11.3 Airfoilscfi-ground Last update: 11-23-2009

preperationobjective The student knows the different Terms related to airfoils and the Lift/Drag produced with them.

schedule5min Introduction30min Development5min Conclusion

training aidsWhiteboarddry erase markersPart of an Airfoil

introductionattention What does a wing, a rotor blade, a fan and a sail doe have in common?Can you imagine other airfoils ?

motivation It is important to understand the different Terms used to describe an airfoil. So everybody talks about the same stuff.

overviewDifferent terms used on an airfoilDifferent AirfoilsLift/Drag on an Airfoil

development1. Different terms used on an airfoil

draw a huge picture of an airfoil to describe all parts of itLeading Edge

The most forward point of an airfoilTrailing Edge

The most rearward point of an airfoilchord Line

straight line connecting leading and trailing edgeMean Camber Line

line in the middle of the airfoilstraight in a symetrical airfoil

center of PressureImaginary pointall forces are considered to act thereon the chord line

plane of rotationimaginary circular planeoutlined by rotor blade tips in the circle of rotation

feathering / feathering axisaxis used to rotate blades to change pitch anglestraight line between root of blade and tip

pitch angleangle between chord line andreference plane of the main rotor hubor the plane of rotation

relative windwind moving past the airfoilparallel and opposite to the flight path of airfoilnot affected by pitch angle

induced flowis the mass of air forced down by the rotor actionthe vertical component of relative wind ( flapping = 2nd vertical component)

horizontal airflowspeed of the blademovement of the helicopterwind speed and direction

angle of attackangle between chord line and relative winddetermines the amount of lift produced

2. Different airfoilsdraw a symetrical and an asymetrical airfoil on the board

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11.3 Airfoilscfi-ground Last update: 11-23-2009

Symetricalsame upper/lower cambermost common in Helicopterscheapercenter of Pressure hardly moves if angle of atack chnages

Asymetricalmore liftcenter of pressure moves if angle of attack is changeangle of atacks changes during the whole rotation, tendence to flap, feather and lagmoremore difficult to buildexpensive

The Main rotor in an R22Stainless steel leading edgeAluminum skinsAluminum Honeycomb centre

3. Lift/Drag on an Airfoillift on an airfoil

The direction of lift, is always perpendicular to the relative windLift formula: Lift = 1/2 pressure x Coificent of Lift x Surface area x velocityL=1/2p CL S v

drag on an airfoilis the resistance to motionsame formula as lift, but with the coificent of dragthree types of drag

Profile dragfrictional resistance of the bladesdoes not change much with change in angle of attackincreases moderately with increased airspeedform drag is the wake caused by the seperation of airflow of a structureskin friction is caused by the surface roughness

Induced dragrotor blades develop lift -> causes a vortex trails behind each blademajor cause of drag at lower airspeedsdecreases at higher airspeeds

parasite dragnon lifting components of the helicopter (cabin, mast, tail, gear) against the windmajor cause of drag at higher airspeeds.

Why/how to overcome drag ?Why ?

to maintain airspeedto maintain proper rpm

how in normal powered flightby power of the engine

how in autorotationby airflow enters the disc from belowno induced or profile drag, only parasite

lift vector couplesThrust and Lift work "together"Weight and drag work "together" in the opposite direction

Total thrustuse picture oneeffective Thrust produced by the rotor systemfirst determine lift produced and drag to get the total reactiondetermine rotor thrustsee how the total thrust is acting in a horizontal plane --> total lift and total thrust

conclusion

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11.3 Airfoilscfi-ground Last update: 11-23-2009

completion standards This lesson will be complete when, during oral quizzing, the student demonstrates a thorough understanding ofthe subjects discussed.

student evaluation

What is the difference between symmetrical and asymmetrical airfoils and what are the pros and cons?What parts do we have on an airfoil?What angles do we use on an airfoil?What forces act on an airfoil?What forces act on a helicopter?

summary We heared about different Airfoils, the parts of the Airfoils, and all related terms to lift/drag production.references / further study Rotorcraft Flying Handbook Chapter 2, 3

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11.3 Airfoilscfi-ground Last update: 11-23-2009

pic 1 : Angles and total thrust

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