Cartes mémoires HE 14

Cartes-fiches	56
Langue	Deutsch
Catégorie	Technique
Niveau	Université
Crée / Actualisé	15.06.2015 / 07.06.2018
Lien de web	https://card2brain.ch/box/he_14
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Is a main rotor blade normally free to oscillate (as a rigid body) around the feathering axis (also
called pitch axis)?

Not in all cases, only if the rotor is articulated.

No, blade pitch angle cannot be changed during the flight.

No, blade pitch angle is only determined by the blade flapping angle.

No, blade pitch angle is fixed by the position (height and attitude) of the swashplate.

Not in all cases, only if the rotor is articulated.

No, blade pitch angle cannot be changed during the flight.

No, blade pitch angle is only determined by the blade flapping angle.

No, blade pitch angle is fixed by the position (height and attitude) of the swashplate.

Why are main rotors equipped with lead/lag hinges (also called drag hinges)?

To minimise the mechanical stress on the blade root, originated by centrifugal force.

To minimise the mechanical stress on the blade root, originated by gyroscopic effects (when the blade flaps, it also tends to move in-plane).

To minimise the blade motion in-plane.

To minimise the mechanical stress on the blade root, originated by the dampers forces.

To minimise the mechanical stress on the blade root, originated by centrifugal force.

To minimise the mechanical stress on the blade root, originated by gyroscopic effects (when the blade flaps, it also tends to move in-plane).

To minimise the blade motion in-plane.

To minimise the mechanical stress on the blade root, originated by the dampers forces.

How can the rotor plane (the tip path plane or TPP) be oriented in order to control the helicopter?

By operating the cyclic flapping controls.

By operating the cyclic pitch controls, the consequent flapping of the blades orients the TPP.

By operating the cyclic pitch controls, the consequent lead/lagging of the blades orients the TPP.

By operating the collective pitch control.

By operating the cyclic flapping controls.

By operating the cyclic pitch controls, the consequent flapping of the blades orients the TPP.

By operating the cyclic pitch controls, the consequent lead/lagging of the blades orients the TPP.

By operating the collective pitch control.

In which cases do compressibility effects arise?

In forward flight, at all speed.

In forward flight, at low speed.

In forward flight, at high speed.

In forward flight, at all speed at high collective settings.

In forward flight, at all speed.

In forward flight, at low speed.

In forward flight, at high speed.

In forward flight, at all speed at high collective settings.

How could compressibility effects on the advancing blade be completely removed?

By reducing rotor speed in forward flight.

By increasing rotor speed in forward flight.

By reducing rotor speed in hover flight.

By reducing rotor speed in forward flight.

By increasing rotor speed in forward flight.

By reducing rotor speed in hover flight.

Is the induced velocity in reality uniform in space as the momentum theory assumes?

No, the induced velocity is always dominated by the effects of two large tip vortexes.

No, for instance in hover the induced velocity is dominated by the effects of two large tip vortexes.

No, for instance at high speed the induced velocity is dominated by the effects of two large tip vortexes.

No, the induced velocity is dominated by the effects of a strong horseshoe vortex.

No, the induced velocity is always dominated by the effects of two large tip vortexes.

No, for instance in hover the induced velocity is dominated by the effects of two large tip vortexes.

No, for instance at high speed the induced velocity is dominated by the effects of two large tip vortexes.

No, the induced velocity is dominated by the effects of a strong horseshoe vortex.

Are the blade pitch angle and the local angle of attack related?

Yes, the angle of attack depends exclusively on pitch angle and helicopter attitude.

Yes, the pitch angle also depends the local angle of attack.

Yes, the angle of attack depends exclusively on the pitch angle

Yes, the angle of attack depends on the pitch angle but not only.

Yes, the angle of attack depends exclusively on pitch angle and helicopter attitude.

Yes, the pitch angle also depends the local angle of attack.

Yes, the angle of attack depends exclusively on the pitch angle

Yes, the angle of attack depends on the pitch angle but not only.

