arge Angle of
Incidence that we produce a poor proportion of Lift to Drift; but the
smaller the Angle of the Surface in front of us the less the air is
deflected downwards, and consequently the less Angle is required of us,
and the better our proportion of Lift to Drift, which, of course, makes
us much more effective Controls."

"Yes," said the Lateral and Directional Stabilities in one voice,
"that's so, and the wash-out helps us also, for then the Surfaces
towards their Wing-tips have less Drift or 'Head-Resistance,' and
consequently the gusts will affect them and us less; but such decreased
Angle of Incidence means decreased Lift as well as Drift, and the
Designer does not always care to pay the price."

"Well," said the Ailerons, "if it's not done it will mean more work for
the Rudder, and that won't please the Pilot."

"Whatever do you mean?" asked Efficiency. "What can the Rudder have to
do with you?"

"It's like this," they replied: "when we are deflected downwards we gain
a larger Angle of Incidence and also enter an area of compressed air,
and so produce more Drift than those of us on the other side of the
Aeroplane, which are deflected upwards into an area of rarefied air due
to the SUCTION effect (though that term is not academically correct) on
the top of the Surface. If there is more Drift, i.e., Resistance, on
one side of the Aeroplane than on the other side, then of course it will
turn off its course, and if that difference in Drift is serious, as it
will very likely be if there is no wash-out, then it will mean a good
deal of work for the Rudder in keeping the Aeroplane on its course,
besides creating extra Drift in doing so."

"I think, then," said Efficiency, "I should prefer to have that
wash-out,[7] and my friend the Designer is so clever at producing
strength of construction for light weight, I'm pretty sure he won't
mind paying the price in Lift. And now let me see if I can sketch the
completed Aeroplane."

"Well, I hope that's all as it should be," she concluded, "for to-morrow
the Great Test in the air is due."

PART III. THE GREAT TEST

It is five o'clock of a fine calm morning, when the Aeroplane is wheeled
out of its shed on to the greensward of the Military Aerodrome. There
is every promise of a good flying day, and, although the sun has not
yet risen, it is light enough to discern the motionless layer of fleecy
clouds some five thousand feet high, and far, far above that a fe