CHAPTER IVTHE GERMAN AIRSHIP FLEET
Manyreports have been current concerning the exact dimensions of the airship fleet that Germany can put into action. It has been said that she has been extremely active since the beginning of the present war in adding fresh units to the forces she had available when the war broke out. It has also been rumoured that she is making a new type of Zeppelin—one much smaller, and which will have greater speed than the larger type.
German Airships in the Spring of 1913.
(1) and (2) as in 1911; since then they have been renovated, and no doubt their speed and volume are much greater.
We must accept with some reserve the reports that are current in this respect, and it may be pointed out that in accounts of the doings of Zeppelin airships in the papers it can be reasonably doubted whether all the Zeppelins mentioned are in reality Zeppelins. Probably some are the smaller types, such as the Gross or Parsifal. The word Zeppelin seems to have become synonymous with a German airship, and the wounded soldiers or prisoners who are responsible for many of the stories told would not be likely to have complete knowledge of the distinctions between classes of airships.
Though what Germany is exactly doing in way of new manufacture must remain in much fog, still we can form some opinion as to her preparedness with aircraft on the lighter-than-air principle from our knowledge of what she possessed last year.
The table on the opposite page will show that her fleet of airships, including those under construction, was then by no means negligible.
A nation possessing such a fleet of large airships as Germany does must be provided with sheds (hangars) for their reception in all parts of the country, and by the table that is appended it will be seen that in this way last year Germany was very amply provided.
I am indebted to theAérophilefor the followinglist of German hangars for dirigibles, with dates of construction and names ofowners:—
Such monster airships as the Zeppelin call for a large proportion of pure hydrogen. This is, indeed, manufactured on a large scale in Germany. It is produced in quantities by the electro-chemical works at Bitterfeld, Griesheim, and at Friedrichshafen, specially for the needs of the Zeppelins at the latter place. There are also works for the production of very pure hydrogen by electrolysis at Bitterfeld, Griesheim, Gersthofen, and Dresden.
In the particular way Germany means to use her lighter-than-air fleet in the present war time will show. If, however, there have not yet been attempts at any combination of action, individual Zeppelins have already played the rôle of dreadnoughts of the air. Though their powers have been no doubt exaggerated, they have been the terror of some Belgian cities.
Early in the morning of August 25th a Zeppelin airship visited Antwerp, and drifting silently with the wind steered over the temporary Royal palace. There it discharged six highly explosive bombs. Not one found its intended mark, though all fell near the palace. One appearsto have been very near hitting the tower of the cathedral. Though the bombs failed to attain the object sought, no less than six or seven persons were victims to the outrage. One struck a private house, killed a woman, and injured two girls, killed two civic guards, and wounded another. One bomb fell in the courtyard of the hospital of St. Elizabeth, tore a hole in the ground, smashed the windows, and riddled the walls.
The Zeppelin repeated its visit early in the morning of September 2nd, but this time with less deadly result. The bombs only wounded the victims. The experiences of the first visit had given effective warning against a repetition of aërial invasion. The city had been darkened, and the airship was attacked from the forts and the high points of the city as soon as it made its appearance. The crew of the airship seem to have been struck with panic when it failed to find its bearings over the darkened city.
It appears they suddenly dropped all their bombs as ballast and rose quickly out of harm’sway. The bombs used on this occasion were not of the same type as those used on the previous attempt on the city. The latter were of high explosive power designed to destroy buildings. The former were covered by thin envelopes, and held together by mushroom-shaped rivets. They were filled with iron bolts and nuts, and were evidently designed for the destruction of human life. It is stated that this is a type of bomb which has never been used by artillery, being made on the same model as that used by the notorious French robber, Bonnet.
In reference to airship raids over cities, it has been suggested in America that the air in their immediate neighbourhood should be mined. This could be done by having a number of captive balloons or kites, the mines on which could be discharged electrically from the ground. For future wars there will no doubt be devised some form of travelling aërial torpedoes for destroying the intruding airships. Such torpedoes would, however, have to be capable of guidance. As has been pointed out by Mr. W. F. Reid, in 1884, at the siege of Venice, theAustrians used free balloons for the purpose of dropping bombs upon the town. The bombs were attached to the balloons in such a way that after the burning of a certain length of safety fuse, the connection was severed, and the bomb fell. The length of fuse was calculated according to the speed of the wind; but, unfortunately, when the balloons rose, they entered an upper air-current travelling in a different direction from that below, and many of the bombs burst in the Austrian lines, whence they had started. Thus it would not be expedient to let loose ordinary unmanned balloons loaded with timed explosives, even if the direction of the wind seemed favourable, for their meeting an approaching airship fleet, as an upper current might bring them back over the city, where they might do mischief.
It is, however, quite conceivable that in the future aërial torpedoes may be devised in the shape of unmanned balloons or aëroplanes controlled by wireless waves of electricity. Those who saw the striking experiment of steering a small navigable balloon in a large hall entirelyby wireless electric waves must have realised the possibilities which may thus be opened out in the future.
