Experiences conducted in the 90's showed that longitudinal grooves actually reduce the aerodynamic drag. However, plastic stickers used in that period suffered from inconvenience.
In this programme, it was proposed to realise various shapes of grooved surfaces thanks to a new casting method, developed by the applicant.
The project aimed at providing ONERA with models covered with grooved paint of several profiles, in order to qualify the aerodynamic performance.
After an initial study and process definition, paint films of different shapes were designed and realised against moulding surfaces. Then, films were applied onto a model, to be further tested into a wind tunnel.
The paint film process used approved aeronautical paints with as little modification as possible, so as to prepare future application on aircrafts.
Many technologies are currently under development to address the environmental impact of air transport. A novel EU-funded project 'Grooved paint surface manufacturing for aerodynamic drag reduction testing' (RIFPA) had done so with large-area paint stickers containing longitudinal grooves to reduce drag. The technique is now protected by four international patents. Application of plastic stickers with riblets was attempted in the 1990s but difficulties with adhesion caused edges to lose smoothness.
Paints already contribute substantial weight to planes. In addition, their maintenance and removal takes time and money and requires the use of hazardous chemicals. With its dry paint films in finished layers, RIFPA addressed all these issues at once. The paint films use no volatile organic compounds, require no drying time and there is no materials waste due to spillage. Scientists conducted wind tunnel tests on the paint films with riblets of either sawtooth (V-type) cross-sections or trapezoidal-type cross-sections. The trapezoidal-type riblets reduced drag friction, demonstrating promising potential for reducing fuel consumption and emissions.
RIFPA's revolutionary new dry paint film technology promised to green the aircraft industry like no other paint system — in fact, it is in the position to exploit already improved aeronautical paints. Not only do the films eliminate waste and the use of harmful chemicals, they also promise major improvements in fuel efficiency for decreased emissions.