an introduction to rotor aeromechanicssimilar to a fixed-wing aircraft, a rotary-winged aircraft can...

How Do Helicopters Fly? An Introduction to Rotor Aeromechanics

Rotor Aeromechanics Quiz

1. A helicopter’s engine must always supply power to keep a rotor turning - True or False?

2. When flying forward, a helicopter’s rotor blades flap up and down – True or False?

Lift

Propulsion

Lift and Propulsion

Helicopters vs. Airplanes What’s the difference?

PresenterPresentation NotesLift and propulsion are separated on an airplane: Lift is done by the wing, propulsion is done by the propeller Lift and propulsion are both done by the rotor on a helicopter

What affects the amount of LIFT on a wing?

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=iwq5V4NjkXQhSM&tbnid=zOit0oneFn7_mM:&ved=0CAUQjRw&url=http://fantasystock.deviantart.com/art/Airplane-Wing-in-the-Sky-57391338&ei=sgSvUaykGKPG0wGBhYG4AQ&bvm=bv.47380653,d.dmQ&psig=AFQjCNF9PMWEXSmV2mJUYDGO5utRlzrrnw&ust=1370510152789884

What Affects the Amount of Lift on a Wing?

Bigger wing = MORE LIFT

Lift

Lift

Size


Density is higher at lower altitudes and lower temperatures

Greater air density = MORE LIFT

Lift

Density

air molecules

)

Lift


Higher Angle of Attack = MORE LIFT

Lift

Lift

Orientation and Shape

As the airfoil pitch (angle of attack) is increased, lift increases until the wing stalls

Thicker Wing = MORE LIFT

CL is called the Lift Coefficient – it is a factor that depends on

shape and orientation


Velocity

Greater velocity = MORE LIFT

Velocity

Lift

Lift

Velocity

Measuring Wing Lift

Lift Equation:

Lift effects

Density of Air Size of Wing Velocity of Air Orientation and Shape of Wing

Rotary Wing

V

Helicopter rotors produce lift by rotating their wings The velocity over the rotor wing in a hover is zero at the center and highest at the tip

Velocity

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=tIoxfzcG_1BMoM&tbnid=GXYCrV1dxOGDZM:&ved=0CAUQjRw&url=http://www.tungsten-alloy.com/aerospace-industry.htm&ei=EwWvUY2GBsPb0QGGtYDYAg&bvm=bv.47380653,d.dmQ&psig=AFQjCNGa-bTyVzD2gekGbCuVbVj4f4OKNQ&ust=1370510971827941

Rotary Wing Lift in Hover

Lift is zero at the center and highest at the tips

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=1Yx-S0R94nQMzM&tbnid=JdtuxJE7f9mk_M:&ved=0CAUQjRw&url=http://www.helis.com/70s/h_mi26.php&ei=HK9wUamoJvH-4APslQE&bvm=bv.45373924,d.dmg&psig=AFQjCNFsHxyv0YoMjWVIX_tj6jD5IZUOBw&ust=1366425556163008

Rotor Lift

- Where is the lift the greatest on the spinning rotor? - Where is the lift the least? - How can you increase the total lift?

Maple Seed Flight

PresenterPresentation NotesThe maple seed will rotate in flight without power

Helicopter Autorotation Without any power supplied to the rotor, it is capable of producing thrust approximately equivalent to a parachute of the same diameter.

PresenterPresentation NotesSimilar to a fixed-wing aircraft, a rotary-winged aircraft can glide to a landing in the event of a power failure. Unlike a fixed wing aircraft, a rotorcraft can land with zero forward airspeed.

Helicopter Autorotation

PresenterPresentation NotesSimilar to a fixed-wing aircraft, a rotary-winged aircraft can glide to a landing in the event of a power failure. Unlike a fixed wing aircraft, a rotorcraft can land with zero forward airspeed.

