airfoil terminology

Airfoil TerminologyAirfoil TerminologyAirfoil TerminologyAirfoil Terminology

SpanSpanSpanSpan

Chord LineChord LineChord LineChord Line

Mean Chamber LineMean Chamber LineMean Chamber LineMean Chamber Line

Upper ChamberUpper ChamberUpper ChamberUpper Chamber

Lower ChamberLower ChamberLower ChamberLower Chamber

Leading EdgeLeading EdgeLeading EdgeLeading Edge

Trailing EdgeTrailing EdgeTrailing EdgeTrailing Edge

Center of PressureCenter of PressureCenter of PressureCenter of Pressure

Types of AirfoilsTypes of AirfoilsTypes of AirfoilsTypes of Airfoils

SymmetricalSymmetricalSymmetricalSymmetrical•Equal chamber on each sideEqual chamber on each side

•Each half mirror image of otherEach half mirror image of other

•Mean chamber line and chord line are coincidentalMean chamber line and chord line are coincidental

•Produces zero lift at zero angle of attackProduces zero lift at zero angle of attack

•Constant center of pressure with varying angles of Constant center of pressure with varying angles of

attackattack

•Equal chamber on each sideEqual chamber on each side

•Each half mirror image of otherEach half mirror image of other

•Mean chamber line and chord line are coincidentalMean chamber line and chord line are coincidental

•Produces zero lift at zero angle of attackProduces zero lift at zero angle of attack

•Constant center of pressure with varying angles of Constant center of pressure with varying angles of

attackattack

NonsymmetricalNonsymmetricalNonsymmetricalNonsymmetrical •Greater curvature above the chord line then belowGreater curvature above the chord line then below•Chord and chamber line are not coincidentalChord and chamber line are not coincidental•Produces useful lift even at negative angles of attackProduces useful lift even at negative angles of attack•Produces more lift at a given angle of attack than Produces more lift at a given angle of attack than symmetricalsymmetrical•Better stall characteristics than symmetricalBetter stall characteristics than symmetrical•Good lift to drag ratioGood lift to drag ratio•Limited to low relative wind velocity, <300 knotsLimited to low relative wind velocity, <300 knots•Excessive center of pressure travel up to 20% of chord lineExcessive center of pressure travel up to 20% of chord line

•Greater curvature above the chord line then belowGreater curvature above the chord line then below•Chord and chamber line are not coincidentalChord and chamber line are not coincidental•Produces useful lift even at negative angles of attackProduces useful lift even at negative angles of attack•Produces more lift at a given angle of attack than Produces more lift at a given angle of attack than symmetricalsymmetrical•Better stall characteristics than symmetricalBetter stall characteristics than symmetrical•Good lift to drag ratioGood lift to drag ratio•Limited to low relative wind velocity, <300 knotsLimited to low relative wind velocity, <300 knots•Excessive center of pressure travel up to 20% of chord lineExcessive center of pressure travel up to 20% of chord line

Airfoil (Rotor Blade) AnglesAirfoil (Rotor Blade) AnglesAirfoil (Rotor Blade) AnglesAirfoil (Rotor Blade) Angles

Angle of IncidenceAngle of Incidence(pitch angle)(pitch angle)

Angle of IncidenceAngle of Incidence(pitch angle)(pitch angle)


Tip Path PlaneTip Path PlaneTip Path PlaneTip Path Plane

The mechanical angle between the The mechanical angle between the chord linechord line of the airfoil of the airfoil and the and the plane of rotation of the rotorplane of rotation of the rotor ( (tip path planetip path plane).).Changed by collective and cyclic feathering. Any change inChanged by collective and cyclic feathering. Any change inthe angle of incidence changes the angle of attack.the angle of incidence changes the angle of attack.

The mechanical angle between the The mechanical angle between the chord linechord line of the airfoil of the airfoil and the and the plane of rotation of the rotorplane of rotation of the rotor ( (tip path planetip path plane).).Changed by collective and cyclic feathering. Any change inChanged by collective and cyclic feathering. Any change inthe angle of incidence changes the angle of attack.the angle of incidence changes the angle of attack.

