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.

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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:

= turn,

= for-/backward,

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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:

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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

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= for-/backward,

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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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= 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 is “blade sailing”? (A) An excessive rigid and elastic motion of rotor blades occurring when the rotor speed is low and the helicopter on the ground, (B) An excessive rigid and elastic motion of rotor blades occurring when the rotor speed is zero and the helicopter is airborne, (C) An excessive rigid and elastic motion of rotor blades occurring when the blades are damaged, (D) An excessive rigid and elastic motion of rotor blades occurring when the pilot has forgotten to switch on the centrifugal force,

(A) An excessive rigid and elastic motion of rotor blades occurring when the rotor speed is low and the helicopter on the ground,

The forces acting on a rotating blade are: (A) Inertial and centrifugal forces, (B) Aerodynamic forces, (C) Centrifugal forces, (D) Aerodynamic and centrifugal forces,

(D) Aerodynamic and centrifugal forces,

Explain the reason why co-axial helicopters do not have a tail rotor. (A) Co-axial rotors are counter rotating; the lift force transmitted by the gearbox to the rotors are consequently opposite, (B) Co-axial rotors are counter rotating; the torques (moments) transmitted by the gearbox to the rotors are consequently opposite, (C) Co-axial rotors are counter rotating and consequently the aerodynamic interaction is enough to guarantee torque balance, (D) Co-axial rotors are counter rotating and consequently generate lift force in opposite directions,

(B) Co-axial rotors are counter rotating; the torques (moments) transmitted by the gearbox to the rotors are consequently opposite,

Have rotorcraft drones (UAV) been popular in the recent years? (i.e. have many of them been sold?) (A) Yes, rotorcraft drones have been very successful for many different types of mission, (B) Yes, rotorcraft drones have been very successful but mainly as toys, (C) Yes, rotorcraft drones have been very successful but mainly for delivery service (e.g. Amazon), (D) Yes, rotorcraft drones have been very successful in spite of being very difficult to develop,

(A) Yes, rotorcraft drones have been very successful for many different types of mission,

Name two materials currently used in the manufacturing of (the structural parts of) rotor blades: (A) Aluminium alloy, rubber, (B) Wood, aluminium alloy, (C) Carbon-fibres, glass-fibres, (D) Steel, aluminium alloy,

When compared to fixed wing aircraft with similar payload, are helicopter more or less manoeuvrable (in terms of time necessary to achieve a given roll or pitch rate)? (A) Helicopters are normally much more manoeuvrable, (B) Helicopters are normally much less manoeuvrable, (C) Both vehicles are equally manoeuvrable, (D) Small helicopters are much less manoeuvrable, large helicopters are as manoeuvrable as fixed wing aircraft,

(B) Helicopters are normally much less manoeuvrable,

Are helicopters more or less aerodynamically efficient than fixed wing aircraft with similar payload? (A) Helicopters are much less efficient, aerodynamically, (B) Helicopters are only slightly less efficient, aerodynamically, (C) Helicopters are just as efficient, aerodynamically, (D) Helicopters are slightly more efficient, aerodynamically,

(A) Helicopters are much less efficient, aerodynamically,

Which options are available if, on ground, power available is lower than power required to hover in-ground-effect (for instance following a sudden temperature increase)? (A) Vertical take-off, (B) None, (C) Rolling take-off if permitted by the helicopter (e.g. wheeled landing gear or smooth ground), (D) Rolling take-off if permitted by the helicopter (i.e. the helicopter has a small wing),

What could be an unpleasant consequence of a horizontal wind component (from behind) on the ground while taking off? (A) Higher fuel consumption, (B) Vortex ring, (C) Lower fuel consumption, (D) Autorotation,

(B) Vortex ring,

Gyroplanes (also known as autogyros) are aircraft with a rotor and a propeller; what is the function of the rotor? (A) Generate lift in emergency landings (autorotation), (B) Generate drag force, (C) Generate thrust force (forward), (D) Generate lift force,

(D) Generate lift force,

What do helicopters and wind turbines have in common? (A) The rotors have very similar rotation speed, (B) Both rotors work in “vortex ring” state, (C) Both rotors can work in “windmilling” state, that is to say, they can absorb energy from the flow, (D) Both rotors can work in “windmilling” state, that is to say, they can dissipate energy into the flow,

