NASA’s X-57 project has marked two critical milestones, taking two major steps toward demonstrating the benefits of electric propulsion for aviation.
More general aviation aircraft are in the air every year, which means that the challenge to address aircraft efficiency, noise and emissions becomes greater. NASA’s X-57 Maxwell, the agency’s first all-electric X-plane, will seek to meet that challenge by demonstrating innovative technology through electric-powered experimental flight.
The X-57 project is achieving this through several successive phases, in which the aircraft, a Tecnam P2006T, will undergo different modifications, or “Mods,” which NASA is tackling simultaneously to progress from one phase to the next, both safely and efficiently.
One of these milestones was achieved as part of X-57’s Mod II activity — the configuration in which the X-57 project will flight test the research propulsion system, and will eventually fly as a fully electric aircraft. Mod II includes the replacement of the baseline aircraft’s two inboard combustion engines with electric cruise motors.
Having integrated much of the initial electric system into the Mod II aircraft, engineers for the first time tested the motors and propellers, integrated onto the vehicle, in an initial spin test.
“This is the first time we’ve had the electric motors installed with propellers and had them spinning,” said Sean Clarke, NASA’s Principal Investigator for X-57. “This was a big milestone, as it was a big systems test where we were able to run both motors on the airplane at the same time.
“It’s really exciting to actually have all of the systems integrated and to be able to operate the vehicle that we’ve been designing for our system tests. It’s a huge opportunity for us, so we’re very excited.”
The test, which took place at Scaled Composites’ facility in Mojave, Calif., verified that the propellers, which pull energy from the motor to provide thrust and propel the aircraft, operate as expected as the motors were provided with significant amounts of power for the first time.
Instead of using batteries, which the vehicle will ultimately use during taxi and flight tests, the spin test was carried out from the ground using a power supply. Following stages of Mod II testing include repeating the test with the use of batteries, and delivery of the Mod II aircraft to NASA’s Armstrong Flight Research Center in Edwards, California. Once delivered to NASA, the Mod II aircraft will undergo verification, followed by taxi tests, and eventually, experimental flight tests.
While Mod II proceeds toward testing, efforts are already well underway for X-57’s Mod III phase.
Mod III includes the replacement of the aircraft’s baseline wing with a new, high-aspect ratio wing, and features the repositioning of the electric cruise motors out to the wingtips – an arrangement that presents the potential to boost aircraft efficiency considerably, but was not feasible with heavier, traditional combustion engines.
X-57’s Mod III activity also achieved a major milestone, as NASA received delivery of the Mod III wing from the project’s prime contractor, Empirical Systems Aerospace, Inc. of San Luis Obispo, California, or ESAero.
Upon delivery of the wing, NASA immediately began running tests to verify that its specifications and components are sound, and that the wing matches NASA’s structure and design models.
NASA’s testing of the wing, which was built by Xperimental LLC in San Luis Obispo, includes weight and balance measurement, ground vibration testing, and wing loading tests. Weight and balance measurement determines the total mass and the center of gravity on the wing, and helps NASA verify that the aircraft will perform correctly during taxi and flight tests.
Ground vibration testing, or GVT, considers the engineering challenges of the relatively thin, high aspect-ratio wing, which could be prone to flutter and other vibration conditions in flight. The GVT lets NASA verify whether the structural properties built into the wing matches what is expected for flight.
Finally, the wing will undergo wing loading tests. These tests will confirm whether the wing structure acts as predicted as it carries the approximately 3,000 pound aircraft through flight.
“I think that getting the wing here really brings Mod III to reality for the team,” said X-57 Deputy Operations Engineering Lead Kirsten Boogaard. “Having the wing come here and people being able to see the size of it, the look of it, just actually see it in person instead of in models, I think, is a really big deal for the project.
“It’s a cool thing when ideas go from concept to reality, but that’s what NASA does.”
After these tests are complete, NASA will then send the wing back to ESAero, where the wing will undergo fit checks onto a second “fit-check” fuselage. Here, the wing will also have 12 nacelles integrated, which will eventually house 12 small, electric high-lift motors and propellers, which will be featured on X-57’s final phase, Mod IV.
NASA’s X-57 project is operated under the agency’s Aeronautics Research Mission Directorate.