Airfoil (Rotor Blade) AnglesAirfoil (Rotor Blade) AnglesAirfoil (Rotor Blade) AnglesAirfoil (Rotor Blade) Angles


Tip Path PlaneTip Path PlaneTip Path PlaneTip Path Plane

Induced FlowInduced FlowInduced FlowInduced Flow

Angle of AttackAngle of Attack(aerodynamic angle)(aerodynamic angle)

Angle of AttackAngle of Attack(aerodynamic angle)(aerodynamic angle)

Resultant RWResultant RWResultant RWResultant RW

The acute angle formed between the The acute angle formed between the chord linechord line of an airfoil of an airfoiland the and the resultant relative windresultant relative wind. As an aerodynamic angle the . As an aerodynamic angle the angle of attack can change with no apparent change inangle of attack can change with no apparent change inangle of incidence.angle of incidence.

The acute angle formed between the The acute angle formed between the chord linechord line of an airfoil of an airfoiland the and the resultant relative windresultant relative wind. As an aerodynamic angle the . As an aerodynamic angle the angle of attack can change with no apparent change inangle of attack can change with no apparent change inangle of incidence.angle of incidence.

StallStallStallStall

6° Angle of Attack6° Angle of Attack6° Angle of Attack6° Angle of Attack 12° Angle of Attack12° Angle of Attack12° Angle of Attack12° Angle of Attack

18° Angle of Attack18° Angle of Attack18° Angle of Attack18° Angle of Attack 24° Angle of Attack24° Angle of Attack24° Angle of Attack24° Angle of Attack

CCL L MaxMaxCCL L MaxMax

Questions?Questions?Questions?Questions?

Enabling Learning Objective #5Enabling Learning Objective #5Enabling Learning Objective #5Enabling Learning Objective #5

From memory, the student will identify, by writing or From memory, the student will identify, by writing or selecting from a list, the principles of cyclic and selecting from a list, the principles of cyclic and collective feathering and the importance of rotary-collective feathering and the importance of rotary-wing flight, the significance of blade flapping and wing flight, the significance of blade flapping and the significance of blade hunting and the forces the significance of blade hunting and the forces involved with hunting IAW FM 1-203involved with hunting IAW FM 1-203

From memory, the student will identify, by writing or From memory, the student will identify, by writing or selecting from a list, the principles of cyclic and selecting from a list, the principles of cyclic and collective feathering and the importance of rotary-collective feathering and the importance of rotary-wing flight, the significance of blade flapping and wing flight, the significance of blade flapping and the significance of blade hunting and the forces the significance of blade hunting and the forces involved with hunting IAW FM 1-203involved with hunting IAW FM 1-203

Rotational AirflowRotational Airflow(no forward movement)(no forward movement)

Rotational AirflowRotational Airflow(no forward movement)(no forward movement)

Tip SpeedTip Speed700 FPS700 FPS




Circular movement of the rotor blades...Circular movement of the rotor blades...Circular movement of the rotor blades...Circular movement of the rotor blades...

...Produces basic rotational relative wind....Produces basic rotational relative wind.Maximum speed is at the tip of the bladeMaximum speed is at the tip of the bladeand decreases uniformly to the huband decreases uniformly to the hub

...Produces basic rotational relative wind....Produces basic rotational relative wind.Maximum speed is at the tip of the bladeMaximum speed is at the tip of the bladeand decreases uniformly to the huband decreases uniformly to the hub

FeatheringFeatheringFeatheringFeathering

Feathering is the rotation of the blade about its Feathering is the rotation of the blade about its span-wise axisspan-wise axisFeathering is the rotation of the blade about its Feathering is the rotation of the blade about its span-wise axisspan-wise axis

•Feathering can be uniform throughout the rotor through Feathering can be uniform throughout the rotor through collective inputs.collective inputs.

•Feathering can be adjusted differentially through cyclic Feathering can be adjusted differentially through cyclic

manipulationmanipulation

•Feathering can be uniform throughout the rotor through Feathering can be uniform throughout the rotor through collective inputs.collective inputs.

•Feathering can be adjusted differentially through cyclic Feathering can be adjusted differentially through cyclic

manipulationmanipulation

Lets look at some examples of Lets look at some examples of feathering...feathering...Lets look at some examples of Lets look at some examples of feathering...feathering...