What is ground effect? (A) An increase in aerodynamic efficiency when hovering / flying close to ground due to a high-pressure cushion, (B) A reduction in aerodynamic efficiency when hovering / flying close to ground due to a highpressure cushion, (C) A loss in stability when hovering / flying close to ground due to a high-pressure cushion, (D) A loss in manoeuvrability when hovering / flying close to ground due to a high-pressure cushion,

(A) An increase in aerodynamic efficiency when hovering / flying close to ground due to a high-pressure cushion,

Below which height from the ground is ground effect significant? (A) Approximately 100 m, (B) Approximately 20 x R, with R = rotor radius, (C) Approximately 0:2 x R, with R = rotor radius, (D) Approximately 2 x R, with R = rotor radius,

(D) Approximately 2 x R, with R = rotor radius,

Is ground effect beneficial or detrimental to helicopter flight? (A) Detrimental, you need more power to fly, (B) Beneficial, you can fly with less power, (C) Beneficial, controls are much more effective, (D) Detrimental, controls are much less effective,

(B) Beneficial, you can fly with less power,

What is a very important requirement for helicopters, which affects the design of rotor blades and blade tips in particular? (A) Noise, (B) Price, (C) Take-off mass, (D) Max speed,

(A) Noise,

How could we justify that low Disc Loading provides high aerodynamic efficiency in hover flight? (A) Power Loading, a measure of helicopter performance, increases when Disc Loading decreases. (B) Power Loading, a measure of aerodynamic efficiency, decreases when Disc Loading decreases. (C) Power Loading, a measure of aerodynamic efficiency, increases when Disc Loading increases. (D) Power Loading, a measure of aerodynamic efficiency, increases when Disc Loading decreases.

(D) Power Loading, a measure of aerodynamic efficiency, increases when Disc Loading decreases.

What is the relation between Induced Velocity and Disc Loading? (A) Induced Velocity is inversely proportional to the square root of Disc Loading. (B) Induced Velocity is proportional to the square root of Disc Loading. (C) Induced Velocity is independent of Disc Loading. (D) Induced Velocity is proportional to the square root of Disc Loading but only in forward flight.

(B) Induced Velocity is proportional to the square root of Disc Loading.

What is the best definition of Figure of Merit (FM) of a rotor? (A) FM compares the power required by a rotor to the power required by an ideal rotor without losses. (B) FM compares the power required by a rotor to the power required by an ideal rotor without Induced Velocity. (C) FM compares the power required by a rotor to the power required by a wing in order to generate the same Lift force. (D) FM compares the power required by a rotor to the power required by a rotor with infinite radius.

(A) FM compares the power required by a rotor to the power required by an ideal rotor without losses.

What is the relation between the Induced Velocity and the horizontal speed of a helicopter? (A) Induced Velocity tends to decrease with increasing horizontal helicopter speed but increases with increasing vertical helicopter speed. (B) Induced Velocity tends to increase with increasing helicopter speed. (C) Induced Velocity is independent of helicopter speed. (D) Induced Velocity tends to decrease with increasing helicopter speed.

(D) Induced Velocity tends to decrease with increasing helicopter speed.

How could the Vortex Ring (VR) flight condition be described best? (A) VR refers to an unstable rotor condition where irregular air re-circulation through the rotor disc is due to the fact that Induced Velocity and horizontal speed have a comparable magnitude. (B) VR refers to a dangerous but stable rotor condition where irregular air re-circulation through the rotor disc is due to the fact that Induced Velocity and Rate of Descent have a comparable magnitude. (C) VR refers to an unstable rotor condition where irregular air re-circulation through the rotor disc is due to the fact that Induced Velocity and Rate of Descent have a comparable magnitude. (D) VR refers to an unstable rotor condition where mast bumping is due to the fact that Induced Velocity and Rate of Descent have a comparable magnitude.

(C) VR refers to an unstable rotor condition where irregular air re-circulation through the rotor disc is due to the fact that Induced Velocity and Rate of Descent have a comparable magnitude.

Tail wind during the approach may cause the helicopter to enter the Vortex Ring condition. This is due to tail wind increasing the amount of air flowing through the rotor disc upwards (from below the rotor disc to above it). How could this lead to Vortex Ring? (A) Tail wind increases helicopter speed. (B) Wind may be turbulent. (C) Tail wind artificially decreases the rate of descent. (D) Tail wind artificially increases the rate of descent.

