GB2062565A - High-speed aircraft with tandem wing arrangement - Google Patents

Abstract

A high speed aircraft has two swept airfoil units 10, 11 one behind the other in the direction of flight, front airfoil 10 having a positive dihedral and rear airfoil 11 having anhedral. The airfoils have their extended planes intersecting and are joined along the line of intersection by a tubular member 12. The arrangement reduces induced drag for the same overall lift and equal wing weight relative to a conventional wing. <IMAGE>

Description

SPECIFICATION A high-speed aircraft airfoil wing This invention relates to an airfoil wing for high speed and mainly high powered aircraft.

For a given lift the induced drag of an aircraft design can be effectively reduced either by increasing the wing span or by fanning out the trailing vortices at the wing tips.

Examples of these arrangements are biplanes, monoplanes with wing-tip fins and wings with bifurcated tips. Most of these solutions suffer from the disadvantage that the reduction of drag is achieved at the cost of an increase in the weight of the wing structure, the bifurcated wing-tips being the only system enabling the said reduction to be effected without altering the weight of the wing.

The configuration shown in DE AS 25 55 718 is an attempt to solve the aforementioned problems by a system in which two swept-back airfoil wings situated one above the other and combining to form a closed framework of rhombic shape with an upper airfoil unit with a negative dihedral and a lower airfoil unit with a positive dihedral, the respective outer zones of the two airfoil units merging into each other. This construction provides a higher lift coefficient and a reduction in weight in comparison with other wing designs.

An object of this invention is to enable the induced drag of the airfoil wing to be reduced without altering the overall lift or the wing weight.

According to this invention there is provided an airfoil wing for a high speed aircraft having two airfoils positioned one behind the other with the planes containing respective wings intersecting, the wings being connected at the intersection.

This enables the object to be achieved in a surprisingly simple and reliable manner.

The invention is further described and illustrated in conjunction with the accompanying drawings showing an example. In the drawings: - Figure 1 shows-diagrammatically a part front view of a wing structure, Figure 2 shows a plan view of the structure of Figure 1, Figures 3a and 3b show graphs of the thickness distribution along the wing span and the bending moments to which the wings are subjected in a known arrangement and in this invention, respectively.

As shown in Figures 1 and 2, two airfoils 10, 11, are positioned in succession (as viewed in the direction of flight) on the fuselage 13, in such a way that the airfoil situated nearer the nose has a positive dihedral while that situated behind it and nearer the tail has a negative anhedral. Both airfoil units are swept and interconnected by a flexurally rigid tube 12. This construction provides that this "cruciform wing" has considerable advantages in comparison with known wing constructions as the bending moments to which the wings are subjected are considerably reduced, as each airfoil unit forms an effective bracing support for the other. Furthermore, the subdivision and separation of the tip vortex enables the induced drag to be greatly reduced for a given overall lift and span.Calculations showed this reduction to be quite considerable and of the order of 24%.

It is also found that a planar wing and the "cruciform wing" are approximately equal in weight if the area subjected to air flow and the relative profile thickness remain the same and if the span of the latter is 0.955 of that of the conventional wing. If account is taken of this comparatively slight reduction in the span an effective reduction of about 179b in the induced drag is obtained.

It has likewise been found that owing to the far smaller cross-sectional area of the two airfoils the wave drag is reduced by almost 30%.

Furthermore, better aerodynamic use is made of the wing surface areas as shown by the diagram in Figure 3a. The reason for this is the bilinear distribution of the wing chord which forms a closer approach to the ideal distribution, the elliptical distribution than does a trapezoidal wing planform.

In Figure 3: - v = front surface; h = rear surface; MB = wing bending moment.

The wing construction described provides for an extremely effective control of lateral forces.

Side force control is effected by deflecting trailing edge control surfaces located on both sides of the forward and the rear wing members in an antisymmetrical and opposite sense.

In the example described the flexurally rigid tube 12 is so designed as to extend across both airfoil units and has ends which project beyond the outer edges, the projecting ends having an advantageous shape from the point of view of the airflow.

1. An airfoil wing for a high speed aircraft having two airfoils positioned one behind the other with the planes containing respective wings intersecting, the wings being connected at the intersection.

2. An airfoil wing according to Claim 1, wherein the wings are connected by a rigid tubular member extending along the line of intersection between the planes of the wings.

3. An airfoil wing in accordance with Claim 1 or 2, wherein the front airfoil has a positive dihedral and the rear airfoil has a negative anhedral.

4. An airfoil wing in accordance with Claim 2 or 3, wherein the tubular member extends across the whole depth of both airfoils.

