Fig. 60. Horizontal and Vertical pull.
The table of lift and drift gives a fairly accurate method of determining this factor, and we refer to the chapter on that subject which will show the manner of making the calculations.
THE POWER MOUNTING.—More time and labor has been wasted, in airship experiments, in poor motor mounting, than in any other direction. This is especially true where two propellers are used, or where the construction is such that the propeller is mounted some distance from the motor.
SECURING THE PROPELLER TO THE SHAFT.—But even where the propeller is mounted on the engine shaft, too little care is exercised to fix it securely. The vibratory character of the mounting makes this a matter of first importance. If there is a solid base a poorly fixed propeller will hold much longer, but it is the extreme vibration that causes the propeller fastening to give way.
VIBRATIONS.—If experimenters realized that an insecure, shaking, or weaving bed would cause a loss of from ten to fifteen per cent. in the pull of the propeller, more care and attention would be given to this part of the structure.
WEAKNESSES IN MOUNTING.—The general weaknesses to which attention should be directed are, first, the insecure attachment of the propeller to the shaft; second, the liability of the base to weave; or permit of a torsional movement; third, improper bracing of the base to the main body of the aeroplane.
If the power is transferred from the cylinder to the engine shaft where it could deliver its output without the use of a propeller, it would not be so important to consider the matter of vibration; but the propeller, if permitted to vibrate, or dance about, absorbs a vast amount of energy, while at the same time cutting down its effective pull.
Aside from this it is dangerous to permit the slightest displacement while the engine is running. Any looseness is sure to grow worse, instead of better, and many accidents have been registered by bolts which have come loose from excessive vibration. It is well, therefore, to have each individual nut secured, or properly locked, which is a matter easily done, and when so secured there is but little trouble in going over the machine to notice just how much more the nut must be taken up to again make it secure.
THE GASOLINE TANK.—What horrid details have been told of the pilots who have been burned to death with the escaping gasoline after an accident, before help arrived. There is no excuse for such dangers. Most of such accidents were due to the old practice of making the tanks of exceedingly light or thin material, so that the least undue jar would tear a hole at the fastening points, and thus permit the gasoline to escape.
A thick copper tank is by far the safest, as this metal will not readily rupture by the wrench which is likely in landing.