AEDC researches possible modifications to C-5M Super Galaxy wings

  • Published
  • By Philip Lorenz III
  • AEDC/PA
ARNOLD AIR FORCE BASE, Tenn. --  A recent landmark aerodynamic test on a scale model of the C-5M Super Galaxy in Arnold Engineering Development Complex's (AEDC) 16-foot transonic wind tunnel (16T) was all about efficiency and the bottom line.

Jack O'Banion, Lockheed Martin's director of air mobility improvements and derivatives, said the high cost of fuel is the driving force behind the recent test.

"There's something on the order of 2.5 billion gallons [of aviation fuel] a year that the Air Force has to secure," said O'Banion. "The largest consumer of jet fuels is air mobility, and jet fuel in itself represents about 84 percent of the Air Force's total energy cost. The kinds of savings we're talking about with regard to equipping C-5s with efficiency improving devices like winglets is reducing the fuel burn of a C-5 by something on the order of 166 gallons per hour.

"That's a significant improvement in fuel flow, particularly as we see the spot price of jet fuel heading upwards to $4 a gallon and probably higher in the future."

The over-arching goal of the recent test was to validate the computational fluid dynamics predicted drag reduction effects of winglets on the C-5M Super Galaxy, the Air Force's most current version of the aircraft.

David Yoder, an ATA Flight Systems Branch project engineer for the recent C-5M test, said Lockheed Martin and AFRL, the test's sponsor, specifically chose AEDC's 16T facility for this entry.

"AEDC is the place they wanted to test because the size of the tunnel allows them to use an existing 4.04-percent wind tunnel model, which is a large enough scale to give them high-fidelity results," he said. "The model is mounted on an internal strain gage balance which is used to measure the aerodynamic force and moments. The balance is mounted to a sting which supports the model in the tunnel, and the sting is mounted to a pitch and roll mechanism."

Marvin Sellers, a senior engineer with ATA's Flight Systems Testing group, said the customer, Lockheed Martin Corp., came to AEDC with two objectives. The primary focus was on acquiring a drag increment from the addition of a winglet to the existing wings with the goal of improving the aircraft's aerodynamic efficiency and lower fuel consumption.

A winglet is a short, near-vertical projection on an aircraft's wing tip that reduces drag and improves fuel efficiency.

"Two different [sets of] winglets were tested to determine the one that provides the best [aerodynamic] improvement," Sellers said. "They also desired to acquire the loads acting on the winglets for structural analysis and investigate the impact of the winglets on aileron stability and control."

Sellers spoke about his role in the testing on the C-5M model, which is approximately 10 feet long with a nine-foot wing span, tip-to-tip.

"The model was designed as a pressure model, but has been modified to accept a balance," he said. "To eliminate the need to refurbish the more than 1,000 pressure taps and decrease the impact on drag measurement of adding approximately one dozen pressure modules, the customer has elected to use Pressure Sensitive Paint (PSP) to acquire full model surface pressure data and activate only 58 pressure taps on the wing surface.

"The PSP will also provide integrated pressure loads on the winglets as well as distributed pressure load on the wings," said Sellers.

The paint is applied to the model in two layers, a white undercoat and the PSP layer. The white undercoat provides a uniform reflective surface for the PSP layer. The illumination source excites the PSP layer, which fluoresces with intensity inversely proportional to the surface pressure on the model.

Chuck Hybart, Lockheed Martin's product development senior manager for air mobility improvements and derivatives, said the approach to the recent test has been a fully collaborative process between Lockheed, Air Force Research Laboratory and AEDC. He credited AEDC's test team with helping to steer the group to a more efficient approach to the project.

"We actually changed the approach that we were going to use for measuring the pressures on the model because of some of the capability that you have in the tunnel," Hybart said.

When asked why Lockheed Martin chose AEDC as the site for the recent C-5 test, O'Banion said, "In particular [when] doing wind tunnel testing on an aircraft the size of the C-5, [it] takes a specific set of tunnels and specific capabilities that are very rare in the world, and fortunately your facility has those capabilities. When we're doing testing particularly for fuels savings and fine tuning of aerodynamic phenomena, the ability to test at a representative Reynolds number is a tremendous asset in being able to do this work accurately and fortunately, you bring those capabilities."

With platforms like the C-5 and testing facilities like AEDC, O'Banion sees the potential for future work in the years ahead.

"We hope this is just the start of a series of refinements for the C-5...if we're able to validate the results and the business case is so compelling to the Air Force that we'll be able to do this and perhaps other improvements to the aircraft," O'Banion said. "There's more performance that can be unlocked in the C-5, and the service life of the airframe means they'll be in the inventory for several decades to come.

"I think there's a lot of potential still here for the C-5 ahead and, with your help, we ought to be able to unlock that for both the warfighter and the taxpayer."

The C-5 Galaxy, a heavy-logistic transport plane with an unrefueled range of more than 6,000 miles with 261,000 pounds of weight, played a significant role providing transportation for the military buildup in the Middle East prior to the start of the Persian Gulf War.

The plane, which is one of the largest in the world, has played a significant role in supporting Operation Desert Storm, Operation Iraqi Freedom and Operation Enduring Freedom.

A combination of C-17 Globemaster IIIs and C-5s flew more than 11,400 sorties during the buildup to Operation Iraqi Freedom. Even though the C-5s flew approximately 900 fewer sorties than the Globemasters, the larger aircraft hauled about 11,500 more tons and 5,300 more passengers.