FR2620106A1 - Light helicopter with two contrarotating rotors - Google Patents

Abstract

The invention relates to a single- or two-seat light helicopter, with two coaxial rotors, in which the mechanical system 7 providing the drive to the two rotors 1, 2 in opposite directions is placed at the level of the rotor hubs at the peak of a non-rotating structural mast 8. It includes one or two engines 5, specific, simplified flight controls and a lightened gyroscopic stabiliser 9. The mast may be folded for storage or towing on the road. This helicopter can be produced economically, and is intended for leisure, for sport, for flying schools, for aeriel surveillance and for light aircraft tasks.

Description

 Helicopters today have a high level of percussion, technology and safety, which makes them suitable for missions inaccessible to other types of aircraft, but also brings them to a complexity and a price such as flight in helicopter remains out of reach of the individual.

 I1 still misses the low-end, that is to say the very small helicopter, which would be to others what L'FILM is to conventional aircraft, and would make helicopter flight accessible to the greatest number.

 Such a device should be extremely light and simple, offer with minimal motorization performance, perhaps limited in speed, but high in stationary to have good margins of maneuver, and present maximum safety in use: ease of piloting, wide possibility of autorotation, if necessary installation of two motors. In addition, it must be easy to maintain, transport and park. And this, for a purchase price much lower than that of the helicopters currently available, say of the order of magnitude of that of a large car.

 The present invention provides a set of technical solutions, which should make it possible to fill this gap. Starting from the well-known type of helicopters with 2 counter-rotating coaxial rotors, it is based on a new architecture, which integrates the main reduction system into all of the rotor hubs, retaining a non-rotating structural mat up to the level of these rotors. From this provision flow a number of advantages, set out below, leading to simplifications of the structure and flight controls, to increased safety and to economic construction, which should make it possible to achieve the aim sought.

 The configuration with 2 counter-rotating rotors was chosen first for its performance and safety. It is known that the majority of current helicopters comprises a single main rotor, which requires to maintain the orientation of the fuselage an auxiliary rotor, said anticouple, placed at the end of the tail. This rotor does not participate in the lift, but nevertheless consumes 5 to 10% of the power, depending on the flight case.

 The 2 counter-rotating coaxial rotors provide an elegant solution to the problem: the couples compensate themselves naturally, without loss of power. In addition, it is acquired that the aerodynamic efficiency is a little better than for a single rotor, because there is in particular no energy dissipation by setting in rotation the flow of alr passing through the rotors. In addition, the absence of tail rotor simplifies the design and the development, and in the evolutions near the ground facilitates piloting and improves safety.

 Many coaxial helicopters have flown perfectly well.

However, the complexity of the rotor drive by two concentric shafts, and the blade pitch control system doubled at the rotors, did not allow them to impose themselves on the markets.

 However, in the case of light helicopters of relatively low power, it is now possible to design speed reduction systems, driving the rotors in the opposite direction, very compact and light. It is then possible to integrate this system with all of the rotor hubs, which allows it to be mounted directly on top of a non-rotating mast.

 We will show later how this new design makes it possible to simplify the structure, the mechanical architecture, the flight controls, and even to install a lightened and simplified gyro stabilizer. But what stands out first is the mechanical simplification, the lightening and the increased safety brought by the direct mounting of the rotors on the structure, without the intermediary of rotating shafts subjected to rotary fatigue, which will constitute a essential quality for these devices.

 This overall architecture appears clearly in Figure 1, which shows seen from the left the main elements of a device built according to this design: The coaxial rotors 1 and 2, rotating in opposite directions, are mounted on top of the non-rotating structural mat 8, by suitable bearing arrangements. The motor 5 drives by the transmission shaft 101st speed reduction system 7 placed at the level of the rotors and driving them in the opposite direction.

 Said rotors are controlled in general step and in cyclic step respectively from the general step lever 3 and the cyclic stick 4, as usual on helicopters, with the possible assistance of a gyroscopic stabilizer 9.

 It is clear that this arrangement seems today well suited and valid for helicopters of the targeted category, that is to say of small size and low power, say 1 to 2 places and less than 100 kW as an order of magnitude.

