GB2308112A

GB2308112A - Helicopter rotor blade control

Info

Publication number: GB2308112A
Application number: GB9624317A
Authority: GB
Inventors: Stefan Schulze
Original assignee: Eurocopter Deutschland GmbH
Current assignee: Airbus Helicopters Deutschland GmbH
Priority date: 1995-12-15
Filing date: 1996-11-22
Publication date: 1997-06-18
Anticipated expiration: 2016-11-22
Also published as: ITMI962344A1; FR2742414B1; IT1287095B1; GB2308112B; DE19546929C2; DE19546929A1; ITMI962344A0; GB9624317D0; FR2742414A1

Description

1 2308112 Rotor Blade Control System. in particular for a Helicopter The

invention relates to a rotor blade control system, in particular for a helicopter and for mono- and bicyclic blade angle adjustment.

Some such blade control systems comprise a double swash plate arrangement with a monocyclic swash plate and a bicyclic swash plate, which is adjustable independently thereof so as to allow tilting movement relative to an axis fixed with respect to the housing, and at least one control lever pair pivotably interconnected in the is manner of an articulated triangle on one hand and to the swash plates on the other with an allocated control rod transmitting the control lever movement relative to the axis fixed with respect to the housing during rotation of the swash plate arrangement to the rotor in such a manner as to adjust the blade angle.

It is known that the necessary rotor power of a helicopter may be clearly reduced at high coefficients of propeller advance and that the noise development and oscillation behaviour of the rotor may be considerably improved, above all in the flight approach phase, by a higher harmonic blade angle control system. In such a system the greatest influence in this respect emanates from the second harmonic, i.e. the bicyclic blade angle control system (2/rev), which is particularly suitable 2 for effective reduction in the monocyclically varied blade angle in the areas of high loss.

Typically individual rotor blade control systems, in which a generally hydraulic actuator, which rotates with the rotor and is multiply activated per rotor revolution, is required to generate the multi-cyclic control movement, involve very high structural and energy expenditure.

However in the rotor blade control systems of the aforementioned type known from United States patent no.

3 144 908, there is included two independently adjustable swash plates and pairs of control levers is acting between the rotating swash plate parts which are respectively connected to the individual rotor blades via control rods connected to the common pivot point of the control lever pairs in such a manner as to adjust the blade angle.

This system generates a higher harmonic control movement variably composed from mono- and bicyclic movement components so that rotating hydraulic actuators working at high frequency are no longer necessary and the structural and energy expense is substantially reduced. However, such rotor blade control systems have the disadvantage that the resulting control curve has substantial distortions in relation to the second higher harmonic and the achievable bicyclic control movements are too small for 3 an effective improvement in power of the rotor.

Preferably the invention provides a rotor blade control system of the aforementioned type in a structurally simple way so as to permit generation of a higher harmonic control movement, which is substantially undistorted with respect to the pure sinusoidal form and comprises monoand bicyclic movement components which are variable within broad limits.

Accordingly, in a first aspect, the present invention provides a rotor blade control system, in particular for a helicopter, for monocyclic and bicyclic blade angle adjustment, comprising a double swash plate arrangement with a monocyclic swash plate and a bicyclic swash plate, which is adjustable independently thereof so as to allow tilting movement relative to an axis fixed with respect to the housing, and at least one control lever pair pivotably interconnected in the manner of an articulated triangle on one hand and to the swash plates on the other with an allocated control rod transmitting the control lever movement relative to the axis fixed with respect to the housing during rotation of the swash plate arrangement to the rotor in such a manner as to adjust the blade angle, wherein the control lever of the control lever pair (10, 14) connected to the monocyclic swash plate (4) is constructed as an angle lever (10) rotationally mounted in the vertex on the monocyclic swash plate (4) with a vertex angle of essentially 900, and the control rod 4 (18) is pivotably connected to the free lever arm (16) of the angle lever on the control lever pair side.

is Because of the special structure of the control mechanism with an angle lever instead of a linear guide rod and with the blade angle adjustment movement established at the free angle lever end, the kinematics of the rotor blade control system are changed in accordance with the invention such that a broad amplitude bandwidth and a virtually undistorted 2/rev sinusoidal form result with respect to the bicyclic movement components without there being any requirement in this case for hydraulic actuators operated at the bicyclic operating frequency involving high structural and energy expense. Therefore, a clear improvement in the power of the rotor may be achieved in a simple and energy-saving manner with the rotor blade control system according to the invention.

In a further advantageous configuration of the invention, the mutual axial distance between the swash plates is substantially smaller, preferably about fivetimes smaller than the radius of the monocyclic swash plate, as a result of which the changes in amplitude of the bicyclic movement components achievable at the output of the rotor blade control system on the control rod side are increased further and an even clearer improvement in power of the rotor is made possible.

As preferably when the two swash plates are in the non- tilted position relative to the axis fixed with respect to the housing, the control lever articulated at the bicyclic swash plate and the lever arm of the angle lever on the control rod side are essentially parallel to one another and respectively run in a perpendicular plane to the axis fixed with respect to the housing. This has the advantage that a purely monocyclic fundamental component may be achieved with the rotor blade control system according to the invention without bicyclic movement components.

