Can Gross Weight Be Increased?

A US Navy E-2C Hawkeye, a carrier-based electronics aircraft that serves as the eyes and ears of carrier battle groups, recently underwent structural loads tests at NASA Dryden Flight Research Center's Flight Loads Laboratory to determine if increasing the aircraft's gross weight will affect its performance.

The Hawkeye, distinctive with its 24-foot diameter rotating radome and quadruple vertical tails, is part of a fleet of aircraft that has been operational for more than 40 years. The Navy is planning upgrades that will add weight to the aircraft. Navy officials asked NASA Dryden to help formulate loads equations aimed at determining how the additional weight will affect the aircraft's flight envelope.

"A loads calibration test is a primary part of the development of any new aircraft," explained Paul Lundstrom of Spiral Technology, Dryden's lead test engineer on the project. "It's also an important step in determining the flight envelope for any new configuration of an aircraft. So when you get a new configuration or a new aircraft, you absolutely have to know what the structural loads are on the airplane when it's in flight. The only good way to determine that is by doing a test of this nature."

The aircraft arrived at Dryden last fall from its base at the Naval Air Warfare Center Aircraft Division (NAVAIR) at Naval Air Station Patuxent River, Md. A Navy crew removed the engines and propellers, purged fuel tanks and performed other preparations before NAVAIR and Dryden technicians began installing loads sensors and other equipment for the structural tests. The work was completed in mid-March about three weeks ahead of schedule.

The tests in Dryden's Flight Loads Laboratory applied force, or loads, on the aircraft to develop loads equations, using a data-recovery system connected to instrumentation on the airplane, said Lundstrom.

"That data is used to develop what we call loads equations," Lundstrom added. "These loads equations can be used (by Navy flight test engineers) to estimate loads while they're test-flying the airplane. This allows them to know when they're approaching in-flight loads that are too high for the structural capacity of the aircraft. A loads calibration allows us to define the performance parameters of the aircraft while maintaining a safe structure."

The E-2C research isn't the biggest project completed in Dryden's Loads Laboratory, but it is among the largest ever undertaken and could lead to similar work in the future, he added.

An unmodified E-2C weighs about 42,000 pounds empty. The Hawkeye that was tested at Dryden had its weight beefed up with metal plates to simulate an empty weight of about 45,000 pounds -- mimicking the latest weight configuration of the upgraded E-2D Advanced Hawkeye, more commonly known as the "Hummer" in the fleet. Loads were applied to the aircraft's wings and tail.

The E2-C has an 80-foot wingspan, is about 58 feet long and 18 feet tall. Dryden's Loads Laboratory can accommodate the aircraft with room to spare for equipment and fixtures necessary for conducting the research.

NAVAIR personnel installed 226 strain gauges, which measure stress on the aircraft's surface, while NASA technicians mounted 15 string potentiometers, which essentially are electronic measuring tapes, on the aircraft. Six load cells -- instrumentation that records how large a force is being applied to an area -- measured aircraft reactions at fixed points on the ground. An additional 24 load cells were used to monitor and control loads applied to the wings; another eight were used for the tail.

NAVAIR project engineer Jason Brys said the Navy has been pleased with the progress that has been made to date.

"We had a few obstacles during the preparation process, but the three-party team of NASA, NAVAIR, and Northrop Grumman Corp. have come up with timely solutions," he said.

"The Navy decided to use NASA Dryden because they have unique facilities and experience that are hard to find elsewhere, and I am pleased with the support that we have received from Dryden to date," Brys added.

Lundstrom said the tests on the E-2C illustrate one of two core competencies of the NASA Dryden Flight Loads Lab.

"We're one of the few locations in the nation that can do this specific type of test," he said. "Our second very important capability that we're still in the process of developing and growing and learning more about, is testing under extreme thermal conditions. We have a strong tradition here at Dryden for testing for both of those types of information."

The E-2A Hawkeye first entered service in 1961, was updated in 1969 as the E-2B and the E-2C was introduced in 1973. It performs a similar role to the Air Force E-3 Airborne Warning and Control System, also known as AWACS.

FMI: www.dfrc.nasa.gov