AEDC sets record with largest aircraft model to conduct B-52H store separation test

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  The Air Force's oldest legacy bomber still in service, the B-52H Stratofortress, is in the midst of major weapons and flight systems upgrades, including a capability to drop smart bombs from the plane's internal weapons bay.

AEDC has 40-plus years of store separation experience, but this test entry is unique and challenging in several ways, according to Doyle Veazey, the ATA store separation section manager.

"We have never tested a store separation aircraft model of this size in our wind tunnels," he said. "For that matter, our design group and Model Shop have never fabricated a store separation test article this large."

Work started last November when the B-52H Program Office agreed to fund a wind tunnel test program and the Air Force SEEK Eagle Office provided CAD (computer-aided design) geometry files to AEDC's design personnel.

The Air Force is upgrading the B-52's internal weapons bay to expand the aircraft's payload by roughly two-thirds, according to Lt. Gen. James Kowalski, commander of Air Force Global Strike Command.

"The B-52 delivers the widest variety of stand-off, direct-attack nuclear and conventional weapons in the Air Force and we have been investing in multiple improvements," General Kowalski told an audience recently during a National Defense University Foundation-sponsored address in Washington, D.C.

This effort represents the "most significant B-52 modernization since the [1980s] and will add 21st century capability to the aircraft," Kowalski said.

Major improvements include new flight control software to enhance targeting pod capabilities and incorporate miniature air launched decoys onto the B-52, as well as a modern digital communications system. With progress thus far, General Kowalski said he expects the B-52's combat network communications technology upgrade to enter low-rate production by 2013.

For AEDC's role in the B-52H store separation testing, the design team, led by Scott Wieland, has worked concurrently with projects representatives, who established requirements and shop personnel, all on a highly accelerated timeline.

Since January, AEDC's Model Shop has been busy fabricating and assembling the components making up the approximately 3,400-pound aluminum and steel B-52H model, at 10-percent scale, to undergo store separation testing in the center's 16-foot propulsion wind tunnel in August.

Veazey said the upcoming test will support a more efficient and effective weapons system platform.

"The Global Strike Command has a requirement to put weapons into the [internal] weapons bay of the B-52H that historically have not been there, specifically Global Positioning System (GPS) weapons, like the MALD (Miniature Air Launched Decoy), the JASSM (Joint Air-to-Surface Standoff Missile) and the several variants of JDAM (Joint Direct Attack Munition)," he said. "The requirement is to carry them internally in the weapons bay. That reduces the aerodynamic drag on the airplane and allows for extended range missions of the B-52H.

"That's one way to get more energy efficient, to bring those weapons internal. It also allows them to carry more weapons on a B-52H. They can load up the wing pylons' two Heavy Stores Adapter Beams and they can load up the new Conventional Stores Rotary Launcher internally."

Safe release of the stores from the aircraft is imperative for a successful mission to protect the crew, avoid damaging the airplane or the stores and accurately strike the targets.

"Bay separations from any airplane are complex and dynamic enough as it is, but when you combine that bay separation with stores that are not necessarily aerodynamically stable to begin with, it just really makes things even more challenging," Veazey said. "Aside from the safety of the crew, the risk to the weapons and the airplane is a real concern."

The primary measurements obtained during a store separation test are the force and moments of the separating store in the flow field of the airplane.

"There will be captive trajectories, pseudo-freestream and aerodynamic grid data that will be acquired, the usual CTS (captive trajectory support) test techniques," Veazey said. "Pseudo-freestream testing means the aircraft model is in the tunnel during CTS store model freestream data acquisition."

If a test article is too large, it can block enough of the airflow in the wind tunnel to adversely affect the test.

"The total blockage of the model is one of the things we were concerned about," said JT Thompson, ATA project engineer.

Veazey said, "It is about 2.2 percent, which is higher than desired from an aerodynamicist's perspective, but for store separation work, that's tolerable. We're using CFD (computational fluid dynamics) to support that engineering judgment."

The test team plans to use one other tool to ensure the stores deploy safely from the B-52H model and that blockage is not an issue with the test.

"One of the things we're looking at using during the course of the test is Background-Oriented Schlieren (BOS), which may help show some flow characteristics around the test articles," Veazey explained. "This technique, installed and operated by ATA Technology personnel, uses a simple optical set-up consisting of a structured background pattern, an electronic camera with a high shutter speed and a high-intensity light source. Then special COTS (commercial off-the-shelf) software is used to process the images and produce the final product.

"This first B-52H store separation effort will result in AEDC employing all its capabilities from planning, design, fabrication, testing, computations and analysis and reporting. Combining that with the ongoing collaboration with the B-52H Program Office, AFSEO and the several weapons program offices and their contractors makes this a truly 'Integrated Test and Evaluation' program."