HELI

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

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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.

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Technik

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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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Lernkarten

What are the main advantages of a Fenestron-like tail rotor? (A) Low noise, safety for ground personnel, (B) Aerodynamic efficiency, (C) Low vibration level, (D) Low mass,

(A) Low noise, safety for ground personnel,

What are the advantages of a NOTAR-like anti-torque system? (A) Low vibration level, (B) Aerodynamic efficiency, (C) Low noise, safety for ground personnel, (D) Low mass,

What are the advantages of a conventional tail rotor system (i.e. a “normal” tail rotor)? (A) Low vibration level, , (B) Low noise, safety for ground personnel, (C) Good aerodynamic efficiency in most of the flight envelope (D) Low vulnerability (that is to say that the helicopter is difficult to damage in, say, a combat scenario),

What is a category A helicopter? (A) There is no such thing as a category A helicopter, (B) A helicopter without stay-up capability in case of power unit failure, (C) A helicopter with stay-up capability in case of tail rotor failure, (D) A helicopter with stay-up capability in case of power unit failure,

(D) A helicopter with stay-up capability in case of power unit failure,

What is a category 1 helicopter? (A) There is no such thing as a category 1 helicopter, (B) A helicopter with stay-up capability in case of power unit failure, (C) A helicopter without stay-up capability in case of power unit failure, (D) A helicopter with stay-up capability in case of tail rotor failure,

(A) There is no such thing as a category 1 helicopter,

Can a single-engined helicopter be category A? (A) Only in performance class 1 flights, (B) Yes, (C) No, (D) Only if the helicopter has no tail rotor,

What is the relation between manoeuvrability and rotor head geometry? (A) The larger the flapping hinge offset, the larger is the drag force generated by the rotor, (B) The larger the flapping hinge offset, the larger are the control moments, (C) The larger the flapping hinge offset, the smaller are the control moments, (D) The larger the flapping hinge offset, the smaller the lift force generated by the rotor,

(B) The larger the flapping hinge offset, the larger are the control moments,

What are articulated rotors? (A) Rotors with rigid blade attachments, , (B) Rotors with no hinges, (C) Rotors with articulated hinges, (D) Rotors with flapping, lead-lagging and feathering hinges

(D) Rotors with flapping, lead-lagging and feathering hinges

Which is the best definition for hingeless rotors? (A) Rotors with (bending- and torsionwise) flexible blade attachments (and no feathering hinge), (B) Rotors with no hinges, (C) Rotors with flexible blade attachments, (D) Rotors with (bendingwise) flexible blade attachments and a feathering hinge,

(D) Rotors with (bendingwise) flexible blade attachments and a feathering hinge,

Which is the best definition for bearingless rotors? (A) Rotors with (bending- and torsionwise) flexible blade attachments (and no feathering hinge), (B) Rotors with (bendingwise) flexible blade attachments and a feathering hinge, (C) Rotors with no hinges, (D) Rotors with flexible blade attachments,

(A) Rotors with (bending- and torsionwise) flexible blade attachments (and no feathering hinge),

What can be the advantage of a larger hinge offset? (A) Larger moments can be generated around the helicopter axes, (B) Lower drag force, (C) No ground resonance, (D) Larger forces can be generated,

(A) Larger moments can be generated around the helicopter axes,

What can be a disadvantage of a larger hinge offset? (A) Ground resonance, (B) Higher drag forces, (C) Unsteady airloads (e.g. turbulences) are felt more heavily by the passengers, (D) Smaller forces can be generated by the rotor,

See-saw rotors have zero hinge offset. In which situation is the helicopter more difficult to control? (A) Manoeuvres with increase of drag force, (B) Manoeuvres with a large positive load factor, (C) Manoeuvres which require a large lift force, (D) Manoeuvres with small or zero load factor,

(D) Manoeuvres with small or zero load factor,

Are see-saw rotors suitable for helicopters which need to be very manoeuvrable? (A) No, because control moments would be too large, (B) No, because control moments would be too small, (C) Yes, because control moments are very large, (D) Yes, because control moments are very small,

