Download presentation
Presentation is loading. Please wait.
Published byBetty Copeland Modified over 9 years ago
1
Aero Engineering 315 Lesson 21 GR#2 Review
2
GR Breakdown 150 points total 25 multiple choice/matching Mostly conceptual 3 short work outs 2 long work outs worth 46 pts total Hand graded with partial credit available
3
General strategy Prior to class Work your GR review handout Review reading for lessons 12 – 20 Work all problems through #25 Review slides and handouts Lift and drag summary NACA Airfoils Mach effects Know your memory equations—including GR#1 equations (especially dynamic pressure, q) Be familiar with applicable supplemental data info In class Bring calculator, straight edge, pencils
4
2-D Airfoils An airfoil is a __________________ cross-section of a wing. It may be thought of as a _____ object, an _____________ long object, or an object that completely _______ the width of the test section of a wind tunnel, such that no _________ effects influence the flowfield The forward-most point on an airfoil is called the ______________, and the rear-most point is called the _________________ A straight line that connects the leading edge and the trailing edge is called the ___________; the length of this line is _______ (or _______________), abbreviated ___ A curved line drawn from the leading edge to the trailing edge so as to be midway between the airfoil’s upper and lower surfaces is called the ____________________ The maximum distance between the mean camber line and the chord line is called the airfoil’s _________________ (or just __________) two-dimensional infinitely 2-D spans wingtip leading edge trailing edge chord chord line mean camber line c max camber camber chord length
5
2-D Airfoils A symmetrical airfoil has _______ camber For NACA 4-digit series airfoils, the first digit represents _______________ in _________ of chord, the second digit represents ___________________________ in _________ of chord, and the third and fourth digits together represent __________________ of the airfoil, in __________ of chord. By definition, the first two digits for a symmetric airfoil are _____. The length (tip-to-tip) of an airfoil model tested in a wind tunnel is its ______, abbreviated ___ __________area (___) is the area of a projection of the airfoil’s shape onto a horizontal surface beneath it; S = _______ The direction of the freestream velocity is the ___________________; the angle between the relative wind and the chord line is __________________ (___), with leading edge ____ being the positive direction zero max camberpercent location of max camber tenths max thicknesspercent 00 span b b c relative wind angle of attack up S Planform
6
2-D Airfoils The AOA at which an airfoil produces no lift is the ________________________________ (______); l=0 = ___ for symmetric airfoils The aerodynamic force acting on a wing is created by the ___________ and _______________ distributions over the wing surface The aerodynamic force can be resolved into _____, the component perpendicular to ________________, and _____, the component parallel to _______________ Summing upper and lower surface forces, we find the existence of a pitching moment; this moment is positive in the L.E.- ____ direction The ____________________ is the location on an airfoil at which the pitching moment is zero; this location can change with _________ The ____________________ is the location on an airfoil at which the pitching moment is constant (i.e. doesn’t change with _________); for subsonic flight, the aerodynamic center is located at approximately the ________________ point (x = ____) zero-lift angle of attack l=0 0 pressure center of pressure lift relative wind drag up AOA aerodynamic center quarter-chord c/4 shear stress AOA
7
2-D Airfoils At the aerodynamic center, the moment is __________ for positively cambered airfoils and is _____ for symmetric airfoils We define lift coefficient C l = _______, drag coefficient C d = _______, moment coefficient C m = _________; these coefficients are _______________ and can vary with ____, ____, and ____ The NACA airfoil data is for ____, ________________ flow The slope of the linear part of the lift curve is the lift curve slope, _____; C l ≈ _____/deg for thin airfoils The top of the lift curve rolls off due to _________________; the AOA where the curve peaks is _______, and lift coefficient is _______ To determine drag coefficient (C d ) at a given , we must first determine ___ Know how Reynolds number, camber, flaps, and boundary layer control affect the lift and drag curves! Know how to find lift coefficient, drag coefficient, quarter-chord moment coefficient, and moment coefficient at the aerodynamic center from the NACA airfoil data charts! zero negative L/(q S) D/(q S)M/(q S c) nondimensional Re M 2-D incompressible ClCl 0.11 airfoil stall stall C lmax ClCl
8
