HELI

Introduction to Rotary Wing Aircraft, Vorlesung an der ZHAW SoE, Studiengang Aviatik

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About these flashcards

These flashcards delve into the intricate mechanics and dynamics of helicopter flight, covering topics like rotor aerodynamics, blade pitch control, and engine power management. They explore the challenges of scaling down helicopter designs, the physics behind autorotation, and the nuances of ground effect. This set is invaluable for university students and engineers studying aeronautical engineering, offering a deep understanding of helicopter operations and the forces at play during flight.

Flashcards

246

Students

Language

English

Category

Technology

Level

University

Created / Updated

13.06.2018 / 20.06.2018

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What are the difficulties met by the designers of a helicopter main gearbox? (A) Accommodate a reduction ratio (Untersetzung) of about 100 in limited space and mass. (B) Accommodate a reduction ratio (Untersetzung) of about 100 in limited space and mass. Additionally, the design must minimize maintenance and maximize reliability. (C) Accommodate a reduction ratio (Untersetzung) of about 100 at a limited cost. (D) Accommodate a reduction ratio (Untersetzung) of about 100 in limited space and mass. Additionally, the design must keep noise level to a minimum.

(B) Accommodate a reduction ratio (Untersetzung) of about 100 in limited space and mass. Additionally, the design must minimize maintenance and maximize reliability.

How can the reliability of the helicopter gearboxes be improved and the maintenance costs reduced? (A) By the introduction of a control system which reduces vibrations. (B) By the introduction of better suited metallic materials. (C) By the introduction of a monitoring system, which measures wear and tear (Verschleiss) in the various components and sends warnings as soon as one needs replacement. (D) By the introduction of a monitoring system, which measures vibrations in the various components and counterbalances them with small shakers.

(C) By the introduction of a monitoring system, which measures wear and tear (Verschleiss) in the various components and sends warnings as soon as one needs replacement.

What are the differences between Category A and Category B helicopters? (A) Cat A helicopters, unlike cat B, have a certain stay-up capability in case of engine failure. (B) Cat A helicopters, unlike cat. B, are always multi engine. (C) Cat A helicopters, unlike Cat. B, have a significant excess power. (D) Cat. B helicopters are always single engine.

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

Why are all single engine helicopters Cat. B? (A) Because they are less reliable. (B) Because they have less available power. (C) Because they have no stay-up capability in case of engine failure. (D) Because they have less excess power.

C) Because they have no stay-up capability in case of engine failure.

What are Performance Class 1 operations? (A) Flights, or portion of flights, during which an emergency landing may be required in the presence of an engine failure, but only when flying over hostile territory. (B) Flights, or portion of flights, during which an emergency landing may be required in the presence of an engine failure. (C) Flights, or portion of flights, during which an emergency landing is always required in the presence of an engine failure. (D) Flights, or portion of flights, during which an emergency landing is never required in the presence of an engine failure.

(D) Flights, or portion of flights, during which an emergency landing is never required in the presence of an engine failure.

What are Performance Class 2 operations? (A) Flights, or portion of flights, during which an emergency landing is never required in the presence of an engine failure. (B) Flights, or portion of flights, during which an emergency landing may be required in the presence of an engine failure. (C) Flights, or portion of flights, during which an emergency landing is always required in the presence of an engine failure. (D) Flights, or portion of flights, during which an emergency landing may be required in the presence of an engine failure, but only when flying over hostile territory.

(B) Flights, or portion of flights, during which an emergency landing may be required in the presence of an engine failure.

What are Performance Class 3 operations? (A) Flights, or portion of flights, during which an emergency landing is always required in the presence of an engine failure. (B) Flights, or portion of flights, during which an emergency landing is never required in the presence of an engine failure. (C) Flights, or portion of flights, during which an emergency landing may be required in the presence of an engine failure. (D) Flights, or portion of flights, during which an emergency landing may be required in the presence of an engine failure, but only when flying over hostile territory.

(A) Flights, or portion of flights, during which an emergency landing is always required in the presence of an engine failure.

Which physical phenomena can limit the maximum forward speed of helicopters? (A) Retreating blade stall. (B) Compressibility effects on advancing blade. (C) Compressibility effects on advancing blade and retreating blade stall. (D) Compressibility effects and stall of advancing blade.

