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Aviation History
1911
1911 - 0381.PDF
APRIL 29, 1911. [JFJJGHT] AERIAL GUNNERY. By J. H THE article translated by Commander R. H. Keate, R.N., from the Rivista Marittima, and published in FLIGHT NO. 112 (February 18th), dealing with the use of aeroplanes in naval warfare, will no doubt have been perused with considerable interest by your numerous readers. Recent achievements in America have, of course, brought the problem of launching and landing at sea out of the region of theorv into the sphere of practice. Indeed, Curtiss' hydro-aeroplane successes indicate that special launching and landing stages on the decks of ships will prove by no means essential, long before the arrival of the elusive helicopter. The bomb-dropping problem, however, is still in the theoretical stage, at least so far as scientific aiming is con cerned. The only treatment of the subject which I have ever seen in print appeared in Punch some two years ago. A military individual of Teutonic appearance was represented as having dropped a bomb from the car of a dirigible with a view to destroying London ! His remark " Bother ! I've missed it," seems a trifle inadequate. As I have been working at the subject for some time, I was particularly interested to read Claudio Piumatti's treatment of it, and would like to offer a few criticisms and suggestions. First, as to the method for obtaining the speed of the aeroplane through still air, called V in the notation of the article. The value, u, of the component of wind velocity in the direction of flight is assumed, though it would be a difficult quantity to determine if the distance. A B, through which the aeroplane flies were considerable. It is not, however, sufficient to know the component in the direction of flight, since the component at right angles would consider ably affect the problem. Thus if «l denote the component of the wind in a direction perpendicular to A B, then in flying from A to B the aeroplane has really travelled through a distance, A C (Fig. 1), while the wind has carried it through 3. distance, C B. Of course, on a fairly calm day the error involved in ignoring the difference between A B, and A C, might be negligible. Let us suppose, however, that the trial flight is made up and down the wind, so that there is no leeway to allow for. Then if allowance is to be made for the time taken by the aeroplane to reverse before flying back from B to A, it will be necessary to measure the times for the outward and return journey separately. If these be t and tit then t, =-=s U = ,7 andso V = - AB I + - 1, n V + u, - V -u 2 Vi hf The quantity V, is thus determined independent of the value M, of the wind velocity, the only assumption being that the wind velocity is the same at the same, place during the two journeys, even though it may vary from point to point along the course A B. I have already noticed that the two time readings would have to be taken in any case, to correct for the time occupied in turning, so that this method involves no additional readings. Next, as to the determination of the ship's speed. The method suggested involves an accurate knowledge, not only of the length of the ship, but of the position of various objects on deck. How is such information to be obtained ? If the length of the ship were known, the speed could be determined by flying through such a distance that the telescope—first aligned on the stern—points to the bows of the ship. Dividing the ship's length by the time for this flight, the speed of the aeroplane relative to the ship is obtained, the difference between this and the aeroplane's speed being, of course, the ship's speed. The difficulty, however, is that the aeroplane's speed is not known. The aeroplane's speed in still air is IRST, B.A. known, and the velocity of the wind on shore or on the deck of the vessel from which the aeroplane started may have been observed, but this gives little clue to the speed of the particular gust of wind in which the aeroplane happens t» be travelling. I do not know how Capt. Piumatti proposes to allow for the variations of wind in the various strata, though he draws attention to their existence. The anemometer is of no assistance whatever, since, if carried on the aeroplane, it records the velocity of the wind relative to the aeroplane, and this is merely the quantity V, which could be determined at any time, and which, it was suggested, had already been determined by a separate experiment. With regard to the time taken for the bomb to drop, the equation, S = \ g t", is true if we neglect air resistance. This may certainly be done for heights of less than, say, 100 metres, but at 200 metres the effect of air resistance is considerable, and may amount to as much as 15 per cent, for some types of projectile. Bashford's experiments with his chronograph give sonic useful data for calculating the effect of air resistance, but the mathematics of the subject are too intricate for treatment here, The effect can, however, be calculated with sufficient accuracy, if the projectile has some familiar shape (spherical, or cylindrical, with hemispherical, flat, or ogilval head, are the shapes for which Bashford's experiments give data), and if the weight and dimensions are known. For quite irregular shapes the correction could doubtless be estimated with sufficient accuracy. Capt. Piumatti suggests that " a correction for bomb energy due to aeroplane speed must be made." This is surely some thing more than a correction. It is, in fact, the most im portant factor in the whole problem, as an example will show. If a projectile is to be dropped from an aeroplane travelling at 60 miles per hour to hit a stationary target 165 ft. (about 50 metres) below, then the bomb-dropping point is no less than 280 ft. or 85 metres from the target, the distance being measured horizontally. This calculation neglects air resis tance to the motion of the projectile. As I have already indicated the difficulty of obtaining the true speed of the aeroplane, it will be seen that we are still some distance from the solution of the problem. Lastly, even supposing that the various quantities could be obtained in the way suggested, the calculations involved are rather too great to be performed by a passenger in an aeroplane, even though his quiver is full of specially con structed slide rules. If the attack is to be successful, it is essential that the observations, sighting and discharging, should all take place in a few moments, since all the con - ditians, including the "patient expectancy" of the enemy, are liable to change every minute. Realising this fact, I have worked in the direction of producing sighting instruments by means of which the bomb- dropping point may be obtained without calculation, and have so far succeeded in reducing the necessary outfit to two telescopes fitted with suitable adjustments, a barograph, and a watch. The manipulator takes his observations, sets his " sighting" telescope by means of graduated scales which perform the calculations themselves, and discharges his bomb when the target appears on the cross wires. More over, I have not confined myself to the case in which the aeroplane flies in the wake of the ship, as this is a dangerous proceeding, while it unduly limits the attacking capacity of the aeroplane. Others, no doubt, are working along similar lines and will achieve even better results. There is plenty of room for improvement, and as experiments progress the instruments will become simpler and more reliable. The degree of accuracy which it will be possible to achieve iu actual warfare is very difficult to estimate, but if as Mr. Walter F. Reid suggests (as reported in FLIGHT, March 4th), 300 lbs. of explosive can be dropped, it should be possible for an aero plane to do considerable damage, even with a large error in aiming. High Flying in Austria. UP to the present no great amount of attention has been paid to altitude flying in Austria, but on the 21st insL Lieut. Bier improved on Miller's old record of 600 metres by rising to a height of 1,110 metres on his Etrich monoplane. The record was made at the Etrich testing ground near Vienna. 383
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