“Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”

AerodynamicsAerodynamicsAerodynamics

Written for the Notre Dame Pilot Initiative

By the Pilots of the University of Notre Dame

Written for the Notre Dame Pilot Initiative

By the Pilots of the University of Notre Dame

Getting to the PointGetting to the PointGetting to the Point

Orville Wright Wilbur Wright

Four Forces of FlightFour Forces of FlightFour Forces of Flight� Lift opposes Weight

� Thrust opposes Drag

� In straight, unacceleratedflight, L = W & T = D

� Lift opposes Weight

� Thrust opposes Drag

� In straight, unacceleratedflight, L = W & T = D

� Lift created by pressure differential around wing. High pressure on lower surface and low pressure on the upper surface – low pressure caused by increased airflow velocity over top of airfoil.

� Weight – downward force of gravity

� Drag – rearward retarding force

� Thrust – forward force propelling airplane through air

� Lift created by pressure differential around wing. High pressure on lower surface and low pressure on the upper surface – low pressure caused by increased airflow velocity over top of airfoil.

� Weight – downward force of gravity

� Drag – rearward retarding force

� Thrust – forward force propelling airplane through air

AirfoilsAirfoilsAirfoils

�What is NACA?

♣ National Advisory

Committee for Aeronautics

♣ Chartered in 1915, operational

from 1917-1958

♣ The National

Aeronautics and Space Act of 1958

created NASA

from NACA

�What is NACA?

♣ National Advisory

Committee for Aeronautics

♣ Chartered in 1915, operational

from 1917-1958

♣ The National

Aeronautics and Space Act of 1958

created NASA

from NACA

Aerodynamic SurfacesAerodynamic SurfacesAerodynamic Surfaces

Aerodynamic SurfacesAerodynamic SurfacesAerodynamic Surfaces

Jet

Prop

B727 Spoilers

Airfoils - NomenclatureAirfoils Airfoils -- NomenclatureNomenclature

� Chord line - straight line connecting the leading and trailing edges of an airfoil

� Camber line – locus of all points equidistant from top and bottom of airfoil� Camber – distance between chord line and camber line � Thickness – maximum distance between top and bottom surfaces of wing� Leading Edge� Trailing Edge� Wingspan (b)� Aspect Ratio (AR = b2/S)

� Chord line - straight line connecting the leading and trailing edges of an airfoil

� Camber line – locus of all points equidistant from top and bottom of airfoil� Camber – distance between chord line and camber line � Thickness – maximum distance between top and bottom surfaces of wing� Leading Edge� Trailing Edge� Wingspan (b)� Aspect Ratio (AR = b2/S)

Low p

High p

FrostFrostFrost

�If wing is below

dewpoint which is

below freezing, frost

will form

�Sublimation of air to

solid ice crystals

�Disrupts smooth

airflow over the wing

�If wing is below

dewpoint which is

below freezing, frost

will form

�Sublimation of air to

solid ice crystals

�Disrupts smooth

airflow over the wing

�Why is this bad?

♣ Decreases lift

♣ Increases drag

�Frost removed

before take-off

�Rime Ice

�Clear Ice

�Why is this bad?

♣ Decreases lift

♣ Increases drag

�Frost removed

before take-off

�Rime Ice

�Clear Ice

Angle of AttackAngle of AttackAngle of Attack

�Angle between wing chord line and relative

wind

�The angle of attack at which airplane stalls

does not change

�Angle between wing chord line and relative

wind

�The angle of attack at which airplane stalls

does not change

Published NACA Data – NACA 2415Published NACA Data Published NACA Data –– NACA 2415NACA 2415

Airfoils - NomenclatureAirfoils Airfoils -- NomenclatureNomenclature

FlapsFlapsFlaps

� Flaps increase lift and decrease stall speed� Flaps allow steep rate of descent for approaches

without increasing airspeed

� Flaps increase lift and decrease stall speed� Flaps allow steep rate of descent for approaches

without increasing airspeed

Fowler Flap

Split Flap

Slotted Flap

Plain Flap

-Slotted Flap allows high pressure air underneath wing to join airflow above wing. This effectively increases velocity of top airflow and thus increases lift.

-Fowler Flap effectively increases the wing area by rolling backwards on a roller system.

