WO1992019497A1

WO1992019497A1 - A locking mechanism for the tail rotor of stationary helicopters

Info

Publication number: WO1992019497A1
Application number: PCT/NO1992/000059
Authority: WO
Inventors: Asbjørn OLAFSEN; Rudi BOLSØY
Original assignee: Olafsen Asbjoern; Bolsoey Rudi
Priority date: 1991-04-26
Filing date: 1992-03-31
Publication date: 1992-11-12
Also published as: NO172530B; GB2270052A; GB2270052B; NO911655D0; GB9321147D0; NO911655L; AU1682192A; NO172530C

Abstract

A locking mechanism for the tail rotor of a stationary helicopter comprises a central body (10) having a fastening device for each individual rotor blade (1, 2). Such a mechanism serves to secure the rotor blades (1, 2) against the effects of wind. A regulating mechanism for the rotor blades (1, 2) includes the so-called tail rotor star (9). The invention has been to provide a locking mechanism which also is easy to fit and to remove. Thus, said central body consists of a tubular hollow body (10) which, at one end thereof, is provided wiht indentations (11) and, at the opposite end, carries fastening straps (12, 12') with buckles (14, 14'). The indentations (11) correspond in shape, number and position to the design of the tail rotor star (9) which, thus, serves to regulate the positioning of the central hollow body (10) of the locking mechanism, one strap (12, 12') being arranged for each rotor blade (1, 2).

Description

A LOCKING MECHANISM FOR THE TAIL ROTOR OF STATIONARY HELICOPTERS

This invention concerns a locking mechanism for the tail rotor of stationary helicopters intended to provide stabilizing support for the rotor blades in high winds or gusty conditions. The nature of the invention is described in detail in the introductory chapter of the following patent application no. 1.

The tail rotor blades can be rotated to enable adjustment of degree of rotation/pitch. It is further possible to pivot each individual blade about its transverse axis. For this purpose, the base of each rotor blade is attached to a collar which in turn is sectionally connected to a central hub construction by means of a bolt. Adjustments to the individual rotor blade's pitch are effected by means of a control mechanism comprising a central star-shaped control device with radial arms the number of which corresponds to the number^' of rotor blades and which at the tips are connected to each rotor blade via connecting arms such that when the star-shaped control device, the so-called tail rotor star, is turned, the degree of rotation and pitch of the rotor blades is altered.

The way the tail rotor blades are fixed at the cuff causes problems when helicopters are stationary. Wind, and in particular gusts of wind, can cause the rotor blades to turn undesirably. This is obviously quite unacceptable and, consequently, regulations require all helicopters to carry so-called "gust-locks" at all times. These are intended for use when helicopters are stationary to ensure stabilizing support and locking of the moveable tail rotor blades in windy weather.

There are several such gust-locks on the market which vary only slightly in construction and function. All are based on the application of several heavy metal hooks - the number corresponding to the number of tail rotor blades - which are fixed by means of an equally heavy and solid central construction comprising two independently moveable, heavy metal rings of which the outer one may incorporate a crank and the inner one either spacers or similar devices in the form of rods or tubes.

Operation of these locking devices entails each of the metal hooks being fastened to a collar at the base of each rotor blade thereby achieving a pulling effect on the blades towards a stabilized, locked position. This is ahieved when the outer central ring is swung outwards while the spacer rods or spacer tubes of the inner ring provide support against the adjoining tail rotor construction - the effect being that the latter provides resistance.

There is no disputing that when in place such a locking mechanism is effective and does the job as intended. Nevertheless, such mechanisms have several serious shortcomings and limitations and are inconvenient.

