NASA Greased Lightning (defunct)

(Photo credit: NASA)

Greased Lightning (GL-10)
NASA Langley
Hampton, Virginia, USA
www.nasa.gov/langley

Established in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the U.S. federal government responsible for the civil space program, aeronautics research and space research. NASA is headquartered in Washington, D.C. and has 10 major field centers. NASA has made space ships, explored space, the moon, launched satellites, gathered data about Earth from space, made the Skylab Space Station, explored Mars, studied our solar system using space probes and more.

NASA started researching distributed electric propulsion (DEP) electric vertical takeoff and landing (eVTOL) and hybrid-electric VTOL aircraft in 2009. DEP was introduced to the world in November 2009 when Mark Moore, while still at NASA, unveiled the Puffin, a personal an all-battery eVTOL concept design aircraft. For the first time, the world caught a glimpse at how electric propulsion might transform everyday flight. In 2010, according to one website, the first eVTOL aircraft flown was NASA's Puffin subscale eVTOL tailsitting aircraft.

In 2014, NASA built both eVTOL and fixed-wing DEP technology demonstrator aircraft. Some of the key design features for NASA's advanced air mobility (AAM) common reference vehicles is to increase safety exponentially, reduce the complexity of the aircraft, decrease the cost of manufacturing, minimize maintenance costs, lower the final ticket cost to the consumer, lessen or have no carbon footprint for the aircraft and decrease the noise level for the general public.

NASA has continued making passenger eVTOL concept designs, technology demonstrators and research eVTOL aircraft for any company that wants to take advantage of NASA's research. In addition, NASA is now making eVTOL and hybrid-electric eVTOL aircraft to explore planets and their moons, in our solar system. As of 2024, NASA's space probes have not traveled to any other solar systems in the Milky Way galaxy, yet.

Mark Moore, Co-Founder and CEO of Whisper Aero (formerly a Principal Investigator and Chief Technologist for On-Demand Mobility, NASA and Engineering Director of Aviation, Uber Elevate) at the Vertical Flight Society's 7th Annual Electric VTOL Symposium, Jan. 21-23, 2020 in San Jose, California, USA, stated concerning advanced air mobility (AAM), "There has not been this pace in aeronautics since the Wright Brothers."

Greased Lightning uncrewed hybrid-electric VTOL prototype research aircraft
In 2015, NASA Langley researchers completed a carbon fiber uncrewed hybrid-electric vertical takeoff and landing (VTOL) drone prototype named Greased Lightning (or the GL-10). The prototype was successfully remotely piloted from a hover to wing-borne flight back to landing, in untethered flight tests at Fort A.P. Hill, Virginia, USA. The GL-10 was actually a 50% scale prototype and NASA had plans for a 100% scale aircraft but it was never made.

On of the main features of the aircraft is that it had Distributed Electric Propulsion (DEP) and that DEP would work well on a VTOL aircraft. The design of the prototype using distributed electric propulsion allowed engineers to shut down many of the electric motors during forward flight and have the propellers folded for maximum aerodynamic efficiency during forward flight.  The purpose of this research project was to take advantage of new technologies, electric engine propulsion and affordable drone flight controllers (closed loop controllers) and make an aircraft which would take on the best aspects of an airplane and helicopter and fly with superb reliably, affordably and excellent stability.  The project was apparently started in 2013.

Some of the NASA conclusions of flight testing include but are not limited to:

• It was demonstrated that via flight testing, an aircraft with distributed electric propulsion was capable of VTOL flight, forward flight and transition flight.
• The aircraft used thrust vector control rather than slipstream control.
• The aircraft demonstrates that hybrid-electric VTOL aircraft can be scaled up and made commercially viable.
• Operations are safer with distributed electric power.
• The aircraft was more aerodynamically efficient that a similarly sized helicopter when in forward flight.
• They hybrid-electric power source increases the range of the aircraft many times over a conventional helicopter.
• The weight of the aircraft is lighter, more efficient and has lower noise than a helicopter.

The Greased Lightning (GL-10) prototype was reported to have flown at 70 mph (113 km/h) and possibly faster speeds. Flight tests also included unpowered glides and the prototype can take off like a helicopter and fly efficiently like an airplane. The prototype had a satellite communications system. The range and cruise altitude are unknown. The aircraft has 10 propellers (Aeronaut CAM Carbon 16x8”), 10 electric motors (Scorpion SII-4020-360KV) and batteries in the propeller nacelles. The aircraft has two small diesel engines (Launchpoint Technologies Genset) turning alternators which charges on-board batteries which power the aircraft. The aircraft also has a diesel fuel tank. The 10 electric engines weighed about 55 lb (25 kg).