What is the reverse flow region of a rotor in forward flight?

The region of the rotor disc where the relative velocity experienced by the rotor blades goes from the leading edge to the trailing edge.

The region of the rotor disc where the relative velocity experienced by the rotor blades goes from the trailing edge to the leading edge.

The region of the rotor disc where the aerodynamic force generated by the blade sections is oriented downwards.

The region of the rotor disc where the aerodynamic force generated by the blade sections is zero.

The region of the rotor disc where the relative velocity experienced by the rotor blades goes from the leading edge to the trailing edge.

The region of the rotor disc where the relative velocity experienced by the rotor blades goes from the trailing edge to the leading edge.

The region of the rotor disc where the aerodynamic force generated by the blade sections is oriented downwards.

The region of the rotor disc where the aerodynamic force generated by the blade sections is zero.

During the flare at the end of an autorotation:

the work done by the gravitational force (or potential energy) is exploited in order to generate thrust.

the kinetic energy of the rotor is exploited in order to generate additional thrust.

the kinetic energy of the helicopter is exploited in order to generate thrust.

the potential energy of the rotor is exploited in order to generate thrust.

the work done by the gravitational force (or potential energy) is exploited in order to generate thrust.

the kinetic energy of the rotor is exploited in order to generate additional thrust.

the kinetic energy of the helicopter is exploited in order to generate thrust.

the potential energy of the rotor is exploited in order to generate thrust.

During the descent phase in an autorotation:

the work done by the gravitational force (or potential energy) is exploited in order to generate thrust.

the kinetic energy of the rotor is exploited in order to generate thrust.

the kinetic energy of the helicopter is exploited in order to generate thrust.

the potential energy of the rotor is exploited in order to generate thrust.

the work done by the gravitational force (or potential energy) is exploited in order to generate thrust.

the kinetic energy of the rotor is exploited in order to generate thrust.

the kinetic energy of the helicopter is exploited in order to generate thrust.

the potential energy of the rotor is exploited in order to generate thrust.

What would be the consequences of flying into the “vortex ring” working state?

The rotor thrust would become unsteady (irregular in time) and unbalanced (not originating from the geometrical centre of the rotor).

The rotor thrust would slowly drop to zero.

The rotor thrust would become unsteady (irregular in time).

The rotor thrust would become unsteady (irregular in time) and unbalanced (not originating from the geometrical centre of the rotor) only if the SAS (Stability Augmentation System) is switched off.

The rotor thrust would become unsteady (irregular in time) and unbalanced (not originating from the geometrical centre of the rotor).

The rotor thrust would slowly drop to zero.

The rotor thrust would become unsteady (irregular in time).

The rotor thrust would become unsteady (irregular in time) and unbalanced (not originating from the geometrical centre of the rotor) only if the SAS (Stability Augmentation System) is switched off.

Does a rotor generate an induced velocity when operating in the so-called “windmilling” working
state?

Yes, if the rotor generate a thrust.

No, even if the rotor generates thrust.

Yes, in any case.

No, never.

Yes, if the rotor generate a thrust.

No, even if the rotor generates thrust.

Yes, in any case.

No, never.

Induced velocity at the helicopter max speed is:

u is advance ratio.

Smaller than induced velocity in hover.

Smaller than induced velocity in hover but larger than induced velocity at (u = 0:1).

Larger than induced velocity in hover.

Larger than induced velocity at (u= 0:1).

Smaller than induced velocity in hover.

Smaller than induced velocity in hover but larger than induced velocity at (u = 0:1).

Larger than induced velocity in hover.

Larger than induced velocity at (u= 0:1).

The Figure of Merit:

is a measure of rotor efficiency in hover.

is a measure of rotor efficiency in forward flight.

is a measure of rotor efficiency in hover and forward flight.

is a measure of pilot’s performances

is a measure of rotor efficiency in hover.

is a measure of rotor efficiency in forward flight.

is a measure of rotor efficiency in hover and forward flight.

is a measure of pilot’s performances

Aerial work requires the helicopter to spend most of its operative life in hover or at low speed.
Is a low disc loading suitable for this kind of operations?

