Exercise 21 - Rapid Decelerations

PREPARATORY INSTRUCTION

Aim

For the student to learn how to come to the hover into wind from cruising speed, at a constant altitude.

Review

Airspeed and Power Changes - Exercise 4

Motivation

Rapid decelerations straight ahead are a useful exercise for developing co-ordination and accuracy during training. They are also a means of aborting a departure from larger confined areas. Those involving a level minimum radius turn, have a practical application in the avoidance of obstacles or weather conditions under operational conditions.

Airmanship

  • Lookout
  • Engine and Airframe limitations.

Teaching Points

Straight Ahead Into Wind

    1. Describe how to carry out a rapid deceleration straight ahead into wind as follows:
      1. from cruise at 30-50 ft AGL, commence a gentle flare;
      2. at low forward speed, start levelling the aircraft;
      3. anticipate loss of tranlational lift, establish a hover;
      4. maintain height throughout with collective;
      5. maintain RPM throughout with throttle; and
      6. prevent yaw with pedals.
    2. Explain that the deceleration will initially be gentle and gradual, from a fairly low speed of entry, in order to concentrate on smoothness and accuracy. The manoeuvre can be speeded-up as necessary after the basic ability has been acquired.
    3. Explain that when making a more rapid deceleration, there is a larger change of attitude in the flare and a greater resultant tendency to gain height. This in turn will require larger collective movements to prevent a climb, and larger pedal movements to prevent yaw.
    4. Point out that at no time should the flare be so harsh that it is necessary to split the needles in order to prevent an overspeed. It is important however, to explain and demonstrate the recovery sequence should this happen inadvertently.
    5. Review the dangers of vortex ring if height is lost at low or nil forward speed.

With Level Turn Into Wind

6. Describe the technique for performing a rapid deceleration involving a level turn of up to 180° into wind, as follows:

  1. from cruise at 30-50 ft. AGL, commence a level, balanced turn;
  2. initiate a flare while in the turn;
  3. rollout facing into wind;
  4. at a low forward speed, level the aircraft;
  5. come to a hover or resume forward speed;
  6. maintain height throughout; and
  7. maintain balanced flight and prevent yaw.

7. Emphasize that the student must keep the aircraft in balance and the airspeed above translation in the 180 degree turn into wind, otherwise the helicopter will be set up for vortex ring.

Confirmation  

PRE-FLIGHT BRIEFING

AIR LESSON
    1. Demonstrate a straight-ahead deceleration from cruising flight into wind.
    2. Student practice.
    3. Demonstrate a straight-ahead rapid deceleration into wind.
    4. Student practice.
    5. Demonstrate a rapid deceleration involving a 90° turn into wind.
    6. Student practice.
    7. Demonstrate a rapid deceleration involving a 180° turn into wind.
    8. Student practice

POST-FLIGHT DEBRIEFING

TIPS FOR INSTRUCTORS
    1. Decelerations involving a turn into wind require a high level of co-ordination and accuracy. They should be introduced as an advanced exercise towards the end of the training syllabus.
    2. It is important to stress smoothness and accuracy. The student should initially master gentle decelerations from 50 MPH to the hover with the accent on smoothness, accuracy of height and RPM. Overpitching, yaw and tail rotor drift are common errors in the early stages and should be corrected before speeding up the manoeuvre.
    3. After smoothness and accuracy have been established, the entry speeds can gradually be increased to the cruise and the rate of deceleration increased.
    4. Loss of height as translational lift is lost, is a common fault and is potentially dangerous, since the conditions necessary for vortex ring will be present.
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