A laminar boundary layer is a layer in which ? [ Certification weather ]

Question 225-1 : No velocity components exist normal to the surface the vortices are weak the velocity is constant the temperature varies constantly

exemple 325 No velocity components exist, normal to the surface. — .'vertical axis' is also call 'normal axis' by 'normal' they mean 'perpendicular to the wing surface' .the airflow in the laminar boundary layer is parallel to the wing surface in a horizontal direction and hence there are no flows perpendicular to the surface No velocity components exist, normal to the surface.

The subsonic static pressure ?

Question 225-2 : Decreases in a flow in a tube when the diameter decreases is the total pressure plus the dynamic pressure is the pressure in a point at which the velocity has become zero increases in a flow in a tube when the diameter decreases

exemple 329 Decreases in a flow in a tube when the diameter decreases. — Decreases in a flow in a tube when the diameter decreases.

The lift and drag forces acting on a wing cross section ?

Question 225-3 : Depend on the pressure distribution about the wing cross section are normal to each other at just one angle of attack are proportional to each other independent of angle of attack vary linearly with the angle of attack

exemple 333 Depend on the pressure distribution about the wing cross section. — .the distribution of velocities with resulting pressure distribution is determined by the shape or profile of the surface and the angle of attack cl or cd .the aerodynamic force of lift results from the pressure differential between the top and bottom surfaces of the wing .drag is the product of dynamic pressure drag coefficient and surface area Depend on the pressure distribution about the wing cross section.

The lift force acting on an aerofoil no flow separation ?

Question 225-4 : Is mainly caused by suction on the upperside of the aerofoil increases proportional to the angle of attack until 40 degrees is mainly caused by overpressure at the underside of the aerofoil is maximum at an angle of attack of 2 degrees

exemple 337 Is mainly caused by suction on the upperside of the aerofoil. — Is mainly caused by suction on the upperside of the aerofoil.

The relative thickness of an aerofoil is expressed in ?

Question 225-5 : % chord camber meters degrees cross section tail angle

The aerofoil polar is ?

Question 225-6 : A graph of the relation between the lift coefficient and the drag coefficient a graph of the relation between the lift coefficient and the angle of attack the relation between the horizontal and the vertical speed a graph in which the thickness of the wing aerofoil is given as a function of the chord

exemple 345 A graph of the relation between the lift coefficient and the drag coefficient. — . /com en/com080 1264 jpg.airfoil and aircraft polars have been used for a long time in aeronautics the correct german term is lilienthal'sches polardiagramm indicating that this method of graphing results of airfoil tests has been used first by otto lilienthal he plotted the lift and drag forces of his experimental results as lift versus drag as we still use it today using coefficients instead of the actual forces A graph of the relation between the lift coefficient and the drag coefficient.

Aspect ratio of a wing is the ratio between ?

Question 225-7 : Wing span squared and wing area wing span and dihedral angle wing root chord line and wing tip chord line wing span and wing root chord

exemple 349 Wing span squared and wing area. — .aspect ratio is the ratio of the square of the wing span to the total wing.planform area .you could have two aerofoils of equal surface area but different aspect ratios depending on what they were designed for the higher the aspect ratio of length to width the more lift you get with less induced drag at the tips .a wing with higher aspect ratio with long wingspan and small chord reaches higher lift coefficient but stalls at a lower angle of attack than the wing with low aspect ratio Wing span squared and wing area.

Dihedral of the wing is ?

Question 225-8 : The angle between the 0 25 chord line of the wing and the lateral axis the angle between the leading edge of the wing and the lateral axis the angle between the 0 25 chord line of the wing and the vertical axis the angle between the 0 25 chord line of the wing and the horizon

exemple 353 The angle between the 0.25 chord line of the wing and the lateral axis. — .the dihedral is the angle between the wings and the horizontal looked at from the front where the wingtips are higher than the roots .it is an angle that raises the centerline of the wing tip above the centreline of the root . /com en/com080 208 jpg.notice horizon isn't a plane neither an axis .the angle between the 0 25 chord line of the wing and the lateral axis is the correct answer The angle between the 0.25 chord line of the wing and the lateral axis.