3-D Wings The length (tip-to-tip) of a wing is the ______ (___) and its projected area is the _______________ (___) Aspect ratio (AR) = _______ and describes whether the wing is “_____________________” or “_______________________” Taper ratio (__) is the ratio of _____________ to ______________, or c t /c r Leading edge sweep angle (__) is the angle between the wing’s leading edge and a line _______________ to the root chord line To delay stall near the wingtips, we can use ___________ twist (wingtip twisted ______) or ______________ twist (different airfoil) Due to the top surface-to-bottom surface pressure imbalance on a wing, rotating ____________ form at the wingtips Wingtip vortices form a downward velocity component, or _________, on the wing’s upper surface, deflecting the local flow velocity downward by the _________ angle (___) and reducing the effective angle of attack ( eff = _______), causing a _____________ in lift spanb planform areaS b 2 /S long and skinny short and stubby tip chord root chord perpendicular geometric down aerodynamic vortices downwash reduction
9
3-D Wings The 3-D lift curve slope is _______ than the 2-D lift curve slope, but the zero-lift AOA ( L=0 ) is ____________( L=0 ___ l=0 ) Wingtip vortices also cause a spanwise flow component: root-to- tip on the _______ surface, tip-to-root on the _______ surface Wingtip vortices also tilt the net force vector back by the _________ angle, causing an increase in drag; this “drag due to lift” is called __________ drag. Physically, this drag results because the energetic vortices are “robbing” energy from the plane’s __________. The span efficiency factor (___) is 1 for __________ wings, and ________ than 1 for all other types of wings We can minimize induced drag by using ___________ wings, high-_____________ wings, _________ on the wingtips, ________ wingtips, or wingtip ________ (i.e. air-to-air missile) lower the same= lowerupper downwash induced engines e elliptical less elliptical aspect ratio winglets drooped stores
10
3-D Wings Total drag for a 3-D wing is the sum of _________ drag (composed of _____________drag and __________ drag) and __________ drag Know how to calculate lift for straight-and-level flight (L = W), how to calculate 3-D lift coefficient (C L = L/qS), how to calculate induced drag coefficient (C Di = C L 2 /eAR), how to calculate total drag coefficient (C D = C d + C Di, where C d is found in the NACA airfoil charts), and how to calculate 3-D wing total drag (D = C D q S) Or alternately, know how to calculate 3-D lift curve slope (C L = C l /[1+57.3° C l /eAR]) and then calculate 3-D lift coefficient (C L = C L (- L=0 ), where L=0 = l=0, found in the NACA airfoil charts) profile skin friction pressure induced
11
High-Lift Devices For straight level unaccelerated flight (______), lift __ weight, and velocity required to maintain lift is V ∞ = ____________ The stall velocity, V stall, occurs at ______: V stall =___________; in equivalent airspeed, V e-stall = ____________ We must fly at relatively slow airspeeds during _________ and _________; takeoff speed is limited by ________ length and available engine ________, while landing speed is limited by _________ effectiveness, ______ specifications, and runway ____________ For a given aircraft weight, if you want to fly slower, you must increase ____, so we use __________ devices to improve C L Trailing edge flaps increase wing ________, thereby increasing C L (the lift curve is shifted ___ and to the ______) Flaps also increase ______ (the drag polar is shifted ___ and to the ______) A plain flap’s effectiveness can be reduced because of flow ___________; split flaps and slotted flaps attempt to overcome this problem SLUF= C Lmax takeoff landing runway thrust braking tire condition CLCL high-lift camber upleft dragup right separation
12
High-Lift Devices Similar to slotted flaps, _______ flaps help delay flow separation, but also increase wing _________________, further increasing lift Like a trailing edge flap, a leading edge flap can increase C L by increasing wing ________ Boundary layer control devices, such as a fixed _____, a leading edge _____, upper surface ________, and upper surface _________ increase C Lmax by helping keep the boundary layer _________, delaying stall Another approach to supplementing lift is _________ thrust, such as that used by the AV-8B Harrier and the Marine Corps JSF Leading edge strakes produce strong _________ and direct them over the top of the wing; the very low _________ in the core of the vortices augments the _____ produced by the wing— especially at high _________________ Strakes cause the lift curve to rotate ___ and _______ Fowler surface area camber slot slatsuction blowing attached vectored vortices pressure lift angles of attack up extend
13
