The Four Forces Acting On An Aircraft Flashcards

1
Q

Where does the weight force on the aircraft act through ?

A

Centre of gravity

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2
Q

Where does thrust vector act along?

A

Force parallel to the longitudinal axis of the aircraft.

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3
Q

Where does lift force act through?

A

Centre of pressure, perpendicular to the relative airflow.

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4
Q

What is the total reaction?

A

Sum of the lift and drag forces that act through the centre of pressure on the wing.

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5
Q

What direction does drag act through?

A
  • Parallel to the relative airflow.

- Acts through the centre of pressure

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6
Q

What is the lift equation?

A

L = 0.5 x rho x V^2 x Cl x S

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7
Q

Within the lift formula , what can the pilot change?

A
  • Altering the Cl by changing the AOA or configuration
  • Altering velocity
  • Altering wing area by using Fowler flaps
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8
Q

What is the boundary layer?

A

Layer of air closest to the aero foil that is affected by friction from the wing.

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9
Q

What is laminar flow?

A

Smooth flow over the wing

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10
Q

What is the adverse pressure gradient? Where does it start on the wing? What is this point called?

A
  • As flow starts to slow down it will encounter an adverse pressure gradient
  • This starts after the transition point
  • This occurs at the point of maximum thickness/chamber of the aerofoil.
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11
Q

What is the separation point?

A

Point where flow will not be able to overcome the adverse pressure gradient and will separate from the surface of the aerofoil

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12
Q

How do Cp, transition point and separation point move with increasing angle of attack?

A

Move closer to the leading edge of the wing.

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13
Q

Where are the two stagnation points on the aerofoil? Are these greater than static freestream velocity?

A
  • Leading edge and trailing edge

- yes

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14
Q

Which angle of attack is the point of maximum lift achieved on the aerofoil?

A

Just before stall angle.

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15
Q

How does lift dependent drag vary with the speed?

A

Decreases with the square of the speed.

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16
Q

Does lowering the flaps increase or decrease the critical angle of attack?

17
Q

What occurs to the critical angle of attack with slats it leading edge devices?

A

Increases the critical angle of attack.

18
Q

What occurs to critical angle of attack when wing trailing edge and leading edge flaps/slats are deployed?

A

Increases critical angle of attack

19
Q

What is the drag equation?

A

Drag = Cd x 0.5 x rho x V^2 x A

20
Q

What are the two main drag effects?

A
  • Lift dependent drag

- Zero lift drag

21
Q

What are the three components to zero lift drag?

A

1) Skin friction
2) Form drag
3) Interference drag

22
Q

What causes wingtip vortices?

A

Spanwise flow on top and bottom of wing that collided at trailing edge and forms vortices.

23
Q

What is the cause of lift dependent drag?

A

Wingtip vortices.

24
Q

What part of the wig are wingtip vortices the strongest ?

25
What does the downwash do to the angle of attack?
Reduces it
26
What does the wingtip vortices, downwash do to total reaction on the wing?
Tilts it rearwards
27
What are some methods to reduced wingtip vortices?
1) Wing fence 2) Modified wingtip 3) Winglet 4) Wingtip tank
28
What is ground effect?
Reduction in drag when close to the ground (half a wingspan)
29
What is the ratio between lift to drag called? At what angle is this greatest normally?
4 deg
30
When does the aerofoil have the greatest lifting capability?
At the critical angle of attack - around 16 degrees for an average wing
31
What angle of attack does min drag occur normally?
0 deg
32
What is the angle of incidence?
The angle at which the wing root chord line is set relative to the fuselage reference line.
33
What modern design features can reduce zero-lift drag?
- Streamlined canopy = less form drag - retractable undercarriage = less firm drag - Polishes surfaces = less friction drag - Less interference drag = smoothed fairings
34
When for minimum total drag speed occur?
Max L/D at bottom of drag curve
35
What speed does min power speed occur?
Smallest area contained by two lines to the total drag curve.
36
What is best range speed?
Line drawn tangent to drag curve.
37
What will increased weight and density altitude do to the drag curve?
Move it up and to the right
38
What is wake turbulence ?
Turbulence caused by the wingtip vortices of another aircraft.