Locking mechanisms of the prior art are not only extremely cumbersome but also dangerous to use. The large and heavy metal construction (approximately 9,5 kg for a normal six-blade tail rotor) has been regarded as essential to ensure their ability to withstand the load imposed by the tail rotor blades when helicopters are stationary and fitting requires at least two men. Working height is about 5 and one man is needed to support the ladder on the ground. Particularly in strong winds it can be very difficult, if at all possible, to position the hooks of such a locking mechanism. Furthermore, there is a serious potential risk of accident due to the mechanism's great weight should someone lose their grip and the mechanism, as a result, fall down during fitting/removal. Such locking mechanisms are expensive to buy, just under NOK 70.000,- for a six-blade tail rotor. They take up a lot of space because of the long, extending hooks, and space is at a premium in helicopters.

Locking mechanisms of the prior art, whi-ch weigh about 9,5 kg, also pose a serious threat of accident during transportation on board helicopters. They can easily cause injury to personnel or damage to equipment in the event of sudden and subsequent uncontrollable movement.

It is obviously a great disadvantage that such locking mechanisms are made of steel. Even when fixed in position there will inevitably be some minor relative movements between the mechanism and the rotor blade collars. Such mechanisms may also cause scratching or dents in the tail rotor hub during fitting/removal. Such damage may be so extensive as to make frequent, expensive overhaul of the tail rotor hub necessary.

Experience tells us that such mechanisms are often mistreated, resulting in the long metal hooks suffering permanent bending/twisting. If any of the hooks is in the wrong position then the tail rotor blade will not be securely fastened but will instead be able to move to and fro in the wind which in turn will cause abnormal wear of the relevant collar.

The aim of this invention is to remedy any deficiencies, inconveniences and limitations associated with existing technology and thus provide a considerably lighter and more compact locking mechanism of a relevant type, a mechanism designed to provide much more reliable and stable locking of the tail rotor blades in windy conditions, including the ability to withstand the pressures and loads imposed. As per the invention, this objective is realised by means of a considerably simplified, much lighter and more manoeuvrable device. Particular emphasis has been placed on making it considerably easier and faster to fit the mechanism onto the tail rotor blades.

This objective is achieved in that this locking mechanism has been designed in accordance with the features specified in patent application no. 1 below.

As per the invention, a locking mechanism intended to stabilize the tail rotor blades in windy conditions comprises a central hollow body, primarily manufactured in plastic or a similar light-weight material. This central hollow body which in a particularly simple design might be shaped like a cylindrical tube could in fact have virtually any shape and cross-section. It may be designed on the basis of a shortened cone or a shortened pyramid. Although a circular cross-section might be preferable there is no reason why the cross-section should not be triangular, square, rectangular, pentagonal, etc. with the number of angles corresponding to the number of blades. Two concentric rings held apart by means of spacers would equally serve the purpose.

As per the invention, the central hollow body would at one end be shaped with indentations complementary to the (radial) arms of the tail rotor star and would at the other end be equipped with fastening straps and buckles, the number corresponding to the number of rotor blades.

A locking mechanism of this type would be extremely easy to fit and it would also weigh very little (about 1,5 kg for a six-blade tail rotor) . One of the straps would be secured around the rotor blade (this being only short) after it had temporarily been fastened in its relevant buckle. Following this, the central hollow body can be fixed in place with its indentat ons resting against the adjoining rotor hub construction. This would normally be the previously mentioned tail rotor star which forms part of the pitch control device for the rotor blades. Then the fastening strap which is diametrically opposite would be fastened causing the central hollow body to be held in place even more firmly and making it very easy and quick to fasten the remaining straps. The straps would be made to stay on the cuffs. It is obvious that this locking mechanism would be equally simple to fit and remove. The straps and the central hollow plastic body could possess some degree of elestacity -although this is not essential.

When stored, the straps are pressed into the hollow body such that only the length and breadth of the latter will determine space requirements. The whole locking mechanism will be considerably smaller than any existing mechanisms intended for the same purpose. In comparison with mechanisms of the prior art which have thick, heavy rings and massive, long hooks the advantages of the present invention are obvious.

