In a still air hover induced flow velocity is affected by ? [ Explanation maintenance ]

Question 250-1 : Disc loading and density the mass of the aircraft only the rotatonal velocity and rotor drag density only

exemple 350 Disc loading and density. — Disc loading and density.

What are the conditions necessary for ground resonance in addition to having a ?

Question 250-2 : An out of balance force at the rotor head low rotor rpm high wind flapping of the blades with wind on the beam the ground must be sloping

exemple 354 An out of balance force at the rotor head. — An out of balance force at the rotor head.

Dynamic roll over is ?

Question 250-3 : A condition whereby a rolling motion with wheels in contact with the ground cannot be restrained by cyclic control caused by inflow roll and cannot be restrained by cyclic control reduced in helicopters with a high cg because of reduced angular momentum about the undercarriage only experienced when taking off or landing on sloping ground

exemple 358 A condition whereby a rolling motion with wheels in contact with the ground cannot be restrained by cyclic control. — A condition whereby a rolling motion with wheels in contact with the ground cannot be restrained by cyclic control.

The minimum value of the power required curve determines ?

Question 250-4 : The t a s for maximum rate of climb speed the t a s for maximum range the t a s for maximum angle of climb the aircraft's v n o

exemple 362 The t.a.s. for maximum rate of climb speed. — Admin . 1356.at minimum value of the power required curve where the gap between power available and the maximum power available is greatest you will find the tas for maximum rate of climb speed The t.a.s. for maximum rate of climb speed.

In a level balanced turn ?

Question 250-5 : Retreating blade stall will occur at a lower i a s than in straight and level flight retreating blade stall will occur at the same i a s as in straight and level flight the large the angle of bank the higher the i a s at which retreating blade stall will occur retreating blade stall will occur at a higher i a s than in straight and level flight

exemple 366 Retreating blade stall will occur at a lower i.a.s. than in straight and level flight. — Retreating blade stall will occur at a lower i.a.s. than in straight and level flight.

With forward flight thrust on the advancing side of a tail rotor system ?

Question 250-6 : Is kept approximately constant because movement of the blade about its flapping axis reduces the angle of attack decreases by the 'upward' flapping movement of the blade increasing the angle of attack increases by the 'downward' flapping movement of the blade decreasing the angle of attack is kept constant because the pilot reduces the blade pitch angle with the rudder pedals

exemple 370 Is kept approximately constant because movement of the blade about its flapping axis reduces the angle of attack. — Is kept approximately constant because movement of the blade about its flapping axis reduces the angle of attack.

On a main rotor if the flapping hinge is offset ?

Question 250-7 : It improves cyclic control response it increases control movement it maintains thrust symmetry it has no effect on the control power of the helicopter

exemple 374 It improves cyclic control response. — It improves cyclic control response.

The centre of pressure is the point on an aerofoil section ?

Question 250-8 : Through which the resultant aerodynamic force acts where the weight of the helicopter acts where the airflow separates from the aerofoil section where maximum velocity of the airflow occurs

exemple 378 Through which the resultant aerodynamic force acts. — Through which the resultant aerodynamic force acts.

In autorotation the tail rotor thrust on a helicopter with anti clockwise main ?

Question 250-9 : To the left to the right not required as there is no fuselage torque reaction equal in magnitude to that required in powered flight but in the opposite direction

exemple 382 To the left. — Admin .think back to basic vector diagrams of the main rotor which way does total rotor thrust act answer = up .ok a tail rotor is exactly the same just on its side when we enter auto we are removing all the torque from the main rotor in an anti clockwise rotor with power applied this normally wants to spin us round to the right viewed inside the cockpit that is what would happen if the tail rotor failed remove tq and the fuselage is effectively now going to move in the opposite direction to the main rotor newtons laws equal and opposite blah it is not anywhere near as significant though as there is no tq to really drive it it is just trying to follow the main rotor but there will be an amount of left yaw the tail assembly design will assist with directional stability in this instance but we will still need a little extra help from the tail rotor .aircraft nose wants to go left or anti clockwise viewed from above and tail wants to go right we just need to counter this remember here we have created a moment and we need to balance it as i said before think about your vector diagram and which direction does the thrust need to act up or in this case the rotor is on its side so to the left in order to pull the tail back and push the nose back to the right .therefore we need a little thrust to the left to do this the key is the fact that the aircraft wants to follow the main rotor once we have removed all the torque To the left.

Induced power ?

Question 250-10 : Is a maximum at the hover without wind increases with forward speed decreases in direct proportion to forward speed is affected only by a change of speed

exemple 386 Is a maximum at the hover without wind. — Is a maximum at the hover without wind.

In the flare the resultant aerodynamic forces on the blades ?

