ially devised for airship propulsion is that in
which the cylinders are arranged horizontally instead of vertically, the
main advantages of this form being the reduction of head resistance and
less obstruction to the view of the pilot. A casing, mounted on the top
of the engine, supports the air-screw, which is driven through bevel
gearing from the upper end of the crankshaft. With this type of engine
a better rate of air-screw efficiency is obtained by gearing the screw
down to half the rate of revolution of the engine, this giving a more
even torque. The petrol consumption of the type is very low, being only
0.48 lbs. per horse-power per hour, and equal economy is claimed as
regards lubricating oil, a consumption of as little as 0.04 lbs. per
horse-power per hour being claimed.

Certain American radial engines were made previous to 1914, the
principal being the Albatross six-cylinder engines of 50 and 100
horse-powers. Of these the smaller size was air-cooled, with cylinders
of 4.5 inches bore and 5 inches stroke, developing the rated power
at 1,230 revolutions per minute, with a weight of about 5 lbs. per
horse-power. The 100 horse-power size had cylinders of 5.5 inches bore,
developing its rated power at 1,230 revolutions per minute, and weighing
only 2.75 lbs. per horse-power. This engine was markedly similar to the
six-cylindered Anzani, having all the valves mechanically operated, and
with auxiliary exhaust ports at the bottoms of the cylinders, overrun
by long pistons. These Albatross engines had their cylinders arranged in
two groups of three, with each group of three pistons operating on one
of two crank pins, each 180 degrees apart.

The radial type of engine, thanks to Charles Manly, had the honour of
being first in the field as regards aero work. Its many advantages,
among which may be specially noted the very short crankshaft as compared
with vertical, Vee, or 'broad arrow' type of engine, and consequent
greater rigidity, ensure it consideration by designers of to-day, and
render it certain that the type will endure. Enthusiasts claim that the
'broad arrow' type, or Vee with a third row of cylinders inset between
the original two, is just as much a development from the radial engine
as from the vertical and resulting Vee; however this may be, there is
a place for the radial type in air-work for as long as the internal
combustion engine remains as a power plant.

IV. THE ROTARY TYPE

M. Laurent Se