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In forward flight, the relative air speed around rotor’s blades depend on the blade position:

the relative airspeed around the advancing blade is higher, the relative airspeed around the retreating blade is lower,

the relative airspeed around the advancing blade is lower, the relative airspeed around the retreating blade is higher,

the relative airspeed around the front blade is lower, the relative airspeed around the back blade is higher,

he relative airspeed around the back blade is lower, the relative airspeed around the front blade is higher,

What is the most relevant consequence of different airspeed values in different blade positions?

different pitch angles,

different lead/lag angles and hence different lift forces,

different dynamic pressure values and hence different aerodynamic forces,

different dynamic pressure values and hence different centrifugal forces,

What is the relation between lift dissymmetry (= lift forces changes with blade position) and the flapping motion of the blade?

flapping motion changes the dynamic pressure and therefore compensate lift dissymmetry,

flapping motion changes the angle of attack and may therefore worsen the effect of different dynamic pressure values,

flapping motion changes the angle of attack and may therefore balance the effect of different dynamic pressure values,

none, the two physical quantities are unrelated,

What can be said about the lift forces generated by a perfectly rigid rotor with no hinges?

All blades generate an identical lift force,

The advancing blade generates a greater lift force,

The retreating blade generates a greater lift force,

The advancing and the retreating blades generate larger lift forces than the front and back blades,

What happens when horizontal wind starts blowing onto an articulated rotor in hover? (Assume that the pilot does not act on the controls)

The rotor does not react,

The collective pitch increases on all blades,

The rotor tilts in the same direction as the wind (this is called “flapback”),

The rotor tilts in the opposite direction, thus generating a thrust component opposite to wind,

What is the pitch angle of a blade section?

The angle between a reference line of the blade section (typically, the chord) and the relative velocity vector,

The angle between a reference line of the blade section (typically, the chord) and a reference plane (typically, the plane of rotation),

The angle between the longitudinal axis of the blade and the plane of rotation,

The angle between a reference line of the blade section (typically, the chord) and the centrifugal force vector,

Does induced velocity affect rotor aerodynamics in forward flight?

Yes, induced velocity is smaller than in hover but its effects are not negligible: it reduces the angle of attack,

Yes, induced velocity is smaller than in hover but its effects are not negligible: it increases the angle of attack,

es, induced velocity is greater than in hover and its effects are very significant: it reduces the angle of attack,

Yes, induced velocity is greater than in hover and its effects are very significant: it increases the angle of attack,

The max horizontal speed reached by a conventional helicopters is normally around 140-160knots. What are the physical causes which limit the max speed to such low values?

Compressibility effects on advancing blade and stall on retreating blade,

Compressibility effects on retreating blade and stall on advancing blade,

Compressibility effects and consequently stall of the advancing blade,

Compressibility effects and consequently stall of the retreating blade,

The point of theoretical autorotation is a working state of the rotor, in which the blades . . .

..generate lift at zero power available,

..generate zero lift,

..generate lift at zero pitch angle,

...generate lift at zero induced velocity,

The term autorotation normally indicates an emergency manoeuvre. This manoeuvre can be de- scribed as: . . .

A fast descent with engines on, followed by a flare which reduces the helicopter horizontal and vertical speed components in order to allow a soft touchdown,

A fast descent with engines shut off or disconnected from the rotors, followed by a flare which reduces the helicopter horizontal speed component,

A fast descent with engines shut off or disconnected from the rotors, followed by a flare which reduces the helicopter horizontal and vertical speed components in order to allow a soft touchdown,

A fast descent with engines shut off or disconnected from the rotors, followed by a flare which reduces the helicopter vertical speed component in order to allow a soft touchdown, ,

An avoid area on a V-h diagram represents a range of height and speed values, which sould beavoided by the pilot. In particular, an avoid area at low forward speed and low height from the ground is indicated on the flight manual of many helicopters. What are the physical reasons?

The reduced visibility above the heliport,

The need to avoid interference with air traffic,

The need to limit air pollution in proximity of the heliport,

It is difficult to initiate autorotation and complete an emergency landing in these condi- tions,

An avoid area on a V-h diagram represents a range of height and speed values, which sould beavoided by the pilot. In particular, an avoid area at high forward speed in proximity of the ground is indicated on the flight manual of many helicopters. What are the physical reasons?

The reduced visibility above the heliport,

It is difficult to initiate autorotation and complete an emergency landing in these condi- tions,

The need to limit air pollution in proximity of the heliport,

The need to avoid interference with air traffic,

What is the advantage of performing autorotation at V–best endurance?

V-best endurance normally corresponds to the minimum of the power required curve; at this speed the descent rate for autorotation is therefore minimal,

V-best endurance normally corresponds to the minimum of the power required curve; at this speed the descent rate for autorotation is therefore maximal,

V-best endurance normally corresponds to the maximum of the power required curve; at this speed the descent rate for autorotation is therefore minimal,

-best endurance normally corresponds to the maximum of the power required curve; at this speed the descent rate for autorotation is therefore maximal,

What could be the advantage of performing autorotation at V-best range?

