Lift & Drag Flashcards
Blade angle is the angular difference between the _____________ of the blade and the (plane of rotation / axis of rotation).
- Chord.
- Plane of rotation.
Feathering a blade means changing its __________ angle around the _____________ axis.
- Blade.
- Feathering.
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).
- Total Reaction.
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.
- At right angles.
- Parallel.
When an airflow is made to speed up, the pressure within the flow (increases / decreases) provided the flow remains ___________________.
- Decreases.
- Streamlined.
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.
- The same.
The lift coefficient of an airfoil is determined by its ______________ and _______________.
- Shape.
- Angle of Attack.
The peak of the CL curve represents (CLmax / CLmin), the associated angle of attack is called the ____________ angle.
- CLmax.
- Stall.
The centre of pressure is the point on the ______________ line through which all _________________ forces are said to act.
-Chord.
- Aerodynamic.
The centre of pressure of a symmetrical airfoil (moves forward / moves aft / remains steady) with changes in angle of attack.
- Remains steady.
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).
- Aerodynamic centre.
The drag coefficient of an airfoil is determined by its _____________ and ______________, its minimum value is found at (zero / four) degrees angle of attack.
- Shape.
- Angle of Attack.
- Zero.
The three types of drag experienced by a helicopter in forward flight are ____________, _____________ & _______________.
- Induced.
- Profile.
- Parasite.
When the speed of a helicopter increases from 20 knots to 60 knots, parasites drag increases by a factor of (three / four / six / nine).
- Nine.
Form drag can be reduced by ________________.
- Shaping.
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 ______________ ___________.
- Boundary.
- Retarded.
- Relative Airflow.
A laminar boundary layer is normally (thick / thin), it produces (much / little) skin friction drag and it (is / is not) readily subject to breakdown.
- Thin.
- Little.
- Is.
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.
- Thick.
- Much.
- Is not.
The point at which the laminar boundary layer changes to a turbulent boundary layer is called the (separation / transition) point.
- Transition.
With an increase in airspeed, skin friction drag (increases / decreases) because the transition point moves (forward / aft) and the boundary layer (thickens / thins).
- Increases.
- Forward.
- Thickens.
Induced drag is the result of difference in _________________ above and below the airfoil and is (directly / inversely) proportional to the induced flow.
- Pressure.
- Directly.
With an increase in airspeed, induced drag (increases / decreases) and parasite drag (increases / decreases).
- Decreases.
- Increases.
An increase in aspect ratio tends to (increase / decrease) induced drag.
- Decrease.
Wash-out is a structural design which (increases / decreases) the (blade angle / angle of attack) from blade root to blade tip.
- Decreases.
- Blade angle.
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).
- High.
- Decreases.
- Increases.