Conventional helicopters need a tail rotor for directional control. How does the power required by the tail rotor relate to the total power required? (A) It may require up to approximately 50% of the total power required, depending on the flight condition. (B) It may require up to approximately 10% of the total power required, depending on the flight condition. (C) It may require up to approximately 1% of the total power required, depending on the flight condition. (D) Tail Rotor normally works in windmilling condition and does not require any power to work.

(B) It may require up to approximately 10% of the total power required, depending on the flight condition.

What are the main contributions to the power required of a helicopter? (A) Induced power, parasitic power, viscous losses, losses in the gearboxes. (B) Induced power, parasitic power, air conditioning, anti-torque system power, transmission losses. (C) Induced power, parasitic power, viscous losses, anti-torque system power, transmission losses. (D) Induced power, parasitic power, viscous losses, air conditioning, hydraulic power, transmission losses.

What is the largest contribution to the power required of a helicopter in hover flight? (A) Induced power only out-of-ground-effect. Parasitic power when hovering in-ground-effect. (B) Induced power. (C) Aircraft systems (air conditioning etc). (D) Viscous losses or compressibility effects, depending on the blade section aerofoils.

(B) Induced power.

What is Ground Effect (GE) in a conventional helicopter and what are the consequences on power required? (A) GE generates high-energy vortexes between rotor and ground. As a consequence, the power required to generate a Thrust force T is normally smaller. (B) GE generates a low-pressure air cushion between rotor and ground. As a consequence, the power required to generate a Thrust force T is normally smaller. (C) GE generates a high-pressure air cushion between rotor and ground. As a consequence, the power required to generate a Thrust force T is normally larger. (D) GE generates a high-pressure air cushion between rotor and ground. As a consequence, the power required to generate a Thrust force T is normally smaller.

(D) GE generates a high-pressure air cushion between rotor and ground. As a consequence, the power required to generate a Thrust force T is normally smaller.

What may be the most important advantage - beside the absence of a Tail Rotor - of co-axial rotors in forward flight at high advance ratio? (A) The retreating blades of each rotor happen to be on opposite sides (left / right), causing the asymmetric lift distribution over the two rotor discs to compensate each other. (B) The compressibility effects on the advancing blades of each rotor are much smaller due to the rotors geometry. (C) The retreating blades of each rotor happen to be on the same side (left / right), causing the asymmetric lift distribution over the two rotor discs to compensate each other. (D) The retreating blades of each rotor happen to be on opposite sides (left / right), causing the problems due to excessive flapping to compensate each other.

(A) The retreating blades of each rotor happen to be on opposite sides (left / right), causing the asymmetric lift distribution over the two rotor discs to compensate each other.

In which phases can Autorotation be broken down into (sequence is relevant)? (A) Engine(s) disconnection, violent collective pull-up, stabilized descent, final flare, touchdown with (small) residual kinetic energy. (B) Reduction of collective pitch until rate of descent stabilises, stabilized descent, engine(s) disconnection, final flare, touchdown with (small) residual kinetic energy. (C) Engine(s) disconnection, reduction of collective pitch until rate of descent stabilises, stabilized descent, final flare, touchdown with (small) residual kinetic energy (D) Engine(s) disconnection, activation of the automatic autorotative system, stabilized descent, final flare, touchdown with large residual kinetic energy.

(C) Engine(s) disconnection, reduction of collective pitch until rate of descent stabilises, stabilized descent, final flare, touchdown with (small) residual kinetic energy

During the stabilized descent phase of an Autorotation, what can be said about potential and kinetic energy? (A) Kinetic energy is zero during Autorotation, as engines are shut off. (B) Kinetic energy of the helicopter and of the rotor, as well as the potential energy, continuously decrease. (C) All energies remain constant at all times. (D) Kinetic energy of the helicopter and of the rotor is kept constant, whereas potential energy reduces.

(D) Kinetic energy of the helicopter and of the rotor is kept constant, whereas potential energy reduces.