 It could no longer be for larger devices, due to the rapid increase in size and weight of the reducing system, although, technically, nothing prevents in the future an evolution towards heavier devices. The basis of the invention would then remain valid, although we only describe here light helicopters.

 The design of the reducing system, light and compact, is important for the validity of the invention. We give below the principle of a particular realization, which seems well adapted to the problem posed. Based on belt drives, it will also be relatively silent. It should be noted, however, that it is possible to design many other systems, based on transmissions with gears, chains, rollers, belts of all kinds, with different arrangements.

 It is obvious that any other embodiment, as long as it fulfills the same functions under similar or even better conditions of weight and size, does not depart from the scope of the invention.

 FIG. 2 shows the principle of this particular embodiment: the axial primary transmission shaft 10 drives by the belt 11 an eccentric relay shaft 12, carrying at its ends the pulleys 13 and 14.

 The pulley 13 drives the drum 16 by the belt 15, in the sers of the shaft. The pulley 14 drives the belt 17, but the latter is returned by rollers 18, so as to be applied by its external face to the drum 19, 1 'thus driving in the opposite direction to the shaft.

 The drums 16 and 19 are each secured to a rotor hub, as shown in FIG. 3, which represents a possibility of producing a complete rotor head, including the conventional blade pitch controls by swash plate.

 We can see the axial transmission shaft 10, driving the relay shaft 12 carrying the pulleys 13 and 14, and the belts 15 and 17 which drive the drums 16 and 19 respectively. The hub 21 secured to the drum 16 drives the blades 23 in the direction of the shaft 12. The hub 22 secured to the drum 19 drives the blades 24 in the opposite direction to the shaft 12.

 The flight controls, in general step and in cyclic step, are carried out in the usual way by a double swash plate 25, mounted on a ball joint 26 which can itself slide axially on the fixed body 20. The position of the plate, in altltude and in inclination, is controlled from the pitch lever 3 and the cyclic stick 4 by three connecting rods 27 (only one is shown). The rotating parts 28 and 29 respectively control the pitch of the blades 23 of the upper rotor and of the blades 24 of the lower rotor, by appropriate linkages.

 These controls are entirely conventional, and do not form part of the invention, the essential characteristic of which consists in the presence at the level of the rotors of a non-rotating structural body 20, on which the hubs 21 and 21 are mounted directly in rotation. 22, and a transmission shaft 10 rotating at a speed much higher than that of the rotors1 which it drives by an integrated reduction gear 7.

 The invention does not prejudge either the embodiment of the hubs 21 and 22 themselves, or the number of blades which can be 2 or 3 per rotor depending on the qualities that are sought. It is known that the blades of helicopters are in principle connected to the hub by 3 articulations: pitch, flapping, drag, which allow the control of the lift and the inclination of the rotor. But recent rotors, called "rigid", do without one or two, or even all these joints, replacing them with flexible connections using modern materials. The two-bladed hubs are also usually mounted on a pendulum. All these provisions are valid, as long as they accommodate mounting on the drums, and, at least for the lower rotor, the presence in the central region of the non-rotating body 20.

 I1 should also be noted that the primary shaft 10 is not necessarily axial, and that then there may be several. Figure 4, where for clarity has not been shown the upper stage of the pulleys 13 and drum 16, shows such an arrangement of 2 eccentric primary shafts 10a and 10b. They each drive a relay shaft 12a and 12b, and the pulleys 14a and 14b, in turn driving the belts 17a and 17b, returned and stretched by the rollers 18a and 18b.

 Such an arrangement essentially makes it possible to double the power transmitted to this stage, in practically the same size, but it is also well suited to a twin-engine device. It also brings another advantage, in terms of flight controls, which will be explained below.

 We will first show a first important possibility of simplifying flight controls, which immediately emerges from the new provision brought by the invention.

 Indeed, if it is difficult to avoid the command in general steps, which remains essential on the one hand for the precision of the maneuvers close to the ground, on the other hand for the autorotation in the event of engine failure, where it is necessary quickly reduce the pitch to approximately 2 ", we can eliminate the cyclic tilt tilt controls, as we have seen quite complex, and obtain the same functions by direct tilting of the rotor head assembly.

 This type of control is not possible for devices with rotating rotor shafts, which all include cyclic controls.

