Basics of Flight
Transcript of Basics of Flight
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