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Aerodynamics – What Makes Airplanes Fly
Doylestown Pilots Association
Boy Scouts Aviation Day 10/13/2012
Maj William J. Doyle, Jr.
Civil Air Patrol, New Jersey Wing, Assistant StanEval Officer
Check Pilot / Instructor-Pilot
CFI A&I, AGI, IGI, CFAI, FAAST Rep
Aerodynamics Lesson Plan
• What is an Airplane and What Makes It Fly
• The Airplane
• Flight Controls
• Axes of Rotation
• Forces Acting on the Airplane in Flight
• Dynamics of the Airplane in Flight
• Ground Effect
• How Airplanes Turn
• Torque (Left-Turning Tendency)
• Airplane Stability
• Stalls and Spins
How Do the Flight Controls Work?
• Push the stick (or yoke) forward and the houses get bigger.
• Pull the stick (or yoke) back and the houses get smaller.
• Hold the stick (or yoke) back too long and the houses get really small
then they get bigger again. (You just did a loop.)
Parts of An Airplane
Airplane Components
Airplane Components - Fuselage

Open truss


clearly visible struts and wire braces
Stressed skins

monocoque


skin supports all loads
semi-monocoque

sub-structure riveted to skin to maintain shape and
increase strength
Airplane Stressed-Skin Types
Airplane Truss-Type Fuselage Structure
Airplane Components - Wings

Monoplane


Biplane


single set of wings
two sets of wings
Ailerons



move in opposite directions for turns
controls roll (or bank)
controlled by yoke or stick



right pressure turns right
left pressure turns left
Flaps


extend downward to increase lifting force for landings and
sometimes takeoffs
controlled by flap handle or switch

pre-selected positions or variable positions
Airplane Wings: Monoplane vs. Biplane
Airplane Wing Components
Airplane Components - Empennage

Vertical Stabilizer and Horizontal Stabilizer


help steady airplane for straight flight
Rudder controls yaw

controlled by floor pedals



Elevator (stabilator on Cherokee) controls pitch

controlled by yoke or stick



right pressure moves nose to right
left pressure moves nose to left
forward pressure lowers nose
back pressure raises nose
Trim Tab helps hold pitch attitude

controlled by trim wheel


move wheel forward for nose down trim
move wheel back for nose up trim
Airplane Empennage
Airplane Components - Landing Gear

Gear Types





Landing Gear Struts





Fixed Gear
Retractable Gear
Tricycle Gear
Conventional Gear (tail dragger)
Spring steel struts
bungee cord struts
oleo struts
shock disks
Brakes


Disc brakes
Differential braking
Airplane Landing Gear
Airplane Components - Powerplant

Engine



Firewall



provides power to turn propeller
distinguishes airplane from glider
separates cockpit from engine
mounting point for engine
Propeller

translates engine rotational force into forward-acting
force called thrust
Airplane Powerplant
Wing Planforms
Aspect Ratio = Wing Span ÷ Average Chord
What Makes an Airplane Fly?
• For an airplane to takeoff, thrust must overcome drag and lift must
overcome gravity (sometimes called weight)
• So is there relevancy here to what you study in school?
– Applicable Subject in School = Science
– High School Course = Physics (study the chapter on Bernoulli’s Law)
What Makes an Airplane Fly?
• The laws of physics apply to everything.
• They apply to F-16 fighters and to the USAF Thunderbirds.
What Makes an Airplane Fly?
• The laws of physics
apply to everything.
• They apply to ultra
lights.
What Makes an Airplane Fly?
• The laws of
physics apply to
everything.
• They even
applied to the
Wright Brothers
in the Wright
Flyer at Kitty
Hawk, NC.
Four Forces of Flight
Vector
Vector
Vector
Vector
Four Forces of Flight

Lift


Weight


downward force of gravity
Thrust


upward force from airflow over and under wing
forward force propelling airplane through air
Drag

rearward force retarding force limiting speed
Four Forces of Flight
Newton’s Laws of Force and Motion