The vertex angle of the angle lever is preferably slightly, i.e. about 5100, smaller than 900. As a result of this, even greater bicyclic control movements are possible. The resulting deviations from the pure sinusoidal oscillation are extremely small and therefore have no appreciable influence on the control curve.

In a further advantageous configuration of the invention, the multicyclic arrangement is combined with a collective blade angle control means so that the double swash plate arrangement is additionally adjustable in height relative to the axis fixed with respect to the housing.

In a particularly preferred manner, the control device for adjusting the tilt position of the bicyclic swash plate relative to the monocyclic swash plate is provided between the non-rotating parts of the two 6 swash plates. The monocyclic and bicyclic movement components can thus be adjusted independently of one another with respect to phase position and amplitude by separate control commands. It is recommended in this case to provide at least three control members acting between the swash plates through which the axial distance between the bicyclic and monocyclic swash plates may also be changed, as a result of which the application range of the rotor blade control system is extended to cases where, in addition to a purely sinusoidal higher harmonic, a control movement deviating purposefully from this is required.

Power-reinforcing hydraulic actuators operated by control commands are preferably used as control members for the individual adjustment of the tilt position of the monocyclic and the bicyclic swash plate.

The invention will now be explained in more detail on the basis of an example in conjunction with the drawings, wherein in schematic views:

Figure 1 shows the basic structure of a higher harmonic mechanical rotor blade control system with the two swash plates in the zero tilt position; Figure 2 shows a view corresponding to Figure 1 with the swash plate monocyclic and the bicyclic swash plate in different tilt positions; 7 Figure 3 is a diagram for illustration of the monocyclic (a), the bicyclic (b) and the higher harmonic control movement (c) resulting therefrom through linear combination; and Figure 4 in a more detailed view of the rotor blade control system with swash plates tilted differently relative to the axis fixed with respect to the housing.

The rotor blade control system shown in the figures includes a double swash plate arrangement 2 with a lower monocyclic swash plate 4 and an upper bicyclic swash plate 6 as well as a control lever pair 8 for each rotor blade, which acts in the manner of an articulated triangle between the swash plates 4, 6 and which comprises a 900 angle lever 10 rotatably mounted in the vertex on the monocyclic swash plate 4 and a control lever 14 pivotably connected to the bicyclic swash plate 6 on one side and to one angle lever arm 12 on the other side. The free end 30 of the other angle lever arm 16 is connected via a control rod 18 running essentially parallel to the axis A to the associated rotor blade (not shown) in such a manner as to adjust the blade angle.

The two swash plates 4 and 6 are adjustable in height coaxially to one another on a common axis A - the rotational axis of the rotor according to Figure 4 - 8 and are arranged so as to allow individual tilting movement depending on size and direction respectively via a universal or ball-type joint arrangement 20.1 or 20.2. Otherwise, each swash plate 4, 6 comprises in the usual manner a non-rotating part 4A and 6A respectively and a swash plate part 4B and 6B respectively rotating jointly with the control lever pairs 8 in synchronisation with the rotor around axis A. The synchronisation of the swash plate parts 4B and 6B with the rotor is effected by drivers 24 coupled to the rotor shaft 22, as shown in Figure 4.

For adjustment of the tilt angle and the tilt direction as well as the height position of the monocyclic swash plate 4 relative to the axis fixed with respect to the housing, three control members in the form of control command operated hydraulic actuators 26 (only two of which are shown in the figure) are provided, each acting between swash plate 4 and a support point fixed with respect to the housing. Independently of this, the tilt angle and tilt direction as well as possibly also the axial distance of the bicyclic swash plate 6 with respect to the monocyclic swash plate 4 are adjustable by means of two or three hydraulic actuators 28 acting between the two swash plates.

The distance between the swash plates in the direction of axis A is about five-times smaller than the radius of the monocyclic swash plate 6. The lengths of the lever arm 12 and the control lever 14 are selected so 9 that the lever arm 12 remains oriented parallel to the axis A when both swash plates 4 and 6 are tilted jointly and parallel to one another around their respective pivot point 20.1 and 20.2, i.e. the control lever 14 is as long as the difference in radius of the swash plates 4, 6 and the length of the angle lever arm 12 corresponds to the mutual distance between plates. The length ratio of the lever arms 16 and 12, by which the amplitude of the bicyclic movement components in the direction of the rotating control rod 18 is also influenced, amounts to about one in the shown embodiment.

So long as the two swash plates 4 and 6 remain oriented parallel to one another, the double plate arrangement 2 acts in each tilt and height position like a conventional swash plate control system with a purely monocyclic control movement of the rotating control rods 18 at the free lever arm end 30, whereby the angle lever arm 16 remains oriented essentially perpendicular to axis A. The curve of the monocyclic control movement, the phase position and amplitude of which are fixed by appropriate selection of the tilt angle and the tilt direction of the swash plate 4, is shown in Figure 3 in broken lines (curve a).

