Engineers with ingenuity create customized spray bar

  • Published
  • By 773rd Test Squadron
  • 773rd Test Squadron
EDWARDS AIR FORCE BASE, Calif. --  The Air Force Flight Test Center routinely tests aircraft to the limit of their operating envelope and one of the more difficult tests is high speed brake testing on a wet runway. These tests require the pilot to accelerate to the test speed, which could be as high as 140 knots (161 mph), and slam on the brakes while the runway is wet. The pilot keeps the brakes fully applied until the aircraft comes to a stop, and then taxis off the runway so the brakes can cool down.

Wet runway testing requires that water be sprayed in a defined pattern that controls the water depth so the aircraft does not hydroplane but still has a runway coefficient of friction that replicates conditions expected during fleet operations. The wet runway test section is centered on the runway with dry runway beyond and to both sides. The dry runway areas provide a safety zone that allows the pilot to stop on a dry runway if the anti-skid response is unstable. The need for these dry runway safety zones means the testing is not normally done while raining. 

Performing wet runway tests in the high desert environment is a complex task that requires the careful timing of events for safe and repeatable test execution. Timing of the water application and starting the test is very important because water sprayed onto the dry, usually hot runway, rapidly soaks in, runs off, then evaporates.

Wet runway testing requires a large amount of coordination between different departments and base personnel. 

The crews of the Edwards Fire Department have always provided support in laying down water exactly when and where it is needed and they were instrumental in the successful and safe execution of numerous wet runway test programs. For many years a locally made spray nozzle on the back of their 4,800 gallon water tankers was used to discharge water in a 25 foot wide spray, however, these nozzles could not be used after the tankers were retrofitted with new water tanks.

Thane Lundberg, 773rd Test Squadron, technical expert for the Subsystems Integration Flight, designed a custom spray bar with four adjustable water spray nozzles. The new spray bars provide the ability to tailor the wet runway test section width from approximately 10 to 100 feet and the applied water volume by selecting one to four nozzles as test conditions require. The new spray bars allow increased water drops at speeds over 18 mph.

"Custom spray bars were needed to accommodate the high water pressure and flow rate generated by the water tanker's powerful pump and to allow tailoring of the spray patterns to meet the unique requirements of wet runway test surface preparation," said Mr. Lundberg. "The spray bars commonly seen on construction company water tankers at Edwards are not strong enough for this application."

The new spray bars will significantly decrease the time required to prepare a wet runway test section, increase test repeatability and validity and provide the ability to tailor the water pattern and flow rates for specific wet runway testing objectives. These improvements will result in better data, decreased test times and more repeatable test conditions. As an added benefit, the spray bar can be used for a variety of fire department tasks such as wildfire suppression, dilution of chemical spills and dust control.

"Off the shelf commercially available components were modified to allow their use on our water tankers," Mr. Lundberg said. "The installation was a team effort that used the ingenuity of a variety of personnel to quickly fabricate and install a mounting system that greatly exceeded all expectations."

"Installation of the spray bars required the ingenuity and cooperation of many Edwards personnel and demonstrated one of the strengths of the AFFTC-its personnel."  said Patrick Wellman, 773rd Test Squadron, subsystems engineer at the Global Vigilance Combined Test Force. 

Mr. Wellman volunteered to coordinate the installation of the spray bars and went to great efforts to ensure both spray bars were installed and tested in time to support Global Hawk Block 20 testing this past month.

"The best part of this project was working together with so many professionals from different disciplines in the Edwards community," said Mr. Wellman. "This task could not have been accomplished to meet the Global Vigilance urgent need without the quality and prompt workmanship of the experts we have here."

Mr. Wellman sought out the expertise of a number of personnel on base to rapidly design, fabricate and install custom fit, easily removeable, spray bar attachments on both water tankers. Stan Lopata, 412th Maintenance Squadron, experimental aircraft welder, came up with the idea for the innovative fittings which didn't require holes to be drilled in the tankers. The crew at the Corrosion Control Surfaces team, also with the 412th, provided rapid service and quality craftsmanship with painting of all the pipes, fittings and supports.

Jerry Keltner, 95th Air Base Wing, Civil Engineering and Transportation Directorate, an experienced pipefitter, provided support in the fabrication and mounting of the necessary pipes and fittings. The crew at Station One was instrumental in the testing and calibration of the final configuration.  Jan Rehacek and Dave Tangren, 773rd Test Squadron, Subsystems engineers, at the Global Vigilance CTF, assisted in everything from moving hardware to critiquing and improving the final design.

"Testing of the spray bars has demonstrated the significant improvements that they provide," added Mr. Lunberg. "The ability of the combined AFFTC team to take on additional work and rapidly design and execute the installation and testing of this new capability is a testament to the dedication of all who work here."