Practice Questions – Principles of Flight (H) | ICE Helicopters

If the critical angle of attack is exceeded, the…

laminar boundary layer turns into a turbulent boundary layer.
transition point starts moving towards the airflow direction.
boundary layer on the lower side of the rotor blade begins to separate.
boundary layer on the upper side of the rotor blade begins to separate.

What types of airflow can be observed around a rotor blade aerofoil?

Laminar airflow at the leading edge, turbulent airflow further back
Laminar airflow on the entire upper surface
Turbulent airflow at the leading edge, laminar airflow further back
Turbulent airflow on the entire upper surface

What is the advantage of a turbulent airflow compared to a laminar airflow at an aerofoil with a high angle of attack?

It adheres to the aerofoil for a longer time
The separation point moves further forward
It has no form drag
It has a thinner boundary layer

The virtual rotation axis of a rotor is…

perpendicular to the plane which contains the swash plate.
parallel with the main rotor shaft.
perpendicular to the hub plane.
perpendicular to the tip path plane.

The effective angle of attack is the angle between…

chord line and tip path plane.
effective airflow and chord line.
effective airflow and tip path plane.
tip path plane and rotor blade.

What kind of drag is caused by a lift-producing aerofoil?

Parasite drag
Frictional drag
Interference drag
Induced drag

What force affects the braking torque of the rotor in cruise?

Inclined forward drag force
Inclined forward lift
Upward directional rotor thrust
Inclined rearward tangential force

The rotor thrust is…

opposite to the rotation of the rotor blade element.
parallel with the main rotor shaft.
perpendicular to the hub plane.
perpendicular to the tip path plane.

What happens to thrust and tangential force if the rotor RPM decreases by about 10 % in cruise flight?

The thrust and the tangential force decrease
The thrust decreases and the tangential force remains constant
The thrust remains constant and the tangential force increases
The thrust and the tangential force increase

The effective airflow velocity of a rotor blade element varies with the distance from the rotor shaft axis, because the…

peripheral speed increases if the displacement to the rotor blade tip decreases.
helicopter airframe disturbs the airflow.
tangential force and airflow reversal vary.
drag force in direction of the rotaion axis is increased.

Which of the stated relationships between lift and drag applies best for a flying helicopter (lift : drag)?

1:2
2:1
45:1
1:45

The reason for a stall at a given pitch angle can be…

smaller effective angle of attack and small peripheral speed.
smaller frontal resistance and turbulent airflow.
smaller vertical airflow through the rotor and constant peripheral speed.
constant peripheral speed and great vertical airflow through the rotor.

The neutral point is a point where…

the aerodynamic forces act torque-free.
the imaginary axes of a helicopter meet each other.
the entire helicopter mass can be assumed to attack.
the torque at the chord line remains constant for changing angles of attack.

What shape of a rotor blade has a positive impact on the lift distribution?

Rectangular trapezoidal blade with no aerodynamic twist
Double trapezoidal rotor blade with a radius at the blade tip
Trapezoidal blade without radius at the blade tip
Rectangular blade with a geometric setting of 1°

The rotor blade shape takes effect on the…

lift distribution.
structural take-off mass.
noch sensitivity.
rotor head used.

The drive system of an autogyro’s main rotor is based on…

a fan in the cabin.
the speed of the airflow.
an engine at the rotor blade tip.
an engine in the cabin.

The rotor RPM is kept constant in the helicopter by the engine RPM. The engine can be adjusted by the…

cyclic stick.
collective.
throttle and the governor.
starter and the impulse coupling.

Which ratio corresponds to the rotor disc loading?

Helicopter mass / rotor disc area
Rotor thrust / rotor mass
Rotor thrust / rotor disc area
Rotor disc area / helicopter mass

During hover flight, the induced airflow velocity…

increases further having passed the rotor.
is equal above and below the rotor.
remains constant after having passed the rotor.
decreases after having passed the rotor.

Why is a helicopter’s climb initially accelerated after an increase of the pitch angle?

The initially high airflow increases the rotor thrust until the lower air density reduces the rotor thrust again
The conversion of energetic air into kinetic rotor energy decreases continuously with increasing density altitude
The larger pitch angle causes a decrease and a compression of the airflow until the climb rate corresponds to the induced velocity through the main rotor disc
The inertia of the air increases the effective angle of attack temporarily until an additional component of the climb rate reduces the effective angle of attack again

A helicopter with a rotor turning in an anti-clockwise direction seen from above, hovers sideways to the right. What is the azimuth angle where the main rotor blades have the biggest pitch angle?

