Innovative Surface Treatments to Reduce Air Resistance

16/03/2016

A technological breakthrough has been achieved in the Smart Fixed Wing Aircraft (SFWA) ITD, with the production of seamless large surface shims containing extremely sharp tipped microscopic riblet structures. The surface characteristics resulting from the shim are similar to those found on shark skin and will be applied to the outer surface of aircraft to reduce fuel consumption during flight.

This Riblet project is a key part of the larger Applicator project that enables riblets to be applied to both new and existing aircraft.

You can read more about this project in the Success Stories Section.

Riblets machined into a polymer shim
Nominal riblet height - 51 microns

 

It is known in the natural world that a textured surface (containing an exactly controlled riblet structure) can impart benefits with regard to air flow and liquid flow along a surface. At the commencement of this project the complexity and scale of the optimum textured surface exceeded the capabilities of commercial application. This project employed state-of-the-art techniques to reproduce a continuous landscape of discrete riblets that are evenly spaced and capable of being applied to both new aircraft surfaces and retrofitted to existing aircraft.

This project is an integral part of a larger project to combine riblet production with controlled application.

The Partners have pushed the limits of nano-sized riblet structured shim production to well beyond state-of-the-art at the commencement of the project.

Initially it was thought that the riblet areas would be created on narrow strips or rectangular patches of shims that would require welding together to create a master shim. This project has proven that it is possible to manufacture, in one piece, a giant 1350mm x 1350mm shim that can be cut down (to remove edge effects) to 1250mm x 1250mm allowing master moulds of 1250mm x 500mm in each riblet orientation to be produced. These could then be precision welded at the ends to produce a continuous cylindrical shim with only a single discreet 15µm welded seam. In addition, the Partners have demonstrated that micro welding can be achieved that creates a virtually seamless join. It was known at the outset of the project that welding seams can be the cause of air flow disruption and undesirable visual impact and therefore should be minimised. This advance in welding techniques has proven to be a significant achievement of the project.

The riblet construction and format target for the project was set by IFAM to 51 microns high and a pitch of 96 microns. This produced a polymer construction of:

 

 

The final giant polymer shim was manufactured and is shown here on the chuck of the laser system:

 

Including riblets into the surface profile of an aircraft will improve the air flow past the surface, which will reduce fuel consumption. Only laboratory scale tests have been done to date and these indicate fuel savings of 1-3%.

Until the shims have been fitted to applicators and the riblets applied directly to a lacquered surface of an aircraft and tested over a protracted period of use, it will not be possible to accurately determine the full extent of the benefits. Riblets consume no power when included in an airframe surface and may be retrofitted to an existing aircraft.

 

For more information about the project and technology, see the website of the project Partner responsible for the design and structure of the shims, M.T.I.: www.machovia.eu

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