GB1599633A - Aerofoils - Google Patents

Description

(54) AEROFOILS (71) I, DAVID IRVIN HODGSON of Brooklyn, Albert Promenade, Halifax, in the county of York, a British Subject, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to aerofoils.

In the description which follows, the following definitions are used, relating to the cross-section of an aerofoil: Chord line: a straight line joining the leading edge of the aerofoil section to the trailing edge.

Point of maximum thickness: the point on the upper surface of the section which is the maximum distance away from the chord line in a direction perpendicular to the chord line.

Line of maximum thickness: a straight line perpendicular to the chord line and passing through the point of maximum thickness.

Many different types of aerofoil are known, but in all aerofoils, it is necessary to deflect fluid over the top of the aerofoil and this produces a certain amount of turbulence at the leading edge of the aerofoil. Such turbulence is undesirable and it is preferable for, the aerofoil to split the fluid flow as cleanly as possible with maximum streamline flow and minimum turbulence.

The invention provides an aerofoil, the aerofoil section having a profile such that on the upper surface of the aerofoil, between the leading edge of the aerofoil and the point of maximum thickness of the aerofoil, there is a portion which is flat or concave, the chord line lying within the section of the aerofoil, at least between the leading edge and the line of maximum thickness.

I have realised that if a flat or concave portion is provided between the leading edge of the aerofoil and the point of maximum thickness, fluid flow will follow a less turbulent path as it approaches the full aerofoil thickness, unlike conventional aerofoils which are wholly convex between the leading edge and the point of maximum thickness.

Preferably the aerofoil section is such that there is a concave portion on the upper surface of the aerofoil lying between the leading edge and the point of maximum thickness, theleading edge of the aerofoil is convex, although with a smaller radius of curvature than the radius of curvature of the said concave portion, and there is a portion lying between the said concave portion and the point of maximum thickness which is convex and has a larger radius of curvature than the said concave portion.

The said convex portion may extend from the point of maximum thickness for less than 50% of the distance from the point of maximum thickness to the leading edge, but it is preferred that the said convex position extends from the point of maximum thickness for at least 50Vo of the distance from the point of maximum thickness to the leading edge.

It is preferred that the aerofoil has a projection on the underside of the aerofoil, lying between the leading edge of the aerofoil and the point of maximum thickness, the projection having a convex leading portion and a concave trailing portion.

The invention includes a device such as an airborne vehicle fitted with one more aerofoils according to the invention.

By way of example, specific embodiments of the invention will now be described, with reference to the accompanying drawings, in which: Figure 1 shows a section of a first embodiment of aerofoil according to the invention, suitable for use with airborne vehicles, helicopter rotors, propellors, and the like; Figure 2 shows a similar embodiment of aerofoil according to the invention, having a greater ratio of thickness to width; Figure 3 shows another embodiment of aerofoil according to the invention, similar to that shown in Figure 2 but having a conventional aerofoil shape below the chord line; Figure 4 shows yet another embodiment of aerofoil according to the invention, similar to that shown in Figure 1 but having the shape of a conventional aerofoil section below the chord line; and Figure 5 shows yet another embodiment of aerofoil according to the invention, having a flat portion on its upper surface.

Referring firstly to Figure 1, there is shown an aerofoil section having a leading edge 10 and a trailing edge 12. The chord line 14 is shown, joining the tip to the trailing edge, and the line of maximum thickness 16 is also shown. Point 16a is the point of maximum thickness.

The trailing edge 12 is a sharp edge but the leading edge 10 is convex with a small radius of curvature A conventional aerofoil section is convex on the upper surface all the way from the leading edge 10 to the point of maximum thickness 1 6a but the aerofoil section shown only has a convex portion 18 immediately forwards of the point of maximum thickness 16a. A tangent 20 is shown drawn between the convex tip 10 and the convex portion 18 and it can readily be seen that the portion 22 of the section lying below the tangent is concave.