(D) Tail wind artificially increases the rate of descent.

How can the Windmilling state be best described? (A) Blade pitch angle and rate of descent are such that the aerodynamic forces generated drives the rotor. (B) Blade pitch angle and rate of descent are such that the aerodynamic forces generates the lift required. (C) Blade flapping angles and rate of descent are such that the aerodynamic forces generated drives the rotor. (D) Blade pitch angle and rate of descent are such that the aerodynamic forces are zero.

(A) Blade pitch angle and rate of descent are such that the aerodynamic forces generated drives the rotor.

What is at the origin of the asymmetry of aerodynamic forces in forward flight? (A) The combination of rate of descent and forward speed, observed in a frame of reference rotating with the blade. (B) The combination of rotation and rate of descent, observed in a frame of reference rotating with the blade. (C) The combination of rotation and forward speed, observed in a frame of reference rotating with the blade. (D) The combination of rotation and forward speed.

What is the relation between flapping and a blade’s angle of attack? (A) The angle of attack does not depend on flapping. (B) The angle of attack decreases, when a blade flaps upwards. (C) The angle of attack decreases, when a blade flaps upwards, but only in hover flight. (D) The angle of attack increases, when a blade flaps upwards.

(B) The angle of attack decreases, when a blade flaps upwards.

What are the causes of the so-called “flapback” of the rotor in forward flight? (A) Flapback normally indicates the excessive flapping of the blades due to lift asymmetry in forward flight. (B) Flapback normally indicates the tilting backwards of the rotor disc due to the pilot operating on the longitudinal cyclic pitch control. (C) Flapback normally indicates the tilting backwards of the rotor disc due to compressibility effects. (D) Flapback normally indicates the tilting backwards of the rotor disc due to lift asymmetry in forward flight.

(D) Flapback normally indicates the tilting backwards of the rotor disc due to lift asymmetry in forward flight.

Which physical phenomena may be listed among the compressibility effects on the advancing blade? (A) Generation of a shock wave on the outboard part of the blade, significant increase of the drag force and possibly separation of the boundary layer. (B) Generation of a shock wave on the inboard part of the blade, significant increase of the drag force and possibly separation of the boundary layer. (C) Stall due to excessive angle of attack of the outboard part of the blade and significant increase of the drag force. (D) Generation of shock waves along the blade and strong increase of Induced Velocity.

(A) Generation of a shock wave on the outboard part of the blade, significant increase of the drag force and possibly separation of the boundary layer.

Are compressibility effects relevant on the retreating blade? (A) Not in the normal range of helicopter speed, as Mach number on the retreating blade is limited. (B) Not in the normal range of helicopter speed, even if Mach number on the retreating blade may also reach values of 0.7 – 0.8. (C) As the helicopter approaches its max horizontal speed, Mach number on the retreating blade may be close to 1.0. (D) Not in the normal range of helicopter speed, as the flow on the whole retreating blade is always stalled.

(A) Not in the normal range of helicopter speed, as Mach number on the retreating blade is limited.

What is the action of the collective pitch control on the blades’ angle of attack? (A) Collective pitch control does not affect the angle of attack but only the pitch angle. (B) Collective pitch control increases the pitch angle on all blades simultaneously and hence it decreases the angle of attack. (C) Collective pitch control increases the pitch angle on the retreating blade and hence also the angle of attack on that blade. (D) Collective pitch control increases the pitch angle on all blades simultaneously and hence also the angle of attack.

(D) Collective pitch control increases the pitch angle on all blades simultaneously and hence also the angle of attack.

The tip of the advancing blade is the rotor area where the highest relative airspeed is observed in forward flight. What might be the phenomena affected by the tip geometry at high speed? (A) Strength and the position of the tip vortex. (B) Strength and position of the shock wave. (C) Strength and position of the shock wave and the position of the tip vortex. (D) Separation of the boundary layer.

As a results of the physical phenomena mentioned in the previous question, which environmental aspects may be strongly affected by the blade tip geometry? (A) Generation of noise. (B) Autorotation performance. (C) Generation of noise and safety for ground personnel. (D) Generation of noise, safety for ground personnel and Autorotation performance.

