LiftLift The component of the total aerodynamic force of an airfoil that is perpendicular to the resultant relative wind The component of the total aerodynamic force of an airfoil that is perpendicular to the resultant relative wind 90°90° Resultant Relative Wind LiftLift TAFTAF L = C LL XX SS XX VV22XX          

Factors affecting lift C L (coefficient of lift)C L (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) C L (coefficient of lift)C L (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)

C L (coefficient of lift) C L (coefficient of lift) A dimensionless number, determined through wind tunnel tests. Denotes the lift producing capability of an airfoil Values range from 0 to 2 or more Factors that determine the value of C L 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 (surface area) S Measured in square feetMeasured in square feet Physically constant, but effective size can be changed by other variablesPhysically constant, but effective size can be changed by other variables Measured in square feetMeasured in square feet Physically constant, but effective size can be changed by other variablesPhysically constant, but effective size can be changed by other variables

Measured in slugs of air per cubic foot. A cubic foot of standard day air has a mass of slugs. Factors affecting air density Pressure  density increases as pressure increases. Density decreases with altitude because pressure decreasesPressure  density increases as pressure increases. Density decreases with altitude because pressure decreases Temperature  density decreases as temperature increasesTemperature  density decreases as temperature increases Humidity  density decreases as water vapor content increasesHumidity  density decreases as water vapor content increases Pressure  density increases as pressure increases. Density decreases with altitude because pressure decreasesPressure  density increases as pressure increases. Density decreases with altitude because pressure decreases Temperature  density decreases as temperature increasesTemperature  density decreases as temperature increases Humidity  density decreases as water vapor content increasesHumidity  density decreases as water vapor content increases Air Density = rho  

V (relative wind velocity, feet per second) Lift increases with the square of wind velocity

Lift/Drag ratio (L/D) (L/D) Any airfoil operates at its maximum efficiency at one angle of attack, that angle of attack must be determined. Airfoil designers can determine the best angle of attack by dividing the C L by the C D for a number of angles of attack. Any airfoil operates at its maximum efficiency at one angle of attack, that angle of attack must be determined. Airfoil designers can determine the best angle of attack by dividing the C L by the C D for a number of angles of attack. The C L /C D ratio resulting in the largest quotient is referred to as L/D. L/D ratios also indicate optimum glide ratio of an airfoil. The C L /C D ratio resulting in the largest quotient is referred to as L/D. L/D ratios also indicate optimum glide ratio of an airfoil. maxmax

L/DL/D Angle of Attack C/LC/L C/DC/D °0°2°2°4°4°6°6°8°8°10°10°12°12° °14°16°16°18°18°20°20°22°22° C/LC/LMaxMax L/DL/D C/LC/L C/DC/D StallStall Lift to Drag Ratio L/DL/DMaxMax HighestHighest LiftLift toDragtoDrag RatioRatio

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

QuestionQuestion What combination of temperature, pressure and humidity would produce the greatest air density? What combination of temperature, pressure and humidity would produce the greatest air density? Answer: Low temperature, high pressure, and low humidity

Enabling Learning Objective #7 From memory, the student will describe, by writing or selecting from a list, the three types of drag and identify the factors affecting drag IAW FM From memory, the student will describe, by writing or selecting from a list, the three types of drag and identify the factors affecting drag IAW FM 1-203

DragDrag The resistance to an object’s passage through the air Types of Drag InducedInduced ProfileProfile ParasiteParasite

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

Profile Drag Parasitic drag of the rotor systemParasitic drag of the rotor system At a constant RPM, profile drag is relatively constant but does increase slightly with airspeed.At a constant RPM, profile drag is relatively constant but does increase slightly with airspeed. Increases rapidly with very high airspeeds due to onset of blade stall or compressibilityIncreases rapidly with very high airspeeds due to onset of blade 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 drag of the rotor systemParasitic drag of the rotor system At a constant RPM, profile drag is relatively constant but does increase slightly with airspeed.At a constant RPM, profile drag is relatively constant but does increase slightly with airspeed. Increases rapidly with very high airspeeds due to onset of blade stall or compressibilityIncreases rapidly with very high airspeeds due to onset of blade 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 Drag The resistance offered by the fuselage and other nonlifting surfaces to the flow of air The resistance offered by the fuselage and other nonlifting surfaces to the flow of air CausesCauses Form or shape of the helicopter, the more streamlined the helicopter, the less parasitic dragForm or shape of the helicopter, the more streamlined the helicopter, the less parasitic drag Skin friction, the smoother the skin of the fuselage, the less parasitic dragSkin friction, the smoother the skin of the fuselage, the less parasitic drag Form or shape of the helicopter, the more streamlined the helicopter, the less parasitic dragForm or shape of the helicopter, the more streamlined the helicopter, the less parasitic drag Skin friction, the smoother the skin of the fuselage, the less parasitic dragSkin friction, the smoother the skin of the fuselage, the less parasitic drag Increases rapidly with airspeed

Total Drag Curve The summation of all drag forces acting on the helicopter Total drag is high at a hover, decreases to a minimum value at a particular airspeed, then starts increasing with airspeed Total drag is high at a hover, decreases to a minimum value at a particular airspeed, then starts increasing with airspeed Minimum rate of descent for autorotation Maximum endurance airspeed Maximum rate of climb airspeed Best maneuvering airspeed Minimum rate of descent for autorotation Maximum endurance airspeed Maximum rate of climb airspeed Best maneuvering airspeed The above are airspeeds that fall within the lowest drag area of the total drag curve. Theses speeds typically range from 60 to 80 kts

Drag Forces DragDrag Forward Speed Torque Available InducedDrag ProfileDrag ParasiteDrag Total Drag

Questions?Questions?