Rotary Wing Aero Qs Flashcards
A blade of a helicopter main rotor is
Symmetrically cambered
A misaligned blade of a semi rigid rotor will result in
Decrease in medium and high frequency vibration
Blade sailing occurs
During engine shut down
Translational flight is
Achieved by tilting the rotor disc in the required direction of flight
Maximum forward helicopter speed is achieved when
Cyclic control is no longer available to overcome disc flapback
The coning angle is a product of
Lift and centrifugal force
With an increase in helicopter gross weight the retreating blade stall speed would be
Increase
The forces acting on a helicopter in steady forward flight are
Thrust is equal to and opposes drag, lift is equal to and opposes weight
A coaxial helicopter utilises
Counter rotating shafts on inside the other
On a piston engine helicopter the engagement of centrifugal clutch is indicated by
Normal rpm with operating limits
A cyclic pitch change
Will cause the rotor disc to tilt in a selected direction
Wash out is used
To help reduce the bending moment in the blades
A cyclic friction device allows
Control inputs to be set at specific values
A variable incidence horizontal stabiliser
Has negative camber and is unaffected by downwash of the helicopter
The tail rotor produces a reaction
Opposite to the torque reaction
Ground cushion effect is
Extra lift increased by the downwash when the helicopter hovers close to the ground
The Notar system
Doesn’t not require a tail rotor
Induced drag in a helicopter occurs
At the blade tips
The collective is on which side of the pilot
Left
A helicopter has a main rotor which rotates anti-clockwise viewed from above what happens if a loss of anti torque device at cruise speed in flight
No appreciable change
A helicopter has a main rotor which rotates anti clockwise viewed form above and is fitted with a tail rotor it will tend to drift sideways to
Starboard which ever way the tail rotor is fitted
A helicopter fin helps to give
Directional stability about the normal axis
Autorotation
Is the product of lift from a freely rotating main rotor
A full articulated main rotor permits the following movements
Feathering flapping and dragging
Phase lag is due to the blades
Inertia
The mixing unit
Ensures that the pilot can use the cyclic input at the same time as collective input
A horizontal stab of a helicopter
Prevents excessive nose down attitude in forward flight
A helicopter derives it’s lift
And thrust from a power driven main rotor
The amount of lift produced by a rotor depends on the
Angle of attack and relative airspeed
Rotor blade pitch angle is the angle between
Chord line and hub reference surface
A rigid rotor is on that can
Feather only
A helicopter hovering 2m above the ground subject to a strong cross wind will
Lose lift due to recirculation
A swash plate and sleeve assy
Is titled or moved vertically by flight control inputs
As a helicopter accelerates in forward flight above about 15 knots it will be necessary to
Reduce power because of additional lift in translational flight
A helicopter hovering near a tall building will
Drift towards it
If the helicopters engine stops during flight the
Main rotor will continue to rotate due to the up flow of air
A collective pitch change
Is a simultaneous pitch change of all the blades by the same amount
The Actuator position indicator on a helicopter is centred by
Operating the Force trim release and moving the cyclic stick
A cyclic pitch change
Will cause the rotor disc to tilt in a particular direction
Phase lag is due to
Gyroscopic precession
A helicopter is hovering and the pilot applies right pedal. Assuming the main rotor rotates anti clockwise viewed from above the helicopter will
Ascend unless the the pilot decrease the rotor rpm
During autorotation what maintains the rotor rpm
A reactive thrust force generated by the up flow of air
When the pilot applies left foot forward on the tail rotor control pedals the tail rotor moves
To give a net increase on thrust to the right
The direction of the total lift force
Always acts from the centre of and at 90 degrees to the rotor disc
Dissymmetry of lift
Will tilt the main rotor disc in a particular direction
The airflow over part of the main rotor will be in reverse direction
At high forward speed
Pressing the force release trim on a helicopter
Relieves the servo load to allow repositioning of the controls on pitch and roll
A helicopter is said to be statically stable if after a disturbance from a stable condition if
It’s initial tendency is to return to its original position with or without overshoot
A helicopter is said to have beaut RAL dynamic stability if after an initial disturbance it continues to oscillate at
The same rate
A helicopter main rotor blade is twisted from root to tip
Equalise lift along the blade
A helicopter main rotor blade pitch change mechanism may be arranged so that when the blade flaps up the pitch reduces in order to
Prevent dissymmetry of lift
A helicopter with anti clockwise rotating rotor when moving backwards will have its rotor blade pitch at maximum at
90 degrees to the right of longitudinal
A helicopters stabiliser assists in
Pitch stability
A shrouded tail rotor
Reduces the need for cyclic feathering
A two bladed rotor on a central gimbal is called
Semi rigid rotor
After a change in collective pitch the rotor rpm will rise and fall this called
Transient droop
After a change in pitch of. Rotor blade the blade will be at maximum flap at
90 degree
After a roll to the left of a statically stable helicopter the helicopter would
Come back to level flight
After a roll to the left of a statically unstable helicopter the helicopter would
Continue to roll further
After over pitching a helicopter centrifugal force
Will remain constant at a fixed rotor rpm, the area of the disc decreases and blade coning angle increases
Airflow through the main rotor disc is autorotation is
