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Aviation History
1920
1920 - 0866.PDF
basis of argument alone else it degenerates into something resembling that ancient impasse : " Are the mountains better than the seashore ? " As a matter of fact, the effect of any proposed change in military characteristics can be calculated in a sufficiently approximate manner to make possible a decision based upon evidence. For rigid airships which closely resemble vessels, I propose the use of a naval architect's method for analysing such problems due originally to that eminent French designer of torpedo craft, M. Normand, and subsequently extended and perfected by Prof. Hovgaard. By Normand's method, a" rapid estimate can be made of the cost in displacement involved by almost any proposed change in the ship. In the fourth appendix to this paper, I have developed Normand's method to apply to airships by forming the so- called weight equation as the sum of the principal weight groups each, expressed in terms of the independent and de- pendent variables of the design. This weight equation is then differentiated to exhibit the effect of a change in any of these variables and formulae deduced, analogous to those which apply to vessels, by which a quantitative estimate can be made for the effect of such change. An airship can be changed in two ways, by preserving similitude of form and permitting the volume to vary or by holding constant volume and changing the ratio of length to diameter. Considering the first case, the factor of propor- tionality N computed in the fourth appendix is about 4-5 for a ship of L.49 type. This means that an addition of 1,000 lbs. to the weight of any item in the ship calls for such increase in other items, to keep the performance the same, that the total lift must be increased 4,500 lbs. For battleships N is of the order of only 2-5, indicating a much more favourable situation. The principal reason airships appear to be at a disadvantage comes from the longitudinal members of the hull structure whose weight increases as the fourth power of the length of the ship. Consider, now, the effect of holding volume constant and changing the fineness of the ship. The longitudinal members of the hull vary in weight as the third power of the length and the first power of the diameter, while the weight of the transverse frames varies as the fourth power of the diameter. If the ship be fattened up, weight is saved on the longitudinals and lost on the transverses. But if the ship be too long originally there will result an important nett saving in weight. Finally, I have applied the method to a rigid airship of the Zeppelin type (L.49) in an example to show how practical answers may be obtained. The displacement of L.49 is assumed to be 1,940,000 cu. ft., or 129,800 lbs. If it be proposed to make a new design which shall be similar to L.49, except to have 2,000 lbs. more bombs, a 25 per cent, heavier outer cover, a 15 per cent, more speed, the new ship must be given 13,890 lbs. more displacement, or a total volume of 2,145,000 cu. ft. The net price paid in displacement is, therefore, about six tons. On the other hand, if the ratio of length to diameter be AUGUST 5, 1920 reduced from 8 to 7, the ship can be built lighter, and the calculations show that a saving in the new design of nearly five tons is due to this change of form alone. As a final result a new ship resembling L.49 might be built having the proposed changes incorporated, and only be slightly larger than L.49 ; i.e., 1,990,000 cu. ft. The principal dimensions compare as follows :— ' ;. Length L.49, 634 ft., new ship 584 ft. *i Diameter L.49, 78:7 ft., new ship 83-5 ft. It would appear that a decrease in the length diameter ratio is of great advantage, and were it not for the necessity to consider the height of existing hangar door, airships might well be made fatter than the German models. Normand's MethodNormand's weight equation W + Wg= W WB Wc etc. = 2WZ A typical member of the weight equation isW AL^D^07" t or where ratio L/D is constantW AL etc. and W =. kU > AW AL .. •After differentiating (4), ^v~ = 3 T~ iW AL Aa After differentiating (3), -^- =*"•£+ *"„"+ etc- After substituting (5) in (6) AW = 2AWZ = N2WZ ( z *± + etc.), (1) (2) (3) (4) (5) (6) (7) Where N = ^W~=4"&7 for L-49 3wIf weight variables and volume are constant and L/D only changes AW AL . 2AD o (8) (9) w = ALD2 and AWZ w ~ w - AL x T7 L + , + "D AD " D~ and AW = Z =^JWZ [X - ^ 14.770^ for L-49. I Ft. Original : L. 643 Plus additional 2,000 lb. bombs L. 657 And 25 per cent, heavier cover fabric -.. L. 665 And 15 per cent, saved on longi- tudinals and main transvers s L. 650 And 5 per cent, more speed .. L. 665 And length/diameter reduced from 8 to 7 L. 584 (To be Concluded) Ft. 0.78-7 D. 80-5 Cu. ft. 1,940,000 2,080,000 D. 81-5 2,145,000 D. 79-6 D. 81 -5 2,008,000 2,145,000 D. 83-5 1,990,000 COMMERCIAL AVIATION IN NORWAY IN the report on the Commerce and Industry of Norway down to the end of the year 1919, Mr. C. L. Paus, commercial secretary to H.M. Legation, Christiania, states that there was on December 31, 1919, only one company in Norway whose object it is to carry on air traffic on a commercial basis. The name of this company is Det Norske Luftfartrederi A./S., Christiania. "No air service has as yet actually been commenced, and the date of its commencement depends upon the attitude of the Norwegian Government towards an application made by the company for financial assistance. The Norwegian Ministry of Commerce have been petitioned to make a grant of Kr. 1,200,000 to be applied to the initiation and operation between May 1, 1920, and June 30, 1921, of an air service from Christiania via Kristianssand S. to • Stavanger, and from Christiania via Goteborg to Copenhagen. It appears, how- ever, that the Ministry are unwilling to recommend the grant of a larger sum than 60,000 kroner for the period in question, and if this decision is maintained it is, therefore, improbable that air traffic will be opened during 1920. In any case, it is unlikely that operations will pass beyond the experimental stage during the coming year. It is understood that the company have not yet purchased any aeroplanes, and that they are not altogether unwilling to postpone their opera- tions on the ground that commercial aviation is still in its infancy." R.A.F. Marriage Allowances :•,.-"-;: BY the Air Ministry Weekly Orders, dated July 19, the separation allowance, dependant's allowance, and special parents' allowance to the families of married airmen of the Royal Air Force are discontinued. In substitution for them marriage allowances are to be issued. In the case of airmen who extended their service in the Royal Air Force under the terms of the Order of January 3, 1919, or re-enlisted in the Royal Air Force under the terms of the Order of May 10, 1919, the new Regulations shall not apply to such of them as retained during their present engagement a reserved right to the continuation of Army separation allowance, allotments of pay, and family allowance. With effect from September 30, the rates of marriage allowance will be as follows :—(a) For a wife, gs. 6d. per week ; wife and one child, 19s. ; wife and two children, 26s. bd. ; wife and three children, 325. ; for each additional child, 3s. (b) For children where no allowance is admissible for a wife—First child, 95. 6d. ; second child, 7s. bd. ; third child, 5s. 6d. ; each additional child, 3s. The rates of marriage allowance will vary annually according to the index figure for the cost of living as published by the Ministry of Labour. Marriage allowance is normally issuable for the wives and legitimate children or step-children of—(a) airmen who have attained the age of 26 years; or who are over 26, now- serving and already married. 868
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