GL-10 Greased Lightning
United States · Digital Age (2010–present)
The NASA GL-10 Greased Lightning was a 10-engine all-electric tilt-wing VTOL UAV demonstrator built by NASA Langley Research Center between 2011 and 2014. It was a 10%-scale model of a notional 4-passenger electric VTOL transport, with eight smaller motors on the wing and two larger motors on the tail. The GL-10 first flew on 5 May 2014 in horizontal cruise, then completed its first hover-to-cruise transition on 5 August 2015. It is a direct conceptual predecessor of the eVTOL air-taxi designs (Joby S4, Beta Alia, Archer Midnight) now in commercial development.
The configuration combined two ideas. Tilt-wing — the entire wing rotates between vertical (for hover) and horizontal (for cruise), keeping the propellers and the wing always in correct mutual aerodynamic relationship. Distributed electric propulsion — many small electric motors on the wing leading edge, blowing air over the wing at low speeds for high lift, dropping the required wing area. The combination gave NASA a small testbed for the propulsion + flight-control technology stack the larger production-class eVTOLs would need.
The GL-10 was tiny. Wingspan 12.4 ft (3.78 m), gross weight 62 lb (28 kg). Each motor delivered about 4.5 kW peak. Lithium-polymer battery pack, ground-controlled flight only. Cruise speed about 35 knots. The aircraft was deliberately small and cheap so that NASA Langley could iterate on the flight-control algorithms — the hover-to-cruise transition is the hardest part of any tilt-wing design — without risking expensive hardware. The GL-10 made about 20 flights between 2014 and 2016 before retirement.
The GL-10 demonstrated that distributed electric propulsion + tilt-wing transition was achievable and had quiet community-noise behaviour at hover power. Joby Aviation, Beta Technologies, Archer Aviation, and Wisk all draw on the GL-10 reports for their commercial eVTOL designs. The airframe itself is in NASA Langley storage; NASA's own follow-on programme moved to the larger X-57 Maxwell distributed-electric-propulsion testbed (later cancelled).
For Kids — a shorter, friendlier version
The NASA GL-10 Greased Lightning was a small flying robot built by NASA. It had ten electric motors and could take off straight up like a helicopter. Then it tilted its wings forward and flew like a regular plane. NASA built it between 2011 and 2014.
The GL-10 was tiny. Its wings were just over 12 feet wide — smaller than a small car is long. It weighed only 62 pounds. Eight small motors sat on the wings, and two bigger motors were on the tail.
The cool trick was its tilting wing. The whole wing rotated up for hovering and then swung forward for fast flying. This kept the propellers working well in both positions. It made the drone very good at saving energy.
NASA first flew it in May 2014. Then in August 2015, it made its first full switch from hovering to flying forward. That was a big moment for the team!
The GL-10 was a test model — only one-tenth the size of a real flying taxi for four passengers. Its ideas helped inspire real air taxis like the Joby S4 and Archer Midnight that companies are building today.
Fun Facts
- The GL-10 had ten electric motors — eight on the wings and two on the tail!
- It was smaller than a small car, with wings just over 12 feet wide.
- The whole wing tilted up and down to switch between hovering and forward flight.
- It weighed only 62 pounds — lighter than most adult humans!
- NASA first flew it on May 5, 2014, in forward flight mode.
- Its first hover-to-cruise transition happened on August 5, 2015.
- It was a one-tenth scale model of a flying taxi that could carry four passengers.
- The GL-10 helped inspire real air taxi designs now being built by companies around the world.
Kids’ Questions
How did the GL-10 take off and fly forward?
The GL-10 tilted its whole wing straight up to hover like a helicopter. Then it slowly rotated the wing forward to fly like a normal plane. This smart trick let it do both jobs well.
Why did NASA build such a tiny drone?
NASA made it small so testing was cheaper and safer. It was a scale model of a much bigger flying taxi. The things NASA learned helped other companies build real air taxis.
What makes the GL-10 different from a regular drone?
Most drones either hover or fly forward — not both smoothly. The GL-10 used ten motors and a tilting wing to do both really well. That combo was very new and exciting at the time.
Variants
- GL-10 Greased Lightning
- Single airframe. 12.4 ft wingspan, 62 lb gross weight, 10 electric motors. First horizontal flight 5 May 2014; first hover-to-cruise transition 5 August 2015. ~20 total flights through 2016. Stored at NASA Langley.
Notable Operators
- NASA Langley Research Center
- Designer, builder, and sole operator. NASA Langley engineers Mark Moore, Dave North, and Bill Fredericks led the programme; the airframe was hand-built in-house.
Frequently Asked Questions
What is a tilt-wing aircraft?
An aircraft where the entire wing rotates between vertical (for hover takeoff and landing) and horizontal (for normal cruise flight). Tilt-wing differs from tilt-rotor (where only the engine rotates relative to a fixed wing), as on the V-22 Osprey. Tilt-wing keeps propellers and wing in correct mutual aerodynamic relationship at all times.
What is distributed electric propulsion?
An aircraft propulsion arrangement where many small electric motors are distributed across the wing leading edge instead of one or two large engines. The small motors blow air over the wing at low speeds, increasing effective lift and letting the wing be much smaller in cruise.
Did the GL-10 lead to commercial eVTOL aircraft?
Yes — the technical reports from the GL-10 programme are cited in the engineering basis for Joby Aviation S4, Beta Technologies Alia, Archer Aviation Midnight, and Wisk Cora. NASA's role was to validate the propulsion-and-flight-control technology stack at small scale; commercial eVTOLs are now scaling it up to passenger-carrying size.
How big was the GL-10?
Wingspan 12.4 ft (3.78 m), gross weight 62 lb (28 kg) — roughly the size of a hobby UAV. The aircraft was a 10%-scale model of a notional 4-passenger production eVTOL.
Where is the GL-10 today?
In storage at NASA Langley Research Center, Hampton, Virginia. Not currently on public display. The follow-on NASA programme moved to the larger X-57 Maxwell.
Sources
See Also
- Bell-Boeing V-22 Osprey — Production tilt-rotor aircraft
- Bell X-22A — Earlier ducted-fan V/STOL research
- Bell X-14 — Earlier vectored-thrust VTOL research
- NASA X-57 Maxwell — Sister NASA distributed-electric-propulsion testbed
- Bell XV-15 — Tilt-rotor research aircraft