第20章

Horizontal motors were practically abandoned some time ago in favor of the vertical type, but Santos Dumont had a logical reason for reverting to them. He wanted to secure a lower center of gravity than would be possible with a vertical engine. Theoretically his idea was correct as the horizontal motor lies flat, and therefore offers less resistance to the wind, but it did not work out as desired.

At the same time it must be admitted that this Darracq motor is a marvel of ingenuity and exquisite workmanship.

The two cylinders, having a bore of 5 1-10 inches and a stroke of 4 7-10 inches, are machined out of a solid bar of steel until their weight is only 8 4-5pounds complete. The head is separate, carrying the seatings for the inlet and exhaust valves, is screwed onto the cylinder, and then welded in position. A copper water-jacket is fitted, and it is in this condition that the weight of 8 4-5 pounds is obtained.

On long trips, especially in regions where gasolene is hard to get, the weight of the fuel supply is an important feature in aviation. As a natural consequence flying machine operators favor the motor of greatest economy in gasolene consumption, provided it gives the necessary power.

An American inventor, Ramsey by name, is working on a motor which is said to possess great possibilities in this line. Its distinctive features include a connecting rod much shorter than usual, and a crank shaft located the length of the crank from the central axis of the cylinder. This has the effect of increasing the piston stroke, and also of increasing the proportion of the crank circle during which effective pressure is applied to the crank.

Making the connecting rod shorter and leaving the crank mechanism the same would introduce excessive cylinder friction. This Ramsey overcomes by the location of his crank shaft. The effect of the long piston stroke thus secured, is to increase the expansion of the gases, which in turn increases the power of the engine without increasing the amount of fuel used.

Propeller Thrust Important.

There is one great principle in flying machine propulsion which must not be overlooked. No matter how powerful the engine may be unless the propeller thrust more than overcomes the wind pressure there can be no progress forward. Should the force of this propeller thrust and that of the wind pressure be equal the result is obvious. The machine is at a stand-still so far as forward progress is concerned and is deprived of the essential advancing movement.

Speed not only furnishes sustentation for the airship, but adds to the stability of the machine. An aeroplane which may be jerky and uncertain in its movements, so far as equilibrium is concerned, when moving at a slow gait, will readily maintain an even keel when the speed is increased.

Designs for Propeller Blades.