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Testing the F-22

The standard press photo for a test subject in the McKinley lab most often shows an aircraft parked and covered in snow. The first photo, from 24 May 1947, shows six aircraft?including a Lockheed P-80?in the main chamber. The photos create an impression that the tests done in the lab are static. In actuality, the tests are almost all highly dynamic, with pilots in the cockpit, maintainers and crew chiefs working in the elements, aircraft systems operating, and engines running.

The lab is one the few facilities in the world where jet engines can be operated in a closed hangar, so air has to get in and exhaust has to get out in order for the engines to run. That air also has to be the same temperature as the test chamber. Otherwise, the results aren?t accurate.

The lab gets that much air from a huge storage tank outside the hangar. The tank provides up to 800,000 cubic feet per minute of either pre-conditioned hot or cold air (depending on the test) to replace the air inhaled by the engines on a real-time basis. The same amount of air goes in the chamber as comes out. When the tank is completely emptied, it takes approximately twenty-four hours to replenish the reservoir with conditioned air, particularly with extremely cold or extremely hot air needed for tests in extremely cold or hot conditions.

?Every project is unique,? adds Velasco, who has worked at the lab for more than eighteen years. ?We had stealth aircraft in here before, so we have dealt with special materials. But every vehicle has its own unique tie-down requirements and ducting needs.? In the case of the F/A-22, a Y-shaped duct, fitted with a system to dampen the exhaust at the back of the aircraft and keep the rest of the tube cool, is built so the aircraft?s two engines can be run during the tests. A separate duct?one set up so the small door on the aircraft?s top-mounted auxiliary power unit can open?is constructed and installed by the lab?s onsite team.

Once installed in the chamber, the Raptor looks like a creature out of a science fiction movie. With ducting in place, the aircraft is tied down in multiple places (each tie-down being equipped with strain gauges to measure stress on the airframe during the tests) and perched on jacks so the landing gear could be cycled and the hydraulics checked. Several small, movable, modular buildings surround the aircraft to house the twenty or so people necessary (including a fire chief) to conduct each test. The picture is made complete by the ski resort-type snow cannons, wind machines on the floor or, alternatively, banks of heat lamps or rain making equipment suspended from the ceiling on a rack shaped to the planform of the aircraft.

The elaborate apparatus is necessary. The weather extremes, the sophistication of the tests, everything is geared to one goal: ?We want to match operations in the real world. We want to see if the Raptor can take it,? Poulson observes.

Going to Extremes

Each of the environmental tests begins just like an F/A-22 flight. The pilot and crew chief perform a walk-around of the aircraft then the pilot climbs the ladder and straps into the cockpit?regardless of the conditions in the chamber. The pilot starts the engines and operates various systems on the aircraft in each weather condition. ?Part of the tests are to run the checklists,? adds Poulson. ?We want to see how the cockpit warms up and how the aircraft warms up. If it is raining, the pilot gets wet.?

The aircraft is subjected to all manner of weather extremes in a battery of separate tests. The individual trials range from cold soaking the aircraft at minus sixty-five-degree cold before ?warming? it to minus forty degrees; to a buildup of eight inches of snow, which at about twenty pounds of weight per square foot over the approximately 1,000 square feet of surface area on the Raptor results in a load of 20,000 pounds on the top of the aircraft; to a wind-blown snow at approximately forty-four feet per second. And that?s just the cold stuff.

After the snow melts (and is cleared through large drains in the chamber floor to a special retaining pond), heat testing begins. The trials start at a comfortable eighty degrees and build up to 120 degrees with the engines running. A later battery of tests subjects the aircraft to ninety-five degrees with seventy-four percent relative humidity and 105 degrees with eighty percent humidity to see where condensation occurs inside the aircraft.

Then the rains come. In one test, Raptor is inundated with 1.4 inches of rain per hour for close to eight hours to see how the drain holes on the bottom of the aircraft perform. Wind-blown rain tests identify where puddles may form in the weapons bays and in other openings. These tests are followed by an overnight in freezing rain. The resulting ice requires almost 1,200 gallons of deicing fluid to thaw the aircraft. The ice test is followed by a ground fog test at zero degrees and a vortex icing test (where the engines suck in standing ground water) to see where ice forms in the engine inlets.

?That is about the normal range of tests most aircraft are put through,? notes Wayne Drake, the lab?s technical director. ?The programs are very thorough.?

Concurrent with the aircraft tests are maintenance, loading, and auxiliary equipment tests. ?You have many more problems in the cold,? says MSgt. Paul Stauffer, one of the Air Force technicians who weathers the conditions with the F/A-22 as the tests progress. ?Equipment that is supposed to work even at minus twenty degrees acts differently at minus forty,? he says. ?The Raptor is no exception.?

After one cold-soak, the canopy would not close because the power-operated systems stopped working. The maintainers helped the pilot close the canopy manually before the next test, an engine run at minus forty degrees, begins.

Once, an auxiliary power unit failed and had to be replaced in the cold. ?That actually worked out,? notes Poulson. ?Changing an APU at low temperatures is one of the maintenance points we want to check.? Adds TSgt. Greg Auzenne, another crew chief participating in the tests, ?Even simple things require more thought and effort at these conditions. Moving an equipment cart three feet can take twenty minutes because of the ice and snow.?

In one particularly arduous test, maintainers load four AIM-120 missiles in the F/A-22?s main weapons bay and an AIM-9 missile in one of the side weapons bays. They also attach underwing external fuel tanks and load the jet?s main tanks with fuel?all the while wearing full chemical/biological warfare gear with the temperature in the chamber set at zero degrees Fahrenheit.

?We change a battery in the blowing rain and we perform a pre- and post-flight inspection in the blowing snow,? explains Stauffer. ?We are validating the maintenance database just by doing the things that will be typical flightline crew chief jobs. The conditions we work in aren?t always great, though.?

At the completion of the tests, the aircraft is returned to flight status. After a functional check flight on 9 September, the Raptor leaves Eglin for Edwards. It makes an intermediate stop at the Lockheed Martin plant in Fort Worth, Texas. Company employees, who build one-third of each F/A-22 in Texas, are treated with their first look at the complete fighter. The aircraft is flown back to Edwards on 17 September.

?Overall, we found a few aircraft anomalies in the climatic lab, and we will have to go tweak them,? concludes Poulson. ?Nearly all of the tweaks will be minor software adjustments, though. The engines start slower in the cold and the rest of the systems depend on the engines for power. How those engines come up and how the power is distributed is a software fix. But those are the kinds of things we came to Eglin to learn.?

The McKinley Climatic Laboratory is truly a matchless national resource. With its unique capabilities, there is little wonder why this facility has been designated as a National Historic Mechanical Engineering Landmark. But the bottom line is practicality.

?We have tested the F-22 in every conceivable operational condition,? says Drake, who has been at the laboratory for nearly thirty years. ?Getting the same kind of data we get here in three months would have taken years without this facility, and at a much greater cost. We now know the F-22 can work in the weather.?