The mirror., 1918-06-13
AIR BOAT DESIGN A SUCCESS
Power of Motor. Efficiency of Propeller and Speed
When Flying Important Factors
By C. III. Claudy, in Motor Boating

pressed on one side and rarihed on
the other. If the inclination be
downward, from fore to aft, the re-
suit is a lifting force.
The airplane has such an inclined
surface or surfaces. The stream
of air comes from its motion
through the air, which is caused,
of course, by the propeller. But
no surface is weightless-nor is an
engine, a man, the fuselage he sits
in, the wires, struts, wheels, etc.,
which form the completed flying
machine. So the lifting force
must first overcome the weight be-
fore the whole can get off the
ground or out of the water.
The result is that the total force
available is used in two ways-one
for the lift, and one part to over
come drift, which is the engineers
term for the resistance of the planes
as such. Head resistance is the
total of the skin friction and the
resistance of all the parts of the
structure which strike the air with.
out giving any lift.
Obviously. the greater the pro-
portion of lift over the drift the
more the machine can carry and
the faster it can climb. The great
er the angle of incidence at which
the planes strike the air the greater
the lift. but. also, the greater the
drift. Now, the longer the plane
from tip to tip the greater the sur
face-the greater the surface the
less the angle must be to produce
the necessary lift, and the less the
angle the less the drift. Therefore,
argues the theorist, planes of tre-
mendous width and little depth are
most efficient!
But! Planes require ribs, and
ribs require strength, and strength
requires size. The Gambler or cur
vature of the top and bottom of q
plane must be just right for the
particular angle of incidence being
used. The less the angle the less
the Gambler, and, consequently, too
wide wings with too little curva-
ture will have no room for the
parts necessary to produce
strength.
Hence the aspect ratio, which is
the proportion of depth of plane
to width of plane, is and must al.
ways be compromise.
But the designer has fought
good fight against this compro-
mise. The biplane, which is rapid
ly becoming the standard type, is
the weapon he uses. By having
one plane above another he gets
double the surface with little addi-
tion of weight, and by halving the
span he gets strength without many
additional spars and wires; and
while he does increase head re-
sistance with two planes instead of
one, his planes need not be so
strong. and therefore not so thick,
his angle of incidence may be less
and 80 his drift is less.
But compromise still persists.
Roughly speaking, the bottom of a
moving surface compresses- the
top surface sucks-air. If one is
above another. the top surface of
the bottom plane sucks air and pre-
vents the top surface from having
its maximum compression. To in
crease the distances between the
surfaces is the first thought, but
that means longer and heavier
struts, more wires and more head
resistance, top heaviness and other
similar troubles. So compromise
comes into play again and the
planes are staggered that is, the
bottom one is put somewhat to the
rear of the top one, to get it out of
the way of the air reaction. Again,
the top surface or plane is built out
on the ends (overhung) as wide as
can be accomplished without need