In which of the following cases must an emergency landing be performed? (A) Engine failure in a twin engined helicopter. (B) Engine failure in a twin engined helicopter during take-off. (C) Tail rotor complete failure in a twin engined helicopter. (D) Engine failure in a twin engined helicopter during landing.

(B) Engine failure in a twin engined helicopter during take-off.

Every point in the “AVOID” areas in the Height-Velocity diagrams (also said “dead man curves”) indicate a combination of height and horizontal speed. What is the use of such a diagramme? (A) Help the pilot avoiding inefficient flight conditions. (B) Indicate the height-speed combinations, where flight is legal. (C) Indicate the height-speed combinations, where an emergency landing would prove difficult for the average pilot. (D) Indicate the height-speed combinations, where an emergency landing would be easy even for the inexperienced pilot.

What must be the pilot’s reaction to the development of Ground Resonance? (A) Immediately interrupt the contact with the ground, if the rotor RPM are high enough, otherwise stop the rotor. (B) Immediately switch on the stability augmentation system. (C) Immediately reduce collective pitch. (D) Immediately stop the rotor by starting the rotor brake.

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

Speaking of scaling down an aircraft design, we might recall that the mass are proportional to the cube of the scale of length, l3; the aerodynamic forces are proportional to l2. What can be said about the development of smaller scale helicopters? (A) Sizing of load-carrying components may become impossible. (B) Sizing of load-carrying components is more problematic. (C) Sizing of load-carrying components is less problematic. (D) Sizing of load-carrying components is trivial.

What can be said about the aerodynamics of smaller scale helicopters as compared to full scale ones? (A) Since Reynolds number is much smaller, the aerodynamic effects may also be very different. (B) Since Reynolds number is much bigger, the aerodynamic effects may also be very different. (C) Given the special nature of helicopters, no significant changes are expected. (D) Since Reynolds number does not change much, no significant changes are expected.

(A) Since Reynolds number is much smaller, the aerodynamic effects may also be very different.

Why is the generation of an induced velocity a consequence of the generation of lift (by a heli rotor)?A. Because of the conservation of momentum B. Because of the conservation of energy C. Because of air viscosity D. Because of rotation speed Omega

Keyboard commands:

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A. Because of the conservation of momentum

In hover, induced velocity is inversely proportional to rotor area. This means, with respect to a reference radius: A. That a rotor with a smaller radius will generate a higher induced velocity but will have the same efficiency – while generating the same thrust force B. That a rotor with a smaller radius will generate a smaller induced velocity – while generating the same thrust force C. That a rotor with a smaller radius will generate the same induced velocity – while generating the same thrust force D. That a rotor with a smaller radius will generate a higher induced velocity – while generating the same thrust force

Keyboard commands:

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D. That a rotor with a smaller radius will generate a higher induced velocity – while generating the same thrust force

Induced velocity in autorotation is: A. Zero B. Equal to descent velocity, without considering the final flare C. Smaller than descent velocity, without considering the final flare D. Larger than descent velocity, without considering the final flare

Keyboard commands:

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= for-/backward,

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C. Smaller than descent velocity, without considering the final flare

Induced velocity in autogyrus / gyroplanes is: A. Zero because the rotor is windmilling B. Non-zero because the rotor does generate lift C. Zero because the rotor is not driven by the engine D. Non-zero because the rotor turns

Keyboard commands:

= turn,

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B. Non-zero because the rotor does generate lift

What is normally meant by “vortex ring”? A. A working state of a rotor characterized by stable re-circulation through rotor disc B. A working state of a rotor characterized by a strong wake C. A working state of a rotor characterized by circulation D. A working state of a rotor characterized by unstable re-circulation through rotor disc

Keyboard commands:

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D. A working state of a rotor characterized by unstable re-circulation through rotor disc

What is meant with the term windmilling? A. Windmilling is the working state of a rotor in which the flow gives energy to the rotor system – i.e it is the state in which wind turbines work when they generate power B. Windmilling is the working state of a rotor in which the rotor accelerates its rotation speed C. Windmilling is the working state of a rotor in which the rotor system gives energy to the flow- i.e it is the state in which wind turbines work when they generatie power D. WIndmilling is the working state of a rotor in which the flow gives energy to the rotor system – i.e it is the state in which helicopter rotors work

Keyboard commands:

