GB2464678A

GB2464678A - Twistable aircraft rotor blades

Info

Publication number: GB2464678A
Application number: GB0819223A
Authority: GB
Inventors: David Hostettler Wain
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-10-21
Filing date: 2008-10-21
Publication date: 2010-04-28
Anticipated expiration: 2028-10-21
Also published as: GB0819223D0; GB2464678B

Abstract

Twistable aircraft rotor blades (A) feature an inner circular rod (B) fixedly attached to the tip end of the blade (A), but with the blade (A) otherwise freely rotatable around the inner circular rod (B). The blade (A) is thus twistable, in a helical fashion, along its length, such as by a control bar arrangement (C,D) located at the root of the blade. The twisting arrangement may be under cyclical computer control to optimise the blade profile efficiency in the forward and / or return cycles of the blade, when the blades are used to provide lift in a helicopter main rotor.

Description

TWISTING ROTOR BLADES

This patent relates to a method of twisting rotor blades or propellers.

Many aircraft today still use rotor blades or propellers for powered flight. The most interesting example of this application is, of course, helicopters. Single rotor helicopters have a main large rotor near to the centre of gravity spinning on the horizontal plane and small fan in a vertical plane at the rear.

The main rotor accelerates air downwards to create lift and the rear fan counters the tendency of the body to spin. As the torque applied to the main rotor acts through the fuselage, the tail rotor reacts a counter torque to control the yaw.

The lift of the main rotor is controlled by two controls. The cyclic control controls the pitch and roll, basically like the joystick of a conventional aeroplane. The concentric pitch control controls the total amount of lift of the main rotor, and normally looks like a handbrake lever.

The cyclic and concentric pitch levers control a device called a swash plate, mounted just under the main rotor. The swash plate looks like a large washer, and its angle of tilt relative to the body is controlled by the cyclic pitch lever.

The elevation of the swash plate is controlled by the concentric pitch lever.

With most swash plates the bottom does not rotate, whereas the top of the swash plate rotates in-sync with the rotor blade. The swash plate is basically a flat bearing.

The top of the swash plate is connected to the blades so as to control their pitch.

The bottom of the swash plate Is connected to the control actuators. As the blades rotate, the "cyclic" angle of pitch of the blades changes, controlled by the "static" elevation and tilt of the swash plate.

During hovering, the tilt of the swash plate is basically horizontal, and the elevation of the swash plate determines whether the helicopter rises or falls.

During translational flight the swash plate is tilted, providing differential lift, thus pitching the body forwards, backwards or sideways.

However, for example, as a helicopter moves forward, the advancing blades generate more lift than retreating blades, thus causing the helicopter to roll.

Most early helicopters have hinged blade roots so that the advancing blade lags and rises above the horizontal plane, and the retreating blade "de-lags" and drops below the horizontal blade.

Using hinged rotors partially corrects the differential lift of the blades, automatically adjusting for the velocity of the blade through the air. Some more advanced helicopters have "rigid" blades, whereby automatic compensation of the swash plate depending on airspeed compensates the tendency of roll of the helicopter.

However, as the helicopter moves faster though the air, the roll effect becomes more pronounced. Since the tip of the advancing blade cannot break the sound barrier, the maximum speed of advanced helicopters is normally limited to about 250 miles-per-hour.

This is because the retreating blade still has to move fast enough though the air to generate sufficient lift (on the reverse traversal). Since the blades merely flex through the airflow, the optimum angle of the blades along their length cannot be achieved.

As the helicopter moves through the air, it may be seen that although the advancing blade's pitch generates lift, part of the retreating blade actually generates negative lift. The airspeed difference between the inner and outer parts of the blade causes inefficiency throughout the rotation because the pitch of the blades cannot compensate for this disparity.

According to the present invention there is provided a method for twisting rotor blades comprising an outer aerodynamic blade and an inner circular rod; the inner rod is attached rigidly to the tip rather than the root such that the root of the blade may be twisted relative to the tip of the blade.

A specific embodiment of the invention will now be described with reference to the drawings in which: Figure 1 shows the cross section of the blade root showing the pitch control levers, one connected to the rotor root, the other connected to the inner rod, which is in turn connected to the rotor tip.

