Greater velocity would
be secured if the surface, angle,
and camber were smaller and designed
to just maintain horizontal
flight with a horizontal thrust.
Also, in such case, the propeller
would not be thrusting downwards,
but along a horizontal line
which is obviously a more efficient
arrangement if we regard
the aeroplane merely from one
point of view, i.e., either with
reference to velocity OR climb.
OPTIMUM ANGLE
(Thrust horizontal)
The velocity is less than at the
smaller minimum angle, and, as
aeroplanes are designed to-day, the
area and angle of incidence of the
surface is such as to secure a
slight ascent at a low altitude. The
camber of the surface is designed
for this angle of incidence and
velocity. The lift-drift ratio is
best at this angle.
BEST CLIMBING ANGLE
The velocity is now still less by
reason of the increased angle
producing increase of drift. Less
velocity at A GIVEN ANGLE produces
less lift, but the increased angle
more or less offsets the loss of lift
due to the decreased velocity, and
in addition, the thrust is now hauling
the aeroplane upwards.
MAXIMUM ANGLE
The greater angle has now produced
so much drift as to lessen
the velocity to a point where the
combined lifts from the surface
and from the thrust are only just
able to maintain horizontal flight.
Any greater angle will result in a
still lower lift-drift ratio. The lift
will then become less than the
weight and the aeroplane will
consequently fall.
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