It is known that aircrafts are widely used which employ a simple delta wing as lifting structure, typically hang gliders and simple ultra-light aircrafts which include a tricycle fuselage or an inflatable boat for the use as flying boats. The wings presently used on these aircrafts essentially consist of two spars hinged at their inner end so as to open compass-like in order to make taut the cloth fixed therebetween. In practice, the two spars act as leading edge of the wing which for the rest only includes a cross-shaped tubular structure to which the fuselage or the control bar is attached, as well as stiffening ribs used to make the cloth tighter.

Such a wing can be easily folded compass-like in order to reduce its wing span and carry it by hand thanks to its lightness. However, its size is still large due to the length of the spars which usually reach about six meters and over. This size most times makes it impossible to use certain transport means, e. g. small cars, or to mount said wing on small inflatable boats.

Therefore the object of the present invention is to provide a wing suitable to overcome the above-mentioned drawbacks.

This object is achieved by means of a wing which can be easily folded not only compass-like, like prior art wings, but also in the longitudinal direction so as to reduce to half the length of the folded wing. Other advantageous characteristics are disclosed in the dependent claims.

The main advantage of this wing is that it allows a significant decrease in size without requiring any disassembly, so that it can be easily transported also by small means.

Another advantage of said wing stems from the simplicity of the selected structural solution, which allows for a strong and cheap structure which is easily folded with a very small increase in terms of weight and aerodynamic drag.

These and other advantages and characteristics of the wing according to the present invention will be clear to those skilled in the art from the following detailed description of an embodiment thereof, with reference to the annexed drawings wherein : Fig. l is a schematic perspective view of a hang glider provided with a wing according to the invention ;

Fiv. 2 ils a partial front view of the hang glider of fig. 1 ; Fig. 3 is an enlargement of detail S of the preceding figure which shows the length of spar including the fold joint ; Fig. 4 is similar to the preceding figure and shows the spar ready for folding ; Figs. 5 and 6 are sectional views taken along lines A-A and B-B of fig. 4, respectively, showing the two members which make up the joint ; Fig. 7 is a top plan view of the spar in the state of fig. 4 ; Fig.8 is similar to the preceding figure and shows the spar during the folding ; and Fig. 9 is similar to the preceding figure and shows the spar in the folded state.

Referring to figs. 1 and 2, there is shown a conventional hang glider with the two spars L acting as leading edge of the wing and hinged so as to open and close compass-like at a prow hinge P. Obviously, what is being said here with reference to a hang glider also applies to any aircraft using a delta wing according to the present invention.

The novel aspect of this wing is the particular structure of the spars, having an intermediate joint S which is preferably located about at mid-length but can also be formed at any position along the spar. The structure and functionality of these special spars are illustrated in detail in the following figures 3 to 9.

With reference to said figures, there is seen that a spar L is made up of a distal portion LP of smaller diameter which is telescopically inserted into a proximal portion LG of greater diameter for a length d usually in the range of 80-100 cm.

The exact locking position inside portion LG is defined by a pin or the like (not shown). It is clear that the structure could be made also the other way around, i. e. with the proximal portion LG of smaller diameter which is inserted telescopically into a distal portion LP of greater diameter.

In the vicinity of the area where the two portions of spar are fitted one into the other, there are located two collars CG and CP on the proximal portion and on the distal portion, respectively. As best shown in figures 5 to 7, each collar consists of two halves joined by screws V. The front halves MA, MA'have substantially the same shape but different size, whereas the rear halves MP, MP'have extensions F, F'of complementary shape located in a plane orthogonal to the plane of the collars.

In other words, collar CG has two fork-like arms F between which there is fitted the extension F'of collar CP, so as to achieve a joint hinged around an orthogonal axis X along which there are formed aligned holes in the extensions F, F'. A pivot (not shown) is fixed into said holes to join the collars CP, CG so as to keep the two

spar portions LG, LP restrained.

The spar folding procedure is very simple and easily understood from the above-mentioned figures. Starting from fig. 3, the distal portion LP is extracted from the proximal portion LG by pulling in the direction of arrow A, upon disengagement of the locking pin and of the wing cloth cap fitted onto the distal end of portion LP. The sliding of collar CP is made possible by the fact that its inner diameter is slightly greater than the outer diameter of portion LP, whereas collar CG is tightly secured onto portion LG and therefore can note slide even if pulled through the joint. It should be noted that in order to prevent collar CP from completely slipping off, it is preferable to provide in the end area of portion LP a retractable stop which springs out as soon as it is extracted from portion LG. Such a stop can be made much in the same way as the pin used at the end of the suction tube of a vacuum cleaner for locking the different interchangeable accessories.

Once the position illustrated in figures 4 and 7 has been reached, the distal portion LP can be folded towards the inside of the wing by rotating around axis X of the joint, as shown in fig. 8. At the end of the rotation, portion LP overlaps portion LG (fig. 9) and the length of spar L is substantially reduced by half. In this state, the wing can be folded compass-like around the prow hinge P thus obtaining a structure which is quite small and easy to transport.

The presence of joint S is also advantageous in terms of handling and operative safety. For example, the alignent of the spar portions LG, LP for the telescopic re-insertion during the wing unfolding results automatically.

Furthermore, the permanent restraint between the two portions LG, LP prevents the risks of excessive stress on the wing cloth fixed thereon during the unfolding and folding operations.

It is clear that the above-described and illustrated embodiment of the wing according to the invention is just an example susceptible of various modifications.

In particular, the exact shape, location and orientation of collars CG, CP may be freely changed according to the needs, for example by rotating them so that the hinge axis X is not perpendicular to the wing plane but takes any inclination between 0° and 90°, yet remaining obviously perpendicular to the axis of spar L.

Furthermore, the collar extensions F, F'may be shaped with other complementary shapes as long as they are suitable to form a joint.