Type of Rotor System

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Semirigid

Semirigid rotor system

The semirigid rotor can also be referred to as a teetering or seesaw rotor. Thissystem is normally composed of two blades that meet just under a common

flapping or teetering hinge at the rotor shaft. This allows the blades to flap togetherin opposite motions like aseesaw.This underslinging of the blades below the

teetering hinge, combined with an adequate dihedral or coning angle on the blades,minimizes variations in the radius of each blade's center of mass from the axis of

rotation as the rotor turns, which in turn reduces the stress on the blades from leadand lag forces caused by theCoriolis effect.Secondary flapping hinges may also

be provided to provide sufficient flexibility to minimize bouncing. Feathering is

accomplished by the feathering hinge at the blade root, which allows changes tothe pitch angle of the blade.

Flybar (stabilizer bar)

The flybar has a weight or paddle (or both for added stability on smaller

helicopters) at each end. These keep the bar relatively stable in the plane of

rotation and reduce crosswind thrust on rotors. Through mechanical linkages, the

stable rotation of the bar mixes with the swashplate movement to damp internal(steering) as well as external (wind) forces on the rotor. This makes it easier for the

pilot to maintain control of the aircraft.Stanley Hiller arrived at a similar methodto improve stability by adding short stubby airfoils, or paddles, at each end.

However, Hiller's "Rotormatic" system also delivered cyclic control inputs to the

main rotor as a sort of control rotor, and the paddles provided the added stabilityby damping the effects of external forces on the rotor.

The Lockheed rotor system used a control gyro, similar in principle to that of the

Bell stabilizer bar, but designed for both hands-off stability and rapid controlresponse of the hingeless rotor system.

Infly-by-wire helicopters or RC models, amicrocontroller withgyroscope sensorsand aVenturi sensor can replace the stabilizer. This flybar-lessdesign has theadvantage of easy reconfiguration and fewer mechanical parts.
http://en.wikipedia.org/wiki/Seesawhttp://en.wikipedia.org/wiki/Coriolis_effecthttp://en.wikipedia.org/wiki/Stanley_Hillerhttp://en.wikipedia.org/wiki/Fly-by-wirehttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Gyroscopehttp://en.wikipedia.org/wiki/Venturi_effecthttp://en.wikipedia.org/wiki/Venturi_effecthttp://en.wikipedia.org/wiki/Gyroscopehttp://en.wikipedia.org/wiki/Microcontrollerhttp://en.wikipedia.org/wiki/Fly-by-wirehttp://en.wikipedia.org/wiki/Stanley_Hillerhttp://en.wikipedia.org/wiki/Coriolis_effecthttp://en.wikipedia.org/wiki/Seesaw


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Stabilizer Bar

Aircraft subjected to Semi Rigid Rotor System

Bell 206

Robinson R22
http://en.wikipedia.org/wiki/Bell_206http://en.wikipedia.org/wiki/Robinson_R22http://en.wikipedia.org/wiki/Robinson_R22http://en.wikipedia.org/wiki/Bell_206


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Fully articulated

Juan de la Cierva developed the fully articulating rotor for theautogyro.The basis of

his design permitted successful helicopter development. In a fully articulated rotor

system, each rotor blade is attached to the rotor hub through a series of hinges that letthe blade move independently of the others. These rotor systems usually have three or

more blades. The blades are allowed to flap, feather, and lead or lag independently of

each other.

The Horizontal hinge, called the flapping hinge, allows the blade to move up and

down. This movement is called flapping and is designed to compensate

fordissymmetry of lift.The flapping hinge may be located at varying distances from

the rotor hub, and there may be more than one hinge. The Vertical hinge, called

the lead-lag hinge or drag hinge, allows the blade to move back and forth. This

movement is called lead-lag, dragging, or hunting.

Dampers are usually used to prevent excess back and forth movement around the drag

hinge. The purpose of the drag hinge and dampers is to compensate for acceleration

and deceleration caused byCoriolis effect.Later models have switched from using

traditional bearings toelastomericbearings. Elastomeric bearings are naturally fail-

safe and their wear is gradual and visible. The metal-to-metal contact of older

bearings and the need for lubrication is eliminated in this design.

The third hinge in the fully articulated system is called the feathering hinge about the

feathering axis. This hinge is responsible for the change in pitch of rotor bladesexcited via pilot input to the Collective or Cyclic.

A variation of the fully articulated system is the "soft-in-plane" rotor system. This

system is similar to the fully articulated type in that each blade has the ability to

lead/lag and hunt independent of the other blades. The difference between a fully

articulated system and soft-in-plane system is that the soft-in-plane system utilizes a

composite yoke. This yoke is attached to the mast and runs through the blade grips

between the blades and the shear bearing inside the grip.

This yoke does transfer some movement of one blade to another, usually opposing

blades. While this is not fully articulated, the flight characteristics are very similar and

maintenance time and cost are reduced.
http://en.wikipedia.org/wiki/Juan_de_la_Ciervahttp://en.wikipedia.org/wiki/Autogyrohttp://en.wikipedia.org/wiki/Dissymmetry_of_lifthttp://en.wikipedia.org/wiki/Coriolis_effecthttp://en.wikipedia.org/wiki/Elastomerichttp://en.wikipedia.org/wiki/Elastomerichttp://en.wikipedia.org/wiki/Coriolis_effecthttp://en.wikipedia.org/wiki/Dissymmetry_of_lifthttp://en.wikipedia.org/wiki/Autogyrohttp://en.wikipedia.org/wiki/Juan_de_la_Cierva


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Aircraft subjected to Fully Articulated System

AgustaWestlandAW109


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Rigid

The term "rigid rotor" usually refers to a hingeless rotor system with blades flexiblyattached to the hub.Irven Culver of Lockheed developed one of the first rigid rotors,

which was tested and developed on a series of helicopters in the 1960s and 1970s.

In a rigid rotor system, each blade flaps and drags about flexible sections of the root.

A rigid rotor system is mechanically simpler than a fully articulated rotor system.

Loads from flapping and lead/lag forces are accommodated through rotor blades

flexing, rather than through hinges. By flexing, the blades themselves compensate for

the forces that previously required rugged hinges.

The result is a rotor system that has less lag in control response because of the largehub moment typically generated. The rigid rotor system thus eliminates the danger of

mast bumping inherent in teetering rotors.
http://en.wikipedia.org/w/index.php?title=Irven_Culver&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Irven_Culver&action=edit&redlink=1


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Aircraft subjected to Rigid System

MBB BO 105

Eurocopter EC135

Type of Rotor System

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