Propeller blade

Abstract

 Screw-propeller blade, equipped with a support (2) comprising a base (202) to which said blade (1) is connected through suitable means, and a shank (302) axially protruding from said base (202) on the opposite side with respect to that to which said blade (1) is connected, which has to be connected with a suitable housing (32) obtained in the boss (30) of said screw-propeller; said means for connecting the blade (1) to said base (202) comprise a substantially wing-shaped element (102) axially protruding from said base (202) and firmly connected to the latter, to which said blade (1) is coupled through suitable coupling means (112).

Description

[0001] The present invention relates to screw-propeller blades, and in particular to screw-propeller blades for devices such as torpedoes and the like.

[0002] As is generally known, propulsion means for torpedoes have to combine an effective and constant thrust with an extremely low noise level, so as to reduce the detectability of the targeting weapon.

[0003] It is known about propulsion systems consisting of screw-propellers equipped with blades made of plastic, in particular a composite material comprising carbon fiber. However, the problems inherent to the structure of propulsion means do not allow to use plastic for the whole impeller, so that the boss is made of metal, whereas the blades are made of composite material, as was said before.

[0004] The connection between boss and blades is carried out by mounting the blades made of composite material onto metal shanks, which are in their turn introduced into suitable hollows obtained radially with respect to the boss. Figure 1 of the enclosed drawings shows a known blade, referred to with 10, made of a composite material and equipped inside with fiber threads 11. The blade 10 is placed on the base 21 of the support 20, which is provided with through holes 23 near its edge, and the central channel 24 communicating with the channels 23 within the shank 22, axially protruding from the support 20. As can be inferred from the figure, the threads 11 are led through the holes 23 and the channels 24 and 24, and are fastened to the opposite ends with respect to the entry, so as to make the blade 10 integral with the support 20.The support is then secured to the impeller boss by means of the cooperation of the groove 26 obtained on the edge of the shank 22 with suitable locking means.

[0005] The connection thus established has some drawbacks; in particular, the fastening of the blade to the support by introducing into the holes and channels within said support the threads incorporated into the plastic material of the blade, gives the latter a sufficient axial stability but a small transversal stiffness. To put it otherwise, the blade can have undesired oscillations in the direction corresponding to the sense of rotation of the impeller; this can compromise at least partly its efficiency, not so much its duration, since the turbine is mounted on a manufactured item to be destroyed, but its performance, since a blade with a small transversal stiffness provides a smaller propulsive thrust with respect to a given amount of applied energy.

[0006] Another problem that can easily be inferred from Figure 1 showing the prior art, concerns the actual difficulty in assembling the blade with its support, due to the specific position taken by fiber threads in the channels within the plate and the shank of said support. These constructive complications, especially for a "non-returnable" item, result in a wholly undesirable increase of working costs.

[0007] The present invention therefore aims at providing a screw-propeller blade, in particular for torpedoes or the like, which can be firmly connected to the impeller boss without oscillations that can make the propulsive thrust less efficient. The invention further aims at providing a blade whose construction involves a limited number of steps and is easy and therefore advantageous from the economic point of view.

[0008] The object of the present invention therefore is a screw-propeller blade equipped with a support comprising a base to which said blade is connected through suitable means, and a shank axially protruding from said base on the opposite side with respect to that to which said blade is connected, which has to be connected with a suitable housing obtained in the boss of said screw-propeller, characterized in that said means for connecting the blade to said base comprise a substantially wing-shaped element axially protruding from said base and firmly connected to the latter, to which said blade is coupled through suitable coupling means.

[0009] The wing-shaped element can be carried out with a substantially helical shape, just like the blade itself. Furthermore, said element can extend on a relevant portion of the length of said blade.

[0010] Said blade is preferably made of a plastic or composite material, whereas said support, i.e. said base, said shank and said wing-shaped element are preferably made of metal.

[0011] In a preferred embodiment the base, the shank and the wing-shaped element are carried out together as one piece. The blade can be obtained directly by moulding on said wing-shaped element of the support.

[0012] Further advantages and characteristics of the device according to the present invention will be evident from the following detailed description of an embodiment of said invention, which is carried out as a mere non-limiting example with reference to the enclosed drawings, in which:

Figure 2 shows the screw-propeller blade according to the present invention mounted onto the boss of said screw-propeller, in side elevation with sectioned portions;

Figure 3 shows the support of said screw-propeller blade in side elevation; and

Figure 4 shows the same support in front elevation.

