1102 - Struc Princ of Flight

8/13/2019 1102 - Struc Princ of Flight

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2

Basic Concepts of Flight

PHAK Chapter 1



3

The Four Force Diagram

• The Four Force Diagram is a basic andimportant concept of aviation – For level flight:

• Thrust = Drag• Lift = Weight



4

The Four Forces in Balance

• A common misstatement is that “all forcesare equal”. Not so!

• In mathematic terms:Thrust = Drag << Lift = Weight

In layman’s terms:

– Thrust and Drag are equal – Lift and Weight are equal – (but) Thrust and Drag are much less than Lift

and Weight



5

The Four Forces in Balance

• Thrust = Drag• Lift = Weight

• Thrust and Dragare significantlyless than Liftand Weight



6

Axes of Movement

• In flight, aircraft are free to move about allthree axes: – Vertical, Lateral, Longitudinal

• Aircraft movements are described in termsof: – Roll, Pitch, and Yaw



7

Pitch

• Pitch is aircraftrotation about thelateral axis -or-

• Pitch is placement ofthe nose relative tothe horizon – May be described as

“nose up” and “nosedown”



8

Roll

• Roll is aircraftrotation about thelongitudinal axis

• Roll is an aircraftmotion than changesthe angle of bank – Expressed relative to

the horizon



9

Yaw

• Yaw is motion of thenose left or rightabout the vertical

axis -or-• Displacement of the

nose left or right ofthe flight path – Generally a transient

motion or condition



10

Vertical Forces in Flight

• In level flight, the sum of vertical forces iszero

– Lift is producedby the wing

– Weight acts atthe Center ofGravity (CG)

– Down force isproduced by thetail to balanceabout the CG



11

Aircraft Structure and

ComponentsPHAK Chapter 1



12

Aircraft Structure

• Five 5 mainparts – Fuselage – Wings – Empennage – Landing gear – Power Plant

or Engine



13

Fuselage

• The fuselage includes: – Cockpit and Cabin – Cargo Area (typical)

– Attach Points for other parts of the structure• Bulkheads are used to separate

compartments of the cabin

• A firewall separates the cabin from theengine compartment



14

Construction

• Construction types were historically – Truss Type (Truss Frame) – Monocoque (“single shell”), and/or

– Semi-monocoque• Modern composite construction uses

multiple elements

• Current trainers are largely semi-monocoque with composites advancing



15

Truss Frame Construction

• Truss construction provides a skeleton,generally tubular metal, and usuallycovered to provide less aerodynamic drag

• Major structural parts of the truss arelongerons and web members or bracescall struts

• Frames were (eventually) covered withskin to reduce aerodynamic drag



16

Truss Frame Construction

• Longerons givestrength overlongitudinal length

• Struts are cross-bracesfor rigidity

• Bulkheads give shapeto the skin

• Stringers help supportthe skin



17

Monocoque Construction

• Monocoque is French for “single shell” • Monocoque construction uses internal

bulkheads and formers for shape with astressed-skin covering thatprovides themajority ofthe strength



18

Semi-monocoque Construction

• Semi-monocoque is similar to monocoque – The skin is a structural member and bears

loads

• Semi-monocoque is a hybrid (skin oversubstructure) – Some truss-frame type members are used for

heavy loads and long dimensions – Formers and stringers are used to provide

shape and stiffness to the stressed skin



19

Semi-monocoque Construction

• Stringers allow the use of thinner sheetmetal in larger areas

• Thinner sheet metal provides less weight – Less weight = better performance, smaller

power plant, lighter landing gear



20

Advantages/Disadvantages

• Truss frame – Strong but heavy – Not particularly aerodynamic

• Monocoque – Lighter than truss frame in most areas – More easily streamlined

– Requires thick skin for long supportdimensions



21


• Semi-monocoque is the best of both – Truss-type members where needed for

strength – Monocoque where skin is effective in load

bearing – Selective support for skin to reduce weight

• Adds manufacturing complexity



22


• Monocoque and semi-monocoque bothsuffer from one serious problem: stressedskin – Once stressed skin is punctured, dented, torn,

or buckled it looses a significant amount ofstrength



23

Composite Construction

• Composite construction uses a matrixsuch as fiberglass, carbon fiber, or Kevlaras a web for epoxy resin

