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Robinson 22 > Helicopter Aerodynamic Conditions > Flashcards

Helicopter Aerodynamic Conditions Flashcards

1
Q

Dissymmetry of Lift (Where does it happen)

A

Cruise flight

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2
Q

Dissymmetry of Lift (What is it)

A

“Difference of lift”. In forward flight the advancing rotor blade produces more lift than the retreating side.

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3
Q

Dissymmetry of Lift (Why does it happen)

A

The advancing rotor blade (right side) is going faster (Rotor tip speed + forward speed) than the retreating rotor blade (left side), which is (Rotor tip speed - forward speed)

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4
Q

Dissymmetry of Lift (Aerodynamic/Control forces)

A

Aerodynamic: Lifting force produced by the right side is felt at the front of the helicopter producing a pitching up moment. Control: blade flapping, cyclic feathering

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5
Q

Dissymmetry of Lift (Solution)

A

Slow the helicopter’s airspeed

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6
Q

Transverse Flow Effect (Where does it happen)

A

Takeoff/Landing (10-15 KIAS)

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7
Q

Transverse Flow Effect (What is it)

A

Changing of flow from stationary flight to forward flight.

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8
Q

Transverse Flow Effect (Why does it happen)

A

Airflow on the front of the rotor is more horizontal (produces more lift). Airflow on the rear of the rotor is still more vertical (producing less lift).

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9
Q

Transverse Flow Effect (Aerodynamic forces felt)

A

Aerodynamic: Lifting force produced by the front of the rotor is felt on the left side of the rotor causing right roll

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10
Q

Transverse Flow Effect (Solutions)

A

Input left cyclic to counteract right roll

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11
Q

Effective Translational Lift (ETL) (Where does it happen)

A

Takeoff/Landing (16-24 knots)

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12
Q

Effective Translational Lift (ETL) (What is it)

A

Rotor outruns old vortices, works in clean air, starts to become more efficient

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13
Q

Effective Translational Lift (ETL) (Why does it happen)

A

Clean air allows the rotor to be more efficient

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14
Q

Effective Translational Lift (ETL) (Aerodynamic forces)

A

Aerodynamic: Greater lift on the right side is felt in the front of the rotor

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15
Q

Effective Translational Lift (ETL) (Solutions)

A

Control: Forward cyclic, right pedal

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16
Q

Translating Tendency in Helicopters (What is it, two definitions)

A

Drifting of the helicopter to the right.

Tendency of the helicopter to drift in the direction of tail rotor thrust.

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17
Q

Translating Tendency in Helicopters (Where does it happen)

A

In ground effect hover

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18
Q

Translating Tendency in Helicopters (Why does it happen)

A

The tail rotor is producing a thrust to the right (downwash to the left), to counteract the CW motion of the helicopter body. This thrust to the right causes the nose of the helicopter to yaw right, causing right drift.

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19
Q

Translating Tendency in Helicopters (Aerodynamic forces felt)

A

Drift to the right

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20
Q

Translating Tendency in Helicopters (Solutions)

A

Left cyclic, outset rotor, helicopter computer compensation

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21
Q

What did vortex ring state used to be called?

A

Settling with power

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22
Q

Vortex Ring State (Where does it happen)

A

Pretty much anywhere as long as the conditions are right. Steep approach is the main place it can happen.

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23
Q

Vortex Ring State (Why does it happen) (2 things)

A

Up flow through the rotor overcomes down flow.

Helicopter is descending faster than the downflow. Upward flow starts to turn in on itself

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24
Q

Vortex Ring State (Aerodynamic forces felt)

A

Vibrations, reduced cyclic authority, loss of collective authority (more collective makes the situation worse)

25
Q

Vortex Ring State (Solutions)

A

Lower collective, Forward cyclic, regain airspeed

26
Q

Dynamic Rollover (Where does it happen)

A

T/O and Landing in general (T/O and Landing on a slope, more specifically)

27
Q

Dynamic Rollover (What)

A

The CG of the helicopter crosses over the pivot point and the critical angle is exceeded due to a rolling motion caused by an outside force

28
Q

Dynamic Rollover (Why does it happen)

A

The CG of the helicopter crosses over the pivot point and the critical angle is exceeded due to a rolling motion caused by an outside force.
- Tiedowns
- Skid contact
- Stuck landing
- T/O and Landing on a slope

29
Q

Dynamic Rollover (Solutions)

A

Focus and slow down on T/O and Landing. Freeze the movement. Lower collective if you don’t feel comfortable with the situation.

30
Q

What is loss of tail rotor effectiveness?

A

An unanticipated yaw, defined as an uncommanded, rapid yaw towards the advancing blade which does not subside of its own accord. (Interaction between the main rotor and tail rotor, not mechanical failure)

31
Q

Why does loss of tail rotor effectiveness occur?

A

It is an aerodynamic condition that is a result of control margin deficiency in the tail rotor.

