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Global Hawk wet runway testing yields positive results

by Kenji Thuloweit
95th Air Base Wing Public Affairs

4/1/2010 - EDWARDS AIR FORCE BASE, Calif. (AFNS) -- Airmen, civilians and contractors of the 452nd Flight Test Squadron here conducted RQ-4 Global Hawk wet runway testing with positive results throughout March here.

The wet runway test required the Global Hawk to demonstrate taxiing and stopping from 6, 12, 30, 50 and 70 knots.

The Block 20 Global Hawk recently taxied down the 8,000-foot runway at 70 knots, coming smartly to a stop and thus completing the final speed requirement in the testing phase.

"This testing is for specification compliance, whether we can meet our targeted landing and distance goal on a wet runway," said Dave Tangren, the 452nd FLTS lead engineer for flight systems. "Because our plane has a completely new landing gear and brake system, we're looking closely at anti-skid and stopping performance."

The Block 20 Global Hawk has a new electrical braking system with a differential brake capability and anti-skid functions, making it the only remotely piloted aircraft with this brake design. Its predecessor, the Block 10 Global Hawk, uses a hydraulic brake system. The different braking system on this significantly larger Global Hawk version makes these tests crucial.

Civil engineers come out in the early morning darkness to sweep the runway for foreign object debris before the test starts. The runway is then watered down by contractors followed by firefighters who spray a diluted protein foam solution, which slows the water run-off and helps keep the runway slippery.

The water and foam solution are applied to the runway using a unique spray bar that has nozzels and is attached to a truck, specifically designed by engineers in the squadron. After the runway is wet down, a truck equipped with a runway-friction-measuring-system drives through the water to measure the runway condition reading. The RCR needs to be between 13 and 17 indicating that the runway is indeed wet and provides enough friction.

"Basically a 21 or above is dry, a 13 to 17 is wet, and 12 and below is icy," said Jan Rehacek, 452 FLTS subsystems engineer. "This method quantifies how slippery the runway is."

Once it is determined the runway is ready and personnel are clear, the "go" command is sent and the Global Hawk begins its taxi down the runway. The aircraft is followed by base officials in a truck who serve as the eyes and ears of the test. The Global Hawk must begin its taxi and acceleration within approximately 30 seconds after getting the green light.

"All of this is timed with only minutes and seconds apart," said Thomas Stiles, the 452nd FLTS project manager. "If the time delay is too great then the RCR will go up, and water will diminish across the runway, so timing is critical."

The wet runway test takes an enormous amount of coordination and setup. Along with CE and firefighters, there are engineers, controllers from Ridley Mission Control Center, contractors and Airmen.

"The choreography is phenomenal," Mr. Stiles said. "It's not like an airplane taking off on a mission because there is so much more ground activity involved and the choreography is critical. Everybody is an intricate part of the testing, a total team effort."

The 452nd FLTS staff is scheduled to wrap up the wet runway testing in April. The successful completion of wet runway testing marks some of the final testing requirements in the overall Block 20 Global Hawk testing prior to the initial operational test and evaluation.

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