= turn,

= for-/backward,

= scroll

A. Windmilling is the working state of a rotor in which the flow gives energy to the rotor system – i.e it is the state in which wind turbines work when they generate power

Why is a rotor less efficient than a wing in forward flight at high speed, at an advance ratio mü=V/(Omega x R) = 0.40 for instance? A. Because the flow around the retreating blade is disturbed by compressibility effects and the advancing blade experiences inverse flow or very high angle of attack B. Because the flow around the blades is disturbed by compressibility effects C. Because the flow around the advancing blade is disturbed by compressibility effects and the retreating blade experiences inverse flow or very high angle of attack D. Because wing increase their efficiency as speed increases

Keyboard commands:

= turn,

= for-/backward,

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C. Because the flow around the advancing blade is disturbed by compressibility effects and the retreating blade experiences inverse flow or very high angle of attack

What is the physical phenomenon at the origin of ground effect? A. While flying close to the ground a high-pressure cushion appears between rotor and ground B. While flying close to the ground a high-pressure cushion appears above the rotor C. While flying close to the ground a high-pressure cushion appears between rotor and ground D. While flying close to the ground a high-pressure cushion appears above the rotor

Keyboard commands:

= turn,

= for-/backward,

= scroll

A. While flying close to the ground a high-pressure cushion appears between rotor and ground

How would you describe the effects of ground effect on a helicopter performances? A. Power required and lift decrease proportionally B. Power required decreases while generating the same lift C. Power required increases while generating the same lift D. Power required and lift increase proportionally

Keyboard commands:

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B. Power required decreases while generating the same lift

Why is forward speed of conventional helicopter limited about 150 – 160kt? A. Fuselage drag B. Compressibility effects on retreating blade and stall of advancing blade C. Fuselage drag and tail rotor stall D. Compressibility effects on advancing blade and stall of retreating blade

Keyboard commands:

= turn,

= for-/backward,

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D. Compressibility effects on advancing blade and stall of retreating blade

Why does the above limitation not apply to tilt-rotors such as Bell-Boeing MV22? A. Because the rotors are tilted forward at high-speed B. Because the fuselage has a much smaller drag coefficient C. Because the radius of the rotors is much smaller than a conventional helicopter D. Because the rotors are tilted forward at high-speed interference between rotor downwash and fuselage is reduced

A. Because the rotors are tilted forward at high-speed

Why does the above limitation not apply to compound helicopters such as the Eurocopter X3 (= helicopters with a main rotor but also a small wing and propellers)? A. Because at high speed the main rotor is partially unloaded since wing and propellers generate most of the necessary forces (forward thrust) B. Because at high speed the main rotor is partially unloaded since wing and propellers generate most of the necessary forces (lift) C. Because at high speed the main rotor is partially unloaded since wing and propellers generate most of the necessary forces (forward thrust and lift) D. Because at high speed the main rotor is partially unloaded since wing and propellers generate most of the necessary forces (drag and lift)

C. Because at high speed the main rotor is partially unloaded since wing and propellers generate most of the necessary forces (forward thrust and lift)

The main rotor head types are: A. Semi-rigid (also called “see-saw”), semi articulated, articulated, hingeless and bearlingless B. Semi-rigid (also called “see-saw”), articulated, hingeless and bearingless C. Semi-rigid (also called “see-saw”), articulated, hingeless D. Rigid, hingeless and bearingless

B. Semi-rigid (also called “see-saw”), articulated, hingeless and bearingless

What are hingeless rotor heads? A. Rotor heads without mechanical hinges around flap and lead/lag axes B. Rotor heads without hinges around flap and lead/lad axes C. Rotor heads with rigid connections to blades, like propellers D. Rotor heads without mechanical hinges

A. Rotor heads without mechanical hinges around flap and lead/lag axes

What are bearingless rotor heads? A. Rotor heads without hinges around flap and lead/lag axes B. Rotor heads without mechanical hinges around flap and lead/lag axes C. Rotor heads with rigid connections to blades, like propellers D. Rotor heads without mechanical hinges

D. Rotor heads without mechanical hinges

Which type of rotor head provide the highest control moments? (A) Hingeless and bearingless, because these constructions (Bauweise) accommodate large hinge offset more conveniently. (B) Hingeless and bearingless, because these constructions (Bauweise) accommodate small hinge offset more conveniently. (C) Hingeless and bearingless, because these constructions (Bauweise) are more suitable to large size helicopters. (D) Hingeless and bearingless, because these constructions (Bauweise) do not have mechanical hinges.