Yes, low disc loading implies high power loading.

Yes, low disc loading implies low power loading

No, low disc loading implies high power loading.

No, low disc loading implies low power loading.

Yes, low disc loading implies high power loading.

Yes, low disc loading implies low power loading

No, low disc loading implies high power loading.

No, low disc loading implies low power loading.

How must the pilot react when he or she realizes that a ground resonance episode is developing?

Immediately reduce collective pitch.

Immediately switch on the stability augmentation system.

Immediately stop the rotor by starting the rotor brake.

Immediately interrupt the contact with the ground, if the rotor RPM are high enough, otherwise stop the rotor.

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

Immediately reduce collective pitch.

Immediately switch on the stability augmentation system.

Immediately stop the rotor by starting the rotor brake.

Immediately interrupt the contact with the ground, if the rotor RPM are high enough, otherwise stop the rotor.

What are the consequences of a main gearbox failure on a conventional multiengine helicopter?

Emergency landing by autorotation must be performed.

Emergency landing by autorotation does not need to be performed

Emergency landing by autorotation must not be performed except in the early take off and late landing phases.

Emergency landing by autorotation must be performed only by Cat B and C helicopters.

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

Emergency landing by autorotation must be performed.

Emergency landing by autorotation does not need to be performed

Emergency landing by autorotation must not be performed except in the early take off and late landing phases.

Emergency landing by autorotation must be performed only by Cat B and C helicopters.

What can you say about the power required by a fixed wing aircraft and the one required by a
conventional helicopter, when the two aircraft have the same payload and fly at the same height
and at a speed of approximately 150 kt?

The power required by the fixed wing aircraft is normally smaller.

The power required by the helicopter is normally smaller.

The power required by the two aircraft is normally very similar, as it depends on speed and mass only for both of them.

The power required by the two aircraft is normally very similar, as it is a function of height only for both of them.

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

The power required by the fixed wing aircraft is normally smaller.

The power required by the helicopter is normally smaller.

The power required by the two aircraft is normally very similar, as it depends on speed and mass only for both of them.

The power required by the two aircraft is normally very similar, as it is a function of height only for both of them.

Smaller rotors are aerodynamically more efficient at high speed. Of course they also generate a
higher induced velocity and hence require a higher induced power. Is this a significant problem?

No, it is an advantage: the bigger the induced velocity, the smaller the power required.

No, at high speed induced velocity is normally very small.

No, at high speed induced velocity is normally very large.

No, induced power is negligible at all speed on helicopters.

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

No, it is an advantage: the bigger the induced velocity, the smaller the power required.

No, at high speed induced velocity is normally very small.

No, at high speed induced velocity is normally very large.

No, induced power is negligible at all speed on helicopters.

What can we say about the power required by the tail rotor of a conventional helicopter?

It is normally lower at low speed.

It is normally lower in hover.

It is normally lower at high speed.

It depends only on main rotor collective settings.

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

It is normally lower at low speed.

It is normally lower in hover.

It is normally lower at high speed.

It depends only on main rotor collective settings.

What are the causes of the limited max speed of conventional helicopters?

Retreating blade stall.

Compressibility effects on advancing blade.

Compressibility effects and stall of advancing blade.

Compressibility effects on advancing blade and retreating blade stall.

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

Retreating blade stall.

Compressibility effects on advancing blade.

Compressibility effects and stall of advancing blade.

Compressibility effects on advancing blade and retreating blade stall.

Which requirements distinguish performance class 3 operations form the other performance
classes?

The need to perform an emergency landing if one engine failure occurs.

The need to perform an emergency landing if one engine failure occurs in the early take off or late landing phases.

The need to perform an emergency landing if the helicopter is single engine and the engine fails.

