3. ROTOR HUB AND BLADES

HUB/BLADE REQUIREMENTS1. ENABLE BLADE GEOMETRIC PITCH TO CHANGE AS A FUNCTION OF AZIMUTH (FEATHERING)

2. ACCOMDATE CHANGES IN BLADE LIFT AND DRAG PRODUCED BY CHANGING BLADE GEOMETRIC PITCH WHICH CAUSES BLADE FLAPPING AND LEAD-LAG MOTION

RIGID BLADE MOTIONFEATHERINGFeathering: Blade RotationAbout Axis Perpendicular to MastSteady Feathering=Collective Pitch < 15 degrees1/Rev Feathering=Cyclic Pitch +/- 15 degrees

RIGID BLADE MOTIONFLAPPINGFlapping: Blade Motion Parallel to MastSteady State Flapping= Coning ~3-8 degreesTilt of Tip Path Plane=1/Rev Flapping +/- 15 degrees

RIGID BLADE MOTIONLEAD-LAGLead-Lag: Blade Motion in a Plane Perpendicular to Mast1/Rev Lead Lag +/- 1 degreeCan combine with fuselage motion to Produce Ground Resonance

OFFSET FLAPPING HINGEeeCFCFKey Parameter0

FLAPPING FLEXURECFCFe METHOD OF ACCOMODATING OUT/PLANE OSCILLATORY LOADS

DISCRETE HINGEAdvantages: Simplicity Large Range of Motion

Disadvantages: High maintenance Large volume High Contact Stresses Weight

ELASTIC DEFORMATIONAdvantages: Reduced Parts Count Lower Maintenance Reduced Weight Ideal use of composites

Disadvantages: Fatigue Damage Limited Range of Motion Design Complexity Manufacturing Complexity

eLead Lag DamperTo Prevent Ground ResonanceCFOFFSET LEAD LAG HINGEMETHODS OF ACCOMODATING IN PLANE OSCILLATORY LOAD

CFLead Lag DamperTo Prevent Ground ResonanceMETHODS OF ACCOMODATING IN PLANE OSCILLATORY LOADElastic Flexure

EVOLUTION OF LEAD LAG DAMPERSHYDRAULIC High Maintenance MessyELASTOMERIC Spring and Damping Effect Subject to Temperature Effects

METHODS OF FEATHERING BLADEFEATHERING BEARINGS BALL BEARING HIGH CONTACT STRESSES SMALL AMPLITUDES OF MOTION ELASTOMERIC TEMPERATURE SENSITIVITY TENSION TORSION STRAP ELASTIC TWISTING OF FLEXURE

FEATHERING BEARING CFCFCFMASTFeathering +/- 15 degreesVery High Contact StressesVery Small Ball Rotation

TENSION TORSION STRAP

TENSION TORSION STRAP

ELASTOMERIC FEATHERING BEARINGFixed to MastFeathers With BladeFlapping Lead Lag MotionTorsion Motion

HINGELESS/BEARINGLESS ROTOR

EVOLUTION OF BEARINGSMETAL ROLLER BEARINGS High Contact Stresses Limited Ball Motion Pitting DirtElastomeric Low maintenance Ideally suited for small motions

HUB CONFIGURATIONTEETERING ROTORFlappingAxisFlappingAxisCenter ofRotationBladeFeathering AxisPitch HornTension Torsion StrapNote: All 2 Bladed Teetering Rotors are Stiff in Plane

BLADE PITCHFlapping HingeTension Torsion StrapPitch Link

MODEL 47 STAB BAR

Robinson R-221 Centrally Located Flapping Hinge2 Offset Coning HingesFlapping Hinge CF=0Coning HingeCF>>0

MULTIBLADEDFULLY ARTICULATEDPitch armCenter ofRotationLag HingeDamperBladeOffset Flapping HingeFeathering AxisDamper may be required to preclude Ground Resonance

KAMAN CONTROL TAB ROTORControl Tab Hinge LineFeathering AxisNo Mechanical Constraints on Rigid Blade FeatheringControl Tab Motion via Speedometer Cable Passing From Root to Tab

FULLY ARTICULATED ROTORFeathering AxixFlapping AxisLead-Lag Axis

HINGELESS BEARINGLESS HUBFlapping AxisFeathering AxisLead Lag AxisFlapping, Feathering, Lead-Lag via Elastic Deformation of Flexure

