Brainstorming and Barnstorming:Brainstorming and Barnstorming:

Basics of FlightBasics of Flight

Flight HistoryFirst flight: The Wright Flyer 1903Break Speed of Sound: Bell X-1A 1947Land on Moon: Apollo 11 1969Circumnavigate Earth on one tank of gas: Global Flyer 2005We’ve come a long way

Major Topics

Terminology and TheoryForces of FlightAircraft Design

Basic Aircraft TerminologyAirfoil: Cross sectional shape of a wingLeading Edge: Front edge of wingTrailing Edge: Back edge of wingChord Line: Line connecting LE to TECamber: Center line between top and bottom of wing

High camber found on slow flying high lift aircraft

Wing LayoutPlanform: Vertical projection of wing area

Elliptical: good for high speedStraight: root stalls, but cheap to makeTapered: good stall characteristicsDelta: used for supersonic flight

Wing LayoutSweep: Angle between the lateral axis and the wing (high speed aircraft)Taper: Chord decreases as you move to the wing tipIncidence: Angle between the longitudinal axis and the wing chordAngle of Attack: Angle between the wing and the relative wind

Wing Layout

Twist: Bending of wing about lateral axis (helps prevent tip stall by changing angle of attack)Anhedral: Downward bend in wing (helps with stability)Dihedral: Upward bend in wing

Corsair: WWII Fighter

Wing LayoutAspect ratio(AR)= Span^2/Wing AreaMore efficient for slow aircraftTypical Values

Glider: 20-30Trainer: 7-9Loadstar: 18.5

U2 spy plane: High AR

SR-71: Low AR

6 degrees of freedomThree axes of an aircraft

Longitudinal: Parallel to the fuselageLateral: Parallel to the wingNormal: Perpendicular to the ground

Control Surfaces: Change Wing by altering the Angle of Attack

Ailerons: horizontal surfaces located on wing tips

Roll: rotation about the longitudinal axisElevator: horizontal surface located on the tail

Pitch: rotation about the lateral axisRudder: vertical surface located on the tail

Yaw: rotation about the normal axis

Stabilizing Surfaces: Balancing MomentsVertical Stabilizer: The vertical part of the tail which prevents unwanted yawHorizontal Stabilizer: Horizontal portion of the tail (or the Canard) that prevents unwanted pitch

Flaps

Change the shape of wingIncrease Lift and DragUsed on takeoff and landing

Neutral Point: Location of resultant lift forceCG: Center of gravityHigh Wing: Wing on top (very stable)Mid Wing: Wing in middle (acrobatic)Low Wing: Wing on bottom ( less drag)

Reynolds NumberReynolds Number (Re): ratio of inertial forces to viscous forces

Re = (D*V*p)/muD=characteristic lengthV=velocityp=densityMu= dynamic (absolute) viscosity

A non-dimensionalized number that can be used to relate models to actual aircraftDetermines whether a flow is laminar or turbulent in the Boundary Layer (laminar is good)Very useful for aircraft design

S1223 at various Reynolds numbers

-0.4

0

0.4

0.8

1.2

1.6

2

2.4

-10 -5 0 5 10 15 20 25

Angle of Attack (degrees)

Cl

Re=61000

Re=101600

Re=122600

Re=147400

Re=171400

Re=198100

Re=251900

Re=302200

Re=149500

Re=198900

Reynolds Number

Note the difference in stall characteristics for different Re

Boundary LayerNo slip condition at surface (V=0)Effectively alters the shape of the airfoilSeparation of the B.L. results in a stallLead to major advances in aircraft design

Boundary Layer

Forces of FlightLiftDragThrustWeight

For steady, level flight these four forces and the moments they generate must be in equilibrium. An airplane is a force and moment balancing machine.

LiftControlled by

Airspeed, angle of attack, altering airfoil, and altering the planform area

Lift = ½ * p * V^2 * A *ClP=density, V=velocity, A = wing area Cl=coefficient of lift

How is lift actually generated???