The intention behind providing the concave portion 22 is to try to give, to the airstream which will strike the aerofoil when it is in use, a less turbulent path before it reaches the full aerofoil thickness. In other words instead of suddenly striking a convex surface the air is gently steered along a gradually increasing gradient until it reaches the thicker portion of the aerofoil having the convex surface. The aerofoil section shown should produce less leading edge turbulence than conventional sections thus allowing the airstream to maintain a good boundary layer over the vital leading rise of the pressure hill, giving a progressively faster air flow until a maximum is reached at about the point of maximum thickness.

For a given airstream speed, the form of aerofoil section shown should make it possible to provide the same amount of lift, with no increase in drag, while using an aerofoil section which is thicker than a conventional aerofoil, which means that an aircraft wing or other member employing such an aerofoil can be made more robust.

On the underside of the aerofoil shown in Figure 1 there is a projection 24 having a convex leading portion and a concave trailing portion. This projection may result in the provision of a high pressure pocket underneath the aerofoil, giving greater lift.

Figure 2 shows an aerofoil section which is similar to that shown in Figure 1, except that the ratio of thickness t to width w is 15%, whereas in Figure 1 it is 10%.

Figure 3 shows an aerofoil section which is similar to that shown in Figure 2 on its upper surface, but the underside of the aerofoil has a shape similar to that of a conventional aerofoil, without the projection 24 having a concave trailing portion.

Similarly, Figure 4 corresponds to an aerofoil section as shown in Figure 1, but having a conventional underside.

While the use of a concave portion 22 is preferred, any non-convex portion will have a tendency to reduce turbulence. The concave portion should not be curved too sharply. In other words it should have a relatively large radius of curvature and in the limiting condition, with an infinite radius of curvature, the portion 22 will be flat as viewed in Figure 5.

The invention is not restricted to the details of the foregoing embodiments. For example the relative dimensions and proportions of the aerofoil sections may vary, provided that there is a flat or concave portion on the upper surface of the aerofoil, lying between the leading edge ofthe aerofoil and the point of maximum thickness of the aerofoil. For example the dimensions of the aerofoil may be such that the line of maximum thickness 16 lies midway between the leading edge 10 and the trailing edge 12, or alternatively the line of maximum thickness may lie nearer to the trailing edge 12 than to the leading edge 10. The upper surface of the aerofoil may also be provided with a concave portion between the point of maximum thickness 16a and the trailing edge 12.

WHAT I CLAIM IS 1. An aerofoil, the aerofoil section having a profile such that on the upper surface of the aerofoil between the leading edge of the aerofoil and the point of maximum thickness of the aerofoil, there is a portion which is flat or concave, the chord line lying within the section of the aerofoil, at least between the leading edge and the line of maximum thickness.

2. An aerofoil as claimed in Claim 1, in which there is a concave portion on the upper surface of the aerofoil lying between the leading edge and the point of maximum thickness, the leading edge of the aerofoil is convex, although with a smaller radius of curvature than the radius of curvature of the said concave portion, and there is a portion lying between the said concave portion and the point of maximum thickness which is convex and has a larger radius of curvature than the said concave portion.

3. An aerofoil as claimed in Claim 2, in which the said convex portion extends from the point of maximum thickness for at least 50% of the distance from the point of maximum thickness to the leading edge.