However, when the bicyclic swash plate 6 tilts relative to the monocyclic swash plate 4 (Figure 2), then the control lever pair 8 acts in such a way that the control lever 14 executes a swinging movement relative to the bicyclic swash plate 6 during rotation around the axis A fixed with respect to the housing in such a way that it is swung the most downwards at the high point of the swash plate 6 (right-hand portion of Figure 2) and is tilted the farthest upwards relative to the swash plate 6 at its low point (left-hand portion of Figure 2).

As a consequence, the angle lever 10 is additionally swung inwards relative to the monocyclic swash plate 4 by the control lever 14, and that is approximately as far at the high point of the bicyclic swash plate 6 as at the low point. This results in a bicyclic control movement of the free lever end 30, the amplitude and phase position of which are dependent on the selected tilt angle and the selected tilt position of the bicyclic swash plate relative to the monocyclic swash plate.

This bicyclic control movement, the curve of which is shown in Figure 3 in dot-dash lines (curve b), overlaps the monocyclic fundamental component a, and from the linear combination of the two oscillation components a and b the higher harmonic control movement c of the second order results which is transmitted via the control rod 16 to the corresponding rotor blade.

The higher harmonic control curve is adjusted by computer control over a characteristic diagram in which the optimum amplitudes and phase positions corresponding to the respective flight situation are stored. The position of the control column as well as data concerning flight position and speed are necessary as input quantities for this. The associated regulating distances of the hydraulic actuators are calculated from this. In order to permit exact regulation of the actuators, these are equipped with path recorders.

The bicyclic swinging movement of the angle lever 10 relative to the swash plate 4 may be increased by selecting the vertex angle of the angle lever 10 at about 5-100 less than 900 and extending the control lever 14 accordingly, as is shown in broken lines in Figure 1. While this results in the monocyclic control curve component deviating from the pure sinusoidal form, this deviation is so slight that its effect is barely noticeable.

As already mentioned, the two swash plates 4 and 6 may also be arranged so as to be adjustable in height independently of one another on axis A or the rotor shaft 22 as shown in Figure 4 and may be coupled to one another by more than two operating cylinders 28 so that the bicyclic swash plate 6 is not only variably adjustable with respect to the tilt angle and tilt direction but with respect to its axial distance relative to the monocyclic swash plate 4. This enables the curve of the control curve established at the free angle arm end 30 to be purposefully deformed in accordance with the plate distance adjusted via the 12 operating cylinders 28 in relation to the purely sinusoidal oscillation curve c shown in Figure 3.

13

Claims

PATENT CLAIMS:

1. Rotor blade control system, in particular for a helicopter, for monocyclic and bicyclic blade angle adjustment, comprising a double swash plate arrangement with a monocyclic swash plate and a bicyclic swash plate, which is adjustable independently thereof so as to allow tilting movement relative to an axis fixed with respect to the housing, and at least one control lever pair pivotably interconnected in the manner of an articulated triangle on one hand and to the swash plates on the other with an allocated control rod transmitting the control lever movement relative to the axis fixed with respect to the housing during rotation is of the swash plate arrangement to the rotor in such a manner as to adjust the blade angle, wherein the control lever of the control lever pair connected to the monocyclic swash plate is constructed as an angle lever rotationally mounted in the vertex on the monocyclic swash plate with a vertex angle of essentially 900, and the control rod is pivotably connected to the free lever arm of the angle lever on the control lever pair side.

2. Rotor blade control system according to Claim 1, wherein the mutual axial distance of the swash plates is substantially smaller than the radius of the monocyclic swash plate.

14

3. Rotor blade control system according to Claim 2, wherein the mutual axial distance of the swash plates is about five-times smaller than the radius of the monocyclic swash plate.

4. Rotor blade control system according to one of the preceding claims, wherein when the two swash plates are in the non-tilted position relative to the axis (A) fixed with respect to the housing, the control lever articulated at the bicyclic swash plate and the lever arm of the angle lever on the control rod side are essentially parallel to one another and respectively run in a perpendicular plane to the axis fixed with respect to the housing.

is

5. Rotor blade control system according to one of the preceding claims, wherein the vertex angle of the angle lever is slightly, i.e. about 5-100, smaller than 900.

6. Rotor blade control system according to one of the preceding claims, wherein the double swash plate arrangement is additionally adjustable in height relative to the axis (A) fixed with respect to the housing for collective blade angle adjustment.

7. Rotor blade control system according to one of the preceding claims, wherein for adjusting the tilt position of the bicyclic swash plate relative to the monocyclic swash plate, a control device (control members 28) acting between the non-rotating parts MA, is 6A) of the two swash plates is provided.

8. Rotor blade control system according to Claim 7, wherein the control device includes at least three control members acting between the swash plates through which the axial distance of the bicyclic swash plate relative to the monocyclic swash plate is variably adjustable.

9. Rotor blade control system according to Claim 7 or 8, wherein the control members are constructed as power-reinforcing hydraulic actuators.

10. A rotor blade control system substantially as any one embodiment herein described with reference to the accompanying drawings.