The fastening straps incorporated in the locking mechanism as per the invention could easily be manufactured such that each would be able to tolerate a load of approximately 2,000 kg. Any load and pressures imposed on the central hollow body would be of a magnitude which would permit the body to be constructed of a thin-walled tubing of a suitable existing plastic coated alloy or composite material. One example of a design of the hollow body might be a cylindrical tube (approximately 30 cm long) with a diameter of about 20 cm.

However, the dimensions would be tailored to fit the dimensions of the particular tail rotors, eg. tail rotors with three, four, etc. blades.

At the end of the central hollow body to which the fastening straps are to be secured, there are slits of around 2,5 cm, one for each strap, at a distance of around 5 cm from the near end of the hollow body. Each slit is around 0,3 cm wide. It is preferable to sew the end of each strap to itself at a distance of around 10 cm in the direction towards the buckle. This ensures that the straps do not slip.

The straps, which may have a combined length of 1,5 m, for example, will have a breadth and thickness somewhat less than 2,5 cm and 0,3 cm respectively, given the above measurements.

Where a so-called tail rotor star is used in the rotor blade pitch regulating mechanism, the indentations, by means of which the hollow body is positioned and secured and which are situated on the inner edge of the central hollow body, are shaped so as to complement the adjacent section of the star arms, preferably such that each indentation has a cross-sectional shape which fully complements the cross-section of the star arm, thus ensuring particularly secure fixing of the hollow body in relation to the adjacent, stationary tail rotor and hub. However, adequate and satisfactory fixing of the hollow body can also be achieved by shaping the indentation such that they each complement only the nearest part of the cross-section of the tail rotor star, that is, only a part of the cross-section. These tail rotor stars are often T-shaped in cross-section, and in the former case the indentations of the hollow body also have a T-shaped cross-section, while in the latter case they may have a cross-section which complements the end of the T-shape.

In a tubular hollow body with a diameter of 20 cm, the indentations would be shaped according to the shape of the tail rotor star 10 cm from its centre, insofar as the star arms have a varying cross-section between the base and the cuff, where using connecting rods, they are linked with the rotor blade sections so as to allow movement.

An example of a specific design is shown in the enclosed illustration, where the diagram shows in perspective a locking mechanism as per the invention brought into locking position on the six-blade tail rotor of a helicopter.

In the diagram, the tail rotor blades are partly cut away, the number 2 referring to the cuff of the rotor blade. The actual devices for the mounting and fitting of the individual rotor blades 1,2, as well as their rotation, are not the direct object of this invention, and here we shall only mention briefly that each rotor blade 1,2 has a connecting joint to a central hub 4 via a collar 3 by means of a transverse bolt 5, upon which each blade can rotate to a limited extent.

Each rotor blade 1,2 can rotate, and for this purpose is provided with a revolving ring 6, which is linked via an a^ttachment 7 to a connecting rod 8, whose other end is linked to the outer end of one of the arms of the tail rotor star 9, five of whose arms are visible in the diagram. As mentioned above, the tail rotor star 9 serves to regulate/adjust the angle of rotation or pitch of the rotor blades 1. If the star 9 rotates in one direction, the pitch of the rotor blades 1 increases, and vice versa.

The locking mechanism as per the invention, which is designed to prevent the rotor blades 1,2 of a stationary helicopter from moving on their rotor bolts 5 as a result of the wind, comprises, as per the design shown, a central tubular hollow body 10, which at_ιone end is provided with indentations 11 which complement the arms of the tail rotor star 9, each of which, as per the design example, is formed so as to take the full cross-section of the adjacent star arm, which is shown in the diagram to be approximately T-shaped.

In a six-blade tail rotor there are six arms on the tail rotor star 9 and consequently six indentations 11 placed with complementary spacing on the edge of the hollow body 10.

At the opposite end, the central hollow body 10 of the locking mechanism is attached to six fastening straps 12, one for each rotor blade 1,2. Each strap 12 is pushed through a slit 13 in the end section of the hollow body 10, and has a buckle 14 for securing each strap. The end of each strap is sewn to itself 15 at a distance of around 10 cm in the direction of the buckle 14.