On the other hand, a rotor with its blades presents a little the behavior of a gyroscope: it is necessary to exert a significant effort to move it, and it responds initially to 90 "of the wanted direction, which is annoying for the However, in the case of 2 counter-rotating rotors, the gyroscopic effects compensate for each other from one rotor to the other. There only remains the mass inertia effects, which in the case of small rotors remain very acceptable.

 In the context of the invention, it is sufficient to articulate the upper part of the non-rotating mast 20, which supports the hub and reduction unit, on the fixed lower part by two crossed articulations forming a cardan joint and allowing the longitudinal and lateral tilting of all. The transmission shaft 10 must naturally have a universal joint at the same level.

 FIG. 5 represents a possible embodiment of the tilting control. We have only shown the lower part of the body 20, which ends in a fork articulated around the axis AA on an intermediate fork 25, itself articulated around the axis BB on the fixed lower part 26 of the mast.

 The cyclic handle 4 controls by the connecting rod 27, the relay 28 and the connecting rod 29 the longitudinal tilting of the body 20, and therefore of all the rotor hubs and blades, in the same direction. By rotation of the shaft 30, it controls by the lever 31 and the connecting rod 32 the lateral tilting of the fork 25, driving the body 20, in the same direction.

 The transmission shaft 10 has, in the vicinity of the intersection of the axes AA and BB, a universal universal joint 33 allowing the angular displacement of the upper part of the shaft, linked to the body 20, relative to the lower part linked to the structure. .

 The whole of the body 20, of the reduction gear 7 and of the rotors thus follows the movements of the handle 4, performing the same flight control functions as the usual cyclic controls on conventional helicopters.

 It is clear that these various joints have limited deflections, and can be produced both by smooth joints or with bearings as by flexible connections, based on rubber sleeves, for example, or of steel-rubber laminates, or of flexible blades, as long as the arrangement is such that it allows tilting of the assembly in both directions, without allowing rotation.

 It is still possible to simplify and lighten this assembly, by replacing the handle 4 and its connecting rods by a simple lever, or a trapezoid, 34, directly attached to the tilting body 20.

 FIG. 6 represents an assembly having the same functions as that of FIG. 5, with a different arrangement of the axes AA and BB.

The handle 4 and all of its connections to the rotor head are eliminated. The trapezoid 34, whose horizontal bar 35 is within the reach of the pilot, directly ensures the tilting in both directions of the body 20 of which it is integral.

 Note the attractive simplification provided by this arrangement.

However the movements of the trapezoid are reversed at the pilot level (pull to go forward, push left to tilt right).

Piloting is similar to that of a glider or a pendular LZM with delta wing, and with learning will also be instinctive. We nevertheless believe that this type of piloting should be reserved for the lightest and single-seaters.

 Another type of simplification can be obtained, when two eccentric drive shafts 10 are available, as indicated above, they can then replace the control rods 29 and 32.

 FIG. 7 shows one possible embodiment, among others, for a single-engine apparatus. The tilting body 20 is mounted on the fixed mast 26 by an intermediate spider 25 with 2 axes AA and BB. The shafts 10a and 10b are placed behind the axis BB, and on either side of the axis AA. They have universal joints 33a and 33b at these axes, and also universal joints 36a and 36b connecting them at their lower part to the drive pulleys 37a and 37b. These pulleys are mounted rotating on a triangular frame 38, as well as the motor pinion 39 which drives them by the belt 40. The pinion 39 is driven by the motor 5 via a universal joint 41, which allows to the frame 38 to tilt in all directions.

 The cyclic handle 4, inclined longitudinally, drives by the relay 42 the links 43 and 44 in the same direction, the frame 38 then simultaneously moving the shafts 10a and 10b which, acting as connecting rods, tilt the body 20 longitudinally. Laterally, the handle 4 causes the rods 43 and 44 to rotate in opposite directions by rotation of the shaft 30, as do the shafts 10a and 10b which then cause the lateral inclination of the body 20. It can be seen that this arrangement provides control conventional, while reducing the number of connecting elements to the rotor head, the shafts 10 providing the 2 functions of mechanical drive and control rods.

