Sailplane

Abstract

A sailplane wherein a flexible sail is loosely connected at its corners to the ends of a rigid framework comprising a central longitudinal rod and a pair of oblique rods directed laterally and backwards, whereby during flight the sail assumes, under the air pressure, a conformation including forward portions of general positive incidence and rearward portions of general negative incidence.

Description

BACKGROUND OF THE INVENTION

This invention relates to a sailplane whose construction is unexpensive and whose performance is good.

As is known, the sailplanes having stability features and especially aerodynamic efficiency features, such as to assure a long lasting flight, an efficacious height elevation by traction effect and a good utilization of the ascending currents encountered, do not lend themselves to economical industrial manufacture.

BRIEF SUMMARY OF THE INVENTION

The first object of the invention is to provide a sailplane suitable to be used either as a toy or for sporting objects, for meteorologic observations and for the transport of suspended objects, which due to a particular configuration of its active aerodynamic surfaces presents marked features of longitudinal, transverse and heading stability, together with a remarkably high aerodynamic efficiency, so that its performances are clearly more satisfactory than those of the known analogous sailplanes.

Another object of the invention is to provide a sailplane suitable to plane with a good efficiency while still engaged to the tow cable, so that it may switch from the free flight to the towed flight and vice versa, simply by actuating or interrupting the towing action, to permit a control from ground at least concerning the distance from the operator and some simple manipulations, these features being particularly intended to permit the use of the sailplane within a limited space as well as to facilitate its use which, in the versions having a toy character, is also suitable for school-children.

Said objects are attained, according to the invention, by means of a sailplane of the type comprising a framework and a sail formed by a sheet of a flexible material connected at its vertices to said framework, characterized in that said framework comprises a central rod located along a longitudinal central line of the sailplane, a rigid connecting element along said central rod in its front half, and a pair of oblique rods rigidly connected to said connecting element and extending towards the backward section of the sailplane forming an acute angle with respect to said central rod, and in that the sheet of flexible material forming the sail is connected to the ends of said rods forming the framework and its dimensions exceed the framework dimensions so that it is loose or flabby at rest and assumes when flying, due to the effect of the air pressure, a configuration including two forward portions located in front of the oblique rods and having a general positive incidence, and two rear portions located behind the oblique rods, having a general negative incidence and forming a pair of channels which diverge with respect to the longitudinal central line of the sailplane.

It has been ascertained that the mutual cooperation of these forward and rear portions of the sail produces aerodynamic effects partiuclarly favourable, if considering separately the qualities of said single portions of the sail. In this effect both the forward and the rear portions contribute to the lift, the forward portions contribute principally to the longitudinal stability, and the rear portions, due to their divergent channel shape, contribute principally to the transverse stability, which is particularly high, so that there is no need to give to the sail the V shape usually necessary for that purpose but which is not favourable to lift, and contribute indirectly to the heading stability.

According to an important feature of the invention, the connection of the sail lateral vertices to the outer ends of the oblique rods of the framework is effected by means of connecting members which extend towards the vertices of the sail with parts which are rotatably inserted on the rods in order to allow some orientability of the wing ends under flight conditions.

This feature provides advantageous conditions for the behaviour of the sailplane, particularly because the stress applied to the rear portions of the sail is transmitted through the orientable ends to the forward portions of the sail, deforming them and displacing in an advantageous manner the pressure center.

Preferably, the plan view shape of the sail substantially derives from a square or a rhombus located with a diagonal along said longitudinal center line, the rear vertex of said square or rhombus being cut off along a line nearly perpendicular to said longitudinal center line, and said oblique lines terminate at the side vertices of said square or rhombus.

The distance between the side vertices of said square or rhombus being defined as the wing span, the length of the sail between its forward end and its after end is preferably comprised between 65% and 90% ( preferably the 82% ) of the wing span, and the distance of forward end of the sail from the point of the longitudinal center line where said oblique rods depart is preferably comprised between 10% and 25% (preferably 15%) of the wing span, while the length of the rear transverse side of the sail is preferably comprised between 25% and 50% (preferably 38%) of the wing span. The angle formed between each of said oblique rods and the rear part of the longitudinal center line is preferably comprised between 40.degree. and 75.degree. (preferably 55.degree.).

