Engineers conduct the first test of an electric aircraft engine in NASA’s Electric Aircraft Testbed (NEAT) at Plum Brook Station. Credits: NASA. Click to enlarge.

As large airline companies compete to reduce emissions, fuel burn, noise and maintenance costs, it is expected that more of their aircraft systems will shift to using electrical power.

What we’re hoping to learn now is how to make it more efficient and light-weight. Next year we’re going to upgrade the size of these motors—we’ll use the same technology to test the higher-power stuff next.

—Dr. Dyson

By increasing efficiency and reducing weight, the technology developed here can eventually be applied to larger, commercial aircraft, potentially resulting in reduced flying costs for airline companies and travelers.

NEAT is one element in a larger NASA effort investigating green aeronautics in general and electric propulsion in particular.

For example, researchers at NASA’s Armstrong Flight Research in California are using a unique test stand to understand the intricacies of how electric motor systems work.

Made of steel and aluminum, the 13.5-foot tall Airvolt test stand is one of the newest tools in NASA’s multi-center approach to explore the use of electric propulsion on future aircraft. Airvolt was designed and fabricated at Armstrong and can help researchers anticipate system integration challenges and verify and validate electric propulsion components, said Yohan Lin, Airvolt integration lead.

The AirVolt test stand at Armstrong. The propulsion system under test is attached to the top of the stand. Credits: NASA. Click to enlarge.

The test stand will help us to understand electric propulsion and the nuances of different systems. A lot of claims are made about the efficiency of electric motors and we want to verify that and gain experience with commercial off-the-shelf, or custom-designed systems.

—Yohan Lin

Airvolt also permits researchers to evaluate early-stage technology and build confidence in its use for future systems. For example, Airvolt research has already confirmed a challenge—electro-magnetic interference (EMI). EMI occurs when an electric circuit is interrupted by an internal or external force or condition, which results in noise interference.

EMI issues impacted data collection and real-time displays, resulting in false indicators in the control room, Lin said. It was caused by the propulsion system’s noise.

The solution was to install a combination of hardware filters on the test instrumentation and use digital filters on the acquired data. With the challenges eliminated, researchers in the control room were able to safely monitor key parameters.

The first tests on Airvolt in late 2015 focused on the energy-efficient Pipistrel Electro Taurus electric propulsion system, which is typically used for motor gliders. The system consists of an EMRAX motor and Pipistrel-designed motor controller, propeller, lithium polymer batteries, and throttle controller.

The motor produces 40 kilowatts of power, which are monitored by the Airvolt that is capable of accommodating systems that use up to 100 kilowatts of power. The test stand can also withstand 500 pounds of thrust.

Researchers using Airvolt are interested in determining voltage, current, power, torque and thrust performance of the commercial off-the-shelf components and learning about the characteristics of such a system, Lin explained. In addition, researchers are looking to build competencies in electric propulsion system verification and validation.

Airvolt is now testing the Joby Aviation JM-1 motor to provide information for modeling simulations of the electric propulsion elements.

The NASA ARMD Advanced Air Transportation Technologies hybrid gas electric propulsion subproject funds the current Airvolt work. The AATT subproject aims to explore and develop technologies and concepts for improved energy efficiency and environmental compatibility for future fixed wing subsonic transports.