Chapter 1 - Rotor Aerodynamics and Control Flashcards
Wash-out is the structural design of a blade in which the pitch angle is:
A. Lowest at the root and increases towards the tip.
B. Highest at the middle of the blade and reduced towards root and tip.
C. Constant throughout the whole length of the blade.
D. Highest at the root and reduces towards the tip.
D
Streamlining is a method used to: A. Reduce form drag B. Reduce induced drag C. Reduce skin friction drag D. Reduce tip vortices
A
Overpitching condition occurs when:
A. Blade pitch is increased and excessive engine power applied causing too high rpm.
B. Blade pitch is increased and insufficient engine power available to compensate for extra rotor drag.
C. RPM remains constant but blade pitch angle increased too suddenly causing structural damage.
D. RPM remains constant but blade pitch angle moved beyond designed limits, causing vibration.
B
Comparing two identical aerofoils: one at high altitude and the other at low altitude. If their angles of attack and airflow velocities are the same, the high altitude aerofoil will produce:
A. More life due to lower drag
B. Less lift due to lower lift coefficient
C. Less lift due to lower air density
D. More life due to higher lift coefficient
C
Rotational Airflow(Vr) near the rotor hub is:
A. Faster than at the tip
B. Slower than at the tip
C. Of the same value as at the tip
D. Faster or slower than at the tip depending on RPM
B
Lift is generated by an aerofoil when airflow over its upper surface:
A. Decreases in velocity and decreases in pressure.
B. Increases in velocity and decreases in pressure.
C. Increases in velocity and increases in pressure.
D. Decreases in velocity and increases in pressure.
B
What effect does induced flow have on the rotor blade? A. It increases its angle of attack B. It decreases its angle of attack C. It increases its blade pitch angle D. It decreases its blade pitch angle
B
In helicopter rotor blade design, the disadvantage of using a normal asymmetrical aerofoil is that:
A. Its centre of pressure does not move during changes in angle of attack
B. It is too flexible
C. It is too rigid
D. Its centre of pressure moves during changes in angle of attack
D
When a helicopter is feathering, it is: A. Changing its pitch angle B. Moving about its drag hinge C. Moving about its flapping hinge D. Tilting its rotor disc forward
A
The pitch angle of a helicopter blade is:
A. Controlled by the pilot’s collective and cyclic controls.
B. Defined as the angle between the relative airflow and chord line.
C. Fixed by the aircraft manufacturer and cannot be changed.
D. Always the same as its angle of attack.
A
For the rotor blade to be efficient:
A. Its total reaction must “lean” close to the drag.
B. Its life/drag ratio must be low.
C. Both the lift and drag must be at maximum values.
D. Its total reaction must “lean” close to the lift.
D
On a rotor blade, tip vortex is formed due to:
A. Air from upper surface of the blade flowing to bottom surface around the blade tip.
B. Downwash of the airflow at the trailing edge of the blade.
C. Wash-out design of the blade.
D. Air from bottom surface of the blade flowing to upper surface around the blade tip.
D
What happens to the airflow within the boundary layer?
A. Airflow is accelerated
B. Airflow is retarded
C. Airflow is retarded over the first half of the aerofoil and then accelerates after that
D. There is no difference in behaviour compared to airflow outside the boundary layer
B
What type of drag is the result of lift production by the aerofoil? A. Induced drag B. Parasite drag C. Skin friction D. Form drag
A
What is the danger resulting from blade tip speed reaching sonic speed?
A. Shock waves causing over torqueing of transmission system.
B. Shock waves causing increased drag and high vibration.
C. Excessive airflow causing failure of engine.
D. Excessive airflow causing blade failure.
B