The prototype has one high main swept back tilt-wing with a 10 foot (3.05 meters) wingspan and one rear tilting tail tilt-horizontal stabilizer, dihedral angled, with 3 vertical stabilizers. The final design settled on a 15 degree leading edge wing sweep and with 93% of the weight of the aircraft carried by the high main tilt-wing and 7% of the weight carried by the tail.

There is an area in the cockpit area for a payload. The empty weight of the prototype is 46 lb (21 kg), has a maximum payload weight of 16 lb (7 kg) and has a maximum takeoff weight of 62 lb (28 kg). The prototype was built with carbon fiber composite for a high strength to low weight ratio. The aircraft was reported to have retractable landing skids.

Greased Lightning (GL-10) is an aircraft configuration that combines the characteristics of a cruise efficient airplane with the ability to perform vertical takeoff and landing (VTOL). This aircraft has been designed, fabricated and flight tested at the small unmanned aerial system (UAS) scale.

The GL-10 design utilized two key technologies to enable this unique aircraft design; namely, distributed electric propulsion (DEP) and inexpensive closed loop controllers. These technologies enabled the flight of this inherently unstable aircraft. Overall it has been determined thru flight test that a design that leverages these new technologies can yield a useful VTOL cruise efficient aircraft.

There are three primary advantages to Greased Lightning technology relative to conventional rotorcraft. The first is no speed limit due to retreating blade stall.

The second significant advantage over rotorcraft is improved aerodynamic efficiency. Typical fixed wing aircraft achieve a best lift to drag ratio of 14 to 20. Rotorcraft typically have an effective lift to drag ratio of 4 to 5. Note this equation can also be applied to a fixed wing aircraft and the result is equal to the aerodynamic lift to drag ratio. Aircraft with low effective lift to drag ratio, specifically rotorcraft, are limited in range and consume more energy to fly the mission. This leads to higher operating costs of the aircraft.

The third shortcoming of rotorcraft is they have multiple single point of failure modes, for example the pitch links. Granted that with proper inspection and maintenance the likelihood of a pitch link failure is very low, but these inspection and maintenance requirements increase operating costs.

There are many reasons for the limited success of previous VTOL aircraft, but they fall into four main categories. First, the resulting useful load fraction of the aircraft was small because the cross shafting and other VTOL systems significantly increased the empty weight of the aircraft. Second, the Effective L/D (Lift to drag ratio) of the aircraft is noticeable less than their fixed wing counter parts, and therefore overall performance suffers. Third, while these aircraft were flyable, their handling qualities were usually poor and required highly trained and skilled test pilots to safely operate.

Additionally, in general many of these aircraft would be disturbed by wind gusts more than rotorcraft and thus had smaller allowable wind environment envelopes. Fourth, the inspection and maintenance requirements were large due to the numerous single points of failure. Considering these previous shortcomings, when new technology can be infused into products, it is worthwhile reinvestigating concepts that were previously considered infeasible, or iterating from previous lessons into new concepts.

NASA July 2017 Greased Lightning Flight Testing PDF report (page 3-4) .

A unique aspect to NASA's project was the willingness of their engineers to accept risk in the planning of the project. NASA's approach to flight testing for the Greased lightning had several phases to make this happen. First was using a "Foamie" aircraft frame to test the functionality of the avionics hardware and flight software. There was no intention to fly this model. Then a Greased Lighting Almost Ready to Fly (GLARF) realistic model was made and used as a flying simulator for multiple tests. Then the actual Greased Lighting prototype was constructed, made its first flight and more testing continued. NASA built 12 prototypes during this project.

NASA stated that the use of the technologies in a VTOL aircraft enabled the flight of this inherently unstable aircraft, achieves excellent lift to drag ratio, can safely and repeatably transition into cruise efficient wing born flight, can robustly handle disturbances throughout the transition corridor, have ultra safe operations, have the cruise efficiency of a fixed-wing aircraft and still have true VTOL capability, is resilient to any motor failing, can be scaled to have a maximum take-off weight of approximately 3,000 lbs (from one to four people), is easy to fly and has low noise.

While not formally verified, NASA believed in 2015, the Greased Lightning set the record for the highest lift to drag ratio VTOL aircraft that has flown and transitioned. According to NASA documents, the two year long project totaled approximately $1.8 million USD in full cost accounting.

Some of NASA's other VTOL projects include the NASA LA-8 eVTOL Testbed and NASA Puffin.