Laminar v. TurbulentLaminar v. TurbulentLaminar v. Turbulent

Laminar flow about a sphere

Laminar v. TurbulentLaminar v. TurbulentLaminar v. Turbulent

Turbulent flow about a sphere

Bernoulli’s Principle - LiftBernoulliBernoulli’’s Principle s Principle -- LiftLift

� “As the velocity of a fluid increases, its internal pressure decreases.”

♣ From Newton’s 2nd (F=ma)

♣ Shown by Venturi tube

� “As the velocity of a fluid increases, its internal pressure decreases.”

♣ From Newton’s 2nd (F=ma)

♣ Shown by Venturi tube

Low Pressure

High Pressure

A1V1=A2V2

Bernoulli’s Principle AgainBernoulliBernoulli’’s Principle Agains Principle Again

Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B

Bernoulli’s Principle AgainBernoulliBernoulli’’s Principle Agains Principle Again

Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B

Bernoulli’s Principle AgainBernoulliBernoulli’’s Principle Agains Principle Again

Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B

Lift VectorLift VectorLift Vector

Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B

Drag TypesDrag TypesDrag Types

�Induced drag is the unavoidable by-product of lift

and increases as the angle of attack increases

�Parasite drag is caused by any aircraft surface

that deflects or interferes with smooth airflow

around airplane

♣Skin-friction drag - between the outer surfaces

of the aircraft and the air through which it

moves. Reduced by using glossy, flat finishes on

surfaces

♣Form drag - resistance of air to the shape of the

aircraft. Form drag can be reduced by

streamlining the aircraft shape.

�Induced drag is the unavoidable by-product of lift

and increases as the angle of attack increases

�Parasite drag is caused by any aircraft surface

that deflects or interferes with smooth airflow

around airplane

♣Skin-friction drag - between the outer surfaces

of the aircraft and the air through which it

moves. Reduced by using glossy, flat finishes on

surfaces

♣Form drag - resistance of air to the shape of the

aircraft. Form drag can be reduced by

streamlining the aircraft shape.

Drag – Body ComparisonDrag Drag –– Body ComparisonBody Comparison

cylinder

airfoil

sphere

Wingtip Vortices – “Twin Tornadoes”Wingtip Vortices Wingtip Vortices –– ““Twin TornadoesTwin Tornadoes””

‘High pressure on the lower surface creates a natural airflow that makes its way to the wingtip and curls upward around it to the area of low pressure. When flow around the wingtips streams out behind the airplane, a vortex is formed. These twisters represent an energy loss and are strong enough to flip airplanes that blunder into them.’

A few words on wingtip vortices:

Wingtip VorticesWingtip VorticesWingtip Vortices

Why Winglets?Why Winglets?Why Winglets?

�Equivalent to span extension w/o increased wingspan�Reduces wingtip vortices�Reduces drag

�Equivalent to span extension w/o increased wingspan�Reduces wingtip vortices�Reduces drag

NASA B-727 Wingtip Vortex Test Flight

http://www.airspacemag.com/ASM/Mag/Index/2001/AS/htww.html

Learn more about winglets:

Drag – Ground EffectDrag Drag –– Ground EffectGround Effect

TIP:

On a soft-field

runway, you can

takeoff at a lower

speed and then

accelerate while in

“Ground Effect.”

Drag vs Angle of AttackDrag Drag vsvs Angle of AttackAngle of Attack

Relationship between drag and angle of attack

Torque / P-factor (Left-Turning Tendencies)Torque / PTorque / P--factor (Leftfactor (Left--Turning Tendencies)Turning Tendencies)

�Newton’s 3rd law: “For every action there is an equal and opposite reaction.”♣ Propeller rotates CW

when viewed from pilot’s seat.

♣ Torque reaction rotates the airplane CCW about longitudinal axis

�P-factor (asymmetrical thrust) caused by descending blade taking a greater “bite” of air than ascending blade at high angle of attack

�Newton’s 3rd law: “For every action there is an equal and opposite reaction.”♣ Propeller rotates CW

when viewed from pilot’s seat.