Newton’s First Law


Newton’s Second Law


A body at rest tends to remain at rest, and a body in
motion tends to remain moving at the same speed and in
the same direction.
When a body is acted upon by a constant force, its
resulting acceleration is inversely proportional to the
mass of the body and is directly proportional to the
applied force.
Newton’s Third Law

For every action there is an equal and opposite reaction.
Bernoulli’s Principle
Bernoulli’s Principle
• Explains how the pressure of a moving fluid (liquid or gas) varies with its speed of
motion.
• States that as the velocity of a moving fluid (liquid or gas) increases, the pressure
within the fluid decreases.
• Explains what happens to air passing over the curved top of the airplane wing.
Bernoulli’s Principle - 1 of 3
Bernoulli’s Principle - 2 of 3
Bernoulli’s Principle - 3 of 3
In-Flight Application of Bernoulli
Illustration of Vectors
and Resultant Vectors
Types of Air Foils
Components of an Airfoil
•
•
Airfoil: a structure designed to obtain reaction upon its surface from the air through which it
moves or that moves past such a structure.
Camber: curvatures of the upper and lower surfaces of the airfoil. The camber of the
upper surface is more pronounced than that of the lower surface, which is usually
somewhat flat.
•
•
Chord Line: a straight line drawn through the profile connecting the extremities of the
leading and trailing edges.
Mean Camber Line: reference line drawn from the leading edge to the trailing edge,
equidistant at all points from the upper and lower surfaces.
•
•
Leading Edge faces forward in flight and is rounded.
Trailing Edge faces aft in flight and is narrow and tapered.
Relationship of Flight Path
to Relative Wind
Angle of Attack Examples
Angle of Attack Examples
Angle of Attack and Wing Stalls
Air circulation around an
airfoil occurs when the front
stagnation point is below the
leading edge and the aft
stagnation point is beyond
the trailing edge.
Effect of Wingtip Twist
Wingtip
Wing Root
Effect of Stall Strip
Wingtip
Wing Root
Flaps Increase Both Lift and Drag
Types of
Flaps
and
Leading
Edge
Devices
Types of Drag

Parasite Drag


Caused by any aircraft surface which deflects or interferes
with smooth airflow around airplane
Form drag


Interference drag


occurs when varied currents of air over an airplane meet and interact
Skin friction drag


results from turbulent wake caused by the separation of airflow from
the surface of the structure
caused by roughness of the airplane’s surfaces
Induced Drag

Generated by the airflow circulation around the wing as it
creates lift
Examples of Drag
Examples of Reducing Drag
Total Drag and L/Dmax Ratio
Ground Effect



Result of earth’s surface altering the airflow patterns
around the airplane.
Occurs within one wingspan above the ground.
When in ground effect


Induced drag decreases and excess speed in the flare may
cause floating.
Airplane may become airborne before it reaches its
recommended takeoff speed.
Three Axes of Flight
Longitudinal Stability and Balance

Longitudinal Stability



Center of Pressure



Pitching motion or tendency of airplane to move about its
lateral axis.
Determined by the location of the center of gravity in
relation to the center of pressure.
Point along wing chord where lift is considered to be
concentrated.
Sometimes called the center of lift.
Center of Gravity