The induced drag ?

Question 225-9 : Increases as the lift coefficient increases increases as the aspect ratio increases has no relation to the lift coefficient increases as the magnitude of the tip vortices decreases

exemple 357 Increases as the lift coefficient increases. — Increases as the lift coefficient increases.

Flap extension at constant ias whilst maintaining straight and level flight ?

Question 225-10 : Maximum lift coefficient clmax and the drag lift coefficient and the drag stall speed lift and the drag

exemple 361 Maximum lift coefficient (clmax) and the drag. — .lift = cl x 1/2 rho v² x s.cl = lift coefficient.rho = density.v = tas in m/s .s = surface.clmax available increases with all types of flap so will drag the pilot adjusts attitude and power to maintain speed and straight and level flight Maximum lift coefficient (clmax) and the drag.

When trailing edge flaps are extended whilst maintaining straight and level ?

Question 225-11 : The centre of pressure moves aft the lift coefficient and the drag coefficient increase the stall speed increases the total boundary layer becomes laminar

exemple 365 The centre of pressure moves aft. — .to maintain straight and level flight at constant ias while deploying trailing edge flaps you have to lower the nose decreasing angle of attack so your lift coefficient will remain constant .the centre of pressure moves backward when the angle of attack decreases The centre of pressure moves aft.

Which of the following situations leads to a decreasing stall speed ias ?

Question 225-12 : Decreasing weight increasing altitude increasing air density increasing load factor

exemple 369 Decreasing weight. — Decreasing weight.

The difference between ias and tas will ?

Question 225-13 : Decrease with decreasing altitude increase with decreasing temperature increase with increasing air density decrease with increasing speed

exemple 373 Decrease with decreasing altitude. — .true air speed tas is obtained from indicated air speed ias by correcting for instrument position compressibility and density errors .use the very simple 'ertm' diagram ertm for e as/ r as rectified air speed or cas / t as/ m ach . /com en/com080 103a jpg.if altitude increases difference between ias and tas increases inversely if altitude decreases difference between ias and tas decreases .for rapid calculation .tas = ias + 2% per 1000 ft altitude Decrease with decreasing altitude.

Compared with stalling airspeed vs in a given configuration the airspeed at ?

Question 225-14 : Greater than vs 1 30 vs 1 12 vs 1 20 vs

exemple 377 Greater than vs. — .a stick shaker is a mechanical device to rapidly and noisily vibrate the control yoke the 'stick' of an aircraft to warn the pilot of an imminent stall it is connected to the control column of most business jets airliners and military aircraft .when the angle of attack alpha approaches a critical value the stick is made to shake as a warning .example stalling airspeed vs is 100 kt stick shaker activation is at 110 kt the airspeed at which stick shaker will be triggered is greater than vs to give enough time to the pilot to react by increasing speed and/or reducing the angle of attack Greater than vs.

The term angle of attack in a two dimensional flow is defined as ?

Question 225-15 : The angle between the wing chord line and the direction of the relative wind/airflow the angle between the aeroplane climb path and the horizon the angle formed by the longitudinal axis of the aeroplane and the chord line of the wing the angle for maximum lift/drag ratio

exemple 381 The angle between the wing chord line and the direction of the relative wind/airflow. — The angle between the wing chord line and the direction of the relative wind/airflow.

The critical angle of attack ?

Question 225-16 : Remains unchanged regardless of gross weight increases if the cg is moved forward decreases if the cg is moved aft changes with an increase in gross weight

exemple 385 Remains unchanged regardless of gross weight. — .the angle at which the stall occurs is called the critical angle of attack . a fixed wing aircraft by definition is stalled at or above the critical angle of attack rather than at or below a particular airspeed the airspeed at which the aircraft stalls varies with the weight of the aircraft the load factor bank angle the center of gravity of the aircraft and other factors however the aircraft always stalls at the same critical angle of attack Remains unchanged regardless of gross weight.