The descent rate for autorotation is minimal,

The descent rate for autorotation is maximal,

The duration of the descent can be maximized,

The pilot can select the best landing spot within a larger area,

The Sikorsky X-2 prototype is based on a concept with two counter-rotating, co-axial, rigid (without flapping hinges) rotors. How is the problem of lift-dissymmetry (= advancing blade generating more lift than retreating blade) solved, without flapping hinges?

Lift dissymmetry is prevented by lead/lag hinges,

Since there are two counter-rotating and co-axial rotors, lift dissymmetry of one rotor is compensated by the lift-dissymmetry of the other,

Both rotors generate lift dissymmetry, which cannot be compensated; it is a very bad concept,

Rigid rotors do not generate lift-dissymmetry since there are no flapping hinges,

The (then) Eurocopter X-3 prototype (now, Airbus Helicopters) is based on a concept with one conventional articulated main rotor, a small wing and two propellers (which provide yaw control). How is the problem of lift-dissymmetry (= advancing blade generating more lift than retreating blade) alleviated (= reduced) at higher speed?

At high speed the propellers generate the largest part of the lift, the main rotor is consequently partially offloaded; this reduces the effects of the lift-dissymmetry,

It cannot be compensated; it is a very bad concept,

At high speed the wing generates the largest part of the lift, the main rotor is conse- quently partially offloaded; this reduces the effects of the lift-dissymmetry,

At high speed the wing generates the largest part of the lift, the main rotor is consequently overloaded; this reduces the effects of the lift-dissymmetry,

The tail rotor of a conventional helicopter generates a controllable lateral force. Its functions are therefore:

allowing the pilot to control the helicopter around the yaw axis,

allowing the pilot to control the helicopter around the yaw axis and balancing the rotor torque,

balancing the rotor torque,

supporting the pilot in manoeuvres,

In conventional helicopters, at higher speed, the main rotor torque may be picked up (= reacted) by the moment generated by two lateral forces: the one generated by the tail rotor and the one generated by . . .

..the main rotor,

..the vertical tail (fin),

.the fuselage

..the landing gear,

Co-axial helicopters are often slow because the two rotor heads generate large drag forces. How- ever, they also have advantages, for instance they do not need a tail rotor because . . .

. the large drag force is sufficient to prevent the helicopter from rotating around the yaw axis,

...the two engines are counter rotating,

..the two main rotors are counter-rotating,

. the swashplates are mounted in a clever way,

Rotor blades were manufactured out of light metal alloys until the 1980s. Afterwards, blades have been manufactured out of . . .

.carbon-fibresandglass-fibrescomposites,

...steel and titanium,

..magnesium alloy,

..sandwich elements,

From an engineering standpoint (materials, type of structural components), the fuselage of a heli- copter may be similar to the one of a fixed wing aircraft of comparable payload. In which cases is this similarity more evident?

Smaller helicopters,

Expensive helicopter,

Cheap helicopters,

Larger helicopters,

Manoeuvrability can be assessed as the period of time necessary for the helicopter to reach a given rotation rate (around the principal axes) following pilot’s input. 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)?

Both vehicles are equally manoeuvrable,

Small helicopters are much less manoeuvrable, large helicopters are as manoeuvrable as fixed wing aircraft,

Helicopters are normally much less manoeuvrable,

Helicopters are normally much more manoeuvrable,

The aerodynamic efficiency of an aircraft can be assessed in various ways, one of them is to mea- sure L/D (lift over drag ratio). Lift-over-drag can also be measured for helicopters. Let us consider a medium size helicopter, designed for passenger transportation, and a fixed-wing aircraft with com- parable payload, also designed for passenger transportation. How do the L/D values of the two vehicles compare?

Helicopters’ L/D is always zero,

The helicopter’s L/D is lower,

The two values are very close to each other,

The helicopter’s L/D is higher,

Let us assume that on a given day and place, the power available on a helicopter is slightly lower than the power required to hover OGE (out-of-ground effect). A regular take-off, starting vertically and stabilizing the flight in a hover, is therefore not possible. Assuming that the helicopter can perform a rolling take-off, would this manoeuvre allow taking off and continuing the flight safely?

Yes,

It would allow taking-off but not continuing flying, since power required increases from hover into forward flight,

It depends on the ability of the pilot, the whole manoeuvre is possible only if performed in ground effect,

No,

Let us assume that a helicopter suddenly and unexpectedly finds itself immersed into a strong back wind (a horizontal wind component from behind) right after lifting off and transitioning towards forward flight. Why can this condition lead to vortex ring and be therefore potentially very dangerous? Assume that the rotor is tilted forward at the moment when the wind starts blowing.

