Set of flashcards HE 14 (Page 2 of 2)

Flashcards	56
Language	Deutsch
Category	Technology
Level	University
Created / Updated	15.06.2015 / 07.06.2018
Weblink	https://card2brain.ch/box/he_14
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What is a problem connected with semi-articulated rotors (also called see-saw or semi-rigid)
when total rotor thrust is zero or very small?

The pilot has no means to increase the rotor thrust.

The pilot has no means to generate a significant control moment around the pitch and yaw axes of the helicopter.

The pilot has no means to generate a significant control moment around the pitch and roll axes of the helicopter.

The pilot has no means to generate a significant control moment around the yaw and roll axes of the helicopter.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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

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.

HE 14

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