If, when
climbing, the propeller thrust is at such an angle as to tend
to haul the aeroplane upwards, then it is, in a measure,
acting as a helicopter, and that means inefficiency. The
reason of a helicopter being inefficient in practice is due to
the fact that, owing to mechanical difficulties, it is impossible
to construct within a reasonable weight an air-screw of the
requisite dimensions. That being so, it would be necessary,
in order to absorb the power of the engine, to revolve the
comparatively small-surfaced air screw at an immensely
greater velocity than that of the aeroplane's surface. As
already explained, the lift-drift ratio falls with velocity on
account of the increase in passive drift. This applies to a
blade of a propeller or air-screw, which is nothing but a
revolving surface set at angle of incidence, and which it is
impossible to construct without a good deal of detrimental
surface near the central boss.
4. The velocity being low, then it follows that for
that reason also the angle of incidence should be
comparatively large.
5. Camber.--Since such an aeroplane would be of
low velocity, and therefore possess a large angle
of incidence, a large camber would be necessary.
Let us now consider the essentials for an aeroplane of
maximum velocity for its power, and possessing merely
enough lift to get off the ground, but no margin of lift.
1. Comparatively HIGH VELOCITY.
2. A comparatively SMALL SURFACE, because, being
of greater velocity than the maximum climber,
a greater mass of air will be engaged for a given
surface and time, and therefore a smaller surface
will be sufficient to secure the requisit lift.
Pages:
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92