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165
The Aeroplane Speaks. Fifth Edition
·
H. Barber
16
"Thank
you
so
much,"
said
Efficiency.
"I
think
I
have
now
at
any
rate
an
idea
of
the
Elementary
Principles
of
Flight,
and
I
don't
know
that
I
care
to
delve
much
deeper,
for
sums
always
give
me
a
headache;
but
isn't
there
something
about
Stability
and
Control?
Don't
you
think
I
ought
to
have
a
glimmering
of
them
too?"
"Well,
I
should
smile,"
said
a
spruce
Spar,
who
had
come
all
the
way
from
America.
"And
that,
as
the
Lecturer
says,
'will
be
the
subject
of
our
next
lecture,'
so
be
here
again
to-morrow,
and
you
will
be
glad
to
hear
that
it
will
be
distinctly
more
lively
than
the
subject
we
have
covered
to-day."
[Footnote
1:
Propeller
Slip:
As
the
propeller
screws
through
the
air,
the
latter
to
a
certain
extent
gives
back
to
the
thrust
of
the
propeller
blades,
just
as
the
shingle
on
the
beach
slips
back
as
you
ascend
it.
Such
"give-back"
is
known
as
"slip,"
and
anyone
behind
the
propeller
will
feel
the
slip
as
a
strong
draught
of
air.]
[Footnote
2:
Helicopter:
An
air-screw
revolving
upon
a
vertical
axis.
If
driven
with
sufficient
power,
it
will
lift
vertically,
but,
having
regard
to
the
mechanical
difficulties
of
such
construction,
it
is
a
most
inefficient
way
of
securing
lift
compared
with
the
arrangement
of
an
inclined
surface
driven
by
a
propeller
revolving
about
a
horizontal
axis.]
[Footnote
3:
Pancakes:
Pilot's
slang
for
stalling
an
aeroplane
and
dropping
like
a
pancake.]
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