Maybe up or down
An advantage of the symmetrical section blades used in helicopters is that
The position of the feather axis and the c of p and c of g coincide providing stability
An elastomeric bearing requires
No lubrication
As the aoa of a rotor blade increases it affects the
Dragging and the flapping forces
As the rotor head is titled to travel forward what happens to the rearward travelling blades pitch angle
Increases
Aspect ratio is the ratio of the
Blade span to the chord
Assuming the phase lag of a rotor blade is 90 degrees and the control advance angle is 15 degrees then the pitch operating arm must be at the highest point of the swash plate
75 degrees ahead of the highest flapping point
At a given power setting ground cushion effect is most effective when a helicopter is hovering over
A hard level surface
Autorotation
Is the product of lift from freely rotating rotor blades
Authoritative force attempts to pull the rotor blade
In the direction of normal rotation
Autorotative force is the
Component of the total reaction which acts forward in the plane of rotation in opposition to drag
Certain helicopters tend to tilt laterally when landing this problem can be overcome by placing the tail rotor thrust
I’m line with the main rotor hub
Changes in aircraft weight
Cause corresponding changes in total drag due to the associated lift change
Climbs with forward speed require less power than vertical climbers because of
Translational lift
Disc loading is defined as the
Ratio of gross weight to disc area
Dropping off helicopter blades is compensated by
Centrifugal force
During an autorotation decent rotor rpm will be
Higher than in powered flight
During autorotation the rudder pedals
Would need to be backed off due to the loss of torque
During decent with power on on a helicopter
Lift drag thrust and weight are acting on the helo
During forward flight the advancing blade will
Flap up
During forward flight the retreating blade will
Flap down
During the flare in autorotation the rotor rpm will
Increase
For a helicopter in autorotation what forward speed will achieve the maximum glide distance
Greater than minimum glide speed
Forward velocity causes the advancing blade to
Flap up and reduce lift
Ground cushion effect is due to
Increased pressure under the rotors
Ground cushion effect is produced by
Increased pressure under the main rotor disc
Ground effect is only apparent
I’m low speed translational flight up to one times the disc diameter from the ground
Ground effect will be most apparent when
Hovering close to the ground
Helicopter blades are usually
Symmetrical
Helicopter derives it’s lift from
The blade of the helicopter creates a low pressure above it
Helicopter experiences VOR text ring state
It experiences turbulence and descends
Helicopters in forward flight are usually
Directionally stable
How do you measure HUMS gearbox vibration
Accelerometers
How many rotor blades are on a helicopter
Depends on helicopter design
If a helicopter rotor disc is rotating anti-clockwise viewed from above where would a pitch input be fed into the disc to move the helicopter rearward
Right of the longitudinal axis
If a helicopters main rotor blades are over pitched
Rotor rpm will decrease
If the aoa is increased on a main rotor blade
There is in an increase in drag
If the blade aoa increases
Lift and drag increases
If the main rotor of a helicopter rotates in anti-clockwise direction when viewed from above and a hovering left turn is required the following movements of the controls are selected
Rudder pedal to the left and increase throttle
I’m a NOTAR system air is ducted down the tail boom to produce a predetermined amount of lift
Over one side of the boom to counteract changing torque from the main rotor
In forward flight the relative air velocity at each blade
Is greatest for the advancing blade
I’m forward flight if a helicopter had no flapping hinges it would tend to
Roll towards the side of the retreating blade
In forward flight the advancing blade would be expected to
Flap up
Instead of the flapping hinge being mounted at right angles to the spans of the blade the delta three hinge is set at an angle
Such that when a blade flaps up the pitch angle of the blade is reduced
Lift generated by a blade is proportional to the
Relative airflow and the aoa
Lift in a helicopter is a result of
Aoa x velocity squared
Lift is generated by
Low pressure above the blade
Movement of the collective control will
Increase the pitch of the main rotor blades
On a helicopter rotor disc lift happens
Immediately
On a helicopter the rotor disc is
The swept area between the blade tips
On a helicopter what is blade dragging
Movement of each blade horizontally about the vertical hinge
On a helicopter what is a vortex ring state
tip vortex build up during hover
Over pitch causes
Blades to cone up
Over pitching of a helicopter collective control may lead to
Excessive blade coning and an attendant loss of rotor useful force
Relative airflow over a helicopter blade
Increases at the tip
Relative velocity of a helicopter rotor
Increases at forward travelling blade
Rotor blade sailing is a problem at
Low rotor rpm at engine shut down
Rotor tip vortices are strongest when
Hovering with high weight
Solidity of the rotor is the ratio of
Blade area to disc area
Stability of a helicopter is its
Ability to return to original attitude after displacement
Switches on the collective of turbine powered helicopters
Searchlight controls force trim release switch landing light and collective trim where four axis autopilot is fitted
Tail rotor effects the helicopter in
Horizontal axis
The advancing blade of a helicopter is the on moving
One moving forward into the relative airflow
The aerofoils shape of a main rotor blade is symmetrical in order to make the blade have
A relatively stable c of p position with changes in aoa
The aoa of a blade is the.
