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FLIGHT INSTRUCTOR'S MANUAL          57

The idea is also prevalent that low engine speeds are a saving of the engine. This may be true in some cases, but in most it is not. The engine is designed to be operated between the limits of a certain speed range as recommended by the manufacturer. The engine should be operated at the r.p.m. in this range which affords the smoothest and most efficient operation. The manufacturer is responsible for the service of his product and his recommendations should be followed.

                      TAXIING

Before the days of brakes, taxiing was a fine art in itself, much more difficult to completely master than flying. As a matter of fact, it was one that was never completely mastered under all conditions of wind and terrain.
It required a high degree of coordination of forward speed, throttle and unusual control use, plus a sensing of the effect of the wind to prevent the aircraft from taking charge despite the best efforts of the pilot.
With the advent of brakes taxiing has been much simplified, but it is still important to know how to do a creditable job of taxiing without them since all the principles of taxiing without brakes apply to taxiing with them, and particularly since brakes do fail occasionally, usually when they are most needed.
Taxiing practice without brakes is also valuable as a preliminary to instruction in take-offs and landings. The principles involved will make the control of the aircraft during the take-off, and immediately after the landing is affected, much more easily learned. A few extra minutes spent in taxiing practice may save hours of other practice in eliminating ground looping tendencies.
It is evident that to taxi with enough speed for the airflow over the control surfaces to be sufficient for good control of the airplane would be impractical and dangerous, for either the speed would have to be excessive, or the control surfaces would have to be so large that they would be unsuitable for flight conditions, which is their primary function.
Taxiing, therefore, requires a fine blending of speed, control, and throttle use, as well as a well-developed sense of anticipation of the tendencies of the aircraft. Very often controls and throttle must be used before the aircraft starts to follow its tendencies, not only in order to keep the ship from deviating from the desired course, but also in order to maintain any control.
It requires much more power to start the aircraft moving, or to start or stop a turn, than it does to keep it moving in any given direction. For this reason all controls, including the throttle, that will assist in maneuvering or in maintaining control must be used, and used liberally and promptly. In this regard, particular care must be taken in the use of the throttle or overheating and possible mechanical damage may result to the engine as previously discussed.

WITHOUT BRAKES

While the aircraft is moving on the ground, it is considerably affected by the direction and velocity of the wind. When taxiing