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While writing, the news has come that another Zeppelin has dropped three bombs on Ostend, the casualty list being one dog. Two unexploded projectiles were found on a field near Waeragheim. These were probably thrown from the same airship. They show how constantly missile throwing from a moving airship may fail to come near the mark. There is no doubt that to hit particular objects aimed at from airships is by no means an easy matter. Success would seem to require considerable training in this particular method of warfare. The late Colonel Moedebeck, in his well-known pocket-book of aëronautics, makes the following remarks on the throwing of balloonmissiles:—
We may assume that, if handled skilfully, the object aimed at will be hit very exactly. We must distinguish between the throw when the airship is at rest and that when it is in motion. In throwing out while at rest, which is only possible when theairship can travel against the wind, the following points must beconsidered:—(a)The height of the object.—This may be accurately determined from the contour lines on the map, or from a determination of its normal barometric height. Both must be done before starting.(b)The height of the airship above the object.—The barometric height is read and reduced to normal conditions. The difference in heights as found from (b) and (a) gives the height above the object.(c)The velocity of the wind.—May be read on an anemometer in the airship, or determined beforehand by captive balloons.(d)The time of fall.—Given by the law of gravitation from the determination under (b).The height of fall = h = gt²/2.Whence the time of fall t = √(2h/g).(e)The resistance of the air.R = (γ/g)Fv².(f)The leeway.—The longer the fall, and the lighter and larger the falling body, the stronger is the drift. For known missiles, the drift for different heights and wind velocities may be determined practically.(g)Unsteadiness of the airship.—The irregularity of the pressure of the wind, and its constant variation in direction, renders it impossible for the airship to remain perfectly steady.The elements stated under (b) and (f) must be rapidly determined, and suitable tables have been prepared for this purpose. The irregularity of the wind and the peculiarities of the airship mentioned under (g) render a preliminary trial necessary. The drift also is determined by this method, before the large air-torpedo is cast out.The air-torpedo must be brought by sight vertically over the object by steering the airship, the value of the mean drift previously determined being allowed for.In throwing out a missile while actually travelling, the velocity of the airship must be taken into account, as well as the elements (a) to (g) given above, since this velocity is also possessed by the body thrown out.The determination of the proper point is now greatly increased in difficulty. Its position is a function of the relative height of the airship above the object, of the velocity, and of the drift, and allowance must be made for all these factors. For this purpose, motion, either with or against the wind, is the simplest. On account of the point on the earth over which the missile must be thrown out not beingin general well marked, it is necessary to use also angles of sight.The problem before the aëronaut is, then, as follows:—For a given height, velocity, and drift to find the necessary angle of depression at which the missile must be thrown out in order that it may fall on to the object.The casting out of the missile against the object while travelling is governed, therefore, by the same rules as those governing the discharge of a torpedo from a torpedo-boat.
We may assume that, if handled skilfully, the object aimed at will be hit very exactly. We must distinguish between the throw when the airship is at rest and that when it is in motion. In throwing out while at rest, which is only possible when theairship can travel against the wind, the following points must beconsidered:—
(a)The height of the object.—This may be accurately determined from the contour lines on the map, or from a determination of its normal barometric height. Both must be done before starting.(b)The height of the airship above the object.—The barometric height is read and reduced to normal conditions. The difference in heights as found from (b) and (a) gives the height above the object.(c)The velocity of the wind.—May be read on an anemometer in the airship, or determined beforehand by captive balloons.(d)The time of fall.—Given by the law of gravitation from the determination under (b).The height of fall = h = gt²/2.Whence the time of fall t = √(2h/g).(e)The resistance of the air.R = (γ/g)Fv².(f)The leeway.—The longer the fall, and the lighter and larger the falling body, the stronger is the drift. For known missiles, the drift for different heights and wind velocities may be determined practically.(g)Unsteadiness of the airship.—The irregularity of the pressure of the wind, and its constant variation in direction, renders it impossible for the airship to remain perfectly steady.
(a)The height of the object.—This may be accurately determined from the contour lines on the map, or from a determination of its normal barometric height. Both must be done before starting.
(b)The height of the airship above the object.—The barometric height is read and reduced to normal conditions. The difference in heights as found from (b) and (a) gives the height above the object.
(c)The velocity of the wind.—May be read on an anemometer in the airship, or determined beforehand by captive balloons.
(d)The time of fall.—Given by the law of gravitation from the determination under (b).
The height of fall = h = gt²/2.Whence the time of fall t = √(2h/g).
(e)The resistance of the air.R = (γ/g)Fv².
(f)The leeway.—The longer the fall, and the lighter and larger the falling body, the stronger is the drift. For known missiles, the drift for different heights and wind velocities may be determined practically.
(g)Unsteadiness of the airship.—The irregularity of the pressure of the wind, and its constant variation in direction, renders it impossible for the airship to remain perfectly steady.
The elements stated under (b) and (f) must be rapidly determined, and suitable tables have been prepared for this purpose. The irregularity of the wind and the peculiarities of the airship mentioned under (g) render a preliminary trial necessary. The drift also is determined by this method, before the large air-torpedo is cast out.
The air-torpedo must be brought by sight vertically over the object by steering the airship, the value of the mean drift previously determined being allowed for.
In throwing out a missile while actually travelling, the velocity of the airship must be taken into account, as well as the elements (a) to (g) given above, since this velocity is also possessed by the body thrown out.
The determination of the proper point is now greatly increased in difficulty. Its position is a function of the relative height of the airship above the object, of the velocity, and of the drift, and allowance must be made for all these factors. For this purpose, motion, either with or against the wind, is the simplest. On account of the point on the earth over which the missile must be thrown out not beingin general well marked, it is necessary to use also angles of sight.
The problem before the aëronaut is, then, as follows:—For a given height, velocity, and drift to find the necessary angle of depression at which the missile must be thrown out in order that it may fall on to the object.
The casting out of the missile against the object while travelling is governed, therefore, by the same rules as those governing the discharge of a torpedo from a torpedo-boat.