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Aviation History
1929
1929 - 0763.PDF
FLIGHT, APRIL 11, 1929 HANDLING AND MOORING OF AIRSHIPS Lecture Delivered before the R.Ae. Society by Maj. G. H. Scott WE give below a summary of the very interesting lectureon " Handling and Mooring of Airships," deliveredby Maj. G. H. Scott on April 4, before the Royal \cronautical Society and Inst. of Aeronautical Engineers. In his opening remarks, Maj. Scott considered the essential requirements and limitations existing. Although, he said, i he hull of an airship was strong enough to withstand the wind pressure, any restriction to free motion must be exerted at individual points on the hull, and the principal problem lacing the designer was the distribution of the local load exerted at those points—either by the mooring tower, the miy ropes, or other devices—through the members of the structure in order to counter the wind pressure exerted over the large surface of the hull or fins, and the limiting factor was largely controlled by the amount of local load that could satisfactorily be dealt with. Probably the easiest point at which to obtain real strength in the structure of an airship was the extreme nose, and this was one of the reasons why tower mooring, in which the airship was attached to the tower by the nose, would appear to be the logical method of mooring. It must not be assumed that the loads at the nose in tower mooring only affected the actual nose piece itself; the tower mooring condition actually con- trolled the design of the main framework of the airship for about one-third of its length from the bow aft. But when moored to a tower and allowed to swing freely in the wind, no other important external local loads were exerted on the airship. When handling an airship on the ground it was necessary to manoeuvre the ship into a position not in line with the wind, necessitating the exerting of external forces at points other than the nose, and to obtain the necessary local strength at those points was not so simple ; there was also the problem of restricting vertical motion. Handling In and Out of the Shed In dealing with this section, Maj. Scott mentioned an article written by Prof. O. Krell, which dealt very fully with many types of sheds. One noticeable fact in this article was that the whole question had been considered on the assumption that the lee doors of a shed were always used, whereas, in this country, the tendency had been to use the weather door, or where possible, to take an airship into the shed tail first and out bow first. Maj. Scott said there were many advantages in employing this method of handling, the most important being that the large fins of the airship, more particularly the top fin, were more affected by gusts and eddies than the bow. Another advantage was that, with the wind blowing at an angle to the shed, the airship was allowed to swing about the bow into the wind as soon as clear of the siied, and if handled bow first she would swing away from the shed, whereas, if handled stern first, she would swing towards the shed. .Maj. Scott next dealt with the various types of sheds, and regarding revolving sheds, he stated that there was no doubt that they considerably facilitated the handling of airships, but largely due to their big initial cost no attempt had been made to construct one since the war. The intro- duction of the mooring tower had removed the necessity of a revolving shed, as an airship could moor and await suitable weather to enter the shed. In his opinion, with airships of the size of R.100 and R.101 and upwards, it would be practically impossible to handle them on the ground or in and out of the sheds, except in light winds whose direction was up and down the shed, and not at all in winds that had any appreciable component across the shed. In this country handling had always been carried out by man power, no mechanical method having so far been adopted. The intro- duction of handling rails, as used in Germany and at Lake- uurst, would appreciably reduce the number of landing party required, but would not permit of handling an airship in and out of a shed in increased wind velocities to any appreciable extent. The handling rail could, however, "be acceptedj s a proved method and would probably be fitted to all operating sheds in the future, as where continuous operations or any considerable amount of handling had to take place, r!n savmg.in Personnel would justify the expenditure on the on t]' Scott thea described the construction and Onl «?° handIiag rails, and other methods of handling, ^ieotner method, under construction in the U.S.A., was a withthYu mooriQg mast consisting of a tripod stub mast The legs of the mast resting on caterpillar tractors. e proposed method of operation was to moor the airship to the stub mast and then move the mast complete with airship into the shed, the after guys being manned by the landing party or attached to the "trolleys of the handling rails. There would appear to be a number of objections to such a scheme—any unevenness of the aerodrome would be magnified by the height of the mast and cause sudden accelera- tion or deceleration of the mooring point, which would put heavy stresses in the nose of the airship. This could probably be eliminated by substituting for the tractors,bogeys running on carefully laid down tracks. As regards landing to a landing party, Maj. Scott thought that only one factor had been introduced in recent years, and that was the effect of increase of size. The principal effect of this increase was to reduce at any given velocity the dynamic forces on the airship as compared with her gross lift, and as variations in buoyancies due to variations in air temperature were proportional to the gross lift, either the pilot must accurately forecast these variations or land faster. An endeavour to forecast more accurately the conditions was being made by fitting electrically recording thermometers in the meteorological hut, giving the temperature at two or more levels, and by improving the organization for the trans- mission of the information to the airship before landing, but even then it would probably be necessary to land the two new airships, the R.IOO and R.101, faster than the older R.33 class. This introduced another point, owing to the good aero- dynamic form of these ships compared with previous airships and their greatly reduced head resistance as compared with their gross weight. These two airships would maintain their air speed for a considerably greater time and distance than the previous airships. The necessity for ample astern power was therefore increased. That the necessity for astern power increased with the size of the airship was borne out by past experience. With the small non-rigid airship of the Blimp and Coastal type, the necessity for astern power was never felt, as these airships could be landed comparatively slowly even in a dead calm and rapidly lost headway when the engine was stopped or slowed down. As size was increased it was found essential to fit astern power, and although rarely used in the 1,000,000 cub. ft. airships of the R.23 class, was almost invariably used in the better streamlined and larger R.33 class. Another danger that became increasingly great as the size of airship increased was the danger of carrying away one or more members of the landing party, if the air ship was landed too light, as the amount of surplus buoyancy an airship should have when landing was roughly proportional to the gross lift. Therefore, with larger airships it became more and more essential to land to a mechanically- operated system such as a mooring tower. He thought the airship pilot of the future would look with horror at the idea of landing to a landing party ; it was a manoeuvre only to be carried out in cases of extreme emergency. Mooring Towers Maj. Scott next turned to the mooring tower. Since he read his paper on the " Development of Airship Mooring," three years ago, new problems and new proposals had arisen. One of the most important was the American proposal of a short or stub mooring mast as opposed to the tall tower hitherto used. This proposal briefly consists in mooring an airship close to the ground with the nose of the ship received to a mast just sufficient height to keep the cars clear of the ground when on a horizontal keel, the cars being secured to trolleys or weighted bogeys so that they prevent any vertical motion of the tail. The advantages and disadvan- tages of the two systems, said Maj. Scott, were :— High Mast.—Advantages.—(a) Landing can be made pos- sible with safety in comparatively bad weather, (b) Even in bad weather a party of 14 to 20 men is all that is required. (c) The airship can be slipped from the mast with safety in any weather, (d) It is eas\' to standardise it for a number of different sizes and shapes of airships. Disadvantages.— a) Difficulty of carrying out repairs to the outside of the airship while moored, probably common to all types of mooring mast, (b) Strain on personnel if long periods of mooring are carried out, also common to all types, and can be largely overcome by having duplicated crews. (c) Danger of airship being driven down by snow. Stub Mast.—Advantages.—(a) Certain types of repairs are probably more easily carried out than at a high mast. (b) Airship not so likely to be driven down by snow as at a 305
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