♣ Torque reaction rotates the airplane CCW about longitudinal axis

�P-factor (asymmetrical thrust) caused by descending blade taking a greater “bite” of air than ascending blade at high angle of attack

Stability & ControlStability & ControlStability & Control

� Center of Gravity concerns:

♣ Unable to compensate with elevator in pitch axis

♣ Weight and Balance becomes critical – taught in a coming lecture

� Center of Gravity concerns:

♣ Unable to compensate with elevator in pitch axis

♣ Weight and Balance becomes critical – taught in a coming lecture

� Inherently stable airplane returns to its original condition after being disturbed. Requires less effort to control

� Inherently stable airplane returns to its original condition after being disturbed. Requires less effort to control

Stability & ControlStability & ControlStability & Control

yaw

roll

pitch

� The 3 axes of motion: roll, pitch, yaw

� The 3 axes of motion: roll, pitch, yaw

Tail PlacementsTail PlacementsTail Placements

Looks like the A-10Also called “H-Tail”

CanardsCanardsCanards

�Stabilizer located in front of the main wings

�Used on the Wright Flyer

�More aerodynamically efficient than an elevator b/c canards provide positive lift

�Stabilizer located in front of the main wings

�Used on the Wright Flyer

�More aerodynamically efficient than an elevator b/c canards provide positive lift

Accident Report – Loss of ElevatorAccident Report Accident Report –– Loss of ElevatorLoss of Elevator

AIRCRAFT FINAL REPORTTHE AIRCRAFT HAD JUST BEEN REPAIRED AFTER RECEIVING TORNADO DAMAGE. THIS REPAIR INCLUDED REMOVAL AND REPLACEMENT OF THE ELEVATOR CONTROL TUBE. THE PILOT TAXIED TO THE RUNWAY FOR THE PURPOSE OF A TEST FLIGHT. ALL FLIGHT CONTROL CHECKS APPEARED NORMAL. AFTER LIFT-OFF, THE PILOT INTENDED TO LEVEL OFF AT 5 TO 10 FEET, THEN TOUCH DOWN AGAIN. HOWEVER, AFTER THE AIRPLANE BECAME AIRBORNE, HE LOST ELEVATOR CONTROL, AND THE AIRCRAFT CLIMBED STEEPLY TO 50 TO 75 FEET. THE PILOT THEN REDUCED POWER, THE AIRCRAFT'S NOSE DROPPED, AND THE AIRCRAFT DESCENDED. WITH NO ELEVATOR CONTROL, THE PILOT WAS UNABLE TO ARREST THE DESCENT, AND THE AIRCRAFT IMPACTED THE GROUND. A POST-CRASH EXAMINATION REVEALED THAT A BOLT AND NUT WERE MISSING FROM THE ELEVATOR CONTROL LINKAGE, WHICH ALLOWED THE LINKAGE TO BECOME DISCONNECTED.

AIRCRAFT 1 CAUSE REPORTFAILURE OF MAINTENANCE PERSONNEL TO PROPERLY REINSTALL A BOLT AND NUT IN THE ELEVATOR CONTROL LINKAGE, WHICH RESULTED IN A DISCONNECT OF THE LINKAGE AND LOSS OF ELEVATOR CONTROL.

AIRCRAFT FINAL REPORTTHE AIRCRAFT HAD JUST BEEN REPAIRED AFTER RECEIVING TORNADO DAMAGE. THIS REPAIR INCLUDED REMOVAL AND REPLACEMENT OF THE ELEVATOR CONTROL TUBE. THE PILOT TAXIED TO THE RUNWAY FOR THE PURPOSE OF A TEST FLIGHT. ALL FLIGHT CONTROL CHECKS APPEARED NORMAL. AFTER LIFT-OFF, THE PILOT INTENDED TO LEVEL OFF AT 5 TO 10 FEET, THEN TOUCH DOWN AGAIN. HOWEVER, AFTER THE AIRPLANE BECAME AIRBORNE, HE LOST ELEVATOR CONTROL, AND THE AIRCRAFT CLIMBED STEEPLY TO 50 TO 75 FEET. THE PILOT THEN REDUCED POWER, THE AIRCRAFT'S NOSE DROPPED, AND THE AIRCRAFT DESCENDED. WITH NO ELEVATOR CONTROL, THE PILOT WAS UNABLE TO ARREST THE DESCENT, AND THE AIRCRAFT IMPACTED THE GROUND. A POST-CRASH EXAMINATION REVEALED THAT A BOLT AND NUT WERE MISSING FROM THE ELEVATOR CONTROL LINKAGE, WHICH ALLOWED THE LINKAGE TO BECOME DISCONNECTED.

AIRCRAFT 1 CAUSE REPORTFAILURE OF MAINTENANCE PERSONNEL TO PROPERLY REINSTALL A BOLT AND NUT IN THE ELEVATOR CONTROL LINKAGE, WHICH RESULTED IN A DISCONNECT OF THE LINKAGE AND LOSS OF ELEVATOR CONTROL.