A) Hingeless and bearingless, because these constructions (Bauweise) accommodate large hinge offset more conveniently.

Do rotor heads with large hinge offsets provide a lower “comfort” for passengers when flying in turbulence? (A) No, because turbulence might cause a non-symmetric loading on the rotor blades. (B) No, because aerodynamic forces generated by turbulence on the blades are transmitted to the fuselage through the rotor head. (C) Yes, because aerodynamic forces generated by turbulence on the blades are transmitted to the fuselage through the rotor head. (D) No, because turbulence does not alter (ändert) the distribution of aerodynamic forces.

(C) Yes, because aerodynamic forces generated by turbulence on the blades are transmitted to the fuselage through the rotor head.

Why is a helicopter equipped with a semi-rigid (“see-saw”) rotor slower than other rotor head types to react to pilot’s inputs? (A) Because semi-rigid rotors have large hinge offsets. (B) Because semi-rigid rotors are an old solution. (C) Because semi-rigid rotors have mechanical hinges. (D) Because the hinge offset of semi-rigid rotors is zero.

(D) Because the hinge offset of semi-rigid rotors is zero.

Which materials are commonly used on modern helicopters to manufacture main rotor blades? (A) Carbon fibers and glass fibers composite. (B) Aluminum. (C) Carbon fibers composite. (D) Wood.

(A) Carbon fibers and glass fibers composite.

What is the function of the tail rotor system? (A) Provide control around the pitch axis. (B) Preventing the helicopter from spinning around. (C) Provide control around the yaw axis. (D) Provide control around the roll axis.

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Flashcards

What are Performance Class 3 flights? (A) A flight in which an engine failure - depending on pilot’s ability and experience - might force the pilot to perform an emergency landing. (B) A flight in which an engine failure - occurring at any moment of the flight - would not force the pilot to perform an emergency landing. (C) A flight in which an engine failure - occurring at any moment of the flight - would force the pilot to perform an emergency landing. (D) A flight in which a transmission failure (Getriebe, Kraftübertragung) - occurring at any moment of the flight - would force the pilot to perform an emergency landing.

(C) A flight in which an engine failure - occurring at any moment of the flight - would force the pilot to perform an emergency landing.

Can you perform a Performance Class 1 flight with a Category B helicopter? (A) No. (B) Yes. (C) Yes but not over hostile territory. (D) It depends on take-off mass.

(A) No.

Can you perform a Performance Class 1 flight with a Category A helicopter? (A) Always. (B) It depends on take-off mass. (C) Never. (D) It depends on take-off mass and outside air density (or density altitude).

(D) It depends on take-off mass and outside air density (or density altitude).

What could be the reason why a Cat. A helicopter may not perform a PC 1 flight? (A) The OEI (= One Engine Inoperative) power available might not be sufficiently higher than the power required in cruise flight. (B) The OEI (= One Engine Inoperative) power available might not be sufficiently higher than the power required for the whole or part of the flight. (C) The OEI (= One Engine Inoperative) power available might not be sufficiently higher than the power required in an emergency landing. (D) The power available might not be sufficiently higher than the power required in an emergency landing.

(B) The OEI (= One Engine Inoperative) power available might not be sufficiently higher than the power required for the whole or part of the flight.

Why is the power required by a tilt-rotor at high-speed lower than the power required by a conventional helicopter of comparable mass? (A) Because at high speed the lift force on a tilt-rotor is generated by the wing, which is aerodynamically more efficient than a rotor. (B) Because tiltable rotors are aerodynamically more efficient. (C) Because at high speed the lift force on a tilt-rotor is generated by the wing, which has a larger surface than rotor blades. (D) Because tilt-rotors fuselages are much less draggy.

(A) Because at high speed the lift force on a tilt-rotor is generated by the wing, which is aerodynamically more efficient than a rotor.