 This arrangement is still valid when the apparatus comprises 2 motors each driving one of the shafts 10. The frame 38 is then replaced by 2 simple frames each carrying a motor pinion and a receiving pulley, and provided at the motors with a single articulation allowing the longitudinal tilting under the action of one of the rods 43 or 44. The operation remains identical.

 It goes without saying that a helicopter according to the invention, which does not have an anti-torque rotor, will have to use for the control of orientation of the fuselage from the pedals one or a combination of means such as general differential step on the 2 rotors, braking on one or the other of the rotors, or orientation of a profiled surface in the air flow passing through the rotors. These means are not new, and although necessary and perhaps easier to install, are not an integral part of the invention.

 On the other hand, there remains a piloting difficulty, to which the arrangement presented makes it possible to provide a light and elegant solution.

 I1 is known that by nature the helicopter is dynamically unstable, that is to say that in the absence of pilot reaction, the device takes rocking movements, in longitudinal and lateral, which are amplified . For heavy aircraft, it is not very annoying, because the movements are slow, the amplification rates low, and a pilot a little trained controls them easily. But the smaller the aircraft, the faster their reactions, and the more difficult the pilot's task becomes.

 The remedies are well known, and of two kinds. First, you need to keep relatively heavy blades, which have the property of slowing down the oscillating movements, and make piloting easier. The solution chosen for medium aircraft, in principle 4-5 seats or more. Then, use the properties of a gyroscope which, tending to keep a fixed position in space, and acting on the cyclic control of the rotor, can stabilize it completely.

 But it must also be able to maneuver, and this gyroscope must be slaved to the control position, that is to say that it must obey the orders of the pilot and arrive at the desired position, with a delay certaln giving the device a sufficient stability, but with sufficient speed and precision for good handling.

 The HILLER and BELL stabilizer bars, in the public domain for a long time, still used on these devices and on all flying models of helicopters, proceed from this principle: they act as a gyroscope, and are slaved to the cyclic control by aerodynamic surfaces or shock absorbers. But they rotate with the rotors, and are only applied to two-blade monorotors. They are not suitable for our devices, which require a system that can control the 2 rotors, and very light.

 However, everyone knows that the efficiency of a gyroscope depends on its inertia and its speed of rotation, and therefore that the faster it is, the more it can be lightened. In the system according to the invention, the presence at the level of the rotors of the drive shaft 10 (see fig 2) rotating at high speed precisely favors the installation of a fast gyroscope, and in combination with a simple method of 'servo control by spherical friction, should allow the realization of a light stabilizer suitable for the type of device.

 FIG. 8 shows a particular embodiment of this gyroscopic stabilizer, adapted to the mode of control by tilting of the body 20, described above. The gyroscope 50 has at its center a spherical ball joint 51, held axially and driven in rotation by a hollow spherical sleeve 52, comprising friction parts 53, kept applied to the ball joint with a defined tightening, by circular springs 54, the sleeve 52 comprising slots and flexibilities adapted to this purpose. Mounted rotating on the body 20, by a roller or needle bearing allowing axial movement, the sleeve 52 is rotated by the end of the shaft 10 provided with grooves.

 We can verify theoretically and practically that when the axis of rotation of the gyroscope makes an angular difference with the axis of rotation of the sleeve, it develops between the spherical surfaces of the ball joint and of the sleeve friction forces, which exert on the ball joint moment, whose orientation and direction are such that the axis of the gyroscope is brought directly to the axis of the sleeve, with a speed which depends directly on the friction forces, and vice versa of the angular moment of the gyroscope. This is called a slaving of the gyroscope to the control, materialized by the position of the body 20.

 The gyroscope 50 angularly drives, by the bearing 56, a non-rotating ring 57, which, by 3 connecting rods 58, controls the movements of the double swash plate 25, already seen in FIG. 2, which controls the pitch of the blades 23 and 24 of the rotors. The plate 25 is no longer controlled by the connecting rods 27, and the general pitch acts by the connecting rod 55 on a lever 59 which defines the height position of the sleeve 52 by a roller 60 engaged in a groove formed on the rod of the sleeve.

 The operation is then as follows: in general, the connecting rod 55 causes the sleeve 52, the gyroscope 50, to move vertically with the plate 25, acting on the 2 rotors. For the longitudinal and lateral tilting commands, the body 20 is tilted as seen previously.

