GB2043572A

GB2043572A - Aerodynamic lateral flow body, for example, an airfoil

Info

Publication number: GB2043572A
Application number: GB8005691A
Authority: GB
Original assignee: Dornier GmbH
Current assignee: Dornier GmbH
Priority date: 1979-03-09
Filing date: 1980-02-20
Publication date: 1980-10-08
Also published as: IT8067112A0; DE2909245C2; IT1127987B; FR2450744A1; JPH0258159B2; FR2450744B1; GB2043572B; JPS55119595A; DE2909245A1

Abstract

An aircraft wing (Fig. 2) has an end portion (6) which increases the length of the wing so as to increase the span, without unduly increasing the weight of the wing. The end portion (6) is generally triangular in plan, with its leading edge (13) swept back. The curvature of the median line of the transverse cross section of the end portion (6) progressively increases in the direction of the span towards the wing tip at least over part of its length, starting from the main wing portion (12). <IMAGE>

Description

SPECIFICATION Aerodynamic lateral flow body, for example, an airfoil This invention relates to an aerodynamic lateral flow body, for example an airfoil.

There is a tendency in aviation to make aircraft more economical because of rising fuel costs. One way of achieving this is to reduce resistance. The complex "resistance of the aircraft" is composed of various factors.

One, for example, is surface friction in general. Other factors are interference resistance, profile resistance or also the induced resistance dependent upon lift, which is the factor on which the present invention is based.

The performance of civil aircraft, for example climbing performance and range, can be improved by increasing wing span. One prnb lem which then arises, however, is that increase in span is accompanied by a considerable increase in weight of the wing, which cancels out the advantages gained. In a conventional airfoil having its leading edge in the direction of the airflow, the increase in span is accompanied by an increase in weight which at a first approximation is proportional to the increase in span, i.e. proportional to the square of the increase in span.

It is an object of the invention to improve the efficiency of an aircraft by designing an airfoil so as to reduce the resistance dependent on lift by increasing the wing span in such manner that the increase in weight is kept low.

According to the invention, there is provided an aerodynamic lateral flow body, for example an airfoil, wherein (i) the body has a wing end portion which increases the length of the main wing portion in the direction of the wing span for the purpose of increasing the span; (ii) the wing end portion is substantially triangular in plan with its leading edge swept back, and (iii) the curvature of the median line of the transverse cross section of the end portion increases in the direction of the span towards the wing tip at least over part of its length, starting from the main wing portion. The transverse cross-section is the cross-section transverse to the span of the wing and substantially parallel to the direction of motion of the wing. The cross-section of the end portion is such that the local no-lift direction remains the same as that at the end of the main wing portion.With an airfoil in accordance with the invention, the total resistance at a given lift is considerably less than that of an airfoil with a conventional wing end portion at a given surface load. Although the increase in span is accompanied by an undesirable increase in the weight of the airfoil, this is much less than an airfoil with a conventional wing end portion. The advantage is obtained by the change in the distribution of lift over the whole wing span due to the special function of the wing end portion. This change comprises mainly a flatter downward slope of the curve of lift distribution towards the wing tip. As a result, there is a smaller root bending moment than in a conventional wing of the same span, due to a lighter structure of the wing as a whole.

The increase in local coefficient of lift produced by the backward sweep of the leading edge of the wing end portion, and the resulting earlier separation of the air flow at the wing end portion compared with the separation of the flow in the main wing portion, are counteracted by the change in the curvature of the median line, as well as by the alteration in the radius of the leading edge while the nolift direction remains unchanged. The theoretical induced resistance on the airfoil, and the total resistance, can be considerably reduced by the increase in span. The saving in weight compared with a conventional method of increasing the length of an airfoil to the same span is approximately 75%. Construction and manufacture of a wing in accordance with the invention are no more difficult or expensive than a known wing.

According to another feature of the invention, the local no-lift direction of the end portion remains unchanged from the crosssection at which the end portion joins the main wing portion. An increase in the induced resistance in the region of the end portion at a given lift is-thereby avoided.

The special formation of the end portion such that its cross-section which adjoins the main wing portion is at an angle of about 90 with the corresponding trailing edge, while its leading edge is at an angle of about 45 with the corresponsing trailing edge, reduces the induced resistance compared with that of a conventional wing end portion.

According to another feature of the invention, the increase in the radius of the leading edge of the end portion corresponds to the increase in the curvature of the median line.