0°
90°
270°
180°

The airframe of an accelerating helicopter continues to bend until the…

horizontal thrust component equals the drag.
thrust passes in front of the centre of gravity.
thrust passes behind the centre of gravity.
vertical thrust component equals the drag.

What is the reason for retreating blade stall?

Small pitch angle and large effective airflow
Large pitch angle and small effective airflow
Large centrifugal forces of the peripheral speed
Small cone angle and constant peripheral speed

The induced airflow on the rotor of a helicopter in level flight has the greatest value at the…

advancing rotor blade.
front rotor area.
rear rotor area.
retreating rotor blade.

Which option describes the term “asymmetric airflow”?

The displacement of the driving forces to the advancing rotor blade in a vertical autorotation
The greater lift in the outer region of the rotor as opposed to the inner region
During cruise flight the advancing rotor blade has more airflow than the retreating rotor blade
The difference in required performance during hover in and out of ground effect

The transitional lift can be noticed by…

vibrations.
an aural warning.
a loss of engine rpm.
strong load factors.

Which statement about the rotor disc loading in a horizontal curve, maintaining altitude, is correct?

It increases with increasing bank angle
It decreases with increasing bank angle
Effects depend on the type of helicopter
No change in relation to the cruise flight

What action is necessary in a modern helicopter during the transition to a horizontal turn?

Open the throttle in a helicopter with a rotor turning in an anti-clockwise direction seen from above
Lower the collective
Raise the collective
Open the throttle in a helicopter with a rotor turning in a clockwise direction seen from above

Why does a stall begin on the retreating rotor blade at high cruise speeds?

The airflow reaches subsonic speed and causes an increase of the induced drag
The large pitch angle and relatively low relative airspeed cause a large effective angle of attack
The small pitch angle and a relatively low relative airspeed cause a small effective angle of attack
The airflow reaches supersonic speed and causes an increase of the parasite drag

Without corrective movement, a helicopter hovering in ground effect in no-wind conditions, will execute…

rolling movements to about 60°.
fast yaw motions.
slight upward and downward movements.
pitching motion about the centre.

The ground effect is noticeable by…

lower power requirements.
strong vertical oscillations.
larger power requirements.
strong horizontal vibrations.

What can be expected during a hover flight in ground effect within a forest glade?

Aspiration of the tail rotor in the direction of the forest and a performance gain
Recirculation of air masses and an impairment of the ground effect
No air turbulence through the slipstream and stable attitude
Useful ground effect caused by a smaller induced airflow

Which landing site (no wind) prevents the impairment of the ground effect?

Narrow forest glade
Plain terrain
Elevated helipad
Sloping ground

What is the result of the vortex ring state?

The helicopter loses power
The sink rate increases uncontrollably
The rotor RPM increases
The helicopter is more stable

What is the correct way to counteract the vortex ring state?

Try to gain airspeed and enter autorotation
Raise collective and decrease rotor RPM
Raise collective and pull back the stick
Open throttle and pull back the stick

What is the effect of vortex ring state?

High rate of descent and irregular pitch, roll, and yaw motions
Fluctuations in rotor and engine RPM
Stable descent and high-frequency vibrations in the helicopter
Decreased rate of descent and strong vibrations from the engine

What is the reason for the driving forces in an autorotation?

Downward tilted effective airflow
Increased pitch angle
High airspeeds
Low rate of descent

During an autorotation the airspeed is limited by…

the displacement of the stall regions in the inner area of the rotor blade.
the landing gear during the touchdown.
the angle of the driving forces on the retreating blade.
the interference drag during low rates of descent.

Which of the following options has an effect on the autorotation characteristics?

Smoothly working tail rotor control and low RPM warning systems
Pressure altitude and wind speed
Helicopter mass and density altitude
Air temperature and wind speed

During an autorotation with forward speed, the driving forces are more centred around the…

region of the retreating rotor blade.
region of the advancing rotor blade.
outer region.
inner region.

During an autorotation a helicopter accelerates from 60 to 90 knots without further corrections. The rotor RPM will…

increase.
vary.
remain constant.
decrease.

What action has no effect on the rotor RPM in an autorotation?

Utilisation of the fuel mixture lever.
Pitch angle change.
Transition into a turn.
Centre of gravity displacement.