At the start, the gyroscope remaining fixed in space, also keeps fixed there the axis of the rotors, by the cyclic controls 58 and 25. Pulls the servo by spherical friction brings back the axis of the gyroscope and the axis of the rotors on the axis of the body 20, with the delay and the speed provided to obtain the desired stability and maneuverability.

 We therefore obtained a stabilizer, lightened due to the rapid rotation of the gyroscope, with a simple servo, however retaining many adjustment parameters for adjustment and focusing.

 The arrangement of Figure 8 is only one possibility among others. In the case where the body 20 is not articulated on the lower part 26 of the mast, it is possible in particular to envisage directly controlling the inclination of the sleeve 52 from the handle 4, and these will be the rotors, controlled cyclically by the gyroscope 50, which will cause the body 20 and the device to tip over. One can also drive the sleeve from eccentric shafts 10a and 10b, or even provide a possibility of direct addition of the displacements of the connecting rod 55 and connecting rods 58, which would avoid the vertical displacements of the gyroscope.

 All these arrangements remain valid within the framework of the invention, the essential character of which is the presence of a gyroscope controlling the position of the rotors, driven at a speed of rotation much higher than that of the rotors and slaved to the tilt control. by the frictions developed between male and female spherical elements in contact.

 Finally, it is not enough that this type of device is simple, light, easy to control, it is also necessary that the user can use it conveniently, that is to say arrange it according to his needs, move it easily on the ground, transport it and easily bring it to work, and also park it in a reduced space and have easy access to all the components for routine checks and maintenance.

 However, the basic design of the invention of a non-rotating structural mast supporting the rotors at its top makes it possible to obtain all this almost from the start and almost free of charge.

 Consider an apparatus comprising a mechanical-rotor assembly produced according to the principle of FIG. 7. FIGS. 9, representing the main parts of such an apparatus in flight condition, and 10, showing the same in transport or garage configuration, show that by articulating the base of the mast 26 on the structure, and taking care to give the articulated segments of the shafts 10 and the mast 26 suitable lengths and freedoms of travel, it is possible to fold the entire upper part forward .

 If in addition the blades 23-24 are easily removable, the tail 61 foldable or removable, and the fuselage 62 organized to receive them and equipped with a wheeled train 63, a compact, mobile, folded assembly is obtained, which can if necessary be towed on the road, easily accommodated in a garage and putting all the essential organs close at hand.

 More generally, all types of apparatus belonging to the invention are capable of being folded up. It is necessary to equip the mast, the shafts 10, the control rods such as 29 or 32, with transverse or universal articulations, at their top and at their base, and arrange them so as to allow compatible movement of the various segments, the simpler being to construct articulated parallelograms.

Certain commands, of general pitch and of direction in particular, can be carried out by cables or flexible commands in sheaths, which can deform during folding.

 The mast 26 is maintained in the flight position by flexible stays 64 and 65 connecting it to the structure. The rear shrouds 65 comprise a disconnection means 66 and a mechanical or elastic tensioning member 67, facilitating their release and their replacement. The mast can also be connected to the structure by rigid struts, which can be dismantled at one end, serving the same purpose as the shrouds.

 It should be noted that not only do the shrouds provide the structure with a stiffening favorable to its lightening, but that they also allow adjustment of the longitudinal position of the mast. They can be returned to the fuselage by pulleys 68 or guides 69 and connected to a rack 70 for example, the movement of which is controlled by a toothed pinion actuated by a flywheel 71 within reach of the pilot.

 This possibility of adjustment, commonly called "centering control", is very useful on a small device, because by acting on the distance from the axis of the rotors to the center of gravity of the device, it makes it possible to adjust the attitude depending on the weight and position of the pilot, whose influence becomes relatively very important.

 Thus, it appears that the devices built according to the methods of the invention should meet the technical criteria set out in the preamble for the design of very light helicopters. The performance that we can ask them, dependent on a motorization which cannot be increased too much, will remain modest in speed, but should reach a relatively good level in carried load, due to the good performance of the chosen configuration and the reduction of the empty mass that should be brought by the proposed simplifications and the progress still to be made during the study.

