One of the most recent developments in aviation is the hydroplane, or
water-plane as it is most commonly called. A hydroplane is an aeroplane
fitted with floats instead of wheels, so that it will rise from, or
alight upon, the surface of the water. Often water-planes have their
floats removed and wheels affixed to the chassis, so that they may be
used over land.
From this you may think that the construction of a water-plane is quite
a simple task; but such is not the case. The fitting of floats to an
aeroplane has called for great skill on the part of the constructor, and
many difficulties have had to be overcome.
Those of you who have seen an acroplane rise from the ground know that
the machine runs very quickly over the earth at a rapidly-increasing
speed, until sufficient momentum is obtained for the machine to lift
itself into the air. In the case of the water-plane the pilot has to
glide or "taxi" by means of a float or floats over the waves until the
machine acquires flying speed.
Now the land resistance to the rubber-tired wheels is very small when
compared with the water resistance to the floats, and the faster the
craft goes the greater is the resistance. The great problem which the
constructor has had to solve is to build a machine fitted with floats
which will leave the water easily, which will preserve the lateral
balance of the machine, and which will offer the minimum resistance in
the air.
A short flat-bottomed float, such as that known as the Fabre, is good at
getting off from smooth water, but is frequently damaged when the sea is
rough. A long and narrow float is preferable for rough water, as it
is able to cut through the waves; but comparatively little "lift" is
obtained from it.
Some designers have provided their water-planes with two floats; others
advocate a single float. The former makes the machine more stable when at
rest on the water, but a great rawback is that the two-float machine is
affected by waves more than a machine fitted with a single float; for
one float may be on the crest of a wave and the other in the dip. This
is not the case with the single-float water-plane, but on the other hand
this type is less stable than the other when at rest.
Sometimes the floats become waterlogged, and so add considerably to the
weight of the machine. Thus in Mr. Hawker's flight round Britain, the
pilot and his passenger had to pump about ten gallons of water out of
one of the floats before the machine could rise properly. Floats are
usually made with watertight compartments, and are composed of several
thin layers of wood, riveted to a wooden framework.
There is another technical question to be considered in the fixing of
the floats, namely, the fore-and-aft balance of the machine in the air.
The propeller of a water-plane has to be set higher than that of a land
aeroplane, so that it may not come into contact with the waves. This
tends to tip the craft forwards, and thus make the nose of the float
dig in the water. To overcome this the float is set well forward of the
centre of gravity, and though this counteracts the thrust when the craft
"taxies" along the waves, it endangers its fore-and-aft stability when
aloft.