Comparing the lift coefficient and drag coefficient at normal angle of attack ?

Question 225-17 : Cl is much greater than cd cl is much lower than cd cl has approximately the same value as cd cl is lower than cd

exemple 389 Cl is much greater than cd. — .for maximum aerodyamic efficiency it is necessary to generate enough lift to balance the weight while at the same time generate as little drag as possible the higher the lift/drag ratio the greater the aerodyamic efficiency therefore at normal angles of attack cl is much higher than cd between 10 and 20 times greater Cl is much greater than cd.

Which statement is correct regarding cl angle of attack ?

Question 225-18 : For a symmetrical aerofoil section if the alpha is zero cl is zero for a symmetrical aerofoil section if the alpha is zero cl is not zero for an asymmetrical aerofoil section if the alpha is zero cl is zero for an asymmetrical aerofoil section with positive camber if alpha is greater than zero cl is zero

exemple 393 For a symmetrical aerofoil section, if the alpha is zero, cl is zero. — . /com en/com080 878 jpg.a symmetrical aerofoil need to have a positive angle of attack to produce lift it the pitching moment is zero the lift is zero .a positively cambered aerofoil produces lift with a zero angle of attack For a symmetrical aerofoil section, if the alpha is zero, cl is zero.

The mean aerodynamic chord mac for a given wing of any planform is ?

Question 225-19 : The chord of a rectangular wing with same moment and lift the chord of a large rectangular wing the average chord of the actual aeroplane the wing area divided by the wing span

exemple 397 The chord of a rectangular wing with same moment and lift. — .for a rectangular wing of constant aerofoil dimensions and constant chord the mac is just the chord .'same moment and lift' means equilibrium on a rectangular wing mac permits to define a point where the lift forces acting this single point is about half way out along the wing and at about 25% back from the leading edge The chord of a rectangular wing with same moment and lift.

Induced drag may be reduced by ?

Question 225-20 : An increase in aspect ratio the use of a wing tip with a much thinner aerofoil a decrease of the aspect ratio an increase in the taper ratio of the wing

exemple 401 An increase in aspect ratio. — .induced drag varies with lift speed and aspect ratio is inversely proportional to aspect ratio and v² so multiply by 1/v² and directly proportional to lift²/cl²/weight² . /com en/com080 38 jpg.aspect ratio is defined as the square of the wingspan divided by the area of the wing planform An increase in aspect ratio.

The relationship between induced drag and the aspect ratio is ?

Question 225-21 : A decrease in the aspect ratio increases the induced drag there is no relationship induced drag = 1 3 aspect ratio value an increase in the aspect ratio increases the induced drag

exemple 405 A decrease in the aspect ratio increases the induced drag. — .it is reduced because the effect of wing tip vortices is reduced .coefficient of induced drag cdi = cl² / pi x aspect ratio .aspect ratio is defined as the square of the wingspan divided by the area of the wing planform . /com en/com080 38 jpg.induced drag varies with lift speed and aspect ratio is inversely proportional to aspect ratio and v² so multiply by 1/v² and directly proportional to lift²/cl²/weight² A decrease in the aspect ratio increases the induced drag.

A high aspect ratio wing produces ?

Question 225-22 : A decrease in induced drag an increase in induced drag less sensitivity to gust effects a decrease in stall speed

exemple 409 A decrease in induced drag. — .it is reduced because the effect of wing tip vortices is reduced .coefficient of induced drag cdi = cl² / pi x aspect ratio .aspect ratio is defined as the square of the wingspan divided by the area of the wing planform . /com en/com080 38 jpg.induced drag varies with lift speed and aspect ratio is inversely proportional to aspect ratio and v² so multiply by 1/v² and directly proportional to lift²/cl²/weight² A decrease in induced drag.

What will happen in ground effect ?