Investigations have shown that in regions of large angles of incidence, separation of the airflow begins in the outermost part of the wing end portion. The special formation of the leading edge and the curvature of median line of the end portion enables the range of clinging flow at these parts to be increased to relatively high angles of incidence.

The attachment of the wing end portion to the main portion with a view to increasing the span, and the formation of the cross-sectional shapes of the two portions so that they continuously merge one into the other, not only simplify the construction necessary to join the main portion to the end portion, but has an advantageous effect on flow separation, since one cross-sectional shape continuously merges into the other.

The fact that the trailing edge of the end portion is a straight line continuation of the trailing edge of the main wing portion results in a saving in weight without any deleterious effect on the lift characteristics.

An embodiment of the invention will now be described by way of example, with reference to the drawing, in which: Figure 1 is a top plan of an aircraft with triangular wing end portions; Figure 2 is a top plan drawn to a larger scale than in Fig. 1 of one wing end portion; and Figure 3 comprises three transverse crosssections of the wing end portion on the planes lill-1111, lli2-1112 and 1113-1113 of Fig. 2.

Referring to the drawing, the two halves 3 of a wing 2 are attached to a fuselage 1 at wing roots 4 to form a high wing monoplane.

The usual construction is used for attachment of the two halves 3 to the fuselage.

Wing end portions 6 are joined to main wing portions 9 by the end rib 7 (Fig. 2) to increase the wing span. The cross-section 10 at which the two portions are joined is at right angles to the wing span Fs and is in a vertical plane. The leading edge 1 3 of the wing end portion 6 is swept back at an angle of about 45 from the leading edge 1 2 of the main wing portion 9 and is continuous with the trailing edge 1 6 and with the leading edge 1 2 of the main wing portion 9 through transitional curves 15' and 15, respectively.Up to a terminal line indicated by the dash-dot line a in Fig. 2, starting as shown from the trailing edge 1 6 of the wing end portion 6, the vertical cross-sectional shape of the end portion may extend to the wing tip as a continuation of that of the main portion of the wing 2.

The reference numerals 20 and 21 indicate the upper and lower surfaces of the wing.

Fig. 3 shows three transverse cross-sections of the wing end portion and illustrates the increasing median line curvature. In the crosssection on plane IIl2IIl2 the median line is indicated by S. It is equidistant at all points along it from the upper and lower wing surfaces. Fig. 3 also shows the radius r, r' and r11 of the leading edge 1 3. The curvature of the median line S increases in the direction of the wing span as far as a vertical sectional plane indicated by the dash-dot line b. (Fig. 2).

Beyond this plane, the curvature of both the median line and the leading edge radius remain constant to the tip of the wing and the local no-lift direction is unchanged.

Claims

1. Aerodynamic lateral flow body, for example an airfoil, wherein (i) the body has a wing end portion which increases the length of the main wing portion in the direction of the wing span for the purpose of increasing the span; (ii) the wing end portion is substantially triangular in plan with its leading edge swept back, and (iii) the curvature of the median line of the transverse cross section of the end portion increases in the direction of the span towards the wing tip at least over part of its length, starting from the main wing portion.

2. A body according to claim 1 wherein the said curvature increases progressively.

3. A body according to claim 1 or claim 2, wherein the radius of the leading edge of the end portion increases over at least part of the length of the end portion in the direction of its span, starting from the main wing portion.

4. A body according to any preceding claim, wherein the local no-lift direction of the end portion remains unchanged between the main wing portion and end portion, starting from the cross-section at which the main wing portion adjoins the end portion.

5. A body according to claim 2, wherein the increase in radius of the leading edge of the end portion corresponds to the increase in the curvature of the median line of the end portion.

6. A body according to any preceding claim wherein the cross-sections of the main wing and wing end portions continuously merge one into the other.

7. A body according to any preceding claim, wherein the trailing edge of the wing end portion extends outwards in rectiiinear projection of the trailing edge of the main wing portion.

8. A body according to any preceding claim, wherein the cross-section of the connection of the end portion to the main portion is at an angle of substantially 90 to the corresponding trailing edge, while the leading edge of the end portion is at an angle of substantially 45 to the corresponding trailing edge.

9. An airfoil constructed and arranged substantially as herein described and shown in the drawing.

10. An aircraft having a wing made up of airfoils according to any preceding claim.