11-Rotor hubs 2013 [Modo de Compatibilidade] · • Helicopter blades are attached to the rotor...

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Helicopters / Filipe Szolnoky CunhaSlide 1Rotor hubs

• Helicopter blades are attached to the rotor shaft with aseries of hinges:– Flapping hinges (or a soft flex-beam) , that allow blades to

freely flap up or down. This ensures that lift is transferred to theshaft, but not the moments.

– Lead-Lag Hinges. When the blades rotate, and flap, Coriolisforces are created in the plane of the rotor. In order to avoidunwanted stresses at the blade root, lead-lag hinges are used.

– Pitch bearing/pitch-link/swash plate: Used to control the bladepitch.

• The blade loads are affected by the motion of the bladesabout these hinges.

• From an aerodynamic perspective, lead-lag motion can beneglected. Pitching and flapping motions must beincluded.

Introduction

Blade movement

Rotor Hub Types

Boeing AH-64 Apache rotor hub: Fully articulated

Rotor Hub Types

Kamov Ka-29TB Helix: Fully articulated

Fully Articulated Rotor Hub

• Hinges allow the flap and lag movement

• Bearing allow the feathering movement

• Mechanical dampers added to the lag hinge

• Complicated to design and maintain

• Heavy and produces high drag in forward flight

Rotor Hub Types

Bell UH-1D Teetering

Rotor Hub Types

Bell UH-1D Teetering

Rotor Hub Types

Robinson R-22 Teetering

Rotor Hub Types

Robinson R-22 Teetering

Rotor Hub Types

Bell V-22 Osprey 3 blades teetering rotor

Teetering Hub

• No independent flap or lag hinge

• Independent feathering bearing

• Mechanically simple

• High parasitic drag in forward flight

• Variation is the underslung teetering hub

Rotor Hub Types

Westland Lynx: Hingeless

Rotor Hub Types

Westland Lynx: Hingeless

Rotor Hub Types

Eurocopter Bo105M: Hingeless

Hingeless Hub

• No flap or lead hinge

• Blade motion are performed by flexure

• Coupling between the flap and lag motion

• Mechanically simple

• Complicated design

• Low drag in forward flight

• Good manoeuvring capabilities

Rotor Hub Types

Eurocopter AS355 TwinStar : Bearingless

Rotor Hub Types

Bearingless Hub

• No flap or lead hinge

• No feathering bearing

• Motion obtained by bending, flexing and twisting

• Coupling between the all motion

• Mechanically very simple

• Very complicated design

• Low drag in forward flight

Swash Plate

Pitch Control

Controls

• Collective control: Lever (left side)

– Increases (decreases) the same amount of pitch

angle independently of the azimuth angle.

Controls

Pitch Control

Controls

• Cyclic control: Lever

– Changes the pitch angle with the azimuth

position (changes the rotor orientation in space)

Pitch Control

Collective control

Control

Flap motion

• Zero offset

Lead-Lag Motion

• Shifting the rotor

CM with out of

pattern blades.

Order of hinges

• The order on which the flapping, dragging and

feathering hinges are disposed is subjected to a

certain amount of variation.

• The use of coincident flapping and dragging

hinges is common because is allows a compact

bearing assembly. Feathering bearing is normally

positioned after this hinge

• But the three hinges are not necessarily orthogonal

Order of hinges

Flapping axisDragging axis

Feathering axis

Order of hinges

• Flapping

• Coupling

between

flapping and

feathering

Order of hinges

• Coupling between flapping and feathering

Order of hinges

• No Coupling between flapping and feathering

Order of hinges

• Flapping

• Coupling

between

Flapping and

Dragging

Order of hinges

• In a general case:

• Flapping Hinge

• δ3≠0

– Flapping and Feathering

• δ1≠0

– Flapping and Dragging

Order of hinges

• In a general case:

• Dragging Hinge

• α3≠0

– Dragging and Feathering

• α1≠0

– Dragging and Flapping

11-Rotor hubs 2013 [Modo de Compatibilidade] · • Helicopter blades are attached to the rotor...

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