Sometimes the tail-
plane is mounted on the aeroplane at the same angle as the
main surface, but it actually engages the air at a lesser angle,
owing to the air being deflected downwards by the main
surface. There is then, in effect, a longitudinal dihedral
as explained and illustrated in Chapter I.
CLIMBS BADLY.--Such a condition is, apart from engine
or propeller trouble, probably due to (1) distorted surfaces,
or (2) too small an angle of incidence.
FLIGHT SPEED POOR.--Such a condition is, apart from
engine or propeller trouble, probably due to (1) distorted
surfaces, (2) too great an angle of incidence, or (3) dirt or
mud, and consequently excessive skin-friction.
INEFFICIENT CONTROL is probably due to (1) wrong setting
of control surfaces, (2) distortion of control surfaces, or
(3) control cables being badly tensioned.
WILL NOT TAXI STRAIGHT.--If the aeroplane is uncontrollable
on the ground, it is probably due to (1) alignment
of undercarriage being wrong, or (2) unequal tension of shock
absorbers.
CHAPTER IV
THE PROPELLER, OR ``AIR-SCREW''
The sole object of the propeller is to translate the power
of the engine into thrust.
The propeller screws through the air, and its blades, being
set at an angle inclined to the direction of motion, secure
a reaction, as in the case of the aeroplane's lifting surface.
This reaction may be conveniently divided into two
component parts or values, namely, Thrust and Drift.
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