Page:Aircraft in Warfare (1916).djvu/60

§11 drift and earth's rotation automatic; this could be done without difficulty, and would mean the elimination of errors whose combined value may amount to something like 60 ft, at 6000 ft, altitude—i.e., an angular magnitude represented roughly by the apparent diameter of the sun or moon.

The height to which aircraft artillery will carry is by no means subject to the same limitation as that of the small-bore machine-gun or rifle, the resistance of the air being many times greater than that due to gravity. Thus the ordinary rifle bullet, at 2,000 foot-seconds muzzle velocity, would carry to a height of over 60,000 ft. in vacuo, instead of approximately 7,000 ft, actual. If we take the case of a 1-pounder having the same velocity, its effective vertical range is well over 12,000 ft., and from that calibre upwards the range will, in practice, be more a question of the shell being properly directed than whether it will attain the height. At the best, firing from the ground at an aeroplane at high altitude, will require skilful gunnery, and when near the limit of the trajectory nothing but sheer good luck will render a hit effective. The angle of "lead" it is necessary to give to allow for the velocity of flight, as already stated, is one of the difficulties of high-altitude shooting. This angle is only constant so long as the velocity of the projectile is constant, assuming (as fairly represents the conditions) the flight speed not to vary; at extreme heights the velocity of the projectile has fallen so low that a very slight error in range-finding will be fatal to accuracy. The solution of this difficulty may be found in the employment of guns of about 3-in. bore—i.e., a 12-pounder or 15-pounder, with the concurrent advantage of a full shrapnel charge, and, in shot-gun terminology, a larger killing circle. The obvious disadvantages, however, of artillery, in place of a light automatic or