GB2149061A - Propeller shafts - Google Patents

Abstract

In a tubular propeller shaft (1), a tubular core (2), made of metal or composite material, is provided with an integral network covering (3) made of lightweight composite material, such as graphite threads soaked in synthetic resin. When furnace heated the network 3 ensures a firm grip on core 2. <IMAGE>

Description

SPECIFICATION Stiffened tubular propeller shaft The present invention relates to a stiffened tubular propeller shaft.

For transmitting twisting moments between a power generating unit and any type of utilizing equipment, tubular propeller shafts are known to be employed, the torsional resistance of which, even in the presence of relatively small sections, provides for transmitting even relatively high torques.

The section size of propeller shafts used up to now, on motor vehicles, for example, increases in proportion with the size of the power generating unit and the length of the drive span involved, and, in any case, is always such as to ensure that, under all operating conditions, the shafts are never subjected to critical vibration. What is more, propeller shaft sections are further increased in cases where the shafts are operated in the presence of external stress, such as impact from piercing bodies, in which case, the shafts must be capable of transmitting the applied twisting moment even when pierced in one or more points.

In short, therefore, the weight of known types of propeller shafts increases in proportion with the torque being transmitted, the length of the drive span and the extent to which the shaft is exposed to impact.

The weight of a drive is not usually a critical problem on ground vehicles, whereas it may assume vital importance in the case of an aircraft. If one considers, for example, that the tail rotor on a standard helicopter is connected to the power plant over a propeller shaft that is not only relatively long but usually also exposed, for part of its length, to external agents, the weight of the shaft is clearly a tough problem to solve.

And solving it is of even more vital importance when it comes to military helicopters, the propeller shaft sections of which must be such as to withstand collapse in the presence of piercing of around 2 cm2, and the thickness of which must be such as to slow down crack propagation as far as possible.

Unfortunately, to achieve such results, helicopters are perforce fitted with shafts which, despite being critical or even supercritical insofar as vibration is concerned, are invariably overheavy with a negative effect on pay load.

The aim of the present invention is to provide a relatively lightweight, small-section propeller shaft which, nevertheless, provides for relatively high torsional resistance, a low crack propagation rate and piercing resistance such as to withstand collapse.

With this aim in view, the present invention relates to a tubular propeller shaft, characterised by the fact that it comprises a core having an integral network covering extending over and contacting its outer surface; the said network covering being made of lightweight composite material.

The present invention will now be described by way of a non-limiting example, with reference to the attached drawing showing a side view in perspective of a preferred arrangement.

Number 1 on the attached drawing indicates a portion of a propeller shaft which, though ideally suited for use on aircraft, particularly helicopters, may be employed equally well for transmitting drive torques between any type of drive unit and any type of utilizing equipment. Shaft 1 comprises a tubular core 2, made of metal or composite material, and an outer network covering 3, made of lightweight composite material and consisting of at least two filaments, 4 and 5, criss-crossed to form links 6. In the example shown, filaments 4 and 5 are wound round core 2 in opposed cylindrical spiral formation, but any other winding arrangement is equally acceptable.

Filaments 4 and 5 are preferably formed of "Kevlar" (RTM) or graphite threads wound round the outer surface 7 of core 2 and soaked in appropriate synthetic resin which, when furnace-heated together with core 2, ensures a firm grip of network cover 3 on core 2.

The torsional-bending resistance of the composite material of which network 3 is formed results in a considerable increase in the torsional-bending resistance of shaft 1, alongside a negligible increase in weight. Cover 3 thus enables shafts to be made with a very high torsional-bending resistance and relatively small diameters. Furthermore, each link 6 forms a "break cell" preventing any breakage or piercing of core 2 from spreading beyond its boundary. Filaments 4 and 5, in fact, not only resist physical crack propagation, but also act as stress conveyors for preventing dangerous loads from concentrating within the break area and thus eliminating the root cause of crack propagation.

1. Tubular propeller shaft, characterised by the fact that it comprises a core having an integral network covering extending over and contacting its outer surface; the said network covering being made of lightweight composite material.

2. Shaft according to Claim 1, characterised by the fact that the said network covering comprises at least two filaments criss-crossed to form links.

3. Shaft according to Claim 3, characterised by the fact that the said filaments are each wound round the said core in spiral formation.

