Its
momentum in the direction of its first course causes it to
travel along a line the resultant of such momentum and the
thrust. In other words, it more or less skids sideways and
away from the centre of the turn. Its lifting surfaces do
not then meet the air in their correct attitude, and the lift
may fall to such an extent as to become less than the weight,
in which case the aeroplane must fall. This bad effect is
minimized by ``banking,'' i.e., tilting the aeroplane sideways.
The bottom of the lifting surface is in that way opposed to
the air through which it is moving in the direction of the
momentum and receives an opposite air pressure. The
rarefied area over the top of the surface is rendered still more
rare, and this, of course, assists the air pressure in opposing
the momentum.
The velocity of the ``skid,'' or sideways movement, is
then only such as is necessary to secure an air pressure equal
and opposite to the centrifugal force of the turn.
The sharper the turn, the greater the effect of the centrifugal
force, and therefore the steeper should be the ``bank.''
Experentia docet.
The position of the centre of gravity affects banking. A low
C.G. will tend to swing outward from the centre of the turn,
and will cause the aeroplane to bank--perhaps too much, in
which case the pilot must remedy matters by operating the
ailerons.
A high C.G. also tends to swing outward from the centre
of the turn.
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