The Loss of the Dixmude
The mystery concerning the loss of the Dixmude (former1y the Zeppelin airship LZ-72) has not been cleared up. Newspapers reported that the airship was burned. Charred remains of the airship and crew had been found, with the conclusion drawn by the press that the airship was struck by lightning pure guesswork. The recovered parts of the airship and of a corpse indicated, rather, that the airship was not struck by lightning (i.e., that the hydrogen in the gas cells was not set on fire by a flash of lightning, but that the airship was, far more probably, destroyed by the gasoline taking fire.
In the cases investigated during the Great War, when an airship fell in flames after her gas had been igaited, it was found that the bodies of the occupants were not at all or only slightly burned. It often happened, in fact, that individual members of the crew escaped with their lives. The newspapers tell, on the contrary, of burnt fragments of flesh which still cling to portions of a uniform; such burns can only be sustained in a gasoline fire in the keel corridor and therefore raised the question as to whether such a fire may not have been the original cause of the burning of the Dixmude. This question will probably never be answered.
The public, however, believed the Dixmude was set on fire by lightning. It considers this the greatest danger for airships and consequently accepts it as the most probable cause when there is no good reason for such an assumption. In fact, the question as to the magnitude of the danger from lightning is of extraordinary importance in estimating the longevity of commercial airships and therefore to determine what conditions may have led to the destruction of the Dixmude by lightning.
It may be taken for granted that an airship with a metal frame, like a Zeppelin, is exposed in only a very slight degree to the danger of being set on fire by lightning. This has been demonstrated by both theory and practice. It must be borne in mind, however, that an airship is not proof against being struck by lightning, so much as against being set on fire by lightning. An airship with a metal frame, when moving between electrically charged clouds, is not only occasionally, but very frequently, struck by lightening, which is harmlessly received by the mass of metal. Theoretically considered, there are two principal cases in which electrical flashes or sparks may pass from a cloud to an airship. A cloud and the breaching airship may be oppositely charged and thus cause a discharge as soon as they are near enough or, in the other case, tne airship may simply serve as a good metal conductor for discharges between oppositely charged clouds. The latter case, by far the more frequent, because the electrical tension of the airship is ordinarily nearly the same as that of the surrounding air, due to the immense radiating surface and to the exhaust gases.
Theoretically considered, the exchange of electricity between the clouds, through the metal frame of the airship, would take place in a harmless manner, because the masses of metal at bow and stern (the probable entrance and exit of the flash) are large enough for the transmission to take place without melting the metal conductor. The correctness of this theory has been demonstrated on numerous occasions which have left noticeable lightning marks on the bow of the airship. In these instances, no damage was done the airship, except, perhaps, the fusing of certain parts of the radio apparatus.
The assumption that the Dixmude was really set on fire by lightning must raise the question as to vhether the gas valves were opened in a thunderstorm. This must then seem at least very probable. There are three possibilities as to how this might happen. Either the commander of the airship, out of ignorance, disregarded the rule not to open the gas valves, or his airship was carried, against his wi11 and in spite of the running engines, above the altitude at vhich the gas valves opened.automatically, or the airship was sailing as a free balloon no longer under control.
The first possibility is improbable, since the unfortunate comnmander seems to have been a good pilot. The second possibility might rather be the case. It can and should not be assumed (if the use of airships was not to be condemned outright) that it is impossible to keep an airship's engines running, below the altittude at which her gas valves open automatically, provided the cruising altitude is far enough below the altitude at which the valves automatically open. In prudent piloting, it is always possible to fulfill this condition for entering the storm clouds. In the case of the Dixmude, however, the pilot probably did not know her location and did not descend far enough below the valve-opening altitude for fear of encountering mountains.
From the whole course of the voyage, so far as it can be made out from newspaper reports, it seems to me most probable that the Dixmude encountered the storm practically as a free balloon and was carried above the valve-opening altitude by vertical currents.
There is an almost absolute lack of information concerning what happened between 8 PM December 20, when the airship was sighted near Biskra, and 3 AM, December 21, when she fel1 into the sea off the Sicilian coast. Since she was driven during this time from Biskra to Sicily, after the announced intention of the commander to keep away from the coast, it appears probable that the Dixmude was carried away by the storm, as a free balloon. There was the danger of the airship being driven into the high mountains back of Biskra, when perhaps one or the other engine stopped and when, perhaps, it was endeavored to fly as lov as possible, in order to escape the stronger winds higher up. In this event there was great danger of being carried against the cloud-enveloped mountains, perhaps by some descending mountain current. At any rate, it is noteworthy that, early in the evening of December 20, all radio communication with the airship suddenly ceased; also the circumstance that only the body of the commander was found and indeed with serious injuries, which cannot be explained simply by the impact of the car with the water. The falling speed, even of the completely burned airship, for an assumed weight of about 99,000 pounds, could not have exceeded 50 feet per second. What then broke the arms and legs of the commander and what became of the many other occupants of the pilot car?
The French Navy was making an entirely unwarrantable and careless use of the Dixmude. It is true that the airship had a carrying capacity of over 100,000 pounds, but this was for the purpose of making raids of one to two days duration and was accordingly designed for carrying as much water ballast as possible, but not for packing full of gasoline in order to make endurance trips of four to five days, as the French Navy employed her. All parts of the airship were made as light as possible, in order to be able to perform her military tasks. This light construction, which introduced an element of risk from excessive stresses, was justified only by the necessity of flying high in ordex to avoid the danger of falling a victim to hostile incendiary fire. Under these circumstances, it was almost a miracle and a proof of her good construction that the French had already been able to carry out a series of very long flights with the Dixmude, especially as they lacked the experience in the handling of Zeppelins.
