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201.

What is the graph that is represented in the airfoil section?(a) Lift-moment ratio(b) Coefficient of lift-coefficient of drag ratio(c) Angle of attack-drag ratio(d) Lift–angle of attack ratioThe question was posed to me in quiz.The question is from Airfoil Characteristics in portion Incompressible Flow over Airfoils of Aerodynamics

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Right option is (B) Coefficient of lift-coefficient of drag ratio

To elaborate: The CHARACTERISTICS of any particular airfoil section can conveniently be represented by a graph, showing the AMOUNT of lift and drag obtained at a various angle of attack, the lift-drag ratio, and the movement of the center of pressure. With these graphs, we can choose SUITABLE airfoil for the AIRCRAFT.

202.

Is turbulence flow is irregular?(a) False(b) TrueThis question was posed to me in my homework.Origin of the question is Turbulent Flow in portion Incompressible Flow over Airfoils of Aerodynamics

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Correct ANSWER is (b) True

To explain: TURBULENT flows are ALWAYS highly irregular. For this reason, TURBULENCE problems are normally treated statistically rather than deterministically. Turbulent FLOW is chaotic however, not all chaotic flows are turbulent.

203.

The total skin-friction drag coefficient for laminar flow with Reynolds number at the trailing edge being Rec=40000 and chord length is 1m, is _____(a) 0.01328(b) 0.00664(c) 0.02656(d) 0.664The question was asked during an interview for a job.My question is based upon Laminar Flow topic in portion Incompressible Flow over Airfoils of Aerodynamics

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The correct CHOICE is (a) 0.01328

The explanation: The total skin-friction drag coefficient for laminar flow is twice the value of the skin-friction drag coefficient for laminar flow, CF=\(\frac {1.328}{\sqrt{Re_c}}\). PUTTING the given values, we GET the ANSWER as 0.01328.

204.

The essential assumption of airfoil being a flat plate with a zero angle of attack gives accurate results always.(a) False(b) TrueI had been asked this question in final exam.The above asked question is from Laminar Flow topic in division Incompressible Flow over Airfoils of Aerodynamics

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Right option is (a) False

The BEST I can explain: This assumption is a first order approximation and the results become more accurate as the AIRFOIL gets thinner and angle of attack approaches zero. It gives good results but the LEVEL of ACCURACY varies.

205.

Is interface between the solid and fluid, shear stresses develop as the solid attempts to slow down the fluid flowing?(a) True(b) FalseThe question was posed to me by my school principal while I was bunking the class.This intriguing question comes from Viscous Flow topic in division Incompressible Flow over Airfoils of Aerodynamics

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Right CHOICE is (a) True

To explain I WOULD say: The interface between the solid and fluid, shear STRESSES develop as the solid attempt’s to slow down the fluid flowing over it. This shear stress gives rise to a skin friction DRAG. It is proportional to the product of a quantity CALLED viscosity.

206.

A higher value of L/D ratio deteriorates climbing performance for the flight.(a) True(b) FalseI got this question in an interview for job.This intriguing question comes from Modern Low Speed Airfoils in section Incompressible Flow over Airfoils of Aerodynamics

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Correct ANSWER is (b) False

For EXPLANATION I WOULD say: The higher value of L/D ratio IMPROVES the climbing PERFORMANCE. It can be visualized as a higher lift with lower drag, which is essentially beneficial.

207.

The quarter-chord is the aerodynamic center for a cambered airfoil.(a) True(b) FalseI have been asked this question in quiz.I'd like to ask this question from The Cambered Airfoil topic in division Incompressible Flow over Airfoils of Aerodynamics

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The correct CHOICE is (a) True

The explanation: The coefficient of MOMENT about the quarter chord (cm,l/4=\(\frac {\PI }{4}\)(A2-A1)) is independent of angle of attack α, thereby making it the aerodynamic center (moment coefficient independent of angle of attack) for a thin cambered AIRFOIL.

208.

Select the statement which is not true for the solution of \(\frac {1}{2\pi } \int_0^c \frac {\gamma(\xi)d\xi}{x-\xi}\)=V∞(α-\(\frac {dz}{dx}\)) for a cambered airfoil.(a) An depends on chord length of the airfoil(b) A0 depends on the slope of the camber line(c) An depends on the slope of the camber line(d) A0 depends on the angle of attackThis question was posed to me by my school teacher while I was bunking the class.My doubt is from The Cambered Airfoil in section Incompressible Flow over Airfoils of Aerodynamics

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Correct option is (a) An DEPENDS on chord length of the airfoil

To EXPLAIN I would say: The given equation is the fundamental equation of thin airfoil THEORY. For a CAMBERED airfoil, the solution is in the FORM γ(θ)=2V∞(A0\(\frac {1+cos\theta }{sin⁡\theta }\) + Σ\(_{n=1}^∞\)sin⁡ nθ An) where An depends on the slope of camber line and A0 depend both on the slope of camber line and angle of attack.