Collective FeatheringCollective FeatheringCollective FeatheringCollective Feathering

• The changing of the angle of incidence equally and in the The changing of the angle of incidence equally and in the same direction on all of the rotor blades simultaneouslysame direction on all of the rotor blades simultaneously• Changes the angle of attack, which changes the Changes the angle of attack, which changes the coeffiecient of lift, which changes the overall lift of the rotorcoeffiecient of lift, which changes the overall lift of the rotor

• The changing of the angle of incidence equally and in the The changing of the angle of incidence equally and in the same direction on all of the rotor blades simultaneouslysame direction on all of the rotor blades simultaneously• Changes the angle of attack, which changes the Changes the angle of attack, which changes the coeffiecient of lift, which changes the overall lift of the rotorcoeffiecient of lift, which changes the overall lift of the rotor

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Cyclic FeatheringCyclic FeatheringCyclic FeatheringCyclic Feathering

•Fore or aft cyclic movements result in changes in angle of Fore or aft cyclic movements result in changes in angle of incidence at the 3 and 9 o’clock positions around the rotorincidence at the 3 and 9 o’clock positions around the rotor

•Lateral cyclic movements result in the angle of incidence Lateral cyclic movements result in the angle of incidence changing at the 12 and 6 o’clock positions around the rotorchanging at the 12 and 6 o’clock positions around the rotor

•Fore or aft cyclic movements result in changes in angle of Fore or aft cyclic movements result in changes in angle of incidence at the 3 and 9 o’clock positions around the rotorincidence at the 3 and 9 o’clock positions around the rotor

•Lateral cyclic movements result in the angle of incidence Lateral cyclic movements result in the angle of incidence changing at the 12 and 6 o’clock positions around the rotorchanging at the 12 and 6 o’clock positions around the rotor

Differential change in angle of incidence around the rotorDifferential change in angle of incidence around the rotorDifferential change in angle of incidence around the rotorDifferential change in angle of incidence around the rotor

Forward cyclic inputsForward cyclic inputsForward cyclic inputsForward cyclic inputs

A forward cyclic input increases pitch angle at the 9 o’clock A forward cyclic input increases pitch angle at the 9 o’clock position, and decreases it at the 3 o’clock position. Due to position, and decreases it at the 3 o’clock position. Due to phase lag,phase lag, the greatest upflap occurs at the 6 o’clock the greatest upflap occurs at the 6 o’clock position. Total aerodynamic force inclines forward.position. Total aerodynamic force inclines forward.

A forward cyclic input increases pitch angle at the 9 o’clock A forward cyclic input increases pitch angle at the 9 o’clock position, and decreases it at the 3 o’clock position. Due to position, and decreases it at the 3 o’clock position. Due to phase lag,phase lag, the greatest upflap occurs at the 6 o’clock the greatest upflap occurs at the 6 o’clock position. Total aerodynamic force inclines forward.position. Total aerodynamic force inclines forward.

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Aft cyclic inputsAft cyclic inputsAft cyclic inputsAft cyclic inputs

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An aft cyclic input increases in the pitch of the blade at the An aft cyclic input increases in the pitch of the blade at the 3 o’clock position while decreasing it at the 9 o’clock position. 3 o’clock position while decreasing it at the 9 o’clock position. Due to phase lag, the highest upflap occurs at the 12 o’clock Due to phase lag, the highest upflap occurs at the 12 o’clock position. Total aerodynamic force inclines to the rear.position. Total aerodynamic force inclines to the rear.

An aft cyclic input increases in the pitch of the blade at the An aft cyclic input increases in the pitch of the blade at the 3 o’clock position while decreasing it at the 9 o’clock position. 3 o’clock position while decreasing it at the 9 o’clock position. Due to phase lag, the highest upflap occurs at the 12 o’clock Due to phase lag, the highest upflap occurs at the 12 o’clock position. Total aerodynamic force inclines to the rear.position. Total aerodynamic force inclines to the rear.

