BLADE PITCH CONTROL

Abstract

A blade pitch adjustment system comprising a yoke arranged to be moved in a first direction in response to an actuator; a plurality of trunnion pins arranged to be attached to a respective propeller blade; a respective contact surface between the yoke and each trunnion pin such that movement of the yoke causes rotation of the blades, and wherein the contact surfaces differ so as to create different angles of rotation of the blades at different points of yoke movement or actuator stroke.

Claims

1. A blade pitch adjustment system comprising a yoke arranged to be moved along a first axis (A); a plurality of trunnion pins arranged to be attached to respective propeller blades; a respective contact surface between the yoke and each of the trunnion pins such that movement of the yoke along the first axis (A) results in rotation of the blades, and wherein the contact surfaces are configured such that as the yoke moves along the first axis (A) some or all of the blades are rotated to have an angle of rotation different from that of others of the blades.

2. The system of claim 1, wherein at least one contact surface has a characteristic different from other contact surfaces to give rise to the difference in rotation angle.

3. The system of claim 2, wherein the characteristic is a profile.

4. The system of claim 2, wherein the characteristic is an angle or orientation.

5. The system of claim 1, wherein all of the contact surfaces have a different configuration such that at any point of yoke movement all blades have a different angle of rotation.

6. The system of claim 1, wherein the contact surfaces for diametrically opposite blades are similarly configured, such that the diametrically opposite blades have substantially the same angle of rotation.

7. The system of claim 1, wherein the contact surfaces are defined on a surface of the yoke.

8. The system of claim 1, wherein the contact surfaces are defined on a surface of the trunnion pin(s).

9. The system of claim 1, wherein the contact surfaces are defined by one or more components (not shown) positioned between the yoke and the trunnion pin(s).

10. A propeller system comprising a plurality of blades and a blade pitch adjustment system as claimed in claim 1, the blade pitch adjustment system comprising a plurality of trunnion pins, wherein each trunnion pin is attached to a respective blade for rotation of the blade by movement of a yoke in the blade pitch adjustment system above.

11. The propeller system of claim 10, further comprising an actuator for causing movement of the yoke.

12. The system of claim 10, wherein the yoke forms a part of the actuator

13. The propeller system of claim 10, wherein the blades all have identical geometric characteristics.

14. The propeller system of claim 10, wherein the blades do not all have identical geometric characteristics.

Description

DRAWINGS

[0020] FIG. 1 is a perspective view of a pitch adjustment system.

[0021] FIG. 2A shows a contact surface of conventional systems.

[0022] FIG. 2B shows a contact surface of the present system.

[0023] FIG. 3 shows a relationship between actuator stroke and blade pitch for a conventional system.

[0024] FIG. 4 shows a desired pitch shift between blades.

[0025] FIG. 5 shows how the blade pitch shifts as the contact surface is translated for a given blade.

DETAILED DESCRIPTION

[0026] A conventional pitch change mechanism comprises each of a plurality of propeller blades attached to a yoke by means of a respective offset trunnion pin. An actuator, e.g. a hydraulic piston or the like is controlled to move the yoke to change the pitch of the blades. The trunnion pins are received by the yoke at one end and are attached to respective blades, offset from the blade axis, at the other end. As the yoke transits axially, due to the actuator, the trunnion pins are rotated in an arcuate manner to cause a pitch change in the blades. Because the trunnion pins are offset relative to the blade axes, axial movement of the yoke, caused by the actuator, results in rotation of the blades about a change axis or, in other words, a pitch change of the blades.

[0027] FIG. 1 shows the main components of a pitch adjustment system in which the present invention can be incorporated.

[0028] A propeller includes a plurality of blades 1 only one of which is partially shown in FIG. 1. The adjustment of the pitch of the blade is caused by movement of a yoke 2 in the direction of the arrow, due to operation of an actuator (not shown).

[0029] For each blade, a trunnion pin 3 is provided defining a contact surface between the yoke and the blade. The trunnion pin is offset relative to the axis of the blade and is connected to the yoke by means of a bearing assembly.

[0030] To adjust the pitch of the blade, the actuator (5) causes the yoke 2 to transit in the direction of the arrow A causing the blade to rotate and change its pitch.

[0031] During transition of the yoke 2, if the yoke rotates with the trunnion pins 3, there will be no relative movement at the contact surface between the yoke 2 and the pins 3. To avoid this problem it is known to provide the yoke with an anti-rotation device (not shown) also known as an anti-torque arm, to ensure the yoke does not rotate with the pins as it translates.

[0032] As mentioned above, in prior art systems, the contact surfaces between the yoke 2 and the trunnion pin 3 are essentially the same—i.e. the same ‘attack’ is made to all trunnion pins, and, hence, all blades during axial movement of the yoke as shown in FIG. 2A which causes the pitch of the blades to vary with respect to actuator stroke.

[0033] FIG. 3 shows a typical relationship between blade pitch or angle and actuator stroke. This relationship results from a surface contact between pin and the yoke which is planar and perpendicular to the axis A.

[0034] As mentioned above, there is a desire to reduce noise, and the system of this disclosure has been designed to achieve this by introducing a difference in pitch between different blades or sets of blades (for stability it is desireable for diametrically opposite blades to have substantially the same pitch but different from that of other pairs or sets of diametrically opposite blades). This is represented in the graph of FIG. 4.

[0035] To achieve this, the relationship of FIG. 3 needs to be adapted. In the present disclosure, this is done by changing the location of the contact point between the respective trunnion pins and the yoke.

[0036] In the present disclosure, the pitch of the blades can be made more individual by providing a different contact surface 4 between the yoke 2 and some or all of the trunnion pins 3, an example of which is shown in FIG. 2B.

[0037] In one example, a profile is machined into the surface of the yoke for contacting the trunnion pins at different positions of yoke transition. Other ways can be conceived of providing this profile, for example by providing a profiled plate or other component between the trunnion pins and the yoke. Alternatively (but not shown) the profile can be machined into the surface of the trunnion pins 3.

[0038] FIG. 5 shows how blade pitch shifts for an offset contact surface during actuator stroke.

[0039] Pitch angles are typically provided to manage propeller speed and power and can range from a so-called fully feathered minimum drag angle, to a pitch angle that provides reverse thrust.

[0040] During propeller reverse transition, there is a time where no torque is absorbed by the propeller blades. The zone associated with this time is known as the ‘keep out zone’. During this time zone, the propeller speed regulation with pitch variation is not possible and an engine fuel flow control needs to be implemented in order to avoid propeller overspeed.

[0041] The independent pitch angle adjustment mechanism of the present disclosure also results in the ability to suppress the keep out zone. Because the present disclosure allows each blade to have its pitch adjusted according to an individual function, not all blades need to be in the keep out zone at the same time when the propeller goes into reverse transition. It is possible, therefore, to have some blades consuming torque and power while the full reverse capability of the propeller is conserved.

[0042] Further advantages of the individual pitch adjustment capabilities of the present disclosure mean that the best aerodynamic compromise can be obtained for different flight conditions.