Helicopter rotor

The main rotor, the two or more sheets of a helicopter dynamic system component, which ensures through its rotation around the rotor axis and the lift by the cyclic change of the angle of attack of the rotor blades the steering and propulsion. The main rotor is basically composed of the rotor shaft ( 1), the swash plate (2), the control rods ( 4 and 10), the rotor head to the rotor hub (6), the rotor blade holders with the pivots (7) and the blades (9).

Note: All figures mentioned in this article in brackets refer to the legend in the graph on

2.1 reverse thrust on the tail boom 2.1.1 tail rotor configuration
2.1.2 No- Tail - Rotor System

2.2.1 Tandem configuration
2.2.2 Transverse rotors
2.2.3 Flettner rotor double
2.2.4 coaxial rotor

3.1 rotor shaft
3.2 swashplate
3.3 Control rods
3.4 rotor head rotor hub 3.4.1 Fully movable rotor system
3.4.2 Joint Loose rotor system
3.4.3 Rigid Rotor System
3.4.4 Semi-rigid rotor system

3.5.1 materials
3.5.2 rotor blade shapes
3.5.3 airfoils

4.1 Dynamic lift
4.2 rotor blade flow
4.3 efficiency

Terms

Chord

The chord line is the imaginary line connecting the leading edge and the trailing edge for balanced and unbalanced rotor blade profiles.

Skeleton line

The skeleton line is a measure of the curvature of the profile with asymmetrical blade profiles. This is obtained by circles are drawn in the profile indicates that the edge of both touch the top and the bottom of the profile. The line joining the center points of all the loop to each other, the camber line. For unsymmetrical sections is not the intersection of the profile nose with the chord but the with the skeleton line of aerodynamic importance: 56 (see details in the adjacent diagram ). For symmetric profiles, the chord with the skeleton line is congruent.

Rotor plane

The rotor plane, also called leaf tip plane, the plane of motion in the moving blades.

Pressure point

The pressure point is defined as the intersection of the chord and the rotor plane. There, grab all the aerodynamic forces on the rotor blade.

Helicopter main rotor configurations

The drive of the main rotor, produces in dependence on the angle of attack of the rotor blades a acting against the direction of rotation of the main rotor torque to the fuselage of a helicopter. To counteract the rotation of the hull about the vertical axis, various structures can be used: 230 et seq.

Counter thrust to the tail boom

A system comprising a main rotor and a counter- thrust generating apparatus is mounted to a tail boom, is the best known and most common configuration of helicopter. Here, two systems can be distinguished.

Tail rotor configuration

In the configuration of a horizontal tail rotor thrust is generated to oppose the rotation of the body about the vertical axis by a boom mounted on the rear tail rotor. This thrust is not constant, but must be of the pilots at each change of torque ( other angle of attack of the rotor blades, modified engine power) to be adjusted. For right-handed main rotors (top view ) of the tail rotor is always located on the right, with the left rotating main rotors on the left side of the tail boom.

A particular design is the fenestron, the encapsulated design permits a smaller diameter rotor with the same power in conjunction with the larger number of blades, as well as a higher speed.

No- Tail - Rotor System

In the tail rotor configuration, an air jet is mounted at the end of one of the tail boom pivotable steering blown out, which produces the counter torque to the main rotor, and ensures the control of the helicopter about its vertical axis.

Double rotor configurations

A system with two counter-rotating main rotors called dual-rotor configuration. There are four systems can be distinguished.

Tandem configuration

In this tandem configuration, two identical opposing main rotors are arranged one behind the other in the direction of flight, wherein the rear of the rotor planes is always higher than the front. This configuration is particularly useful for larger transport helicopters such as the Piasecki H -21 or Boeing Vertol CH- 47 to the application.

Transverse rotors

Transversely disposed rotors are also assigned to the tandem configuration wherein two equally large but opposite main rotors are arranged side by side on the ends of side arms transverse to the direction of flight. This configuration is for example at the Focke- Achgelis Fa 223, Mil Mi -12 and Kamov Ka -22 apply.