Question 250-11 : Moves forward towards the axis of rotation moves further aft away from the axis of rotation moves very little remaining substantially vertical reduces due to the decrease in the angle of attack

exemple 390 Moves forward, towards the axis of rotation. — Moves forward, towards the axis of rotation.

The camber line of a biconvex symmetrical section is ?

Question 250-12 : Common with the chord line curved towards the upper surface curved towards the lower surface a circular arc

exemple 394 Common with the chord line. — Common with the chord line.

The angle of attack of an aerofoil is the angle between ?

Question 250-13 : The chord line and the relative air flow the upper surface and the relative air flow the camber line and the undisturbed air flow the resultant of lift and the vertical axis

exemple 398 The chord line and the relative air flow. — The chord line and the relative air flow.

A reduction in blade section pitch angle towards the tip is termed ?

Question 250-14 : Washout washin upwash downwash

The force which acts at right angles to the relative airflow is ?

Question 250-15 : Lift total reaction drag thrust

The point at which the resultant of lift forces acts is ?

Question 250-16 : Centre of pressure centre of gravity the moment arm the hub

exemple 410 Centre of pressure. — Centre of pressure.

On a symmetrical blade element with a positive angle of attack lift is produced ?

Question 250-17 : Airflow velocity increasing over upper surface giving decreased pressure and velocity decreasing over lower surface giving increased pressure airflow velocity increasing downward having been deflected by the blade pitch angle and creating an upward pressure on the blade an increase in flow velocity giving an increase in pressure on the lower surface an increase in flow velocity on the lower surface and decrease on the upper surface

exemple 414 Airflow velocity increasing over upper surface giving decreased pressure and velocity decreasing over lower surface giving increased pressure. — Airflow velocity increasing over upper surface giving decreased pressure and velocity decreasing over lower surface giving increased pressure.

Bernoulli's' theorem indicates that ?

Question 250-18 : The sum of pressure energy and dynamic energy is constant when dynamic energy increases pressure energy increases pressure energy decreases as velocity decreases dynamic energy decreases as velocity increases

exemple 418 The sum of pressure energy and dynamic energy is constant. — The sum of pressure energy and dynamic energy is constant.

The point where a laminar boundary layer becomes turbulent is called ?

Question 250-19 : The transition point the separation point the critical point the deflection point

exemple 422 The transition point. — .transition point the point on the surface of an aerofoil where laminar airflow becomes turbulent the point moves forward as airspeed increases .the separation point point where airflow leaves the surface of an aerofoil The transition point.

The expression 'in a streamlined flow of fluid the sum of all energies is a ?

Question 250-20 : Bernoulli's theorem newton's first law of motion reynold's number the conservation of mass flow

exemple 426 Bernoulli's theorem. — Bernoulli's theorem.

Cl varies with ?

Question 250-21 : Angle of attack density velocity pressure

exemple 430 Angle of attack. — Angle of attack.

Within the normal operating angles of attack the centre of pressure of a ?

Question 250-22 : Moves very little moves nearer the leading edge needs to be offset from the cg line of the rotor blade for control purposes moves nearer the trailing edge

exemple 434 Moves very little. — Moves very little.

That point where airflow leaves the surface of an aerofoil is known as ?

Question 250-23 : The separation point the stagnation point the critical point the transition point

exemple 438 The separation point. — .the separation point point where airflow leaves the surface of an aerofoil .transition point the point on the surface of an aerofoil where laminar airflow becomes turbulent the point moves forward as airspeed increases The separation point.

For a rotor which turns in an anti clockwise direction seen from above with a ?

Question 250-24 : In front of him on his left on his right behind him

exemple 442 In front of him — In front of him

The power requirement of the tail rotor is greatest during ?

Question 250-25 : A hover turn oge in the same direction as the main rotor a transition to the climb a hover outside ground effect a turn in autorotation

exemple 446 A hover turn oge in the same direction as the main rotor — A hover turn oge in the same direction as the main rotor

'a line connecting the leading and trailing edge midway between the upper and ?

Question 250-26 : The camber line the chord line the mean aerodynamic chord line the upper camber line

exemple 450 The camber line. — The camber line.

What is the effect on induced drag of an increase in aspect ratio ?

Question 250-27 : Induced drag decreases because the effect of tip vortices decreases induced drag increases because a larger aspect ratio increases the frontal area induced drag increases because the effect of tip vortices increases induced drag decreases because a larger aspect ratio causes more downwash

exemple 454 Induced drag decreases, because the effect of tip vortices decreases. — 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 Induced drag decreases, because the effect of tip vortices decreases.

What is the stagnation point ?

