Presentation on theme: "Aerodynamics Getting to the Point"— Presentation transcript:
1 Aerodynamics Getting to the Point -K 2, 9 / G 1, 12 / HW1-K 5, 6 ?Orville WrightWilbur WrightWritten for the Notre Dame Pilot InitiativeBy the Pilots of the University of Notre Dame“Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”
2 Four Forces of Flight Lift opposes Weight Thrust opposes Drag In straight, unaccelerated flight, L = W & T = DLift created by pressure differential around wing. High pressure on lower surface and low pressure on the upper surface – low pressure caused by increased airflow velocity over top of airfoil.Weight – downward force of gravityDrag – rearward retarding forceThrust – forward force propelling airplane through airWhat is the name of the “condition” that the air has to speed up over top of airfoil?Kutta Condition?
3 Airfoils What is NACA? National Advisory Committee for Aeronautics Chartered in 1915, operational fromThe National Aeronautics and Space Act of 1958 created NASA from NACA
5 Aerodynamic Surfaces Prop Jet B727 Spoilers -Spoilers pop up hydraulically on passenger jets to disrupt flow over wing during landing…they slow down airplane-Top Gun Speed Brakes (Chap 26, 138:30, Chap 10, 31:27)How do speed brakes work?B727 Spoilers
6 Airfoils - Nomenclature Low pHigh pChord line - straight line connecting the leading and trailing edges of an airfoilCamber line – locus of all points equidistant from top and bottom of airfoilCamber – distance between chord line and camber lineThickness – maximum distance between top and bottom surfaces of wingLeading EdgeTrailing EdgeWingspan (b)Aspect Ratio (AR = b2/S)-Chord is line from leading edge to trailing edge-Camber is line equidistant from top and bottom of airfoil at every given point along chord-symmetrical airfoil at 0 angle of attack yields 0 liftS = planform wing area
7 FrostIf wing is below dewpoint which is below freezing, frost will formSublimation of air to solid ice crystalsDisrupts smooth airflow over the wingWhy is this bad?Decreases liftIncreases dragFrost removed before take-offRime IceClear Ice-Rime ice forms a brittle and frost-like surface. It develops when small drops, like those in stratiform clouds or in light drizzle, freeze on impact without spreading. It is rough and opaque. An example is like the frost in a home freezer.-Clear ice forms a hard and glossy surface. It develops when water droplets which touch the airplane flow across the surface before freezing. This ice can accumulate as a smooth sheet. Clear ice is likely to form in areas of large water droplets, such as in rain or cumuliform clouds.
8 Angle of Attack Angle between wing chord line and relative wind The angle of attack at which airplane stalls does not changeStall speed does not change with altitude, loading, or airplane weightLarger angle of attack, more lift
9 Published NACA Data – NACA 2415 -Lift goes up with increasing angle of attack-Drag goes up with lift-Show stall angle
10 Airfoils - Nomenclature Right most picture:Cambered airfoil:Zero lift angle is negative, i.e. at zero degrees angle of attack, airfoil is still producing liftFor symmetric airfoil, zero lift at zero degree angle of attack
11 Flaps Flaps increase lift and decrease stall speed Plain FlapFlaps increase lift and decrease stall speedFlaps allow steep rate of descent for approaches without increasing airspeedSplit FlapFowler Flap-Fowler Flap effectively increases the wing area by rolling backwards on a roller system.-Slotted Flap allows high pressure air underneath wing to join airflow above wing. This effectively increases velocity of top airflow and thus increases lift.-Fowler Flap effectively increases the wing area by rolling backwards on a roller system.Graph on left basically shows that for the same angle of attack, a wing with flap extended produces more liftSlotted Flap-Slotted Flap allows high pressure air underneath wing to join airflow above wing. This effectively increases velocity of top airflow and thus increases lift.
12 Laminar v. TurbulentLaminar flow about a sphere
13 Laminar v. TurbulentTurbulent flow about a sphere
14 Bernoulli’s Principle - Lift A1V1 = A2V2Continuity the mass flow into the control volume must equal the mass flow exiting the control volume“As the velocity of a fluid increases, its internal pressure decreases.”From Newton’s 2nd (F=ma)Shown by Venturi tubeLow PressureHigh PressureA1V1=A2V2
15 Bernoulli’s Principle Again Next 3 slides link together to help student understand why airfoils generate liftCourtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B
16 Bernoulli’s Principle Again Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B
17 Bernoulli’s Principle Again Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B
18 Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B Lift Vector-This resultant vector plus the forward thrust of the propeller causes the airplane to go.Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B
19 Drag TypesInduced drag is the unavoidable by-product of lift and increases as the angle of attack increasesParasite drag is caused by any aircraft surface that deflects or interferes with smooth airflow around airplaneSkin-friction drag - between the outer surfaces of the aircraft and the air through which it moves. Reduced by using glossy, flat finishes on surfacesForm drag - resistance of air to the shape of the aircraft. Form drag can be reduced by streamlining the aircraft shape.More lift, more induced drag Ground effectParasite Drag hinges, etc.Skin-friction drag ice or frost on wings increases skin-friction drag
20 Drag – Body Comparison sphere cylinder airfoil Form Drag, airfoil is streamlined and thus has less drag, frontal surface area of airfoil is smaller than both sphere and cylinderairfoil
21 Wingtip Vortices – “Twin Tornadoes” -Draw a picture of birds on the chalkboard?A few words on wingtip vortices:‘High pressure on the lower surface creates a natural airflow that makes its way to the wingtip and curls upward around it to the area of low pressure. When flow around the wingtips streams out behind the airplane, a vortex is formed. These twisters represent an energy loss and are strong enough to flip airplanes that blunder into them.’
