WO2010120215A1

WO2010120215A1 - Procedure for causing a friction reducing surface structure

Info

Publication number: WO2010120215A1
Application number: PCT/SE2009/000192
Authority: WO
Inventors: Ragnar Winberg
Original assignee: Ragnar Winberg
Priority date: 2009-04-16
Filing date: 2009-04-16
Publication date: 2010-10-21

Abstract

The procedure to make a friction-reducing surface-structure on aircraft, characterized by the fact that first the parts of the aircraft which you wish to provide with the special surface structure are painted with a paint containing very little or no solvent and after this paint has hardened somewhat a totally tight plastic foil is applied, whose inside has a stamped surface opposite to the one the aircraft shall have at which by the foil with a tool with a roll being pressed against the paint it penetrates into the depressions of the foil and air between the foil and the paint is pressed out and that the foil sticks to the paint and the foil may remain on the paint until it has hardened and after that the foil can be pulled away without any paint remaining in the depressions of the foil.

Description

Procedure for causing a friction reducing surface structure

While flying at a constant altitude it is only the air resistance that requires energy in the form of fuel consumption. Even if much energy is required to reach the intended altitude, it is yet long-distance flying, flying at a constant altitude, that requires the most fuel. Since also an insignificant reduction of the air resistance of an aircraft can result in fuel saving, it can motivate a somewhat higher cost when painting an aircraft. Even if the atmospheric pressure is low at the flying altitudes used by passenger planes, the speed is often about 250 metres per second. For aircraft there is no alternative to liquid fuels which emit carbon dioxide. IPPC (Integrated Pollution Prevention and Control) states according to LFVs web page that air traffic today is responsible for about two per cent of the global outlets of carbon dioxide and that the share of outlet of carbon dioxide of aviation can increase to about three per cent in 2050.

It is known since long that an entirely smooth surface gives a somewhat greater friction against air streaming past it than a surface which has a special microstructure.

The purpose of this invention is, in a simple way and at a low cost, to make a surface layer on aircraft, which somewhat reduces the friction between the aircraft and its surrounding air.

In the patent journal WO2007/036349A1, for example, several procedures are described, where the surface of a varnish layer is formed by pressing a stamping tool straight against the surface of the varnish when the varnish is formable or a cylinder with a negative impression in motion is pressed against the varnish surface. The surface will then get a structure corresponding to that of the cylinder. In these cases the tool or the cylinder are in contact with the varnish for a very short time and it is important that the stamping does not take place too early since the surface pattern can deteriorate. Nor must it take place so late that the varnish has hardened too much and is not possible to stamp or that a very hard pressure must be applied for the wanted pattern stamping to result.

In the article "The first JAS 39 Gripen has been blasted and lightning-modified with new technology", Fδrsvarsmakten 26 June 2003, the need of lightning protection on aircraft whose exterior parts consist of composite material is described. On these aircraft a thin aluminium foil is first applied in a known way and then paint is applied without being finished.

The present invention has the special characteristics which are evident from the patent claims.

According to the procedure a cylinder is first made whose surface layer has a special structure through the removing of material so that depressions are formed in the surface through one of several known methods, for instance as at cylinders for photo gravure.

With the use of a cylinder according to the text above a plastic foil is stamped of for instance polythene during its production so that one side remains plane while the surface against the cylinder gets a structure quite opposite to that of the cylinder, since the plastic penetrates into the depressions of the cylinder. This foil can be produced or cut into strips of a suitable breadth, for instance 200 millimetres. A strip can be rolled up on a roll and have a length of for instance 100 metres. A suitable thickness can be 0.2 millimetres.

When an aircraft is to be painted either for the first time or re-painted, one or more layers of epoxy compound paint which do not contain solvents, or only insignificantly, are first applied with a sprayer, a brush or a roller. When this paint has hardened somewhat, a foil is applied according to the text above by means of a roll. The paint is then pressed between the plane and the foil and the paint penetrates into the depressions of the foil at the same time as air between the foil and the paint is pressed out. The roll should be moved lengthways on the foil. The foil adheres strongly enough to the paint and shall remain on it. When a strip is pressed onto the paint, the pressure of an adjacent strip is started. It can overlap the earlier one a little. The small windows of a passenger plane do not involve an obstacle but it only means that the roll must not be pressed against the foil there. It is recommended that the foil and the roll are in the same tool. The foil may then remain on the paint until it has hardened enough which can vary in time depending on the paint and the surrounding temperature of the aircraft. This may take up to 24 or 36 hours. After the paint has hardened, the foil can be split open and pulled off without any paint remaining in the depressions of the foil. The foil can then be thrown away or used again.

The aircraft body itself on commercial planes has often mostly a cylindrical form. At the application of plastic strips lengthways the roll should be shaped in such a way and of such surface material that, when pressed in the direction of the foil, it presses evenly against the aircraft along its whole breadth.

For foil on the wings a more cylindrical roll can be used. It is not necessary that the whole surface of the aircraft gets the friction reducing surface structure. The important thing is that a large part of the surface of the aircraft will get the friction reducing surface structure.

Since air always contains more or less dust which, at the high speed of the airflow, tears on the surface, a re-paint may be justified when the structure has been torn down.

When re-painting it may be advisable to grind down the old paint so that its surface becomes smooth and without a remaining structure before new paint is applied.

A structure on aircraft can have the form of ribs separated by grooves parallel lengthways with the aircraft. The height of the ribs over adjacent grooves can be less than 0.1 millimetres and the distance between the ribs can be smaller than 0.2 millimetres. The ridges can have breaks. Also another form of structure can appear suitable to give aircraft a surface layer which reduces the friction against the surrounding air.

Paint in this document also means paint that is transparent and has no pigment, usually called varnish. Hardenable varnish can contain a powder of various kinds which does not prevent the forming or the hardening.

Of course different colours can be used on the same aircraft and be applied at different times.

Claims

1 The procedure to make a friction-reducing surface-structure on aircraft, characterized by the fact that first the parts of the aircraft which you wish to provide with the special surface structure are painted with a paint containing very little or no solvent and after this paint has hardened somewhat a totally tight plastic foil is applied, whose inside has a stamped surface opposite to the one the aircraft shall have at which by the foil with a tool with a roll being pressed against the paint it penetrates into the depressions of the foil and air between the foil and the paint is pressed out and that the foil sticks to the paint and the foil may remain on the paint until it has hardened and after that the foil can be pulled away without any paint remaining in the depressions of the foil.

2 Procedure according to Claim 1, characterized by the fact that the structure of the aircraft has the form of parallel ridges lying closely together with the longitudinal direction in the main coinciding with the longitudinal direction of the aircraft.

3 Procedure according to Claim 2, characterized by the fact that the ridges have a height over adjacent grooves of less than 0.15 millimetres.

4 Procedure according to Claim 1, characterized by the fact that the distance between the ridges is less than 0.2 millimetres.

5 Procedure according to Claim 2, characterized by the fact that the ridges have interruptions.

6 Procedure according to any previous claim, characterized by the fact that the plastic foil is in the shape of strips.

7 Procedure according to Claim 6, characterized by the fact that the plastic strips are applied in the longitudinal direction of the aircraft.