Flettner rotor double

In this configuration, two rotor shafts are slightly outwardly inclined in a V shape close to each other, so that the two counter-rotating rotors mesh with each other. This configuration is for example Flettner Fl 282 or at the Kaman K -Max on the application.

Coaxial rotor

In this tandem configuration, two identical opposing main rotors are arranged one above the other on a rotor shaft. This configuration is for example Kamov Ka -32 in or Kamov Ka-50 apply. In addition, this configuration is used on entry level model helicopters.

Blade tip drive

Main rotors with blade tip drive are exceptions to this driving method is the recoil of compressed air, partially offset by fuel combustion support ( hot tip drive ), used to move the main rotor to rotate and so to generate lift. The compressed air is guided through the main rotor mast and the rotor blades to the blade tip, where it exits the nozzle. Since this force does not act on the rotor shaft, no torque balancing is necessary. This drive method, however, was not pursued due to the high noise and high fuel consumption. This drive came, for example, in the Sud-Ouest SO 1221 " Djinn ", the only successful helicopter blade tip drive for application: 35 On main rotors with blade tip drive will not be discussed further here.

Gyroplane

The main rotor of an autogyro is not an engine, but because of the acting from the bottom flow of the slightly inclined to the rear rotor passive in rotation ( auto-rotation ). This rotation of the main rotor blades generate lift: 80 Our instant driving the autogyro, as in the fixed-wing aircraft, by an attached mostly at the rear propeller. Main rotors gyroplanes are not considered further here.

Kawasaki OH -1 " Ninja" with fenestron

Boeing Vertol CH -47 tandem configuration

Focke- Wulf Fw 61 in transverse configuration

Kaman K -Max with Flettner rotor double

Kamov Ka -32 with Koaxialrotoren

Blade tip driving the " Djinn "

Gyroplane Arrow- Copter AC10

Components of the main rotor,

The main rotor of a helicopter -carrying, as well as pitch -controlled model helicopters are essentially for the following components.

Rotor shaft

The rotor shaft ( 1 ) is the central component of the rotor. It is connected at the lower end via a gear with the drive. In man-carrying helicopters combustion engines or turbines are used. Model helicopters are operated in addition to these drives with electric motors. The drive causes the rotor shaft into rotary motion. At the upper end of the rotor shaft, the rotor hub is rigidly connected to the rotor head (6): 35 The imaginary line through the center of the rotor shaft, the rotor pole axis. This rotates the rotor shaft. This is in most flight situations not with the axis of rotation of the rotor plane are identical, because the rotor plane obtained by the flapping of the rotor blades, an additional tilt: 80

The speed of the rotor shaft has a direct impact on the speed of the rotor blade tips of the main rotor. This speed in kilometers per hour (km / h) is calculated using the following formula:

Where d is the diameter of the rotor circuit in meters, and the constant 0.06 for the conversion factor in km / h. For example, results for the Sikorsky S-65 rotor blade speed at the blade tip ( radius = 12 m rotor diameter, rotor normal speed = 185 rpm) of 836.92 km / h In forward flight, the speed of the helicopter rotor blade speed must be added. Due to the aerodynamic characteristics of the helicopter becomes uncontrollable, when the speed of the rotor blade tip speed of sound (about 1235 km / h ) approaches. This results in excluding atmospheric air currents (wind) a theoretical maximum speed of the Sikorsky S-65 of about 390 km / h ( actually 295 km / h ).

In the following table, the rotational speed of the main rotor - indicated in revolutions per minute (min- 1) - shown some selected helicopter. In addition, the calculated speed from the rotor blade tip is shown in relation to the rotor diameter.

Swashplate

The swash plate ( 2) is used to transfer the control of movements of the rigid cell to the rotating rotor blades. It is made up of two rings ( a) (b ), via a bearing (C ) are mutually rotatably connected manufactured. This with the help of a sliding sleeve ( d) up and down sliding rings are mounted with a ball bearing (s) around the rotor shaft and are gimbaled.