4. An aerofoil as claimed in any one of the preceding claims, in which there is a projection on the underside of the aerofoil, the projection having a convex leading portion and a concave trailing portion.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. shape of a conventional aerofoil section below the chord line; and Figure 5 shows yet another embodiment of aerofoil according to the invention, having a flat portion on its upper surface. Referring firstly to Figure 1, there is shown an aerofoil section having a leading edge 10 and a trailing edge 12. The chord line 14 is shown, joining the tip to the trailing edge, and the line of maximum thickness 16 is also shown. Point 16a is the point of maximum thickness. The trailing edge 12 is a sharp edge but the leading edge 10 is convex with a small radius of curvature A conventional aerofoil section is convex on the upper surface all the way from the leading edge 10 to the point of maximum thickness 1 6a but the aerofoil section shown only has a convex portion 18 immediately forwards of the point of maximum thickness 16a. A tangent 20 is shown drawn between the convex tip 10 and the convex portion 18 and it can readily be seen that the portion 22 of the section lying below the tangent is concave. The intention behind providing the concave portion 22 is to try to give, to the airstream which will strike the aerofoil when it is in use, a less turbulent path before it reaches the full aerofoil thickness. In other words instead of suddenly striking a convex surface the air is gently steered along a gradually increasing gradient until it reaches the thicker portion of the aerofoil having the convex surface. The aerofoil section shown should produce less leading edge turbulence than conventional sections thus allowing the airstream to maintain a good boundary layer over the vital leading rise of the pressure hill, giving a progressively faster air flow until a maximum is reached at about the point of maximum thickness. For a given airstream speed, the form of aerofoil section shown should make it possible to provide the same amount of lift, with no increase in drag, while using an aerofoil section which is thicker than a conventional aerofoil, which means that an aircraft wing or other member employing such an aerofoil can be made more robust. On the underside of the aerofoil shown in Figure 1 there is a projection 24 having a convex leading portion and a concave trailing portion. This projection may result in the provision of a high pressure pocket underneath the aerofoil, giving greater lift. Figure 2 shows an aerofoil section which is similar to that shown in Figure 1, except that the ratio of thickness t to width w is 15%, whereas in Figure 1 it is 10%. Figure 3 shows an aerofoil section which is similar to that shown in Figure 2 on its upper surface, but the underside of the aerofoil has a shape similar to that of a conventional aerofoil, without the projection 24 having a concave trailing portion. Similarly, Figure 4 corresponds to an aerofoil section as shown in Figure 1, but having a conventional underside. While the use of a concave portion 22 is preferred, any non-convex portion will have a tendency to reduce turbulence. The concave portion should not be curved too sharply. In other words it should have a relatively large radius of curvature and in the limiting condition, with an infinite radius of curvature, the portion 22 will be flat as viewed in Figure 5. The invention is not restricted to the details of the foregoing embodiments. For example the relative dimensions and proportions of the aerofoil sections may vary, provided that there is a flat or concave portion on the upper surface of the aerofoil, lying between the leading edge ofthe aerofoil and the point of maximum thickness of the aerofoil. For example the dimensions of the aerofoil may be such that the line of maximum thickness 16 lies midway between the leading edge 10 and the trailing edge 12, or alternatively the line of maximum thickness may lie nearer to the trailing edge 12 than to the leading edge 10. The upper surface of the aerofoil may also be provided with a concave portion between the point of maximum thickness 16a and the trailing edge 12. WHAT I CLAIM IS

1. An aerofoil, the aerofoil section having a profile such that on the upper surface of the aerofoil between the leading edge of the aerofoil and the point of maximum thickness of the aerofoil, there is a portion which is flat or concave, the chord line lying within the section of the aerofoil, at least between the leading edge and the line of maximum thickness.

2. An aerofoil as claimed in Claim 1, in which there is a concave portion on the upper surface of the aerofoil lying between the leading edge and the point of maximum thickness, the leading edge of the aerofoil is convex, although with a smaller radius of curvature than the radius of curvature of the said concave portion, and there is a portion lying between the said concave portion and the point of maximum thickness which is convex and has a larger radius of curvature than the said concave portion.

3. An aerofoil as claimed in Claim 2, in which the said convex portion extends from the point of maximum thickness for at least 50% of the distance from the point of maximum thickness to the leading edge.

4. An aerofoil as claimed in any one of the preceding claims, in which there is a projection on the underside of the aerofoil, the projection having a convex leading portion and a concave trailing portion.

5. An aerofoil constructed and arranged

substantially as herein described with reference to Figure 1, or Figure 2, or Figure 3, or Figure 4, or Figure 5 of the accompanying drawings.

6. An airborne vehicle having an aerofoil as claimed in any one of the preceding claims.