LiftLiftLiftLift

The component of the total aerodynamic force of an The component of the total aerodynamic force of an airfoil that is perpendicular to the resultant relative windairfoil that is perpendicular to the resultant relative windThe component of the total aerodynamic force of an The component of the total aerodynamic force of an airfoil that is perpendicular to the resultant relative windairfoil that is perpendicular to the resultant relative wind

90°90°90°90°

Resultant Relative WindResultant Relative WindResultant Relative WindResultant Relative Wind

LiftLiftLiftLiftTAFTAFTAFTAF

L = CL = CL = CL = CLLLLXXXX SSSS XXXX VVVV

2222XXXX

Factors affecting liftFactors affecting liftFactors affecting liftFactors affecting lift

•CCLL (coefficient of lift) (coefficient of lift)

•Surface area of the airfoil measured in square feet.Surface area of the airfoil measured in square feet.•Air density measured in slugs of air per cubic foot.Air density measured in slugs of air per cubic foot.•V (relative wind velocity in feet per second)V (relative wind velocity in feet per second)

•CCLL (coefficient of lift) (coefficient of lift)

•Surface area of the airfoil measured in square feet.Surface area of the airfoil measured in square feet.•Air density measured in slugs of air per cubic foot.Air density measured in slugs of air per cubic foot.•V (relative wind velocity in feet per second)V (relative wind velocity in feet per second)

CCLL (coefficient of lift)(coefficient of lift)

CCLL (coefficient of lift)(coefficient of lift)

A dimensionless number, determined through wind A dimensionless number, determined through wind tunnel tests. Denotes the lift producing capability of tunnel tests. Denotes the lift producing capability of an airfoilan airfoil

A dimensionless number, determined through wind A dimensionless number, determined through wind tunnel tests. Denotes the lift producing capability of tunnel tests. Denotes the lift producing capability of an airfoilan airfoil

Values range from 0 to 2 or moreValues range from 0 to 2 or moreValues range from 0 to 2 or moreValues range from 0 to 2 or more

Factors that determine the value of CFactors that determine the value of CLL include includeFactors that determine the value of CFactors that determine the value of CLL include include

•Shape and design of an airfoilShape and design of an airfoil•Angle of AttackAngle of Attack

•Shape and design of an airfoilShape and design of an airfoil•Angle of AttackAngle of Attack

S S (surface area)(surface area)

S S (surface area)(surface area)

•Measured in square feetMeasured in square feet•Physically constant, but effective size can be Physically constant, but effective size can be changed by other variables changed by other variables

•Measured in square feetMeasured in square feet•Physically constant, but effective size can be Physically constant, but effective size can be changed by other variables changed by other variables

Measured in slugs of air per cubic foot. A cubic foot Measured in slugs of air per cubic foot. A cubic foot of standard day air has a mass of .002377 slugs.of standard day air has a mass of .002377 slugs.Measured in slugs of air per cubic foot. A cubic foot Measured in slugs of air per cubic foot. A cubic foot of standard day air has a mass of .002377 slugs.of standard day air has a mass of .002377 slugs.

Factors affecting air densityFactors affecting air densityFactors affecting air densityFactors affecting air density

•Pressure Pressure density increases as pressure increases. Density density increases as pressure increases. Density

decreases with altitude because pressure decreasesdecreases with altitude because pressure decreases

•Temperature Temperature density decreases as temperature increasesdensity decreases as temperature increases

•Humidity Humidity density decreases as water vapor content increasesdensity decreases as water vapor content increases

•Pressure Pressure density increases as pressure increases. Density density increases as pressure increases. Density

decreases with altitude because pressure decreasesdecreases with altitude because pressure decreases

•Temperature Temperature density decreases as temperature increasesdensity decreases as temperature increases

•Humidity Humidity density decreases as water vapor content increasesdensity decreases as water vapor content increases

Air DensityAir DensityAir DensityAir Density = rho= rho= rho= rho

V V (relative wind (relative wind velocityvelocity, feet per second), feet per second)V V (relative wind (relative wind velocityvelocity, feet per second), feet per second)

Lift increases with the square of wind velocityLift increases with the square of wind velocityLift increases with the square of wind velocityLift increases with the square of wind velocity

Lift/Drag ratio Lift/Drag ratio (L/D)(L/D)

Lift/Drag ratio Lift/Drag ratio (L/D)(L/D)

Any airfoil operates at its maximum efficiency at oneAny airfoil operates at its maximum efficiency at oneangle of attack, that angle of attack must be determined.angle of attack, that angle of attack must be determined.Airfoil designers can determine the best angle of attackAirfoil designers can determine the best angle of attackby dividing the Cby dividing the CLL by the C by the CDD for a number of angles of attack. for a number of angles of attack.

Any airfoil operates at its maximum efficiency at oneAny airfoil operates at its maximum efficiency at oneangle of attack, that angle of attack must be determined.angle of attack, that angle of attack must be determined.Airfoil designers can determine the best angle of attackAirfoil designers can determine the best angle of attackby dividing the Cby dividing the CLL by the C by the CDD for a number of angles of attack. for a number of angles of attack.