Determined by the distribution of weight, either by design
or by the pilot.
Can affect longitudinal stability.
Center of Pressure
Three Axes of Flight
Center of Gravity (CG)
CG Range - Forward CG & Aft CG
CG Range - Forward CG & Aft CG
Longitudinal Stability
• Quality that makes an aircraft stable about its lateral axis.
• Involves the pitching motion as the aircraft’s nose moves up
and down in flight.
– A longitudinally unstable aircraft has a tendency to dive or climb
progressively into a very steep dive or climb, or even a stall.
– An aircraft with longitudinal instability becomes difficult and
sometimes dangerous to fly.
• Static longitudinal stability or instability in an aircraft, is
dependent upon three factors:
– Location of the wing with respect to the CG
– Location of the horizontal tail surfaces with respect to the CG
– Area or size of the tail surfaces
Longitudinal Stability
Horizontal Stabilizer
and Tail Down Force
Static Stability
• Initial tendency, or direction of movement, back to
equilibrium.
– Refers to the aircraft’s initial response when disturbed from a
given angle of attack (AOA), slip, or bank.
• Positive static stability
– the initial tendency of the aircraft to return to the original state of
equilibrium after being disturbed
• Neutral static stability
– initial tendency of the aircraft to remain in a new condition after its
equilibrium has been disturbed
• Negative static stability
– initial tendency of the aircraft to continue away from the original
state of equilibrium after being disturbed
Static Stability
Dynamic Stability
• Dynamic stability refers to the aircraft response over time
when disturbed from a given angle of attack (AOA), slip, or
bank. It has three subtypes:
• Positive dynamic stability
– over time, the motion of the displaced object decreases in
amplitude and, because it is positive, the object displaced returns
toward the equilibrium state.
• Neutral dynamic stability
– once displaced, the displaced object neither decreases nor increases
in amplitude. A worn automobile shock absorber exhibits this
tendency.
• Negative dynamic stability
– over time, the motion of the displaced object increases and
becomes more divergent.
Dynamic Stability
Horizontal Stabilizer
and Tail Down Force
Center of Lift
Center of
Gravity
Directional Stability

Directional Stability


Stability about the airplane’s vertical axis.
Steadying influence of the vertical stabilizer.


Acts like a weather vane.
Interaction of Directional Stability with
Lateral Stability

Dutch Roll



Combination of rolling / yawing oscillations caused by control
inputs or wind gusts.
Dihedral (lateral stability) more powerful than directional stability.
Spiral Instability

Directional stability more powerful than lateral stability.
Lateral Stability

Lateral Stability



Stability about the airplane’s longitudinal axis (nose to tail).
Tendency to resist lateral roll.
Dihedral



Common design approach to build in lateral stability.
Upward angle of the wings with respect to the horizontal.
Less dihedral in high wing airplanes than in low wing
aircraft.


Cessna 172 versus Mooney M20J
Keel Effect

Steadying influence of side area of the fuselage and the
vertical stabilizer.
Illustration of Dihedral
Illustration of Dihedral
Airspeed Indicator (ASI) and V-speeds

V-speeds



Vx = best angle *
Vy = best rate *

Va = maneuvering *
Vfe = flap extend
Vs = stall clean configuration
Vso = stall landing configuration
Vno = max structural cruising speed

Vne = never exceed speed
*
not on ASI



• Arcs

white



green



bottom = Vs
top
= Vno
yellow



bottom = Vso
top
= Vfe
bottom = Vno
top
= Vne
red line
= Vne
Airspeed Indicator (ASI)
Types of Airspeed

Indicated Airspeed (IAS)




Calibrated Airspeed (CAS)


Corrected for instrument and installation errors
True Airspeed (TAS)


Speed indicated on ASI
Uncorrected for instrument and installation errors
No variations in air density
CAS corrected for

altitude

nonstandard temperature
Groundspeed (GS)

Speed over the ground

TAS adjusted for wind
Types of Stalls

Proficiency Stalls (Student Mastery)



Demonstration Stalls (CFI Demonstration)




Power-off stalls: landing conditions & configuration
Power-on stalls: take-off conditions & configuration
Secondary stalls
Cross-control stalls
Accelerated stalls
Stall Recovery



Decrease angle of attack
Smoothly apply maximum power
Adjust power & configure for normal, coordinated flight.
V-g Diagram
V-g Diagram
Spins

Definition of a Spin



Types of Spins




Aggravated stall accompanied by autorotation.
One wing stalled more than the other wing.
Erect
Inverted
Flat
Stages or Phases