The lower (in the case of other construction of the inner) ring (a) of the swash plate does not rotate with the rotor shaft and is connected via control rods ( 10), ( f) mechanically, hydraulically or electronically with the joystick mounted in front of the pilot's seat (stick ) and the side of the pilot's seat attached collective lever ( collectiv pitch) connected: 39

The upper (in the case of other construction of the outer) ring ( b) of the swash plate is connected to the carrier ( 3 ) ( g) with the rotor shaft and rotates with the same speed as the latter. This ring is connected to the mounted on the hinge of the blade holder collective stick (5) co-rotating control rods (4) (h). Thus, the joints can be controlled and the pitch of the rotor blades ( 9) be amended: 38

By the gimbal in conjunction with the sliding sleeve, the swash plate can perform the following movements:

Translation along the rotor shaft to the collective control of the rotor blades. This control movement is entered with the collective lever. Of all the setting angle of the rotor blades is changed simultaneously and by the same amount;
Inclination of the swash plate at any desired longitudinal or transverse direction of the cyclical control of the rotor blades. This control movement is entered with the control stick. Thus, the rotor blades perform each revolution of the rotor shaft, a wave -like change of the pitch;
Combinations of the swash plate movements mentioned above.

Note: All Letters in brackets refer to the legend in the graph on

Control rods

The controls collective lever and joystick are not part of the main rotor, but have a direct effect on those. Therefore, here a brief discussion. The collective lever is operated by the pilot with the left hand. For this additional instruments can operate, the collective lever does not establish a restoring force, but always remains in the last set by the pilot position. If the helicopter is not equipped with an automatic speed control, for example, is via a rotary knob controls the speed of the drive. The collective lever is used to initiate the collective control of the rotor blades. In this case, the setting angle of all rotor blades is changed by the same amount, so that the buoyancy of all the rotor blades is changed equally. The helicopter rises or falls.

The joystick is operated with the right hand. With it the longitudinal and transverse control inputs are initiated, which tilt the swash plate in the direction which results from the two tilting angles. A result, the rotor plane is coming. The helicopter rotates about its longitudinal (roll) or transverse axis ( pitch): 39

Since both joint lever and joystick can act on the control rod at the same time, the control inputs must be able to be mixed. For mechanical mixing gears, the control rods are articulated kinematic indirect lever and the control inputs mechanically mixed: 25 When hydraulic or electronic control support the mixture of control inputs via the hydraulic or electronic system takes place.

The control inputs of the two control elements are transmitted via the control rods to the swash plate. To ( a) the non-rotatable ring of the swash plate (2) on three control rods (F) and with the control stick of the collective lever connected. To define the position of the swash plate in the area clearly, this must always be controlled by three control inputs: 39 The video shows the interaction of the control rods.

If the collective lever is pulled upward, all non-rotatable control rods (10 ) ( f) moves depending on the design of the collective stick (5) by the same amount upwards or downwards, so that the swash plate by means of the sliding sleeve ( d ) along the rotor shaft (1) is moved in parallel. Wherein the adjustment angle of all rotor blades is changed to the same extent, so that the helicopter increases or decreases (without consideration of other factors ). In most man-carrying helicopters, the rotor blades are set at the lowest position of the collective lever so that they produce no lift: 22 The rotor blades of art airworthy model helicopters can be set so that they produce negative buoyancy so that they can perform a back flight.

When the control lever is moved, the control rods in accordance with the control input can be of different magnitude is moved depending on the design of the collective stick up or down, so that the swash plate of each rotor blade driving different, which by means of different angles of attack of the rotor blades in their orbit around the rotor shaft (1) pitch and / or roll movements initiates.

The co-rotating control rods (4 ) ( h) at one end of the co-rotating ring ( b) of the swash plate (2) and at the other end to the collective stick (5) of the rotor blade ( 9). Enter the already mixed control inputs of the collective lever and joystick from the swash plate directly to the rotor blades on.

Rotor head rotor hub

All the rotor blades (9 ) of the main rotor can be mechanically fixed to the rotor hub of the rotor head (6). About one per blade holder with swivel ( 7), which also angulation Stock: 35 is called the rotor blades can be rotated individually within specified limits around its longitudinal axis. By this rotation, the adjustment angle of the respective rotor blade, and thus the lift produced by it will change.