When is a rolling take off maneuver useful and why? (A) (At low speed) power required decreases with increasing forward speed; a rolling take-off is performed on hot days at high altitude. (B) (At low speed) power required increases with increasing forward speed; a rolling take-off is performed when power required in hover would be too high for a given power setting. (C) (At low speed) power required increases with increasing forward speed; a rolling take-off is only performed in demo-flights. (D) (At low speed) power required decreases with increasing forward speed; a rolling take-off is performed when power required in hover would be too high for a given power setting.

(D) (At low speed) power required decreases with increasing forward speed; a rolling take-off is performed when power required in hover would be too high for a given power setting.

Why do you need to perform an emergency landing when a tail rotor failure occurs on a conventional helicopter - even if power available remains unchanged? (A) Because the pilot would lose the control around the yaw axis. (B) Because the helicopter would lose static stability around the yaw axis. (C) Because the helicopter would spin around the yaw axis - in all flight conditions. (D) Because the pilot would lose the control around the pitch axis.

(A) Because the pilot would lose the control around the yaw axis.

Does a multi-engine helicopter always have to perform an emergency landing when an engine failure occurs? (A) No, never. (B) Yes, always. (C) No, it depends on power available (OEI) and required. (D) No, it depends on power available and required.

What is the best forward speed to perform an emergency landing per autorotation? (A) Best range, in order to ease (vereinfachen) the choice of the place to land on. (B) Best range, in order to fly as far as possible. (C) Zero (Hover). (D) Best endurance, in order to delay the impact to the ground.

(A) Best range, in order to ease (vereinfachen) the choice of the place to land on.

What is an autorotation? (A) A maneuver in which a constant rate of descent is established, at which power required is minimum. (B) A maneuver in which a constant rate of descent is established, at which power required is zero. (C) A maneuver in which a cruise flight is established, at which power required is zero. (D) A maneuver in which a landing is performed with engines off.

(B) A maneuver in which a constant rate of descent is established, at which power required is zero.

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? (A) Yes, low disc loading implies high power loading. (B) Yes, low disc loading implies low power loading. (C) No, low disc loading implies high power loading. (D) No, low disc loading implies low power loading.

(A) Yes, low disc loading implies high power loading.

The Figure of Merit: (A) is a measure of rotor efficiency in hover and forward flight. (B) is a measure of rotor efficiency in forward flight. (C) is a measure of rotor efficiency in hover. (D) is a measure of pilot’s performances.

Induced velocity at the helicopter max speed is: (A) Larger than induced velocity at (_ = 0:1). (B) Smaller than induced velocity in hover but larger than induced velocity at (_ = 0:1). (C) Larger than induced velocity in hover. (D) Smaller than induced velocity in hover.

(D) Smaller than induced velocity in hover.

Does a rotor generate an induced velocity when operating in the so-called “windmilling” working state? (A) Yes, if the rotor generate a thrust. (B) No, even if the rotor generates thrust. (C) Yes, in any case. (D) No, never.

(A) Yes, if the rotor generate a thrust.

What would be the consequences of flying into the “vortex ring” working state? (A) The rotor thrust would become unsteady (irregular in time). (B) The rotor thrust would slowly drop to zero. (C) The rotor thrust would become unsteady (irregular in time) and unbalanced (not originating from the geometrical centre of the rotor). (D) 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.

During the descent phase in an autorotation: (A) the kinetic energy of the rotor is exploited in order to generate thrust. (B) the work done by the gravitational force (or potential energy) is exploited in order to generate thrust. (C) the kinetic energy of the helicopter is exploited in order to generate thrust. (D) the potential energy of the rotor is exploited in order to generate thrust.

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

During the flare at the end of an autorotation: (A) the kinetic energy of the rotor is exploited in order to generate additional thrust. (B) the work done by the gravitational force (or potential energy) is exploited in order to generate thrust. (C) the kinetic energy of the helicopter is exploited in order to generate thrust. (D) the potential energy of the rotor is exploited in order to generate thrust.