Lift: Equal Transit Time (Wrong)Air splitting at LE must meet at TEAir on top has a longer path; must travel fasterExample: Boeing 747

Weight: 775,000 lbsAirspeed: 550 mph or 810 ft/secDistance across top: 1.059*bottomDensity: 1/39 lb/ft^3Wing Area: 5,500 ft^2

Boeing 747 ExamplePressure difference:

Punder-Pover=1/2*p*(Vbottom^2-Vtop^2)Punder-Pover=18.75 lbs/ft^2

Lift=P*A=(18.75 lbs/ft^2) * (5500 ft^2)Lift=103,000 lbsWeight=775,000 lbs…………Ooops!!!This theory says that air accelerates thereby causing a pressure gradient.This is completely wrong. A pressure gradient will cause a fluid to accelerates.

Einstein and LiftEinstein hired by the German Air ForceHe designed a wing based on the previously described theoryIt failed miserablyHe was still relatively successful

Lift is complicated!!!!!!!!

Newton Vs BernoulliNewton: deflection of air Bernoulli: Pressure gradientCoanda effectCirculation3-D fluid flow is hard

Pressure Gradient

Newton and BernoulliA wing forces air downThus air forces a wing upA change in the momentum of the fluid results in a forceAir in motion creates a pressure difference around the wing

Air being forced down

Coanda Effect

Tendency of a fluid in motion to stick to an objectDue to skin friction between fluid and surfaceThe top of the wing also directs air downExperiment with a rolled up paper.

3-D effects of lift

Spanwise flowHigh pressure on bottomLow pressure on topAir from bottom tries to move to top Wing Tip Vortex

Return to the lift equationLift = ½ * p * V^2 * A * ClLift can be explained by the pressure gradient as indicated by the equationThe gradient cannot solely be explained by air moving faster over the top of the wingWhat about this Cl factor????

Coefficient of LiftMagic number of lift; determined experimentallyConstant for any size wing with same airfoilAccounts for unknownsVaries with angle of attackThere is an angle where the wing produces zero liftExplains how a wing can fly upside down

Loss of Lift: StallEvery wing has a stall angleStall angle is the angle of attack at which the wing loses liftStall angle range from 12-20 degreesWhat actually causes a stall???

Stall at high AoABoundary layer separates from the surface (inertial vs viscous effects)Effectively changes wing shapeTurbulence results that causes more drag and less lift

Drag: Form Drag: shape of objectSkin Friction Drag: surface of objectInduced Drag: component of liftParasitic Drag = Form Drag + Skin DragTotal Drag = Induced Drag + Parasitic Drag

Total Drag = ½ * p * V^2 * A * CdCd is the key and is determined experimentally just like Cl.

Form and Skin Friction DragForm Drag

Greatly affects slow flying planesDepends upon the frontal areaDepends upon how streamlined What does it mean to be streamlined??

Examples of things that are streamlinedSkin Friction

Depends upon the surface roughness

Form DragHow do we know if an object is streamlined?

Nature, wind tunnel testing, conformal mapping

If these shapes are so aerodynamic, why aren’t race cars shaped this way????

Induced DragEqual to horizontal component of lift

Therefore increases with AoAActually caused by the wing tip vortex discussed earlierReduced with use of a high AR wingCan be reduced with the use winglets

Tradeoff: Skin Friction vs FormTurbulators: prevent the B.L. from separatingIncreases skin frictionDecreases form dragFor slow aircraft; tradeoff is beneficialFound on sea animals, new swim suits, and golf balls

Turbulator Examples

Aircraft StabilityStatic Stability: When disturbed, the aircraft returns to original flight path

Longitudinal, Lateral, RollDynamic Stability: Returns to original flight path without excessive oscillation

Longitudinal StabilityLongitudinal Stability: Locate the Neutral Point behind CGCreates a correcting momentTo move the Neutral Point backwards, increase the horizontal tail area

Lateral StabilityLargely depends upon tail sizeCLA: Center of lateral areaSize tail to locate the CLA 25-28% of tail length behind the CGPrevents Spiral Instability

Side gust rotates planeOne wing speeds upCreates more lift

Directional StabilityAlso depends upon tail size and CLAA high wing adds stability

The plain acts like a pendulumNaturally returns to stable position

Aircraft ControlLongitudinal, Lateral, and DirectionalControl surfaces generate forces These forces create moments that rotate the planeProper location and sizing results in excellent controlStall must always be considered

Ailerons are located at the wing tips

3rd Place

KSU Aero Design Team 2005

Ft. Worth, Texas