Figure 2 shows the mast of a cyclic swash plate system (with two swash plates separated vertically for clarity) showing how the inner swash plate controls the rod connected to the tip of the rotor, and the outer swash plate controls the root of the rotor.

Figure 3 shows a "top-down" diagram that shows how the lift of the advancing blades is greater (or even opposite to) the lift of the retreating blades.

Figure 4 shows a graph or map of blade inclination of a cyclic swash plate system showing that the inner and outer pitch (thus lift) can be varied to an optimum configuration, especially at high speed.

The example shown is the simplest embodiment comprising an aerodynamic blade with a circular hole along its length. An inner rod is then inserted along its length such that the outer blade may rotate about the rod. The rod is then attached rigidly to the tip of the blade, rather than its root. Pitch control levers at the root of the blade may then be used to twist the blade along its length.

Since varying the twist of blades cyclically is the most useful application of this invention, a dual swash plate system is shown as the example. Both swash plates shown in figure 2 are exactly like normal swash plates, basically two giant rigid "washers", with a bearing between them. The top "washer" rotates in-sync with the blades whilst the bottom "washer" remains stationary relative to the body.

In the diagram, the swash plates are shown vertically separated for clarity. In any practical system both swash plates would probably spin within the same approximate plane since the method of "meshing" the upper "washers" to the rotors' rotation would be similar to most conventional systems.

The inner rod pitch levers (Figure 2 b) are attached by linkages to one of the swash plates and the outer blade pitch levers (Figure 2 e) are attached to the other plate. This allows not only the pitch of the blades to be varied cyclically, but also their twist.

Unlike most helicopters however, two sets of three actuators are required to control the lift, pitch and roll of both the inner and outer parts of the rotors. The actuators (not shown) would be attached to the bottom swash plate washers" in a similar arrangement as most conventional systems.

As the helicopter moves though the air, the advancing blade generates more lift than the retreating blade (Figure 3). Using the six actuators, both the pitch and twist of the blades may be altered. During fast forward flight, both the inner and outer pitch can be altered cyclically to reasonably optimum pitch.

Finally the six actuators are controlled by a flight control computer wherein the blade pitch map or model (which may vary according to other factors such as angle-of-attack, lift or altitude) is stored (Figure 4). The flight control system must be Flight Level 1 Safety Critical if the helicopter is to carry people.

Since the lift of the inner part of the blade and the outer part can be optimised separately during each cycle, the rate of rotation of the blades can be reduced, and therefore the maximum theoretical velocity of the helicopter may be increased before the effects differential lift or the sound barrier become noticeable.

Using the dual swash plate system, and subject to practical designs, pitch can even be reversed during part of the backward sweep, increasing lift and reducing the amount of bending or flexing of the blades due to aerodynamic or structural instability.

Of course, the forward swept blade is kept reasonably stable by the centrifugal forces of the blade rotating, but the amount of induced vibration should also be reduced by using twisting blades.

DIAGRAM KEY

Figure 1 a -the outer aerodynamic part of the blade b -the inner circular rod connected to the tip of the blade.

c -the blade root pitch lever d -the blade tip pitch lever Figure 2 a -the blades comprising an inner and outer part b -the blade tip pitch levers c -the blade tip connecting rods d -the blade tip swash plate e -the blade root pitch levers f -the blade root connecting rods g -the blade root swash plate Figure 3 a -the wind velocity b -the direction of rotation x -thexaxis y -theyaxis 8 -theta, the rotation angle of a blade Figure 4 a -the pitch angle or inclination b -forward traversal c -backward traversal d -the pitch of the blade tips e -the pitch of the blades roots 8 -theta, the rotation angle of a blade

S 55.5* * S

S 5S55 * * * 55 * S S * 5. 55.

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Claims

CLAIMS1. Twisting rotor blades comprising an outer aerodynamic blade and an inner circular rod; the inner rod is attached rigidly to the tip rather than the root such that the root of the blade may be twisted relative to the tip of the blade.
2. Twisting rotor blades as claimed in Claim 1 wherein the cyclic pitch and twist can be controlled by two swash plates attached to the inner and outer pitch levers.