Question 225-23 : The induced angle of attack and induced drag decreases an increase in strength of the wing tip vortices a significant increase in thrust required the wing downwash on the tail surfaces increases

exemple 413 The induced angle of attack and induced drag decreases. — .ground effect changes airflow . /com en/com080 821 jpg.when entering the ground effect it requires a decrease in angle of attack to maintain the same cl the induced angle decreases The induced angle of attack and induced drag decreases.

Which statement is correct about the laminar and turbulent boundary layer ?

Question 225-24 : Friction drag is lower in the laminar layer friction drag will be equal in both types of layers friction drag is lower in the turbulent layer separation point will occur earlier in the turbulent layer

exemple 417 Friction drag is lower in the laminar layer — Friction drag is lower in the laminar layer

Behind the transition point in a boundary layer ?

Question 225-25 : The mean speed and friction drag increases the boundary layer gets thinner and the speed increases the mean speed increases and the friction drag decreases the boundary layer gets thicker and the speed decreases

exemple 421 The mean speed and friction drag increases. — . /com en/com080 247 jpg.the laminar boundary layer the one at the front of the wing is smooth and thin inside it the speed of the air reduces smoothly from the free stream value to near zero at the surface because of this regular reduction in speed the average speed inside the layer is about half the free stream value and this fact and the fact that the layer is very thin mean that the total kinetic energy inside the layer is relatively small .the turbulent layer is thicker and the turbulence pulls down free stream air deep into the layer this has two results one is that the turbulent layer has more kinetic energy and the other is that near the surface the airflow slows down very rapidly causing more drag drag is bad but kinetic energy is good for the turbulent layer punches through problems and keeps the airflow attached to the wing as you get nearer the stall .in summary the turbulent layer is thicker has a higher mean speed within the layer more drag but more internal energy The mean speed and friction drag increases.

When trailing edge flaps are extended in level flight the change in pitching ?

Question 225-26 : Nose down nose up zero dependent on cg location

exemple 425 Nose down. — .pitch behavior depends on flap type wing position and horizontal tail location the increased camber from flap deflection produces lift primarily on the rear portion of the wing this produces a nosedown pitching moment . /com en/com080 253 jpg. Nose down.

Extension of leading edge flaps will ?

Question 225-27 : Increase critical angle of attack decrease clmax decrease drag not affect critical angle of attack

Slat extension will ?

Question 225-28 : Increase the critical angle of attack reduce tip vortices create gaps between leading edge and engine nacelles decrease the energy in the boundary layer on the upperside of the wing

exemple 433 Increase the critical angle of attack. — Increase the critical angle of attack.

What factors determine the distance travelled over the ground of an aeroplane ?

Question 225-29 : The wind and the lift/drag ratio which changes with angle of attack the wind and the aeroplane's mass the wind and clmax the wind and weight together with power loading which is the ratio of power output to the weight

exemple 437 The wind and the lift/drag ratio, which changes with angle of attack. — .a headwind will decrease the distance travelled over the ground .a tailwind will increase the distance travelled over the ground .the angle of attack for the best ratio varies with the design of the wing but is around a third to a quarter of the size of the stalling angle flying at the best lift/drag ratio is flying at the maximum range speed most lift for the least drag for the most economy and the most distance for altitude lost .the wind and lift/drag ratio determine the distance travelled over the ground of an aeroplane in a glide The wind and the lift/drag ratio, which changes with angle of attack.

The following unit of measurement kgm/s² is expressed in the si system as ?

Question 225-30 : Newton pascal joule watt

Chikarelly .the correct answer is watt ..what .could you please give more explanation if you are sure an answer is wrong .watt = kgm²/s3 . patorules .si unit kg = mass and m/s² = acceleration .mass x acceleration = force and si unit for force is newton

Excluding constants the coefficient of induced drag cdi is the ratio of ?

Question 225-31 : Cl² and ar aspect ratio cl²and s wing surface cl and cd cl and b wing span

.coefficient of induced drag cdi = cl² / pi x aspect ratio .the constant is pi 3 14159 so excluding the constant the coefficient of induced drag cdi is the ratio of cl² and ar aspect ratio

One important advantage the turbulent boundary layer has over the laminar type ?