BRIEF DESCRIPTION OF THE DRAWINGS

The particular features and the operation of the sailplane according to the invention will more clearly appear from the following specification of an exemplifying and not limiting embodiment, schematically represented on the accompanying drawing, wherein:

FIG. 1 is a plan view, on a very reduced scaple, of a sailplane according to the invention;

FIG. 2 is a cross section along line B-E of FIG. 1, viewed in the direction of arrow II;

FIG. 3 is a cross section along line III--III--III of FIG. 1 and viewed from the rear; FIGS. 2 and 3 showing the sailplane in flight conditions;

FIG. 4 illustrates on cross section and in a larger scale the detail of an orientable member connecting the wing ends;

FIG. 5 illustrates a longitudinal cross section of a member for the coupling of the tow cable;

FIG. 6 is a view of the front part of the coupling member according to FIG. 5; and,

FIG. 7 illustrates a detail of the orientable wing end, viewed in the axial direction of the framework oblique rod.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Geometrically, the sail of the sailplane is symmetrical with respect to a longitudinal center line a and is delimited by two front sides b, b which extend between the forward end A and the side vertices B,B, by two inclined rear sides c,c extending between the lateral vertices B,B and rear vertices C,C, and by a rear transverse side d extending between the rear vertices C,C and passing through the after end D of the sail. Each of the right hand and the left hand parts ABCD of the sail, which are symmetrical with respect to line a, is subdivided in two portions: 1 the forward and 2 the rear, by an oblique line e extending from a point E, located in the forward half of line a, to the lateral vertex B. The lateral vertices B lie in a same plane with the central line a.

The sail is formed by a sheet of a substantially flexible material which may preferably be a thin rolled polyester, and cooperates with a substantially rigid framework formed, e.g., by rods of wood or other suitable and relatively light material. In said framework, a longitudinal rod 3 materializes the longitudinal center line a, two oblique bars 4 materialize the oblique lines e and a junction member 5 materializes point E, and four connecting members 6, 7, 8, located between the sail and the ends of rods 3 and 4, materialize the forward and after points A and D as well as the lateral vertices or wing ends B,B. But the dimensions of the sail are slightly greater with respect to the lengths of the rods, so that in the rest condition (FIG. 5) the sail is applied loosely to the underside of the framework.

In flight, the whole lift and resistance effects applied to the sail include pressures which are perpendicular to the same sail and put it in tension with respect to the framework but, due to the greater dimensions of the sail, this assumes an arcuate configuration, with respect to the framework, with the concavity facing downward and, precisely, the forward portions 1 assume a positive incidence and the rear portions 2 assume a negative incidence and divergent channel shapes with respect to the central rod 3.

The sail forward portions 1 having a positive icidence, besides their contribution to the lift, give an essential contribution to the longitudinal stability of the sailplane.

The rear portions 2 of the sail, shaped as described, generate, for reasons which are not yet completely clear, an aerodynamic effect highly stabilizing on the transverse trim of the sailplane, while the greater encumbrance of the rear curved surfaces, viewed from the sides, with respect to the forward surfaces, causes a backward displacement of the lateral pressure center with respect to the barycenter, whose consequence is a high heading stability.

The aerodynamic efficiency of the sail assembly so formed is remarkably high and, ensures the capability of the sailplane to plane with a stable trim and heading, with a slight gliding angle, in calm air, to rise rapidly by traction effect obtained by means of a cable 9 dragged with respect to the calm air or retained with respect to the wind, and to keep at height under the effect of even the slightest ascensional currents encountered.

It has been ascertained that while keeping steady the specified arrangement, the efficiency and the stability of the sailplane may be increased by providing some orientability, relative to the framework, for the wing ends of the sail, so that under the stresses applied by the air during flight, the ends of the sail forward portions displace slightly downward. This displacement is due to the prevalent forces acting on the sail rear portions giving them a negative incidence, and to the fact that this negative incidence is transmitted to the sail forward portions as the effect of the orientability of the wing ends. This causes a displacement of the pressure centers on the sail forward portions and it is thought this is the principal reason of the ascertained increase of stability and aerodynamic efficiency.

The desired orientability of the wing ends, has been obtained with very simple and economical means by providing each of the caps 8, intended to be inserted on the outer ends of the lateral rods 4 of the framework, with an extension blade 8' formed integrally with the cap 8 by molding from a suitable synthetic material. Blade 8', which is provided with an adhesive layer on its lower face, is an excellent means for the fastening of the connecting members 8-8' onto the wing ends, that is, in correspondence with the lateral vertices of the synthetic material sheet forming the sail. Cap 8 is rotatingly inserted, that is not forced, onto the end of the corresponding lateral rod 4. The wing ends so sustained with mobility orientate, in flight, as indicated in FIGS. 2 and 3, namely the sail rear portion 2, assuming a negative incidence, drags with it blade 8' rotating cap 8 on rod 4 and thereby transmits a corresponding negative incidence to the side end of the sail forward portion 1, as particularly illustrated in greater scale on FIG. 7, as compared with the plane configuration at rest indicated by a chain line on the same figure.