32
Q

What are the aerodynamic forces felt during loss of tail rotor effectiveness?

A

Unanticipated yaw, right or left, depending on the situation. Main rotor interferance: right yaw acceleration during a right turn. Weathercock: unexpected right or left yaw. Vortex Ring State: left crosswind, rapid and continuous pedal movements are needed

33
Q

What are the factors that contribute the LTE

A

Left crosswinds, tailwinds during approach, OGE/high power demand/speeds less than 30 knots

34
Q

What are some solutions to avoid LTE?

A

Be aware of the winds, don’t do approaches with tail winds, avoid OGE operations in high power demand situations below 30 knots, execute right turns slowly (limits turning inertia)

35
Q

What are transient torque spikes?

A

Aerodynamic phenemenon that occurs given lateral cyclic. Rapid cyclic movement, leads to reduced RPM, governor reacts by shooting fuel into the engine in order to maintain RPM and there is a torque spike

36
Q

Why do transient torque spikes occur?

A

Governor trying to maintain RPM by shooting fuel into the engine results in a torque spike

37
Q

What contributes to transient torque spikes? (5 things)

A

1) Rate of movement
2) Magnitude of movement
3) Power applied
4) Airspeed
5) Weight

38
Q

How can you reduce the affects of transient torque spike?

A

Think string theory, attach an imaginery string from the collective to the cyclic. If the cyclic goes left then you need to reduce the collective to maintain tension in the string.

39
Q

What is blade flapping?

A

The ability of the rotor blade to move in a vertical direction. Blades may flap independetly or in union. It is the primary means of countering dissymmetry of lift.

40
Q

Where is blade flapping felt?

A

Forward cruise flight

41
Q

Why does blade flapping happen?

A

the advancing blade flaps up and develops a smaller angle of attack due to a change in relative wind vectors, thus producing less lift than a rigid blade would.

42
Q

What is mast bumping?

A

Action of the rotor head striking the mast, occurring on underslung rotors only. Pilot experiences a right roll, tries to correct with cyclic INCORRECT, causes rotor to hit the mast

43
Q

In what rotor systems does mast bumping occur?

A

Semirigid, tettering, underslung rotor types

44
Q

Why does mast bumping occur?

A

Caused by an incorrect response of the pilot to an abrupt and unexpected change in the helicopter’s pitch-and-roll attitude

45
Q

What are the aerodynamic forces felt in a mast bumping situation?

A

Right roll in a low “g” or zero “g” condition

46
Q

What are the solutions to mast bumping?

A

Avoid this by making smooth, gradual control movements by the cyclic aft to recover from low “g” conditions

47
Q

Where does retreating blade stall occur?

A

Cruise flight

48
Q

What is retreating blade stall?

A

the rotor blade on the retreating side of the rotor disc in forward flight and therefore with the smaller resultant relative wind exceeds the critical angle of attack.

49
Q

Why does retreating blade stall occur?

A

Airflow over the retreating blade slows down at faster forward cruise speeds, leading to eventually exceeding the angle of attack.

50
Q

What makes retreating blade stall worse?

A

Lower Vne caused by high gross weight and high density altitude, low RPM, steep turns, turbulent air

51
Q

What are the aerodynamic forces felt in retreating blade stall?

A

Three things are going to happen: abnormal vibrations, pitch up of the nose (due to gyroscopic precession), roll to the retreating side

52
Q

What are solutions for retreating blade stall?

A

Reduce collective pitch, increase RPM, Reduce forward airspeed, minimize maneuvering

53
Q

What is an autorotation?

A

It is the condition of flight during which the main rotor is driven only by aerodynamic forces with no power from the engine.

54
Q

What are the phases of an autorotation? (4 things)

A

Entry, Glide, Flare (40 feet), Level (8 feet)

55
Q

What do you do during the entry phase of an autorotation?

A

Down (collective in order to reduce blade pitch and keep RPM up), right (pedal), aft (cyclic to prevent the nose from falling), wrist (off engine), tach (look at the tach in order to catch the RPM), catch (the RPM)

56
Q

What do you do during the glide phase of an autorotation?

A

RPM (between 90 and 110%), Airspeed (target 65 KIAS), Eyes outside (to keep pitch level)

57
Q

What do you do during the flare phase of an autorotation?

A

Aft cyclic to start reducing rate of descent and forward airspeed. This in turn increases the RPM, giving you extra energy in the RPM to help cushion landing.

58
Q

What do you do during the level phase of an autorotation?

A

Level the ship, push the cyclic forward in order to level the skids. Pull up on collective to cushion the landing

59
Q

Describe why an “in ground effect” hover requires less power than a “out of ground effect hover”

A
  • Interference of the airflow with the ground
  • Increased air pressure near the ground, acts to decrease the downwash (induced flow)
  • Making the resultant relative wind more horizontal
  • Therefore producing more lift.

Robinson 22 (17 decks)

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