We here illustrate one of a couple of compound engines designed and
constructed by Messrs. Ahrbecker, Son & Hamkens, of Stamford Street,
S.E., for Captain Mojaisky, of the Russian Imperial Navy, who intends
to use them for aeronautical purposes. The larger of these engines has
cylinders 33/4 in. and 71/2 in. in diameter and 5 in. stroke, and when
making 300 revolutions per minute it develops 20 actual horse
power, while its weight is but 105 lbs. The smaller engine--the one
illustrated--has cylinders 21/2 in. and 5 in. in diameter, and 31/2 in.
stroke, and weighs 63 lbs., while when making 450 revolutions it
develops 10 actual horse power.

The two engines are identical in design, and are constructed of forged
steel with the exception of the bearings, connecting-rods, crossheads,
slide valves and pumps, which are of phosphor-bronze. The cylinders,
with the steam passages, etc., are shaped out of the solid. The
standards, as will be seen, are of very light T steel, the crankshafts
and pins are hollow, as are also the crosshead bolts and piston rods.
The small engine drives a single-acting air pump of the ordinary type by
a crank, not shown in the drawing. The condenser is formed of a series
of hollow gratings.

[Illustration: LIGHT STEAM ENGINE FOR AERONAUTICAL PURPOSES]

Steam is supplied to the two engines by one boiler of the Herreshoff
steam generator type, with certain modifications, introduced by the
designers, to insure the utmost certainty in working. It is of steel,
the outside dimensions being 22 in. in diameter, 25 in. high, and weighs
142 lb. The fuel used is petroleum, and the working pressure 190 lb. per
square inch.