Part II — The Ground and Air Instruction Syllabus — Exercise 20 — Illusions Created by Drift — Low Flying
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To teach the student:
(1) To cope with the illusions created by drift by maintaining co-ordinated flight in turns.
(2) How to maintain a desired track by compensating for the effects of drift while manoeuvring at low level.
Essential Background Knowledge
- Illusions and effects of flight at low level in a strong wind:
- into-wind — reduced ground speed produces an illusion of reduced airspeed;
- downwind — increased ground speed produces an illusion of increased airspeed;
- when turning from downwind an illusion of a skid outwards results;
- when turning from into-wind an illusion of a slip inwards results.
B. Situations where illusions can produce potentially dangerous flight conditions, e.g., low level circuit and approach while operating under conditions of low ceilings, turns at low level associated with high winds, etc.;
- look well ahead;
- maintain safe airspeed;
- turn accurately in spite of deceptive illusions — maintain co-ordinated flight;
- keep a good look-out, and cross-check instruments;
- maintain safe altitude — observe local regulations;
- avoid annoying others and frightening livestock;
- do not turn too steeply;
- allow sufficient space to manoeuvre when at low altitude.
(2) Question student on exercise and clarify as necessary.
Advice to Instructors
(1) The minimum height in this exercise should be governed by local restrictions. Adequate look-out is essential. Use this demonstration to point out inherent dangers of flight at low altitudes.
(2) Choose a day when the wind is strong enough for the effect of drift to be noticeable. An ideal opportunity is when solo flying has been cancelled due to strong winds.
(3) Since the illusions may lead to inaccurate and potentially dangerous flying, the pupil must thoroughly understand them and adequate practice must be given in flight below normal altitudes.
(4) Let the pupil try to find the wind direction by judging the drift and adjusting direction until there is no drift. The student will not find it easy, but it is good practice.
(5) Dangerous situations develop rapidly due to illusions created by drift, when practising forced or precautionary landings in a strong wind. Instructors must not allow the student to attempt to increase the rate of turn with rudder, particularly when turning from base to final approach in these exercises.
(6) This is a good exercise to acquaint the student with the practical application of the Canadian Aviation Regulations regarding flight over built-up areas.
(7) Refer to the diagrams on pages 117 and 118 which show suggested in-flight procedures which may be used to effectively demonstrate this exercise.
(8) When teaching circuits and forced and precautionary landing procedures, take advantage of windy conditions to apply the principles learned in this exercise.
Instruction and Student Practice
(1) At low level, in a suitable area:
- Fly into wind and note reduced ground speed;
- Turn downwind and note increased ground speed;
- While turning 180° from downwind into-wind, note apparent skid outwards — maintain co-ordinated flight — note the effect of wind drift on the anticipated flight path during the turn;
- Following this, while turning 180° from into-wind to downwind, note apparent slipping inwards — maintain co-ordinated flight — note the effect of wind drift on the anticipated flight path during the turn;
- As an additional exercise, note apparent slipping and skidding when performing a 360° turn — the angle of bank needs to be varied to achieve a proper circular path;
- Refer to Advice to Instructors for suggested demonstrations showing the practical application of this demonstration;
- Demonstrate a precautionary landing procedure in windy conditions to apply the principles learned in this exercise.
(2) Repeat the above using flaps as necessary to demonstrate increased visibility — better control.
NOTE: This exercise should be demonstrated with both left and right hand turns.
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