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Aviation History
1921
1921 - 0818.PDF
DECEMBER 8, 1921 THE PRESENT STATE OF AIRSHIP DEVELOPMENT* By Major G. H. SCOTT, C.B.E., A.F.C. IN his introduction Major Scott stated that, in his opinion,if air transport is to take its place with other existing forms of transport, the long-distance routes of the world must beestablished. In considering the present state of technical development it is possible to deal with each of the individualparts separately under the following headings : hull, fabric, engines, safety, handling on the ground, handling in the air,navigation and wireless. Under the first heading the lecturer dealt with the generalconstruction of airship hulls, and pointed out how construction, especially as regards external and internal keels, has alteredsince the early days. The first stream-line airship was the Schutte-Lanz, which was introduced as early as 1909, andwhich had a fineness ratio of 7 • 1 to 1, as compared with 9 to 1 for the contemporary Zeppelins. The reduction in finenessratio reached its limit in the German commercial airship " Bodensee," with a ratio of 6-5 to 1. This ship had aspeed of 81-2 miles per hour. With the introduction of larger diameter airships it was found that the stresses inthe radial wires became excessive from the end pressure of the gas bags. To release this tension in radial wires anaxial wire was introduced. This wire runs longitudinally through the centre of the ship. Shear wires were alsointroduced leading from the top of one main transverse frame through the gasbag to the keel at the foot of the adjacentframe. In the earlier ships fins, rudders and elevators were of the box type. These were superseded later by the simplefin, but as the speed of the ships increased the resistance of this type of fin became excessive owing to the large amountof external wiring, and in 1918 streamlined or cantilever fins were introduced. " This," the lecturer said, " brings theBritish airship up to the "R.36" class, which can be taken as a thoroughly proved design, embodying no experimentalfeatures. Her dimensions, etc., are :— "Length, 672-2 ft.; diameter, 78 • 75 ft; capacity,2,101,000 cubic ft. ; gross lift, 63-8 tons; useful lift, 23-5 tons ; horse-power, 1,570 ; full speed, 56 knots ; cruisingspeed, 45 knots." As regards gasbags. Major Scott stated that Germany hasproved one step ahead of this country by the introduction of 15-metre gasbags instead of 10-metres, as in British andprevious German airships. These 15-metre gasbags were employed in all ships of the " L.60 " class, and in the " L.71 "and "L.72," and proved satisfactory. The wider spacing of the main transverse frames caused vibration of the keel, andstirrup wires were introduced. These lead from the top of the main transverse frames through the gasbags on tothe corridor midway between main transverse frames, sup- porting the corridor at this point." The next step taken by this country," the lecturer said, " was the construction of ' R.38,' which embodied the 15-metregasbags, but omitted stirrup wires. Other new features introduced were :—Increased diameter from 80 ft. to 85-6 ft.Modified form of corridor, the old triangular form being superseded by a four-sided section. New method of gasbagwiring, the nets and diamond form of gasbag wiring being replaced by circumferential wires, running parallel about9 ins. apart right round the ship. The lift of the gas is taken by these wires, and is transmitted from them to themain transverse frames by catenary wire, a new feature of this design. Larger petrol tanks were introduced in orderto concentrate the loads at the main frames. Previous tanks were of 80 gallons capacity, and the new ' R.38 ' tankswere of 160 gallons capacity. A modified form of balanced rudder and elevator were also introduced. " As stated in the report of the Court of Inquiry,' R.38' waswrecked due to structural failure in the air. A careful investigation into the causes of this failure is at present beingundertaken Ipy the Accidents Investigation Sub-Committee of the Aeronautical Research Committee. I am not atliberty to make any statement at present. Some of the features introduced into ' R.38' are no doubt sound, and it mustbe realised that' R.38' was designed for a very special perform- ance, and the trials indicated that this performance wouldhave been realised. " Summarising, there is in existence today an airship of the' R.36' type, proved and tried out, with a performance as stated earlier. Also it would be possible to build an airshipof 2,500,000 cubic ft. capacity without embodying any new features that have not already been tried out and proved inthis country or in Germany." The lecturer then dealt with the question of fabric, and • Extracts of a paper