Lateral Cyclic InputsLateral Cyclic InputsLateral Cyclic InputsLateral Cyclic Inputs

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Lateral cyclic inputs change the pitch angle at the 12 o’clockLateral cyclic inputs change the pitch angle at the 12 o’clockand 6 o’clock position. Due to phase lag those changes areand 6 o’clock position. Due to phase lag those changes aremanifested in the rotor system 90 degrees later. The resultingmanifested in the rotor system 90 degrees later. The resultingrotor attitude change causes the helicopter to move in the rotor attitude change causes the helicopter to move in the desired directiondesired direction

Lateral cyclic inputs change the pitch angle at the 12 o’clockLateral cyclic inputs change the pitch angle at the 12 o’clockand 6 o’clock position. Due to phase lag those changes areand 6 o’clock position. Due to phase lag those changes aremanifested in the rotor system 90 degrees later. The resultingmanifested in the rotor system 90 degrees later. The resultingrotor attitude change causes the helicopter to move in the rotor attitude change causes the helicopter to move in the desired directiondesired direction

FlappingFlappingFlappingFlapping

Flapping is the up and down movement of the rotor blades Flapping is the up and down movement of the rotor blades about a flapping hinge (or flexible hub)about a flapping hinge (or flexible hub)Flapping is the up and down movement of the rotor blades Flapping is the up and down movement of the rotor blades about a flapping hinge (or flexible hub)about a flapping hinge (or flexible hub)

•Blades flap in response to changes in lift caused by Blades flap in response to changes in lift caused by changes in velocity of the relative wind across the airfoil, or changes in velocity of the relative wind across the airfoil, or by cyclic feathering by cyclic feathering •No flapping occurs when the tip path plane is perpendicular No flapping occurs when the tip path plane is perpendicular to the mastto the mast

•Blades flap in response to changes in lift caused by Blades flap in response to changes in lift caused by changes in velocity of the relative wind across the airfoil, or changes in velocity of the relative wind across the airfoil, or by cyclic feathering by cyclic feathering •No flapping occurs when the tip path plane is perpendicular No flapping occurs when the tip path plane is perpendicular to the mastto the mast

ContributionsContributionsContributionsContributions

•Helps prevent dyssemmetry of liftHelps prevent dyssemmetry of lift•Allows the rotor system to tilt in the desired direction in Allows the rotor system to tilt in the desired direction in response to cyclic inputsresponse to cyclic inputs

•Helps prevent dyssemmetry of liftHelps prevent dyssemmetry of lift•Allows the rotor system to tilt in the desired direction in Allows the rotor system to tilt in the desired direction in response to cyclic inputsresponse to cyclic inputs

Lead and LagLead and LagLead and LagLead and Lag

Rotor blades in an articulated system lead ahead Rotor blades in an articulated system lead ahead and lag behind their normal position in the rotor and lag behind their normal position in the rotor systemsystem

Rotor blades in an articulated system lead ahead Rotor blades in an articulated system lead ahead and lag behind their normal position in the rotor and lag behind their normal position in the rotor systemsystem

CausesCausesCausesCauses

•Angle of attack changes and drag forcesAngle of attack changes and drag forces•Coriolis force, or the change in the relative Coriolis force, or the change in the relative center of gravity along the span of the bladecenter of gravity along the span of the blade

•Angle of attack changes and drag forcesAngle of attack changes and drag forces•Coriolis force, or the change in the relative Coriolis force, or the change in the relative center of gravity along the span of the bladecenter of gravity along the span of the blade

R R 11

R R 22

Sequence when blade flaps upSequence when blade flaps upSequence when blade flaps upSequence when blade flaps up

As the center of gravity moves inboard, a smaller radius of travel isAs the center of gravity moves inboard, a smaller radius of travel isproduced. This causes the advancing blade to speed up or hunt. A vertical produced. This causes the advancing blade to speed up or hunt. A vertical hinge pin (articulated rotor) allows the blade to sweep forward and hinge pin (articulated rotor) allows the blade to sweep forward and absorbs stress that would otherwise be transmitted to the blade.absorbs stress that would otherwise be transmitted to the blade.

As the center of gravity moves inboard, a smaller radius of travel isAs the center of gravity moves inboard, a smaller radius of travel isproduced. This causes the advancing blade to speed up or hunt. A vertical produced. This causes the advancing blade to speed up or hunt. A vertical hinge pin (articulated rotor) allows the blade to sweep forward and hinge pin (articulated rotor) allows the blade to sweep forward and absorbs stress that would otherwise be transmitted to the blade.absorbs stress that would otherwise be transmitted to the blade.

Blade CGBlade CGBlade CGBlade CG

airfoil terminology

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