 The scope of the invention and its various variants covers a whole range of aircraft, from the ultralight single-seat amateur with pendulum control, to the twin-engine twin cockpit offering all the qualities of a modern helicopter.

 The equipment that these devices will be able to receive: wheeled, skates, skis, floats train, equipment for transporting loads, agricultural treatment, will make them suitable for multiple tasks: flight school, walk, forest surveillance, maritime, power lines, aerial photography, transport in difficult areas, agricultural treatments on small areas, and many others.

 These light, reliable, high-performance helicopters, pleasant to fly, easy to move, to park, inexpensive to buy and maintain, will always find many applications which should open up a large market to them.

Claims (7)

 1) Light helicopter, with one or two cockpits, comprising two counter-rotating coaxial rotors (1,2) controlled in general and cyclic steps by a swash plate (25) from the general step lever (3) and the cyclic stick (4), driven by at least one motor (5) by a transmission (10) with clutch, freewheel, brake, and a speed reduction system (7) driving the rotors in opposite directions, characterized in that said speed reduction system is placed at the level of the rotor hubs, that is to say that there is a non-rotating structural mast extending up to the said rotors and carrying at its upper part said reduction system (7) integrated at the level of the hubs, and at least one power transmission shaft (10) substantially parallel to the mast and rotating at a speed greater than that of the rotors.  2) A particular configuration of the reduction system (7) driving the two rotors in opposite directions according to claim 1, characterized in that, each of the rotor hubs (21) and (22) being respectively secured to a drum (16) and (19), said drums are driven by one or more external relay shafts (12) by belts or chains, one of the belts (15) driving its drum (16) by its internal face, the other belt (17 ) driving its drum (19) in the opposite direction by its external face after passing over idler rollers (18), said relay shafts (12) being themselves driven by the axial transmission shaft (10) or by several shafts ( lOa, lOb) non-axial.  3) A particular embodiment of the flight controls of an aircraft according to claim 1, characterized in that the longitudinal and lateral tilt control of the rotors is achieved by the overall tilting of the upper part (20) of the mast carrying the reduction system and the two rotors, tilting on the fixed lower part (26) by a link with two crossed axes, of the articulated or flexible type, this tilting being controlled either by connecting rods connected to the cyclic handle (4), or by a lever (34, 35) integral with the body (90) and actuated directly by the pilot, the transmission shafts (10) comprising, at the level of the articulated connection of the masts, universal cardan joints.  4) A particular configuration of the flight controls of an aircraft according to claims 1, 2 and 3, characterized in that the speed reduction system (7) comprises two transmission shafts (10a, 10b) eccentric but not arranged in the same plane diametral, and that the longitudinal and lateral inclination controls of the rotors are obtained by the axial displacement of these shafts provided with cardan joints at both ends, these displacements being controlled from the handle (4).  5) A gyroscopic flight stabilizer for an apparatus according to claim 1, or according to claims 1, 2, 3 and 4, characterized in that the gyroscope (50) rotated at a speed greater than that of the rotors is controlled by the position of the rotor tilt control, from the handle (4) or the direct lever (34-35), by the friction forces developed between two spherical rotating surfaces integral one of the gyroscope, the other a rotary element (52) whose axis materializes the position of the imposed tilt control, and controls the attitude of the rotors by means of a plate (25) for cyclic control of the pitch of the blades1 in addition to the general pitch control controlled by the pitch lever (3).  6) A configuration of an apparatus according to claims 1 and 3, or 1, 3 and 4, characterized in that the structural mast (20) or (26) is provided at the base with a hinge arranged so as to allow its folding back onto the fuselage, said mast being maintained in the flight position by flexible or rigid fuselage connection elements (64, 65), some of which have disconnection means (66) and for putting into flight (6 /), the other elements joining the structure to the rotor head, such as the transmission shafts or the flight controls being either flexible, or also articulated at both ends and arranged to allow the mast to be folded back, and the fuselage can be designed to receive the blades and the tail, provided for this purpose with disassembly means.  7) A device for adjusting the longitudinal flight attitude of an aircraft according to claim 6, characterized in that the elements holding the structural mast in the flight position comprise means for longitudinal adjustment of this position, available to the pilot.