Forward Flight

Thrust Forward velocity

Hover

V

Velocity evenly distributed along blades

Forward Flight

Hover

Flow backward over blade

Forward flight speed

V V

Increased velocity on advancing blade Decreased velocity

on retreating blade

Velocity evenly distributed along blades

19

Forward Flight Changes Lift on Rotor Forward speed

Less Lift

Rolling moment

More Lift

Uneven lift makes the helicopter want to flip over

V

20

If the rotor blades are allowed to flap up and down, the lift will be balanced side to side

No rolling moment

Advancing blade flaps up reducing angle of attack

Retreating blade flaps down increasing angle of attack

Blade Flapping Equalizes Lift

Flapping Hinge

Same amount of lift on either side

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=E182v3VLQZAQOM&tbnid=4b_wOjs8f_5URM:&ved=0CAUQjRw&url=http://www.clker.com/clipart-196538.html&ei=aMS5UbDrD5XI4APbooDoBA&bvm=bv.47883778,d.dmg&psig=AFQjCNFiSceHTu4_jtdernOWkUpwojspNA&ust=1371215324646963

The response of a flapping rotor blade lags the force by 90o Maximum flapping occurs 90o after maximum angle of attack is applied. OR maximum flapping occurs 90o after maximum velocity is applied.

Rotor Phase Lag

Higher velocity here so higher lift here

Top view


Rotor Phase Lag

Higher velocity on the advancing blade = increased lift

Side view

Velocity


Rotor Phase Lag

Phase lag causes rotor to flap up 90o later (front flaps up)

Velocity

Which way will this rotor want to tilt next?

More lift here due to rear tilt

front

back

left right

Rotor tilts to the right!

right

rear

left front

Blade flaps UP here

How does this helicopter tilt its rotor?

Rotor Activities

• Rotor Build \ Test – Operate rotor in vertical and forward autorotation

• Whirly gig flight target practice – Attempt to land whirly-gig on target anticipating

flapping response

• Parrot UAV flying skills course – Fly the Parrot quad-rotor, determine how quad-

rotor is controlled

Rotor Build Instructions

cork

bend

bend bend

bend

wire

Insert wire through the holes in the cork rotor head and bend as shown


Balsa rotor blade tape

Attach rotor blades to rotor head with masking tape. Wrap masking tape around the blades several times to ensure blades do not separate in flight!

- Turn rotor upside down and insert skewer into rotor head perpendicular to the surface


- Adjust rotor blade angle of attack (both blades must have equal pitch) - Determine direction of rotation for positive lift - Spin rotor to test operation

- Observe downwash - Observe coning

- Slide straw over skewer - Secure small cork into skewer - Test over fan and adjust pitch to achieve maximum thrust and

maximum forward flight speed. Observe flapping.

Questions?

Rotor Aeromechanics Quiz – Post Lesson

3. A helicopter’s engine must always supply power to keep a rotor turning - True or False?

4. When flying forward, a helicopter’s rotor blades flap up and down – True or False?

Video Links Early video of rotor blade motion from blade perspective https://www.youtube.com/watch?v=Ug6W7_tafnc Animation of rotor control in operation https://www.youtube.com/watch?v=83h6QK-oJ4M Early NASA autorotation studies for spacecraft recovery: http://www.youtube.com/watch?NR=1&v=gAYaEBd6L94&feature=endscreen Roton demonstration (rotor powered by tip jets) http://www.youtube.com/watch?v=ZhtvCAZgz0Q

https://www.youtube.com/watch?v=Ug6W7_tafnchttps://www.youtube.com/watch?v=83h6QK-oJ4Mhttp://www.youtube.com/watch?NR=1&v=gAYaEBd6L94&feature=endscreenhttp://www.youtube.com/watch?v=ZhtvCAZgz0Q

How Do Helicopters Fly?�An Introduction to Rotor AeromechanicsRotor Aeromechanics QuizHelicopters vs. AirplanesWhat affects the amount of LIFT �on a wing?What Affects the Amount of Lift on a Wing?What Affects the Amount of Lift on a Wing?What Affects the Amount of Lift on a Wing?What Affects the Amount of Lift on a Wing?Measuring Wing LiftRotary Wing Slide Number 11Rotor Lift Maple Seed FlightHelicopter Autorotation Helicopter Autorotation Forward FlightSlide Number 17Slide Number 18Forward Flight Changes Lift on RotorSlide Number 20Slide Number 21 Rotor Phase Lag Rotor Phase Lag Rotor Phase LagSlide Number 25Slide Number 26Slide Number 27Rotor ActivitiesRotor Build InstructionsRotor Build InstructionsRotor Build InstructionsSlide Number 32Slide Number 33Questions?Rotor Aeromechanics Quiz – �Post LessonVideo Links

an introduction to rotor aeromechanicssimilar to a fixed-wing aircraft, a rotary-winged aircraft can...

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