Question 225-32 : It has less tendency to separate from the surface it is thinner skin friction drag is less energy is less

exemple 449 It has less tendency to separate from the surface. — .the laminar boundary layer is a very smooth flow while the turbulent boundary layer contains swirls the laminar flow creates less skin friction drag than the turbulent flow but is less stable boundary layer flow over a wing surface begins as a smooth laminar flow as the flow continues back from the leading edge the laminar boundary layer increases in thickness at some distance back from the leading edge the smooth laminar flow breaks down and transitions to a turbulent flow from a drag standpoint it is advisable to have the transition from laminar to turbulent flow as far aft on the wing as possible or have a large amount of the wing surface within the laminar portion of the boundary layer the low energy laminar flow however tends to break down more suddenly than the turbulent layer . /com en/com080 266 jpg. It has less tendency to separate from the surface.

When comparing a rectangular wing and a swept back wing of the same wing area ?

Question 225-33 : Higher critical mach number greater strength increased longitudinal stability lower stall speed

exemple 453 Higher critical mach number. — Higher critical mach number.

High aspect ratio as compared with low aspect ratio has the effect of ?

Question 225-34 : Decreasing induced drag and critical angle of attack increasing lift and critical angle of attack increasing lift and drag increasing induced drag and decreasing critical angle of attack

.high aspect ratio little downwash low aspect ratio great downwash that means that at the same angle of attack the low aspect ratio wing flies at a lower effective angle of attack than the high aspect ratio wing ..suppose ..low aspect ratio wing .angle of attack 10.effective angle of attack 5..high aspect ratio wing .angle of attack 10.effective angle of attack 8..at any given angle of attack the high aspect ratio wing will have a higher effective angle of attack and therefore be closer to stall critical alpha than low aspect ratio wing ..the effective airflow phenomena explains why high aspect ratio is favorable at low speeds why elliptical wing is superior drag wise/horrible stall wise and why ground effect wont let you down

What wing shape or wing characteristic is the least sensitive to turbulence ?

Question 225-35 : Swept wings straight wings wing dihedral elliptical wing

exemple 461 Swept wings. — .turbulence up and down gusts produce transient changes in the angle of attack different wing planforms give different increases in lift coefficient for each degree of angle of attack the swept wing is the least sensitive to turbulence Swept wings.

What is the si unit of measurement for power ?

Question 225-36 : Nm/s kgm/s² pa/m² n/m

exemple 465 Nm/s. — .icao annex 5 units of measurement attachment b . 2 mass force and weight .2 1 the principal departure of si from the gravimetric system of metric engineering units is the use of explicitly distinct units from mass and force in si the name kilogram is restricted to the unit of mass and the kilogram force from which the suffix force was in practice often erroneously dropped is not to be used in its place the si unit of force the newton is used likewise the newton rather than the kilogram force is used to form derived units which include force for example pressure or stress n/m² = pa energy nm = j and power nm/s = w Nm/s.

The use of a slot in the leading edge of the wing enables the aeroplane to fly ?

Question 225-37 : It delays the stall to a higher angle of attack the laminar part of the boundary layer gets thicker it decelerates the upper surface boundary layer air it changes the camber of the wing

For a subsonic flow the continuity equation states that if the cross sectional ?

Question 225-38 : Decreases does not change increases first increases then decreases

If the continuity equation is applicable what will happen to the air density ?

Question 225-39 : Rho1 = rho2 rho1 < rho2 rho1 > rho2 the density depends on the change of the tube area

Bernoulli's equation can be written as pt = total pressure ps = static ?

Question 225-40 : Pt q = ps pt = ps q pt + ps = q pt = q ps

exemple 481 Pt - q = ps — .pt total pressure.ps static pressure.pd dynamic pressure 1/2 x density x tas² ..bernoulli's theorem is .pt = ps + pd Pt - q = ps

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