? 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. Apart from that, we shall require a
larger Angle of Incidence than in the case of a machine designed purely
for speed, and that means a correspondingly _large Camber_.

"On the other hand, if we are thinking merely of Speed, then a _small
Surface_, just enough to lift the weight off the ground, will be best;
also a _small Angle_ to cut the Drift down, and that, of course, means
a relatively _small Camber_.

"So you see the essentials for _Climb_ or quick ascent and for _Speed_
are diametrically opposed. Now which is it to be?"

"Nothing but perfection for me," said Efficiency. "What I want is
Maximum Climb and Maximum Speed for the Power the Engine produces."

And each Principle fully agreed with her beautiful sentiments, but work
together they would not.

The Aspect Ratio wanted infinite Span, and hang the Chord.

[Illustration: Maximum Climb. Maximum Speed.]

The Angle of Incidence would have two Angles and two Cambers in one,
which was manifestly absurd; the Surface insisted upon no thickn