209.

Is supersonic flight uses supercritical airfoil?(a) True(b) FalseThe question was posed to me in unit test.Asked question is from The Cambered Airfoil topic in division Incompressible Flow over Airfoils of Aerodynamics

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Right choice is (a) True

To elaborate: To do different types of maneuvers at a speed Mach GREATER than 1. So, the designers use NEGATIVE camber airfoil this is called SUPER critical airfoil. It is used for near SUPERSONIC flight and produces high lift to drag ratio at near supersonic flight than a traditional airfoil.

210.

Is ‘C’ denotes a dyed circuit, composed of same fluid particles?(a) False(b) TrueI got this question during an online exam.My question is from Kelvin’s Circulation Theorem and the Starting Vortex topic in division Incompressible Flow over Airfoils of Aerodynamics

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Correct choice is (b) True

Explanation: In kelvin’s circulation THEOREM the C denotes a DYED CIRCUIT, composed of the same fluid PARTICLES as time proceeds, the result is not true in GENERAL if C is a closed curve fixed in space then the C does not denote the dyed circuit.

211.

How stagnation point on the topside of the airfoil reaches the trailing edge?(a) Due to viscous forces(b) Due to surface forces(c) Due to pressure forces(d) Due to drag forcesI have been asked this question in an interview.Question is from The Kutta Condition in division Incompressible Flow over Airfoils of Aerodynamics

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The correct OPTION is (a) Due to viscous forces

Easiest explanation: The STAGNATION point on the topside of the airfoil then moves until it reaches the trailing EDGE. The starting vortex EVENTUALLY dissipates due to viscous forces. As the airfoil continues on its way, there is a stagnation point at the trailing edge. The flow over the topside of the airfoil conforms to the UPPER surface of the airfoil.

212.

Is fluid is initially in irrotational motion?(a) True(b) FalseI had been asked this question during an interview.My question is taken from Kelvin’s Circulation Theorem and the Starting Vortex topic in section Incompressible Flow over Airfoils of Aerodynamics

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Correct option is (a) True

Easy explanation: An INVISCID incompressible fluid of CONSTANT density move in the PRESENCE of a CONSERVATIVE body force. Then if a portion of the fluid is initially in irrotational motion, that portion will ALWAYS be in the irrotational motion.

213.

Vortex flow occurs at ___________(a) Leading edge(b) Trailing edge(c) Chord(d) Chamber lineThis question was addressed to me by my college professor while I was bunking the class.Question is taken from The Kutta Condition in section Incompressible Flow over Airfoils of Aerodynamics

Answer» RIGHT answer is (b) Trailing edge

Explanation: VORTEX flow occurs at the trailing edge and because the RADIUS of the sharp trailing edge is zero, the speed of the air around the trailing edge should be INFINITELY fast, real fluid cannot move at infinite speed, they can move extremely fast FINITE speed.
214.

How many stagnation points on the oval cylinder with non-zero angle of attack?(a) Two(b) Zero(c) More than zero(d) OneI got this question at a job interview.My enquiry is from The Kutta Condition topic in chapter Incompressible Flow over Airfoils of Aerodynamics

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Correct choice is (a) Two

Explanation: An oval cylinder moves with a non-zero angle of attack through the fluid there are STILL two stagnation points on the BODY. ONE on the UNDERSIDE of the cylinder, near the front edge and the other on the top side of the cylinder near the BACK edge. The circulation around this smooth cylinder is zero and no lift is generated, despite the positive angle of attack.

215.

How vortex filament are arrange in the vortex sheet?(a) Side by side(b) Front and back(c) Up and down(d) Left and rightThe question was posed to me by my college professor while I was bunking the class.The doubt is from The Vortex Sheet topic in chapter Incompressible Flow over Airfoils of Aerodynamics

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The correct OPTION is (a) Side by side

The explanation: The flow in the planes perpendicular to the vortex filament at ZERO are identical to the flow induced by the point vortex of strength. An infinite NUMBER of straight vortex FILAMENTS side by side.Where the strength of each filament is infinite small. These vortex filament are ARRANGED side by side from the vortex sheet.

216.

Define stalling angle in the graph.(a) The curve increases maximum at a particular section and decreases rapidly in the same section(b) The curve increases at different section and decreases rapidly at different section(c) The curve remains constant at all section(d) Lift curve will increases and drag curve will remain constantI got this question at a job interview.Query is from Airfoil Characteristics in portion Incompressible Flow over Airfoils of Aerodynamics

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The correct choice is (a) The curve increases MAXIMUM at a PARTICULAR section and decreases RAPIDLY in the same section

Easy explanation: The lift curve reaches its maximum for any wing section at certain DEGREE of angle of attack and then rapidly decreases at some degree of angle of attack is therefore the stalling angle. Stalling will OCCURS at particular degree were the maximum lift will be achieved by the aircraft at that point stalling will takes place.