After entering an autorotation a large helicopter mass leads to…

a rapid build-up of the rotor RPM.
a rapid collapse of the rotor RPM.
a large change in center of gravity.
a small rate of descent in a vertical autorotation.

What shall be considered before terminating (rolling out of) a turn in an autorotation?

The decreasing gravity relieves the main rotor and the helicopter cabin
The flight velocity shall be increased to obtain all the kinetic energy
The blade pitch angle must be decreased by using the collective pitch lever again
The Coriolis force causes an increase in the main rotor rpm

Which energies serve to maintain the rotor rpm in an autorotation?

Rotational and linear energy
Mechanical or chemical energy
Frictional and flow energy
Potential or kinetic energy

The maximum range in an autorotation will be achieved by…

a relatively low effective angle of attack.
a relatively high effective angle of attack.
a negative effective angle of attack.
a neutral effective angle of attack.

Why does a flare during an autorotation generate higher rotor RPM?

The ground effect leads to better performance
The tangential force tilts backwards
The vertical airflow through the rotor disc increases
The pitch angle increases

Which movement is caused by the Coriolis effect on the advancing rotor blade?

Lagging backwards
Flapping downwards
Leading forwards
Centre of mass movement outwards

Which factor affects the available response time to initiate an autorotation after engine failure?

Inertia of the main rotor system
Profile shape of the rotor blades
Functionality of the coupling
Movement of the pressure point

What is the risk arising in a vertical autorotation with a subsequent increase in airspeed prior to the landing?

Misjudgement of height loss when increasing the airspeed
High rotor RPM
Loss of the tail rotor efficiency
Vortex ring state

Which statement about the required force to change the pitch angle is correct?

It is the smallest by using an advance angle of 90°
It is the smallest by using a delta-three-hinge
It must be greater than the rotor disc loading
It must be greater than the tangential force

Why do helicopters with a semi-rigid rotor system react slower than others?

The angled lag hinges prevent the transmission of aerodynamic forces on the helicopter frame
The missing lag hinges cause a rotor imbalance
The central flapping hinge does not transmit any moments
The lowered attachment of the rotor blades allows a transmission of forces

The pitch angle of a tail rotor blade is changed…

symmetrically.
asymmetrically.
cyclically.
collectively.

A delta-three hinge is used to allow…

the advancing blade to drag about the hinge.
for a decreased pitch angle at an upwards flapping blade.
the advancing blade to lead about the hinge.
the advancing blade to flap up about the hinge.

What needs to be observed in conjunction with a temporary loss of tail rotor efficiency in a stationary hover?

Loss of the main rotor thrust
Rotating movement in the main rotor direction
Vortex ring stage of the tail rotor
Mechanical blockage of the control

What is caused by an increase of stability in a helicopter?

An increase of general flight safety
An enhance of control under negative load factors
An optimization of the maximum helicopter mass
A decrease of the required control forces

Why are the stability criteria of a helicopter very important?

Low stability reduces the available control forces
High stability prevents low load factors
Large stability increases the maximum take-off mass
A lack of stability may lead to loss of control

The helicopter’s stability is increased by…

decreasing the rotor mass.
pivoting the drag hinge.
reducing the rotor RPM.
attaching vertical and/or horizontal stabilisers

Vx is the speed…

for the best angle of climb.
never to be exceeded.
to rotate.
for the best rate of climb.

Vy is the speed…

never to be exceeded.
for the best angle of climb.
to rotate.
for the best rate of climb.

What relieves the helicopter in a low G manoeuvre?

Weightlessness of the passengers during the push over
Centrifugal force in parabolic flight during the entire manoeuvre
Increased vertical airflow through the rotor
Rolling movement of the helicopter to the right

What is the purpose of the vertical stabilizer?

Improvement of directional stability
Reduction of manoeuvre stability
Compensation of tail rotor stability
Adjustment of longitudinal stability

An increase of stability in a helicopter causes…

an enhancement of control under negative load factors.
a reduced controllability.
a decrease of general aviation safety.
an optimization of the maximum helicopter mass.

What behavior does a helicopter without stabilization systems show after external disturbances in a hover, without a corrective action?

Statically stable and dynamically stable
Statically stable and dynamically unstable
Statically indifferent and dynamically unstable
Statically stable and dynamically indifferent

Practice Questions – Principles of Flight (H)

Practice Questions – Principles of Flight (H)

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