Mi-17-1

Pendulum tuned to 4/Rev or 6/Rev to Reduce 5/Rev Fuselage Vibrations

4 BLADED HINGELESS ROTORWITH ELASTOMERIC DAMPER

ELASTOMERIC LEAD LAG DAMPER

COMPOSITE HUB

MAIN ROTOR BLADE

MR BLADE CONSTRUCTION

METAL BLADE

MR EXPANDABLE BLADE PINS

ROTOR PARAMETERSBladesNumber: 2 to 8Tip speed: 650 820 ft/secRadius: 12 ft- 50 FeetPlan Form: Straight , taperedTwist: 8 15 degrees Linear/NonlinearAirfoil DistributionTip Shape: Noise Construction: Wood, Metal, CompositeProtection: Sand, Ice LightingRadial Distributions: Mass, Stiffness

HUB PARAMETERS

Lead-lag Degree of FreedomFlapping Degree of FreedomSource of Damping Hydraulic Elastomeric AeroelasticBlade FeatheringRadial Sequence of Hinges

ROTOR BRAKE

FREEWHEELING UNITAllows Rotor to Continue Turning After Loss of Engine Power

OTHER ROTOR TYPES

TAIL ROTORS

General Requirements

NO CYCLIC PITCH (ONLY COLLECTIVE CONTROLLED BY PEDALS)

MAY BE CANTED FOR HANDLING QUALITIES

TAIL ROTORS

LIGHT BLADE EMPLOY NEGATIVE DELTA-3HIGH G FIELD ~3500 gs AT TIPNON INTEGER PER/REV GEAR RATIO TO MAIN ROTORMINIMIZE CHORD (TENNIS RACKET MOMENT)DISTANCE FROM TAIL BOOM

Arospatiale SA 342 Gazelle

PAINT SCHEME FOR SAFETY

APACHE SCISSOR TAIL ROTOR2 stacked 2 bladed rotors

UH-60 TAIL ROTOR

TAIL ROTOR DESIGN CHALLENGESLOCATION (High or Low)LOCATION (Which Side of Fin) (Pusher or Tractor)DIRECTION OF ROTATION (Up and Forward or Up and Aft)TWISTED OR UNTWISTEDFATIQUE CYCLE COUNT 2/Rev at 1750 RPM= 200,000 cycles/hourHIGH 2/Rev IN-PLANE CHORD LOADS DUE TO CORIOLIS FORCES PRODUCED BY 1/Rev FLAPPING

TAIL ROTOR DESIGN CHALLENGESFLAPPING CLEARANCE Mast length + or Pitch Flap CouplingAERODYNAMICS ENVIRONMENT Engine Exhaust Main Rotor Downwash Fin Interference SAFETY/WEIGHT/CG EFFECTS/PERFORMANCE

LOSS OF TAIL ROTOR EFFECTIVENESS

TILT ROTORS CONTROL MIXING Helicopter Mode Airplane Mode TransitionINNER-CONNECTIONSTABILITY Ground Resonance Wing/Rotor/Pylon in Forward Flight Matched InPlane/OutPlane StiffnessDOWNWASHFOLDINGVARIABLE RPM??? DIAMETER???

0.15 MACH SCALE ROTOR HUB

Aerodynamics and Dynamics Can be scaledFriction and Damping very difficult to scale

ROTOR SYSTEM DESCRIPTORS1. Number of BladesA. 2 BladedB. Multibladed >2 Equally Spaced2. Attachment of Rigid Blade to MastA. Teetering 2 Blades Bld#1 Up Bld#2 DownB. Gimballed 3 or more bladesBld #1 Up 1ft Bld#2 Down 0.866 ft Bld#3 Down 0.866 ftBld #1 0 Bld#2 Up 0.5 ft Bld#3 Down 0.5 ftC. Articulated/Hingeless/ Bearingless 3 or more bladesAll blades are IndependentArticulated == Mechanical HingeHingeless/Bearingless== Elastically Deformable

ROTOR SYSTEM DESCRIPTORS3. Stiff or Soft in Plane Multibladed RotorsA. Stiff: 1st InPlane Nat. Freq> Operating RPMB. Soft: 1st InPlane Nat. Freq< Operating RPMMay be subject to Ground Resonance

NOTEAll 2 bladed rotor systems are Teetering and Stiff in planeAll Multibladed helicopters are: Soft in Plane and: Articulated, Hingeless, or BearinglessAll Tilt Rotor systems are: Stiff in Plane and Ginballed