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INCOMP Final
| Question | Answer |
|---|---|
| 1st digit of NACA airfoil | Maximum camber as % of chord |
| 2nd digit of NACA airfoil | Location of max camber in tenths of chord |
| 3rd digit of NACA airfoil | Maximum thickness as % of chord |
| Effects of an Elliptical Wing | Elliptic circulation distribution, Minimum induced drag, Constant downwash, No wingtip vortices distortion, and e=1 (span efficiency factor) |
| What is the Center of Pressure (CoP)? | The location where no moment is produced by the distributed load |
| What is the Aerodynamic Center (AC)? | The point along the chord where pitching moment is constant with angle of attack |
| Where is the AC for thin airfoils? | at the quarter chord |
| What is vorticity? | The curl of the velocity field: ๐=โร๐ |
| What is circulation? | Line integral of velocity around a closed loop |
| What is a velocity potential function? | Scalar function ฯ where ๐=โฯ; applies to irrotational flow. |
| What is a stream function? | Scalar function ฯ where u=โฯ/โy, v=โโฯ/โx; |
| What is superposition in potential flow? | Adding solutions linearly to create complex flows, due to linearity of Laplaceโs equation. |
| What is the Kutta-Joukowski theorem? | Lift per unit span is L '=ฯUฮ. |
| How does circulation relate to lift? | Greater circulation leads to greater lift, per Kutta-Joukowski |
| How does lift differ in viscous vs. inviscid flow over a circle? | Inviscid gives lift via circulation; viscous allows actual generation of circulation via boundary layer and Kutta condition. |
| What assumption can be made under elliptical wing? | C L โ Cโ |
| What is the thin airfoil assumption? | lift slope: Cโ=2ฯฮฑ |
| What is the symmetrical airfoil assumption? | angle of attack of zero lift ฮฑ(L=0) =0 because there is no camber. Also, AC=COP= quarter chord |
| What are the steady level flight conditions? | SLF means the aircraft is in static equilibrium such that L=W, D=T, and the moment about the center of gravity is 0. This is called trim. |
| Is drag present in inviscid flow? | No, D'Alembert's paradox states inviscid flow predicts zero drag |
| What is camber? | The curvature of the mean camber line; determines zero-lift angle |
| What is a vortex sheet? | A distribution of bound vorticity along the camber line used in thin airfoil theory to model lift. |
| What is a boundary layer? | Thin region near the surface where viscous effects are significant and velocity changes from 0 to freestream |
| What is displacement thickness ๐ฟ*? | Distance by which external flow is "displaced" due to boundary layer |
| What is momentum thickness ฮธ? | Represents momentum loss |
| What is boundary layer separation? | Point where boundary layer detaches from the surface due to adverse pressure gradient |
| What causes flow separation? | Adverse pressure gradient that decelerates fluid near the wall to zero or negative velocity. |
| What are the two main categories of drag? | Parasite drag and induced drag. |
| What is parasite drag? | Drag not associated with lift, caused by friction and pressure differences on the body |
| What are the components of parasite drag? | Skin friction drag, form drag (pressure drag), and interference drag. |
| What is skin friction drag? | Drag due to shear stress from viscous effects on the surface of a body. |
| What is form drag? | Drag due to pressure differences between the front and rear of a body. |
| What is interference drag? | Drag caused by the interaction of flow around components (e.g., wing-fuselage junctions) |
| What is induced drag? | Drag caused by the generation of lift and the associated downwash from wingtip vortices. |
| How does induced drag vary with aspect ratio? | Induced drag decreases as aspect ratio increases. |
| What is wave drag? | Drag associated with compressibility effects and shock waves; not present in incompressible flow. |
| Geometric Angle of Attack | The angle between the chord line of the airfoil and the freestream velocity. |
| Effective Angle of Attack | The angle between the chord line and the local relative wind, accounting for induced downwash. (Used in finite wing analysis (e.g., lifting line theory) to account for induced angle.) |
| Aspect Ratio | A measure of how long and slender a wing is (span over average chord) |
| Oswald efficiency | Used when trying to represent the entire aircraft. Accounts for inviscid and viscous effects; Empirical correction factor used in the drag polar equation; Accounts for induced drag and all non-parasitic drag deviations from ideal |
| Span efficiency | e_max=1, used for a finite wing not the whole aircraft, used for lifting line theory; Measures how close a wingโs lift distribution is to the ideal elliptical distribution; Used when calculating induced drag of finite wings |
| What is Lifting Line Theory used for? | Predicting lift and induced drag for finite wings in 3D. |
| What are the assumptions of Lifting Line Theory? | Inviscid, incompressible, steady flow with a high aspect ratio wing and small angle of attack |
| What is the induced angle of attack ๐ผ๐? | It is the downward deflection caused by trailing vortices: ๐ผ๐=๐ค/๐โ |
| How is the effective angle of attack defined in LLT? | ฮฑ_eff=ฮฑโฮฑ_i |
| What is the ideal circulation distribution for minimum drag? | Elliptical circulation distribution. |
| What does the span efficiency factor e represent? | A measure of how close the wing is to the ideal elliptical lift distribution (best case: e=1) |
| What is the key difference between TAT and LLT? | TAT applies to 2D infinite wings; LLT accounts for 3D effects like spanwise flow and induced drag |
| What is Thin Airfoil Theory used for? | It estimates the lift characteristics of cambered or symmetric airfoils at small angles of attack in inviscid, incompressible flow. |
| What are the assumptions of Thin Airfoil Theory? | Small angle of attack, thin camber, inviscid and incompressible flow, and linear superposition of elementary flows. |
| What is the significance of the zero-lift angle ๐ผ0? | It is the angle of attack at which a cambered airfoil produces no lift |
| What physical phenomenon does circulation represent in lift generation? | Circulation corresponds to the rotational effect of flow creating a pressure difference that produces lift. |
| Under what conditions is the Kutta-Joukowski theorem valid? | It is valid for steady, incompressible, inviscid, irrotational flows where the Kutta condition is satisfied. |
| What is the Kutta condition? | It states that flow must leave smoothly at the trailing edge of an airfoil, ensuring a unique and physically realistic circulation value; determines the value of circulation needed to produce lift according to the Kutta-Joukowski theorem. |
| What is aircraft endurance? | The amount of time the aircraft can stay in the air |
| Stall Angle of Attack | The angle of attack at which the airfoil reaches its maximum lift coefficient; Beyond this angle, lift decreases rapidly due to flow separation on the upper surface |
| How does max range depend on ๐ถ๐ฟ/๐ถ๐ท and AR? Which has greater effect? | It increases with both factors, but in the equation AR is in a sqaure root, so it has less of a direct effect than CL/CD |
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emmaliza
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