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

What is the reverse flow region of a rotor in forward flight? (A) The region of the rotor disc where the relative velocity experienced by the rotor blades goes from the trailing edge to the leading edge. (B) The region of the rotor disc where the relative velocity experienced by the rotor blades goes from the leading edge to the trailing edge. (C) The region of the rotor disc where the aerodynamic force generated by the blade sections is oriented downwards. (D) The region of the rotor disc where the aerodynamic force generated by the blade sections is zero.

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

Are the blade pitch angle and the local angle of attack related? (A) Yes, the angle of attack depends exclusively on the pitch angle. (B) Yes, the pitch angle also depends the local angle of attack. (C) Yes, the angle of attack depends on the pitch angle but not only. (D) Yes, the angle of attack depends exclusively on pitch angle and helicopter attitude.

Is the induced velocity in reality uniform in space as the momentum theory assumes? (A) No, the induced velocity is dominated by the effects of a strong horseshoe vortex. (B) No, for instance in hover the induced velocity is dominated by the effects of two large tip vortexes. (C) No, the induced velocity is always dominated by the effects of two large tip vortexes. (D) No, for instance at high speed the induced velocity is dominated by the effects of two large tip vortexes.

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

How could compressibility effects on the advancing blade be completely removed? (A) By reducing rotor speed in forward flight. (B) By increasing rotor speed in forward flight. (C) By reducing rotor speed in hover flight. (D) By increasing rotor speed in forward flight.

(A) By reducing rotor speed in forward flight.

In which cases do compressibility effects arise? (A) In forward flight, at low speed. (B) In forward flight, at high speed. (C) In forward flight, at all speed. (D) In forward flight, at all speed at high collective settings.

(B) In forward flight, at high speed.

How can the rotor plane (the tip path plane or TPP) be oriented in order to control the helicopter? (A) By operating the cyclic flapping controls. (B) By operating the collective pitch control. (C) By operating the cyclic pitch controls, the consequent lead/lagging of the blades orients the TPP. (D) By operating the cyclic pitch controls, the consequent flapping of the blades orients the TPP.

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

Why are main rotors equipped with lead/lag hinges (also called drag hinges)? (A) To minimise the mechanical stress on the blade root, originated by gyroscopic effects (when the blade flaps, it also tends to move in-plane). (B) To minimise the mechanical stress on the blade root, originated by the dampers forces. (C) To minimise the mechanical stress on the blade root, originated by centrifugal force. (D) To minimise the blade motion in-plane.

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

Is a main rotor blade normally free to oscillate (as a rigid body) around the feathering axis (also called pitch axis)? (A) No, blade pitch angle cannot be changed during the flight. (B) No, blade pitch angle is fixed by the position (height and attitude) of the swashplate. (C) No, blade pitch angle is only determined by the blade flapping angle. (D) Not in all cases, only if the rotor is articulated.

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

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? (A) The pilot has no means to increase the rotor thrust. (B) The pilot has no means to generate a significant control moment around the pitch and yaw axes of the helicopter. (C) The pilot has no means to generate a significant control moment around the pitch and roll axes of the helicopter. (D) The pilot has no means to generate a significant control moment around the yaw and roll axes of the helicopter.

What is the function of the so-called “_3 (delta 3)” angle on tail rotors? (A) To mechanically maintain the blade flapping within acceptable limits in forward flight. (B) To electronically maintain the blade flapping within acceptable limits in forward flight. (C) To increase tail rotor thrust. (D) To mechanically maintain the blade flapping within acceptable limits in hover.

(A) To mechanically maintain the blade flapping within acceptable limits in forward flight.

How could ground resonance be defined? (A) A kind of dynamic instability involving main rotor blades flapping and the oscillations of the helicopter on the ground. (B) A kind of dynamic instability involving main rotor blades motion in plane (lead / lagging) and the oscillations of the helicopter on the ground. (C) A kind of dynamic instability involving the helicopter oscillating on the ground when rotor max RPM is reached. (D) A kind of dynamic instability involving main rotor blades motion and the oscillations of the helicopter in the air.

(B) A kind of dynamic instability involving main rotor blades motion in plane (lead / lagging) and the oscillations of the helicopter on the ground.

How are conventional helicopters protected against ground resonance? (A) With dampers around the lead / lagging and flapping hinges of the blades, as well as on the landing gear. (B) With dampers around the flapping hinges of the blades and on the landing gear. (C) With the stability augmentation system or SAS. (D) With dampers around the lead / lagging hinges of the blades and on the landing gear.

