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Chapter V.--DOWN-WIND TURNS

As has been previously mentioned there is a prevalent fallacy regarding the reasons for the hazard of down-wind turns close to the ground. This results from the belief that the air speed of the aircraft is affected by the wind. Such is not the case. Once the aircraft is free of the ground, only its speed relative to the air has any bearing on its sustentation in flight. The velocity and direction of the wind does affect the path of the aircraft over the ground, but that is all.

In taxiing the velocity and direction of the wind has a very definite effect on the aircraft and the effectiveness of the controls, because the aircraft is still in contact with the ground.

During down-wind turns close to the ground, it is noticed that when the aircraft is approximately cross wind, it seems to hang momentarily without speed and, as the turn is completed to the down-wind course, the aircraft seems to pick up speed with a rush. Both of these seeming actions are optical illusions caused by watching the ground even though the pilot is not directing his attention to it. The speed of the aircraft relative to the ground alone is affected: The air speed remains constant. If the aircraft is flown properly by feel or instruments, the air speed will not vary during the turn.

It is true that down-wind turns close to the ground are hazardous, particularly immediately after the take-off, but the reasons for this hazard do not include the prevalent fallacy. They are as follows:

1. Any turn, in any direction, is hazardous too close to the ground, but a down-wind turn presents the additional hazard of placing the pilot in the poorest position from which to make a landing in case of motor failure.

2. Some air speed and lift are lost in all turns, as will be discussed under "Turns"; and unless normal speed is maintained, this may have disastrous results when operating too close to the ground.

3. Turns immediately following the take-off are hazardous, due to the fact that the ship barely has flying speed and, under those conditions, can ill afford even the small loss of speed and lift which is incident to turning alone.

4. At low speeds the ship does not respond nearly so rapidly to the controls, and gusts may cause trouble before the reaction of the pilot and the sluggish action of the controls can correct for them.

5. The "reaction time" of the pilot is a serious factor when working close to the ground.

6. Ground objects create turbulence in the wind on their leeward side.

7. There is a variation between the wind velocity just above the ground and at 40 or 50 feet altitude due to the friction of the earth and the objects on it. This will give the ship an additional rolling