Since the wind blows from behind, it blows in the same direction of induced velocity and may increase the mass rate through the rotor,

Since the wind blows from behind, it is deviated by the fuselage and may prevent the air from smoothly flowing through the rotor,

The wind may affect the tail rotor and reduce its thrust force; the helicopter may then start turning around the yaw axis, causing the rotor to slow down,

Since the wind blows from behind, it opposes induced velocity and may prevent the air from smoothly flowing through the rotor,

Ground effect is an aerodynamic phenomenon which consists of a high pressure cushion generated by the ground deviating and slowing down the flow. As far as helicopters are concerned, ground effect changes the relation between thrust and power required (to generate that thrust). In practical terms, what does it mean exactly?

A helicopter may require a greater thrust force in order to hover, in ground effect,

The generation of a given thrust force requires more power, in ground effect,

The generation of a given thrust force requires exactly the same power, in ground effect,

The generation of a given thrust force requires less power, in ground effect,

Over the past 30 years a number of human-powered helicopters have been built by students teams. Geometries and mechanics varied among the different machines. However, two main effects have been exploited in all cases:

High disc loading and the efficiency of carbon fibres composites,

Low disc loading and ground effect,

High disc loading and ground effect,

Coanda effect and ground effect,

When flying in close proximity to the ground, for instance with the rotor hub at a height h = R from the ground, where R is the rotor radius, is ground effect noticeable to the pilot?

Yes, ground effect may reduce power required by as much as 80%,

Yes, ground effect may reduce power required by as much as 30%,

Not always, ground effect may reduce power required by 5% at the most,

No, ground effect may affect power required by less than 1%,

Even in a flight simulator, starting to fly a helicopter gives an “uneasy” feeling. What could be the relevant factors, that determine this impression?

The degrees of freedom (pitch, roll, yaw) are coupled, the helicopter responds to con- trols with a certain lag,

The degrees of freedom (pitch, roll, yaw) are coupled,

The helicopter responds to controls with a certain lag,

The degrees of freedom (pitch, roll, yaw) are coupled, the helicopter responds to controls with a certain lag, it is difficult to keep the rotational speed of the rotor within the acceptable range,

In a flight simulator, for a beginner, trying to keep the helicopter in a hover . . .

..is easy and intuitive,

. . is normally done automatically by the SAS (Stability Augmentation System), as in real heli- copters,

. is easy because the degrees of freedom (pitch, roll, yaw) are uncoupled,

...is neither easy nor intuitive,

Which statement is true about helicopter gearboxes?

Gearboxes are very unreliable,

Gearboxes are the same used for fixed wing aircraft,

Gearboxes are complex mechanical devices,

Gearboxes have a reduction ratio of over one million.

How many and which gearboxes are there on a conventional helicopter (i.e. with a main rotor and a tail rotor)?

Only one: main gearbox,

Three: main, intermediate and tail gearboxes,

Two: main and tail gearboxes,

Two: left and right gearboxes,

Which statement is true about helicopter engines?

Helicopter engines are turboshaft engines designed for use on helicopters,

Helicopter engines are turboprop engines designed for use on helicopters,

Helicopter engines are turboshaft engines, identical to those used on fixed wing aircraft,

Helicopter engines are piston engines designed for use on helicopters,

What are typical requirements for helicopter engines?

No air cooling available, high power setting for long times, large pitch and bank angles,

No air cooling available, low power setting for long time, large pitch and bank angles,

Air cooling instead of oil cooling, large pitch and bank angles,

Air cooling instead of oil cooling, large pitch and bank angles, low power settings,

Does a helicopter pilot need to control the power setting manually, on modern turbine helicopters?

Yes, with the throttle installed on the collective pitch lever,

No, power setting is fixed on helicopters,

Yes, like on fixed wing aircraft,

No, a control system called FADEC controls the engines power setting,

What is the function of a helicopter turboshaft engine?

Providing mechanical power to the turbine,

Providing mechanical power to main and tail rotor,

Providing mechanical power to the main rotor,

Providing mechanical power to the rotors through the gearbox,

Where are helicopters engines installed?

In the front part of the fuselage for air cooling,

Usually on the upper side of the fuselage (helicopter roof), close to the main gearbox,

Usually inside the helicopter cabin (fuselage) for balance reasons,

Halfway between main and tail rotor to minimize the length of the drive system,

Advantages of wheeled landing gears (with respect to skid landing gears) are:

Lower maintenance costs, no ground resonance,

Lower mechanical complexity, easier hangaring, comfort,

Easier hangaring, taxiing, rolling take off and landing, comfort,

Easier hangaring, lower weight, less maintenance,

Advantages of skid landing gears (with respect to wheeled landing gears) are:

Lower weight and maintenance costs,

Better comfort,

Easier hangaring,

Rolling take off possible,

Are landing gears related to ground resonance?

Yes, landing gears instability is the cause of ground resonance,

Yes, the dynamics of the helicopter on the ground also depends on the landing gear,

No, ground resonance only depends on the rotor,

No, ground resonance only depends on the blades,

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