Airco DH.9
The Airco DH.9 – also known after 1920 as the de Havilland DH.9 – is a British single-engined biplane bomber that was developed and deployed during the First World War.
The DH.9 was a development of Airco's earlier successful DH.4, with which it shared many components. These were mated to an all-new fuselage and used the Beardmore Halford Pullinger engine, which promised increased performance. Anticipating its usefulness, the type was ordered in very large numbers for Britain's Royal Flying Corps.
Upon entering service, the DH.9's performance was found to be unsatisfactory. The BHP engine was unreliable and failed to provide the expected power, which gave the DH.9 less performance than the aircraft it had been meant to replace. The performance deficit was blamed for the heavy losses they suffered over the Western Front. The redesigned DH.9A was fitted with a more powerful and reliable American Liberty L-12 engine which rectified the shortcomings of the original DH.9 model.
Development
Origins
During June 1917, partially as a result of attacks by German bombers on London, the War Office issued its recommendation to almost double the size of the Royal Flying Corps to a total of 200 squadrons. In early July 1917, the British Cabinet accepted the recommendation, with the intention that the majority of the new squadrons were to be equipped with bombers. While an order for 700 DH.4s was placed on 28 June 1917, on 23 July 1917, the Air Board were presented with drawings for a modified DH.4 that delivered greater range under a new type number, DH.9.The DH.9 was designed by de Havilland for the Aircraft Manufacturing Company in 1916 as a successor to the DH.4. It used the wings and tail unit of the DH.4 but featured a modified fuselage which moved the pilot closer to the gunner/observer and away from the engine and fuel tank, which facilitated communication and was a more optimal fighting configuration. The other major change from the DH.4 was the choice of the promising new B.H.P engine, which was predicted to produce to provided performance matching enemy fighters.
Based on the performance estimates for the DH.9, and the similarity to the DH.4, which meant that it would be easy to convert production over to the new aircraft, it was decided to place a massive number of orders for the type prior to the aircraft even flying for the first time. Existing contracts originally placed for the DH.4 were also converted to the DH.9. The Air Board had been specifically assured that there would be an initial production delay of no more than a month. According to aviation author J.M Bruce, the selection of the DH.9 "seems to have been taken in a spirit of optimism or blind faith, for its chosen engine was, in July 1917, experiencing serious manufacturing difficulties".
Into flight
In July 1917, the prototype performed its maiden flight from Hendon Aerodrome, Colindale, London. Trials of the type were extensive, including a number of tests performed at RAF Martlesham Heath. Unfortunately, the BHP engine proved unable to reliably deliver its expected power; the engine having been de-rated to in order to improve its reliability. This deficit had a drastic effect on the aircraft's performance, especially at high altitude, with it being inferior to that of the DH.4 it was supposed to replace.The poor performance of the aircraft meant that the DH.9 would have to fight its way through enemy fighters, which could easily catch the DH.9 where the DH.4 could avoid many of these attacks. As early as November 1917, some officials, such as General Hugh Trenchard, raised repeated objections to the aircraft based upon its disappointing performance; however, in his response, President of the Air Council Sir William Weir started that "it was the choice of having the DH.9 with the B.H.P. engine, or of having nothing at all. Additionally, by this point, production of the DH.9 was already well underway.
BHP engines were produced by Siddeley-Deasy and Galloway Engineering. In British military service both Siddeley and Galloway built engines were known as the 230 hp BHP although they had different dimensions and few interchangeable parts. The vast majority of BHP engines in service were built by Siddeley-Deasy.Multiple attempts were made to provide the DH.9 with a better engine. In August 1917, an order for 2,000 Fiat A.12 engines was placed, with delivery between January and June 1918 used on some production batches of the D.H9; however, deliveries of the Fiat engine were unsatisfactory.
An alternative powerplant was the Napier Lion engine. A Napier Lion powered aircraft piloted by Captain Lang and his observer Lieutenant Blowes achieved a World Altitude Record of in 66 minutes on 2 January 1919. At 21,000 ft Lieutenant Blowes oxygen supply failed and he remained unconscious until the aircraft descended to 10,000 feet. Unaware of his observers plight Captain Lang was unable to exceed 30,500 feet because their oil heater failed and their fuel pumps cut out due to a lack of air pressure. Both men needed to be hospitalized after the attempt due to frostbite on their faces, hands, and feet.