What holds true for the airship, as a whole, applied more particularly to the engines. The 260 HP Maybach engine was not built for endurance runs of four to five days, but generally reached the limit of its efficiency in two days, when it should be overhauled and have certain parts replaced,especially the whitemetal bushings, which can hardly stand a longer period of uninterrupted use. Hence it would not be at all strange, but instead, very probable that the Dixmude began to have engine trouble at about the time when the wind increased to a storm, i.e., after a nonstop flight of over 60 hours.Probably she did not have the use of all six engines at that time and had to run the remaining engines all the harder in order not to be carried back too far as the wind grew stronger. This probably soon resulted in putting other engines out of commission, so that the airship no longer had sufficient speed and momentum to respond to the pilot's hand.
In other words, she rapidly became a free balloon. The assumption would be that some sudden catastrophe occured which instantly extinguished all life in the pilot car.
The Dixmude left Toulon on Tuesday, December 18, vith the expectation of reaching In Salah, about 930 miles southwest of Tunis, by 4 p.m. of the following day. Here the airship turned, and at about 9 a.m. Thursday, December 20, reached a point somewhat south of Biskxa. She had now been 50 hours in the air.. Then, as the west wind was increasing, her course was changed to the northwest, toward the city of Algiers, instead of along the coast toward Ttinis. Her ground-speed dimini~hed as the wind continued to increase. Making an average speed of about 25 miles per hour, she reached Bou Saada at 1430 p.m. Here she turned toward the south and at 6.30 p.m. was again south of Biskra. She now remained nearly stationary, apparently with the intention of riding out the storm.
The situation was evidently getting serious. Since the engines were probably no longer in condition to attempt to cross the sea in the face of the storm, the correct course was doubtless to work the airship gradnally southward, with her head to the west wind, in order to avoid the storm center and leave more land behind her to the leeward against the danger of being driven back, since the wind at Bou Saada was blowing directly toward the sea. The commander proceeded accordingly and, if nothing had gone wrong on the airship, might have been able, by the next day, to turn north again toward Algiers. According to radio messages, there was still sufficient fuel for two days, though this esimate was probably based on not running all the engines at the same time.
The situation was not reassuring, however, since tbere were mountains east of Biskra with peaks rising to 7700 feet, into which there was danger of being driven, in case the wind should increase or the engines fail to function. In this,event, it would be necessary to attain a higher altitude by discharging ballast, in order to clear the mountains by night and in the clouds. At higher altitudes, however, the velocity of the wind was doubtless greater, so that the airship would be carried east still more swiftly. Did the Dixmude have enough free ballast for such a case? Hardly, since such an ascent would have necessitated the discharge of 40,000 to 44,000 pounds of ballast at the time of taking off and the fuel thus far consumed was perhaps only 22,000 to 26,000 pounds.
Some seven hours later, around 2 a.m., Friday, Decenber 21, the Dixmude fell into the sea off the coast of Sicily. How did she come to be there? Probably not through the volition of her commander with her engines running, for it is inconceiable that the commander sholld suddenly abandon his previous correct tactics, in order to qo wherever the storm might carry him. There may have been fuel enough at noon to warrant such a course, but not at night, after the supply had been much further reduced. It could hardly have happened unintentionaly, with the engines running against the wind, which must have developed an entirely improbable strength, in order to be able to drive the airship backward 500 miles in seven hours. Hence the only reasonable assumption is that the airship was driven by the wind as a free balloon with but little, if any, available engine power. In this event, it is quite"probable that the airship could have been carried-from the mountains east of Biskra the 435 miles to the coast of Sicily in six to seven hours.
After the airship was once in the center of the storm, with her steering gear disabled or with little engine power and dynamic lift, her flight as a free balloon could only be of short duration, owing to the precipitation of moisture which would cause her to sink gradually, entirely apart from the danger of vertically descending air currents and electrical phenomena.
When the French newspapers blame the Navy for carelessly exposing the Dixmude to destruction, their reproaches are largely justified. The airship was employed, at a very critical and stormy season of the year, to undertake tasks for which she was not designed. It is true that the Dixmude had a carrying capacity""ofover 100,000 pounds and that, in case of necessity, she could carry sufficient fuel for a voyage of at least four or five days. For such a long flight namely from Tours to In,Salah, nearly 1400 miles distant in the Sahara Desert, the possibility that a storm might arise at any time (as demonstrated by the event) should have been taken into account. Moreover, the airship was not designed for long flights, but for military flights of only one or two days. The object of her large relative and absolute carrying capacity was to enable her to ascend to a very high altitude in order to avoid hostile fire. Her engines were not designed for a continuous run of four or five days. The manufacturer of the 260 HP Maybach engines, of which there were six on the Dixrnud, always refused most decidedly to guarantee them for more than 48 hours continuous running. Especially, the crankshaft bearings mere not designed for longer use. Engines and airship mere both made light for high altitude military flights. The Dixmude had already been flying 60 when she encountered the storm, which relentlessly forced engines to their utmost capacity at a time when they were already suffering from the effects of long continued use.
|Join the GlobalSecurity.org mailing list|