Whole Aircraft Lift and Drag When determining whole aircraft lift, the lift of the wing is modified by the __________, ________ and other high-lift devices, and the ____________ tail and/or ________ The general form for the whole aircraft drag coefficient is C D = C Do + k 1 C L 2 + k 2 C L, but the _______ term is generally negligible and can be ignored; we use C D = _____________, an equation known as the whole aircraft ____________ k 1 (often referred to simply as k) = 1/e o AR, where e o is _________ efficiency factor, which will be ______ than span efficiency factor e C Do, which represents _________ drag, is _________ and includes the following drag contributions: ______________ drag, _________ drag at zero lift, _____________ drag from wing/fuselage coupling, and ______ (supersonic) drag fuselagestrakes horizontalcanard linear C Do + kC L 2 drag polar Oswald’s lower parasiteconstant skin friction pressureinterference wave
14
Whole Aircraft Lift and Drag kC L 2 represents drag due to _________ and includes the following drag contributions: wingtip _______-induced drag, __________ drag that varies with lift, and any other drag that varies with lift (due to leading edge _________, for example) Similar to 3-D wing calculations, know how to calculate lift for straight-and-level flight (L = W), how to calculate whole aircraft lift coefficient (C L = L/qS), how to calculate whole aircraft drag coefficient (C D = C Do + kC L 2, where C Do will be given, k may be given or may be calculated by k = 1/e o AR), and how to calculate whole aircraft drag (D = C D q S) lift vortex pressure strakes
15
Supersonic Flow Speed of sound (__) varies only with temperature: a = _________; the ratio of specific heats = 1.4 for air Mach number (__) is the ratio of freestream velocity and speed of sound: M = ______ The Mach angle (__) represents how steeply a Mach wave sweeps back, and sin = _____ Critical Mach number (______) is the freestream Mach number at which the flow somewhere on the airplane first reaches M = __ As Mach number increases beyond M crit, ____________ form on aircraft surfaces, which can cause flow ____________, reducing _____ and increasing _____; the additional drag resulting from shock-induced separation is called ______ drag a M v/a 1/M M crit 1 shock waves separationlift drag wave
16
Supersonic Flow The different flight regimes are __________ flight, at Mach numbers below ______, where the flow is everywhere __________ than the speed of sound; ___________ flight, at Mach numbers above M crit and below about ____, where regions of both ____________ and ___________ flow exist; ____________ flight, where the flow is everywhere ________ than the speed of sound; and ___________ flight, at Mach numbers above about __, where extreme high _____________ significantly change the chemical properties of air As flow crosses a _______ shock (perpendicular to flow direction), ________________and __________ fall, while _________________, _____________, and _________ rise When the freestream exceeds Mach 1, _____________shocks will form in front of bodies with blunt leading edges, while ____________ shocks will attach to bodies with sharp leading edges subsonic M crit slowertransonic 1.3 subsonicsupersonic faster hypersonic 5temperatures normal total pressure velocity static pressure temperaturedensity bow wave oblique
17
Supersonic Flow In the airfoil lesson, we discussed the fact that lift and drag coefficients vary with a, Re, and __; to predict the variation (due to compressibility effects) of lift coefficient with Mach numbers between 0.3 and 0.7, we use the ______________________ correction C l ______ with Mach number until ___________ causes a large drop in C l ; once the shock moves to the trailing edge, C l _________ C Do remains essentially constant below M crit, but begins to _________ rapidly above the __________________ Mach number, M DD When M ∞ > 1, the wing’s aerodynamics center shifts back from the ________-chord point (c/4) to the _______-chord point (c/2) If we want to fly at high subsonic speeds while avoiding wave drag, we want to increase ______; strategies for doing so include the use of _____ wings; less _________ wings; _________ wings; ______, ________ leading edges; and _______________ airfoils M Prandtl-Glauert rises shock stall recovers increasedrag divergence quarterhalf M crit thincambered swept sharp slender supercritical
18
Supersonic Flow Wing sweep __________ M crit by decreasing the velocity component the airfoil “sees” by 1/cos __, although wing sweep increases induced drag by __________ aspect ratio and ___________ span efficiency factor If we want to fly at supersonic speeds, we want to minimize _____ drag; strategies for doing so include the use of a _________ wing-body; an ____________ fuselage (Coke-bottle shape or “wasp waist”); offsetting the ___________ above or below the main wing; sharp, slender _________ (causing oblique shocks, which produce less wave drag than ______________ shocks); and ____________-geometry wings increases decreasing reducing wave blendedarea-ruled tailplane wings bow wave variable
19
Next Lesson (T22) Prior to class Read Study Homework problems EI In class GR#2
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.