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Ten-engine electric plane completes successful flight test

By Kathy Barnstorff, NASA Langley Research Center

The GL-10 prototype takes off in hover mode like a helicopter. [Credits: NASA Langley/David C. Bowman]



Imagine a battery-powered plane that has 10 engines and can take off like a helicopter and fly efficiently like an aircraft. That is a concept being developed by NASA researchers called Greased Lightning or GL-10.

The team, at NASA's Langley Research Center in Hampton, VA, is looking at the idea initially as a potential unmanned aerial vehicle (UAV). "We have a couple of options that this concept could be good for," said Bill Fredericks, aerospace engineer. "It could be used for small package delivery or vertical take off and landing, long endurance surveillance for agriculture, mapping, and other applications. A scaled-up version -- much larger than what we are testing now -- would also make a great one- to four-person-size personal air vehicle."

Video: NASA Langley researchers designed and built a battery-powered, 10-engine remotely piloted aircraft. The Greased Lightning GL-10 prototype has a 10-ft wingspan and can take off like a helicopter and fly efficiently like an airplane. In this video, engineers successfully transition the plan from hover to wing-borne flight in tests at Fort A.P. Hill in Virginia. [Credits: NASA/Gary Banziger]

The GL-10 is currently in the design and testing phase. The initial thought was to develop a 20-ft-wingspan (6.1-m) aircraft powered by hybrid diesel/electric engines, but the team started with smaller versions for testing, built by rapid prototyping.

"We built 12 prototypes, starting with simple 5-lb (2.3 kg) foam models and then 25-lb (11.3 kg), highly modified fiberglass hobby airplane kits all leading up to the 55-lb (24.9 kg), high-quality, carbon fiber GL-10 built in our model shop by expert technicians," said aerospace engineer David North.

"Each prototype helped us answer technical questions while keeping costs down. We did lose some of the early prototypes to 'hard landings' as we learned how to configure the flight control system. But we discovered something from each loss and were able to keep moving forward."

Engineers David North (L) and Bill Fredericks (R) carry the Greased Lightning before one of its flight tests. [Credits: NASA Langley/David C. Bowman]



During a recent spring day, the engineers took the GL-10 to test its wings at a military base about two hours away from NASA Langley. The remotely piloted plane has a 10-ft wingspan (3.05 m), eight electric motors on the wings, two electric motors on the tail, and weighs a maximum of 62 lb (28.1 kg) at takeoff.

It had already passed hover tests -- flying like a helicopter -- with flying colors. But now was the big hurdle -- the transition from vertical to forward "wing-borne" flight. As engineers who have designed full-scale vertical takeoff and landing tiltrotors such as the V-22 Osprey will tell you -- that is no easy task because of the challenging flight aerodynamics.

"During the flight tests, we successfully transitioned from hover to wing-borne flight like a conventional airplane then back to hover again. So far, we have done this on five flights," said Fredericks. "We were ecstatic. Now we're working on our second goal: to demonstrate that this concept is four times more aerodynamically efficient in cruise than a helicopter."

Zack Johns is the GL-10's primary pilot. He says flying the 10-engine aircraft has its ups and downs, but it really flies more like a three-engine plane from a control perspective.

"All four engines on the left wing are given the same command," said Johns. "The four engines on the right wing also work in concert. Then the two on the tail receive the same command."

The prototype successfully transitioned from hover to wing-borne flight during several test flights. [Credits: NASA Langley/Gary Banziger]



One other advantage to the GL-10 besides its versatile vertical takeoff and landing ability is its noise -- or lack of it. "It's pretty quiet," said Fredericks. "The current prototype is quieter than a neighbor mowing the law with a gas-powered motor."

The next step in the GL-10 test program is to try to confirm its aerodynamic efficiency. Part of that UAV research is for NASA Aeronautics' Unmanned Aircraft Systems Integration in the National Airspace System Project, led out of the Armstrong Flight Research Center in Edwards, CA. The goal of the project is to provide research results to reduce the technical barriers associated with integrating unmanned aerial vehicles into the skies.

Published July 2015

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