JAL, JAXA, O-Well, and Nikon Conduct Flight Test with Aircraft for which the World's First Riblet Shape was Applied over External Paint

Contributing to the reduction of CO₂ emissions by improving aircraft fuel efficiency and to the realization of a sustainable society

March 3, 2023

Japan Airlines Co., Ltd. (hereinafter “JAL”), Japan Aerospace Exploration Agency (hereinafter “JAXA”), O-Well Corporation (hereinafter “O-Well”), and Nikon Corporation (hereinafter “Nikon”) have been aiming to reduce CO₂ emissions by improving aircraft fuel efficiency since July 2022. The four companies are conducting flight tests using the world's first^*1 aircraft with riblets^*2 applied over the aircraft's external paint. Although there are cases such as processing riblets to decals and films and attaching them to the airframe, in this case, weight reduction and improved durability are expected as a result of applying riblets directly over the coating.

Riblets, where a skin friction reduction effect^*3 was confirmed by JAXA, were applied locally to the bottom of the fuselages of two Boeing 737-800 aircraft. For one aircraft, O-Well's processing technology was used, and for the other, that of Nikon was used.

Durability tests are currently being carried out by performing repeated inspections, measuring the changes in the shapes of the riblets incurred during test flights.

As of now, more than 1,500 flight hours have been accumulated in the O-Well method aircraft, and more than 750 hours in the Nikon method aircraft, and the riblets applied by both O-Well and Nikon have been confirmed to have sufficient durability.

*1In the operated aircraft as of February 28, 2023. According to JAL, JAXA, O-Well, and Nikon.
*2Riblet: Fine groove structure inspired by the shape of shark skin which reduces water resistance. The skin friction can be reduced by forming a fine groove structure on the aircraft exterior panel along the air flow during flight of the aircraft.

*3Evaluation of skin friction reduction effect by riblets at JAXA

Wind tunnel test
Skin friction reduction resulting from riblets is evaluated in a series of ground tests simulating flight conditions.

Simulation on JAXA supercomputer: Flow is perpendicular to the paper surface
Rotating flows called vortices near the surface of the aircraft increase skin friction (left figure). Skin friction is reduced because the riblets (right figure) move the vortex away from the aircraft surface wall.

■ About “Refresh (RiblEt Flight RESearcH for carbon neutral)” program (^*4)

By leveraging their respective strengths, JAL, JAXA, O-Well, and Nikon aim to develop eco-friendly aviation technology towards the realization of a decarbonized society in this program.
In the field of aviation, various initiatives, such as updating to fuel-saving equipment, and promotion of utilizing SAF (Sustainable aviation fuel) are underway. Among them, the introduction of fuel efficiency improvement technology that reduces skin friction (resistance with the strongest effect during flight), and riblet technology inspired by shark skin, are attracting attention from all over the world. Skin friction is reduced by applying riblets on the aircraft coating surface, resulting in a fuel efficiency improvement of up to 2%, which contributes to reducing CO₂ emissions.
JAXA, which researches and develops the riblet shape, has focused on O-Well's paint and coating technology and Nikon's laser processing technology, promoting efforts to apply the riblets in practical use with the JAL group's knowledge of and operation experience in aircraft, and expertise in aircraft coatings.

Refresh Mark
This mark is the symbol of this program.
With the motif of a shark's dorsal fin, which was the inspiration behind the riblet, the white lines flow smoothly along the riblet and the green lines represent environmental friendliness. The powerful image of a shark reflects the strength of this program and provides a compelling promotional tool.

*4“Refresh” program promotion system

*5Overview of each company's application method

Paint-to-Paint Method (O-Well): A method of forming concavity and convexity on a coating film by means of a water-soluble mold on an existing coating film

Laser Processing Method (Nikon): A method of forming concavity and convexity with laser directly on coating that is additionally painted in advance

On this occasion, 3 companies (JAXA, JAL, and Nikon), have concluded a joint research agreement to confirm the durability of riblets and are conducting flight tests using JAL aircraft with riblets processed directly on the lower part of the fuselage. A long-term riblet effect can be expected even in parts with long replacement cycles, as the original durability of the coating can be maintained by direct processing utilizing Nikon's unique laser processing technology. Nikon will further promote technological development for practical application by analyzing the durability of the processed location and acquiring related data through flight tests totaling 1,500 hours.

Portable optical processing machine for riblet processing developed by Nikon
Laser is emitted from the processing head on the right

Nikon will promote reduction of energy loss through utilization of our unique laser processing technology of attaching riblet-processed film or directly processing riblets, according to the material surface where they are to be applied, such as aircraft bodies and turbine blades.

Moreover, Nikon envisions a future of automatic processing whereby an autonomous control processing machine automatically approaches a large target, such as an aircraft and wind turbine blades, by combining Nikon's specialized optical measurement and laser processing technologies with mobility. Nikon will further advance its business development utilizing riblet processing technology, and contribute to the realization of a sustainable society through improved fuel efficiency, reduction of CO₂ emissions, etc.