The rotor head is like the rotor blade roots because of the occurring centrifugal forces and bending moments as well as the drive - in addition by torsional forces in hingeless rotor systems - heavily loaded.

Fully movable rotor system

A fully articulated rotor system is equipped with at least three rotor blades. For rigid rotor blades vertical and horizontal bending forces act directly on the blade root (8) or to the rotor head. They can be so great that the blade root breaks through these bending forces or the sheet holder is badly damaged on the rotor head, which can lead to a crash of the helicopter. To compensate for these bending forces, with fully movable rotor systems, each rotor blade on a hit and a swivel joint is connected to the hinge of the rotor hub. Thus, they can be moved around three axes ( rotate about the longitudinal axis, suggest vertical and horizontal forward or lag ): 231 The freedom of movement of the pivot joint is limited by steamer: 70 The Sikorsky S-65, known in Germany under the name Sikorsky CH -53 is equipped with this rotor system.

Joint lot rotor system

The hingeless rotor system is very similar to the fully articulated rotor system. Here, however, no impact and pivot joints are installed. The horizontal and vertical bending forces are absorbed by the mechanically flexible blade roots 231 The Bölkow Bo 105 is equipped with this rotor system.

Rigid rotor system

The rigid rotor system is very similar to the hingeless rotor system. The horizontal and vertical bending forces are absorbed by the mechanically flexible blade roots. However, here also no hinges are installed, the torsion of the individual rotor blades must be guaranteed by an appropriate flexibility of the rotor blade root. Therefore, rigid rotor systems of fiber composites and titanium are made: 231 The Eurocopter EC 135 is equipped with this rotor system.

Semi-rigid rotor system

A semi-rigid rotor system is equipped with two rigidly interconnected rotor blades. The blades can only like a seesaw together on or pendant mounting: 231 Bell UH- 1 is provided with this rotor system.

Rotor blade

The rotor blade is the structural member of the main rotor, which generates the lift. In a classic design, it is connected via a rotary, impact and swivel joint with the rotor hub.

Materials

When the rotors of helicopters and gyroplanes steel, titanium, alloy and composite materials such as fiberglass - come (GRP) and carbon fiber composites (CFRP ) are used. Earlier wood was also widely used yet. FRP sheets were first used in the Kamov Ka -26 and then at the Bo 105 in connection with elastic suspension and a hingeless rotor head ( cf. swashplate ). The particularly complex because of the many joints in traditional construction maintenance of the rotor head is so much easier, but the leaves must be regularly examined for material fatigue.

The rotor blades bear the full weight of the helicopter. In addition, they must withstand the centrifugal force of rotation and thereby have the lowest possible weight. To meet these requirements, they are often made of high-strength composite materials. Some rotors are equipped with strain gauges, which in operation, the load is measured.

In the field of model rotor blades made of wood, simple plastic, fiberglass and carbon fiber are used. In modern CFRP blades for model helicopters, a foam core is formed together with a carbon fiber beam and the frame gives the rotor blade, the required compression and bending strength. The profile is formed from multiple layers of carbon fiber mats, which provide the necessary torsional strength.

Rotor blade shapes

With rotor blades for helicopters four basic forms are distinguished. In the rectangular form used, despite poorer aerodynamic properties most often the rotor blade over the entire length has the same depth. This design is more economical both in manufacture and in servicing. In the trapezoidal shape, the rotor blade from the blade root to the blade tip has a decreasing depth. Since the flow velocity and thereby also the lift on the blade tip is higher than at the blade root, the compensation of the dynamic lift of the entire blade length is achieved by the trapezoidal shape. In the double- trapezoidal shape, the depth of the rotor blade from the blade root to the blade center of first increases and then again to the blade tip. In the rectangular trapezoid shape, the depth of the blade root to the blade center is initially equal and then takes the blade tip from back: 231 The ratio of the sheet length (L) to chord length ( t ) is referred to as extension, with shortened and calculated as follows: 68.