Incipient spin
Fully developed spin (steady-state)
Spin recovery
Spin Recovery







Throttle to idle
Neutralize ailerons
Determine direction of spin via turn coordinator
Full opposite rudder
Briskly apply forward elevator pressure
Neutralize rudder
Gradually apply back elevator pressure
Left-Turning Tendencies
•
The left turning tendency of the airplane is made
up of four elements which cause or produce a
twisting or rotating motion around at least one of
the airplane’s three axes.
–
–
–
–
Torque reaction from engine and propeller,
Corkscrewing effect of the slipstream,
Gyroscopic action of the propeller, and
Asymmetric loading of the propeller (P-factor).
Left-Turning Tendencies
Left-Turning Tendencies
Airplanes in Glide

Best Glide Speed



See POH
C-172 = 70 knots
Glide Ratio


See POH
E.G. glide ratio of 10:1 means airplane will travel 10,000
feet (1.6 nm) horizontally for each 1,000 feet of altitude lost



Typical Cessna 172
Typical Piper Cherokee (Warrior)
Factors Affecting Glide



Weight
Configuration
Wind
9.1 : 1
11.5 : 1
Types of Turns

Shallow turns



Medium turns



Less than 15°
Tendency to return to straight-and-level flight
(positive static stability)
15° or more but not more than 30°
Tendency to return to remain in the turn
(neutral static stability)
Steep turns


More than 30°, usually 45°
Tendency to steepen the turn (overbanking tendency)
(negative static stability)
Rate and Radius of Turns

Rate of Turn




Amount of time it takes an airplane to turn a specified
number of degrees
If airspeed increases with angle of bank constant, then rate
of turn decreases.
If angle of bank increases with airspeed constant, then rate
of turn increases.
Radius of Turn



Amount of horizontal distance an airplane uses to
complete a turn
If airspeed increases with angle of bank constant, then
radius of turn increases.
If angle of bank increases with airspeed constant, then
radius of turn decreases.
Forces Acting on Airplane in A Turn
Normal, Slipping and Skidding Turns
Bank Angle Effect on Load Factor
Bank Angle Impact on Load Factor
Bank Angle Impact on Load Factor
and Stall Speed
Components of Lift
• Division of Lift
 Vertical Component of Lift
 Horizontal Component of Lift
• Offsetting Forces
 Vertical Component of Lift  Weight
 Horizontal Component of Lift  Centrifugal Force
 Total Lift  Load Factor
• Horizontal Component of Lift = sideward force
that causes airplane to turn (centripetal force)
Effects of Division of Lift
• Division of lift reduces lift supporting airplane,
produces altitude loss unless:
Increase angle of attack
Increase airspeed
Increase angle of attack and airspeed
Trim up when passing 30º bank into 45º bank
Roll-out to 30º as necessary to regain altitude
Load Factor, Stall Speed, & Bank Angle
 Stall speed increases by LoadFactor
– 30° bank = load factor of 1.1  1.05 * VS
– 45° bank = load factor of 1.4  1.20 * VS
– 60° bank = load factor of 2.0  1.40 * VS
 Maximum bank angle = 50º -- 60º
 Load Factor versus Bank Angle
– 60° bank = 2 g
– 70° bank = 3 g
– General Aviation airplanes stressed for max 3.8 g
Limit Load Factor

Definition of Limit Load Factor


Normal Category



3.8 positive G’s
1.52 negative G’s
Utility Category



Amount of stress or load factor that an airplane can
withstand before structural damage or failure occurs.
4.4 positive G’s
1.76 negative G’s
Acrobatic Category