This arrangement assures further the advantage of a reduction of the length of the sailplane lateral rods 4, for the same wing span, with a consequent reduction of the weight and cost and displacement of the barycenter. It has been ascertained that the described arrangement improves further the behaviour of the sailplane during towing in the presence of a lateral wind.

A connecting member 7-7' substantially similar to member 8-8' described, may be opportunely used for the connection of the longitudinal rod 3 to the tail D of the sail, contributing thereby to the forward displacement of the barycenter. In this case, some elastic flexibility of blade 7' becomes important, as has been ascertained, because it favors particularly the sailplane stability during towing.

Also, an analogous connecting member 6-6', having the blade 6' on the open side of cap 6 instead of the closed side, may be used to connect the sail forward end A to the central rod 3'.

The general shape of the sail preferably derives from a square ABFBA located with a diagonal AF along the longitudinal central line a, and from which a triangular rear part CFC has been cut off with a transverse cut d passing through the after point D.

As the rear edges of the sail are likely to flap under certain conditions, and this may be undesirable, they may be stiffened, if desired, with rods 13 connected to the rear portions of sail 2, said rods starting from vertices C of the sail and being directed towards the junction member 5 (point E) but without reaching it.

In consideration of the well known opportunity to form with wood the framework of sailplanes and kites and the impossibility of standardization of said material, it should be necessary for the construction to select pairs of identical rods to form the lateral parts 4 of the framework in order to have the barycenter and the pressure center located on the median line a where is also normally located the member for the coupling of the towing cable; in effect it is necessary to have a correct alignment of the traction center, the gravity center and the pressure center in order to have correct towing. This involves an operation for the selection and assortment of the rods which is industrially inconvenient.

In order to permit compensation of any accidental lateral displacement of the barycenter and the pressure center, instead of systematically avoiding said displacement, the sailplane has been provided with a member for the coupling of the traction cable 9, substantially as represented in FIGS. 5 and 6. It comprises a sleeve shaped part 10 to be firmly connected to the rods located along the median axis a of the framework, and a lower flange 11 which is provided with a plurality of connection pins 12 arranged side by side of one another so that one of them lies on the center line while the others are more or less laterally displaced, to the right hand and left hand respectively. By a suitable selection of the pin 12 to which the traction cable 9 is coupled or tied, it is possible to locate the traction center in a convenient position with respect to the barycenter and the pressure center, even if these are accidentally slightly displaced with respect to the center line a.

This arrangement permits also improving the behaviour of the sailplane, by the introduction of a wilfull lack of alignment between said centers, in case the sailplane is to be towed, for its lift, along a direction which is transverse to the direction of the wind, namely in conditions of lateral wind.

As the coupling member 10 must not be allowed to rotate around the center line a, said member is suitably connected to the junction member 5 by means of a rod 3" which is not round, which may be advantageously formed by a structural shape, for example H shaped, of a rigid synthetic material. In this way the longitudinal rod of the framework is formed by three sections, forward 3', median 3" and rear 3, whose extreme sections 3 and 3' are advantageously wood rods having a circular cross section, while the intermediate section is a non circular structural shape of a synthetic material.

In the arrangement now preferred, the length of the wing span being indicated by B--B, the length from prow to stern AD is about 82% of the wing span, the distance AE between the prow and the point from which the oblique lines e start, is 15% of the wing span, and the length of the rear side d is about 38% of the wing span. The angle BED formed by the oblique lines e with respect to the rear portion of the longitudinal center line a is about 55.degree..

Nevertheless it must be noted that said proportion may be modified in various ways. It is thought that the distance prow-stern may be preferably comprised between 65% and 90% of the wing span, the distance between the prow and the point from which the oblique lines e start may be preferably comprised between 10% and 25% of the wing span, and the length of the rear transverse side may be preferably comprised between 25% and 50% of the wing span, while the angle BED may be generally and preferably comprised between 40.degree. and 75+. Further, the angles ABC and BAB are not necessarily right angles but they may be generally comprised between 60.degree. and 120.degree., that is, the ideal square ABFB may be replaced by a widened or lengthened rhombus, or generally by a quadrilateral.

