Principles of Flight (Helicopter)

Which ratio corresponds to the rotor disc loading?. Rotor disc / helicopter mass. Rotor thrust / rotor disc. Rotor thrust / rotor disc. Helicopter mass / rotor disc.

What causes the phase lag between the displacement and the flapping of a rotor blade?. Rounding of the rotor blade tips. Inertia, mass, and aerodynamic forces. Friction in the rotor blade spindles. Advance or retreat angle of 90°.

If the critical angle of attack is exceeded, the... transition point starts moving towards the airflow direction. boundary layer on the upper side of the rotor blade begins to separate. boundary layer on the lower side of the rotor blade begins to separate. laminar boundary layer turns into a turbulent boundary layer.

What types of airflow can be observed around a rotor blade aerofoil?. Laminar airflow on the entire upper surface. Laminar airflow at the leading edge, turbulent airflow further back. Turbulent airflow at the leading edge, laminar airflow further back. Turbulent airflow on the entire upper surface.

What is the advantage of a turbulent airflow compared to a laminar airflow at an aerofoil with a high angle of attack?. It has a thinner boundary layer. It has no form drag. The separation point moves further forward. It adheres to the aerofoil for a longer time.

The virtual rotation axis of a rotor is... perpendicular to the hub plane. parallel with the main rotor shaft. perpendicular to the tip path plane. perpendicular to the plane which contains the swash plate.

The effective angle of attack is the angle between... chord line and tip path plane. effective airflow and chord line. tip path plane and rotor blade. effective airflow and tip path plane.

What kind of drag is caused by a lift-producing aerofoil?. Parasite drag. Frictional drag. Interference drag. Induced drag.

What force affects the braking torque of the rotor in cruise?. Inclined forward lift. Upward directional rotor thrust. Inclined forward drag force. Inclined rearward tangential force.

The rotor thrust is... perpendicular to the tip path plane. opposite to the rotation of the rotor blade element. parallel with the main rotor shaft. perpendicular to the hub plane.

What happens to thrust and tangential force if the rotor RPM decreases by about 10 % in cruise flight?. The thrust and the tangential force decrease. The thrust and the tangential force increase. The thrust decreases and the tangential force remains constant. The thrust remains constant and the tangential force increases.

The effective airflow velocity of a rotor blade element varies with the distance from the rotor shaft axis, because the... peripheral speed increases if the displacement to the rotor blade tip decreases. helicopter airframe disturbs the airflow. tangential force and airflow reversal vary. drag force in direction of the rotaion axis is increased.

Which of the stated relationships between lift and drag applies best for a flying helicopter (lift : drag)?. 1:45. 1:2. 2:1. 45:1.

The reason for a stall at a given pitch angle can be... constant peripheral speed and great vertical airflow through the rotor. smaller vertical airflow through the rotor and constant peripheral speed. smaller effective angle of attack and small peripheral speed. smaller frontal resistance and turbulent airflow.

The neutral point is a point where... the aerodynamic forces act torque-free. the imaginary axes of a helicopter meet each other. the entire helicopter mass can be assumed to attack. the torque at the chord line remains constant for changing angles of attack.

What shape of a rotor blade has a positive impact on the lift distribution?. Rectangular blade with a geometric setting of 1°. Double trapezoidal rotor blade with a radius at the blade tip. Trapezoidal blade without radius at the blade tip. Rectangular trapezoidal blade with no aerodynamic twist.

The rotor blade shape takes effect on the... lift distribution. rotor head used. noch sensitivity. structural take-off mass.

The drive system of the autogyro's main rotor is based on... the speed of the airflow. a fan in the cabin. an engine in the cabin. an engine at the rotor blade tip.

The rotor RPM is kept constant in the helicopter by the engine RPM. It can be influenced by the... cyclic stick. throttle and the governor. starter and the impulse coupling. collective.

The beam theory enables statements about the... energy conversion in an autorotation. power requirements during hover flight. transition lift close to the ground. drag in cruise flight.

During hover flight, the induced airflow velocity... is equal above and below the rotor. increases further having passed the rotor. remains constant after having passed the rotor. decreases after having passed the rotor.

Why is a helicopter's climb initially accelerated after an increase of the pitch angle?. The larger pitch angle causes a decrease and a compression of the airflow until the climb rate corresponds to the induced velocity through the main rotor disc. The inertia of the air increases the effective angle of attack temporarily until an additional component of the climb rate reduces the effective angle of attack again. The initially high airflow increases the rotor thrust until the lower air density reduces the rotor thrust again. The conversion of energetic air into kinetic rotor energy decreases continuously with increasing density altitude.

