3 / 20
What measures should be implemented to recover from an established vortex ring state?
  • A
    Apply forward cyclic, raise the collective.
  • B
    Apply aft cyclic, raise the collective.
  • C
    Apply lateral cyclic, lower the collective.
  • D
    Apply forward cyclic, lower the collective.

Refer to figures.
Vortex Ring or ‘Settling with power’ is a flight condition in which a helicopter that is receiving power from its engine(s) loses main rotor lift and subsequently experiences loss of control.

Generally, in all flight circumstances there is a degree of airflow circulation at the tips of the blades where the air forced downwards aerodynamically rotates around the aerofoil tip and forms a vortex.

The vortex generated increases drag and reduces lift.

If a helicopter is descending rapidly, there is an increased upflow of air at the rotor tips, rapidly increasing the vortices' strength and size.

This in turn reduces lift and aerofoil efficiency at the tips of the blades and requires more engine power to overcome the drag.

Because the rotor blades are turning the vortex travels with the blades and the vortex is formed into a “doughnut” shaped ring at the outer edge of the rotor disc.

As the rate of descent increases,

  • There is an increased upflow of air at the blade roots.
  • It is possible for the upflowing air to modify and increase the local angle of attack at the root end such that the root end of the blade stalls.

Additionally, if the collective pitch is further increased the loss of lift at both ends of the blades increases and the area around the middle portion of the blade, that is actually generating lift, reduces.

Total lift is reduced and the helicopter accelerates downwards. This acceleration increases the upflow of air, which aggravates the stalled condition.

In extreme cases, it is possible that the entire length of the blades no longer produces any lift at all.

Enabling conditions:

  • The helicopter has to be in powered flight (20% - 100% engine power).
  • High rate of descent exceeding a true value of approximately 500’/minute. (faster than 700 fpm for modern helicopters)
  • Slow forward speed, less than 30 knots. (slower than effective translational lift.)

Symptoms:

  • Incipient vortex ring.
    • Increased vibration and buffet;
    • Lateral and directional instability.
  • Established vortex ring
    • Rapid increase in the rate of descent towards and beyond 3000 fpm;
    • Reduced effectiveness of cyclic inputs in roll or pitch and
    • The collective pitch failing to arrest the rate of descent and usually increasing the phenomenon

Recovery:

Once recognized, an immediate response is required

  • Incipient Stage
    • Keep the collective position unchanged and apply forward cyclic to achieve an accelerative (nose down) attitude so as to increase forward airspeed quickly.
    • above 30 KIAS, more power can be applied if necessary without waiting until the best rate of climb speed is reached.
  • Established Condition
    • Move the cyclic forward and lower the collective.
    • above 30 KIAS, more power can be applied if necessary without waiting until the best rate of climb speed is reached.

Your Notes (not visible to others)



This question has appeared on the real examination, you can find the related countries below.