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Aviation History
1915
1915 - 0323.PDF
MAY 7. 1915- pitch angle. The conception is, we may say, founded on the idea •of a screw which is a true helix, and when pterygoid sections are employed in the design of the blades it is difficult to fix any definite physical feature of the blade as giving a measure of the pitch angle The difficulty is exactly comparable to that of the chord in wing form discussed in Part I of the present paper. If we take the case of an aerofoil designed to the condition of least gliding angle, then we know that the gliding angle must approximate closely to the trail angle of the primary camber t\, for the dynamic reaction may be represented by the angle of the Jiypothetical chord, which is »j/2, and under the condition of least resistance this is half the total. ("Aerial Flight," Vol. I, § 164.) Two proofs of this may be offered ; firstly, there is the obvious fact that the curvature of the primary camber represents in reality the deflection of a current—that defined by the peripteral area—and implies a uniformly applied acceleration and a uniform pressure •distribution; hence, the mean normal whose inclination to the vertical is v/2 gives the direction of the resultant reaction. Secondly <and really the better proof), a dynamic demonstration may be given. (Part IV.) Taking, then, i\ as equal to the gliding angle, and assuming Mr. Froude's 45° as being the angle of the hypothetical .chord, we find that the author's result and the previous result of Mr. Froude's analysis are identical, for half the gliding angle may be expressed as »)/2, and, adding this to the author's value, we •come back to the 45° of Mr. Froude, Fig. 14. With reference to Fig. 14. it is well to point out that the equality of 7 and n only apply provided the condition of least resistance be assumed (direct resistance = dynamic resistance), also that the camber curve shown is definitely the primary camber and has no physical existence in the final blade form. 14. The basis on which the author derived the curves given in Figs. 8 to 13 is worth mention as bearing on the more complete investigation and solution given in Part III of the present paper. In Fig. 15 the gliding angle aOb - y is shown as superposed on the angle of effective pitch dOb = 8 ; now if we, for the time being, regard the problem as that of a flying machine climbing steeply,* Incidentally the author's solution for maximum efficiency is also the solution of the most economical climbing angle. ® ® Zeppelin Bomb Presented to the King. THROUGH the Marquis of Tullibardine, Chairman of the Royal Aero Club, Mr. William Dunsmore, of Bedlington, presented to H.M. the King an incendiary bomb dropped on his farm by the Zeppelin during the recent raid on the North-East Coast. In acknowledging the souvenir, Lord Stamfordham said :—" The King was much interested in having his first specimen of these bombs, and he thinks it was very kind of Dunsmore, on whose farm the bomb was dropped, to allow it to be sent to His Majesty. Evidently, from your account, the enemy did his best to damage the house, and the King congratulates him on the fortunate escape of himself and his property." The Anti-Aircraft Corps. REPLYING to questions put by Mr. Fell in the House of •Commons last week, Mr. Macnamara said that at the first formation •of the Anti-Aircraft Corps there were 100 special constables, no record of whose ages could be found. Up to March 31st last 45 per cent, of the men of the corps were of non-military age and 55 per cent, of military age, a large proportion of the latter coming from the Office of Works and other Government Departments, who could not release them for more active service. After the reconstruction of April 1st 46 per cent, were of non-military age and 54 per cent, of military age. Large numbers of those of military age were medically unfit for more active service. It was pointed out that 100 discharges had been granted to officers and men to join more combatant units of the forces since the corps first started in November, and that over 200 of those in the corps had served or "were serving abroad with the various anti-aircraft detachments. Any member of the corps who wished to join a more combatant tinit was at once released for this. Lord Kitchener and R.A.F. Workers. FOLLOWING on the recent visit of inspection to the Royal Air craft Factory at Farnborough, Lord Kitchener sent the following message to the workers. This has been printed and a copy given to each employee :— "I am pleased to have the opportunity of expressing my appre ciation of the excellent work which is being done by the employees, male and female, at the Royal Aircraft Factory. I am sure that they are willing to put up cheerfully with discomforts and difficulties, both in connection with their long hours of work and in