Specifications:

• Aircraft type: Uncrewed subscale hybrid-electric VTOL technology demonstrator
• Piloting: Remote piloting
• Capacity: No passengers but there was a small payload area where the cockpit of the aircraft would have been located
• Cruise speed, estimated: 70 mph (113 km/h)
• Range: Unknown
• Cruise altitude: Unknown
• Empty weight: 46 lb (21 kg)
• Maximum payload weight: 16 lb (7 kg)
• Maximum takeoff weight: 62 lb (28 kg)
• Propellers: 10 propellers (Aeronaut CAM Carbon 16x8”)
• Electric motors: 10 electric motors (Scorpion SII-4020-360KV)
• Power source: Batteries and two diesel engines (Launchpoint Technologies Genset)
• Fuselage: Carbon fiber composite with a front SpaceAge Controls Alpha/Beta Pitot Tube
• Windows: No windows
• Wings: 1 main high swept back tilt-wing (10-foot wingspan or 3.05 meters)
• Tail: 1 rear tilt-horizontal stabilizer with dihedral angle with 3 vertical stabilizers
• Landing gear: Retractable landing skids
• Safety features: Distributed Electric Propulsion (DEP) means having multiple propellers (or electric ducted fans) and multiple electric motors on an aircraft so if one or more propellers (or electric ducted fans) or some electric motors fail, the other working propellers (or electric ducted fans) and electric motors can safely land the aircraft. DEP provides safety through redundancy for passengers or cargo. There are also redundancies of critical components in the sub-systems of the aircraft providing safety through redundancy. Having multiple redundant systems on any aircraft decreases having any single point of failure.

Related Aircraft:

• NASA Dragonfly (space probe)
• NASA LA-8 eVTOL Testbed (prototype)
• NASA Lift+Cruise (concept design)
• NASA Multi-Tiltrotor (concept design)
• NASA Puffin (concept design)
• NASA Quadrotor (concept design)
• NASA Quiet Single Main Rotor (concept design)
• NASA Raven (concept design)
• NASA Side-by-Side (concept design)
• NASA Tiltduct (concept design)
• NASA Tiltrotor (concept design)
• NASA Tiltwing (concept design)

Company Insights:

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Resources:

• NASA Langley website
• NASA Langley Facebook
• NASA Langley Twitter
• NASA Langley YouTube Channel
• NASA Langley Flickr
• NASA Langley Instagram
• NASA LinkedIn
• NASA Technical Reports Server
• NASA PDF: NASA Langley Distributed Propulsion VTOL Tilt-Wing Aircraft Testing, Modeling, Simulation, Control, and Flight Test Development, NASA, June 16, 2014
• Video: GL-10 Greased Lightning Tether Test, NASA Langley Research Center, Aug. 22, 2014
• NASA PDF: Experiment Design for Complex VTOL Aircraft with Distributed Propulsion and Tilt Wing, NASA, Jan. 5, 2015
• Article: Ten-Engine Electric Plane Completes Successful Flight Test, NASA, Apr. 30, 2015
• Video: Greased Lightning GL-10 Successful Transition Test, NASA Langley Research Center, Apr. 30, 2015
• Article: Watch NASA's Greased Lightning aerocopter (heliplane?) take off and fly, CNET, May 5, 2015
• Article: NASA's New 10-Engine Drone Is Half Chopper, Half Plane, Wired, May 5, 2015
• NASA PDF: NASA GL-10 Tilt-Wing VTOL UAS Flight Validation Experiments, NASA, June 22, 2015
• Article: Electrical Power Will Change the Look of Aviation, Air & Space/Smithsonian Magazine, Dec. 2015
• Video: 360 Video of Greased Lightning GL-10 in flight, NASA Langley Research Center, Feb. 1, 2016
• Article: NASA's Greased Lightning" Drone Is Quieter Than a Lawn Mower and Has 360-Degree Vision, Inverse, Feb. 4, 2016
• NASA PDF: Greased Lightning (GL-10) Flight Testing Campaign, NASA, July 2017
• NASA PDF: Greased Lightning (GL-10) Performance Flight Research – Flight Data Report, NASA, Nov. 2017
• NASA PDF: Tonal Noise Prediction of a Distributed Propulsion Unmanned Aerial Vehicle, NASA, June 25, 2018
• NASA PDF: Feedback Control of Flight Speed to Reduce Unmanned Aerial System Noise, NASA, June 25, 2018
• NASA PDF: Autonomous Path-Following for a Tilt-Wing, Distributed Electric Propulsion, Vertical Take-Off and Landing Unmanned Aerial System in Hover Mode, NASA, Nov. 2018
• Article: NASA Launches Urban Air Mobility Grand Challenge, Electric VTOL News, November 5, 2018
• Article: NASA Releases Two UAM Consultant Reports, Electric VTOL News, November 12, 2018
• Article: NASA Embraces Urban Air Mobility, Vertiflite, Jan/Feb 2019
• Article: NASA Holds Supply Chain Workshop, Electric VTOL News, Feb. 5, 2020
• Article: NASA’s National Campaign, Vertiflite, May/June 2020