he vertical type, doubling the power of this with only
a very slight--if any--increase in the length of crankshaft, the Vee
or diagonal type of aero engine leaped to success through the insistent
demand for greater power. Although the design came after that of the
vertical engine, by 1910, according to Critchley's list of aero engines,
there were more Vee type engines being made than any other type,
twenty-five sizes being given in the list, with an average rating of
57.4 brake horse-power.

The arrangement of the cylinders in Vee form over the crankshaft,
enabling the pistons of each pair of opposite cylinders to act upon the
same crank pin, permits of a very short, compact engine being built, and
also permits of reduction of the weight per horsepower, comparing this
with that of the vertical type of engine, with one row of cylinders.
Further, at the introduction of this type of engine it was seen that
crankshaft vibration, an evil of the early vertical engines, was
practically eliminated, as was the want of longitudinal stiffness that
characterised the higher-powered vertical engines.

Of the Vee type engines shown in Critchley's list in 1910 nineteen
different sizes were constructed with eight cylinders, and with
horse-powers ranging from thirty to just over the hundred; the lightest
of these weighed 2.9 lbs. per horse-power--a considerable advance in
design on the average vertical engine, in this respect of weight per
horse-power. There were also two sixteen-cylinder engines of Vee design,
the larger of which developed 134 horse-power with a weight of only 2
lbs. per brake horse-power. Subsequent developments have indicated that
this type, with the further development from it of the double-Vee, or
engine with three rows of cylinders, is likely to become the standard
design of aero engine where high powers are required. The construction
permits of placing every part so that it is easy of access, and the
form of the engine implies very little head resistance, while it can be
placed on the machine--supposing that machine to be of the single-engine
type--in such a way that the view of the pilot is very little obstructed
while in flight.

An even torque, or great uniformity of rotation, is transmitted to the
air-screw by these engines, while the design also permits of such good
balance of the engine itself that vibration is practically eliminated.
The angle between the two rows of cylinders is varied according to the