Angle between the chord line and relative airflow
The bell stability argumentation system is based on
Gyroscopic forces
The best design of a rotor blade is where the c of p
Does not move
The blade stalling speed will
Increase with a increase in weight
The c of p of an aerofoils is that point on the chord line
At which the lift forces resultant is said to act
The choice of aerofoils section for a rotor blade is such that
It has a stable c of p
The cyclic stick controls a helicopter in
Pitch and roll
The difference between transient droop and static droop is
Undrswing
The distribution of lift is equalised along the length of a helicopter rotor blade by
Incorporating a twist or change of section towards the tip of the blade
The forces which govern the coning angle are
Lift and centrifugal force
The main rotor assy of a helicopter provides
Lift a component of which is horizontal so thrust is obtained
The main rotor drive shaft is titled laterally on some helicopters to correct tail rotor
Drift
The maximum forward speed of a helicopter is limited by
Retreating blade stall and forward speed of advancing blade
The pilot of a helicopter can overcome vortex ring effect by
Lowering the collective pitch lever and easing the cyclic forward
The pilot of a helicopter that is in a vortex ring state will encounter turbulence and will experience
Vibration a high rate of decent and some partial loss of control
The purpose of an offset vertical stab is to
Relieve some of the load on the tail rotor during forward flight
The purpose of the horizontal stab is to
Maintain the aircraft in as near a horizontal attitude as possible during forward flight
The rotor blades operated at the best lift drag ratio when their
Aoa is about +3 degrees
The rotor cone is formed by
Centrifugal force and lift
The rotor disc is
The distance between tip to tip
The rpm of the rotor blades is constant within small limits to
Prevent blades folding up during flight
The stalling speed of a helicopter blade
Is increased when the helicopter is heavier
The tail rotor
Produces a force opposing torque reaction
The vortex ring state which may develop under conditions of a power on decent at low forward airspeed is
An unstable condition which may result in an uncontrolled rate of decent
To maintain the position of the helicopter with a decrease in air density the pilot must increase
Collective pitch
Tracking is carried out to
Align the main rotor blade tip path
Translational drift is
The tendency for the aircraft to drift laterally
Translational flight is
Achieved by tilting the rotor disc in the direction of flight
Upwash on a helicopter would result in
Increase in lift without an increase in power
Vortex ring state requires
Power on decent
What damps vibrations on a helicopter
Bifilar damper
What design factor govern rpm of helicopter rotor
Weight of the blade
What effect does the ground have on a helicopter
Increases lift
What forces are acting ok the helicopter during decent
Lift and weight
What happens to a helicopter in autorotative flight
The rotor goes in the normal direction of rotation
What is the advancing blade on a helicopter doing
Going to the lowest point
What is the swash plate on a helicopter used for
Control of the pitch of the rotor blades
What principle does the delta 3 hinge use
Offset hinges
When a blade is flapping up
Pitch will decrease
When a blade moves about the flapping hinge
The drag forces on the blade change and the aoa changes
When a helicopter rotor disc is tilted forward what happens to the pitch of the retreating blade
Increases
When air flow velocity over an upper cambered surface of an aerofoils decreases what takes places
Pressure increases
Lift decreases
When an aerofoils stalls
Lift decreases and drag increases
When entering into a stable autorotative state the main rotor rpm will initially
Decrease
When moving from the hover to forward flight it is necessary to
Increase the engine power
When oat increases what happens to a helicopter operating ceiling
Decrease
When the cyclic stick is eased forward in the hover position
Vertical lift is reduced
When the helicopter moves from the hover to translational flight the lift vector will
Remain vertical
When the rotor blade increases it’s aoa the c of p
Does not move
When the rotor blade is flapping down
the pitch angle is less than the aoa
When the rotor blade is flapping up the aoa is
Is less than the pitch angle
When will the needle spilt in a joint rotor / engine rpm instrument
On clutch slip
Which direction is the air flowing through the main rotor during autorotation
Upwards
Which part of the rotor disc produces the most lift during forward flight
The front portion
With a drop in ambient temperature aJ aircraft service ceiling will
Not be affected
With a fixed collective pitch as an autorotating helicopter loses its forward velocity the rotor rpm will
Decrease
With an increase in forward velocity of a helicopter the increase in parasitic drag will cause the fuselage to
Pitch down with a I crease in forward speed
With an increase in its aoa the drag acting on a rotor blade
Increases
With the tail rotor pedals in neutral the tail rotor blade pitch will be
Positive
