers, plenum doors, cooling towers, surge tanks, storage tanks, coil banks, pressure vessels, and large-scale fluid flows. A day’s use of the Main Chamber can cost between $10,000 to $25,000. If all you’re doing is a simple snow-load test of a tent, figure the lower end. “If you have something really complex,” says Velasco, “like a military Joint Strike Fighter, the F-35, the short-takeoff-and-landing version—it’s got a big lifting fan in the middle, it’s got variable exhaust in the back, a very complicated exhaust setup that we have to specially design and build—that gets up to $25,000 a day.”
Velasco, a thin, balding aeronautical engineer in his late 40s, came to Eglin in 1984 after spending three years doing climatic testing at Edwards Air Force Base in California’s Mojave Desert. One of the tests involved bringing a Lockheed F-16 to McKinley for the full treatment. The place impressed him so much that he transferred to Eglin and never left.
In the years since, Velasco has seen it all, but the tradition at McKinley is to maintain a strict code of omerta about test results. After all, any aircraft, military or civilian, is manufactured by a company whose board members would rather that the outside world not know that during one of the lab’s –40-degree tests, its precious airplane’s landing gear wouldn’t retract or, worse, extend.
“I hate to talk about stuff like that,” Velasco admits. Nevertheless: “I remember vividly—and I won’t mention the name of the aircraft—but we had a large aircraft in here and we did a rain test on it, and we filled it up with water. I mean, water was draining out of that aircraft for two days after we shut down. We could open panels and there were wing cavities filled with it. It was like a swimming pool, you could jump in and swim in it. It was leaking in because of the way they built the access panels—they were not sealed properly.
“Believe it or not, rain is a tough test to pass,” Velasco adds. “We create a windblown rain, we don’t just rain overhead and sprinkle on the thing. We have big wind machines blowing 50-mph winds, and you can blow it up under the wings and from all angles. You blow water everywhere.”
Then, because it’s ancient history, he talks about a B-52 test of a much-touted hydraulic fluid that wasn’t supposed to catch on fire the way conventional fluids did when the bomber’s hydraulic lines got hit by ground fire in Vietnam. “This B-52 had a rotating launcher inside of it that carried cruise missiles,” says Velasco. “The thing’s got to rotate and drop a bomb, rotate and drop a bomb, at minus 65 degrees. We were trying a newfangled type of hydraulic system—that was the whole test. The fluid was less flammable, but at the same time it was much more viscous. It was like molasses at minus 65 versus the old stuff, which would flow relatively freely at minus 65.” So much for the new hydraulic fluid, which the Air Force summarily discarded.
The alternative response to the discovery of a defect is to modify the system at fault. “You’ll have landing gear that won’t come up because they made the hydraulic lines too small, so they have to go back and mod the lines, make a bigger hydraulic line,” says Velasco. “They might have an eighth-inch line down to the gear and it’s just too small, not enough fluid getting there fast enough, so they have to put in a quarter-inch line or a three-eighth-inch line.”