• These materials may be placed over afoam core for shape during constructionand minor internal support



24


• Composite construction can be madelighter in many applications – Easily shaped during construction – Varying thickness as required to meet design

loads with sufficient margin



25


• Composite construction – Does not suffer from metal fatigue and can

have longer life – Is not as fragile as stressed skin in the

presence of minor damage – May suffer hidden damage from low-impact

damage



26


• Compositeconstruction – May suffer

hidden damage from even low-energy impact

• Damageassessmentmay be difficult



27

Current Fleet Construction

• Many modern aircraft incorporate semi-monocoque and composite elements inconstruction

– Ease of manufacture – Strength – Weight – Cost



28

Current Fleet Construction

• Aircraft are classified by their majorconstruction type – Most current trainers and GA aircraft are

semi-monocoque• Composite construction is gaining

popularity very rapidly



29

Wings

• An airfoil is a surface that reacts dynamicallywith the air to create lift – More on aerodynamics later

• Wings produce Lift – In opposition to Weight (gravity) – In opposition to maneuvering loads

• Wing shapes are varied to optimize desiredperformance (speed, drag, & weight)



30

Wings

• Placement• Airplanes may be:

– High-, mid-, or low-wing

– Mid-wing is lesscommon due to

the carry-throughstructure required



31

Wings

• Airplane wingsmay be: – Strut-braced – Cantilevered – Semi-cantilevered



32

Wing Configurations

• Airplanes may be: – Mono- or bi-plane – Mono-plane has

one set of wings divided by thefuselage or asingle wing

structure on acontinuous spar



33

Wing components

• Principle parts of a wing are the: – Spar(s) – Ribs – Stringers,

and – Skin



34

The Spar

• The Spar is the major load-bearingmember of the wing

– The spar may bea single carry-through elementor a spar in eachwing connectedto fuselageattach points



35

The Ribs

• Ribs define the section shape of the wing

– Shape

may varyor taperalong thewing,requiringdifferentribs



36

Stringers

• Stringers are spanwise members similar tolongerons along the fuselage

– Stringers areintended toreinforce orstiffenstressed skinrather thanprovide framestrength



37

Other Wing Components

• Wings usuallyprovide space for anintegral or bladder-type fuel tank

• For retractable gearaircraft, the wingoften houses thegear in the retractedposition



38

Other Wing Functions

• Wings provide structural attach points and/ormounts for several other components – Landing gear for many low-wing aircraft

– Wing Flaps – Ailerons – Landing/taxi lights – Position and anticollision lights

– Pitot probe or pitot-static mast



39

Wing-Attached Flight Controls

• Ailerons are used for roll control – Located on the outboard portion of the wing in

general aviation aircraft

– Operatedby acontrol

yoke or joystick



40

Wing-Attached Flight Controls

• Wing Flaps are used to provide additionallift and lower speed for takeoff and landing

– Located on theinboard portionof the wing

– Operated by amotor ormanual lever



Types of Flaps

• Types of flaps are: – Plain: Flap section of

the wing is hinged

– Split: Upper wingportion remains in place – Slotted: Airflow path

from beneath the wing

– Fowler: Travels outand down

41



42

Types of Flaps

• Plain flaps are thesimplest form – Good overall

performance• Split flaps form a

portion of the lowerpart of the wing only – Less added lift than

plain flaps, higher drag



43

Types of Flaps

• Slotted flaps allow airflow path from beneaththe wing – High lift, low stalling

speed• Fowler flaps travel outand down – Increases wing area as

well as shape – Very effective in

producing lift at lowairspeeds

– Generally cause largepitching moments





45

Elements of the Empennage

• The Vertical Stabilizer provides directional(yaw) stability for the airplane



46


• The Horizontal Stabilizers provide pitchstability for the airplane



47


• The Elevator is used to control the Pitchattitude of the airplane – Operated by

a control yokeor joystick



48


• The Rudder is used to control the Yaw ordirectional attitude of the airplane – Operated

by therudderpedals



49


• Trim Tabs may beprovided to relievecontrol forces on the

Rudder and/or theElevator – Alternate

arrangement is

“bungee” or springtrim



50


• An alternatearrangement is a “flyingtail” or stabilator

– Combines horizontalstabilizer and elevatorfunctions into a singlepivoting surface

