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58                           U.S. Civil Aeronautics Authority
 
into the wind, the control effectiveness is increased by the speed of the wind as well as by the tendency of all ships to weather-vane. This last makes the effect of the wind velocity seem even greater and makes taxiing into the wind easier than taxiing in other directions. 
 The tendency of the ship to weather-vane is greatest while taxiing directly cross wind, which makes this maneuver extremely difficult without brakes. It is almost impossible to keep the ship from turning into any wind of considerable velocity.
 In taxing down wind, this tendency to weather-vance seems to be increased, due to the fact that the velocity of the tail wind lessens the effectiveness of the controls. (It should be remembered that this is because the aircraft is still in contact with the ground and that this is not true while in flight.) This requires a different use of the controls than in either cross-wind or up-wind taxiing, particularly if the wind celocity is above that of a light breeze.
 Unless the field is soft, or very rough, it is best to taxi with the stick in neutral or perhaps slightly forward (elevator slightly down). Even in soft fields the elevator should be raised only as much as is absolutely necessary to maintain a safe margin of control in case of any tendency to nose over.
 When taxiing down wind, especially if the wind has any appreciable velocity the elevators must be held well down (stick well forward), the amount depending on the velocity of the wind. For instance, in a 15- to 20-mile wind, it is impractical to taxi a ship at a speed more than that of the wind. Therefore, the "air speed," or is practically zero although the ship is moving over the ground at 15 or 20 miles per hour, and the propeller blast is the only means of getting effectiveness of the tail surfaces. This is reduced in effectiveness and deflected upward when the elevators are raised. As a result, if the aircraft is taxied at a reasonable speed, which in many cases would be less than that of the wind, the wind will tend to get under the uplifted elevators and many be strong enough, particularly if gusty, to lift the tail, as has happened in many cases. This force, in combination with the tendency to weather-vane and general lack of control by which to stop such action, will cause the airplane to yaw violently and go up on its nose.
 If, on the other hand, the elevator are kept well depressed the wind helps to hold the tail down and force it back if lifted momentarily by a blast of the throttle. In this case, consideration need only be given to any yawing tendencies which must be corrected instantly, or better, before the aircraft has had a chance to follow them.
 From the foregoing explanation the student will readily appreciated the importance of the proper use of the throttle in making the controls effective. This is one of the first factors to be learned.
 Ideal taxiing would be at a constant speed of both the ship and the engine and is the goal to be sought, provided, of course, that these speeds are appropriate and reasonable.
 It must be borne in mind that, while taxiing in any direction other than into the wind, every time the throttle is closed the forces causing the weather-waning tendencies immediately act to reduce the effective control as well as get in their work to cause involuntary turning.