''
``Well, that's good news,'' and Efficiency wiped her eyes
with her Fabric and became almost cheerful. ``Suppose
we think about finishing it now? There will have to be an
Engine and Propeller, won't there? And a body to fix
them in, and tanks for oil and petrol, and a tail, and,'' archly,
``one of those dashing young Pilots, what?''
``Well, we are getting within sight of those interesting
Factors,'' said the Lift-Drift Ratio, ``but first of all we
had better decide upon the Area of the Surfaces, their Angle
of Incidence and Camber. If we are to ascend as quickly
as possible the Aeroplane must be SLOW in order to secure
the best possible Lift-Drift Ratio, for the drift of the struts
wires, body, etc., increases approximately as the square
of the speed, but it carries with it no lift as it does in the
case of the Surface. The less speed then, the less such
drift, and the better the Aeroplane's proportion of lift to
drift; and, being slow, we shall require a LARGE SURFACE in
order to secure a large lift relative to the weight to be carried.
We shall also require a LARGE ANGLE OF INCIDENCE relative to
the horizontal, in order to secure a proper inclination of
the Surface to the direction of motion, for you must remember
that, while we shall fly upon an even keel and with
the propeller thrust horizontal (which is its most efficient
attitude), our flight path, which is our direction of motion,
will be sloping upwards, and it will therefore be necessary
to fix the Surface to the Aeroplane at a very considerable
angle relative to the horizontal Propeller Thrust in order to
secure a proper angle to the upwards direction of motion.
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