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Aviation History
1956
1956 - 0389.PDF
6 April 1956 387 798 B.H.P. and Puma engines were built, whereas the output for the last three months of 1917 had been only 241. By October 31st, 1918, however, the R.A.F. had more Pumas on charge than any other individual type of engine: the total was 3,255, in addi- tion to which 89 Galloway Adriatics were held. German bombers demonstrated the effectiveness of daylight bombing in the summer of 1917, when they made several attacks on Southern England. The telling London raid of June 13th, 1917, forcefully impressed on the Cabinet and population that bombing by aeroplanes represented a serious threat, and the Air Board was requested to submit a scheme for the expansion of the British aerial forces. On June 21st a meeting was held at the War Office, and it was decided to increase the number of service squadrons of the R.F.C. from 108 to 200. It was intended that the majority of the additional squadrons were to be bomber units. The Cabinet approved the proposal on July 2nd, and Sii Douglas Haig was informed of the decision on July 13th, in order that he might begin to seek the additional aerodromes which would be needed to accommodate the new squadrons. Haig was not enthusiastic about the nature of this expansion of the R.F.C. which, he maintained, had been planned without regard to the requirements of the British armies in France. He was anxious to see priority given to the establishment of the 76 squadrons he had asked for in November 1916, with the addition of 10 bomb- ing squadrons for attacks on German aerodromes. Finally, the War Office specifically asked Haig to provide for the accommoda- tion of 40 squadrons additional to the 86 he himself regarded as the essential minimum. He was to assume that the last of the squadrons would reach France by the end of August 1918. Haig was therefore entitled to assume that, in a little over twelve months, he would have 50 squadrons available for long- distance operations. He began immediately to arrange for the accommodation of 40 of the units in the British zone and for ten in the French zone near Nancy, where they would be close to the numerous targets lying in the Rhine industrial areas. On August 24th, 1917, he wrote to the War Office, pointing out that enemy fighter opposition to the proposed raids would be intense, and that he thought it would be necessary for 25 per cent of the participating aircraft to fly, without bombs, as escorts to the bombers. For this purpose he recommended that the escorts should each have at least four machine-guns, two firing forwards and two rearwards. The question of the type of aircraft which should equip the new squadrons had been considered by the War Office. The official choice fell first on the D.H.4, a type which was already in pro- duction. Some minor modifications were envisaged, but it was made an overriding condition that their incorporation must not delay production. Sir Douglas Haig was also told that efforts were to be made to produce a design which would have a longer range than the D.H.4. In June 1917 a total of 700 DJH.4s were ordered for the equipment of the new bomber squadrons. On July 23rd, 1917, the controller of technical design laid before the Air Board plans of an extensively-modified D.H.4. So exten- sive were the modifications, in fact, that the aircraft had been given the new designation D.H.9. The B.H.P. engine was to be fitted. In support of the new type it was stated that "whereas the D.H.4 lost 17 miles an hour when flying fully loaded at 10,000 feet" (the authority and validity of that statement are questionable) the D.H.9 would retain its speed of 112 m.pii. at that height and would have a greater range. The Air Board did not immediately transfer their favour to the D.H.9, but at a further meeting on July 26th an assurance was given that adoption of the new type would cause only an initial production delay of some three to four weeks. It was thereupon decided to adopt the D.H.9 in preference to the D.H.4. It is perhaps as well to remember that, at that time and in the light of the information and assurances given to the Air Board, the decision was probably justified. A possible reason for early optimism over the D.H.9's performance is the fact that the first few Siddeley Pumas were rated at 300 h.p.; but the troubles experienced with the cylinder blocks led to the derating of the engine to 230 h.p. The prototype D.H.9 was A.7559, a converted D.H.4, and was flying in July 1917. It was powered by one of the Galloway-built B.H.P. engines and, even without bomb load, its performance fell short of the estimates given to the Air Board. The first pro- duction D.H.9, C.6051, was tested in November 1917 with a Siddeley-built B.H.P. engine. With two 230-lb bombs the speed proved to be 111.5 m.p.h. at 10,000ft; but a month later, by which time a clear-view cut-out had been made in the lower starboard wing root and the engine's total flying time had reached 55 hours, the speed was down to 104.5 m.p.h. at 10,000ft and the aircraft could climb little above 15,000ft. It was obvious that the D.H.9 fell short of requirements, a fact which seriously disquieted Maj-Gen. H. M. Trenchard as soon as he learned of it. As early as November 16th, 1917, he wrote to Maj-Gen. J. M. Salmond, the then Director-General of Military Aeronautics, to say that Mr. Geoffrey de Havilland had told him unofficially that the D.H.9 would have a poorer performance than the D.H.4 with the 275 h.p. Rolls-Royce engine. Trenchard expressed his opinions in these characteristically forthright terms: — "I do not know who is responsible for deciding upon the D.H.9, but I should have thought that no-one would imagine we should be able to carry out long-distance bombing raids by day next year with machines inferior in performance to those we use for this purpose at present. I consider the situation critical and I think every endeavour should be made at once to produce a machine with a performance equal at least to the existing D.H.4 (275 Rolls-Royce) and to press on with the output with the utmost energy. ... I am strongly of opinion that unless something is done at once we shall be in a very serious situation next year with regard to this long-distance day bombing. . . ." Two days previously, on November 14th, Sir Douglas Haig had requested that orders for the D.H.9 be reduced to provide sufficient aircraft for the equipment and maintenance of only 15 squadrons. This request was, of course, inspired by Trenchard, for it was his opinion that the D.H.9 would be out- classed by June 1918. Events were to prove him correct. Salmond urgently reported Trenchard's opinions to the Air Board, but was told by Sir William Weir, the Controller of Aero- nautical Supplies in the Ministry of Munitions, that the choice lay between the D.H.9 with the B.H.P. engine or nothing at all. On November 28th Trenchard attended a meeting of the Air Board and bluntly stated his objections against the aircraft. At that time no D.H.9 had reached France (indeed, only five were completed by the end of 1917). It seems hardly credible that the grim lesson of the B.E.2C and 2E had not been learned, and that another type of inadequate aircraft was about to be introduced into operational service. What charged the situation with the element of catastrophe was the fact that the D.H.9's imperfections had been recognized before it went into service. It would be unjust to describe the machine itself as a bad aero- plane. It was in fact a sound, comfortable and tractable aircraft, marred by an engine which was insufficiently powerful and unreli- able to a degree, and which was obsolete at the time of its selec- tion as the D.H.9's standard power unit. Structurally the D.H.9 differed little from its predecessor, the D.H.4. The mainplanes and tail unit were in fact identical. The wings had spruce spars which were spindled out between the compression struts, and the ribs had plywood webs. The internal bracing was of wire; externally the D.H.9 was braced as a con- ventional two-bay biplane with spruce struts and Rafwires. Ailerons were fitted to upper and lower wings, and the spanwise balance cables ran externally above the upper wing. The tail unit was likewise a wooden structure, and incorporated the same variable-incidence tailplane and horn-balanced rudder which were fitted to the D.H.4. It was in the design of its engine installation that the D.H.9 differed markedly from the earlier type. All the standard engines fitted to the D.H.4, with the exception of the Fiat A-12, had frontal radiators; and the pilot sat directly under the centre- D.H.9 with Fiat engine. (Bottom) A standard D.H.9 (to be compared with the Fiat-powered machine).
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