When fitting, the end section of the fastening strap 12* may, for example, be passed through the buckle 14• such that the strap forms a loop, which is placed over one of the rotor blades thus providing some support when fixing the central hollow body 10 and its indentations 11 onto the adjacent arm sections of the tail rotor star 9. Following this, the diametrically opposite strap is fixed and tightened, after which the locking mechanism 10, 12, 14 is sufficiently stable to allow the other four straps to be easily and quickly placed around the axially adjacent rotor blades 1,2 and tightened using the attached buckle 14.

The central, tubular hollow body 10 of the rotor blade locking mechanism as per the design shown, which when fitted inhibits the movement of the rotor blades 1,2 around their axes 5 due to the effects of wind, is, as per the invention, of thin-walled construction and made of material of low density and therefore light-weight. It should preferably be made of a suitable plastic material, but it may in special designs be made of light-weight metal covered in plastic, since it is important that the hollow body 10 should be light in weight and incapable of causing scratches and marks on the hub 4,9 of the tail rotor. Whatever the choice of material, the light-weight of the straps 12,12' and the buckles 14' ,14 would ensure that the total weight of the mechanism is not significantly increased. The use of flat straps 12,12' would reduce friction and wear and tear on the rotor blade cuffs compared with the steel hooks of the prior art.

The invention is not limited to the design described with reference to the diagram. It is thus possible, for example, to use a hollow body of different design, provided its three main functions are achieved, ie: to fix the whole of the locking mechanism and to prevent it revolving on its own axis; to function as a secure support for the straps and to ensure their relative distances; and to function as a spacer for the straps in relation to the hub 4,9. The central hollow body of the locking mechanism may therefore have, instead of a cylindrical shape, the shape of a shortened cone or pyramid or of two concentric rings of any shape and held together a a constant distance from each other by means of axial connecting elements or similar devices.

Claims

C l a i m s

1- A locking mechanism for the tail rotor of a stationary helicopter, on which each rotor blade (1,3) can pivot on an axis (5) transverse to the hub, including a body (10) in a central position relative to the tail rotor hub (4) , with a fastening device for eacy individual rotor blade (1,2) , such that these rotor blades are held secure against the effects of the wind, and in which each rotor blade (1) can be rotated (6) in order to regulate/adjust its pitch by means of a regulating mechanism which includes a star-shaped device (9) , the so-called tail rotor star, coaxial with the tail rotor hub (4) , and in which the outer sections of the star arms are connected to the rotor blades at their cuff (2) in order to allow movement (7,8), c h a r a c t e r i z e d i n that the central body of the locking mechanism is made of a thin-walled, eg. tubular hollow body (10) , which at one end is provided with indentations (11) whose shape corresponds on the whole to the cross-sectional shape of at least those parts of the said star arms (9) which are in contact with the hollow body, and in that the above fastening devices comprise straps (12,12') provided with fastening buckles (14,14'), the straps being fixed to the other end of the central hollow body (10) .

2. A locking mechanism according to claim 1, c h a r a c t e r i z e d i n that the shape of each of the indentations (11) on the edge of the hollow body corresponds fully to the cross-section of each individual star arm (9) , at a radial distance from the centre of the tail rotor star (9) which is largely the same as half the cross-sectional size of that end of the hollow body (10) on which the indentations appear.

3. A locking mechanism according to claim 1 or 2, c h a r a c t e r i z e d i n that at the opposite end to the indentations (11) , the central hollow body (10) is provided with a number of slits (13) which are positioned at regular intervals and the purpose of each of which is to enable a strap (12,12') to be passed through it, whereas the other part of the strap is passed over the adjacent edge of the hollow body (10) , where, in proximity to their position of fixing, the two sections of each strap are sewn together at a certain distance from the buckle (14,14').

4. A locking mechanism according to claim 1, 2 or 3, c h a r a c t e r i z e d i n that the central hollow body (10) is of cylindrical form.