(B) No, because control moments would be too small,

Hingeless and bearingless rotors may have large hinge offset. In this case, are they suitable for helicopters which need to be very manoeuvrable? (A) No, because control moments are large, (B) Yes, because control moments are small, (C) Yes, because control moments are large, (D) No, because control moments are small,

How can the pilot control the amount of rotor thrust generated by the rotor on a conventional, modern helicopter? (A) By controlling the power available, (B) By acting on the cyclic pitch lever (stick), (C) By acting on the pedals, (D) By acting on the collective pitch lever,

(D) By acting on the collective pitch lever,

How can the pilot change the orientation of the trust force vector generated by the rotor? (A) By acting on the cyclic pitch lever (stick), (B) By acting on the collective pitch lever, (C) By acting on the pedals, (D) By controlling the power available,

(A) By acting on the cyclic pitch lever (stick),

What is the consequence of the pilot acting on the pedals? (A) Tail rotor thrust is modified by a change in tail rotor collective pitch, (B) Tail rotor thrust is modified by a change in tail rotor cyclic pitch, (C) Main rotor thrust is modified by a change in main rotor collective pitch, (D) Main rotor thrust is modified by a change in main rotor cyclic pitch,

(A) Tail rotor thrust is modified by a change in tail rotor collective pitch,

What can be said of the relative velocity on the rotor blades in forward flight, (A) The advancing and the retreating blade are immersed in air moving with the same velocity, (B) The retreating blade is immersed in higher velocity air, the advancing blade is immersed in lower velocity air, (C) The advancing blade is immersed in higher velocity air, the retreating blade is immersed in lower velocity air, (D) The relative velocity is uniform across the rotor disc,

What is the origin of the “lift dissymmetry” in forward flight on rotors without flapping hinges? (A) The identical relative air velocity on the advancing and the retreating blades, (B) The different relative air velocity on the advancing and the retreating blades, (C) Blade flexibility, (D) Blade stiffness,

(B) The different relative air velocity on the advancing and the retreating blades,

What is the reaction of an articulated rotor to a sudden horizontal wind component if not corrected by the pilot? (A) The rotor tilts in the same direction of the wind (this is called “flapback” when referred to wind from front), (B) The rotor tilts in the opposite direction, thus generating a thrust component opposite to wind, (C) The rotor does not react, (D) The rotor becomes unstable,

(A) The rotor tilts in the same direction of the wind (this is called “flapback” when referred to wind from front),

Consider a blade section. What is the “pitch” angle? (A) It is the angle angle between a reference line on the blade section and the induced velocity, (B) It is the angle between a reference line on the blade section and freestream velocity, (C) It is the angle angle between a reference line on the blade section and the relative velocity (freestream + rotation), (D) It is the angle between a reference line on the blade section and the plane of rotation (it is a purely geometric quantity),

(D) It is the angle between a reference line on the blade section and the plane of rotation (it is a purely geometric quantity),

Consider a blade section. Is pitch angle identical to angle of attack? (A) No, angle of attack depends only on induced velocity, (B) Yes, (C) No, angle of attack also depends on the direction of the relative velocity, (D) No, angle of attack is not defined for helicopters,

How would you describe the aerodynamics of the helicopter? (A) It is dominated by the rotor downwash, which generates large vortices and makes aerodynamic forces difficult to predict, (B) It is very similar to the one of fixed wing aircraft, with the rotor behaving exactly like a wing, and generating very small induced velocity, (C) It is dominated by the rotor downwash, which makes the rotor thrust force irregular and unsteady, (D) It is very similar to the one of fixed wing aircraft, with the rotor behaving exactly like a propeller generating very large but concentrated induced velocity,

(A) It is dominated by the rotor downwash, which generates large vortices and makes aerodynamic forces difficult to predict,

Are helicopters fast, compared to fixed wing aircraft (with similar payload)? (A) The flight envelope of both vehicles cover an almost identical speed range, (B) Yes, (C) No, they are normally slower, (D) It depends on the power available,

What are the physical phenomena which limit the helicopter maximum forward speed? (A) High Mach number of the flow around the retreating blade, (B) Compressibility effects on retreating blade and stall on advancing blade, (C) High Mach number of the flow around the advancing blade, (D) Compressibility effects on advancing blade and stall on retreating blade,

