ngines developed 118.5 brake horse-power and weighed
1,100 lbs., whereas a six-cylinder engine by the same manufacturer
developed 117.5 brake horse-power with a weight of 880 lbs., the
respective cylinder dimensions being 7.48 diameter by 9.06 stroke
for the four-cylinder engine, and 6.1 diameter by 7.28 stroke for the
six-cylinder type.

A list of aeroplane engines, prepared in 1912 by Graham Clark, showed
that, out of the total number of 112 engines then being manufactured,
forty-two were of the vertical type, and of this number twenty-four had
four-cylinders while sixteen were six-cylindered. The German aeroplane
engine trials were held a year later, and sixty-six engines entered the
competition, fourteen of these being made with air-cooled cylinders.
All of the ten engines that were chosen for the final trials were of the
water-cooled type, and the first place was won by a Benz four-cylinder
vertical engine which developed 102 brake horse-power at 1,288
revolutions per minute. The cylinder dimensions of this engine were 5.1
inch diameter by 7.1 inch stroke, and the weight of the engine worked
out at 3.4 lbs. per brake horse-power. During the trials the full-load
petrol consumption was 0.53 pint per horse-power per hour, and the
amount of lubricating oil used was 0.0385 pint per brake horse-power per
hour. In general construction this Benz engine was somewhat similar to
the Green engine already described; the overhead valves, fitted in the
tops of the cylinders, were similarly arranged, as was the cam-shaft;
two springs were fitted to each of the valves to guard against the
possibility of the engine being put out of action by breakage of one
of the springs, and ignition was obtained by two high-tension magnetos
giving simultaneous sparks in each cylinder by means of two sparking
plugs--this dual ignition reduced the possibility of ignition troubles.
The cylinder jackets were made of welded sheet steel so fitted around
the cylinder that the head was also water-cooled, and the jackets were
corrugated in the middle to admit of independent expansion. Even the
lubrication system was duplicated, two sets of pumps being used, one to
circulate the main supply of lubricating oil, and the other to give a
continuous supply of fresh oil to the bearings, so that if the
supply from one pump failed the other could still maintain effective
lubrication.

Development of the early Daimler type brought about the four-cylinder
vertical