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Aviation History
1920
1920 - 0600.PDF
JUNE 3, 1920 to obtain the necessary degree of reliability. As a modifyingfactor, however, it should be noted that the efficiency of a direct drive propeller at present falls off greatly in enginesof over 400 h.p., and thus the petrol consumption per unit thrust tends to increase with more powerful engines. Onthe other hand, with more powerful engines it is possible to construct power units of lower head resistance per breakhorse-power, and the weight per brake horse-power of the whole unit also tends to decrease with increase inpower. The question of fitting steam engines to rigid airships inplace of the present internal combustion engines, is a matter of some interest. The steam engine is extraordinarilyattractive but for one drawback, namely, its heavy fuel and water consumption per brake horse-power hour. Till thiscan be got over the steam engine is completely debarred. The actual weight of the installation, however, does not ap-pear excessive. The petrol engine suffers greatly from loss of horse-power with height, as unless fitted with forcedinduction the horse-power tends to decrease as the density of the air. In the case of the steam engine no such loss ofhorse-power with height is experienced, and as an airship requires to fly at various heights owing to meteorologicalconditions, etc., this quality would be of considerable ad- vantage. The very great reliability, ease of reversing, flexi-bility, and silence need hardly be emphasised. The question of the most suitable fuel is one of very greatimportance. Owing to the method of storage, the fuel must not be viscous and likely to clog the pipes bringing it from theinternal keel to the power units. A low freezing point is also essential for flying at great heights or in winter weather, andthis rules out such spirits as benzole. To the uninstructed mind, danger of fire in airships isgenerally thought to be due to the presence of hydrogen, and for this reason one frequently sees in the Press articles dealingwith the desirability of adopting helium at all costs. A far more important question appears, however,, to be completelyignored, namely, the danger of fire due to fuel ignition. If the fate of an airship carrying from 20 to 50 tons of briskly burn-ing petrol, whether inflated with hydrogen or helium, is con- templated, it will be readily realised that the advantages inthe use of helium are not so obvious as would at first sight appear. If, further, the number of aeroplanes shot down inflames during the War, or which caught fire by theftlselves due to some failure* in the petrol system or engine, is con-sidered, it will be seen what an extraordinarily dangerous fuel petrol is. Since the outbreak of war, British airships have patrolledover 2,000,000 miles. During this period of over five years there have been in all only eight cases of a British airshipbeing destroyed by fire, five of these during flight and three on the ground. Of these eight cases, six can be definitely tracedin the first instance either to actual petrol fire or to some cause originating in the engine. Of the remaining two cases,one airship was shot down in flames by a hostile seaplane, the inference being that the hydrogen was ignited by incen-diary bullets ; in the second, an abnormal, case an airship broke loose on the landing ground, and finally drifted on tosome telegraph wires which apparently ignited the hydrogen. It will, therefore, be seen that in the great majority of easesthe fires are attributable to other causes then hydrogen. The heaviness of petrol vapour opposed to hydrogen is anadditional cause of danger, as it tends to hang about the bottoms of the enclosed power cars and in the keel where thepetrol is stored, unless very special precautions are taken, whereas hydrogen, owing to its lightness, tends to rise rapidly.The comparative immunity of airships from fire compared to H.A. craft, excluding enemy action, is probably attributableto the fact that saving in weight at the expense of reliability is not considered of such prime importance in the machineryinstallation of airships, and more rugged fittings have been used and more extensive safety precautions employed. Thegreater accessibility to the actual engine in airships also tends to minimise this risk. Nevertheless, it is clearly most neces-sary that every effort should be made to abandon petrol as a fuel for airship engines, and substitute a less volatile fuelsuch as paraffin. ConclusionI had hoped, in this Paper, after dealing with the various parts of a rigid, to discuss problems such as mooring, waterrecovery, and passenger accommodation, which all have an important bearing on structure and performance. This hasproved to be impossible in the time allowed. In conclusion, let me give some of the salient achievementsof British airships. First, they have collectively patrolled and convoyed for over 2,000,000 miles during the War.Secondly, during the 10 months of 1918 prior to the Armistice the proportion of days upon which airships carried out theirflights was 97 per cent. Since then the problem of mooring rigid airships to a mast has been solved, and it is now aseasy for a rigid airship to fly to, fly away from, and ride to a mooring mast as it is for a surface craft to moor to a buoy.The record of coastal airship No. 9 emphasises the reliability of the individual airship. Her life was two years 75 days, hertime in the air 2,500 hours, giving a flying average of three hours six minutes per day for the whole life of the ship. Thus the actual achievements of British airships, duringthe last five years, both their reliable, useful, and regular patrol work, and their great range as illustrated in the Balticand Transatlantic flights of R 34,fshowlng more strongly than any words the very great future which lies in front of airshir s,especially when the improvement in performance which is automatically achieved merely by increase in size is realised.I hope, however, that this Paper has shown that the actual details of airship construction are still in their infancy, andthat equally important improvement in performance, due to refinements in detail, can be predicted in the near future, ifenergetic airship research and experimental work be carried out. Airship development is now being rapidly pushed forwardin America, France, Italy and Germany. To this country airships are of even more importance, owing to the scatterednature of the British Empire and the undisputed supremacy of the airship for rapid long-distance transport. Great strideshave been made during the War, even though Great Britain came late into the airship field ; but she has now, by severalyears of unremitting effort, gained there a position second only to that of Germany. CORRESPONDENCE ]The Editor does not hold himself responsible for opinions expressed by correspondents. The names and addresses of the writers, not necessarily for publication, must in all cases accompany letters intended for insertion in these columns.] ,j_ SIDE-SLIP LANDING [2023] Having been away for some time I had not noticedbefore the other day the reply of E. J. D. to my article on Airbrakes and the Sideslip Landing. His was a very depressing letter, in that, with all hisexpenditure of ink, he did not come within several miles of the subject of the article. I read his letter in severaldifferent positions before I got the least idea of what he was driving at, and after all, I could only conclude that heregarded my article in this light: If machines get much heavier they will have to land faster, and therefore they willrequire an airbrake to pull them up. He appears to have misunderstood the diagram, I regretto notice, for he says he would not come down in steps, as I indicated, but would swing the nose of his machine, andincrease or decrease his slip as necessary. And it probably has not occurred to him that if he increased or decreased hisslip he would come down in steps, which was precisely what J was timidly trying to indicate. The best answer to his enormous letter will be a summaryof what I was supposed to be writing about. Landing speeds are certainly going to get higher andhigher. Soon probably a commercial landing speed will be 100 m.p.h. Therefore, in order to make the best possibleuse of available landing space, it will be necessary to touch as near as possible to the edge of that space. For thatpurpose the gliding angle will have to be regulated. The principal function of an airbrake is to regulate the glidingangle for a given speed. (No, E. J. D. it is not to regulate the speed.) The greater the resistance the steeper thegliding angle. As mechanical airbrakes are, to my mind, impracticable, hence the sideslip.—Q.E.D. The matter of pulling up after landing is another problemaltogether, and one to which I did not refer in my article. It is a designer's affair rather than a pilot's. F. T. COURTNEY South Kensington, May n 6OO
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