(D) With dampers around the lead / lagging hinges of the blades and on the landing gear.

Are all bearingless rotors free from ground resonance also without dampers? (A) No, only the ones with very soft blade roots, the so called soft-in-plane rotors. (B) Yes. (C) No, not all of them, only the ones with very stiff blade roots, the so- called stiff-in-plane rotors. (D) Yes, but only if the helicopters is equipped with skids.

C) No, not all of them, only the ones with very stiff blade roots, the so- called stiff-in-plane rotors.

Are tail rotors normally equipped with cyclic pitch? (A) No, only if the tail rotor is a see-saw. (B) No, only if the tail rotor is articulated. (C) No, only if the helicopter has a high max speed. (D) No.

(D) No.

What is the main limiting factor for the position of the helicopter centre of gravity? (A) The limited excursion (range) of the longitudinal cyclic pitch control. (B) The limited excursion (range) of the lateral cyclic pitch control. (C) The limited excursion (range) of the collective pitch control. (D) The limited excursion (range) of the tail rotor collective pitch control.

(A) The limited excursion (range) of the longitudinal cyclic pitch control.

Why does a rotor tend to flap back in forward flight? (A) Because the lift generated by the advancing blade is higher than the one generated by the retreating blade. (B) Because the lift generated by the retreating blade is higher than the one generated by the advancing blade. (C) Because of compressibility effects. (D) Because of retreating blade stall.

(A) Because the lift generated by the advancing blade is higher than the one generated by the retreating blade.

Are helicopter rotors statically stable? (In this question, an isolated rotor is considered.) (A) Yes, in forward flight. (B) Yes, in hover. (C) Yes, in hover and forward flight. (D) Yes, in hover and forward flight at low advance ratio.

Are helicopter rotors dynamically stable? (In this question, an isolated rotor is considered.) (A) Not in hover. (B) No, neither in hover nor in forward flight. (C) Not in forward flight. (D) No, neither in hover nor in forward flight at low advance ratio.

(B) No, neither in hover nor in forward flight.

Do helicopters exhibit (= have or show) a higher dynamic stability than isolated rotors? (A) Yes, this may happen in forward flight thanks to the higher mass. (B) Yes, this may happen in hover thanks to aerodynamic surfaces. (C) Yes, this may happen in forward flight thanks to aerodynamic surfaces. (D) Yes, this may happen in hover thanks to the higher mass.

How can dynamic stability of helicopters be further improved? (A) By means of computer-controlled systems such as SAS (Stability Augmentation System). (B) By means of computer-controlled systems such as FADEC (Full Authority Digital Engine Control). (C) By means of auto-stable airfoils. (D) By means of mechanical systems such as SAS (Stability Augmentation System).

(A) By means of computer-controlled systems such as SAS (Stability Augmentation System).

How is directional control on conventional helicopters achieved? (A) Tail rotor collective. (B) Tail rotor cyclic. (C) Main rotor collective. (D) Tail rotor collective and lateral cyclic.

(A) Tail rotor collective.

How are main rotor blades attached to the rotor head (also called rotor hub) on conventional helicopters? (A) Blades are always rigidly attached to the rotor hub, this means that they cannot move or rotate. (B) Blades may be attached by means of mechanical hinges or flexible elements which behave as virtual hinges. (C) Blades are always attached by means of mechanical hinges. (D) Blades are always rigidly attached to the hub, between blade and hub special rubber elements are installed.

(B) Blades may be attached by means of mechanical hinges or flexible elements which behave as virtual hinges.

What is the difference between hingeless and bearingless rotor heads? (A) Hingeless and bearingless are synonyms (= the two words have the same meaning). (B) In bearingless rotor heads the rotation around the feathering (or pitch) axis is accommodated by a mechanical bearing. (C) In hingeless rotor heads the rotation around the feathering (or pitch) axis is accommodated by a mechanical bearing. (D) Hingeless rotors are stiffer.

C) In hingeless rotor heads the rotation around the feathering (or pitch) axis is accommodated by a mechanical bearing.

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