Clad in a parka, snow pants, insulated boots, sweater, and thermal underwear, the crew chief stood off the nose of the C-5M monitoring the engine test. As the new 50,000-pound thrust CF6 engines on the Super Galaxy spooled up, the powerplants whipped the frost and snow on the ground into a frenzy and turned the -25 degree Fahrenheit air into the harshest of winds.
After the aircraft was shut down and secured, the crew chief walked through the heavily insulated door of the hangar and took off his Arctic gear. He then changed into his golf shirt and jeans and walked outside into the balmy breezes and 70 degree temperature of a sunny November afternoon in the Florida panhandle.
Temperatures fit for polar bears inside and gators outside are all in a day's work at the Air Force"s McKinley Climatic Laboratory at Eglin AFB, near Fort Walton Beach, Florida. This test center, conceived during World War II, completed in 1947, and extensively renovated fifty years later, can recreate just about every weather condition on Earth.
Nearly every major US weapon system — as well as many new business jets and automobiles — makes the trek to Eglin to undergo environmental testing in the lab. The C-5M, the fully upgraded version of the Air Force's largest transport, is the latest to be frozen and baked at the lab.
"We successfully completed seven unique test events, completing seventy-five test points in fourteen days. The tests covered items such as engine starts and shutdowns, avionics cooling, and environmental control system performance," notes Bob Russell, the leader of the joint Lockheed Martin-Air Force C-5M climatic chamber test team. "Although the cold weather tests, which went down to -40 degrees, were the higher priority, they were also the higher risk. So we began with the hot weather tests."
The lab's main test chamber — essentially a giant thermos bottle — stands 252 feet long, by 260 feet wide, by seventy feet high. But squeezing the C-5M in took some effort, just as it had in the late 1960s when the chamber had to be expanded to accommodate the C-5A. The C-5M had to be knelt for the top of the horizontal tail to clear the supports for ceiling and then raised once it was in position. The tip of the aircraft's nose was only about six feet from the hangar door.
As one of the objectives was to test the C-5M's new engines and auxiliary power units, or APUs, in temperature extremes, elaborate ducting had be built to allow exhaust to escape the chamber. A restraint system was developed by the laboratory staff to prevent excessive movement of the wings during engine testing. These rigs, which were attached to engine numbers one and four, were required to maintain engine exhaust flow in the ducting.
The McKinley Laboratory has an elaborate system that replaces hot or cold air on a real-time basis, as hot outside air flowing into the chamber during a cold weather engine run would obviously affect the results. Likewise, the fuel for those engines has to be warmed or cooled. Because of the time required to cool or warm the chamber, any required maintenance has to be done in whatever the ambient temperature is — just like it would at any real-world site.
Each of the aircraft systems being tested, such as the APUs, electrical system, or propulsion, had an engineer monitoring it on a computer workstation in a control room upstairs. The maintenance and instrumentation teams were on the floor with the aircraft in climate-controlled booths. The laboratory has a facility maintenance team on the floor as well. The aircraft mechanics rotated between going out to the aircraft and cooling down or warming up in the booth.
Although some C-5M hot weather testing had previously been completed at MCAS Yuma, Arizona, and at the Air Force Flight Test Center at Edwards AFB, California, the test team took the C-5M — one of the three aircraft in the Super Galaxy test program — up to 140 degrees above zero using huge banks of thermal lights to conduct aircraft preconditioning, APU starting, and engine runs. The skin temperature on the aircraft reached a sizzling 165 degrees Fahrenheit in these tests.
The chamber was then brought down to -25 degrees over several days, and the aircraft was cold-soaked, or essentially left to freeze, for a day. "As part of this test, we wanted to use the new APUs to get the temperature as warm as possible in the troop compartment," said Larry Frias, the team's flight engineer. "We got it up to 78 degrees above zero." The twin APUs on the Super Galaxy are some of the more than seventy reliability enhancements made to the C-5M.
"The C-5M Climatic Lab testing was highly successful. We met all our objectives, and we showed that the improvements made to the C-5 improve the operational capabilities of the aircraft," Russell concludes. "Computers can predict what will happen to an aircraft in extreme temperatures, but we need to actually conduct these tests to make sure the aircraft systems perform to specification and are not impacted by weather extremes. Any issues we found on the C-5M, we are addressing by changing the tech orders."
Jeff Rhodes is the associate editor of Code One.
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