``I'm so
heavy that if I am too low down I act like a pendulum
and cause the Aeroplane to roll about sideways, and if I
am too high I'm like a stick balanced on your finger, and
then if I'm disturbed, over I go and the Aeroplane with
me; and, in addition to that, there are the tricks I play
with the Aeroplane when it's banked up,[[6]] i.e., tilted sideways
for a turn, and Centrifugal Force sets me going the
way I'm not wanted to go. No; I get on best with Lateral
Stability when my Centre is right on the centre of Drift,
or, at any rate, not much below it.'' And with that he
settled back into the Lecturer's Chair and went sound
asleep again, for he was so very, very old, in fact the father
of all the Principles.
[[6]] Banking: When an aeroplane is turned to the left or
the right the centrifugal force of its momentum causes it to
skid sideways and outwards away from the centre of the turn.
To minimize such action the pilot banks, i.e., tilts, the aeroplane
sideways in order to oppose the underside of the planes to the air.
The aeroplane will not then skid outwards beyond the slight skid
necessary to secure a sufficient pressure of air to balance the
centrifugal force.
And the Blackboard had been busy, and now showed
them a picture of the Aeroplane as far as they knew it, and
you will see that there is a slight Dihedral Angle, and
also, fixed to the tail, a vertical Keel Surface or fin, as
is very often the case in order to ensure the greater effect
of such surface being behind the vertical turning axis.
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