The need to perform an emergency landing whenever the tail rotor fails.

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

The need to perform an emergency landing if one engine failure occurs.

The need to perform an emergency landing if one engine failure occurs in the early take off or late landing phases.

The need to perform an emergency landing if the helicopter is single engine and the engine fails.

The need to perform an emergency landing whenever the tail rotor fails.

What do performance class 1 operations involve?

The fact that a gearbox failure does never impose an emergency landing.

The fact that a tail rotor failure does never impose an emergency landing.

The fact that one engine failure does never impose an emergency landing.

The fact that one engine failure does never impose an emergency landing except in the early take off and late landing phases.

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

The fact that a gearbox failure does never impose an emergency landing.

The fact that a tail rotor failure does never impose an emergency landing.

The fact that one engine failure does never impose an emergency landing.

The fact that one engine failure does never impose an emergency landing except in the early take off and late landing phases.

Do you always need a Cat. A helicopter for performance class 1 operations?

No.

Yes

No, it does not depend on the helicopter category.

No, also multi engine Cat. B may do that.

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

No.

Yes

No, it does not depend on the helicopter category.

No, also multi engine Cat. B may do that.

Singe engine helicopters are:

Either Cat. A or B depending on take off mass and power available

Always Cat. A.

Always Cat. B

Either Cat. A or B depending on type of rotor (co-axial rotors may be Cat. A).

Commandes clavier:

= tourner,

= avant/arrière,

= faire défiler

Either Cat. A or B depending on take off mass and power available

Always Cat. A.

Always Cat. B

Either Cat. A or B depending on type of rotor (co-axial rotors may be Cat. A).

What are category A and B helicopters?

Cat A helicopters, unlike cat B, have a certain stay-up capability in case of engine failure.

Cat A helicopters, unlike Cat. B, are never single engine.

Cat. B helicopters are always single engine.

Cat A helicopters, unlike cat. B, are always multi engine.

Cat A helicopters, unlike cat B, have a certain stay-up capability in case of engine failure.

Cat A helicopters, unlike Cat. B, are never single engine.

Cat. B helicopters are always single engine.

Cat A helicopters, unlike cat. B, are always multi engine.

What is the ratio (approximately) of the rotation speed of the last turbine stage to the rotation
speed of the main rotor?

About 1000.

Up to 100.

20,000.

Lower than 10.

About 1000.

Up to 100.

20,000.

Lower than 10.

Are the consequences of a main gearbox failure different on a Class A and on a Class B
helicopter?

No, the failure is equally critical.

No, the failure is non-critical in both cases.

Yes, Class A helicopters can fly for a short time without a working gearbox.

Yes, on Class B helicopters it is more critical because of the lack of “stay-up” capability.

No, the failure is equally critical.

No, the failure is non-critical in both cases.

Yes, Class A helicopters can fly for a short time without a working gearbox.

Yes, on Class B helicopters it is more critical because of the lack of “stay-up” capability.

What should the pilot do in case of a failure of the tail rotor transmission?

Disconnect the main rotor from the engines.

Continue flying.

Disconnect the tail rotor from the engines.

Disconnect the main rotor from the engines and perform an emergency landing.

Disconnect the main rotor from the engines.

Continue flying.

Disconnect the tail rotor from the engines.

Disconnect the main rotor from the engines and perform an emergency landing.

Why do helicopter gearboxes need intensive maintenance?

Because of the difficulty of lubricating moving mechanical parts.

Because of the long percentage of flight hours spent in hover flight.

Because of the large number of moving mechanical parts subject to wear and tear (D: wear and tear = Verschleiss).

Because of the large torque generated by the engine.

Because of the difficulty of lubricating moving mechanical parts.

Because of the long percentage of flight hours spent in hover flight.

Because of the large number of moving mechanical parts subject to wear and tear (D: wear and tear = Verschleiss).

Because of the large torque generated by the engine.

HE 14

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