(D) Compressibility effects on advancing blade and stall on retreating blade,

Why is there an “avoid area” at low forward speed and low height from the ground? (A) To limit air pollution in proximity of the heliport, (B) Because it is difficult to initiate autorotation and complete an emergency landing in these conditions, (C) Because the pilot has little visibility on the heliport, (D) To avoid interference with air traffic,

(B) Because it is difficult to initiate autorotation and complete an emergency landing in these conditions,

Why is there an “avoid area” at high forward speed while flying in proximity of the ground? (A) Because the pilot has little visibility on the heliport, (B) To limit air pollution in proximity of the heliport, (C) Because it is difficult to initiate autorotation and complete an emergency landing in these conditions, (D) To avoid interference with air traffic,

Some commercial helicopters are designed to be fast. What could the maximum speed be? (A) About 150 kt, (B) About 250 kt, (C) Almost Mach 1, (D) About 50 kt,

(A) About 150 kt,

What is the function of the tail rotor? (A) Provide lateral and directional dynamic stability, (B) Provide additional forward thrust, (C) Provide torque balance, (D) Provide lateral and directional stability,

Some helicopters have multiple and large vertical tailplanes. What is their function? (A) Provide lower drag force, (B) Provide directional control, (C) Provide a support for the tail rotor, (D) Provide directional stability,

(D) Provide directional stability,

How can autorotation be defined? (A) It is a descent flight at zero collective pitch angle, (B) It is a working state of the rotor, whereby the helicopter can perform descent flight, (C) It is a descent flight, (D) It is a working state of the rotor, whereby thrust is generated without the need of engine power,

(D) It is a working state of the rotor, whereby thrust is generated without the need of engine power,

How is an emergency landing from horizontal flight performed? (A) Lower collective until the autorotative state is reached, descend in autorotation, perform flare manoeuvre, (B) Raise collective until the autorotative state is reached, descend in autorotation, (C) Lower collective until the autorotative state is reached, descend in autorotation, (D) Raise collective until the autorotative state is reached, descend in autorotation, perform flare manoeuvre,

(A) Lower collective until the autorotative state is reached, descend in autorotation, perform flare manoeuvre,

At which horizontal speed should the pilot initiate autorotation, if he/she is in the position to control horizontal speed? (A) Hover, (B) At V-max, (C) At V-best range or V-best endurance, (D) Hover, in ground effect,

What could be the advantage of performing autorotation at V-best range? (A) The pilot can save fuel, (B) The pilot can delay the impact by a few seconds, (C) The pilot can perform a more elegant flare, (D) The pilot has a wider choice for a landing spot,

(D) The pilot has a wider choice for a landing spot,

What can be said of isolated rotors’ stability with respect to translations and rotations? (A) They are statically unstable but dynamically stable, (B) They are statically stable but dynamically unstable, (C) They are statically and dynamically stable, (D) They are statically and dynamically unstable,

(B) They are statically stable but dynamically unstable,

Why can helicopters have a higher dynamical stability than isolated rotors? (A) Because of vertical (and, to a lesser extent, horizontal) tailplanes, (B) Because of the position of the centre of gravity, (C) Because of the presence of the swashplates, (D) Helicopters have a lower dynamical stability than isolated rotors.

(A) Because of vertical (and, to a lesser extent, horizontal) tailplanes,

What can be an important consequence of the dynamic instability of helicopters? (A) Performances are reduced, (B) A low pilot’s workload, (C) Flight safety is endangered, (D) A high pilot’s workload,

(D) A high pilot’s workload,

How is dynamic stability improved on most modern helicopters? (A) By means of the flapping hinges, (B) By means of electronic control systems, which sense the motion and act on rotor thrust, (C) By means of electronic control systems, which sense the motion and act on the rotor’s controls, (D) By means of lead-lag hinges,

How could dynamic rollover be defined? (A) Instability related to a roll maneuvre in the air, (B) Instability related to a roll maneuvre on the ground, (C) A landing technique, (D) Final phase of the emergency landing,

(B) Instability related to a roll maneuvre on the ground,

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