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Principles of flight > Questions on Lift and Drag > Flashcards

Questions on Lift and Drag Flashcards

1
Q

What happens to total drag when accelerating from CL MAX to maximum speed?

A

Decrease then Increase.

CLmax in level flight is highest at low speed. At low speed total drag is high. Thus accelerating to VMD the drag first decreases then accelerating to max speed it increases again.

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2
Q

The maximum angle of attack for the flaps down configuration, compared to flaps up is “Smaller”

A

Flaps down (is like having a cambered wing section) gives higher CLmax values at a smaller angle of attack.

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3
Q

Decreasing sweep angle decreases stall speed….

A

Since straight wings have higher CLMax.

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4
Q

Drag acts in the same direction as the relative airflow and lift….

A

perpendicular to it.

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5
Q

The Cl-alpha curve of a positive cambered aerofoil intersects with…

A

the vertical axis of the Cl-alpha graph “Above the origin”.

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6
Q

If the weight of an aircraft is increased the maximum lift/drag ratio will….

A

“Not be affected”.

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7
Q

Suction above the wing is the greatest factor causing…

A

lift.

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8
Q

Lift is generated when a certain mass of air is accelerated….

A

downwards.

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9
Q

Lift is generated when the flow direction of a certain mass of air is

A

changed.

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10
Q

An aeroplane maintains straight and level flight while the IAS is doubled. The change in lift coefficient will be…

A

0.25

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11
Q

The aerodynamic drag of a body, placed in a certain airstream depends amongst others on the…

A

airstream velocity.

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12
Q

For a given angle of attack the lift/drag ratio is unaffected by…

A

density change.

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13
Q

If the weight of the aircraft is increased, the maximum lift/drag ratio will remain the same but occur at….

A

a higher speed.

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14
Q

What is the purpose of a slat on the leading edge?

A

It allows a greater angle of attack.

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15
Q

What is true regarding deployment of Slats/Krueger flaps?

A

Slats form a slot, Krueger flaps do not.

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16
Q

The aerodynamic centre is the point where all

A

changes in the magnitude of the lift force effectively take place.

17
Q

A body is placed in a certain airstream. The density of the airstream decreases to half of the original value

A

The aerodynamic drag will decrease with a factor of 2. Drag and density have a direct relation (Drag equation).

18
Q

When considering the aerodynamic forces acting on an aerofoil section, lift increases….

A

linearly and drag increases exponentially with an increase in angle of attack.

19
Q

For an aircraft flying at a constant IAS, the drag will be the same at altitude as

A

at sea level.

20
Q

For aircraft of the same weight, flying at the same IAS the angle of attack will be the same at altitude as at

A

sea level.

21
Q

To fly at a given IAS, the thrust required at altitude will be the same as at sea level, but will require

A

the throttle to be advanced.

Thrust required = Drag.

Drag = 1/2 rho V^2 S Cd

Fixed IAS = Fixed 1/2 rho V^2

Thus thrust remains unchanged.

Power = Rate of doing work (FxD/T)

F = Drag and D/T is Speed (TAS)

So power required = Drag x TAS

Less density, same IAS means increased TAS.

Therefore power required is increased.

22
Q

An aeroplane in straight and level flight is subjected to a strong vertical gust. The point on the wing, where the instantaneous variation in wing lift effectively acts is known as

A

the “Aerodynamic Center”.

23
Q

At an aeroplane minimum drag speed, the ratio between induced drag and profile drag is…

A

1/1

24
Q

Extending airbrakes during an approach will reduce

A

the minimum drag speed (VDmin)

25
Q

The effects of very heavy rain (tropical rain) on the aerodynamic characteristics of an aeroplane are….

A

decrease of CLmax and increase of drag.

26
Q

Total Drag at high Mach numbers is a combination of…

A

induced drag, wave drag, form drag, skin friction drag and interference drag.

27
Q

The value of the parasite drag in straight and level flight at constant weight varies…

A

linearly with the square of the speed.

28
Q

An aircraft is required to cruise, maintaining Vmd. As the weight decreases the IAS must be _______, and the angle of attack _______

A

decreased, remain constant.

29
Q

When an aircraft selects its undercarriage and flaps down in flight, its VIMD will _______ and if it maintained the clean configuration VIMD its speed stability would ________

A

(i) REDUCE, (ii) INCREASE.

30
Q

What must happen to the CL when flaps are deployed while maintaining a constant IAS in straight and level flight? It remains constant.

A

The wingtip vortices reduce.

Wingtip vortices are proportianal to angle of attack.

Since the angle of attack is reduced to keep CL constant after lowering flaps to maintain straight and level flight at the same speed.

31
Q

Flap selection at constant IAS in straight and level flight will ________ the maximum lift coefficient (CLmax) and the drag.

A

increase

32
Q

Reduction in CLMax is the most important result/problem caused by …

A

ice formation.

33
Q

In the last part of the rotation (during take off) the aerodynamic effect of ice located on the wing leading edge is

A

most critical.

34
Q

At a ___ weight the maximum level flight speed will be ___ because of a change in ___ drag:

a) lower/less/parasite
b) lower/less/induced
c) higher/less/induced
d) higher/less/parasite

A

c) higher/less/induced

35
Q

For an aircraft flying at a speed above Vmd:

a) a speed increase causes a drag increase which will cause a deceleration
b) a speed increase causes a drag decrease causing further acceleration
c) a speed increase causes a drag increase causing an acceleration
d) a speed decrease causes a drag increase causing a deceleration

A

a) a speed increase causes a drag increase which will cause a deceleration

36
Q

In which situation would the wing lift of an aeroplane in straight and level flight have the highest value? (the engines are mounted below the wing).

A

Forward CG and Idle Thrust

37
Q

If the CG is ahead of the wing CP and there is no thrust/drag couple, for level flight, the wing lift must be ________

A

greater than the weight.

With a forward CG there will be a down force at the horizontal stabilizer. Total lift will be weight + tail down force. In that case lift will be more than the weight.

Principles of flight (30 decks)

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