THE OPTIMUM ANGLE OF INCIDENCE is the angle at
which the lift-drift ratio is highest. In modern
aeroplanes it is that angle of incidence possessed by the
surface when the axis of the propeller is horizontal.
THE BEST CLIMBING ANGLE is approximately half-way
between the maximum and the optimum angles.
All present-day aeroplanes are a compromise between
Climb and horizontal Velocity. We will compare
the essentials for two aeroplanes, one designed for
maximum climb, and the other for maximum velocity.
ESSENTIALS FOR MAXIMUM CLIMB:
1. Low velocity, in order to secure the best lift-drift
ratio.
2. Having a low velocity, a large surface will be
necessary in order to engage the necessary mass
of air to secure the requisite lift.
3. Since (1) such a climbing machine will move
along an upward sloping path, and (2) will climb
with its propeller thrust horizontal, then a large
angle relative to the direction of the thrust will be
necessary in order to secure the requisite angle
relative to the direction of motion.
The propeller thrust should be always horizontal, because
the most efficient flying-machine (having regard to climb OR
velocity) has, so far, been found to be an arrangement of an
inclined surface driven by a HORIZONTAL thrust--the surface
lifting the weight, and the thrust overcoming the drift.
This is, in practice, a far more efficient arrangement than
the helicopter, i.e., the air-screw revolving about a vertical
axis and producing a thrust opposed to gravity.
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