– Antiservo tab is used fortrim and controlfeedback



51

Landing Gear

• May be wheels, floats, skis• May be used in combination

– Retractable wheels with floats

– Retractable or protrudingwheels with skis

• Land wheels may beretractable or fixed – Drag vs. complexity



52

Landing Gear Elements

• Landing gear elements or componentsinclude: – Struts – Tires – Brakes, and – Steering mechanisms



53

Landing Gear Struts

• Struts provide – Lateral spacing for stability – Vertical spacing for propeller ground clearance, and – Shock absorption for takeoff, landing, and operation

over rough surfaces• Struts may be

– Leaf or tubular steel springs – Oleo (pneumatic) struts with integral coil springs and

shock absorbers, or – Swinging or Trailing Link





55

Powerplant

• The Powerplant provides Thrust for flight – Opposes Drag

• The Powerplant also provides power for

various internal systems including – Electrical – Vacuum/Pneumatic

– Environmental, and – Hydraulic systems



56

Powerplant

• A Powerplant may be reciprocating, turbine, orturboprop – Normal GA reciprocating engines generally use

direct-drive props – Turboprops have gearcases for speed reduction – Turbine may be pure jet or provide internal turbofans

• Power plants are housed in nacelles on the

nose, wings, or fuselage



57

Instrumentation



58

Instrument Functions

• Aircraft instrumentsprovide data to the pilotregarding: – Aircraft attitude – Flight performance – Location (navigation)

– Systems performanceand health



59

Performance Instruments

• PerformanceInstruments give: – Altitude – Speed – Rate of Turn – Rate of Climb



60

Control Instruments

• Control Instrumentsgive: – Angle of bank (relates

to Rate of turn) – Pitch angle (relates toSpeed and Climb)

– Engine power• Tachometer• Manifold pressure



61

Navigation Instruments

• NavigationInstrumentsprovide the pilotwith location

information andsituationalawareness – A variety of

navigation

systems areavailable – Much more

later…



62

Principles of Flight

PHAK Chapter 2



63

Structure and Properties of the

Atmosphere



64

Structure of the Atmosphere

• More data in Lesson 16 (Weather), but theatmosphere is layered. We operate in thetroposphere

• The atmosphere is composed of approximately: – 78% Nitrogen – 21% Oxygen, and – 1% other gasses including argon, CO 2, ozone, and

water vapor



65

Structure of the Atmosphere

• Standard pressure at sea level is 29.92”Hg (inches of Mercury), or 1013.25millibars – This translates to 14.7 psi (pounds per square

inch)



66

Ambient Pressure Measurement

• Atmospheric pressure ismeasured by a MercuryBarometer – Vacuum exists in the tube

above the fluid – Ambient pressure pushes the

surface of the pool into the tube• Zero should be at the surface of

the pool

• The height of the liquidcolumn is a measure of theatmospheric pressure





68

Atmospheric Standards

• The International Standard Atmosphere(ISA) is defined as: – 29.92” Hg or 1013.25 mb

– 15 ° C (59 ° F) at sea level



69

Atmospheric Properties

• Air has density or “weight” – This allows it to exert static and dynamic

forces against objects

– An important dynamic force is Lift• The higher the air density, the higher the

force the air can exert



70


• Air provides oxygen for internalcombustion engines – Higher density air means more oxygen is

available – Therefore, higher the density of the air, the

higher the Thrust available from a powerplant



71


• The barometric or ambient pressure andthe temperature determine the density ofthe atmosphere – Higher pressures make the air more dense

• Air molecules are “squeezed” closer together

– Higher temperatures make the air less dense

• Thermal energy drives air molecules farther apart



72


• Changes in ambient pressure occur during – Changes in weather (rising or falling

barometer)

– Changes in altitude• Changes in temperature occur during – Changes in weather – Insolation (sunlight energy) – Changes in altitude



73


• All these things affect: – How much lift the wing produces – How much power the engine produces – How much thrust the prop produces

• … and therefore Performance



74

Pressure Altitude

• Pressure Altitude isthe “height” above atheoretical standarddatum plane (SDP) ata pressure of 29.92”

