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FLIGHT INSTRUCTOR'S MANUAL     91

1. The difficulty of the particular maneuver and the possibility of the student's being able to perform it after a reasonable amount of practice.
2. Whether or not it is a logical extension of the principles already learned and being perfected. (Eights become more difficult in direct proportion to the amount of attention that must be diverted from the actual handling of the controls.)
3. The type of banks to be used. 
4. The degree of judgement of drift and planning required.
5. Whether or not the altitude required is critical with regard to the performance of the eight with the particular aircraft.
6. The selection of ground objectives, whether imaginary paths or pylons, should be such that they are readily apparent.
Ordinarily neither the student's proficiency nor time will permit the introduction of other than the elementary eights before solo. Therefore, only the most elementary will be discussed here. They are the medium and steep "eights" along a road.
It is important that a full explanation of the effect of drift be given the student and that the methods used to compensate for it be again discussed, although he will have had an introduction to it in S turns across a road. To this should be added an explanation of the effects of poorly selected starting banks, and the difficulties to be encountered in attempts to compensate for them. The importance of judging the correct initial bank should be stressed. These explanations should be made on the ground where sketches can be used to clarify the points discussed. Sketches should be drawn and explained showing the different effects of drift which will correspond to the following practical demonstrations to be given in the air. (See figs. 6, 7A-7F, and 8.)
1. Select a road, railroad, or other landmark which appears in a straight line up and down wind. Fly close and parallel to the road and start a medium turn maintaining the same angle of bank and rate of turn for 360°. 
The airplane will return to a point slightly down wind from the starting point, according to the amount of wind present, radius of turn and speed of the airplane. The resultant flight path over the ground will be an elongated circle, although with reference to the air it was a perfect circle. If there were no wind the path over the ground would also be a perfect circle and the airplane would have returned to its starting point. (See figs. 7A-7B.)
2. Start as before, and when 90° of the turn have been completed, steepen the turn considerably and maintain the new angle of bank for the remainder of the 360°. The airplane will not return to its starting point but to a point well inside of the starting position. This is the result of two different radii being used. (See fig. 7C.) The same results would have been obtained had the initial bank been maintained and the wind from the directions shown in figure 7D been causing the drift.
3. Start the maneuver as before, and after 90° of the turn have been completed, shallow the bank considerably and maintain the new bank for the remainder of the 360°. The airplane again will not return to the original starting point but to a point well beyond it.
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