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2FTS Aerodynamics > Aerodynamics A Review > Flashcards

Aerodynamics A Review Flashcards

1
Q

What is the free stream relative airflow (RAF)?

A

The relative direction and speed of the air before it is influenced by the aircraft.

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2
Q

What direction is the free stream RAF?

A

Equal and opposite to the flight path of the aircraft.

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3
Q

What is incompressible flow? Below what speeds and Mach can we assume flow is incompressible?

A
  • Incompressible means the density of the fluid (air) does not change with increased/decreased pressure
  • Can assume incompressible below Mach 0.4 or 300 KTAS
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4
Q

What is compressible flow?

A

Density of the fluid (air) changes with changes in pressure.

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5
Q

For sub sonic aerodynamics, do we generally assume incompressible or compressible flow?

A

Incompressible

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6
Q

What is the equation of continuity?

A

Mass flow is conserved (i.e. mass cannot be created or destroyed)

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7
Q

What is a venturi tube?

A

Constriction or narrowing in a tube

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8
Q

What is the venturi effect?

A

As flow speeds up through the constriction, air pressure is reduced.

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9
Q

What is bernoulli’s principle?

A

As the speed of fluid increases over a curved surface, the static pressure of the fluid decreases.

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10
Q

What is Bernoulli’s equation? Does it assume incompressible flow?

A

P1 + 1/2rhoV^2 = P2 + 1/2rhoV^2

- Hell yeah it’s incompressible!

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11
Q

What are the characteristics of a low-speed/high lift aerofoil?

A
  • Pronounced camber
  • High thickness/chord (t/c) ratio
  • Well rounded leading edge and point of max thickness towards leading edge
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12
Q

What are the characteristics of a symmetrical aerofoil? What are they typically used for? How does Cp movement change with AoA changes?

A
  • Identical convex curvature on upper and lower surfaces
  • Typically used for vertical stabilizer or for aerobatic aircraft (easy to fly inverted)
  • Cp doesn’t move a lot with AoA changes
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13
Q

What are the characteristics of a high-speed aerofoil or supercritical wing? What does the gentle cambered top surface do?

A
  • Little camber
  • Small LE radius
  • Gently cambered top surface (delays onset of shock waves at high subsonic/transonic speeds)
  • Thick wing section
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14
Q

What are the characteristics of a wedge-shaped aerofoil?

A

Used for supersonic aircraft, used to reduced negative lift and drag effects of shock waves at supersonic speeds.

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15
Q

What is the local relative airflow (RAF)?

A

Airflow relative to the aircraft that is not affected or influenced by the passage of an aerofoil or aircraft BUT can be affected by wing downwash, prop rotation, thus changing the RAF relative to those surfaces.

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16
Q

What does wing upwash refer to?

A

Air approaching the leading edge starts to flow upwards due to the region of low pressure on the top of the wing.

17
Q

What does wing downwash refer to?

A

As the air is displaced downwards, the aerofoil is displaced upwards.

18
Q

What causes the tip vortices on an aircraft’s wing?

A
  • Spanwise flow which is due to air trying to flow from high pressure area below the wing around the tip to the low pressure area on top.
  • Vortices are larger at wingtip as the air has an easier path to the top surface of the wing.
19
Q

What causes a Rams Horn Vortex?

A

A wing with a sharp leading edge will create a controlled separated flow known as a Rams Horn Vortex

  • While turbulent flow, it is controlled, and provides increased flow attachment to upper surface of the wing at high AoA, allowing an aircraft to fly to very high Angles of attack
  • Allows aircraft like Superhornet and F-35 to fly at very low speed/high AoA
20
Q

What is the boundary layer?

A

The layer of airflow closest to the wing that produces all of the forces (only a handful of mms thick!)

21
Q

What is laminar flow and where does it occur on a wing?

A
  • Laminar flow consists of straight streamlines that are relatively low in energy.
  • Occurs from leading edge to point of max thickness (transition point)
22
Q

What is turbulent airflow and where does it occur on a wing?

A
  • Turbulent airflow is attached airflow that is higher energy.
  • Higher drag airflow but because of added kinetic energy, flow can stay attached for longer over the wings surface.
  • Turbulent flow occurs from transition point to separation point.
23
Q

What occurs at the separation point?

A
  • Boundary layer encounters the adverse pressure gradient due to the high pressure air escaping around the trailing edge.
  • This turns the flow into separated airflow, which is very high drag and not producing any lift.
24
Q

What is the aspect ratio of a wing? How is it calculated?

A
  • The relationship of wingspan to chord

- Span^2/Wing area

25
Q

What does a high aspect ratio wing indicate? What aircraft typically have these?

A
  • The aircraft has long wings with a short chord.

- Typically used on slower, high lift aircraft like gliders/transport planes

26
Q

What is a low aspect ratio wing?

A
  • Short, stubby wings

- Used on high speed fighter and aerobatic aircraft

27
Q

What aspect ratio is used for medium speed advanced training aircraft (like PC-21 ;) )?

A

Medium aspect ratio wings

28
Q

What are the two main considerations with the aspect ratio of a wing?

A

1) Lift-dependent drag (downwash)

2) Structural considerations.

29
Q

Do low aspect ratio wings have higher lift-dependent drag for the same speed?

A

Yes, due to increased spanwise flow for low aspect ratio wings for a given speed

30
Q

Does downwash reduced the effective AoA of a wing?

A

Yes it does, as local RAF is influenced.

31
Q

What are the characteristics of a high aspect ratio wing?

A

1) Develop greater lift
2) Stall at a lower critical AoA
3) Clear cut airflow breakdown at the stall

32
Q

What are characteristics of a low aspect ratio wing?

A

1) Generate less lift
2) Will stall at a higher critical AoA
3) Less clearly defined airflow breakdown at the stall

33
Q

From a structural point of view, what are differences between low and high aspect rati owings?

A

1) High aspect ratio wings generally have greater bending moments and require increased strength, resulting in higher weight
2) Low aspect ratio wings generally have a stronger build and can withstand high g and dynamic maneuvering.

2FTS Aerodynamics (8 decks)

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