Aerodynamics – What Makes Airplanes Fly
Doylestown Pilots Association
Boy Scouts Aviation Day 10/04/2014
Maj William J. Doyle, Jr.
Civil Air Patrol, New Jersey Wing, StanEval Officer
Check Pilot / Instructor-Pilot
CFI A&I, AGI, IGI, CFAI, FAAST Rep

•
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

• 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.)

 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 Components - Wings




Monoplane
 single set of wings
Biplane
 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




 Vertical Stabilizer and Horizontal Stabilizer
 help steady airplane for straight flight
Rudder controls yaw
 controlled by floor pedals
 right pressure moves nose to right
 left pressure moves nose to left
Elevator (stabilator on Cherokee) controls pitch
 controlled by yoke or stick
 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 Components - Landing Gear


 Gear Types


Fixed Gear
Retractable Gear


Tricycle Gear
Conventional Gear (tail dragger)
Landing Gear Struts
 Spring steel struts

 bungee cord struts oleo struts
 shock disks
Brakes
 Disc brakes
 Differential braking



 Engine
 provides power to turn propeller
 distinguishes airplane from glider
Firewall
 separates cockpit from engine
 mounting point for engine
Propeller
 translates engine rotational force into forward-acting force called thrust

Aspect Ratio = Wing Span ÷ Average Chord

• 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)

• The laws of physics apply to everything.
• They apply to F-16 fighters and to the USAF Thunderbirds.

• The laws of physics apply to everything.
• They apply to ultra lights.

• The laws of physics apply to everything.
• They even applied to the
Wright Brothers in the Wright
Flyer at Kitty
Hawk, NC.

Vector Vector
Vector
Vector

 Lift
 upward force from airflow over and under wing

 Weight
 downward force of gravity
Thrust
 forward force propelling airplane through air
 Drag
 rearward force retarding force limiting speed




Newton’s First 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.
Newton’s Second Law
 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.

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.

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

Wing Root
Wingtip

Types of
Flaps and
Leading
Edge
Devices



Parasite Drag
 Caused by any aircraft surface which deflects or interferes with smooth airflow around airplane
 Form drag
 results from turbulent wake caused by the separation of airflow from the surface of the structure
 Interference drag
 occurs when varied currents of air over an airplane meet and interact
 Skin friction drag
 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/D max
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.

Longitudinal Stability and Balance


 Longitudinal Stability
 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 .
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.

Three Axes of Flight
Center of Gravity (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

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

• 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.

Center of
Gravity
Horizontal Stabilizer and Tail Down Force
Center of Lift

 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
 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.

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
 bottom = Vso
 top = Vfe


 green

 bottom = Vs top = Vno yellow
 bottom = Vno
 top = Vne red line = Vne

Types of Airspeed




Indicated Airspeed (IAS)
 Speed indicated on ASI


Uncorrected for instrument and installation errors
No variations in air density
Calibrated Airspeed (CAS)
 Corrected for instrument and installation errors
True Airspeed (TAS)
 CAS corrected for
 altitude
 nonstandard temperature
Groundspeed (GS)
 Speed over the ground
 TAS adjusted for wind


 Proficiency Stalls (Student Mastery)
 Power-off stalls: landing conditions & configuration
 Power-on stalls: take-off conditions & configuration
Demonstration Stalls (CFI Demonstration)
 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



 Definition of a Spin
 Aggravated stall accompanied by autorotation.
 One wing stalled more than the other wing.
Types of Spins
 Erect
 Inverted
 Flat
Stages or Phases
 Incipient spin
 Fully developed spin (steady-state)
 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

•
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




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)
9.1 : 1
11.5 : 1
Factors Affecting Glide
 Weight
 Configuration
 Wind



 Shallow turns
 Less than 15°
 Tendency to return to straight-and-level flight
(positive static stability)
Medium turns
 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.

• 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)

• 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


Stall speed increases by LoadFactor
– 30° bank = load factor of 1.1 
1.05 * V
S
– 45° bank = load factor of 1.4 
1.20 * V
S
– 60° bank = load factor of 2.0 
1.40 * V
S
 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





Definition of Limit Load Factor
 Amount of stress or load factor that an airplane can withstand before structural damage or failure occurs.
Normal Category


3.8 positive G’s
1.52 negative G’s
Utility Category


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

Cirrus
SR20 with
Ballistic
Parachute

•
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!

• 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

• 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?

•
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.

•
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.

•
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.

Airspeed Indicator Attitude Indicator Altimeter
Turn Coordinator Heading Indicator Vertical Speed Indicator

• 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

• 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