6 positive G’s
3 negative G’s
References and Information
•
•
•
•
Downloading This Presentation
– http://williamjdoylejr.net/pvt/Aerodynamics.ppt
– http://williamjdoylejr.net/pvt/DoyleWJ_CFII/
FAA Airplane Flying Handbook – FAA-H-8083-3A
– Airplane Structure, Chapter 2
http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/PHAK%20%20Chapter%2002.pdf
– Principles of Flight, Chapter 3
http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/PHAK%20%20Chapter%2003.pdf
– Aerodynamics of Flight, Chapter 4
http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/PHAK%20%20Chapter%2004.pdf
– Flight Controls, Chapter 5
http://www.faa.gov/library/manuals/aviation/pilot_handbook/media/PHAK%20%20Chapter%2005.pdf
Pilot Handbook: A Comprehensive Text/Reference for All Pilots (Eighth Edition), Irvin N. Gleim,
Ph.D., CFII and Garrett W. Gleim, CFII, MEI
– Airplanes and Aerodynamics, Chapter 1, pp 15 – 66
Other Resources – Maj Bill Doyle
– http://home.netcom.com/~doylewj/Aviation/student_pilot_flight_training/default.htm
– http://home.netcom.com/~doylewj/default.htm
– http://williamjdoylejr.net/Careers/Career_Awareness_Aviation_St_Marks_2010-06-02.ppt
About the Presenter
• Aviator
– Commercial, Instrument, ASEL & AMEL
– 3,000 hours total time; 850 hours TAA; 500 hours KFC 150; 700 hours Garmin 430,
150 hours Garmin G1000
• Instructor
–
–
–
–
CFI A&I, AGI, IGI, ASC
1,400 hours as CFI
Cessna FITS Course and CFAI Course (G1000 for C182 and U206)
FAA PHL FSDO CFI of the Year 2009-2010
• Civil Air Patrol
– Instructor-Pilot, Check Pilot, and Check-Pilot Examiner
– G1000 Project Officer
• Technologist & Teacher
– Director of Technical Services, Hatboro-Horsham School District
– Nursing Informatics Instructor, La Salle University Graduate School of Nursing
• Author
– Two books on electronic spreadsheets, with a Russian translation
– Self-study manuscript on computer concepts for nurses
– Articles on gear up landings and fuel management published by FAA
The Escape Pod
Cirrus
SR20
with
Ballistic
Parachute
Aim High!
But Not On Final!
If you’ve ever wondered…
•
•
•
•
•
•
•
What are the main parts of an airplane?
What’s a fuselage?
What makes an airplane fly?
How do aircraft wings work?
How is a plane controlled?
What is the instrument panel?
How do you get from one place to another?
…then this class is for you!
Warming Up – Soda Straw Experiment
• Put the end of a soda straw into a glass of
water or a bottle of soda
• Put your finger on the top of the straw
• Lift the straw from the glass or soda
bottle.
• The water or soda remains in the straw
because the effect of the air pressure
up the straw is greater than the weight
of the water or soda.
• Remove your finger and the water or soda
falls out of the straw.
• Do you know why this is important to
aviation?
Courtesy of J. Elfick, University of Queensland, Australia
Why the Soda Straw is Important
• Pilots are taught that airplane fuel gauges
are unreliable
• Do you know at what point the gauges are
required by law to be accurate?
• The straw becomes a calibrated plastic
tube
• The calibrations represent the gallons of
gas remaining in the fuel tank
• Each wing has a fuel tank.
• In the airplane that I currently fly:
• Each wing holds 43½ gallons
• Total fuel is 87 gallons
• Fuel consumption is 12½ to 15 gallons
per hour
• So how long can I stay in the air?
What Are the Main Parts of an Airplane
What Are the Main Parts of an Airplane
Main Parts of an Airplane - Definitions
• Airplane – An airplane is a vehicle heavier than air, powered by
an engine, which travels through the air via the forces of lift and
thrust.
• Fuselage – The fuselage is the central body portion of an
airplane, designed to accommodate the pilot/crew and the
passengers and/or cargo.
• Cockpit – In general aviation airplanes (all except those operated
by airlines and the military) the cockpit is usually the space in the
fuselage for the pilot and passengers; in some aircraft it is just the
pilot’s compartment.
• Propeller – A propeller is a rotating blade on the front of the
airplane. The engine turns the propeller, which pulls the airplane
through the air.
• Wings – Wings are the parts of airplanes that provide lift and