4. Shaft according to any one of the foregoing Claims, characterised by the fact that the said lightweight composite material com

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

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Stiffened tubular propeller shaft The present invention relates to a stiffened tubular propeller shaft. For transmitting twisting moments between a power generating unit and any type of utilizing equipment, tubular propeller shafts are known to be employed, the torsional resistance of which, even in the presence of relatively small sections, provides for transmitting even relatively high torques. The section size of propeller shafts used up to now, on motor vehicles, for example, increases in proportion with the size of the power generating unit and the length of the drive span involved, and, in any case, is always such as to ensure that, under all operating conditions, the shafts are never subjected to critical vibration. What is more, propeller shaft sections are further increased in cases where the shafts are operated in the presence of external stress, such as impact from piercing bodies, in which case, the shafts must be capable of transmitting the applied twisting moment even when pierced in one or more points. In short, therefore, the weight of known types of propeller shafts increases in proportion with the torque being transmitted, the length of the drive span and the extent to which the shaft is exposed to impact. The weight of a drive is not usually a critical problem on ground vehicles, whereas it may assume vital importance in the case of an aircraft. If one considers, for example, that the tail rotor on a standard helicopter is connected to the power plant over a propeller shaft that is not only relatively long but usually also exposed, for part of its length, to external agents, the weight of the shaft is clearly a tough problem to solve. And solving it is of even more vital importance when it comes to military helicopters, the propeller shaft sections of which must be such as to withstand collapse in the presence of piercing of around 2 cm2, and the thickness of which must be such as to slow down crack propagation as far as possible. Unfortunately, to achieve such results, helicopters are perforce fitted with shafts which, despite being critical or even supercritical insofar as vibration is concerned, are invariably overheavy with a negative effect on pay load. The aim of the present invention is to provide a relatively lightweight, small-section propeller shaft which, nevertheless, provides for relatively high torsional resistance, a low crack propagation rate and piercing resistance such as to withstand collapse. With this aim in view, the present invention relates to a tubular propeller shaft, characterised by the fact that it comprises a core having an integral network covering extending over and contacting its outer surface; the said network covering being made of lightweight composite material. The present invention will now be described by way of a non-limiting example, with reference to the attached drawing showing a side view in perspective of a preferred arrangement. Number 1 on the attached drawing indicates a portion of a propeller shaft which, though ideally suited for use on aircraft, particularly helicopters, may be employed equally well for transmitting drive torques between any type of drive unit and any type of utilizing equipment. Shaft 1 comprises a tubular core 2, made of metal or composite material, and an outer network covering 3, made of lightweight composite material and consisting of at least two filaments, 4 and 5, criss-crossed to form links 6. In the example shown, filaments 4 and 5 are wound round core 2 in opposed cylindrical spiral formation, but any other winding arrangement is equally acceptable. Filaments 4 and 5 are preferably formed of "Kevlar" (RTM) or graphite threads wound round the outer surface 7 of core 2 and soaked in appropriate synthetic resin which, when furnace-heated together with core 2, ensures a firm grip of network cover 3 on core 2. The torsional-bending resistance of the composite material of which network 3 is formed results in a considerable increase in the torsional-bending resistance of shaft 1, alongside a negligible increase in weight. Cover 3 thus enables shafts to be made with a very high torsional-bending resistance and relatively small diameters. Furthermore, each link 6 forms a "break cell" preventing any breakage or piercing of core 2 from spreading beyond its boundary. Filaments 4 and 5, in fact, not only resist physical crack propagation, but also act as stress conveyors for preventing dangerous loads from concentrating within the break area and thus eliminating the root cause of crack propagation. CLAIMS

1. Tubular propeller shaft, characterised by the fact that it comprises a core having an integral network covering extending over and contacting its outer surface; the said network covering being made of lightweight composite material.

2. Shaft according to Claim 1, characterised by the fact that the said network covering comprises at least two filaments criss-crossed to form links.

3. Shaft according to Claim 3, characterised by the fact that the said filaments are each wound round the said core in spiral formation.

4. Shaft according to any one of the foregoing Claims, characterised by the fact that the said lightweight composite material com prises "Kevlar" (RTM) threads.

5. Shaft according to Claim 1, 2 or 3, characterised by the fact that the said lightweight composite material comprises graphite threads.