• Pressure altitude isdetermined by

ambient atmosphericpressure only

BarometricPressure

Pressure Altitude

Higher Lower

Lower Higher



75

Density Altitude

• Remember that: – Higher temperatures will make the air less

dense

– Lower temperatures will make the air moredense

• So a temperature change in the air can

mask or offset a pressure change in the air





77

Humidity

• Humidity can affect atmosphericcharacteristics due to the relativemass/volume of water molecules and the

displacement of oxygen molecules (O 2)• Humidity decreases performance but the

effect is not large (typically less than 4%)



78

Physical Laws and Lift





80

Newton’s Laws

• Newton’s 3rd law is predominant in Thrust – The prop pushes against the air, the air

pushes back, and the plane is propelled

through the air – A jet expels high velocity exhaust and the

force required to accelerate the exhaustpropels the plane

• Not so much so for Lift…



81

Magnus Effect

• Air flows uniformlyaround a non-rotating cylinder – Drag is produced,

but not lift



82

Magnus Effect

• When the cylinderis rotated the airflow divides in a

non-uniformmanner – Circulation

increases on oneside of the cylinder- Disregard streamline spacing- Observe the number ofstreamlines above or below





84

Magnus Effect

• This lift is afunction of airflow and air

density, and isquantified byBernoulli’s

Principle- Disregard streamline spacing- Observe the number ofstreamlines above or below



85

The Physics

• After all, this is a college course… • The total energy in “free” air (or any other

fluid) must be constant if no external

energy is added – Total energy is static pressure (potentialenergy) and velocity (kinetic energy)

– When one goes up, the other must go downto keep the sum constant



86

The Physics

• Kinetic energy of a moving body is:½ x Mass x (Velocity) 2

• Each molecule of the fluid is an object thathas kinetic energy – Knowing the total mass and number of air

molecules in a volume and their change invelocity, the change in pressure can becalculated



87

Bernoulli’s Principle*

• *Or more precisely, Bernoulli’s Principle ofDifferential Pressure

• To summarize first: – When velocity of a gas increases, its pressure

decreases – When velocity of a gas decreases, its

pressure increases

ll l



88

Bernoulli’s Principle

• A Venturi tube is a good example ofBernoulli’s Principle – Velocity on the left, pressure on the right

ll ’ l



89

Bernoulli’s Principle

• Remember that these pressure andvelocity changes are highly localized andvery dynamic

– The velocity and pressure entering the tube isthe same as the velocity and pressure exitingthe tube



90

Airfoil Design

Ai f il T



91

Airfoil Terms

• Airfoilspossessattributes

described inthe followingterms:

C b



92

Camber

• Camber isthe curvatureof a surface

– The upperand lowersurfaces ofthe wing

L di Ed



93

Leading Edge

• The LeadingEdge is theforward-most

point on anairfoil sectionrelative to the

movement ofthe wing

T ili Ed



94

Trailing Edge

• The TrailingEdge is theaft-most point

on an airfoilsectionrelative to the

movement ofthe wing

Ch d Li



95

Chord Line

• The ChordLine is astraight line

between theLeading Edgeand the

Trailing Edge

M C b Li



96

Mean Camber Line

• The MeanCamber Line(or averagecamber) is anarc drawnthrough thehalfway pointsof vertical linesbetween the

upper andlower surfaces



Ai f il d Lift



98

Airfoils and Lift

• When air moves over an airfoil, the airfoildivides the flow much like the Magnuscylinder

– More air flows over the top – Its velocity is higher – Therefore its pressure is lower

Ai f il d Lift



99

Airfoils and Lift

• By the same token, lower velocity andhigher pressure exists below the wing – The difference in pressures above and below

the wing are multiplied by the area of thewing (pressure x area = force) …

– … and this is Lift

Angle of Attack



100

Angle of Attack

• The Angle of Attackof a wing is theangle between the

relative wind(opposite the motionof the airplane) and

the Chord Line



Angle of Attack (AOA)



102

Angle of Attack (AOA)

• We capitalize on changein lift to maneuver theairplane

• The change in center ofpressure presents astability problem for the

wing that is offset by thetail section

Critical Angle of Attack (Stall)



103

Critical Angle of Attack (Stall)

• Wing stall occurswhen the criticalangle of attack isexceeded andairflow separatesfrom the uppersurface of the

wing

AFH Figure 4-2



Wingtip Vortices



105

Wingtip Vortices

• A consequence of the production of Lift isthe production of Wingtip Vortices





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1102 - Struc Princ of Flight