However, none of these options were deemed to be entirely satisfactory, it required redesign into the DH.9A, for which an American V-12 Liberty engine was adopted. According to Bruce, aside from the engine issue: "Certainly, there was little wrong with the aircraft itself".
Design
The Airco DH.9 was a single-engine British bomber aircraft, sharing a high level of similarities with the preceding DH.4. The standard flight surfaces were broadly the same, but adopted a highly redesigned fuselage configuration, including the repositioning of the pilot's cockpit to a more rearwards position. Structurally, the fuselage was similar to its predecessor; plywood cladding covered the forward fuselage, which had no internal bracing, while a conventional wire-braced box girder structure was used aft of the cockpits. Internal stowage for a pair of or four bombs was provided for, although little use of this capability was made operationally.While the DH.9 was deemed to be suitable for daytime bombing operations, it was found to be incapable of effective nighttime bombing due to the pilot's view being obstructed and visibility via the bombsight being unsuitable. The revised cockpit positioning of the DH.9 from the DH.4 placed the pilot and the observer closer together, which was viewed by the RAF as being a considerable advantage in aerial combat; however, the pilot's visibility for ground reconnaissance was decreased as a result. Both radio sets and cameras could be installed. The fuel tanks were enclosed in doped fabric, intended to drain fuel away if the tanks were hit by enemy fire. According to the testing squadron, the DH.9 possessed a high level of manoeuvrability, was relatively easy to perform landings aside from a poor view during the approach.
Various improvements and supplementary equipment were trialled and occasionally adopted. Tests of various engines, radiators, silencers and parachutes were conducted to evaluate their performance, however, few of these improvements were ultimately adopted. During the war, numerous customisations and improvised improvements were made to the aircraft by the maintenance crews of individual squadrons, often for the purpose of addressing the type's engine performance issues. After the end of the war, many DH.9s, which had been originally delivered as bombers, were sold; these were often reconfigured to serve in different roles, including passenger and cargo transport, trainer aircraft, and as air ambulances.
Operational history
First World War service
To boost the rate of production, quantity orders for the DH.9 were also placed with Alliance, G & J.Weir, Short Brothers, Vulcan, Waring & Gillow and National Aircraft Factories No. 1 and No. 2. The first deliveries of the type occurred during November 1917 to 108 Squadron RFC; by the end of 1917, a total of five DH.9s had been delivered and passed their final inspections. The first combat engagement of the type, performed over France, was performed in March 1918 by No. 6 Squadron RNAS. By July 1918, a total of nine operational squadrons deployed to the Western Front were using the type.The DH.9's performance in action over the Western Front was typically deemed to have been a disaster; heavy losses of the type were quickly incurred, attributed to both its poor performance and to engine failures, despite the prior derating of its engine to reduce the failure rate. Between May and November 1918, a pair of squadrons stationed at the Western Front had 54 of its DH.9s shot down and another 94 aircraft written off due to accidents. On multiple occasions, less than half of a flight of bombers would reach their intended targets; according to Bruce, the successful missions performed by the DH.9 were frequently a product of "the courage and determination of the pilots and observers that flew them". Squadrons would often implement their own home-built enhancements to their aircraft, such as enlarged carburetor air intakes and modified fuel mixture controls.
Nevertheless, the type proved capable during some engagements; on 23 August 1918, a DH.9 flown by Lieutenant Arthur Rowe Spurling of 49 Squadron, with his observer, Sergeant Frank Bell, single-handedly attacked thirty Fokker D.VII fighters, downing five of them. On 9 August 1918, Lieutenant E.A. Simpson of 49 Squadron, while flying a bombing mission upon bridges at Falvy and Bethencourt, shot down four hostile fighters while defending against repeated attacks upon the formation. In another instance, Captain John Stevenson Stubbs achieved 11 aerial victories in a DH.9, including the highly unusual feat of balloon busting while flying the type.
Despite its general lack of performance, due to its large numbers, the DH.9 was introduced to nearly every theatre of the conflict prior to the signing of the Armistice of 11 November 1918, which ended the conflict. Reportedly, the DH.9 was also more successful in combat against the Turkish forces in the Middle East, where they faced less aerial opposition. Stationed at coastal aerodromes across the British mainland, the type was also used extensively to perform coastal patrol missions with the aim of deterring the operations of enemy U-boats.