It is further to be kept in mind that the rectilinear segments b, c, d, e represent the scheme of the sailplane construction, but that in practice they may be replaced by curves or by sinuous or broken lines either for technical or for aesthetical reasons. Therefore, as an example, the forward sides b may present a slightly concave line while the sides c, d may be replaced by a single curve, and lines e may present central sections perpendicular or nearly perpendicular to the central line a. Further, in correspondence of the prow and stern points A, D, the sail may have extensions which are of no efficacy for aerodynamic purposes but serve e.g. to simulate the shape of a cockpit.

Rods 3, 4 may be connected one to another by a junction member 5 which presents short tubular branches intended to receive the ends of the rods, in a manner well known e.g. in the construction of kites. As already said, the sailplane does not require a lateral V shape, and hence said junction member may be planar. It must yet be understood that no technical reason prevents one from giving to the sailplane a V configuration if considered preferable, as for example for aesthetical reasons.

Claims

Having thus described my invention, what I claim is:

1. In a sailplane comprising a substantially rigid framework and a flexible sail,

said framework comprising a central rod extending in the longitudinal direction of the sailplane, along said central rod in the forward portion thereof, a rigid connection member, and a pair of oblique rods fixedly connected to said connection member and extending towards the rear portion of the sailplane forming an acute angle with respect to said central longitudinal rod,

said sail comprising a sheet of a flexible material having corners connected to the ends of said rods of the framework;

the improvement in which said sheet has front edges which are substantially longer than the distances between the forward end of said central rod and the free ends of said oblique rods, and has rear edges which are substantially longer than the distances between the rear end of said central rod and the free ends of said oblique rods

whereby said sail is loose on said framework at rest and assumes during flight, due to the effect of air pressure, a configuration including two forward portions located in front of said oblique rods and on the right and the left respectively of the forward portion of said central rod, said forward portions of the sail having a positive aerodynamical incidence, and two rear portions located behind said oblique rods and on the right and the left respectively of the rear portion of said central rod, said rear portions of the sail having a negative aerodynamical incidence, and forming a pair of channels which diverge with respect to said central longitudinal rod of the framework of the sailplane.

2. In a sailplane as set forth in claim 1, a pair of connecting caps, each connecting cap having a sleeve portion and an extension integral with said sleeve portion, the extensions of said connecting caps being joined to the flexible sheet forming the sail in vicinity of the corners thereof which are more remote from said central rod of the framework, and the sleeve portions of said connecting caps being inserted rotatably upon the ends of said oblique rods, opposite said connection member.

3. In a sailplane as set forth in claim 1, a rear connecting cap having a sleeve portion and an extension integral with said sleeve portion, said extension being resiliently flexible and being joined to the flexible sheet forming the sail at the rear end thereof, and the sleeve portion of said rear connecting cap being inserted upon the rear end of said central rod of the framework.

4. A sailplane as set forth in claim 1, wherein said flexible sheet forming the sail has a shape derived from a quadrilateral with at least approximately equal sides, located with two opposite corners aligned with said central rod of the framework, and a triangular rear portion of which is cut off along a line transverse to said central rod.

5. A sailplane as set forth in claim 1, further comprising a coupling member fixedly connected to said central rod of the framework, said coupling member having a number of coupling pins located side by side on said coupling member along a direction transverse to said central rod, said coupling pins selectively receiving the coupling of a traction cable for the sailplane.

6. A sailplane as set forth in claim 1, further comprising a coupling member fixedly connected to said central rod of the framework behind said rigid connection member, said coupling member having a number of coupling pins located side by side on said coupling member along a direction transverse to said central rod, and said central rod comprising three separate portions, namely a front portion located in front of said connection member, an intermediate portion located between said connection member and coupling member, and a rear portion located behind said coupling member, said intermediate portion of the central rod being formed by a short non circular structural shape of a synthetic material and being connected non-rotatably to said connection member and coupling member.

7. A sailplane as set forth in claim 1, further comprising a pair of stiffening rods, each stiffening rod being fixedly joined to the flexible sheet forming the sail, and extending from a rear and lateral point of said sheet towards a point of the forward portion of said central rod of the framework, without however attaining said central rod.

8. A sailplane as set forth in claim 1, wherein the length of the flexible sheet forming the sail is comprised between 65% and 90% of the maximum width of said sheet, the distance from the forward end of said central rod of the framework and said connection member is comprised between 10% and 25% of said maximum width, the angle formed by said oblique rods with respect to said central rod is comprised between 40.degree. and 75.degree. and the flexible sheet forming the sail has a rear transverse side whose length is comprised between 25% and 50% of said maximum width.

9. A sailplane as set forth in claim 8, wherein said first-mentioned length is about 82%, said distance is about 15%, said angle is about 55.degree., and the second-mentioned length is about 38%.