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

Helicopters / Filipe Szolnoky CunhaSlide 2Rotor hubs

Blade movement

Helicopters / Filipe Szolnoky CunhaSlide 3Rotor hubs

Rotor Hub Types

Boeing AH-64 Apache rotor hub: Fully articulated

Helicopters / Filipe Szolnoky CunhaSlide 4Rotor hubs

Rotor Hub Types

Kamov Ka-29TB Helix: Fully articulated

Helicopters / Filipe Szolnoky CunhaSlide 5Rotor hubs

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

Helicopters / Filipe Szolnoky CunhaSlide 6Rotor hubs

Rotor Hub Types

Bell UH-1D Teetering

Helicopters / Filipe Szolnoky CunhaSlide 7Rotor hubs

Rotor Hub Types

Bell UH-1D Teetering

Helicopters / Filipe Szolnoky CunhaSlide 8Rotor hubs

Rotor Hub Types

Robinson R-22 Teetering

Helicopters / Filipe Szolnoky CunhaSlide 9Rotor hubs

Rotor Hub Types

Robinson R-22 Teetering

Helicopters / Filipe Szolnoky CunhaSlide 10Rotor hubs

Rotor Hub Types

Bell V-22 Osprey 3 blades teetering rotor

Helicopters / Filipe Szolnoky CunhaSlide 11Rotor hubs

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

Helicopters / Filipe Szolnoky CunhaSlide 12Rotor hubs

Rotor Hub Types

Westland Lynx: Hingeless

Helicopters / Filipe Szolnoky CunhaSlide 13Rotor hubs

Rotor Hub Types

Westland Lynx: Hingeless

Helicopters / Filipe Szolnoky CunhaSlide 14Rotor hubs

Rotor Hub Types

Eurocopter Bo105M: Hingeless

Helicopters / Filipe Szolnoky CunhaSlide 15Rotor hubs

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

Helicopters / Filipe Szolnoky CunhaSlide 16Rotor hubs

Rotor Hub Types

Eurocopter AS355 TwinStar : Bearingless

Helicopters / Filipe Szolnoky CunhaSlide 17Rotor hubs

Rotor Hub Types

Helicopters / Filipe Szolnoky CunhaSlide 18Rotor hubs

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

Helicopters / Filipe Szolnoky CunhaSlide 19Rotor hubs

Swash Plate

Helicopters / Filipe Szolnoky CunhaSlide 20Rotor hubs

Pitch Control

Helicopters / Filipe Szolnoky CunhaSlide 21Rotor hubs

Controls

• Collective control: Lever (left side)

– Increases (decreases) the same amount of pitch

angle independently of the azimuth angle.

Helicopters / Filipe Szolnoky CunhaSlide 22Rotor hubs

Controls

Helicopters / Filipe Szolnoky CunhaSlide 23Rotor hubs

Pitch Control

Helicopters / Filipe Szolnoky CunhaSlide 24Rotor hubs

Controls

• Cyclic control: Lever

– Changes the pitch angle with the azimuth

position (changes the rotor orientation in space)

Helicopters / Filipe Szolnoky CunhaSlide 25Rotor hubs

Pitch Control

Helicopters / Filipe Szolnoky CunhaSlide 26Rotor hubs

Collective control

Helicopters / Filipe Szolnoky CunhaSlide 27Rotor hubs

Control

Helicopters / Filipe Szolnoky CunhaSlide 28Rotor hubs

Flap motion

Helicopters / Filipe Szolnoky CunhaSlide 29Rotor hubs

Flap motion

• Zero offset

hub

Helicopters / Filipe Szolnoky CunhaSlide 30Rotor hubs

Lead-Lag Motion

Helicopters / Filipe Szolnoky CunhaSlide 31Rotor hubs

Lead-Lag Motion

Helicopters / Filipe Szolnoky CunhaSlide 32Rotor hubs

Lead-Lag Motion

• Shifting the rotor

CM with out of

pattern blades.

Helicopters / Filipe Szolnoky CunhaSlide 33Rotor hubs

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

Helicopters / Filipe Szolnoky CunhaSlide 34Rotor hubs

Order of hinges

Flapping axisDragging axis

Feathering axis

Helicopters / Filipe Szolnoky CunhaSlide 35Rotor hubs

Order of hinges

• Flapping

Hinge

• Coupling

between

flapping and

feathering

Helicopters / Filipe Szolnoky CunhaSlide 36Rotor hubs

Order of hinges

• Coupling between flapping and feathering

Helicopters / Filipe Szolnoky CunhaSlide 37Rotor hubs

Order of hinges

Helicopters / Filipe Szolnoky CunhaSlide 38Rotor hubs

Order of hinges

• No Coupling between flapping and feathering

Helicopters / Filipe Szolnoky CunhaSlide 39Rotor hubs

Order of hinges

• Flapping

Hinge

• Coupling

between

Flapping and

Dragging

Helicopters / Filipe Szolnoky CunhaSlide 40Rotor hubs

Order of hinges

• In a general case:

• Flapping Hinge

• δ3≠0

– Flapping and Feathering

• δ1≠0

– Flapping and Dragging

Helicopters / Filipe Szolnoky CunhaSlide 41Rotor hubs

Order of hinges

• In a general case:

• Dragging Hinge

• α3≠0

– Dragging and Feathering

• α1≠0

– Dragging and Flapping