A helicopter with a rotor turning in an anti-clockwise direction seen from above, hovers sideways to the right. What is the azimuth angle where the main rotor blades have the biggest pitch angle?. 270°. 180°. 90°. 0°.

The airframe of an accelerating helicopter continues to bend until the... horizontal thrust component equals the drag. thrust passes in front of the centre of gravity. vertical thrust component equals the drag. thrust passes behind the centre of gravity.

What is the reason for retreating blade stall?. Large centrifugal forces of the peripheral speed. Small cone angle and constant peripheral speed. Large pitch angle and small effective airflow. Small pitch angle and large effective airflow.

The induced airflow on the rotor of a helicopter in level flight has the greatest value at the... rear rotor area. advancing rotor blade. retreating rotor blade. front rotor area.

Which option describes the term "asymmetric airflow"?. During cruise flight the advancing rotor blade has more airflow than the retreating rotor blade. The displacement of the driving forces to the advancing rotor blade in a vertical autorotation. The difference in required performance during hover in and out of ground effect. The greater lift in the outer region of the rotor as opposed to the inner region.

The transitional lift can be noticed by... an aural warning. strong load factors. vibrations. a loss of engine rpm.

Which statement about the rotor disc loading in a horizontal curve is correct?. It decreases with increasing bank angle. It increases with increasing bank angle. No change in relation to the cruise flight. Effects depend on the type of helicopter.

What action is necessary in a modern helicopter during the transition to a horizontal turn?. A control column movement forward or raising the collective. Open the throttle in a helicopter with a rotor turning in an anti-clockwise direction seen from above. Open the throttle in a helicopter with a rotor turning in a clockwise direction seen from above. A control column movement backward or raising the collective.

Why does a stall begin on the retreating rotor blade at high cruise speeds?. The airflow reaches subsonic speed and causes an increase of the induced drag. The small pitch angle and a relatively low peripheral speed cause a small effective angle of attack. The large pitch angle and relatively low peripheral speed cause a large effective angle of attack. The airflow reaches supersonic speed and causes an increase of the parasite drag.

Without corrective moves, a helicopter hovering in ground effect in no-wind conditions, will execute... pitching motion about the centre. fast yaw motions. rolling movements to about 60°. slight upward and downward movements.

The ground effect is noticeable by... strong vertical oscillations. strong horizontal vibrations. larger power requirements. lower power requirements.

What can be expected during a hover flight in ground effect within a forest glade?. Useful ground effect caused by a smaller induced airflow. No air turbulence through the slipstream and stable attitude. Aspiration of the tail rotor in the direction of the forest and a performance gain. Recirculation of air masses and an impairment of the ground effect.

Which landing site (no wind) prevents the impairment of the ground effect?. Plain terrain. Narrow forest glade. Elevated helipad. Sloping ground.

What is the result of the vortex ring state?. The helicopter is more stable. The helicopter loses power. The sink rate increases uncontrollably. The rotor RPM increases.

What is the correct way to counteract the vortex ring state?. Raise collective and decrease rotor RPM. Raise collective and pull back the stick. Try to gain airspeed and enter autorotation. Open throttle and pull back the stick.

What is the effect of vortex ring state?. High rate of descent and irregular pitch, roll, and yaw motions. Stable descent and high-frequency vibrations in the helicopter. Decreased rate of descent and strong vibrations from the engine. Fluctuations in rotor and engine RPM.

What is the risk arising in a vertical autorotation with a subsequent increase in airspeed prior to the landing?. High rotor RPM. Vortex ring state. Loss of the tail rotor efficiency. Misjudgement when increasing the airspeed.

What is the reason for the driving forces in an autorotation?. Downward tilted effective airflow. Low rate of descent. Increased pitch angle. High airspeeds.

During an autorotation the airspeed is limited by... the displacement of the stall regions in the inner area of the rotor blade. the interference drag during low rates of descent. the landing gear during the touchdown. the drift of the driving forces on the returning blade.

Which of the following options has an effect on the autorotation characteristics?. Smoothly working tail rotor control and low RPM warning systems. Air temperature and wind speed. Pressure altitude and wind speed. Helicopter mass and density altitude.

During an autorotation with forward speed of a helicopter the driving forces are located in the... region of the retreating rotor blade. inner region. outer region. region of the advancing rotor blade.