the matter « housing, because they appreciate the fact that work on war munitions, such as aircraft and their parts and accessories, is of vital importance to the British Army. Their work is of real \alue, IfUOWl then an applied force of propulsion sufficient to climb the gradient Oa if no resistance of any kind were experienced, the work being represented by the change of altitude d,>, will, under the real con ditions, result in the machine climbing the gradient Ob, the actual gain of altitude being db ; thus the efficiency is bd/nd. (>n the Imsis of the independent treatment of the annular elements of a propeller, each element is supposed represented by a diagram similar to that given in the figure, and thus each element will have an efficiency proper to its own values of 7 and 8. The author has shown that the efficiency is given by the expression . and its value is maximum when 8 _ ^L Now the angle 8 is definitely re lated to the radius pitch, whereas the angle 7 is, within the limita tion imposed by the condition of minimum value, under the control of the designer ; hence the author has from the outset given the preference to the angle 8 as a datum, that is to say, the angle of effective pitch rather than the blade pitch, which depends upon some arbitrary definition and in any case includes a function of the variable angle 7. A propeller designed on the basis of the 8 angle includes its slip factor in the design, and in any case the quantity which the naval architect terms " slip" requires very careful definition before it can be regarded as one of scientific application. If the hypothetical chord of the blade were something tangible which could be measured, the blade pitch could be appropriately defined as the helical pitch of the chord ; but we have already seen, with reference to F"ig. 7, that the real or " so-called " chord has no necessary relation to the hypothetical chord, and is a measurement of no dynamic import. The difficulty of basing propeller theory of the blade pitch is again complicated by the fact that the designer may elect to vary his 7 angle according to some arbitrary scheme that may lie found advan tageous in practice, and so the blade pitch will vary from point to point in a manner that will defy systematic treatment. For the foregoing reasons the author regards any attempt to rationalise propeller theory on any basis other than that of effective pitch as tending to chaos and foredoomed to failure. To be continued.) ® ® and they can all feel that by their exertions they are helping the troops in the field." Fatal Accident at Gosport IT is with great regret that we record the fatal accident which occurred at Fort Grange, Gosport, on Saturday evening, by which Flight Sergeant W. McCudden lost his life and Second Lieut. N. Read, R.F.C., who was a passenger on the Bleriot monoplane, was seriously injured. According to the evidence given at the inquest it appears that the engine was working badly, due to the carburettor flooding, and owing to the loss of speed the machine side-slipped. As the machine was only about 100 feet up there was not sufficient room to overcome the movement. It was stated that Sergeant McCudden, who was an experienced pilot, was in charge of the machine at the time and giving instruction to Lieut. Read. A verdict of " Accidental Death " was returned. It was announced that Lieut. Read was making a good recovery. Aerial Attacks on Ships. A WALMER pilot, Mr. George Sinclair, on arrival in England last week, reported that a German seaplane had discharged three bombs at the American S.S. " Cushing," which he was piloting to Rotterdam. One of the bombs fell on the stern rail scattering metal all over the deck, but no damage was done. The trawler " Ivis" reported at Lowestoft, on Tuesday, having sighted a Zeppelin at 11.30 a.m. on Monday morning. It was pro ceeding in a westerly direction, but when a stiff breeze sprang up it turned round and went back. In the wireless news sent out from Berlin it was stated, that " on Monday a German naval airship fought in the North Sea with several English submarines and it dropped bombs upon them. One of the submarines was sunk. The airship, although fired at, was not hit, and returned in safety." The Capture of Garros. ACCORDING to accounts printed in German papers, it appears that the capture of Gauos was due to motor trouble. After coming down to forty metres to drop bombs on a railway train, two of them falling on the engine, he was fired at and climbed to a height of 2,500 metres, when the motor stopped. He made a vol plane' and landed in the neighbourhood of Hufte. Directly he alighted he burned his machine and then sought refuge in a cottage, where after a long search the Germans found him. It appears that he is now in a special detention camp at Magdeburg. 323
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