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Aviation History
1956
1956 - 0677.PDF
1 June 1956 677 THE DE HAVILLAND D.H.9A HISTORIC MILITARY AIRCRAFT No. 13 PART II By J. M. BRUCE, M.A. JT is no disparagement of the D.H.9A to say that it was notthe aeroplane it has so frequently been claimed to be:namely, the machine with which strategic bombing was initiated. That distinction was shared by several types of air-craft, and properly belongs to the machines which equipped the R.N.A.S. Third Wing during the winter of 1916-17. There canbe little doubt that the D.H.9A would have proved an excellent instrument for the execution and development of strategic bomb-ing attacks had the war lasted long enough for the aircraft to be used in large numbers. A few D.H.9As were sent to coastal stations in the UnitedKingdom in the late summer of 1918. It was intended that, like the D.H.4s and D.H.9s before them, they should be used forover-sea patrols. They were not used for that purpose, however, because the valve gear of the Liberty engine was not consideredto be sufficiently safe for over-sea flying. If that were the true reason it reflects an odd access of caution at a time when D.H.9swere being sent out over coastal waters, without such considera- tion for the waywardness of their Puma engines. At least oneD.H.9A, E.9689, was fitted experimentally with a form of emergency notation gear which had been designed by J. SamuelWhite and Co., Ltd., of East Cowes, Isle of Wight. The buoyancy element in this gear consisted of a large air-bag fitted under theforward position of the fuselage. When developed, the air-bag was deep and box-shaped, and a modified undercarriage had tobe fitted. The vees were pivoted at the top of the rear legs, and the front legs could be unlocked to enable the entire under-carriage to be swung rearwards, out of the way of the developing air-bag. It is possible that the undercarriage could be raisedbefore ditching. Having been designed from the outset to have the Libertyengine, the D.H.9A found favour in American eyes, and it was adopted as the replacement for the D.H.4 in the United StatesAir Service. In the circumstances, it seems peculiar that the design was so extensively modified by American engineers. Itwas, of course, renamed: its American designation was USD-9A. In construction the USD-9A resembled the D.H.9A. Thelongerons were of Hin-sq ash, and the patons were of spruce. The forward portion of the fuselage was covered with 3/32inplywood which consisted of a poplar core with vertical grain sandwiched between two outer plies of mahogany with grainrunning longitudinally. The aerofoil section of the mainplanes was an American development of R.A.F.15, slightly deeper atthe spars and with reduced undercamber. The spars were of solid spruce, spindled out between the compression struts, ofwhich there were five in each wing panel. Ribs were made of 5/32in plywood; a poplar core 3/32in thick had its grain run-ning longitudinally, and lay between l/32in plies of birch with grain vertical. Figures quoted in a contemporary American description of theUSD-9A indicate that the gap was 7£in greater than that of the D.H.9A, and that stagger was reduced to IZjin. The same re-port quotes areas for ailerons and all tail surfaces which do not tally with the corresponding values for the British aircraft.Although this is not an infallible indicationjtHat the surfaces in question had been re-designed, it is certain that productionUSD-9As were to have had a rudder of more rounded appear- ance than the characteristic D.H. rudder. At least one of theprototypes had the modified rudder. . ......... The USD-9A was fitted with a special fuel system which hadbeen developed at McCook Field. As on the D.H.9A, the main tank was fitted immediately behind the engine. It had a capacityof 134 U.S. gallons, and petrol was passed to the carburettors by two Vane force pumps which were driven from the enginecrankshaft by a flexible drive. A gravity tank of 9 U.S. gallons capacity was mounted in the centre section. Dual control was fitted to the USD-9A, and differed in detailfrom the control arrangements of the D.H.9A. The pilot's armament consisted of a fixed Browning machine-gun with 750rounds of ammunition; the gun was mounted on the starboard side of the fuselage, whereas the Vickers gun of the D.H.9A wason the port side. The USD-9A's observer had a pair of Lewis guns on a Scarff ring-mounting; ten 97-round drums werecarried. It was intended to use the USD-9A either as a bomber or asa reconnaissance aircraft. The maximum load of the bomber version consisted of six 50-lb bombs carried in racks under thewings and two 110-lb bombs under the fuselage. Nine prototypes were built, four by the Dayton-Wright Aero-plane Co., and five by the Engineering Division of the Bureau of Aircraft Production. The first Dayton-Wright USD-9A wasdelivered in October 1918, followed next month by the first machine built by the Engineering Division. A contract for 4,000USD-9As was given to the Curtiss company but was cancelled when the Armistice was signed. No production machines weredelivered. In February 1919 the Engineering Division fitted one of its USD-9As with wings of increased area and installeda Liberty 12-A engine. This modified machine was re-designated USD-9B. After the war the D.H.9A remained in service with the RoyalAir Force for many years, and was outlived only by the immortal Bristol Fighter. The type formed pan of the equipment ofsquadrons Nos. 47 and 221, which operated against the Bol- rheviks in Russia in 1919-20. No. 221 Sqn. arrived at its aero-drome at Petrcvsk in the middle of January 1919, and had most of its aircraft assembled by the 28th of that month. Themachines had to be erected in the open in sub-zero temperatures. The D.H.9AS of No. 221 did not make an auspicious start totheir Russian operations. On February 10, 1919, two of them bombed a cavalry unit south of Astrakhan; each machine carriedone 230-lb and two 65-lb bombs, and a considerable number of casualties were caused. Unfortunately, the cavalry were a WhiteRussian squadron. None of the British aircraft which participated in the Russiancampaign distinguished themselves. Flying was possible in the summer of 1919, but disease took a heavy toll of the personnel ofthe two squadrons. On June 22, 1919, six additional D.H.9As were delivered to No. 221 Sqn. By Christmas 1919 the winter weather again limited operations,and at that time No. 47 Squadron's only serviceable aircraft was a single D.H.9A. By then the White Russian forces were underpressure from the Bolsheviks, and the R.A.F. unit was steadily withdrawn. Its aircraft suffered various mishaps, and there canbe no doubt that some of the D.H.9As fell into the hands of the Bolsheviks. The qualities of the aircraft must have made a favourableimpression on the Reds, for the type was built in post-revolu- tionary Russia—doubtless without the formality of a licence. The Side elevation of USD-9A, showing location of the principal bombing and reconnaissance equipment.
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