[0013] In Figure 2 the numeral 1 refers to the screw-propeller blade according to the present invention; said blade is equipped with a support 2 comprising a base 202, which is the starting point of a wing-shaped element 102 obtained as one piece with the latter, on which element said blade 1 is obtained. The wing-shaped element 102 has near the base 202 two hollows 112, placed in a substantially asymmetric position with respect to the longitudinal axis of said wing-shaped element 102. The base 202 is the axial starting point of the shank 302 obtained as one piece with the latter; said shank includes a groove 312 which can cooperate with the locking means placed on the boss 30 of the screw-propeller impeller. The boss 30 is equipped on its edge with a block 31 provided with radial hollows 35 containing the base 202 of the blade; the seats 32 housing the shank 302 are axially obtained within said hollows. Transversally with respect to said seat is obtained a threaded through hole 34 in which the screw 33 is engaged, whose end cooperates with the groove 312 obtained on said shank, thus locking said shank 302.

[0014] Figures 3 and 4 show the support 2 of the blade according to the present invention; said support 2 is made as one piece, preferably in a light metal, such as aluminum or the like. The base 202 has a disk shape, with different thickness according to the structure of the block 33 in which it has to be placed (see Figure 2). The wing-shaped element gets thinner starting from the end facing the base 102 towards the free end, as is evident from Figure 4, and its width decreases as well. The hollows 112 obtained on the edges of the wing-shaped element 102 are carried out with their top inclined towards the free end of said wing-shaped element 102.

[0015] The working of the blade according to the present invention and its assembly will be evident from the following. By directly comparing the known blade shown in Figure 1 with the one carried out according to the present invention, the advantages characterizing the latter are immediately manifest. First of all, the support 2 equipped with the wing-shaped element 102 avoids for the blade those transversal oscillations with respect to its longitudinal axis that typically characterized blades as shown in Figure 1, thus improving the functional performance of said blade, which can now ensure a higher actual thrust.

[0016] Furthermore, a substantial constructive simplification is also manifest; indeed, whereas in the prior art the threads 11 had to be introduced with a certain precision into the holes 23 and into the channels 25, so as to secure the blade to the support 20, the support 2 represents with its wing-shaped element 102 the "skeleton" of the blade, which can be obtained on said support by direct moulding. The hollows 112 on the edge of the wing-shaped element 102 enable the anchorage of the plastic material of the blade 1 onto said support, and prevent its unfastening. The positioning of the hollows 112 on the wing-shaped element 102 is the result of a choice deriving partly from stability needs for the blade-support coupling, and partly from the maximum working simplification for the support.

[0017] Therefore, if on one side the amount of material to be used for the support increases, the working times needed for manufacturing a single blade are dramatically reduced. It should further be pointed out that the support used in the known blade was certainly lighter but not necessarily easier to be carried out, considering the number and complexity of through holes and channels.

[0018] It can therefore be said that the threads, which represented a substantially valid bond in the axial direction of the blade, though much less in transversal direction, have been replaced by an element, the wing-shaped element 102, that is at least as effective in axial direction, and is further much more reliable from the point of view of stability in the direction of rotation of the screw-propeller.

[0019] The blade is preferably made of plastic or composite material, typically resin strengthened with carbon fiber. On the other hand, the support is made of light metal, such as aluminum or the like, and is preferably carried out as one piece.

Claims

1. Screw-propeller blade, equipped with a support (2) comprising a base (202) to which said blade (1) is connected through suitable means, and a shank (302) axially protruding from said base (202) on the opposite side with respect to that to which said blade (1) is connected, which has to be connected with a suitable housing (32) obtained in the boss (30) of said screw-propeller, characterized in that said means for connecting the blade (1) to said base (202) comprise a substantially wing-shaped element (102) axially protruding from said base (202) and firmly connected to the latter, to which said blade (1) is coupled through suitable coupling means (112).

2. Screw-propeller blade according to claim 1, in which said wing-shaped element (102) is carried out with a substantially helical development, just like the blade (1) itself.

3. Screw-propeller blade according to claim 1 or 2, in which said wing-shaped element (102) extends on a relevant portion of the length of said blade (1).

4. Screw-propeller blade according to any of the claims 1 to 3, in which said blade (1) is made of plastic or composite material.

5. Screw-propeller blade according to any of the claims 1 to 4, in which said base (202), said shank (302) and said wing-shaped element (102) are made of light metal, such as aluminum or the like.

6. Screw-propeller blade according to any of the claims 1 to 5, in which in which the base (202), the shank (302) and the wing-shaped element (102) are carried out together as one piece.

7. Screw-propeller blade according to any of the claims 1 to 6, in which said blades (1) is obtained directly by moulding on said wing-shaped element (102) of said support (2).

8. Screw-propeller blade according to any of the claims 1 to 7, in which means for coupling said blade (1) with said wing-shaped element (102) comprise one or more hollows (112) obtained on the walls of said wing-shaped element (102).

9. Screw-propeller blade according to claim 8, in which said hollows (112) are carried out on the side edge of said wing-shaped element (102), in a substantially symmetric position with respect to the longitudinal axis of the latter, and with their cavity facing the free end of said wing-shaped element (102).

10. Screw-propeller blade according to any of the claims 1 to 9, in which said blade is used in propulsion means of devices such as torpedoes or the like.

Drawing