5. An airfoil wing in accordance with any one of Claims 2 to 4, wherein the tube extends beyond the leading edge of the front airfoil and beyond the trailing edge of the rear airfoil, the tube being aerodynamically shaped.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A high-speed aircraft airfoil wing This invention relates to an airfoil wing for high speed and mainly high powered aircraft. For a given lift the induced drag of an aircraft design can be effectively reduced either by increasing the wing span or by fanning out the trailing vortices at the wing tips. Examples of these arrangements are biplanes, monoplanes with wing-tip fins and wings with bifurcated tips. Most of these solutions suffer from the disadvantage that the reduction of drag is achieved at the cost of an increase in the weight of the wing structure, the bifurcated wing-tips being the only system enabling the said reduction to be effected without altering the weight of the wing. The configuration shown in DE AS 25 55 718 is an attempt to solve the aforementioned problems by a system in which two swept-back airfoil wings situated one above the other and combining to form a closed framework of rhombic shape with an upper airfoil unit with a negative dihedral and a lower airfoil unit with a positive dihedral, the respective outer zones of the two airfoil units merging into each other. This construction provides a higher lift coefficient and a reduction in weight in comparison with other wing designs. An object of this invention is to enable the induced drag of the airfoil wing to be reduced without altering the overall lift or the wing weight. According to this invention there is provided an airfoil wing for a high speed aircraft having two airfoils positioned one behind the other with the planes containing respective wings intersecting, the wings being connected at the intersection. This enables the object to be achieved in a surprisingly simple and reliable manner. The invention is further described and illustrated in conjunction with the accompanying drawings showing an example. In the drawings: - Figure 1 shows-diagrammatically a part front view of a wing structure, Figure 2 shows a plan view of the structure of Figure 1, Figures 3a and 3b show graphs of the thickness distribution along the wing span and the bending moments to which the wings are subjected in a known arrangement and in this invention, respectively. As shown in Figures 1 and 2, two airfoils 10, 11, are positioned in succession (as viewed in the direction of flight) on the fuselage 13, in such a way that the airfoil situated nearer the nose has a positive dihedral while that situated behind it and nearer the tail has a negative anhedral. Both airfoil units are swept and interconnected by a flexurally rigid tube 12. This construction provides that this "cruciform wing" has considerable advantages in comparison with known wing constructions as the bending moments to which the wings are subjected are considerably reduced, as each airfoil unit forms an effective bracing support for the other. Furthermore, the subdivision and separation of the tip vortex enables the induced drag to be greatly reduced for a given overall lift and span.Calculations showed this reduction to be quite considerable and of the order of 24%. It is also found that a planar wing and the "cruciform wing" are approximately equal in weight if the area subjected to air flow and the relative profile thickness remain the same and if the span of the latter is 0.955 of that of the conventional wing. If account is taken of this comparatively slight reduction in the span an effective reduction of about 179b in the induced drag is obtained. It has likewise been found that owing to the far smaller cross-sectional area of the two airfoils the wave drag is reduced by almost 30%. Furthermore, better aerodynamic use is made of the wing surface areas as shown by the diagram in Figure 3a. The reason for this is the bilinear distribution of the wing chord which forms a closer approach to the ideal distribution, the elliptical distribution than does a trapezoidal wing planform. In Figure 3: - v = front surface; h = rear surface; MB = wing bending moment. The wing construction described provides for an extremely effective control of lateral forces. Side force control is effected by deflecting trailing edge control surfaces located on both sides of the forward and the rear wing members in an antisymmetrical and opposite sense. In the example described the flexurally rigid tube 12 is so designed as to extend across both airfoil units and has ends which project beyond the outer edges, the projecting ends having an advantageous shape from the point of view of the airflow. CLAIMS

1. An airfoil wing for a high speed aircraft having two airfoils positioned one behind the other with the planes containing respective wings intersecting, the wings being connected at the intersection.

2. An airfoil wing according to Claim 1, wherein the wings are connected by a rigid tubular member extending along the line of intersection between the planes of the wings.

3. An airfoil wing in accordance with Claim 1 or 2, wherein the front airfoil has a positive dihedral and the rear airfoil has a negative anhedral.

4. An airfoil wing in accordance with Claim 2 or 3, wherein the tubular member extends across the whole depth of both airfoils.

5. An airfoil wing in accordance with any one of Claims 2 to 4, wherein the tube extends beyond the leading edge of the front airfoil and beyond the trailing edge of the rear airfoil, the tube being aerodynamically shaped.

6. An airfoil wing in accordance with any preceding Claim, wherein the airfoils are either swept-back or swept-forward.

7. An airfoil wing having a configuration substantially as herein described and shown in Figures 1 and 2 of the accompanying drawings.