Tail-rotor arrangement for rotor crafts

#The present invention has for its object a tail rotor arrangement for aircraft having rotary aerofoils which is particularly advantageous due to the extremely simple construction of the rotor, its very low manufacturing costs and by the almost total elimination of maintenance.

#Among the numerous types of tail rotors for helicoptors operating with a free airscrew, rotors having two or more blades articulated separately in hunting and in incidence are particularly known. These articulated rotors have the disadvantage of being relatively complicated because their hunting and incidence joints have ball, needle or roller bearings which have to be carefully lubricated to prevent deteriorating in operation. In actual fact these joints are not only subject to high centrifugal loads emanating from the blades, but they are also subject to oscillatory movements which aid brinelling of the bearings.

#Another known type of opposing torque helicopter rotor comprises so-called "in balance" two-bladed rotors with a single hunting joint for the two blades, which are moreover articulated separately in incidence.

#The following description with reference to the attached drawings of non-limitative embodiments gives a better understanding of how the invention is put into practice.

#FIG. 1 shows a plan view of a tail rotor according to the invention;

#FIG. 2 shows a section along the plane II--II of FIG. 1;

#In the two-bladed helicopter tail rotor arrangement shown in the drawings, the rotor 1 substantially comprises a flexible and twistable spar 2 having a flat rectangular cross-section made from fibres having a high strength and low modulus of elasticity coated with a thermoset synthetic resin to form a blade which extends over the entire span of rotor 1. These fibres are glass-fibres whose use is made possible by the fact that the deformation of the first natural drag mode is of the type with two nodes. The movements of the center of the rotor which is located at an antinode of the deformation are in this case (two-bladed rotor) authorised by the flexibility of the rotor-carrying shaft as well as by that of the helicopter tail boom assembly. Under these conditions it is possible to dimension the spar 2 without having to fear excessive dynamic drag stresses by using only fibre-glass so that the first drag mode is above the nominal speed of the rotor, thereby avoiding any resonance on starting the rotor and in flight.

#On the spar 2 and at each of its ends are fitted coverings constituted by two shells 3 and 4 shown partly in FIGS. 1 and 2 and forming with the said spar the two blades 5 and 6 of rotor 1. These two shells 3 and 4 made either from light metal or plastic reinforced with fibre glass are attached as seen in FIG. 7 by bonding to spar 2 over a certain length adjacent to its ends, whilst leaving it free on the side of its sockets or roots in such a way as to permit the hunting of the blades by bending of spar 2 and their pitch variation by its twisting.

#The cross-sectional shape of the root of each blade (FIG. 2) evolves progressively towards the centre of the rotor from the blade section itself to finally form a cylindrical revolution sleeve 7 or 8. This blade root portion in the form of a sleeve covers and is made integral by bonding with a flange 9 or 10 also having a cylindrical shape and each equipped with a circular rigidifying collar 11,41.