23 Why Winglets? Equivalent to span extension w/o increased wingspan Reduces wingtip vorticesReduces dragNASA B-727 Wingtip Vortex Test FlightLearn more about winglets:
24 Drag – Ground EffectTIP:On a soft-field runway, you can takeoff at a lower speed and then accelerate while in “Ground Effect.”-Ground Effect is the result of the interference of the ground surface with the airflow patterns about the airplane-Vertical component of airflow around wing is restricted, which alters the wing’s upwash, downwash & wingtip vortices-Could explain complicated aerodynamics, induced flow, induced angle of attack, etc.-Wing requires a lower angle of attack in ground effect to produce same liftSo, if same angle of attack is maintained, more lift is produced than usual-Within one wingspan above ground, best effect when within ½ wingspan above groundSoft Field Take-off
25 Drag vs Angle of Attack Why is minimum at 4 degrees? Relationship between drag and angle of attack
26 Torque / P-factor (Left-Turning Tendencies) Newton’s 3rd law: “For every action there is an equal and opposite reaction.”Propeller rotates CW when viewed from pilot’s seat.Torque reaction rotates the airplane CCW about longitudinal axisP-factor (asymmetrical thrust) caused by descending blade taking a greater “bite” of air than ascending blade at high angle of attack-Torque effect is greatest at low airspeed, high angle of attack, high power-P-factor causes yawing to left.-Spiraling slipstream
27 Stability & ControlInherently stable airplane returns to its original condition after being disturbed. Requires less effort to controlAirplanes normally pitch down when power is reduced, b/c downwash on elevators is decreased resulting in less effective controlBad Center of Gravity difficulty recovering from stall, less stable at all airspeedsCenter of Gravity concerns:Unable to compensate with elevator in pitch axisWeight and Balance becomes critical – taught in a coming lecture
28 Stability & Control pitch The 3 axes of motion: roll, pitch, yaw roll
29 Tail PlacementsLooks like the A-10Also called “H-Tail”
30 Canards Stabilizer located in front of the main wings Used on the Wright FlyerMore aerodynamically efficient than an elevator b/c canards provide positive lift-Middle pictures is the Beech StarshipCanards are unstable
31 Accident Report – Loss of Elevator AIRCRAFT FINAL REPORT THE AIRCRAFT HAD JUST BEEN REPAIRED AFTER RECEIVING TORNADO DAMAGE. THIS REPAIR INCLUDED REMOVAL AND REPLACEMENT OF THE ELEVATOR CONTROL TUBE. THE PILOT TAXIED TO THE RUNWAY FOR THE PURPOSE OF A TEST FLIGHT. ALL FLIGHT CONTROL CHECKS APPEARED NORMAL. AFTER LIFT-OFF, THE PILOT INTENDED TO LEVEL OFF AT 5 TO 10 FEET, THEN TOUCH DOWN AGAIN. HOWEVER, AFTER THE AIRPLANE BECAME AIRBORNE, HE LOST ELEVATOR CONTROL, AND THE AIRCRAFT CLIMBED STEEPLY TO 50 TO 75 FEET. THE PILOT THEN REDUCED POWER, THE AIRCRAFT'S NOSE DROPPED, AND THE AIRCRAFT DESCENDED. WITH NO ELEVATOR CONTROL, THE PILOT WAS UNABLE TO ARREST THE DESCENT, AND THE AIRCRAFT IMPACTED THE GROUND. A POST-CRASH EXAMINATION REVEALED THAT A BOLT AND NUT WERE MISSING FROM THE ELEVATOR CONTROL LINKAGE, WHICH ALLOWED THE LINKAGE TO BECOME DISCONNECTED.AIRCRAFT 1 CAUSE REPORT FAILURE OF MAINTENANCE PERSONNEL TO PROPERLY REINSTALL A BOLT AND NUT IN THE ELEVATOR CONTROL LINKAGE, WHICH RESULTED IN A DISCONNECT OF THE LINKAGE AND LOSS OF ELEVATOR CONTROL.