Up and down can be on the right side. That’s what NASA researchers set out to test for an efficient wing concept that could be part of the agency’s answer to making future aircraft sustainable.
Research from NASA’s Advanced Air Transport Technology Project Adding the 10-foot model could help NASA engineers validate the concept of a transonic truss-braced wing (TTBW), an aircraft that uses long, thin wings stabilized by diagonal struts. The efficient wings of the TTBW concept add lift and could result in reduced fuel consumption and emissions for future commercial single-aisle aircraft. A team at the Flight Loads Laboratory at NASA’s Armstrong Flight Research Center in Edwards, California, is using the model, called a Mock Truss-Braced Wing, to validate the concept and their test methods.
Instruments are installed to measure the stresses in the model wing and strut, then attached to a rigid vertical test frame. A wire hanging from the top of the frame stabilizes the model wing for testing. For these tests, the researchers chose to mount a 10-foot-long aluminum wing upside down, adding weight to apply tension. The inverted orientation allows gravity to simulate the lift that a wing would experience in flight.
“A strut reduces the structure required on the main wing, and the result is lower structural weight and a thinner wing,” said NASA Mock Wing Test Director Frank Pena. “In this case, the test measured the reaction forces at the base of the main wing and at the base of the strut. There is a certain amount of load sharing between the wing and the strut, and we are trying to measure that the main wing How much of the load stays in the strut and how much is transferred to the strut.”
To collect these measurements, the team added weight to the wing and truss one at a time. In another series of tests, engineers tapped the wing structure at key points with a tooled hammer, monitoring the results through sensors.
“The structure has a natural frequency that depends on its stiffness and mass that it wants to vibrate,” said Ben Park, NASA’s mock-wing ground vibration test director. “Understanding the wing’s frequencies, where they are and how they respond, is key to being able to predict how the wing will respond in flight.”
Adding weight to the wing tip, tapping the structure with a hammer, and collecting vibration response is an unusual testing method because it adds complexity, Park said. The process is worthwhile, he said, if it provides the data engineers are looking for. The tests are also unique in that NASA Armstrong designed, built, assembled, and tested the wing, strut, and test fixtures.
With successful load calibration and vibration tests on the 10-foot wing nearly complete, the NASA Armstrong Flight Loads Laboratory team is working to design a system and hardware to test a 15-foot model made of graphite-epoxy composite. The Advanced Air Transport Technology TTBW team at NASA’s Langley Research Center in Hampton, Virginia, is designing and building the model, called the Structural Wing Experiment Evaluating Truss-bracing.
The large-wing model will be built with a structural design that more closely resembles what could potentially fly on a future commercial airliner. The goals of these tests are to calibrate predictions with measured stress data and to learn to test new aircraft structures such as the TTBW concept.
NASA’s Advanced Air Transport Technology Project falls under NASA’s Advanced Air Vehicles Program, which evaluates and develops technologies for new aircraft systems and explores promising concepts for air travel.