support the entire weight of the aircraft and its contents while in
flight.
Main Parts of an Airplane - Definitions
• Flaps – Flaps are the movable sections of an airplane’s wings that are
closest to the fuselage. They move in the same direction on both
wings at the same time, and enable the airplane to fly more slowly.
• Ailerons – Ailerons are the outward movable sections of an airplane’s
wings. They move in opposite directions (if one goes up, the other
goes down). They are used in making turns, and they control
movement around the longitudinal axis (imagine a line through the
airplane from the nose to the tail).
• Rudder – The rudder is the movable vertical section of the tail that
controls lateral (side-to-side) movement. When the rudder moves one
direction, the aircraft nose moves the same direction, while the tail
moves in the opposite direction.
Main Parts of an Airplane - Definitions
• Horizontal Stabilizer – The horizontal stabilizer is the horizontal
surface at the rear of the fuselage designed to balance the airplane.
• Elevator – The elevator is the movable horizontal section of the tail
that causes the plane to move up and down. When the elevator moves
one direction, the nose moves in the same direction.
• Landing Gear – A landing gear is underneath the airplane and
supports it while on the ground. A landing gear usually includes a
wheel and tire.
Instrument Panel – Cessna 172 Skyhawk
Flight Instruments
Airspeed Indicator
Attitude Indicator
Turn Coordinator
Heading Indicator
Altimeter
Vertical Speed Indicator
Flight Instruments
What Effect Does Wind Have?
• There is always wind. The higher you climb, the stronger it gets.
• You have to fly a heading that offsets the effect of the wind.
• So is there relevancy here to what you study in school?
– Applicable Subject in School = Math
– High School Course = Trigonometry
How Do You Calculate the Effect of Wind?
• The E6B Flight Computer – sort of a circular slide rule.
• Cost = $30
How Do You Calculate the Effect of Wind?
• The Garmin GNS 430 – all-in-one GPS/Navigation/Communication product.
• The Garmin GNS 430 does it all for you.
• Cost = $9,650 installed.
• Having someone else pay for this – priceless!
How Do You Calculate the Effect of Wind?
• Online Flight Planning Tools
– Look at winds for your route of
flight
– Calculate the wind correction
for you automatically
• Costs
– Computer
– Internet connection
– Annual membership in AOPA
• So is there relevancy here to
what you study in school?
– Applicable Subject in School =
Technology
– School Courses = Computer
Applications, Internet
How Much Can an Airplane Weigh?
• Each airplane has a limitation called the maximum gross takeoff
weight. Some airplanes also have a maximum gross landing weight.
• This weight includes everything
–
–
–
–
Airplane (empty)
Fuel
Pilot and passengers
Baggage
• There is another component called “Balance.” The entire process is
called “Weight and Balance.”
• So is there relevancy here to what you study in school?
– Applicable Subject in School = Math
– Elementary and Middle School = Math (Arithmetic for the “Weight” piece)
– High School Course = Physics (Center of Gravity for the “Balance” piece)
What Does Balance Mean?
• Classic example is the playground seesaw:
–
–
–
–
Center bar is the fulcrum which is the center of gravity.
Heavier weight of “big” kid on one end overcomes lesser weight of “little” kid other end
This forces the “little” kid to go up
Is there a way to make the “big” kid go up without adding weight or changing kids?
• So is there relevancy here to what you study in school?
– Applicable Subject in School = Science
– High School Course = Physics (Chapter on Center of Gravity)
What Does Balance Mean for an Airplane?
• The laws of physics
apply to everything.
• Calculate the airplane’s
center of gravity for your
flight.
• If outside the envelope,
move people or baggage
– Recalculate to see if that
helped
• If yes, go fly
• If no, leave something or
somebody behind
Excel Example of Weight & Balance
• So is there relevancy here to what you study in school?
– Applicable Subjects in School = Science, Technology
– High School Course = Physics (Chapter on Center of Gravity), Microsoft Office - Excel