Question 250-28 : The point where the velocity of the relative airflow is reduced to zero the intersection of the total aerodynamic force and the chord line the intersection of the thrust vector and the chord line the point relative to which the sumtotal of all moments is independent of angle of attack

exemple 458 The point where the velocity of the relative airflow is reduced to zero. — The point where the velocity of the relative airflow is reduced to zero.

When an aerofoil section has accelerated from subsonic to supersonic speeds its ?

Question 250-29 : Shifted from approximately 25% to about 50% of the chord shifted aft by about 10% not moved shifted slightly forward

exemple 462 Shifted from approximately 25% to about 50% of the chord. — Shifted from approximately 25% to about 50% of the chord.

Which boundary layer when considering its velocity profile perpendicular to the ?

Question 250-30 : Turbulent boundary layer laminar boundary layer no difference the boundary layer in the transition between turbulent and laminar

exemple 466 Turbulent boundary layer. — Turbulent boundary layer.

The si unit of measurement for pressure is ?

Question 250-31 : N/m² kg/m³ lb/gal bar/dm²

.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

The polar curve of an aerofoil section is a graphic relationship between ?

Question 250-32 : Lift coefficient cl and drag coefficient cd tas and stall speed angle of attack and lift coefficient cl drag coefficient cd and angle of attack

exemple 474 Lift coefficient cl and drag coefficient cd. — Lift coefficient cl and drag coefficient cd.

True airspeed tas is ?

Question 250-33 : Lower than the indicated airspeed ias at altitudes below sea level under isa conditions higher than the indicated airspeed ias at altitudes below sea level under isa conditions equal to the ias multiplied by the air density at sea level eas corrected for compressibility

exemple 478 Lower than the indicated airspeed (ias) at altitudes below sea level, under isa conditions. — .true air speed tas is obtained from indicated air speed ias by correcting for the following errors instrument position compressibility and density .so tas is greater than ias with increasing altitude as density reduces .for this question they state at altitudes below sea level so it is reverse tas will be lower than ias density is higher for altitude below mean sea level .keep in mind that .ias is proportional to 1/2 rho tas² . rho = density Lower than the indicated airspeed (ias) at altitudes below sea level, under isa conditions.

Total pressure is rho = density ?

Question 250-34 : Static pressure plus dynamic pressure static pressure minus dynamic pressure ½ rho v² measured at a small hole in a surface parallel to the local stream

exemple 482 Static pressure plus dynamic pressure. — Static pressure plus dynamic pressure.

The unit of measurement for density is ?

Question 250-35 : Kg/m³ psi kg/cm² bar

The transition point is the point where ?

Question 250-36 : The boundary layer changes from laminar to turbulent the velocity of the relative airflow is reduced to zero changes in lift due to variations in angle of attack are constant the aeroplane becomes longitudinally unstable when the cg is moved beyond it in an aft direction

exemple 490 The boundary layer changes from laminar to turbulent. — The boundary layer changes from laminar to turbulent.

Considering a positively cambered aerofoil section the pitching moment when the ?

Question 250-37 : Negative nose down equal to zero maximum positive nose up

exemple 494 Negative (nose down). — Admin .when a positively cambered airfoil is at zero lift it has to be at a small negative alpha to cancel out the camber which gives some lift at zero alpha the angle of attack has a negative value when the lift coefficient equals zero .it is because the pressure distribution is producing negative lift at the front and positive lift at the back of the airfoil . 1631.a symmetrical aerofoil need to have a positive pitch to produce lift if the pitching moment is zero the lift is zero .a positively cambered aerofoil produces lift with a zero pitching moment thus not to produce lift it need a negative pitching moment . 2416.in this example lift coeffient = 0 when angle of attack = 4° the pitching moment is nose down Negative (nose down).

An aerofoil is cambered when ?

Question 250-38 : The line which connects the centres of all inscribed circles is curved the chord line is curved the upper surface of the aerofoil is curved the maximum thickness is large compared with the length of the chord

exemple 498 The line, which connects the centres of all inscribed circles, is curved. — The line, which connects the centres of all inscribed circles, is curved.

A flat plate when positioned in the airflow at a small angle of attack will ?

Question 250-39 : Both lift and drag lift but no drag drag but no lift neither lift nor drag

exemple 502 Both lift and drag. — Both lift and drag.

Positive static stability of an aeroplane means that following a disturbance ?

Question 250-40 : The initial tendency is to return towards its equilibrium condition the initial tendency is to diverge further from its equilibrium condition the tendency is to move with an oscillatory motion of decreasing amplitude the tendency is to move with an oscillatory motion of increasing amplitude

exemple 506 The initial tendency is to return towards its equilibrium condition. — The initial tendency is to return towards its equilibrium condition.

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