AIRSHIP DISASTER

Dominion, Volume 14, Issue 305, 19 September 1921, Page 8

AIRSHIP DISASTER

STRUCTURAL FEATURES OF R3B

EXTREME LIGHTNESS SOUGHT The R3B, which collapsed and exploded when flying over Hull on August 25, was tlio largest airship ever constructed, and for her size she was tho lightest. The ship did not represent standard practice in airship design; she was a military experiment. Speed, range, and ability to attain tho unprecedented ceiling height of 25,000 ft., so that she might bo almost immune from attack from anti-aircraft guns, were the ends sought by her designers. She was constructed at the .Cardington Airship Works by Messrs. Short Brothers for the Imperial Government. The design was prepared by the Admiralty airship staff, and construction was commenced in 1918. She was to bo ono of four similar ships. But when the armistice was signed it was decided by tho Imperial authorities not to proceed with tho ships, and it is possible that R3B, which at that time was not at a very advanced stage, would have been scrapped had not the United States Government offered to purchase her if she were completed. It was decided to accept this offer. R3B was a reply to the German highflyer Z7l. Tho German ship had a ceiling height of 24,009 ft., so that R3B with 1000 ft. .above this would have had Z7l at her mercy, for airships are extremely vulnerable to attacks from overhead. Z7l was ono of the airships surrendered to the Allies by Germany. If ability to attain great ceiling height depends on lightness, •so for speed everything must bo done to reduce air resistance. I> the case of tho British ship every possible device was introduced to make her slip easily through tho air. It would be impossible to put tho engines inside a hull filled with a gas so inflammable as hydrogen, and so tho “eglets" for housing tho engines had to be retained; but that they might create a minimum of air friction, their form was "streamlined” with the utmost care. Then in other airships tho radiators for cooling ETli engines had always been placed outside tho eglets; but tho radiators’of the R3B were enclosed, and air was admitted to them through the noses of the eglets. which were louvred for the purpose. There were six engines, each developing 350 horse-power, or 2100 horse-power in all. This was sufficient to drive the hull, 695 ft. in length and 85ft. 4in._in diameter, through still air at 70 miles an hour. The ship’s range at full speed

was» 5000 miles without replenishing the petrol tanks. Of these there were 50, and they had a storage capacity of 30 tons. Three engines, all enclosed in egJets were placed to starboard and three to port. The control cabin, which was near the bows, was on tho centre-line, so that the commander’s view ahead was unobstructed.

What was the particular cause of the disaster may never bo known, says a writer in the "Argus,” but without doubt the general cause was structural weakncss. That too much had been sacrificed for the sake of reducing weight is proved by the fact that K3B developed weakness on her trial trips, so that it was necessary to strengthen the frame. 'R ith a simple girder the strengthening presents no difficulties, but engineering experts agree that in an extremely complex structure, such as the framework of an airship, the strengthening of a particular member is a most risky undertaking, for tho very strengthening of .that one member may react in putting stresses on other members that they were never intended to bear. There was a flimsiness about 1138 that was remarked on by the engineering expert of one of the leading British technical journals. When he saw her just before she was completed, it struck him that the method of attaching the engine cars, or egl-ets, to the main framing might be a source or weakness. /This was carried out ,by wooden struts and stay wires. Supposing that some of the struts and wires failed under the strain, the heavy eglet would swing to and fro like a pendulum, and the stresses in that case might have caused a fracture of tha member of the framing to which it was attached. Qhce tho framing failed—whatever might be the cause of ths failure —the inevitable catastrophe would be but a matter of a few moments. gome of the petrol tanks would bo unseated and fractured by the grinding of tho broken framework, then the gas bags would be cut, ami when this had happened the central passage-way, which ran the whole length of the hull, would be flooded by a. violently explosive mixture of petrol vapour, 'hydrogen gas, and air. The frioi tion •created by the grinding of the r broken mass of girder work would be certain to create a shower of sparks, which would, be sure to ignite the explosive mixture. It has been suggested that Lieutenant Wann, who was in command of the 1138, changed the ship’s direction too suddenly when making some rudder tests, with the result that tile bending strains set up broke her- back. This is considered unlikely by airmen. Lieutenant Wann, it is pointed out, ig a thoroughly trained navigator. Nobody knew better than ho the fragility of his ship. That he would handle her with the utmost care when testing her manoeuvring powers is taken as a matter of course. Another suggestion which has been maos ie that the gyroscopic action produced by the engines would oppose itself to any change in the direction of ‘he airship. This view is not generally accepted by experts, for it is pointed out. that, as .the engines had stationary cylinders, any gyroscopic action produced by the revolutions of tlie propeller shafts and the propellers would be so small as to be negligible. Nor does the "aura” theory find much favour. According to this an airship, is surrounded by an aura of hydrogen, which a spark from tlie engines might at any time tiro. But why, it may bo asked, should this aura cling to the hull of an airship, seeing that between the gas-bags and tho fabric which covers the framing there is in air-filled space. That hydro-

gen docs escape into this space is admitted, for it is impossible io make tho gas-bags of material that will be absolutely impenetrable to a gas so tenuous ns hydrogen. But hydrogen is the lightest of all gases, and such quantities as found their way into the air space between ■ the gas-bags and the outer fabric would at once rise and escape through the vents provided along tho top of tho hull. Tho loss of 1138 must sot back aerial navigation by means of lighter-!}) an-air craft, -even though there is little logical reason why it should do so. This ship was not built for passenger service, but for the special purposes already enumerated. If sho had been designed as a passenger liner, sho could have been ■ made very much stronger, for in civil aviation high-ceiling capacity (which means sacrifice of weight, and, therefore, ‘ of strength) is not necessary. Generally • speaking, a maximum ceiling capacity of i 5000 ft. would be ample for an aerial pas- 1 senger liner. j