(A) Generation of noise.

What are the causes of the blade rotation about the lead/lag hinge? (A) The pitching of the blade (due to gyroscopic effects) and the drag force. (B) The flapping of the blade (due to gyroscopic effects) and the drag force. (C) The flapping of the blade. (D) The cyclic pitch control.

(B) The flapping of the blade (due to gyroscopic effects) and the drag force.

How can the rotor disc (tip-path-plane) be oriented by the pilot? (A) By means of the cyclic pitch control which lets the blades rotate about the pitch axis. (B) By means of the collective pitch control which lets the blades flapping. (C) By means of the cyclic pitch control which lets the blades lead/lagging. (D) By means of the cyclic pitch control which lets the blades flapping.

(D) By means of the cyclic pitch control which lets the blades flapping.

Is the rotation of the main rotor blades about the flapping hinges free or constrained (= fixed) during the flight? (A) Free. The moment of the aerodynamic forces about the flapping hinge is balanced by the centrifugal forces. (B) Free. The moment of the aerodynamic forces about the flapping hinge is balanced by Coriolis forces. (C) Mechanically constrained. The moment of aerodynamic forces about the flapping hinge is balanced by the centrifugal forces. (D) Mechanically constrained, otherwise the blades would flap excessively.

(A) Free. The moment of the aerodynamic forces about the flapping hinge is balanced by the centrifugal forces.

How is the amplitude of longitudinal flapping of tail rotors blades in forward flight normally kept within a reasonable range (= limited)? (A) By manually operating the tail rotor longitudinal cyclic pitch control. (B) By the use of an electronic control system. (C) By mechanically coupling flapping and pitching so that flap-up causes a pitch angle reduction. (D) By reducing the helicopter speed.

How can Ground Resonance (GR) be best described? (A) GR is a dynamic instability caused by a coupling of the blades lead/lag motion and the oscillations of the helicopter on the landing gear, on the ground. (B) GR is a dynamic instability caused by the oscillations of the helicopter on the landing gear, on the ground. (C) GR is a dynamic instability caused by a coupling of the blades lead/lag motion and the oscillations of the helicopter in flight. (D) GR is a dynamic instability caused by a coupling of the rotor head motion and the oscillations of the helicopter on the landing gear, on the ground.

(A) GR is a dynamic instability caused by a coupling of the blades lead/lag motion and the oscillations of the helicopter on the landing gear, on the ground.

How is Ground Resonance generally prevented on modern helicopters? (A) Hydraulic dampers are installed on the main rotor head (about the lead/lag hinges). (B) Hydraulic dampers are installed on the main rotor head (about the lead/lag hinges) as well as on the landing gear suspensions. (C) Hydraulic dampers are installed on the landing gear suspensions. (D) Hydraulic dampers are installed on the main rotor head (about the lead/lag hinges), on the landing gear suspensions as well as on the tail rotor head (about the flapping hinge).

(B) Hydraulic dampers are installed on the main rotor head (about the lead/lag hinges) as well as on the landing gear suspensions.

What are the functions of Swashplates (= Taumelscheiben)? (A) Swashplates position and orientation determine the angle of attack of all blades. (B) Swashplates rotation around the rotor mast determines the pitch angles of all blades. (C) The fixed swashplate determines the collective pitch angle, the rotating swashplate determines the cyclic pitch angle. (D) Swashplates position and orientation determine the pitch angles of all blades.

(D) Swashplates position and orientation determine the pitch angles of all blades.

Can Ground Resonance also occur on helicopters without a semi-rigid rotor head (see-saw)? (A) It depends on the type of landing gear. (B) No. (C) Yes. (D) Yes, but only if one or more hydraulic dampers are defective.

(B) No.

Why are Tail Rotors normally equipped with collective pitch control? (A) To control the force generated by the Tail Rotor. (B) To control the power required by the Tail Rotor. (C) To control the orientation of the Tail Rotor disc. (D) To control the longitudinal flapping of the Tail Rotor.

(A) To control the force generated by the Tail Rotor.

What is the phase delay between flapping and lead/lagging (lead/lagging following flapping)? (A) Normally approximately 45°. (B) Normally approximately 180°. (C) Almost zero. (D) Normally approximately 90°.

(D) Normally approximately 90°.

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