Rotor blade shapes

From 1976 to 1986 investigations were carried out to improve the flight performance of helicopters under the British Experimental Rotor Program ( BCRP ). As a result of this cooperation by Westland Helicopters at Royal Aircraft Establishment, a Westland Lynx AH Mk.7 was equipped with BERP blades, who set then on August 11, 1986, 400.87 km / h speed record for helicopters, which are made to May 2010 remained.

This BERP blades feature an aerodynamic twist ( see below) and the rotor blade tips were equipped with paddles, reduce the blade tip vortex. The called sawtooth transition from the blade to the paddle creates a turbulent flow, which provides a 6 ° higher effective angle of attack, before stall occurs. On the other hand, require BERP blades a higher drive power: 69

Airfoils

The rotor blade had previously often a symmetrical profile, to prevent the pressure point hike at various angles of attack and that appropriate compensation forces. Such blades have the top and bottom on a same profile, and producing at a 0 ° angle neither nor output. Symmetrical semi- blades have on the top and bottom of an identical profile that is "thinner" marked on the bottom, however. They generate more lift and with a negative angle of attack more downforce than blades with a symmetrical profile with a positive angle of attack. Rotor blades with S-bend profile are on the bottom almost straight and thus on optimal buoyancy ( " lifting " ) designed. Hold the torque forces at the neutral point low.

Ideally suited for art and 3D flight because the buoyancy is equal in both the normal and in the supine position.
The rotor blade is suitable for both right-and left-rotating rotors.

Efficiency is less than optimum, because all of the lifting has to be generated by the angle of attack of the rotor blade.
Too high incidence there is a danger of a stall.

Better efficiency than the symmetrical profile because even at 0 ° angle of attack lift is generated.
This lower energy consumption and longer flight times.

Limited suitability for aerobatics.
No suitability for 3D flight.
Different blades required for right - or left-turning rotors.

Best efficiency in normal position.
This lower energy consumption and longer flight times.
Ideally suited for models with low rotor speed or high takeoff weight.

Suitability for simple aerobatics.
No suitability for 3D flight.
Different blades required for right - or left-turning rotors.

The design of rotor blades with different depths sheet is very complex. In order nevertheless to achieve an even flow over the entire blade length when using Ratorblättern in rectangular shape, they are often limited. In the geometric setting such as the angle of attack at the blade root is made large, and increases the blade tip ( optionally up to 0 ° ) from: 232 A geometric twist of the rotor blades is eg at the Alouette II, Bölkow Bo 105 and Eurocopter EC 135:67.

Twist

Aerodynamics

Dynamic lift

Rotor blade flow

If not exposed to other influences, to the rotor blades, which focuses on the parallel to the rotor blade edge extending and lanyard hole center line intersecting, due to the centrifugal forces created by the rotation exactly in the extension of the rigid blade holder stretch.

When the center of gravity of the rotor blade is not located on this line, the centrifugal forces do not act as described above at a 90 ° angle to the rotational axis of the rotor blade. The leading edge of the rotor blade will rotate as long as the fastening eye in front of or back through the center of gravity of the rotor blade is again in ° angle 90 to the axis of rotation, provided that no other influences acting on the rotor blade. This behavior is called flow. Pushes the leading edge forward, one speaks of a positive lead ( the blade tip rushes ahead in the direction of rotation ); pushes it backwards, it is called negative lead or lag ( the blade tip hangs in the direction of rotation ).

The flow resistance which is the subject due to its high rotational speed of the rotor blade, the flow is reduced or enlarged to the wake of the rotor blade. Through constructive shift in emphasis, the rotor blade can be adjusted so that it is taking into account the flow resistance as straight as possible in terms of aligning the intended speed of the main rotor to the blade holder and thus has no vested interest in tracking.

In addition to a shifted center of gravity sheet and the flow resistance also aeroelastic effects influence the flow of a rotor blade.

Efficiency

With the circular surface load approximates the efficiency of a rotor can be determined or the increasing with increasing load noise can be estimated.

378604