Swashplate (aeronautics)

The swash plate is an essential control element of the helicopter, which transfers the solid hull, and linear control inputs to the rotor, i.e., the rotating rotor blades. The swash plate is made of a rotating and a fixed part. It is mounted to the rotor mast, can be displaced axially to the rotor mast and cross- tend to the rotor mast. The term swash plate due to the fact that the upper, rotating with the rotor part with a wobbling movement of the inclination is.

It serves on the one hand to the collective pitch, ie the change of the angle of incidence of all the main rotor blades and therefore of lift, and the other part of the cyclic pitch control to control the lateral and longitudinal movement.

Flight and control of the helicopter

A helicopter hovers and moves as a rotorcraft by the lift and thrust of the main rotor. This is in the aerodynamic sense, a wing, which rotates around the rotor mast and within certain limits mechanical ( impact and pivot joints ) or is elastically movable. The helicopter flies in any direction by a corresponding inclination of the rotor plane (assumed surface on which the blades rotate ). The rotor generates lift to support the helicopter. It also generates due to the inclination of the thrust for a horizontal movement.

With the collective pitch, the pitch, the pilot changed the pitch of all rotor blades evenly, resulting in the rise or fall of the helicopter. With the cyclic control, the setting angle of the blades to be changed during the rotation of the rotor ( cyclic), and thereby flow is different. The viability of each rotor blade thus varies during its orbit. By changing the aerodynamic lift and the lifting or lowering of the rotor blades per revolution the rotor plane is in the desired tilt to the side (roll ) or brought to front / rear ( Nick ).

For the collective and cyclic pitch of the helicopter has separate control organs. For the collective control of the pitch, which is operated by the pilot with the left hand serves. For the cyclic control of the stick, which is operated with the right hand is.

In the system of the swash plate both control inputs are mixed and transfer the desired employments of the airfoil about lifting, lowering or tilting of the swash plate by the collective stick to the individual rotor blades rotating.

Description example Bölkow Bo 105

The swash plate of a Bölkow Bo 105 is composed of two via a ball bearing ring against each rotatable annular parts, referred to as image co-rotating and stationary. Both parts are in turn movable about a gimbal ( ball- joint bearings) mounted on the sliding sleeve, which allows a tilting of the unit from the horizontal up to ± 10 °. Furthermore, the complete unit can be displaced on the sliding sleeve on the gear fixed to the rotor support sleeve up and down the mast by approximately ± 30 mm. The interior of the support sleeve of the rotor mast, the middle largely by the swash plate, at the upper end carries the flange for fixing the rotor head running. The upper co-rotating ring of the swashplate is connected to the driving lever to the rotor flange joint, thus making the rotation of the rotor. The joints in the lever while allowing the inclination and the axial up and sliding of the swash plate.

The collective control rod moves the swash plate axial, depending on the movement of the pitch by the pilot up or down. The cyclic control rods put on the differential lever, the inclination of a swash plate depending on the control of movement in the longitudinal direction and / or transverse direction of the sticks. The differential lever mounted on the sliding sleeve ensure that cyclic and collective control inputs do not affect each other. In the axial displacement of the center pivot point of the differential lever goes with; the cyclic setting is not changed.

From the co-rotating ring of the swashplate outer lead the Blattverstellstangen to Blattverstellhebeln to adjust the angle of the rotor blade. Axial displacement of the swash plate and the Blattverstellstangen thus produces an equal angular adjustment of all blades. An inclination of the swash plate produces a different angular setting on each rotor blade, as Blattverstellstangen pulled on one side according to the slope, and are pushed onto the other side upward. As the rotor rotates then the angular adjustment of the rotor blade changing periodically depending circulation of his prescribed by the inclination of the swash plate minimum to the maximum value.

Animations

• Click on image

Cyclic control

Raised the collective control

Inclination of the swash plate and the rotor plane

The movement of a helicopter, according to forward or backward (pitch ) or to the left or to the right ( roll) is initiated by a corresponding inclination of the rotor plane.

So that the plane of the rotor for example at the control input " rollers to the right" also tends to the right, the corresponding rotor blade that is in the sideways tilt of the rotor exactly at the right side in the lateral axis to the lowest point in the plane of the rotor is running, it has been be controlled well before reaching the transverse axis. This is caused by the inertia of the rotor blades and the aerodynamic effect structure. The angle between the driving point and the actual point of action in the rotor plane is called flow angle, and is a function of the model helicopter is between 70 ° and 80 °. The direction of inclination of the swash plate is thus not the same as the inclination direction of the rotor plane and the desired direction of flight. Is the flow angle of the rotor structure due, for example, 78 ° (as in Bo 105), they must at the control input " rollers to the right" will be driven forward and backward running blades already 78 ° before reaching the transverse axis.

The diagram illustrates this with the example of a two-bladed main rotor counterclockwise with a design-related lead angle of 78 °. The backward -going rotor blade (light green) is activated shortly after passing through the longitudinal axis with the required maximum positive angle of attack. This gives it more lift and increases until it reaches the transverse axis to the highest point of the rotor plane. At the same time the forward -going rotor blade (light blue) is already activated shortly after passing through the longitudinal axis with the required maximum negative angle of attack. Thus, the buoyancy is reduced, or even generated output, such that the current to the front rotor blade decreases to reach the transverse axis to the lowest point of the rotor plane. The rotor plane tilts by right. These movements are limited by the flapping hinge or the elasticity of the rotor blade.

Meanwhile, the swash plate, the rotor blades, which are now on the transverse axis, driven so that they momentarily are in the zero position. The further back current rotor blade (light green) with less angle controlled so that it short after passing through the longitudinal axis reaches the maximum required negative angle of attack, while the forward -going rotor blade (light blue) is driven so that it shortly after passing longitudinal axis reaches the maximum required positive angle of attack. This is repeated cyclically at each rotor blade circulation. Finally, the helicopter airframe of the movement of the rotor plane follows, and the helicopter flies laterally to the right.

Development

The construction of the swash plate 105 Bo presented originates from the year 1964. Basically, nothing much has changed in the present state of the art, as the picture shows the example of EC 155. The mixture of collective and cyclic control is done here only elsewhere in the control linkage and not, as in Bo 105 by the differential lever directly on the sliding sleeve.

As in the wing aircraft already state of the art also includes helicopters in the fly- by-wire the future. This means the electronic control via data lines without mechanical connections such as control rods, and thus no mechanical connection to the swash plate. In order to refrain entirely on the swash plate, but further techniques are still needed.

So the manufacturer ZF electrically adjustable in length Blattverstellstangen ( IBC = Individual Blade Control) has developed, which shorten during circulation to electronic signals out or lengthen and so make the setting and angles of the rotor blades. The system was tested by NASA in the wind tunnel and tested since 2006 in Germany at the WTD 61 in Manching on a CH- 53G and in the U.S. on a Sikorsky UH -60 helicopter.