TD 29

Question 1

Vestibular Illusion

Answer 1

System:

1) Semicircular Canals - angular acceleration/ deceleration
2) Otolith Organs - gravity & linear acceleration/ deceleration

Types of vestibular illusions:

1) Somatogyral Illusions - Semicircular Canals
2) Somatogravic Illusions - Otolith Organs

Somatogyral Illusions:

1) The Leans (most common)
2) Graveyard Spin/Spiral ( fixed wing)
3) Coriolis Illusion (most dangerous)
4) Post-Roll Illusion (incorrect input)

Somatogravic Illusions:

1) Oculoagravic - nose up/ down and over-correct/ over-control
2) Elevator Illusion - upward or downward movement
3) G-Excess Illusion
4) Alternobaric Vertigo - Pressure Vertigo
5) Influence of alcohol and drugs

Types of Visual Illusions:
False Horizons
Fascination/fixation
Flicker Vertigo
Confusion with ground lights
Relative motion Illusion
Autokinesis
Size-Distance Illusion
Height-Depth perception Illusion
Crater Illusion
Structural Illusion
Altered planes of reference
Reversible perspective Illusion

Question 2

Dynamic Rollover

Answer 2

The helicopters susceptibility to a lateral-rolling tendency.

Conditions required for D/R:

1) Pivot point - contact w/ the ground
2) Rolling motion
3) Exceeding the critical angle - angle in which recovery is impossible

Types of D/R:

1) Rolling over on level ground (takeoff) most comm.
2) Rolling upslope (takeoff)
3) Rolling downslope (takeoff or landing)

Prevention:
Physical Factors - main rotor thrust, aircraft CG / low fuel, sloped landing area/ ground surface, tail rotor thrust, crosswind component

Human Factors - failure to make timely control movements, loss of visual reference points, inexperience, inattention

Inappropriate Control Inputs:
General Factors - crosswind, high roll rates, left pedal inputs, lateral loading, left skid high/ right skid low

Common Errors - rapid collective during slope landing/takeoff, abrupt cyclic in fully articulated rotor system, large and/or uncoordinated anti-torque pedal inputs, failure to detect lateral drift before landing

Question 3

Settling with Power

Answer 3

A condition of powered flight in which the helicopter settles in its own downwash, also referred to as vortex ring state.

Conditions required for settling with power:

1) vertical/ near vertical rate of descent of 300 FPM
2) slow forward airspeed (less than ETL)
3) rotor system using 20-100% available engine power

Conditions conducive for settling with power:

1) steep approach at a high rate of descent
2) formation flight approach
3) downwind approach
4) OGE hovering above max hover ceiling
5) OGE hover with not-constant altitude
6) masking/unmasking

Corrective Actions:

1) cyclic - forward to gain airspeed (lateral if forward isn’t available)
2) collective - a large application during the initial stage

Question 4

Retreating Blade Stall

Answer 4

Retreating blade eventually stalls in high speed flight because of the high AOA needed to compensate for dissymmetry of lift.

Decreasing velocity of airflow on the retreating blade demands a higher AOA to generate the same lift as the advancing blade.

The stall will begin at the tip of the blade and advance inboard.

Indications:
1) rotor vibrations followed by left roll and pitch up

Conditions that produce retreating blade stall:

1) high gross weight
2) high density altitude
3) high G maneuvers
4) low rotor RPM (rotor droop)
5) turbulent air

Corrective Actions:

1) reduce airspeed
2) reduce collective
3) reduce altitude
4) reduce severity of the maneuver
5) increase rotor RPM to normal limits