The CThe CLL/C/CD D ratio resulting in the largest quotient is referred ratio resulting in the largest quotient is referred

to as L/D . L/D ratios also indicate optimum glide ratioto as L/D . L/D ratios also indicate optimum glide ratioof an airfoil. of an airfoil.

The CThe CLL/C/CD D ratio resulting in the largest quotient is referred ratio resulting in the largest quotient is referred

to as L/D . L/D ratios also indicate optimum glide ratioto as L/D . L/D ratios also indicate optimum glide ratioof an airfoil. of an airfoil.

maxmaxmaxmax

L/DL/DL/DL/D

Angle of AttackAngle of AttackAngle of AttackAngle of Attack

C/LC/LC/LC/L

C/DC/DC/DC/D

.0.0

1.01.0

2.02.0

0°0°0°0° 2°2°2°2° 4°4°4°4° 6°6°6°6° 8°8°8°8° 10°10°10°10° 12°12°12°12°

.020.020.020.020

.040.040.040.040

.060.060.060.060

.080.080.080.080

.100.100.100.100

.120.120.120.120

.140.140.140.140

.180.180.180.180

.160.160.160.160

14°14°14°14° 16°16°16°16° 18°18°18°18° 20°20°20°20° 22°22°22°22°00

22

44

66

88

1010

1212

1414

1616

1818

2020.200.200.200.200

C/LC/LC/LC/L

MaxMaxMaxMax

L/DL/DL/DL/D

C/LC/LC/LC/L

C/DC/DC/DC/D

StallStallStallStall

Lift to Drag RatioLift to Drag RatioLift to Drag RatioLift to Drag Ratio

L/DL/DL/DL/D

MaxMaxMaxMaxHighestHighestHighestHighest

LiftLiftLiftLifttoto

DragDragtoto

DragDrag

RatioRatioRatioRatio

LiftLiftLiftLift

Resultant Lift of the Rotor SystemResultant Lift of the Rotor SystemResultant Lift of the Rotor SystemResultant Lift of the Rotor System

To maneuver the helicopter, the tip path plane must be tilted in the desired To maneuver the helicopter, the tip path plane must be tilted in the desired direction of movement.direction of movement.Tilting the rotor disk will create a horizontal thrust component, the lift Tilting the rotor disk will create a horizontal thrust component, the lift component will be decreased and must be compensated for with collectivecomponent will be decreased and must be compensated for with collective

To maneuver the helicopter, the tip path plane must be tilted in the desired To maneuver the helicopter, the tip path plane must be tilted in the desired direction of movement.direction of movement.Tilting the rotor disk will create a horizontal thrust component, the lift Tilting the rotor disk will create a horizontal thrust component, the lift component will be decreased and must be compensated for with collectivecomponent will be decreased and must be compensated for with collective

Lift Lift andand Thrust ThrustLift Lift andand Thrust Thrust

QuestionQuestionQuestionQuestion

What combination of temperature, pressure and What combination of temperature, pressure and humidity would produce the greatest air density?humidity would produce the greatest air density?What combination of temperature, pressure and What combination of temperature, pressure and humidity would produce the greatest air density?humidity would produce the greatest air density?

Answer: Low temperature, high pressure, and low humidity Answer: Low temperature, high pressure, and low humidity Answer: Low temperature, high pressure, and low humidity Answer: Low temperature, high pressure, and low humidity

Enabling Learning Objective #7Enabling Learning Objective #7Enabling Learning Objective #7Enabling Learning Objective #7

From memory, the student will describe, by writing From memory, the student will describe, by writing or selecting from a list, the three types of drag and or selecting from a list, the three types of drag and identify the factors affecting drag IAW FM 1-203identify the factors affecting drag IAW FM 1-203

From memory, the student will describe, by writing From memory, the student will describe, by writing or selecting from a list, the three types of drag and or selecting from a list, the three types of drag and identify the factors affecting drag IAW FM 1-203identify the factors affecting drag IAW FM 1-203

DragDragDragDrag

The resistance to an object’s passage through the airThe resistance to an object’s passage through the airThe resistance to an object’s passage through the airThe resistance to an object’s passage through the air

Types of DragTypes of DragTypes of DragTypes of Drag

InducedInducedInducedInduced

ProfileProfileProfileProfile

ParasiteParasiteParasiteParasite

Induced DragInduced DragInduced DragInduced Drag

•Drag that is incurred as a result of the production of liftDrag that is incurred as a result of the production of lift•Parallel to and in the same direction as relative windParallel to and in the same direction as relative wind•Increases with increased angle of attackIncreases with increased angle of attack•Decreases with increased airspeedDecreases with increased airspeed

•Drag that is incurred as a result of the production of liftDrag that is incurred as a result of the production of lift•Parallel to and in the same direction as relative windParallel to and in the same direction as relative wind•Increases with increased angle of attackIncreases with increased angle of attack•Decreases with increased airspeedDecreases with increased airspeed

Each blade passes through the previous blade’s disturbedEach blade passes through the previous blade’s disturbedair this condition is most pronounced at high power settings air this condition is most pronounced at high power settings and no or low forward airspeeds.and no or low forward airspeeds.

