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Helicopter Theory > Lift & Drag > Flashcards

Lift & Drag Flashcards

1
Q

Blade angle is the angular difference between the _____________ of the blade and the (plane of rotation / axis of rotation).

A
  • Chord.
  • Plane of rotation.
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2
Q

Feathering a blade means changing its __________ angle around the _____________ axis.

A
  • Blade.
  • Feathering.
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3
Q

When an airflow is deflected by an airfoil, the force acting more or less at right angles to the airfoil is called (total reaction / lift / drag).

A
  • Total Reaction.
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4
Q

The two components of total reaction are lift acting (at right angles / parallel) to the relative airflow and drag, acting (at right angles / parallel) to the relative airflow.

A
  • At right angles.
  • Parallel.
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5
Q

When an airflow is made to speed up, the pressure within the flow (increases / decreases) provided the flow remains ___________________.

A
  • Decreases.
  • Streamlined.
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6
Q

When a symmetrical airfoil is placed at 0 deg angle of attack to a airflow, pressures are (different / the same) above and below the airfoil.

A
  • The same.
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7
Q

The lift coefficient of an airfoil is determined by its ______________ and _______________.

A
  • Shape.
  • Angle of Attack.
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8
Q

The peak of the CL curve represents (CLmax / CLmin), the associated angle of attack is called the ____________ angle.

A
  • CLmax.
  • Stall.
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9
Q

The centre of pressure is the point on the ______________ line through which all _________________ forces are said to act.

A

-Chord.
- Aerodynamic.

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10
Q

The centre of pressure of a symmetrical airfoil (moves forward / moves aft / remains steady) with changes in angle of attack.

A
  • Remains steady.
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11
Q

The point on the chord line about which no change in pitching moment is felt with changes in angle of attack is called the (centre of pressure / aerodynamic centre).

A
  • Aerodynamic centre.
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12
Q

The drag coefficient of an airfoil is determined by its _____________ and ______________, its minimum value is found at (zero / four) degrees angle of attack.

A
  • Shape.
  • Angle of Attack.
  • Zero.
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13
Q

The three types of drag experienced by a helicopter in forward flight are ____________, _____________ & _______________.

A
  • Induced.
  • Profile.
  • Parasite.
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14
Q

When the speed of a helicopter increases from 20 knots to 60 knots, parasites drag increases by a factor of (three / four / six / nine).

A
  • Nine.
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15
Q

Form drag can be reduced by ________________.

A
  • Shaping.
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16
Q

Skin Friction drag is caused by friction between molecules in the _________________ layer which is a (retarded / accelerated) layer of air between the airfoil surface and the ______________ ___________.

A
  • Boundary.
  • Retarded.
  • Relative Airflow.
17
Q

A laminar boundary layer is normally (thick / thin), it produces (much / little) skin friction drag and it (is / is not) readily subject to breakdown.

A
  • Thin.
  • Little.
  • Is.
18
Q

A turbulent boundary layer is normally (thick / thin), it produces (much / little) skin friction drag and it (is / is not) readily subject to separation from the airfoil surface.

A
  • Thick.
  • Much.
  • Is not.
19
Q

The point at which the laminar boundary layer changes to a turbulent boundary layer is called the (separation / transition) point.

A
  • Transition.
20
Q

With an increase in airspeed, skin friction drag (increases / decreases) because the transition point moves (forward / aft) and the boundary layer (thickens / thins).

A
  • Increases.
  • Forward.
  • Thickens.
21
Q

Induced drag is the result of difference in _________________ above and below the airfoil and is (directly / inversely) proportional to the induced flow.

A
  • Pressure.
  • Directly.
22
Q

With an increase in airspeed, induced drag (increases / decreases) and parasite drag (increases / decreases).

A
  • Decreases.
  • Increases.
23
Q

An increase in aspect ratio tends to (increase / decrease) induced drag.

A
  • Decrease.
24
Q

Wash-out is a structural design which (increases / decreases) the (blade angle / angle of attack) from blade root to blade tip.

A
  • Decreases.
  • Blade angle.
25
Q

Total drag of a helicopter is (high / low) at zero airspeed, it (increases / decreases) with an increase in airspeed and beyond medium airspeed it (increases / decreases).

A
  • High.
  • Decreases.
  • Increases.

Helicopter Theory (9 decks)

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