During an autorotation a helicopter accelerates from 60 to 90 knots without further corrections. The rotor RPM will... remain constant. decrease. vary. increase.

What action has no effect on the rotor RPM in an autorotation?. Utilisation of friction brake. Centre of gravity displacement. Pitch angle change. Transition into a turning flight.

After entering an autorotation a large helicopter mass leads to... a rapid collapse of the rotor RPM. a rapid build-up of the rotor RPM. a large change in center of gravity. a small rate of descent in a vertical autorotation.

What shall be considered before terminating a turn in an autorotation?. The Coriolis force causes an increase in the main rotor rpm. The pitch angle must be decreased by using the collective pitch lever again. The decreasing gravity relieves the main rotor and the helicopter cabin. The flight velocity shall be increased to obtain all the kinetic energy.

Which energies serve to maintain the rotor rpm in an autorotation?. Potential or kinetic energy. Mechanical or chemical energy. Rotational and linear energy. Frictional and flow energy.

The maximum range in an autorotation will be achieved by... a relatively low effective angle of attack. a neutral effective angle of attack. a relatively high effective angle of attack. a negative effective angle of attack.

Why does a flare during an autorotation generate higher rotor RPM?. The pitch angle increases. The vertical airflow through the rotor disc increases. The tangential force tilts backwards. The ground effect leads to better performance.

Which movement is caused by the Coriolis effect on the advancing rotor blade?. Mass movement outwards. Drag movement forwards. Tilt movement backwards. Flapping downwards.

Which factor affects the available response time to initiate an autorotation after engine failure?. Movement of the pressure point. Functionality of the coupling. Inertia of the main rotor system. Profile shape of the rotor blades.

Which statement about the required force to change the pitch angle is correct?. It is the smallest by using an advance angle of 90°. It is the smallest by using a delta-three-hinge. It must be greater than the rotor disc loading. It must be greater than the tangential force.

Why do helicopters with a semi-rigid rotor system react slower than others?. The central flapping hinge does not transmit any moments. The missing lag hinges cause a rotor imbalance. The lowered attachment of the rotor blades allows a transmission of forces. The angled lag hinges prevent the transmission of aerodynamic forces on the helicopter frame.

The pitch angle of a tail rotor blade is changed... cyclically. collectively. symmetrically. asymmetrically.

A delta-three hinge is used to allow... for a decreased pitch angle at an upwards flapping blade. the advancing blade to flap up about the hinge. the advancing blade to lead about the hinge. the advancing blade to drag about the hinge.

What needs to be observed in conjunction with a temporary loss of tail rotor efficiency in a stationary hover?. Vortex ring stage of the tail rotor. Rotating movement in the main rotor direction. Loss of the main rotor thrust. Mechanical blockage of the control.

What is caused by an increase of stability in a helicopter?. An optimization of the maximum helicopter mass. An enhance of control under negative load factors. A decrease of the required control forces. An increase of general flight safety.

What is caused by an increase of stability in a helicopter?. A decrease of the required control forces. A relief of the pilot in command. An enhance of control under all load factors. An optimization of the maximum helicopter mass.

Why are the stability criteria of a helicopter very important?. Low stability reduces the available control forces. High stability prevents low load factors. A lack of stability may lead to loss of control. Large stability increases the maximum take-off mass.

The helicopter's stability is increased by... reducing the rotor RPM. attaching a stabilizer. pivoting the drag hinge. decreasing the rotor mass.

What is the purpose of the vertical stabilizer?. Adjustment of longitudinal stability. Compensation of tail rotor stability. Improvement of directional stability. Reduction of manoeuvre stability.

An increase of stability in a helicopter causes... a decrease of general aviation safety. a reduced controllability. an optimization of the maximum helicopter mass. an enhancement of control under negative load factors.

What behavior does a helicopter without stabilization systems show after external disturbances in a hover, without a corrective action?. Statically stable and dynamically instable. Statically stable and dynamically stable. Statically indifferent and dynamically instable. Statically stable and dynamically indifferent.

What relieves the helicopter in a low G manoeuvre?. Weightlessness of the passengers during the push over. Rolling movement of the helicopter to the right. Increased vertical airflow through the rotor. Centrifugal force in parabolic flight during the entire manoeuvre.

Vx is the speed... for the best rate of climb. for the best angle of climb. to rotate. never to be exceeded.

Vy is the speed... to rotate. for the best rate of climb. for the best angle of climb. never to be exceeded.