Each blade passes through the previous blade’s disturbedEach blade passes through the previous blade’s disturbedair this condition is most pronounced at high power settings air this condition is most pronounced at high power settings and no or low forward airspeeds.and no or low forward airspeeds.

Profile DragProfile DragProfile DragProfile Drag

•ParasiticParasitic drag of the rotor system drag of the rotor system•At a constant RPM, profile drag is relatively constant but At a constant RPM, profile drag is relatively constant but

does increase slightly with airspeed. does increase slightly with airspeed. •Increases rapidly with very high airspeeds due to onset of Increases rapidly with very high airspeeds due to onset of

blade stall or compressibilityblade stall or compressibility•Profile drag is greater on 3, 4, 6, etc. bladed systemsProfile drag is greater on 3, 4, 6, etc. bladed systems

•ParasiticParasitic drag of the rotor system drag of the rotor system•At a constant RPM, profile drag is relatively constant but At a constant RPM, profile drag is relatively constant but

does increase slightly with airspeed. does increase slightly with airspeed. •Increases rapidly with very high airspeeds due to onset of Increases rapidly with very high airspeeds due to onset of

blade stall or compressibilityblade stall or compressibility•Profile drag is greater on 3, 4, 6, etc. bladed systemsProfile drag is greater on 3, 4, 6, etc. bladed systems

Parasitic DragParasitic DragParasitic DragParasitic Drag

The resistance offered by the fuselage and other The resistance offered by the fuselage and other nonliftingnonliftingsurfaces to the flow of airsurfaces to the flow of airThe resistance offered by the fuselage and other The resistance offered by the fuselage and other nonliftingnonliftingsurfaces to the flow of airsurfaces to the flow of air

CausesCausesCausesCauses

•Form or shape of the helicopter, the more Form or shape of the helicopter, the more streamlinedstreamlined the the helicopter, the less helicopter, the less parasiticparasitic drag drag•Skin friction, the Skin friction, the smoothersmoother the skin of the fuselage, the less the skin of the fuselage, the less parasitic dragparasitic drag

•Form or shape of the helicopter, the more Form or shape of the helicopter, the more streamlinedstreamlined the the helicopter, the less helicopter, the less parasiticparasitic drag drag•Skin friction, the Skin friction, the smoothersmoother the skin of the fuselage, the less the skin of the fuselage, the less parasitic dragparasitic drag

Increases rapidly with airspeedIncreases rapidly with airspeedIncreases rapidly with airspeedIncreases rapidly with airspeed

Total Drag CurveTotal Drag CurveTotal Drag CurveTotal Drag Curve

The summation of all drag forces acting on the helicopterThe summation of all drag forces acting on the helicopterThe summation of all drag forces acting on the helicopterThe summation of all drag forces acting on the helicopter

Total drag is high at a hover, decreases to a minimum value at a Total drag is high at a hover, decreases to a minimum value at a particular airspeed, then starts increasing with airspeedparticular airspeed, then starts increasing with airspeedTotal drag is high at a hover, decreases to a minimum value at a Total drag is high at a hover, decreases to a minimum value at a particular airspeed, then starts increasing with airspeedparticular airspeed, then starts increasing with airspeed

Minimum rate of descent for autorotationMinimum rate of descent for autorotation

Maximum endurance airspeedMaximum endurance airspeed

Maximum rate of climb airspeedMaximum rate of climb airspeed

Best maneuvering airspeedBest maneuvering airspeed

Minimum rate of descent for autorotationMinimum rate of descent for autorotation

Maximum endurance airspeedMaximum endurance airspeed

Maximum rate of climb airspeedMaximum rate of climb airspeed

Best maneuvering airspeedBest maneuvering airspeed

The above are airspeeds that fall within the lowest drag area of the The above are airspeeds that fall within the lowest drag area of the total drag curve. Theses speeds typically range from 60 to 80 ktstotal drag curve. Theses speeds typically range from 60 to 80 ktsThe above are airspeeds that fall within the lowest drag area of the The above are airspeeds that fall within the lowest drag area of the total drag curve. Theses speeds typically range from 60 to 80 ktstotal drag curve. Theses speeds typically range from 60 to 80 kts

Drag Forces Drag Forces Drag Forces Drag Forces

Dra

gD

rag

Dra

gD

rag

Forward SpeedForward SpeedForward SpeedForward Speed

Torque AvailableTorque AvailableTorque AvailableTorque Available

Induced Induced DragDrag

ProfileProfileDragDrag

ParasiteParasiteDragDragTotal DragTotal Drag

Questions?Questions?Questions?Questions?