read before the Royal Aeronautical Society onDecember i, 1921. permeability, relating to the development of gasbag con- •struction from the early German cotton rubber-proofed bags, to the modern version where fabric in conjunction withgold-beater's skin is used. He pointed out that sticking gold-beater's skin to the fabric with rubber is not a goodmethod for ships to be used in tropical or semi-tropical conditions, but that the employment of gelatine glue appearsto be satisfactory. He finally mentioned that in view of the enormous number of skins required (over 300,000 in the caseof a ship such as ' R.36'), the question of a substitute is of importance, and that a good deal of work has been done onsynthetic substitutes for gold beater's skins, which is very promising.On the question of airship engines, Major Scott stated that the requirements are entirely different from those ofan aeroplane engine, and that we have not yet in this country a British engine specially designed for airship work. Theonly engine designed to meet airship requirements is the German Maybach. Whereas the average requirement of anaeroplane engine is a few minutes at full power, followed by some five or six hours at about three-quarter power, the airshiprequirements are more exacting. For commercial ships, the average duration will be about 50 hours, and the engine willbe required to develop three-quarter full power, with occasional stops, for the full period, or to develop full power for three-quarters of this period. The modern airship starts its journey with about 20 lbs. of fuel for every rated horse-power, while thecorresponding figure for aeroplanes does not often exceed 5. Thus a 10 per cent, increase in fuel economy under workingconditions is equivalent to about 2 lbs. weight per horse- power in the engine. An engine designed for airship workmay, therefore, have a higher weight per horse-power, provided there is a corresponding decrease in consumption,and such an engine running at lower revolutions, would be more reliable and have a longer life. With reference to the question of economising fuel, MajorScott stated that until recently no satisfactory manner of burning hydrogen and petrol mixed had been devised, butthat recent experiments have indicated a method of doing so which should greatly increase the performances of theairship in the future. The use of kerosene or crude oil instead of petrol would decrease the danger of fire, and hethought that the development of their use could be con- fidently predicted once the demand is realised.Regarding propellers, Major Scott gave a brief history of the development of the placing of these, beginning withthe earlier types in which the propellers were placed on brackets attached to the hull and driven by gearing, andleading up to the modern practice of direct-driven propellers placed at the rear of a comparatively small power car.Turning his attention to the question of safety, the lecturer pointed out that the danger to a modern airship must beconsidered under two headings, dangers due to fire and dangers due to weather conditions. The former may besub-divided into the danger due to petrol fuel, and that due to hydrogen. While admitting that there is a certainamount of danger due to petrol, Major Scott pointed out that this is no more serious than that due to the same causein an aeroplane, and that danger of hydrogen is much less serious than that of petrol. " In all cases of fire in rigidairships, " he said, " the ignition of the hydrogen has been a secondary cause."As regards danger from weather conditions. Major Scott said that a hull of 2^ million cubic ft. could be built todaywith the same factor of safety as " R.33 " and " R.34," which ships have safely weathered the worst conditions inthe air. " The chief danger in an electrical disturbance is not," the lecturer pointed out, " due to lighting, as isgenerally thought, but to the very violent air currents which throw excessive strains on the hull structure." It is, however,comparatively easy to avoid thunderstorms, and Major Scott stated that he could say definitely that thunderstorms inthis country do not constitute a danger to airships, nor will they do so in the tropics when the meteorological organisationhas been extended to meet the comparatively simple requirements. The limiting factor in the usefulness of an airship has,until comparatively recently, been the handling of the airship on the ground. An airship operating from a shed is handi-capped by not being able to leave its shed except in moderate winds. Experiments with mooring masts have given excel-lent results, which were summarised as follows by Major Scott :— " It was proved that an airship could remain at a mooring. ;- '-" •
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